#35 DS1 Winter Schedule

As our first semester of dental school winds down, we recently got our new schedule for the Winter semester, which begins in early January. You can look forward to new posts on the following subjects:

Immunology (2.5 CH)
Gross Anatomy II (4 CH)
Physiology (4 CH)
Biochemistry / Molecular Biology (3 CH)
Periodontal Instrumentation I (3.5 CH)
Dental Occlusion (2 CH)
Amalgam Restorative Treatment Techniques (2 CH)

Total of 21 credit hours.

#34 UDM Open House

Open House

I just wanted to thank everyone for coming out to the Open House last Saturday. I hope you enjoyed yourself, the facilities, and hopefully got to meet some influential faculty and students.

For those who didn't get the chance to go, or are preparing to in the future, please feel free to leave a comment at the end of this post, and I'd be happy to answer any questions you have about the school.

#33 Molars

Molars

In preparation for a Dental Anatomy midterm coming up next week, I put together a simple Excel chart outlining the characteristics of the maxillary and mandibular molars. You should be able to construct a three-dimensional image of the molars in your mind when reading over the chart. Here's a download link to the chart:

http://rapidshare.com/files/429235602/Molars.xlsx

(Note: The third molars are rather variable in anatomy, so they aren't included in the chart.)

Permanent Maxillary First Right Molar (Mesial View)
















Permanent Maxillary Right Second Molar (Distal View)

Permanent Mandibular Right First Molar (Distal View)

Permanment Mandibular Right Second Molar (Distal View)

#32 Loupes

Loupes

Today in sim lab, our class spent the entire four hours practicing some Class 1 preparations/restorations (recall: Class 1 are preparations done on carious lesions found in occlusal pits or fissures). We specifically prepped and restored teeth #3, #4, #13, #14, #19, #21, #29, and #31. Given what we did today, I think it's an appropriate time to talk about the pros and cons of loupes.

The pair I use (and cherish) are 3.5x TTL (through-the-lens) EF (extended field) DFV (Design for Vision; company) with Buddy Holly (thick) frames. I also use them with the light that is offered by DFV (can't remember the name of it off the top). Prior to this, I used a pair of 2.5x no-name, cheap clip-ons as a way to get used to using loupes in the beginning. As mentioned above, I absolutely love them. They have a great field; you can see an entire arch with the extended field. This is a feature which is pricey, but absolutely worth it. It gives you both the flexibility of great magnification for a single tooth, while still being able to see the 'big picture'.

The learning curve for me was pretty low. It took me about 3 long (think 2+ hours) sessions of using them before I got to the point where it feels second nature. They allow you to see your prep very clearly; with the light, you do not get any shadowing effects occuring. Plus, the light follows your vision, so no constant adjustment is necessary. Also, they are FANTASTIC on your posture. I am able to perform my work from the ideal, ergonomic position, and have next-to-none muscle/back/neck fatigue after multiple hours of work. This will be invaluable to me during my future years.

The cons: expensive. Even with a student discount, you are going to have to shell out close to a couple grand for them. You do have the option of returning them at full cost prior to 45 days, but you should be comfortable with what you are getting into. As well, you do become dependent on them; looking at my typodont without them on, I question if I could do a respectable preparation without them. This point is slightly moot; it just means that I have to be careful with my loupes and be sure not to break them or lose them. This is unlikely as they have a strap attached to the back of the glasses, and I guard/treat them as if my life depends on it.

To summarize, buying a pair of loupes is a personal preference. However, I implore you to take a look at the pair I use. I am very, very pleased with the decision I made, and look forward to using them for many years to come.

#31 What I Learned Today

Essentials of Clinical Practice

We went down to the third-year clinic and practiced taking impressions on fellow students. They turned out alright, though some practice is definitely needed. The best learning experience today was learning how to modify the stock trays in order to accommodate the size and shape of a patient's mouth. One way which worked well was to use rope wax which could be fitted to the back of the tray in order to extend it a bit farther to capture the gingival areas posterior to the molars. Also, a desktop torch can be used to re-shape the plastic trays so that they fit better.

Part of the impression requirement was also to catch the buccal vestibule by injecting alginate into the area using a syringe. This can be a bit difficult on the maxillary, as you are working against gravity. Doing this also requires having an assistant (or in our case, the other student-patient) mixing up a second bowl of alginate for the syringe at the same time you are packing the tray with another. Recall, that the alginate in the vestibular area and in the tray needs to be setting at roughly the same pace in order to get bondage between them.

Finally, if you are unable to pour up the impression immediately after, it's best to wrap it up in a moist towel and put it in a sealable bag. This will help keep the form of the hydrocolloidal impression material.

#30 What I Learned Today

Sorry for the week-long hiatus! I just wanted to get my administration's blessings with regards to me writing the blog. Regular posts will resume, with the possibilities of seeing posts geared towards the more personal side of being a dental student. Enjoy!

Dental Materials

Our discussion today focused on the different materials that dentists use to take impressions. Impressions are used to capture all anatomical aspects of the dentition and gingiva in order to form a dental cast. The dental cast can be used for a number of reasons, such as diagnostic planning, or used by the lab to fabricate prosthodontic devices.

Some of the older impression materials used to be of the non-elastic variety; these included dental plaster (yikes!) and zinc oxide-eugenol. Current materials allow for elastic impressions, and are typically broken down into hydrocolloids (water based) and non-aqueous elastomers (non-water based).

The hydrocolloid most commonly used is alginate (search this blog to find more specific information on alginate). One propery of alginate that is important to note is that it doesn't have the ability to create great, fine detail reproduction, so it is not accurate enough to use in the fabrication of prosthodontic devices. For such delicate cases, a dentist would typically use one of the elastomers, such as polysulfides, silicones (addition and condensation types) and polyethers.

At the school, we use an addition silicone called polyvinyl siloxane for such cases. The reaction occurs through the mixing of two different pastes through the use of a silicone gun (looks similar to a caulking gun). The resulting mix is then put into a stock or custom tray, and an impression is taken. These impressions are highly accurate, have excellent recovering abilities and are very stable. The impression can be poured for up to a week after, and multiple pours are possible. However, it is important to note that the reaction can release hydrogen gas on setting, which could form bubbles in the impression. Also, sulfur found in latex gloves and rubber dams can interfere with the polymerization process.

#29 What I Learned Today

Essentials of Clinical Practice

In ECP lecture, we discussed the importance of taking a complete physical assessment of the patient as soon as they walk into our office and shake our hand. When preparing for a physical assessment, you should make the patient feel comfortable. This can be done through simple chat with the patient. If we're doing any examination with our hands, simply rubbing them together to warm them up will make the experience more comfortable for the patient. A dentist should also check his or her equipment to make sure that it is in working order; being prepared shows the patient that you are competent and ready. After performing the physical examination, it is important to avoid quickly interpreting the results and jumping to what may be an erroneous conclusion.

A popular way of examining a patient in medicine is done through a SOAP note, which stands for:

• subjective
• objective
• assessment
• plan

Another useful mnemonic for subjective analyzing a patient is by SAMPLE:

• S = signs/symptoms
• A = allergies
• M = medications
• P = past history
• L = last food intake
• E = events leading up to the problem

For analyzing pain, you can use the alphabet mnemonic OPQRST:

• O = onset of pain
• P = provocation
• Q = quality of pain
• R = region/radiation of pain
• S = severity of pain
• T = time pain started or went away
  

Foundation of Evidence-Based Dentistry

In Evidenced-Based Dentistry, we talked about writing PICO questions. PICO is a away of narrowing the scope in regards to a specific topic you want to research, by formatting the question in a structured manner. PICO stands for:

• P = patient population or problem
• I = intervention
• C = comparison
• O = outcome

An example of a PICO question would be: In a patient with moderate plaque accumulation, is brand #1 mouthwash, as compared to brand #2 mouthwash, more effective in removing plaque?

You can then use this specific question to search a journal database to find out the answer to your question.

Gross Anatomy I

Today's Anatomy lecture focused on the kidney and the diaphragm. It's important to note that the venous drainage of the kidney is asymmetrical. The left renal vein is much longer than the right; this is due to the fact that both the renal veins drain into the inferior vena cava, which you'll recall is located on the right half of the torso. The renal arteries are found posterior to the renal veins.

It is important to note that there is some vein and artery overlap going on. The superior mesenteric artery runs over top of the left renal vein. As well, the inferior vena cava initially runs anterior to the abdominal aorta near the diaphragm, but as you approach the posterior portion near the bifurcations, the abdominal aorta runs anterior to the inferior vena cava.

If you take a cross section of the kidney, you'll notice that it was an outer cortex layer and an inner medullary layer. The medullary is ordered in column-pyramid-column arrangements. The pyramids come to a 'point' on the major and minor calyces, where urine flows to the ureter.

