#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)