#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.