NEET MDS Lessons
Dental Anatomy
Dental Terminology.
Cusp: a point or peak on the occlusal surface of molar and premolar teeth and on the incisal edges of canines.
Contact: a point or area where one tooth is in contact (touching) another tooth
Cingulum: a bulge or elevation on the lingual surface of incisors or canines. It makes up the bulk of the cervical third of the lingual surface. Its convexity mesiodistally resembles a girdle encircling the lingual surface at the cervical.
Fissure: A linear fault that sometimes occurs in a developmental groove by incomplete or imperfect joining of the lobes. A pit is usually found at the end of a developmental groove or a place where two fissures intersect.
Lobe: one of the primary centers of formation in the development of the crown of the tooth.
Mamelon: A lobe seen on anterior teeth; any one of three rounded protuberances seen on the unworn surfaces of freshly erupted anterior teeth.
Ridge: Any linear elevation on the surface of a tooth. It is named according to its location or form. Examples are buccal ridges, incisal ridges, marginal ridges, and so on.
Marginal ridges are those rounded borders of enamel which form the margins of the surfaces of premolars and molars, mesially and distally, and the mesial and distal margins of the incisors and canines lingually.
Triangular ridges are those ridges which descend from the tips of the cusps of molars and premolars toward the central part of the occlusal surface. Transverse ridges are created when a buccal and lingual triangular ridge join.
Oblique ridges are seen on maxillary molars and are a companion to the distal oblique groove.
Cervical ridges are the height of contour at the gingival, on certain deciduous and permanent teeth.
Fossa: An irregular, rounded depression or concavity found on the surface of a tooth. A lingual fossa is found on the lingual surface of incisors. A central fossa is found on the occlusal surface of a molar. They are formed by the converging of ridges terminating at a central point in the bottom of a depression where there is a junction of grooves
Pit: A small pinpoint depression located at the junction of developmental grooves or at the terminals of these groops. A central pit is found in the central fossa on the occlusal surfaces of molars where developmental grooves join. A pit is often the site of the onset of Dental caries
Developmental groove: A sharply defined, narrow and linear depression formed during tooth development and usually separating lobes or major portions of a tooth.
A supplemental groove is also a shallow linear depression but it is usually less distinct and is more variable than a developmental groove and does not mark the junction of primary parts of a tooth.
Buccal and lingual grooves are developmental grooves found on the buccal and lingual surfaces of posterior teeth.
Tubercle: A small elevation produced by an extra formation of enamel. These occur on the marginal ridges of posterior teeth or on the cingulum of anterior teeth. These are deviations from the typical form.
Interproximal space: The triangular space between the adjacent teeth cervical to the contact point. The base of the triangle is the alveolar bone; the sides are the proximal surfaces of the adjacent teeth.
Sulcus:-An elongated valley or depression in the surface of a tooth formed by the inclines of adjacent cusp or ridges.
Embrasures: When two teeth in the same arch are in contact, their curvatures adjacent to the contact areas form spillway spaces called embrasures. There are three embrasures:
(1) Facial (buccal or labial)
(2) Occlusal or incisal
(3) Lingual
(NOTE: there are three embrasures; the fourth potential space is the interproximal space ).
MANDIBULAR CENTRAL INCISORS
These are the first permanent teeth to erupt, replacing deciduous teeth, and are the smallest teeth in either arch
Facial Surfaces:-The facial surface of the mandibular central incisor is widest at the incisal edge. Both the mesial and the distal surfaces join the incisal surface at almost a 90° angle. Although these two surfaces are nearly parallel at the incisal edge, they converge toward the cervical margin. The developmental grooves may or may not be present. When present, they appear as very faint furrows.
Lingual: The lingual surface has no definite marginal ridges. The surface is concave and the cingulum is minimal in size.
Proximal: Both mesial and distal surfaces present a triangular outline.
Incisal: The incisal edge is at right angles to a line passing labiolingually through the tooth reflecting its bilateral symmetry.
Root Surface:-The root is slender and extremely flattened on its mesial and distal surfaces.
Nutrition and tooth development
As in other aspects of human growth and development, nutrition has an effect on the developing tooth. Essential nutrients for a healthy tooth include calcium, phosphorus, fluoride, and vitamins A, C, and D. Calcium and phosphorus are needed to properly form the hydroxyapatite crystals, and their levels in the blood are maintained by Vitamin D. Vitamin A is necessary for the formation of keratin, as Vitamin C is for collagen. Fluoride is incorporated into the hydroxyapatite crystal of a developing tooth and makes it more resistant to demineralization and subsequent decay.
