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Anatomy of Primary TeethSteven Chussid D.D.S.

Lecture OverviewPrimary DentitionGeneral Morphological considerationsImplications of Primary tooth morphology

Primary Dentition20 primary teeth as compared to 32 permanent teethNo premolars in the primary dentitionThe primary molars are replaced by the premolarsThe permanent molars erupt distal to the primary second molars

Eruption Patterns of Primary Teeth

Sequence more important than timing

Symmetrical pattern

Mandibular teeth erupt first

Approximate Eruption Schedule

7+4 Guideline

7 Months = First Tooth Erupts

11 Months = 4 Erupted Teeth

7 months + 4 = 11 months

0 teeth + 4 = 4 teeth

General Morphologic considerationsCrownPulpRoot

Crown of Primary TeethShorter Narrower occlusal tableConstricted in the cervical portionThinner enamel and dentin layersEnamel rods in the cervical area directed occlusally Broad and flat contactsColor is usually lighter

Crowns of Primary TeethProminent mesio-buccal cervical bulge seen in primary molars

Incisors have no developmental grooves or mammelons

Primary Crown AnatomyMandibular Central Incisors- Symmetrically flat when viewed from buccalCrown about 1/3 length of rootCingulum present on lingual surfaceMandibular Lateral IncisorSimilar form to central Usually longerIncisal edge slopes toward distal and DI angle more rounded

Primary Crown AnatomyMaxillary Central IncisorOnly tooth that has a greater mesiodistal width than heightProminent cingulumIncisal edge straightMaxillary Lateral IncisorSimilar form to centalSmaller and DI angle rounded

Primary Crown AnatomyMaxillary CanineCrown constricted at cervical regionWell developed, sharp cuspRoot is long, more than 2X crownMandibular CanineSimilar form to maxillaryCrown shorter and narrower labiolingually

Primary Crown AnatomyMaxillary First MolarUnique appearanceThree cusps-MB, DB and LingualProminent MB cervical bulgeMandibular First MolarAlso unique in appearanceFour cusps-MB, DB, ML and DLProminent MB cervical bulgeTransverse ridge

Primary Crown AnatomyMaxillary 2nd Molar Resembles permanent maxillary first molar but smallerMandibular 2nd Molar- Resembles permanent mandibular first molar but smaller

Pulps of Primary TeethRelatively largerPulp horns are closer to the outer surfaceGreat variation in size and locationMesial pulp horn is higher Pulp chamber shallowForm of the pulp follows the external anatomyUsually a pulp horn under each cusp

Pulpal Anatomy

Roots of Primary TeethRoots of anterior teeth are narrower mesio-distallyPosterior teeth have longer and more slender roots in relation to crown sizeMolar roots flare more as they approach the apexApical foramina may be larger and accessory canals often larger and more numerous

Implications of Primary tooth morphologyThe progress of caries is much faster in the primary dentition, so incipient lesions should be restored sooner than later!Thinner enamel and dentinMesial pulp horn higher

Procedures in Primary TeethRestorative DentistryEnamel is thinner, therefore modifications are necessary in the cavity prepBroad contacts need to be restoredBeware of the mesio-buccal pulp hornMay need to do SSC if both proximal surfaces involvedPreserve the buccal cervical ridge to obtain mechanical retention for SSC

Procedures in Primary TeethSurgical ProceduresConical anterior roots facilitate easy removalFlared roots of the molars - use caution as premolar buds are located between the rootsPulp TherapyPulpotomy- beware of perforationsPulpectomyDifficult on molars due to tortuous and irregular pulp canalsBeware of tooth buds

SummaryPrimary teeth haveThinner enamel and dentin layersPulp horns closer to the outer surfaceMesial pulp horn much higherRelatively larger pulpsEnamel rods direct slightly occlusally in the cervical areaCervical area is constricted significantlyRoots flare as they approach the apexMore tortuous and irregular pulp canals

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