Differences Between the Deciduous and Permanent Teeth

1. Deciduous teeth are fewer in number and smaller in size but the deciduous molars are wider mesiodistally than the premolars. The deciduous anteriors are narrower mesiodistally than their permanent successors. Remember the leeway space that we discussed in the unit on occlusion?

2. Their enamel is thinner and whiter in appearance. Side by side, this is obvious in most young patients.

3. The crowns are rounded. The deciduous teeth are constricted at the neck (cervix).

4. The roots of deciduous anterior teeth are longer and narrower than the roots of their permanent successors.

5. The roots of deciduous molars are longer and more slender than the roots of the permanent molars. Also, they flare greatly.

6. The cervical ridges of enamel seen on deciduous teeth are more prominent than on the permanent teeth. This 'bulge' is very pronounced at the mesiobuccal of deciduous first molars.

G. Deciduous cervical enamel rods incline incisally/occlusally.

Root Formation and Obliteration

1. In general, the root of a deciduous tooth is completely formed in just about one year after eruption of that tooth into the mouth.

2. The intact root of the deciduous tooth is short lived. The roots remain fully formed only for about three years.

3. The intact root then begins to resorb at the apex or to the side of the apex, depending on the position of the developing permanent tooth bud.

4. Anterior permanent teeth tend to form toward the lingual of the deciduous teeth, although the canines can be the exception. Premolar teeth form between the roots of the deciduous molar teeth

Introduction. The Jaws and Dental Arches

The teeth are arranged in upper and lower arches. Those of the upper are called maxillary; those of the lower are mandibular.

1. The maxilla is actually two bones forming the upper jaw; they are rigidly attached to the skull..
2. The mandible is a horseshoe shaped bone which articulates with the skull by way of the temporomandibular joint the TMJ.
3. The dental arches, the individual row of teeth forming a tooth row attached to their respective jaw bones have a distinctive shape known as a catenary arch.

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.