The diaphragm has four origins (the sternum, ribs, costal cartilage, and lumbar vertebrae) and inserts on the central tendon of the diaphragm. Its main function is to increase thoracic volume when inspirating. It is innervated by the phrenic nerve, which has both motor and sensory functions. It has surface openings for:

• caval hiatus: inferior vena cava and right phrenic nerve
• esophageal hiatus: esophagus and both vagus nerves
• aortic hiatus: aorta, thoracic duct, and azygous vein

The diaphragm also has arcuating (arcing) ligaments found on its dorsal end. These include the medial arcuate ligament (which houses the psoas muscle), the lateral arcuate ligament (which houses the quadratus lumborum muscle). These arcuate ligaments attach to the vertebral column by the right crus and the left crus.

Gross Anatomy Lab

In lab, we reviewed the structures, nerves and vessels that we've gone over to date.

#28 What I Learned Today

Biochemistry

Today in Biochemistry, we began to look into lipid metabolism. Lipid metabolism is centrally based around the molecule acetyl-CoA, which can be converted to fatty acids, cholesterol, HMG-CoA, through this pathway.

You see two types of fatty acids: saturated and unsaturated. Saturated fatty acids are long alkyl chains of monocarboxylic acids with an even-number of carbons. Unsaturated fatty acids differ in that they contain C=C double bonds. This results in different melting points; saturated fatty acids are straight chains, meaning they have more surface area and are less likely to be able to flow. Unsaturated fatty acids have kinks in the molecule, and thus have less surface area and more ability to flow. As unsaturation increases, melting point decreases, and as chain length increases, melting point increases.

Two important polyunsaturated fatty acids are linoleic acid and linolenic acid. They are commonly known as omega-3 and omega-6 fatty acids, respectively.

Fatty acids are formed by a number of reactions. The first one to note is the De Novo synthesis. It uses an enzyme with two binding sites: one is an acyl carrier protein, which uses pantothenic acid (found in coenzyme A) to attach fatty acids, and the other is a cysteine residue. The ACP begins by binding malonyl-Coa (an acetyl-CoA with a carboxyl group). The cysteine residue binds an acetyl-CoA. The acetyl is then removed from the cysteine and hooks onto the end of the malonyl-CoA, through the enzyme ketoacyl synthase. This reaction removes the carboxyl group in the form of carbon dioxide. At this point, the cysteine is empty, and the pantothenic acid have a four-carbon chain. The ketone group on the pantothenic acid is then reduced, which uses one NADPH (this is why the hexose monophosphate shunt is so important!). The enzyme hydratase then produces water by removing an OH group and another hydrogen, forming a trans C=C (unsautrated!). The four-carbon molecule is then saturated through the use of another NADPH in a reduction reaction. Extra carbon is then added by transferring the four-carbon molecule to a cysteine residue, addding another malonyl-CoA to the pantothenic acid, and finally transferring the four-carbon molecule onto the malonyl-CoA, releasing another carbon dioxide.

#27 What I Learned Today

Introduction to Operative Dentistry

Today in sim lab we performed amalgam restorations on teeth #5, #12, and #14. The type of amalgam that we used for the restoration was Tytin FC (firm condensation) 600 mg, which has modified spherical particles. The alloy material percentage breakdown is:

• 61% Ag
• 26% Sn
• 13% Cu

The overall mixture contains 44.5% mercury by weight. The capsule is triturated (mixed) at 4000 cpm for 7 seconds.

The amalgam is first brought to the preparation by an amalgam carrier and condensed. Small increments seem to work best, as spillage can occur if you use excess. Start with a small condenser to make sure the pulpal line angles are well condensed and increase in size from there. Remember to also move quickly.

Once the preparation is slightly overfilled, you begin to carve. You can use a number of different hand instruments; personally, I started with a lateral condenser (can be roughly described as christmas tree-shaped) and then used a cleiod side of the cleiod-discoid instrument to clean up the margins. At this time, you make sure to incorporate any occlusal anatomy into the carving as you are trying to replace the initial lost tooth structure. Also of important note, you want to always have part of the carving instrument lying on healthy tooth structure while you are working; this helps simulate proper tooth structure shape.

Towards the end, you can use a ball burnisher to run it along the surface. Another useful tip is to take wet cotton and rub it along the surface of the restoration; it helps give a nice smooth finish. Once you are done carving, you should check the occlusion by having a patient bite down and side-to-side on articulating paper. This will also you to check the contact points and ensure they are restored. If not, modification to the restoration might be necessary. One final go-over of the restoration should be done with a lateral condenser, to ensure a good finish after occlusion is checked.

Also note: In a real patient, dentin sealer should be added to block the dentin tubules and help close up the microscopic space that is found between tooth structure and amalgam (recall: amalgam doesn't bond to tooth!). This should last until the amalgam restoration corrodes from being in the oral environment; the corrosion products help form a better seal. It also helps with post-op sensitivity and discolouration.

#26 What I Learned Today

Essentials of Clinical Practice

Today's lecture in ECP focused on how important it is for a dentist to take an accurate and complete medical history. A health assessment begins with a complete history taking of the patient, including:

• biographic/demographic/social/family history
• medical history (and current status)
  
• dental history (and current status)
• medication history

Of the most importance is the chief complaint (CC) of the patient. In other words, the reason the patient is seeking help. These can include simple lines such as, "I have cavities and I wanted them fixed" or "I want my smile to look better". Once you have the chief complaint, it is important to get the history of present illness (HPI). This is pretty much a narrative which explains how the patient got to be in his or her present condition. Many probing questions should be asked, especially focusing on the what/when/where/how/how long/intervention questions. The HPI can often give the dentist vital information which may ultimately affect diagnosis.

Finally, we began to look at different medical conditions and how they affect the oral cavity and how you would treat them. An example is dry mouth. It is often a side effect of taking specific medications. Consequently, you often see higher rates of decay as saliva helps remove the oral bacteria and remineralize enamel. Another example is cancer. IV Bisphosphonates are used to treat a number of common cancers, and have been shown to cause jaw bone necrosis in some patients.

Patients often come in with allergies. It's important to probe the specifics of the allergy, such as how the patient feels upon reaction, what happens (rash, swelling). It is important to determine if analphylaxis is a symptom of the allergy. Also, you also have to be aware of latex allergies in a dental office, since there are many latex-based products used including gloves and rubber dams.

Hypertension and its medications can also have side effects which are relevant in a dental setting. Orthostatic hypotension is one, which is low blood pressure occuring when the patient sits up. This can lead to dizziness or a fainting spell, which could cause the patient to fall and injure him or herself. You also tend to see dry mouth, angiodema of the facial region (swelling of the dermis and underlying structures), taste alteration and gingival enlargement.

Fainting situations can also occur to patients who have diabetes, and have a hypoglycemic episode. It is important for a diabetic patient to use a glucometer to take a reading of sugar level before treatment. If the reading is less than 70 mg/dl, then action should be taken.

Finally, asthma can be a factor in a dental office. It is important to probe the patient to determine information such as the severity of attacks, duration, when the last attack was, how they dealt with it (stayed at home, or hospital), what triggers it (odours in dental setting, and stres from appointment often can be a trigger). If the patient does have frequent attack, than an inhaler should be kept close and at the ready.

This is followed up by a physical examination, diagnosis, and finally an assessment of the benefits and risk of performing the treatment in mind.

General and Oral Histology

For histo, we discussed cementum, root and pulp structures of teeth. Cementum is found on the outer surface of the radicular part of a tooth, and is continuous with the periodontal ligament (PDL). It is anchored in the alveolar bone by Sharpey's fibers (type 1 collagen) which span the cementum and PDL. Pre-cementum is secreted by cementoblasts, and is slowly formed throughout life. The pre-cementum is mineralized by the cementoblasts, until its contents are about 50% hydroxyapatite crystals. Over time, cementoblasts may become mineralized in cementum and are called cementocytes. They help by diffusing nutrients from the vascularized PDL to the non-vascularized cementum.

There are a number of different kinds of cementum. Two of them include acellular extrinsic fiber cementum (AEFC) which contains no cementocytes, but has Sharpey's fibers from the PDL. Its function is to anchor the root to the PDL, and is often found in the cervical third of the root. Cellular intrinsic fiber cementum (CIFC) contains cementocytes and is important in repairing resporptive defects in the roots of teeth. Mixed stratified epithelium of both AEFC and CIFC are important in reshaping the tooth surface in order to compensate for drift and shifting of teeth in the alveolar sockets.

Some clinical problems that arise in the cementum include hypercementosis, where you get excessive deposition of cementum on the root surface. This can interfere with tooth extractions. Also, you may see concresence where the roots of two adjacent teeth are joined by cementum. This is often due to sufficient space during tooth development.

I'll finish up with roots and pulp later.

