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 ).
HISTOLOGIC CHANGES OF THE PULP
Regressive changes
Pulp decreases in size by the deposition of dentin.
This can be caused by age, attrition, abrasion, operative procedures, etc.
Cellular organelles decrease in number.
Fibrous changes
They are more obvious in injury rather than aging. Occasionally, scarring may also be apparent.
Pulpal stones or denticles
They can be: a)free, b)attached and/or c)embedded. Also they are devided in two groups: true or false. The true stones (denticles) contain dentinal tubules. The false predominate over the the true and are characterized by concentric layers of calcified material.
Diffuse calcifications
Calcified deposits along the collagen fiber bundles or blood vessels may be observed. They are more often in the root canal portion than the coronal area.
Histology of the Cementum
Cementum is a hard connective tissue that derives from ectomesenchyme.
Embryologically, there are two types of cementum:
Primary cementum: It is acellular and develops slowly as the tooth erupts. It covers the coronal 2/3 of the root and consists of intrinsic and extrinsic fibers (PDL).
Secondary cementum: It is formed after the tooth is in occlusion and consists of extrinsic and intrinsic (they derive from cementoblasts) fibers. It covers mainly the root surface.
Functions of Cementum
It protects the dentin (occludes the dentinal tubules)
It provides attachment of the periodontal fibers
It reverses tooth resorption
Cementum is composed of 90% collagen I and III and ground substance.
50% of cementum is mineralized with hydroxyapatite. Thin at the CE junction, thicker apically.
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.
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Maxillary (upper) teeth |
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Permanent teeth |
Central |
Lateral |
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First |
Second |
First |
Second |
Third |
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Initial calcification |
3–4 mo |
10–12 mo |
4–5 mo |
1.5–1.75 yr |
2–2.25 yr |
at birth |
2.5–3 yr |
7–9 yr |
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Crown completed |
4–5 yr |
4–5 yr |
6–7 yr |
5–6 yr |
6–7 yr |
2.5–3 yr |
7–8 yr |
12–16 yr |
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Root completed |
10 yr |
11 yr |
13–15 yr |
12–13 yr |
12–14 yr |
9–10 yr |
14–16 yr |
18–25 yr |
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Mandibular (lower) teeth |
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Initial calcification |
3–4 mo |
3–4 mo |
4–5 mo |
1.5–2 yr |
2.25–2.5 yr |
at birth |
2.5–3 yr |
8–10 yr |
|
Crown completed |
4–5 yr |
4–5 yr |
6–7 yr |
5–6 yr |
6–7 yr |
2.5–3 yr |
7–8 yr |
12–16 yr |
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Root completed |
9 yr |
10 yr |
12–14 yr |
12–13 yr |
13–14 yr |
9–10 yr |
14–15 yr |
18–25 yr |
HISTOLOGY OF SALIVARY GLANDS
Parotid: so-called watery serous saliva rich in amylase
Submandibular gland: more mucinous
Sublingual: viscous saliva
Parotid Gland: The parotid is a serous secreting gland.
There are also fat cells in the parotid.
Submandibular Gland
This gland is serous and mucous secreting.
There are serous demilunes
This gland is more serous than mucous
Also fat cells
Sublingual Gland
Serous and mucous secreting
Serous cells in the form of demilunes on the mucous acini.
more mucous than serous cells
Minor Salivary Glands
Minor salivary glands are not found within gingiva and anterior part of the hard palate
Serous minor glands=von Ebner below the sulci of the circumvallate and folliate papillae of the tongue; palatine, glossopalatine glands are pure mucus; some lingual glands are also pure mucus
Functions
Protection: lubricant (glycoprotein); barrier against noxious stimuli; microbial toxins and minor traumas; washing non-adherent and acellular debris; calcium-binding proteins: formation of salivary pellicle
Buffering: bacteria require specific pH conditions; plaque microorganisms produce acids from sugars; phosphate ions and bicarbonate
Digestion: neutralizes esophageal contents, dilutes gastric chyme; forms food bolus; brakes starch
Taste: permits recognition of noxious substances; protein gustin necessary for growth and maturation of taste buds
Antimicrobial: lysozyme hydrolyzes cell walls of some bacteria; lactoferrin binds free iron and deprives bacteria of this essential element; IgA agglutinates microorganisms
Maintenance of tooth integrity: calcium and phosphate ions; ionic exchange with tooth surface
Tissue repair: bleeding time of oral tissues shorter than other tissues; resulting clot less solid than normal; remineralization
MAXILLARY CUSPIDS (CANINE)
The maxillary cuspid is usually the longest tooth in either jaw. canines are considered the corner stones of the dental arch They are the only teeth in the dentition with a single cusp.
Facial Surface:- The facial surface of the crown differs considerably from that of the maxillary central or lateral incisors. In that the incisal edges of the central and lateral incisor are nearly straight, the cuspid has a definite point, or cusp. There are two cutting edges, the mesioincisal and the distoincisal. The distoincisal cutting edge is the longer of the two. The developmental grooves prominent on the facial surface extending two-thirds of the distance from the tip of the cusp to the cervical line. The distal cusp ridge is longer than the mesial cusp ridge
Lingual Surface: Distinct mesial and distal marginal ridges, a well-devloped cingulum, and the cusp ridges form the boundries of the lingual surface. The prominent lingual ridge extends from the cusp tip to the cingulum, dividing the lingual surface into mesial and distal fossae.
Proximal: The mesial and distal aspects present a triangular outline. They resemble the incisors, but are more robust--especially in the cingulum region
Incisal: The asymmetry of this tooth is readily apparent from this aspect. It usually thicker labiolingually than it is mesiodistally. The tip of the cusp is displaced labially and mesial to the central long axis of this tooth.
Root Surface:-The root is single and is the longest root in the arch. It is usually twice the length of the crown.
lntraarch relationship refers to the alignment of the teeth within an arch
1. In an ideal alignment teeth should contact at their proximal crests of curvature. A continuous arch form is observed in occlusal view
Curves of the occlusal plane (a line connecting the cusp tips of the canines, premolars, and molars) are observed from the proximal view
Curve of Spee: anterior to posterior curve; for mandibular teeth the curve is concave and for maxillary teeth it is convex
Curve of Wilson- medial to lateral curve for mandibular teeth the curve is also convex and for the maxillary it is convex
2. Contact does not always exist Some permanent dentitions have normal spacing
Primary dentitions often have developmental spacing in the anterior area: some primary den titions have a pattern of spacing called primate spaces between the primary maxillary lateral incisors and canine and between the mandibular canine and first mo1ar
Disturbances to the intraarch alignment are described as
a. Qpen contact where interproximal space exist because of missing teeth oral habits, dental disease, or overdeveloped frena
b. where contact or position is at an unexpected area because of developmental disturbances, crowding, dental caries or periodontal ligament for their misplaced position: facial, lingual. mesial, supra(supraerupted) infra (infraerupted) and torso (rotated) version