difference between primary and permanent teeth 1

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Alexandria University

Morphological differences between deciduous and permanent teeth.

IntroductionWhat are deciduous teeth? The term deciduous means that these teeth are shed in order to make way for their permanent successors.

Other terms for deciduous teeth: a. Milk teeth. b. Baby teeth. c. Temporary teeth.

ChronologyDeciduous teeth are in use from the age of 6 months till age of 12 years. Therefore premature loss of deciduous teeth is to be avoided. Dental formula: I 2/2 C 1/1 M 2/2 2 = 20

Deciduous teeth numbering systemi. Palmer s notation system:

ii. FDI 2-digits teeth numbering system:

Facts1) Deciduous anteriors are replaced by permanent anteriors. 2) Deciduous molars are replaced by permanent premolars. 3) No premolars in deciduous set. 4) Deciduous teeth are usually lighter in color than the permanent. 5) Deciduous teeth provide space for permanent teeth. 6) Deciduous teeth have more upright position in the jaws while the permanent are more inclined labially. 7)Calcification of 1ry teeth occurs before birth.


Crowns of 1ry teeth are much smaller, but more bulbous than their permanent successors. For this reason a small bur(330) should be used. Constricted neck: an excessive extension of the gingival seat toward the cervical line in class II cavity preparation should be avoided to avoid loss of the gingival floor of the preparation. The more the gingival seat is placed cervically, the more is the chance of a pulp exposure in the axial wall 1ry teeth are lighter in colour than the permanent teeth due to: a- less thickness of enamel and dentine. a- less mineralization of the enamel which renders it less translucent, while permanent teeth are more calcified and are therefore more translucent . This reflects the colour of dentin which is darker in permanent teeth. b- the prismatic structure of the enamel. c-the child is less subjected to staining from external factors(e.g. tea and coffee)



4) Prominent cervical ridge especially on the buccal surface of the 1ry molars. It is similar to the buccal deflection ridge in permanent teeth but is situated more towards the cervical line. This ridge has an important role in the retention of stainless steel crown.

5) Flat buccal and lingual surfaces. 6) Occlusal convergence. 7) Narrow occlusal table therfore buccal and lingual extensions of the occlusal preparation should be avoided.

8) The crown is wider mesio-distally compared to the occluso-cervical dimension. 9) Pits and fissures are shallow ,cusp ridges are not well defined. 10) Absence of mamelons. 11) Flat and broad contact areas which are located more gingivally. It is therefore more difficult to diagnose incipient proximal lesions except by a bitewing x-ray. 12) The teeth are in an upright (vertical) position in the jaws, for this reason there is no curve of Spee. 13) Physiologic spacing exists for proper alignment of permanent teeth later on. 14) Crowns are more liable to attrition due to lower calcium content.

Root: 1) Narrow and short root trunk(furcation area is nearer to the crown). Consequently an abscess in 1ry teeth is usually detected radiagraphically at the furcation area. This is also due to the numerous accessory canals present at this area. 2) Divergant roots especially at the apical third, to give room for the development of their permanent successors. 3) Long, narrow, thin slender roots. 4) Root: Crown ratio in primary teeth is more than in permanent.

Pulp: 1) Large pulp chamber in relation to the crown size. 2) High pulp horns especially mesially. For these reasons, exposure can easily occur 3) Root canals are narrow and tortuous. 4) It is common to find accessory canals located at the furcation area as well as in other sites throughout the canals.

Histologically Enamel:1)Uniform thickness(1mm). 2) Less enamel thickness than in permanent teeth. 3) At the ginigival margin the enamel rods are directed occlusally therefore there is no need for bevel in classII cavity preparation. 4) Finish line of enamel cap cervically is in the form of a bulge(rounded) not knife edge as in permanent teeth.

Dentine: 1) Wider dentinal tubules. 2) Irregular. 3) Thickness of the dentine covering the pulp is less. Accordingly the ideal depth of the cavity is 1mm in enamel and 0.5 in dentin.

I-Morphological differences between deciduous and permanent anterior teeth1. Crowns of deciduous anterior teeth are wider mesio-

distally than occluso-cervically in comparison to the permanent successors. 2. Cervical ridge at cervical third of anterior crowns labially and lingually is much more prominent in deciduous than permanent teeth. 3. Roots of deciduous anterior teeth are narrower and longer than those of permanent anterior teeth.