#25 What I Learned Today

Professionalism and Ethics

We broke into groups today and worked at putting together a code of ethics that we wanted our class to follow. It was pretty open-ended, ranging from things like specific do's-and-do-not's, to personal characteristics to follow.

When the code is put together and made available on-line, I'll be sure to post it here.

Biochemistry

We continued our look at energy metabolism by moving from the Kreb's cycle to oxidative phosphorylation and the electron transport chain. In summary, this step takes the hydrogen transporters, releases their hydrogens via oxidative phosphorylation. This sets up a hydrogen gradient, which the enzyme ATP synthase uses to produce ATP molecules.

The first step is to get NADH produced outside the mitochondria by glycolysis into the cell so that it can be processed by the enzymes in oxidative phosphorylation. Since the transporters cannot move freely across the membrane, two specific shuttles are put to good use:

Glycerol Phosphate Shuttle
Both the cytoplasm and mitochondria share an identical reaction: dihyroxyacetone phosphate can be converted to glycerol phosphate. In the cytoplasm, this oxidizes NADH to NAD+. Glycerol phosphate in then shuttled across the membrane and into the mitochondria, where it is converted back to dihydroxyacetone phosphate. This reaction reduces FAD+ to FADH2. However, as you probably know, FADH2 generates less ATP than NADH, so some energy is lost in this shuttle. The better way is to transfer the hydrogen from an NADH cytoplasm to a mitochondrial NADH. This is what the malate shuttle does.

Malate Shuttle
In the cytoplasm, oxaloacetate is reduced to malate, which converts an NADH to NAD+. Malate is then transported into the mitochondria, using a transporter which also sends alpha-ketoglutarate into the cytoplasm. Once in the mitochondria, malate is oxidized back to oxaloacetate, which converts NAD+ to NADH. Oxaloacetate then undergoes transamination with glutamate to become aspartate, where it is shuttled out to the cytoplasm. The aspartate then undergoes transamination with alpha-keoglutarate to regenerate the oxaloacetate and convert the A-K to glutamate.

Electron Transport Chain
Energy from the electron transporters then form the electrochemical hydrogen gradient by releasing H+ in a step-by-step oxidative phosphorlation process. The five components of the process include 4 oxidoreductases, and ATP synthesis.

Step 1: NADH transfers electrons to ubiquinone
Step 2: FADH2 transfers electrons to ubiquinone

The ubiquinone from these two separate steps come together to continue with grouped oxidative phosphorylation:

Step 3: ubiquinone transfers electrons to ferricytochrome b
Step 4: ferricytochrome transfers electrons to oxygen (to form water)
Step 5: ATP Synthesis

With ATP syntheis, hydrogen binds to the 'stalk' portion of ATP synthase, which is embedded in the membrame. This changes the shape and makes the 'wheel' portion go from wanting to bind ADP and inorganic phosphate to wanting to bind ATP. This shape changes produces sufficient energy to force ADP and Pi together to form ATP. As more hydrogen molecules pass through, the shape changes again and favours ADP and Pi binding again.

#23 What I Learned Today

Introduction to Operative Dentistry

No lecture; we had an exam and a rubber dam isolation practical. However, I don't want to leave you empty handed, so here is some bonus content on the physiological characteristics of enamel!

General and Oral Histology

Enamel is formed from ameloblasts, which differentiate from inner enamel epithelium of the enamel organ. This differentiation occurs to the cells on the other side of the basement membrane, adjacent to the dental papilla cells. The ameloblasts begin to deposit enamel shortly after odontoblasts begin depositing dentin (layering process in both is referred to as apposition).

Enamel is one of the hardest substances in the human body, and consists of rods made of hydroxyyapatite (HAP) crystals from calcium and phosphates. Also find some proteins called alemogenin, ameloblastin, and enamelin

You commonly see six different life stages in ameloblasts:

1. morphogenic: begin to see IEE cells differentiate into pre-ameloblasts
2. organizing: odontoblasts sectrete growth factors which leads to further differentiation into columnar secretory cells, or ameloblasts.
3. formative: basement membrane between ameloblasts and odontoblasts disappears, and enamel crystals are secreted along mantle dentin to form the DEJ
4. secretory: ameloblasts secrete enamel from Tomes' processes and move away from DEJ
5. maturative: ameloblasts undergo structural changes. These include the loss of the Tomes' processes, and the ameloblasts are no longer able to secrete enamel.
6. protective/desmolytic: ameloblasts collapse to form the reduced enamel epithelium
   

At the maturative stage, the cells function in increasing the mineralization of the enamel rods up to a content level of ~96%. This development process is important for both dentist and patient to know because it is the reason why enamel is nonvital and cannot be self-repaired (not including arrested enamel lesions) after removal.

Enamel rods are arranged in rows that extend from the DEJ to the outer surfaces. They form 'S' like paths, with the most oblique angles (as compared to the DEJ) occuring towards the incisal edge. Clinically, this is important, as isolated enamel rods, or parts of enamel rods are brittle and break easily. The strength of the enamel is dependent on the dentin support underneath.

#22 What I Learned Today

Biochemistry

Today in Biochemistry, we looked at regulation methods for the citric acid cycle. The cycle can be regulated a number of ways.

The first method uses the products of the cycle to perform allosteric inhibition. Two of the products of the reaction, NADH and acetyl-CoA, inhibit the initial step where pyruvate is converted to acetyl-CoA by pyruvate dehydrogenase.

The cycle can also be covalently regulated by the addition or removal of a phosphate group. When phosphorylated, the enzyme is inactivated. When dephosphorylated, the enzyme is activated. With that in mind, two products of CAC, NADH and acetyl-CoA, activate the activity of protein kinase. Thus, the formation of lots of product results in the shutting down of the cycle. Protein kinase is inhibited by high levels of pyruvate and ADP. Thus, lots of reactants leads to the subsequent production of ATP through the running of Kreb's cycle, and ultimately the electron transport chain.

Finally, the citric acid cycle can be regulated by controlling the activity of enzymes in irreversible steps of CAC. This includes the steps with the following enzymes:

1. citrate synthase
2. isocitrate dehydrogenase
3. alpha-ketoglutarate dehydrogenase

Deficiencies in pyruvate dehydrogenase complexes can have devastating results as it becomes difficult to get energy from pyruvate and glucose. It tends to affect neural tissues since the brain is essentially only able to use glucose for energy.

Principles of Dental Materials

In dental materials, we began to look at the composition and structure of dental amalgam. This lecture is a re-hash of what we learned in Operative class last week. To summarize, amalgam is a setting procedure where amalgam alloy (powder) reacts with mercury (liquid) to form set amalgam (solid).

Advantages of amalgam include:

• high durability (lasts longer than most direct restorative materials)
• setting material (allow for easier placement by the dentist)
• good consistency (easy placement and shaping)
• low cost

Disadvantages of amalgam include:

• gray-metallic luster (unnatural appearance)
• contains mercury (very small amount released during chewing; greatest exposure comes from the setting and removal of the amalgam)
• low tensile, ductility and toughness (brittle alloy that cannot be used in thin sections)
• setting reaction takes time (strength builds over 24 hours, patient needs to be careful about mastication initially)
• Creep, dimensional change (can lead to marginal breakdown, but vary rarely seen in new copper amalgams)
• tarnish (the darkening of metal in oral cavity. Rarely seen in newer amalgam, but some patient's saliva content may still cause it)
• corrosion (due to gamma-2 phase, but rarely seen in newer amalgam)

Dental Anatomy

We had a practical examination today, which consisted of stations of Fuller & Denehy drawings and Kilgore teeth. Some of the questions asked for tooth identification, while others asked for specific tooth structures. It's important to know 'standard' (understanding that there is quite a bit of variation, especially within root structures) anatomical dentition in order to detect anomalies and be able to restore teeth to working form.

#21 What I Learned Today

Essentials of Clinical Practice

Exam today; no lecture.

Gross Anatomy I

Today we discussed anatomical structures found in the anterior body wall and peritoneal cavity. The muscles of the anterior body wall consist of three major layers, from external to internal: external oblique muscle, internal oblique muscle, and transversus abdominis muscle. Each have a specific direction in which their muscle fibers run. External runs downwards; same direction as your fingers if you put your hands in your pant pockets. Internal runs approximately perpendicular and upwards to external. Transversus abdominis runs horizontally, like the name implies.