Deficiencies of these nutrients can have a wide range of effects on tooth development. In situations where calcium, phosphorus, and vitamin D are deficient, the hard structures of a tooth may be less mineralized. A lack of vitamin A can cause a reduction in the amount of enamel formation. Fluoride deficency causes increased demineralization when the tooth is exposed to an acidic environment, and also delays remineralization. Furthermore, an excess of fluoride while a tooth is in development can lead to a condition known as fluorosis.
Enamel
Composition: 96% mineral, 4% organic material and water
Crystalline calcium phosphate, hydroxyapatite
Physical characteristics: Hardness compared to mild steel; enamel is brittle
Support from dentin is necessary
Enamel has varies in thickness
Structure of enamel
Ground sections of enamel disclose the information that we have about enamel
Enamel is composed of rods
In the past we used the term prism (do not use)
Enamel rod
The rod has a cylinder-like shape and is composed of crystals that run parallel to the longitudinal axis of the rod. At the periphery of the rod the crystals flare laterally.
Interrod region: surrounds each rod; contain more enamel protein (fish scale appearance)
Rod sheath: boundary where crystals of rods meet those of the interrod region at sharp angles (We used to describe that as a keyhole configuration)
Each ameloblast forms one rod and together with adjacent ameloblasts the interrod region Very close to dentin there is no rod structure since the Tomes' processes develop after the first enamel is formed.
Striae of Retzius and cross striations
Incremental lines
Enamel structure is altered along these lines
Cross striations are also a form of incremental lines highlighting the daily secretory activity of ameloblasts
Bands of Hunter and Schreger
Optical phenomenon produced by changes in rod direction
Gnarled enamel
Twisting of rods around each other over the cusps of teeth
Enamel tufts and lamellae
They are like geologic faults
Tufts project from the DE junction, appear branched and contain greater concentrations of enamel protein than enamel
Lamellae extend from the enamel surface
Enamel spindles
Perikymata
Shallow furrows on surface of enamel formed by the striae of Retzius
Cementum
Composition
a. Inorganic (50%)—calcium hydroxyapatite crystals.
b. Organic (50%)—water, proteins, and type I collagen.
c. Note: Compared to the other dental tissues, the composition of cementum is most similar to bone; however, unlike bone, cementum is avascular (i.e., no Haversian systems or other vessels are present).
Main function of cementum is to attach PDL fibers to the root surface.
Cementum is generally thickest at the root apex and in interradicular areas of multirooted
Types of cementum
a. Acellular (primary) cementum
(1) A thin layer of cementum that surrounds the root, adjacent to the dentin.
(2) May be covered by a layer of cellular cementum, which most often occurs in the middle and apical root.
(3) It does not contain any cells.
b. Cellular (secondary) cementum
(1) A thicker, less-mineralized layer of cementum that is most prevalent along the apical root and in interradicular (furcal) areas of multirooted teeth.
(2) Contains cementocytes.
(3) Lacunae and canaliculi:
(a) Cementocytes (cementoblasts that become trapped in the extracellular matrix during cementogenesis) are observed in their entrapped spaces, known as lacunae.
(b) The processes of cementocytes extend through narrow channels called canaliculi.
(4) Microscopically, the best way to differentiate between acellular and cellular cementum is the presence of lacunae in cellular cementum.
Types of dentitions:
1. Diphyodont. Teeth develop and erupt into their jaws in two generations of teeth. The term literally means two generations of teeth.
2. Monophyodont. a single generation of teeth.
3. Polyphyodont. Teeth develop a lifetime of generations of successional teeth
4. Homodont. all of the teeth in the jaw are alike. They differ from each other only in size.
5. Heterodont. There is distinctive classes of teeth that are regionally specialized.
MANDIBULAR FIRST BICUSPID
Facial: The outline is very nearly symmetrical bilaterally, displaying a large, pointed buccal cusp. From it descends a large, well developed buccal ridge.
Lingual: This tooth has the smallest and most ill-defined lingual cusp of any of the premolars. A distinctive feature is the mesiolingual developmental groove
Proximal: The large buccal cusp tip is centered over the root tip, about at the long axis of this tooth. The very large buccal cusp and much reduced lingual cusp are very evident. You should keep in mind that the mesial marginal ridge is more cervical than the distal contact ridge; each anticipate the shape of their respective adjacent teeth.
Occlusal: The occlusal outline is diamond-shaped. The large buccal cusp dominates the occlusal surface. Marginal ridges are well developed and the mesiolingual developmental groove is consistently present. There are mesial and distal fossae with pits,
Contact Points: When viewed from the facial, each contact area/height of curvature is at about the same height.
Root Surface:-The root of the mandibular first bicuspid is usually single, but on occasion can be bifurcated (two roots).