📖 Dental Anatomy
MAXILLARY SECOND MOLAR
Dental AnatomyMAXILLARY SECOND MOLAR
The second molars are often called 12-year molars because they erupt when a child is about 12 years
Facial: The crown is shorter occluso-cervically and narrower mesiodistally whe compared to the first molar. The distobuccal cusp is visibly smaller than the mesiobuccal cusp. The two buccal roots are more nearly parallel. The roots are more parallel; the apex of the mesial root is on line with the with the buccal developmental groove. Mesial and distal roots tend to be about the same length.
Lingual: The distolingual cusp is smaller than the mesiolingual cusp. The Carabelli trait is absent.
Proximal: The crown is shorter than the first molar and the palatal root has less diverence. The roots tend to remain within the crown profile.
Occlusal: The distolingual cusp is smaller on the second than on the first molar. When it is much reduced in size, the crown outline is described as 'heart-shaped.' The Carabelli trait is usually absent. The order of cusp size, largest to smallest, is the same as the first but is more exaggerated: mesiolingual, mesiobuccal, distobuccal, and distolingual.
Contact Points; Height of Curvature: Both mesial and distal contacts tend to be centered buccolingually below the marginal ridges. Since themolars become shorter, moving from first to this molar, the contacts tend to appear more toward the center of the proximal surfaces.
Roots: There are three roots, two buccal and one lingual. The roots are less divergent than the first with their apices usually falling within the crown profile. The buccal roots tend to incline to the distal.
Note: The distolingual cusp is the most variable feature of this tooth. When it is large, the occlusal is somewhat rhomboidal; when reduced in size the crown is described as triangual or 'heart-shaped.' At times, the root may be fused.
Dental Formula, Dental Notation, Universal Numbering System
Dental AnatomyDental Formula, Dental Notation, Universal Numbering System
A. Dental Formula. The dental formula expresses the type and number of teeth per side
The Universal Numbering System. The rules are as follows:
1. Permanent teeth are designated by number, beginning with the last tooth on the upper right side, going on to the last tooth on the left side, then lower left to lower right
2. Deciduous teeth are designated by letter, beginning with the last tooth on the upper right side and proceeding in clockwise fashion
Nerve and vascular formation
Dental AnatomyNerve and vascular formation
Frequently, nerves and blood vessels run parallel to each other in the body, and the formation of both usually takes place simultaneously and in a similar fashion. However, this is not the case for nerves and blood vessels around the tooth, because of different rates of development.
Nerve formation
Nerve fibers start to near the tooth during the cap stage of tooth development and grow toward the dental follicle. Once there, the nerves develop around the tooth bud and enter the dental papilla when dentin formation has begun. Nerves never proliferate into the enamel organ
Vascular formation
Blood vessels grow in the dental follicle and enter the dental papilla in the cap stage. Groups of blood vessels form at the entrance of the dental papilla. The number of blood vessels reaches a maximum at the beginning of the crown stage, and the dental papilla eventually forms in the pulp of a tooth. Throughout life, the amount of pulpal tissue in a tooth decreases, which means that the blood supply to the tooth decreases with age. The enamel organ is devoid of blood vessels because of its epithelial origin, and the mineralized tissues of enamel and dentin do not need nutrients from the blood.
Classification of Cementum
Dental AnatomyClassification of Cementum
- Embryologically
Primary and secondary
2. According to cellular component
Acellular: Thin, Amorphous, First layer to seal the dentin tubules
Cellular: Thick, Better structure, Apical surface
Layers of cellular and acellular cementum alternate (randomly)
3. Based on the origin of the collagenous matrix
Extrinsic
Intrinsic
Mixed
4. Combined classification
a. Primary acellular intinsic fiber cementum
b. Primary acellualar extrinsic fiber cementum
c. Secondary cellular intrinsic fiber cementum
d. Secondary cellular mixed fiber cementum
e. Acellular afibrillar cementum
5. Depending on the location and patterning
Intermediate and mixed stratified cementum
Participating Cells
Cementoblasts
Active
Cells are round, plump with basophilic cytoplasm (rough endoplasmic reticulum)
Inactive
Cells have little cytoplasm
Cementocytes
- Cementocyte lacuna
- cementocyte canaliculus
Cells have fewer organelles compared to cementoblasts. They are found in lacunae and have numerous processes toward the periodontal ligament. Eventually they die due to avascularity
Cementicles
a) free
b) attached
c) embedded