MORPHOLOGY OF DECIDUOUS TEETHMORPHOLOGY OF DECIDUOUS TEETH

Dental Anatomy & OcclusionDental Anatomy & Occlusion

Dent 202Dent 202

Deciduous dentition Set traits

Smaller in size Smaller crown height/tooth length ratio Greater crown width/height ratio

Set traits More bulging B & L cervical ridges

Constricted cervix Buccal cervical ridges on deciduous

molars Occlusal aspect: constricted occlusal table

Deciduous dentition

Set traits Molar roots

• More slender & relatively longer

• More bowed & flared outward

• Shorter root trunk Milk-white in color Enamel is thinner & pulp chamber is large

Some class, arch & type traits in permanent dentition are applied to deciduous dentition

Only new traits will be discussed

Deciduous incisorsEruption

Mandibular before maxillary incisors Central before lateral incisors

No mamelons, labial grooves or lobes

Maxillary Central incisor

The only incisor with MD breadth > crown height

M & esp. D profiles overhang root profiles

No labial grooves, depressions or lobes

Cingulum Bulging & more incisally located May extend further toward the incisal

edge – lingual ridge Unmarked by pits or grooves

MRs are clearly evident

Maxillary Central incisor

Constricted cervix from all aspects

In proximal surfaces CL is more convex incisally

Conical root with rounded apex

Diamond-shaped from incisal aspect

Maxillary lateral incisorMuch smaller than centralM & D profiles are more in line

with root profilesDistal incisal angle is more

roundedLabial surface is more convex

MDLingual fossa is deeperMRs more prominentCL is similar to that of centralRounded from incisal aspect

Mandibular central incisor

Bilaterally symmetrical90 degree MI & DI angles Incisal margin is horizontalProminent cingulum with lingual

margin extending incisallyMRs are less marked than those of

max. incisorsLingual fossa is shallower

Mandibular central incisor

Labial surface is flat MDCL is similar to that of Max. incisorsRoot

3 times the height of the crown Narrow & conical with pointed apex

Mandibular lateral incisor

Incisal edge slopes distallyDI angle is roundedD profile is more roundedGreater crown height/MD ratio than mand. centralLL diameter > MD

Mandibular lateral incisor

Cingulum, fossa & MRs are similar to those of mand. Central

Root Narrow & conical Apex has D inclination D surface has narrow

vertical depression

Maxillary canine

MD width > crown heightLabial or lingual views: diamond in

shapeM & D profiles overhang root’sHOCs are much near the cervix than in

permanentLabial & lingual cervical 1/3s are

markedly convexMR prominence is related to race

Minimal in Caucasians Prominent in Mongoloid

No labial ridge or depressions

Mandibular canine Crown height > MD width Less cervically converging M & D

profiles Labial or lingual aspects: arrow in

shape No labial ridge or grooves HOCs are much near the cervix than

in permanent LL diameter < that of deciduous

max. canine Less prominent cingulum or MRs &

shallower fossae than in deciduous max. canine

Maxillary 1st molar

Most atypical of all primary or permanent molars Intermediate between a premolar & a molarSmallest molar in all but BL diameter

Cusps Bicusped (only MB & ML cusp

are present) A small DB cusp is frequently

present on the D cusp ridge of the MB cusp

Parastyle on the M ridge of MB cusp

DL cusp rarely occurs In some cases, a nodular tubercle

on the L portion of the D MR resembles a DL cusp

Maxillary 1st molar

Buccal aspect MD diameter >> crown height M part is higher OC than D

because it is more projected cervically onto the root area

Marked cervical constriction Root

• Very little root trunk• 3 roots strongly divergent• L root is midway between the 2 B

roots

Maxillary 1st molar

Mesial aspect Mesial marginal groove B HOC is more cervically

located than L Buccal cervical ridge is more

prominent in 1st molars than in 2nd

Roots• B roots are straight & buccally

directed• L root is banana shaped with

strong B curved apical 1/3

Maxillary 1st molar

Occlusal aspect Trapezoidal M & D profiles are straight & slightly L convergent B cusp > L B triangular ridge more prominent than L B groove separates DB cusp from MB Central pit Central groove Transverse ridge (oblique ridge?) between B groove & D MR H-shaped pit/groove pattern

• Central groove• Triangular supplemental grooves

M & D marginal grooves

Maxillary 1st molar

Morphologically considered a model for the permanent 1st maxillary molar

Allows prediction of what the 1st maxillary molar will look like

This concordance is called isomorphy

Set traits Cervical constriction Cervical 1/3 bulging Little root trunk Roots thinner & divergent

Maxillary 2nd molar

Molariform unlike max. 1st

4-cusped toothBuccal aspect

2 cusp: MB & DB M half > D half M half projects more occlusally &

occupies 2/3s of crown area M profile is straight D profile is curved and overhanging CL inclines downward from D to M Roots

• 2 divergent roots; M & D• M is longer

Mandibular 1st molar

Lingual aspect 2 cusps: ML & DL ML cusp is conical & larger

than DL Outlines of B cusps are

visible CL is more straight &

horizontal than that of the B aspect

Mandibular 1st molar

Mesial aspect Buccal cervical ridge (BCR) From MB cusp tip a straight incline to

BCR Transverse ridge connecting MB & ML M MR is high & prominent Mesial marginal groove separates M MR

from ML cusp ridge CL is convex occlusally & lower on the

B end Root

• Extremely broad BL (sometimes as broad as the crown)

• Frequently bifid apex

Mandibular 1st molar

Distal aspect All 4 cusps & M root profiles

are visible B profile is less bulging than

from mesial aspect D MR is lower and less

prominent than M MR CL is more straight &

horizontal than that of M aspect

Mandibular 1st molar

Occlusal aspect Without the BCR, it is rectangular BL width is grater from M than D MB cusp is the largest, followed by

ML, DB & DL M Transverse groove, interrupted by Central groove; extends from M pit to

central pit M pit

• 2 supplemental grooves; of which ML crosses M MR

Central pit B& L grooves Often a D pit

Mandibular 1st molar

Morphologically considered a model for the permanent 1st mandibular molar

Allows prediction of what the 1st mandibular molar will look like

This concordance is called isomorphy

Set traits Cervical constriction Cervical 1/3 bulging Little root trunk Roots thinner & divergent

Mandibular 2nd molar

Deciduous teeth - size & eruption

ToothCrown height

MD crown diameter

BL crown diameter

Tooth length

Age at eruption

51 or 61 6.0 mm 6.5 mm 5.0 mm 16.0 mm 7.5 mths

52 or 62 5.6 mm 5.1 mm 4.0 mm 15.8 mm 8 mths

81 or 71 5.0 mm 4.2 mm 4.0 mm 14.0 mm 6.5 mths

82 or 72 5.2 mm 4.1 mm 4.0 mm 15.0 mm 7 mths

53 or 63 6.5 mm 7.0 mm 7.0 mm 19.0 mm 16-20 mths

83 or 73 6.0 mm 5.0 mm 4.8 mm 17.0 mm 16-20 mths

54 or 64 5.1 mm 7.3 mm 8.5 mm 15.2 mm 12-16 mths

55 or 65 5.7 mm 8.2 mm 10.0 mm 17.5 mm 20-30 mm

84 or 74 6.0 mm 7.7 mm 7.0 mm 15.8 mm 12-16 mm

85 or 75 5.5 mm 9.9 mm 8.7 mm 18.8 mm 20-30 mm