B. Natural History
C. Why we do this
- Paul Revere—identifying victim of Boston Massacre
- Geo. Washington
Silver and Ivory
Dentist to modify O.S.S. agent’s teeth
L pills and continental fillings
III. Natural History
A. Hard substances, last very long time
1 Teeth form from the cooperative interaction of two germ layers–ectoderm and ectomesenchyme (a neural crest derivative).
2 Enamel is formed from the ectodermal components.
3 Dentin, pulp, cementum, the supporting PDL, and bone are all derived from ectomesenchyme.
1. Better to be a hunter-gatherer
2. Farming hard life.
D. Baby teeth
1. 20 4 incisors, 2 cuspids, 4 molars
2. Incisors first, (6mos) molars last (20-30 mos.)
E. Adult teeth
1. 32 4 incisors, 2 cuspids, 2 bicuspids, 6 molars
2. 6 years to 17-24 years
F. Don’t always follow the book
a. Microdontia refers to teeth that are smaller than normal. Generalized microdontia is a rare condition associated with uncommon conditions such as pituitary dwarfism. More often, microdontia is limited to just one or two teeth. “Peg-shaped” upper lateral incisors and small third molars are seen.
b. Macrodontia refers to teeth that are larger than normal. Generalized macrodontia is rare, seen infrequently in conditions such as pituitary gigantism. It can be localized involving just one or a few teeth. Macrodontia is much less common than microdontia.
a. Fewer teeth
1. Anodontia is the congenital absence of all teeth.
2. Edenulous is the clinical absence of teeth.
3. True anodontia is an extremely rare occurrence.
b. Extre teeth
1. Supernumerary teeth
2. Most (90%) occur in the maxilla.
3. Most supernumerary teeth do not erupt; they often are unknown until detected on X-ray films.
4. Fourth molars, themselves a rare occurrence are infrequently called ‘paramolars’ or ‘distomolars.’
|-Dilaceration is a severe bend in the long axis of the tooth. The bend it located at the junction between the crown and the root. The bend can be as much as 90 degrees. Dilaceration usually results from trauma to the unfinished tooth when development is in progress. Such a tooth in the old literature is sometimes called a ‘hawk billed tooth’.
-Flexion is a deviation or bend restricted just to the root portion of the tooth. Usually the bend is less than 90 degrees. It may be a result of trauma to the developing tooth. Carefully contrast and compare the definitions for flexion and dilacertaion.
-Taurodontism literally means ‘bull-like teeth’. Taurodont teeth are usually molars. They have an abnormally long pulpal chamber and shortened roots. The pulp chamber has no constriction near the CEJ as do normal teeth. Clinically these teeth appear normal. Taurodontism was relatively common amongst the European Neandertals. It is also found on occasion in people living today. The implication of its appearance in modern people is unknown. No treatment of the condition is necessary apart from due prudence when doing root canal therapy.
-Dens in dente literally means ‘tooth within a tooth’. It is an uncommon developmental abnormality that primarily affects maxillary lateral incisors. It is in fact a deeply invaginated lingual pit with an important clinical implication: these are very susceptible to caries and they ought to be restored promptly. Left unattended, these teeth tend to decay very rapidly. Modern literature will often refer this condition as dens invaginatus. This is a term you should know.
-Supernumerary cusps, or as they are often called, extra cusps are occasionally found on teeth. We review here the common types.
|(1) The most common one is the Carabelli Cusp which is found on the mesiolingual aspect (on the mesiolingual cusp) of maxillary first molars AND maxillary second deciduous molars.|
-This occlusal landmark can appear with varying degrees of intensity either as a cusp or pit. These conditions are known collectively as the Carabelli trait. Clinically it is worth checking out during a dental exam: it is frequently a site of early dental caries. It is a heritable trait most commonly seen in European populations. The Carabelli trait is best understood as a variation, not an anomaly.
|(2) A talon cusp is an extra cusp that resembles an eagle’s talon (a talon is the claw of a bird of prey). A talon cusp appears as a projection from the cingulum of incisor teeth. These can interfere with occlusion; however, grinding them down is a hazardous endeavor. Talon cusps often contain a prominent pulp horn which is very susceptible to exposure in the younger patient.|
(3) Very rarely, a similar projection of enamel can occur on the occlusal surface of the premolar teeth. It forms a tubercle called a ‘dens evaginatus’. (Do not confused this with the early condition, dens invaginitus mentioned above.) Dens evaginitus can also contain a pulp horn as does the talon cusp mentioned earlier. Fortunately, these conditions are infrequent.
(4) One other variation of the upper first premolar is the ‘Uto-Aztecan’ upper premolar. It is a bulge on the buccal cusp that is only found in Native American Indians, with highest frequencies of occurrence in Arizona. The name is not a dental term; it comes from a regional linguistic division of Native American Indian language groups.
(5) Peg-sbaped lateral incisors.
(6) No discussion of ‘disturbances in shape’ is complete without mention of root variation. Certain teeth exhibit a variation in the number of roots.
Incidentally, most root variation is in the distal third of the root. Sometimes roots can be blunted or shortened. It tends to occur without apparent cause. On occasion, root resorption and root blunting can be unfortunate consequence of orthodontic treatment with fixed appliances. A few patients are very susceptible to this condition, and the practitioner’s heart sinks when it is found–without warning–on the post treatment X-ray films. Below is a brief discussion of extra or fused roots.
|(a.) Upper first premolars usually have two roots; however, one root is occasionally found in these teeth. More rarely there are three roots.
(b.) Lower permanent canines on occasion have a bifurcation near the apex resulting in two short roots. A question about this condition has appeared frequently on Part I National Boards for dental students.
(c.) Sometimes lower first permanent molars have three roots. It is the mesial molar root that is bifurcated. Clinical articles often consider it an anomaly. It is just a variation. Three rooted lower first molars are found in greater frequency amongst North American Indians with origins in Asia.
(d.) In upper third molars, and on occasion with fused roots, second molars, the roots can be fused together. This is a variation, not a pathological condition.
|Shovel shaped incisors display enhanced marginal ridges and present with a distinctive shovel-shaped appearance on the lingual aspect. They appear frequently in many persons of Asian origin, including many Native American Indians. They are especially prominent in Eskimo/Inuit who are descendants of Siberians about 4,000 years ago.|
A. Clues to patient
4. “Meth” mouth
5. T-T ratio
1. Compare pre and post mortem x-rays