Found between the epidermis and abdominal muscles is two layers:

• fatty layer (Camper's)
• fascia layer (Scarpa's)

The anterior body wall has a number of major arteries running through it, including:

• descending aorta
• superior epigastric arteries (from subclavian -> internal thoracic)
• musculophrenic arteries (from subclavian -> internal thoracic)
• superficial circumflex iliac artery
• deep circumflex artery
• inferior epigastric artery

An important structure in the body wall is the inguinal canal, which is formed by the aponeurosis of the external oblique muscle and the inguinal ligament. The inguinal ligament stretches from the anterior superior iliac spine to the pubic tubercle, and acts as the base of the canal. The inguinal canal has two openings through the body wall at the deep inguinal ring and the superficial inguinal ring. The spermatic cord passes through the canal, to bring sperm from the testes, up through the abdomen to get processed, and eventually ejaculated through the penis. The spermatic cord consists of:

• ductus (vas) deferens
• testicular artery
• pampiniform plexus of veins
• genitofemoral nerve
  

Spermatogenesis begins in the testes, where sperm is formed and stored in the epididymis. The sperm then travels up through the ductus deferns to the seminal vesicle, where more fluid is added to the volume of the sperm. The sperm continues through the ejaculatory duct and the prostate gland. It passes by the bulbourethral gland, which adds mucous to the sperm. Finally, the sperm passes through the urethra and the penis.

Gross Anatomy Lab

In dissection lab, we opened up the neck to identify the muscles, bones, vessels, nerves and glands in the area. Some of the noted structures included:

• sternocleidomastoid muscle (cut back to access the hyoid-related muscles)
  
• thyroid gland
• hyoid bone
• sternothyroid muscle
• sternohyoid muscle
• thyrohyoid muscle
• thoracic duct (hard to find)
  
• carotid sheath, containing: common carotid artery, internal jugular vein, and vagus nerve
• cartilages, including: thyroid cartilage (Adam's apple!), cricoid cartilage.
• trachea and esophagus

#20 What I Learned Today

Professionalism and Ethics I

We discussed what constitutes sexual harrassment, how to identify it, and what to do if you are sexually harassed. Obviously, it's not tolerated at school, in practice, or anywhere. One has to be careful with his or her actions; it is easily for actions to be misconstrued. What may be funny to one can be offensive to another. If someone says 'no' or 'stop', then do so. Common sense.

Biochemistry

Exam today; no lecture.

#19 What I Learned Today

Introduction to Operative Dentistry

Our session in the sim lab gave us the opportunity to get the feel for condensing amalgam. We started off by going over the characteristics and composition of amalgam (please refer a week prior to our dental materials lecture). Amalgam has been used in dentistry for over 150 years, and is primarily used for posterior restorations, crown build-ups (when left with little tooth structure), and small cervical lesions on buccal surfaces. Amalgam is cheap and easy to use. However, it does have some disadvantages, such as poor esthetics, brittle (tends to shear easily), initially weak before it fully sets, doesn't bond directly to tooth (needs mechanical retention), and may exhibit creep (permanent deformation from constant bending).

Amalgam is composed by mixing an amalgam alloy (typically silver, tin, and copper) with liquid mercury; a process referred to as trituration. The alloy comes in powdered form, and comes in a number of specific powder types, including:

• lathe cut: angular and irregularly shaped chunks
• spherical: microspheres of different sizes
• admixed: both lathe cuts and spheres
• modified spherical: elongated round particles

Spherical amalgams typically require less mercury than lathe cut amalgams to form a workable mass, and they tend to flow better. As well, by overfilling the prep, the mercury accumulates in top layers due to condensing, which is then carved away using a Ward's carver. This helps eliminate as much mercury as possible.

Older amalgam typically used low-copper alloys (5% or less). When mixed, the mercury and metal alloying would form various compounds, with the two main ones being silver mercury (called gamma-1) and tin-mercury (gamma 2). The gamma-2 proved to be a weak, easily corrodible phase which showed high levels of creep.

Current amalgam uses high-copper alloys (13-30%), which results in the elimination of the gamma-2 phase, through tin reacting with copper instead of mercury. This allows for much superior chemical and mechanical properties.

In lab today, we condensed four types of amalgam into cavity preps in wooden blocks. The types experimented with were:

1. Tytin regular set (100% spherical)
2. Tytin FC fast set (modified spherical)
3. Contour regular set (admixed; 70% spherical, 30% lathe)
4. Dispersalloy regular set (admixed; 30% spherical, 70% lathe)

The powdered alloy and liquid mercury came in pre-packaged containers, which were mechanically triturated at different set cycles per minute (CPM) and seconds, based on manufacturer's request. The amalgam was then transfered from carrier to bowl, and added to the blocks using condenser instruments. One needs to work fast and make sure all line angles get filled properly using a smaller condensing instrument, before switching over to the larger one.

#18 What I Learned Today

Essentials of Clinical Practice

We were in the wet lab today, to take impressions and pour up stone models of our typodont. To take an impression, you first find a suitable size tray that will fit to the posterior teeth, without allowing for too much facial-to-lingual movement. Trays can be manipulated in a number of ways in order to better fit the patient, including heating up of the plastic in order to bend it, or adding Triad composite material to the end of the tray if it is too short.

Once you have the correct size tray, you can start by mixing the alginate. Based on the product we used, for each pouch of pre-packaged alginate, you add 55 mL of cold water (recall: cold water = retards setting). The water is added to a mixing bowl first, and then the alginate powder. Initially, you want to mix the water and powder in order to dampen it; this keeps the material in the bowl when you begin to mix it vigourously. You then begin to systematically spread it along the side of the bowl using your spatula. When it begins to have a uniform paste-like feel, you begin to transfer it to the tray. This should be done in two scoops, with the top smoothed. It is also important to make sure it is pushed down into the holes on the bottom of the tray so that it is mechanically locked into the tray. This ensures that the alginate impression does not get separated from the tray upon removal. Finally, place the tray from posterior to anterior, ensuring that you don't 'burn' the occlusal surface by pushing the arch in too deep. As well, make sure that alginate covers the entire vestible up to the land area in order to get a good gingival impression.

Remember, this all has to be done as quick as possible, as the alginate sets quickly. And no bubbles.

Once the impression sets, then you remove from mouth (should take 3-5 minutes). The stone powder also comes pre-packaged, and ours needs 40 mL of water. Same mixing procedures, all though time is not as imperative. Once it's mixed, you need to place the mixing bowl on the vibrator to work out any air bubbles in the stone. You follow this up with a double pour procedure. You take small amounts of stone, and run it through the occlusal surface, seeing every tooth get filled. Once you get to the end, you vibrate off any extra. This helps limit any bubbles from occuring at the occlusal surface. You then proceed to fill it up at a quicker pace, giving it a nice large base for further processing. You then let it harden for about 45 minutes (recall: the two setting phases of stone, dental materials lecture!). Carefully pry off the impression tray. It may be necessary to use a buffalo knife to remove any stone mixture that may have slopped over the edge and mechanically locked the model in place.

How to make a base comes next lecture.

General and Oral Histology

Histo lecture today focused on the histology of the oral cavity. We first looked at salivary glands, which classified based on type (whether they are major or minor) and classified by if they secrete serous, mucous, or a mixture of both.

There are three major salivary glands in the oral cavity, those being:

• parotid gland: drained by Stenson's duct, secretes only serous fluid
• submandibular gland: drained by Wharton's duct, secretes both serous and mucous, but mainly serous
• sublingual gland: drained by ducts of Rivinus (many), secretes both serous and mucous, but mainly mucous

Saliva has a number of functions, including:

• moistening oral mucosa and dry food, cooling hot food
• buffers acids through bicarbonate ions
• breaks down carbohydrates by alpha-amylase and fats by lingual lipases
• controls bacterial flora
• helps in remineralization through calcium and phosphate concentrations
• protects teeth by forming enamel pellicle (micrometer of organic film that adsorbs onto enamel surface

You tend to see increased salivary flow rates when chewing. It can also be increased through pregnancy-related hormonal changes, olfactory stimuli, and certain medicines and drugs. Flow rate can be decreased by menopause-related hormone changes, stress, and anti-adrenergic and anti-cholinergic drugs. Dry mouth is clinically referred to as xerostomia.

We then discussed the tissues of the mouth: the oral mucosa. Consists of three layers, including the epithelium, basal lamina and lamina propria (layer of loose connective tissue). May also find a submucosa as well.

Typically find four types of cells in oral mucosa, including the keratinocytes (protection), melanocytes (secretes melatonin), Merkel Cells (touch receptors), and Langerhan's cells (antigen-presenting cells).

You see two types of epithelial layers, a non-keratinized stratified squamous layer called the lining mucosa, and a parakeratinized stratified squamous layer called the masticatory mucosa. The soft tissues (lips, gingiva, soft palate) are lined with lining mucosa, and you find many minor salivary glands that secrete mucosa and submucosa. The epithelium covering hard tissues (ie. the hard palate) have masticatory mucosa to protect the tissue from mastication forces. The masticatory mucosa typically doesn't have submucosa, and are attached directly to the hard tissue.

We finished up by talking about the specialized salivary glands, or the papillae. Four types: filiform papillae (no real taste buds), fungiform papillae, foliate papillae, and circumvallate papillae.