A-Deciduous maxillary central and lateral incisors: 1) These teeth resemble the permanent maxillary incisors but are smaller in size . 2) Lateral incisor differs form central in that the cervico-incisal length of the crown is greater than its mesio-distal width and the disto-incisal angle is more rounded . B-Deciduous mandibular central and lateral incisors: These teeth resemble their permanent successors except that they are smaller in size

C-Deciduous maxillary canine:

The tooth is similar to the permanent except that:1) The deciduous maxillary canine is smaller. 2) The crown is more constricted at the cervix in relation to its mesio-distal width. The mesial and distal surfaces are more convex. 3) The mesial and distal contact areas are at the same level nearly in the center of the middle third. 4) The cusp is much longer and sharper than that of the permanent. The mesial slope is longer than the distal (opposite to the permanent). 5) The root length is more than twice the crown length

D-Deciduous mandibular canine: 1)this tooth resembles the permanent mandibular canine ,but is much smaller. 2) the deciduous mandibular canine has the mesial slope shorter than the distal as in permanent mandibular and maxillary canines.

II-Morphological differences between deciduous and permanent posterior teeth1) The buccal and lingual surfaces of crowns of deciduous molar are flatter coronal to the cervical curvatures than those of permenant molars, there is narrowing in the occlusal surface buccolingually. 2) Cervical ridge buccally on deciduous molars is more pronounced especially on 1st molars. 3) Crowns and roots of deciduous molars are narrower mesio-distally at the cervical third than those of permanent teeth. 4) Roots of deciduous molars are more slender and longer than those of permanent molars, they have very short root trunks , they flare out apically. This flare allows more room between the roots for the development of permanent teeth crowns. 5) The roots of deciduous teeth flare out more apically extending beyond projected outlines of the crown. 6) The pulp chambers are large and pulp horns are high.

Primary Root Canal AnatomyGeneral features: 1-smaller depth of dentin between the pulp chambre and the enamel. 2-very thin, highly projecting pulp horns in the molars,especially the mesial. 3-the pulp chamber is relatively larger. 4-long root canals, irregular and ribbon-like. 5-the root furcation is very close to the level of the cemento-enamel junction. 6-the apical 3rd of the root has many accessory canals.

Maxillary incisorsresemble the exterior form of the tooth, it is fan-shaped when viewed from the labial aspect. The pulp chamber has three small projections on its incisal border and tapers evenly toward the cervix. The pulp canal varies from a round shape to a slight labiolingual compression. The root canal is wide with a realtively wider apical cross section than that of the permanent. The 1ry insisors have only one root canal with an oval cross-section. The pulp chamber and canals

Mandibular central incisor The pulp chamber conforms

to the external anatomy of the crown. There is usually a definite constriction between the pulp chamber and the pulp canal. The pulp canal tapers evenly towards the apex.

Mandibular lateral incisor Similar to the lower central except that there is no

constriction between the pulp chamber and pulp canal.

Maxillary and mandibular canines Pulp morphology shows three

projections at the incisal aspect of the pulp chamber the central is the largest and longest followed by the distal and mesial projections. The root canal tapers evenly as it approaches the apex. In cross-section the root canal appears flattened on the mesial and distal sides, giving an oval shape.


st 1


y The coronal pulp is similar to the external form. y There are three pulp horns, the mesiobuccal is

the largest followed by the mesiolingual and the distobuccal. y There are three pulp canals corresponding to the three roots.


nd 2


contour of the crown. y There is one pulp horn corresponding to each cusp, the mesiobuccal is the largest followed by the mesiolingual, distobuccal, and distolingual. y The shape of the access opening from the occlusal view is trapezoidal or square in shape.

y The pulp chamber conforms to the external

Mandibular 1st molarthe largest and longest. y There are three pulp canals, the distal, Mesiobuccal and mesiolingual. y The 2 mesial canals generally extend from the pulp chamber separately or in a ribbon shape, but usually become more confluent via branching as they approach the apex. y From the occlusal view, the shape of the access opening is nearly trapezoidal or rectangular in shape .y The pulp chamber has four pulp horns,the MB is


nd 2


y The pulp chambre has five pulp horns and

three pulp canals,the MB and M

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