NEET MDS Lessons
Dental Anatomy
AGE CHANGES
Progressive apical migration of the dentogingival junction.
Toothbrush abrasion of the area can expose dentin that can cause root caries and tooth mobility.
Histology of the alveolar bone
Near the end of the 2nd month of fetal life, mandible and maxilla form a groove that is opened toward the surface of the oral cavity.
As tooth germs start to develop, bony septa form gradually. The alveolar process starts developing strictly during tooth eruption.
The alveolar process is the bone that contains the sockets (alveoli) for the teeth and consists of
a) outer cortical plates
b) a central spongiosa and
c) bone lining the alveolus (bundle bone)
The alveolar crest is found 1.5-2.0 mm below the level of the CEJ.
If you draw a line connecting the CE junctions of adjacent teeth, this line should be parallel to the alveolar crest. If the line is not parallel, then there is high probability of periodontal disease.
Bundle Bone
The bundle bone provides attachment to the periodontal ligament fibers. It is perforated by many foramina that transmit nerves and vessels (cribiform plate). Embedded within the bone are the extrinsic fiber bundles of the PDL mineralized only at the periphery. Radiographically, the bundle bone is the lamina dura. The lining of the alveolus is fairly smooth in the young but rougher in the adults.
Clinical considerations
Resorption and regeneration of alveolar bone
This process can occur during orthodontic movement of teeth. Bone is resorbed on the side of pressure and opposed on the site of tension.
Osteoporosis
Osteoporosis of the alveolar process can be caused by inactivity of tooth that does not have an antagonist
FUNCTIONS OF PERIODONTIUM
Tooth support
Shock absorber
Sensory (vibrations appreciated in the middle ear/reflex jaw opening)
Transient structures during tooth development
Enamel knot: Thickening of the internal dental epithelium at the center of the dental organ.
Enamel cord: Epithelial proliferation that seems to divide the dental organ in two.
Review the role of these two structures
Enamel niche: It is an artifact that is produced during section of the tissue. It occurs because the dental organ is a sheet of proliferating cells rather than a single strand. It looks like a concavity that contains ectomesenchyme.
MAXILLARY CENTRAL INCISORS
Viewed mesially or distally, a maxillary central incisor looks like a wedge, with the point of the wedge at the incisal (cutting) edge of the tooth.
Facial Surface- The mesial margin is nearly straight and meets the incisal edge at almost a 90° angle, but the distal margin meets the incisal edge in a curve. The incisal edge is straight, but the cervical margin is curved like a half moon. Two developmental grooves are on the facial surface.
Lingual Surface:- The lingual aspect presents a distinctive lingual fossa that is bordered by mesial and distal marginal ridges, the incisal edge, and the prominent cingulum at the gingival. Sometimes a deep pit, the lingual pit, is found in conjunction with a cingulum.
Incisal: The crown is roughly triangular in outline; the incisal edge is nearly a straight line, though slightly crescent shaped
Contact Points: The mesial contact point is just about at the incisal, owing to the very sharp mesial incisal angle. The distal contact point is located at the junction of the incisal third and the middle third.
Root Surface:-As with all anterior teeth, the root of the maxillary central incisor is single. This root is from one and one-fourth to one and one-half times the length of the crown. Usually, the apex of the root is inclined slightly distally.
Maxillary Second Deciduous Molar.
-The notation is A or J.
-It looks like a first permanent molar
-There are three roots.
-Usually it has four well developed cusps.
-It is somwhat rhomboidal in outline.
-They often have the Carabelli trait.
- the shape the maxillary first permanent molar strongly resembles that of the adjacent deciduous second molar.
The periodontium consists of tissues supporting and investing the tooth and includes cementum, the periodontal ligament (PDL), and alveolar bone.
Parts of the gingiva adjacent to the tooth also give minor support, although the gingiva is Not considered to be part of the periodontium in many texts. For our purposes here, the groups Of gingival fibers related to tooth investment are discussed in this section.
MANDIBULAR LATERAL INCISORS
The mandibular incisor is a little wider mesiodistal than the mandibular central incisor, and the crown is slightly longer from the incisal edge to the cervical line.
Facial Surface:-The facial surface is less symmetrical than the facial surface of the mandibular central incisor. The incisal edge slopes upward toward the mesioincisal angle, which is slightly less than 90°. The distoincisal angle is rounded. The mesial border is more nearly straight than the distal border.
Lingual Surface:- The incisal portion of the lingual surface is concave. The cingulum is quite large but blends in smoothly with the rest of the surface.
Root Surface:-The root is single and extremely flattened on its mesial and distal surfaces.