#17 What I Learned Today

Biochemistry

We started reviewing Kreb's Cycle (aka TCA cycle, citric acid cycle) in depth. To summarize, it takes acetyl CoA, adds an acetyl group to oxalocetate, and cycles this compound through several forms. In doing so, it releases 2 carbons worth of carbon dioxide (in order to maximize energy output), removes hydrogens to form 3 NADH and 1 FADH2 (which is used later in the electron transport chain to create water), and releases 1 GTP molecule. By the end of the citric acid cycle, all the carbons from the initial glucose have been converted to carbon dioxide.

Before Kreb's cycle occurs, the pyruvate molecule needs to be converted into acetyl CoA. This is performed mainly through the enzyme pyruvate dehydrogenase, and a bunch of different cofactors (including thiamin dehydrogenase, lipoic acid, and Coenzyme A). I won't bore you with specifics about the reaction, but ultimately, you get:

pyruvate + NAD + Coenzyme A -> CO2 + acetyl CoA + NADH

The citric acid cycle begins with the formation of citrate. This is catalyzed by the enzyme citrate synthase. An acetyl group is removed from coenzyme A and added to oxaloacetate. This step is physiologically irreversible.

The citrate is then converted to isocitrate via a two-step mechanism that is catalyzed by acontiase. A double-bond is added to citrate to form cis-aconitate, and then the end-carbon is oxidized to form the alcohol isocitrate.

Isocitrate is then converted to alpha-ketoglutarate, which is also done in two steps. Hydrogens are removed by NAD+ to form NADH (for usage in ETC later on), forming an unstable intermediate. A carboxylic acid is then removed in the form of carbon dioxide, which results in alpha-KG. This process is also physiologically irreversible.

You get the formation of more NADH and carbon dioxide when alpha-ketoglutarate is oxidized (more NAD+ to NADH). Another carboxylic acid is removed, to form more carbon dioxide. The end product is succinyl-CoA. At this point, all carbons have been fully oxidized to carbon dioxide at this point.

Finally, more hydrogens are removed from succinyl-CoA, to form GTP (an analog to ATP). This returns the carbon molecule back into oxaloacetate; its original form.

Principles of Dental Materials

Midterm today. Nothing was lectured.

Dental Anatomy

We went over mandibular premolars. I will cover this more tomorrow.

#16 What I Learned Today

Essentials of Clinical Practice

Today's lecture moved away from infection control and focused on the importance of keeping good patient records and progress notes. The legalities of record keeping for the state of Michigan is stated in the Dental Practice Act, which can be found via Google.

The act states that a treatment record is required for each patient, regardless of their relationship to the dental practitioner. Each record requires:

• procedures performed
• dates of procedures
• who actually performed the procedure
• charting of clinical finding
• any medication, prescribed, dispensed, or administered
• radiographs

The dental healthcare is responsible for the physical custody and security of the record. The dentist is responsible for keeping information confidential, and must obtain consent from the patient, unless disclosure is for purposes of treatment, payment or healthcare operations. This is all governed under HIPAA. The dentist is obligated to keep all original records to at least 10 years from the date of last treatment. The dentist must keep the original record, and can only distribute a copy of the record if requested by the patient.

All record content should be about personal information/demographics, patient history, examination findings, consultation and referral letters, appointment information, treatment planning, laboratory work, and patient education. Financial information and personal opinions should be kept out.

Lastly, the dentist should avoid using record templates, as they tend to not give the specifics of the case in question. You should be able to go back over the record at a later date and recall what happened with the recorded case.

Gross Anatomy I

Today's lecture focused on the structures found at the root of the neck; the area bounded by the body of the first thoracic vertebra, the first rib, and the manubrium of the sternum. This can be described as the area between the thorax and the neck.

A number of arteries branch off the arch of the aorta and pass through the root of the neck, including the brachiocephalic trunk on the right side, and the left subclavian artery and left common carotid artery on the, you guessed it, left. A number of smaller arteries branch off the thyrocervical trunk, including the transverse cervical artery, suprascapular artery, and the inferior thyroid artery.

The sympathetic trunk also runs up the root of the neck, and you find three sympathetic ganglia:

1. superior cervical ganglion
2. middle cervical ganglion
3. inferior cervical ganglion (lowest)

The phrenic nerve, vagus nerve, and ansa cervicalis are also evident.

You also find a carotid sheath in the root of the neck, and it engulfs the common carotid artery, the internal jugular vein, and the vagus nerve.

Also important to note is the presence of the carotid triangle, which is bounded by the sternocleidomastoid muscle, posterior of digastric muscle, and the superior of the omohyoid muscle. The carotid triangle contains:

• superior laryngeal nerve, which divides into the internal & external laryngeal nerve
• pharyngeal plexus of nerves
• common carotid artery
• internal carotid artery
• external carotid artery

A number of muscles can be found in the root of the neck, some of which include:

• stylohyoid muscle
• sternohyoid muscle
• sternothyroid muscle
• omohyoid muscle
• anterior scalene muscle
• middle scalene muscle

And to finish up, two major glands are found in the region: the thyroid gland, and the parathyroid gland.

Gross Anatomy Lab

After lecture, we headed over to the lab to identify structures in and on the heart. We isolated the main coronary arteries and cardiac veins. These supply blood to the heart structure itself, then dump it back into the right atrium via the coronary sinus. You see two major coronary arteries, shooting off to the left and right, just off the ascending aorta. The left coronary artery branches off into the circumflex artery and the anterior interventricular artery. The right coronary artery branches off into the marginal artery and the posterior interventricular artery. The coronary sinus has three major branches of veins coming off, including the great cardiac vein, the middle cardiac vein, and the small cardiac vein.

We also made incisions to gain access to both of the atriums and ventricles. We further identified structures inside, all of which can be found on Google. The neatest structures to note was the complexity of the pectinate muscles and trabeculae carnae lining the atriums and ventricles, respectively. As well, the setup of the semilunar and cuspid valves were interesting. The bicuspid/tricuspid valves have cusps that are collected to papillary muscle by chordae tendinae, which stops regurgitation of the blood back into the atriums from systolic pressure. This differs from the semilunar valves, which sit freely in the openings, and catch any flowback blood that occurs in the pulmonary trunk or aorta.

#15 What I Learned Today

Professionalism and Ethics I

Today we had a pretty interesting class discussion as to whether or not dentists should have to perform mandatory community service outside of their dental practice. There was definitely mixed feelings: some individuals felt that dentists have the obligation in giving back to their community and should do extra volunteer work such as donating time and money to local organizations. They felt that volunteering was an important part of their application when applying to dental school, and that this is value should be continued on in practice outside of dental school as well.

Others took that stance that dentists should not be made to do additional volunteer work, and that they should be able to use their extra time off work to focus on their family or pursue other hobbies. The dental profession can be a pretty demanding and stressful job; it is imperative for the healthcare professional to relax and reduce stress levels however he or she deems fit.

And others felt that the dentist's obligation was to their own professional bodies. In order to obtain autonomy in the profession, dentists must take care of their own, in other words.

Interesting thoughts.

Biochemistry

Our Biochem lecture was cut short today as we spent a block of time going over review questions for an upcoming midterm. We spent the time finishing up our discussion of gluconeogenesis and gave some examples of diseases arising from problems in its regulation.

We said prior that gluconeogenesis and glycolysis can be quickly regulated through phosphorylation and dephosphorylation. In times of low blood sugar, the body releases glucagon and adrenaline, which work to produce cAMP. cAMP stops the synthesis of glycogen and initiates the breakdown of glycogen by activating phosphorylases.

Another method of regulation involves the functioning of Fructose-1,6-Bisphosphate, which acts as an allosteric effector (small molecule that binds to an enzyme and alters its function). It inhibits fructose-1,6-bisphosphatase which is important in running gluconeogenesis, and inhibits/activates fructose-2,6-bisphosphatase and phosphofructokinase.

Type I glycogen storage disease (aka von Gierke disease) is caused by a deficiency in the enzyme glucose-6-phosphatase. It is an enzyme found in liver/kidneys which removes phosphate to make glucose, so it can leave the cell and enter the blood stream. However, with th edisease, glycogen can't be broken down into glucose and is trapped in the cells. As a result, the liver swells up in size (hepatomegaly), you see hypoglycemia because the liver cannot release glucose, and hyperuricemia, since the body begins to use proteins for energy. The excess nitrogen is converted by the body into uric acid.

Other diseases includes:

• Type 4 glycogen storage disease; a deficiency of a branch enzyme in glycogen. Muscles cannot store up as much glycogen, and you are left with muscle fatigue
• Type 6 glycogen storage disease (Her disease); a deficiency of liver phosphorylase, so you seee the same symptoms as Type 1 glycogen storage disease (but only effects liver)
• Type 2 glycogen storage disease (Pompe disease); a deficiency in lysosomal cells, which affects all organs and leads to cardiomegaly and ultimately heart failure at an early age.

