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.

Dentin

1. Composition

a. Inorganic (70%)—calcium hydroxyapatite crystals.

b. Organic (30%)—water and type I collagen.

2. Types of dentin

a. Primary dentin

(1) Dentin formed during tooth development, before completion of root formation.

It constitutes the majority of dentin found in a tooth.

(2) It consists of a normal organization of dentinal tubules.

(3) Circumpulpal dentin

(a) The layer of primary dentin that surrounds the pulp chamber.  It is formed after the mantle dentin.

(b) Its collagen fibers are parallel to the DEJ.

b. Secondary dentin

(1) Dentin formed after root formation is complete.

(2) Is deposited unevenly around the pulp chamber, forming along the layer of dentin closest to the pulp.

It therefore contributes to the decrease in the size of the pulp chamber as one ages.

(3) It consists of a normal, or slightly less regular, organization of dentinal tubules. However,

as compared to primary dentin, it is deposited at a slower rate.

(4) Although the dentinal tubules in secondary dentin can be continuous with those in primary

dentin, there is usually a tubular angle change between the two layers.

c. Tertiary (reparative, reactive) dentin

(1) Dentin that is formed in localized areas in response to trauma or other stimuli such as caries, tooth wear, or dental work.

(2) Its consistency and organization vary. It has no defined dentinal tubule pattern

d. Mantle dentin
 

(1) The outermost layer of dentin
(2) Is the first layer of dentin laid down by odontoblasts adjacent to the DEJ.

(3) Is slightly less mineralized than primary dentin.

(4) Has collagen fibers that are perpendicular to the DEJ.

(5) Dentinal tubules branch abundantly in this area.

e. Sclerotic (transparent) dentin

(1) Describes dentinal tubules that have become occluded with calcified material .

(2) Occurs when the odontoblastic processes retreat, filling the dentinal tubule with calcium phosphate crystals.

(3) Occurs with aging.

f. Dead tracts

(1) When odontoblasts die, they leave behind empty dentinal tubules, or dead tracts.

(2) Occurs with aging or trauma.

(3) Empty tubules are potential paths for bacterial invasion.

3. Structural characteristics and microscopic features:
 

a. Dentinal tubules

(1) Tubules extend from the DEJ to the pulp chamber.

(2) The tubules taper peripherally (i.e., their diameters are wider as they get closer to the pulp). Since the tubules are distanced farther apart at the periphery, the density of tubules is greater closer to the pulp.

(3) Each tubule contains an odontoblastic process or Tomes’ fiber.

Odontoblastic processes are characterized by the presence of a network of microtubules, with

Occasional mitochondria and vesicles present.

Note: the odontoblast’s cell body remains in the pulp chamber.
 

(4) Coronal tubules follow an S-shaped path, which may result from the crowding of  odontoblasts as they migrate toward the pulp during dentin formation.

b. Peritubular dentin (intratubular dentin)

(1) Is deposited on the walls of the dentinal tubule, which affects (i.e., narrows)the diameter of the tubule .

(2) It differs from intertubular dentin by lacking a collagenous fibrous matrix. It is also more mineralized than intertubular dentin.
 

c. Intertubular dentin

(1) The main part of dentin, which fills the space between dentinal tubules

 (2) Is mineralized and contains a collagenous matrix.

d. Interglobular dentin

(1) Areas of hypomineralized or unmineralized dentin caused by the failure of globules or calcospherites to fuse uniformly with mature dentin.

(2) Dentinal tubules are left undisturbed as they pass through interglobular dentin; however,

No peritubular dentin is present.

(3) Interglobular dentin is found in the:

(a) Crown—just beneath the mantle dentin.

(b) Root—beneath the dentinocemental junction, giving the root the appearance of a granular

layer (of Tomes).

e. Incremental lines

(1) Dentin is deposited at a daily rate of approximately 4 microns.

(2) As dentin is laid down, small differences in collagen fiber orientation result in the formation of incremental lines.

(3) Called imbrication lines of von Ebner.

(a) Every 5 days, or about every 20 µm, the changes in collagen fiber orientation appear more

accentuated. This results in a darker staining line, known as the imbrication line of von

Ebner.

(b) These lines are similar to the lines of Retzius seen in enamel.

f. Contour lines of Owen

(1) An optical phenomenon that occurs when the secondary curvatures of adjacent dentinal tubules coincide, resulting in the appearance of lines known as contour lines of Owen.
 

(2) Contour lines of Owen may also refer to lines that appear similar to those just described; however, these lines result from disturbances in mineralization.

g. Granular layer of Tomes

(1) A granular or spotty-appearing band that can be observed on the root surface adjacent to the dentinocemental junction, just beneath the cementum.

Nerve 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.

Permanent teeth

1. The permanent teeth begin formation between birth and 3 years of age (except for the third molars)

2. The crowns of permanent teeth are completed between 4 and 8 years of age, at approximately one- half the age of eruption

The sequence for permanent development

Maxillary                     

First molar → Central incisor → Lateral incisor → First premotar → Second pmmolar  → Canine → Second molar → Third molar

Mandibular

First molar → Central incisor → Lateral incisor → Canine → First premolar → Second premolar → Second molar → Third molar

Permanent teeth emerge into the oral cavity as

                                      Maxillary                       Mandibular

Central incisor               7-8 years                        6-7 years

Lateral incisor                8-9 years                        7-8 years

Canine                           11-12 years                    9-10 years

First premolar                10-Il years                      10-12 years

Second premolar            10-12 years                  11-12 years

First molar                       6-7 years                      6-7 years

Second molar                 12-13 years                    11-13 years

Third molar                      17-21 years                    17-21 years

The roots of the permanent teeth are completed between 10 and 16 years of age, 2 to 3 years after eruption

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.

MAXILLARY 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.