#14 What I Learned Today

Introduction to Operative Dentistry

In sim lab, we learned how to isolate teeth using a rubber dam. Isolation is great (and necessary) for many reasons:

1. get improved vision by contrast of the coloured dam
2. allows for much easier access for tougher to reach posteriors
3. protects from airborne contamination
4. keeps the isolated area dry
5. blocks objects from being inhaled or ingested by accidental dropping
   
6. some patients may find it comforting as a direct barrier
   

The application is pretty basic: you punch holes in the rubber sheet with size and location corresponding to the tooth it is meant to surround, fasten it to the most posterior tooth with a clamp, lead the rest of the teeth through their holes, make sure the edges of the dam extends into the gingival sulcus, and finish off by placing a floss ligature between the last tooth isolated and attaching a metal frame.

Now for the specifics.

The hole puncher has a number of different sizes. I found the following to be effective for my rubber dam puncher:

• first (smallest) hole = do not use.
• second hole = mandibular incisors
• third hole = maxillary incisors
• fourth hole = canines and premolars
• fifth (second biggest) = molars
• sixth = do not use.
  

When practicing on a typodont, there are a number of things that you need to take into account to make life a little easier when placing the rubber dam. First, the typodont teeth are constructed to have very tight contacts. This makes slipping the dam better the interproximal spaces to be near impossible. Use your screwdriver to loosen up the screws on the back a bit, enough to allow the teeth to wobble. This will open up the contacts and make it much easier. As well, the typodont obviously is a very dry setting as compared to a patient's mouth. Lube it up a bit with whatever the school supplies. But note that some lubricants like Vaseline can actually react with the rubber and affect its properties, so be wary about what you use (must be water-soluble).

For the clamps, there are many different kinds and variations a dentist could use for different isolation situations and teeth, including winged clamps, non-winged clamps, and specialty clamps. The key is that the clamp is able to make four strong contact points with the tooth, and be stable (no wiggling or movement). We used these clamps for the following situations:

• #5 winged clamp: for molars on maxillary or mandibular
• 00 winged clamp: for premolars and canines
• W8A clamp: for maxillary molars
  
• 14 Clamp: for maxillary molars
• 212 Clamp: for anterior teeth
  

Some other important things to note, after you get the dam over the teeth, you should use floss to work the dam down into the gingival sulcus. Make sure that when removing the floss, you do so through the facial embrasure in order to not accidently remove the dam from the sulcus you just placed it in. As well, always tie a foot length of floss around the body of the clamp so that it can easily be retrieved in case it is dropped.

#13 What I Learned Today

Essentials of Clinical Practice

Today in ECP we got to have our first clinical-like experience. We went to the third-year clinic and started by setting up the cubicle for usage. The table needs to be wiped down with a disinfectant cloth twice: once to clean, the second time to disinfect. The table is then covered with paper. As well, the following things need to have a plastic cover put over them:

• 1 large cover on the top of the chair
• 1 large cover on the dental unit
• small covers over each of the handpieces, syringes and vaccuums
• small covers over the handles of the overhead light
• small covers over levers on bottom of chair
  

Also, the water bottle must be refilled and both the water synringes must be flushed for about 20 seconds each into a dixie cup.

Before the examination can begin, the patient's pulse and blood pressure must be measured and recorded. The pulse is taken by counting pulses from the radial artery on the lateral side of the wrist, with palm facing forward. Simply take the number of pulses that occur in a 15 second span and multiply it by 4 to get an average number of beats per minute. For blood pressure, the cuff is placed snugly around the patient's arm, about an inch above the crest of the elbow; be sure to follow cuff instructions: ours have an arrow that should be pointing towards the artery, and the cuff tubing needs to be facing towards the elbow. Pump up the cuff until approximately 180-200 mm Hg, and deflate at a fairly rapid place. When you hear the first beat, you record the systolic pressure from the gauge. On the last beat that you hear, you record the diastolic pressure.

We also did a brief intra-oral examination on a classmate in order to get comfortable with viewing angles using the mirror, as well as manipulating the patient's tongue, lips and cheek in order to get an optimal view.

General and Oral Histology

We lectured on facial development and odontogenesis. Facial development begins by week 4 of development, where the fetus has a primitive mouth called a stomodeum and three major prominences including the frontonasal, maxillary and mandibular prominence. The frontonasal prominence gives rise to an intermaxillary segment, which forms into the philtrum and the primary palate. Maxillary prominences combine with lateral nasal prominences to form the nose and upper cheek area. Mandibular prominences form the lower third of the face, including the chin, nmandible, lower lip and lower cheek. Deformities in these layers can lead to facial clefts and hemifacial microsomia (facial asymmetry with underdeveloped tissues and deviation of mandible upwards).

The tongue develops from pharyngeal artch 1, and is comprised of three major swellings: the tuberculum impar (median swelling) and two lateral lingual swellings. Part of the tongue also develops from pharyngeal arch 3, and it comprised of a swelling called the hypobranchial eminence (aka copula). The tongue is innervated by the trigeminal nerve and the hypoglossal nerve. Some tongue developmentla abnormalities include: bifid tongue, macroglossia, microglossa, and ankyloglossia (tongue tied).

The palate of the mouth develops from three tissues: a median palatine process (forms the primary plate) and two lateral palatine processes (forms the secondary plate). Trapped epithelium during palate fusion can lead to palatine cysts.

Odontogenesis is the formation of teeth, and requires two specific types of tissue: the dental lamina and ectomesenchyme. The dental lamina comes from ectoderm, and forms enamel organ, which subsequently forms enamel from the inner enamel epithelial layer. Ectomesenchyme comes from the mesoderm of cranial nerve cells, and forms both the dental papilla and the dental follice. The dental papilla becomes the dental pulp, and the dental follicle becomes the perodontial ligament, cementum, and alveolar.

Teeth develop morphologically in five stages:

1. bud stage: thickening of dental lamina around ectomesenchyme
2. cap stage: dental lamina differentiates into enamel organ and forms a cap over the ectomesenchyme
3. bell stage: enamel organ forms a deeply invaginated concavity where dental papilla is located
4. crown stage: see dentin forming, then followed by enamel in a layered process
5. root formation: crown is completely formed, and Hertwig's epithelial root sheath induces dental papilla to become odontoblasts and form root dentin, and signals dental sac to create cementum

Tooth development also has some histological stages as well:

1. Initiation: thickening of dental lamina
   
2. Proliferation: mitotic activity of dental lamina
3. Morphodifferentiation: folding of inner enamel epithelium determines crown shape
4. Histodifferentiation: cells differentiate (enamel organ -> ameloblasts, dental papilla -> odontoblasts, dental follicle -> cementoblasts)
5. Apposition: incremental growth of mineralized tissue.

Some developmental abnormalities that occur in odontogenesis include:

• adontia/hypodontia: congentical absense of teeth
• hyperdontia: extra (supernumerary) teeth
• microdontia: abnormally small teeth
• macrodontia: abnormally large teeth
• tooth agenesis: lack of tooth formation
• dens in dente: tooth within a tooth
• fusion: abnormally wide-shaped tooth due to two tooth germs joining together (results in less teeth in dentition)
  germination: abnormally wide tooth due to one tooth germ attempting to divide into two (however, still retain normal number of teeth in dentition)

#12 What I Learned Today

Biochemistry

We shifted gears today from glycolysis and looked at gluconeogenesis. Obviously, wasn't much different as gluconeogenesis is just the reverse of glycolysis with some slight differences. So the process begins with pyruvate in the mitochondrial matrix, and it looks to end with having glucose in the cytoplasm. The processes mainly differ at these irreversible steps:

(1) In glycolysis, you have a phosphate being added to Fructose-6-Phosphate to make Fructose-1,6-Bisphosphate. The reverse happens in gluconeogenesis: Fructose-1,6-Bisphosphate looses a P to Fructose-6-Phosphate through the actions of the enzyme Fructose-1,6-Bisphosphatase.

(2) In glycolysis, you have a phosphate being added to glucose when it enters the cell. The reverse happens in gluconeogenesis: a phosphate is removed from Glucose-6-Phosphate by Glucose-6-Phosphatase. This allows the glucose to be able to leave the cell; you will only find this specially functioning enzyme in liver and kidney cells.

(3) In glycolysis, you have pyruvate kinase removing a phosphate from phosphoenoylpyruvate to generate ATP and pyruvate. Since this cannot easily be reversed, gluconeogenesis uses a combination of reactions instead:
(a) carbon dioxide is added to pyruvate by pyruvate carboxylase, to form oxaloacetate
(b) oxaloacetate is transformed back to phosphoenol pyruvate by a long-named kinase.

At this point, oxaloacetate cannot move freely across the mitochondrial membrane in order to get to the cytoplasm, so it needs further conformation. It gets converted to malate, which can pass through, and then reconverted back to oxaloacetate. This process also generates NADH, which makes sense as glycolysis converts NAD+ to NADH; this allows for gluconeogenesis to take the NADH and convert it to NAD+ (remember, reverse of glycolysis!).

Principles of Dental Materials

Today we continued our look at gypsum (recall: dental plaster used to make models from alginate impressions). Some factors that change gypsum's properties include:

(1) the amount of water added; extra water makes models porous and weaker. If you find that the gypsum is setting too quickly, throw it out and start again.

(2) the temperature of the water: if water is too hot (about body temperature hot), it will affect the reaction and the gypsum will not set well. Cold water slows the setting down slightly, while warm water will speed up setting slightly.

(3) hardening solutions can be added to give gypsum a stronger microstructure (eg. colloidal silica, superplasticizers)

(4) environment it is stored in. Gypsum powder will pick up moisture from the environment.

(5) wetting agents

(6) accelerators and retarders. Potassium sulfate accelerates setting. Terra alba (water from grinding wheel) will accelerate setting. Colloidal organic particles (blood, saliva, unset alginate) will retard setting.You should clean off impressions with cold water before setting!

We also began to talk about different metals used in dentistry. There are two main types: nobel metals and base metals. Noble metals tend to be naturally resistant from oxidizing (eg. gold, platinum, iridium, osmium, palladium, rhodium, etc.), while base metals tend to oxidize, but can form a natural adherent oxide coating (eg. iron and cobalt with chromium [acts as a corrosion preventer], titanium, etc.).

An important theory in regards to dental materials is the Metal Deformation Theory. It states that metals develop slip systems, which are planes and directions within the crystal lattice along with atoms slip more easily. Results in materials to be more ductile (deformed). Face-centered cubic materials tend to have more slip systems than body and hexagon-close packed materials.
Can reduce dislocations through four techniques:

(1) create dislocation tangle
(2) add alloying elements for solid solution strengthening
(3) make dispersions of fine second phases
(4) increasing grain boundaries

Note: the fourth method is the best as it increases strength of the metal without decreasing its ducility.

Dental Anatomy

Today in DA we had an exam, so no new lectures. Next week will look at the anatomy of maxillary and mandibular premolars.

#11 What I Learned Today

Essentials of Clinical Practice

We continued our look into infection control in a dental clinic, specifically in regards to bloodborne pathogens. Bloodborne pathogens are obviously of concern in a dental setting (as it is in any healthcare setting), since there are a number of vectors by which viruses can be transmitted. The main culprits include needle sticks, cuts from burs, flying spittle, and to a lesser extent scalpel cuts.

The main viruses of concern in a dental setting include Hepatitis B, Hepatitis C, and HIV. Overall, the risk of contracting the diseases is very low. Hepatitis B is the main culprit: a study found that a needle stick that was used on a patient who is HBV-positive and is positive for the E-antigen is roughly 37-62% at risk for virus transmission. Without the E-antigen, it drops to about 23-27%. HCV has a risk factor of 1.8% and HIV has a risk factor of only 0.3%

These low risk factor numbers are due to the fact that the gauge of the needles used in dentistry are relatively small. These means that the average number of viruses entering one's bloodstream through a needle stick is relatively small. With HIV, there has been no documented cases of a dentist getting the HIV virus from a patient; however, there is a questionable case of a dentist giving the HIV virus to a patient years back. The higher transmission rates of HBV can be combated through vaccination.

There are a number of other viruses and bacteria that can be transmitted in a dental setting, including Influenza, Mumps,Measles, Strep and Staph infections, Herpes, Tuberculosis, etc. That's why it is important to use standard precautions and other infection controls in order to minimize possible risk.

We also briefly talked about HIPAA. Long story short, HIPAA stands for the Health Insurance Portability and Accountability Act and it is the law which governs dentists to protect confidential information that they collect from their patients.

Gross Anatomy I

Today's lecture continued our look at the different anatomical parts of the heart. The right atrium and right ventricle are separated by a tricuspid valve, which has its cusps held shut by chordae tendineae, which in turn are attached to papillary muscles. The left atrium and right ventricle are separated by a bicuspid valve (commonly known at the mitral valve). The right ventricle is C-shaped and thin-walled, while the left ventricle is circular and thick-walled (requires more contraction force to pump blood through whole systemic vessels). The valve of the aorta is made up of three cusps, with two openings to coronary arteries just on the other side. This allows blood to passively flow and oxygenate the heart.

Conduction of the heart is regulated by the vagus nerve, which innervates the sinoatrial node -> atrioventricular node -> atrioventricular bundle (Bundle of His) -> Bundle branches -> Purkinje fibers.

The anterior mediastinum consists primarly of two structures: thymus gland and the internal thoracic vessels.

I will continue this more tomorrow. Exam.

Gross Anatomy Lab

Long story short, we removed the lungs and heart, and identified local vessels and nerves.

#10 What I Learned Today

Professionalism and Ethics I

The focus of today's lecture was to look at the characteristics of a profession, and the professionals committed to it. A profession was defined as job that needs someone who possess esoteric but useful knowledge and skills, based on specialized training or education of exceptional duration and difficulty. Some characteristics of a profession include:

• special/advanced education
• identifiable membership
• strong service orientation
• autonomy of practice
• self-regulating
• adherence to a code of ethics

A professional is a person who belongs to a learned profession, and is an expert at his or her work. Some characteristics of a professional include:

• selfless
• compassionate
• competent
• good communicator
• evidence-based
• ethical
• patient advocate
• responsible
  

Biochemistry

We continued our lecture on carbohydrate metabolism by looking at some other metabolic pathways, aside from the pentose phosphate pathway. These included the metabolic pathways for fructose, galactose, and mannose. We finished off by looking at the synthesis, branching, and debranching of glycogen.

Fructose is not the preferred substrate for sugars entering a cell (as glucose is), and can get across cell membranes via two different enzymatic pathways. Fructo-hexokinase can convert fructose to fructose-6-P, which is the product of the reversible pentose phosphate pathway. The second enzyme, fructo-kinase, converts fructose to fructose-1-P. Since this molecule cannot enter the pentose phosphate pathway, it gets but by aldolase B to get glyceraldehyde (which is an intermediate in the PP pathway!).

Galactose is processed through a isoenergetic transfer. The enzyme galactokinase puts a phosphate on galatctose to form galactose-1-P. It is useless to a cell in this form, so it is further converted. An activated form of glucose called UDPG (has a glucose-1-P 'tail') reacts with galactose-1-P, and transfers/switches the glucose-1-P tail with the galactose-1-P. The molecule then converts the galactose-1-P to glucose-1-P, and the UDPG molecule is taken back in order to start the process up again.

Mannose metabolic pathway will be described later.

With high levels of glucose-6-P ina cell, you get an increase in osmotic pressure as water tends to flow into the cell, which can eventually lead to its lysis. Thus, the cell prevents this by storing glucose-6-P as a glycogen polymer, by these steps:

• glucose-6-P is converted to glucose-1-P by phosphoglucomutase
• since the addition of glucose-1-P is not thermodynamically favoured, it is transformed by UTP (a high phosphate anolog of ATP)
• the glucose-1-P is then added to the Carbon-4 on the glycogen chain
• a PPi product is released, which ensures that the reaction will not be reversed

The glycogen chain has two ends: a reducing end, which is a 'free' carbon-1 (which is actually connected to a tyrosine residue on the protein glycogenin), and a non-reducing end, which is the last glucose molecule which has a free hydroxyl group at Carbon-4.

You also tend to see lots of branching in the glycogen polymers, in order to become more compact through alpha-1,6 branching. A 1,4-alpha-glucan branching enzyme separates an alpha-1,4 chain and moves it over to an alpha-1,6 branch.

Branching is reversed by a process called glycogenolysis, which involves three specific enzymes. Phosphorylase cleaves the alpha-1,4 bond with inorganic phosphate at the terminal end of a chain. This process requires the cofactor pyridoxal. Glucan transferases then transfers three glucose residues from one branch to another, leaving just the lsat sugar with an alpha-1,6 bond. A debranching enzyme then hydrolyzes the alpha-1,6 bond and at this point the branch has been fully removed.

#9 What I Learned Today

Introduction to Operative Dentistry

Today's simulation lab assignment focused on the preparation of Class I amalgam restorations on premolars and molars. Like any preparation, three specific forms need to be met in order to perform a competent preparation. The retention form ensures that the restorative material remains intact in the preparation once placed. This can be done through the use of parallel walls for deep preparations (roughly in excess of 4 mm), convergent walls (in instances less than 4 mm in depth), and dovetails (rounded walls at mesial and/or distal portions in order to resist lateral movment of restorative material). The resistance form makes sure that the placed restoration will be able to withstand occlusal forces and not fracture. This includes providing adequate thickness for restorative material (amalgam requires at least 2 mm, composite requires less), keeping the preparation small in order to maintain strong cusps and ridges, and making a flat pulpal floor that is perpendicular to occlusal forces. Finally, the convenience form needs to be met in order for the dentist to easily access (and see) the preparation and place the restorative material.

We performed Class I preparations on teeth #12 (permanent maxillary left first premolar) and #14 (permanent maxillary left first molar). We used a #330 bur, as we were only looking to penetrate the tooth to a depth of 2 mm (the same length as the working part of the bur). A #245 can be used for deeper preparations. In each case, the tooth was penetrated to the depth of 2 mm at the mesial/distal pit of the central groove. The bur was brought straight back up, and the resulting hole was measured with a periodontal probe to ensure proper depth. The bur was reinserted, and the groove was traced towards the opposite mesial/distal.

When making a Class I preparation, it is important to make all cavosurface line angles rounded. The walls of the buccal and lingual are made to be convergent in order to increase retention of the amalgam material. Distal and mesial walls are made to be divergent to 6 degrees. Pulpal floor is made to be flat from the buccal to the lingual, and slightly rounded from the mesial to the distal (in order to match the curvature of the DEJ). Finally, no unsupported enamel (enamel without dentin underneath) should be left, due to it being easily fractured. This means that any preparations nearing the mesial/distal marginal ridges should leave up to at least 1.6mm of enamel in order to be supported. Otherwise, a Class II preparation might be necessary.

#8 What I Learned Today

Essentials to Clinical Practice

Our focus in Essentials today was on communication techniques that can be used by a dental practitioner. We watched some movies and were asked to pick up on subtle cues which may be an indication of negative body language. An example would be a patient who tends to inch or crawl away from the dentist throughout the visit. This is an indication of anxiety; in such an instance it may be a good idea to slow down and allow the patient to regain his or her composure.

We also looked at the use of open-ended versus close-ended question during the recording of health history. Often there can be a discord between what a dentist is asking for, and how a patient responds. By asking open-ended questions, you are likely to obtain more information which can often shed more light on facts that may be important to diagnosis. This also allows for the dentist to ask further questions and help guide the patient into reporting information.

General and Oral Histology

General and Oral Histology focused on embryology. It is important for a dentist to understand the orgins and growth of hard and soft dental tissues. Embryology starts with fertilization of a sperm and egg cell, which grows consecutively from a zygote, to a morula, to a blastocyst, to an embryo. An inner cell mass develops into a bilaminar embryonic disc. Gatrulation turns the bilaminar disc into a trilaminar disc, which is the basis of the three germ layers: mesoderm, ectoderm, and endoderm. Enamel is derived from the ectoderm.

Later on in embryo development, one sees the formation of a neural tube, which gives rise to the neural crest and ultimately the central nervous system. The neural crest eventually folds to form pharyngeal arches. Pharyngeal arch #1 forms Meckel's cartilage, which eventually undergoes intramembranous ossificaiton and forms the manidble. The maxilla, trigeminal nerve, masticatory muscles, tongue, and oral epithelium also form from PA #1. Pharyngeal arch #2 forms the facial nerves and palatine tonsils.

#7 What I Learned Today

Biochemistry

Today in biochemistry, we lectured on the hexose monophosphate shunt (which is also known as the pentose phosphate pathway). The pathway is a major one in the metalbolic usage of glucose. The cell can use it for many processes including lipid synthesis, nucleotide synthesis (through the molecule ribose) and antioxidant synthesis. It does this mainly through the formation of NADPH, which is a molecule often used for many anabolic (creating) processes; NADP is often used in catabolic (destroying) processes.

The pathway takes 3 glucose-6-phosphate molecules and 6 NADP molecules and converts them to 2 glucose-6-phosphate, 3 carbon doxide, 1 glyceradehyde-3-P and 6 NADPH. This pathway occurs mainly in two distinct steps; however, the reaction is typically reversible, and thus can be used by a cell in a number of ways, depending on what molecules it needs at the time.

The first step is an oxidative phase, where glucose-6-P is oxidized first at Carbon-1, which converts the hydroxyl group into a ketone (gluconolcatone). This reduces an NADP to an NADPH. Water is then used to hydrolyze the bond between Carbon-1 and Oxygen to form an open-chained carboxylic acid (phosphogluconate). Next, the molecule is oxidized at Carbon-3 to produce another NADPH molecule, and an unstable keto-acid. This molecule is then stabilized by giving off a CO2 molecule, forming ribulose-5-phosphate (only 5 carbons!).

The second step is a rearrangement phase, where carbon is shuffled around in order to get as many 6-carbon fragments back as possible. At this point, ribulose-5-phosphate can take two different pathways, depending on the cell's needs:

(1) if ribose is NOT needed, the molecule flips it's hydroxyl group to form xylulose-5-P. It is then cut by transketolase where 2 carbons are removed from xylulose-5-phosphate, and added to ribose-5-P to form a 3-carbon and 7-carbon molecule. The 7-carbon molecule is then cut by transaldolase, which takes 3 carbons off and adds them to the 3-carbon sugar, forming a 4-carbon molecule (erytherose-4-P) and a 6-carbon molecule (fructose-6-P).

Fructose-6-P is essentially equivalent to glucose-6-P!

(2) if ribose is needed for nucleotide synthesis, the double-bonded O in ribulose is swapped from Carbon-2 to Carbon-1, which forms ribose-6-P.

This reaction is also very important in RBC as they form many free radicals due to having both iron and oxygen in their system. The cell converts these harmful radicals to H2O2 (peroxidase), and further use the enzyme glutathione reductase to break down the peroxidases before they damage the cell. NADPH is important in the formation of the GR enzyme. When deficient, precipitaiton of the RBC occurs, causing the cell membrane to become rigid, and thus the macrophages attack the RBC, causing acute hemolysis.

Principle of Dental Materials

We discussed the properties of two common hydrocollodial dental materials: alginate and gypsum. Alginate is the material used to take impressions of the mouth, which form an inverted mold. Gypsum is the plaster material that is poured into the alginate impression in order to form an actual model of the patient's mouth. The model can then be used in diagnosis and in crown preparation.

Alginate is derived from seaweed, and is made up of a linear polymer of anhydro-beta-D-mannuronic acid. Algiante reacts with hydrated calcium sulfate and water to form calcium alginate and other products. This is a non-reversible reaction which sets in about 1-5 minutes, depending on the type of alginate used. Alginate is very cheap, is flexible, easy to use and can reproduce oral detail to an acceptable level. There are some rubber-based impression materials that can capture more detail, but they tend to be of higher price. When taking alginate impressions, it is important to take into account some important things which may affect the properties of alginate, including the amount of water mixed (too much is bad!), rate of impression removal from mouth, storage time, and saliva and blood contaminations.

For the gypsum reaction, calcium sulfate hemihydrate (half a mol of water) reacts with water to form gypsum. Gypsum comes in many different types, depending on the model's use. These include model plaster for study models, and dental stone for lab cases. When adding water, one must be careful not to add too much as excess water causes porosity in the plaster, ultimately lowering its strength. One must be careful as the gypsum has two separate setting phases. The initial set takes between 8-16 minutes and is still very weak and fractures easily. After 20-60 minutes, the set stone is much harder and at this point is ready to be separated from the impression.

Dental Anatomy

Our lecture today focused on the permanent maxillary and manibular canines.

The canines are considered to be the most important tooth in the dentition. Not only is it important in tearing food, but it also acts to support the facial muscles and is one of the strongest tooth in the mouth due to having the longest root in the mouth. The shape of the labial surface is that of a pentagon, with a cusp tip that is centered over the body of the crown. This tip results in two incisal cusp ridges, with the distoincisal ridge being longer than the mesioincisal ridge. The resulting mesial outline is slightly convex, while the distal outline is slightly concave With wear, the cusp tip moves distally.

The height of contour in the mesial is found on the junction of the incisal and middle third, while the height of contour in the distal is found in the middle third. Two ridges are found on the labial and lingual surfaces, forming mesiolabial and distolabial developmental depressions on the front, and mesiolingual and distolingual fossa on the back. The lingual of the tooth also has a cingulum (offset to distal), mesial and distal marginal ridges; all of which are very prominent on the maxillary. The distal marginal ridge is often more irregular than the mesial margin.

From the incisal view, the shape is seen as an asymmetrical diamond, with the mesial half being more bulky than the distal. The distal also sees a distolingual concavity on the maxillary.

The root often has two concavities on both the distal and mesial, with the distal being more prominent.

The mandibular differs from the maxillary in that the crown is actually longer incisogingivally, but smaller on both the mesial-distal and facial-lingual dimensions. As well, the distoincisal line angle is more rounded. This results in the mesial outline to be a bit longer and straighter than the distal.