different

• The human dentition : upper and lower arches

• Heterodont: Different teeth to perform

functions

• Two dentitions : primary and permanent.

NUMBER Primary number of teeth: 20 (5 in each quadrant)

Permanent number of teeth: 32 (8 in each

quadrant)

DURATION

Primary teeth -6months to 5 1/2 years

Permanent teeth - 6 years onwards

Chronology of primary teeth -Maxilla

TOOTH 1ST EVIDENCE OF CALCIFICATION (WKS IN UTERO)

ENAMEL COMPLETED

ERUPTION ROOT COMPLETED

MAXILLARY

Central incisor

14(13-16) 1 ½ mo 10(8-12)mo 1 ½ yr

Lateral incisor

16(14 ½-16 ½) 2 ½ mo 11(9-13)mo 2 yr

Cuspid 17(15-18) 9 mo 19(16-22)mo 3 ¼ yr

1st molar 15 ½ (14 ½ -17) 6 mo 16(13-19)mo 2 ½ yr

2nd molar 19(16-231/2 ) 11 mo 29(25-33)mo 3 yr

Chronology of primary teeth-Mandible

TOOTH 1ST EViDENCE OF CALCIFICATION (WKS IN UTERO)

CROWN COMPLETED

ERUPTION ROOT COMPLETED

MANDIBULAR

Central incisor 14(13-16) 2 ½ mo 8(6-10) mo 1 ½ yr

Lateral incisor 16(141/2-) 3 mo 13(10-16) mo 1 ½ yr

Cuspid 17(16-) 9 mo 20(17-23)mo 3 ¼ yr

1st molar 151/2 (141/2 -17) 5 ½ mo 16(14-18)mo 2 ¼ yr

2nd molar 18(17-191/2 ) 10 mo 27(23-31) mo 3 yr

Chronology of permanent teeth

TOOTH HARD TISSUE FORMATION BEGINS

CROWN COMPLETED

ERUPTION ROOT COMPLETED

MAXILLARY

Central incisor 3-4 mo 4-5 yr 7 – 8 yr 10 yr

Lateral incisor 10-12 mo 4-5 yr 8-9 yr 11yr

Cuspid 4 -5 mo 6-7 yr 11-12 yr 13-15 yr

1st premolar 1 ½ -1 ¾ yr 5-6 yr 10-11yr 12-13 yr

2nd premolar 2 – 2 ¼ yr 6-7 yr 10-12 yr 12 -14 yr

1st molar At birth 2 ½ -3 yr 6-7 yr 9-10 yr

2nd molar 2 ½ -3 yr 7-8 yr 12-13 yr 14-16 yr

3rd molar 7-9 yr 12-16 yr 17-21 yr 18 -25 yr

Chronology of permanent teeth

TOOTH HARD TISSUE FORMATION BEGINS

AMOUNT OF ENAMEL AT BIRTH

ENAMEL COMPLETED

ERUPTION ROOT COMPLETED

MANDIBULAR

Central incisor 3 -4 mo 4-5 YR 6-7 yr 9 yr

Lateral incisor 3-4 MO 4-5 YR 7-8 yr 10 yr

Cuspid 4-5 mo 6-7 yr 9-10 yr 12-14 yr

1st premolar 1 ¾ – 2yr Sometime a trace

5-6 yr 10-12 yr 12-13 yr

2nd premolar 2 ¼ - 2 ½ yr 6-7 yr 11-12 yr 13-14yr

1st molar At birth 2 ½ -3 yr 11-12 yr 9 -10 yr

2nd molar 2 ½ -3 yr 7-8 yr 6 -7 yr 14 -15 yr

3rd molar 8 – 10 yr 12-16 yr 11-13 yr 18 – 25 yr

Morphologic difference between

primary and permanent teeth

CROWN

COLOUR • Primary teeth are

usually lighter in color,

bluish white(milky

white)

Permanent teeth are

darker, grayish or

yellowish in color.

Size

• T a

• T t a

he Primary teeth re smaller in all dimensions.

he Permanent

eeth are larger in ll dimensions.

Bucco – lingual surface • Primary teeth-

Buccal – lingual surface of molars especially 1st molar converge towards occlusal surface so they have narrow occlusal table.

• Permanent teeth –

There is less occlusal convergence of buccal lingual surface of molars towards occlusal surface.

• Pri the in r oc cu tee

Per

the hei me

MESIO DISTAL DIMENSION

mary teeth are wider in ir mesiodistal diameter elation to their cervico- clusal height which give p appearance to anterior th .

manent teeth are larger in

ir cervico-occlusal ght in relation to the siodistal diameter.

Shape

• Cuspid in PRIMARY

TEETH are slender and

tend to be more conical

• Cuspid in PERMANENT

TEETH are less conical

Cervical

• Primary teeth - Molars are more bulbous and are sharply constricted cervically (bell shape).

• Permanent teeth - They have less constriction on neck.

Cervical ridge

• Primary teeth- cervical ridges are more pronounced especially on the buccal aspect of the 1st molar.

• Permanent teeth- cervical ridges are flatter.

Occlusal Plane

• PRIMARY TEETH

– relatively flat

• PERMANENT

TEETH – more

curved contour

Contact area

• Primary teeth-

The contact areas between

molars are broader , flatter

and are situated gingivally.

• Permanent teeth –

The contact point between

permanent molars are

situated occlusally.

Clinical significance

• Buccal and lingual margins of proximal box in

class II restoration should extend towards the

embrasure to make them accessible for self

cleansing

As proximal caries starts below the contact

area gingival seat must be taken below the

contact area.

• Pri

ma

• Per

ma

Mamelons

mary teeth have no

melons .

manent teeth have

melons.

Molar dimension

• Permanent teeth- 1st molar is larger in dimension than second molar.

• Primary teeth- 1st molar is

smaller in dimension than second molar.

Size

• Primary teeth – roots are larger and more slender in comparison to crown size

• Permanent teeth – root

are short and bulbous in comparison to crown size

Maxillary and mandibular anterior teeth

• Extraction of anterior teeth is accomplished

with a rotational movement.

Maxillary and mandibular molars

• Primary molars – roots smaller in diameter and

more divergent than permanent molars.

• Slow

force

continuous palatal/lingual and buccal

allowing for the expansion of the

alveolar bone to accommodate the divergent

roots and reduce the risk of root fracture.

Furcation

• Primary teeth – more towards cervical area , root trunk smaller

• Permanent teeth –

towards apical , root trunk is larger

Clinical implication

• Slightest infection in the pulp can lead into the

bifurcation area.

• Care must be taken during access opening into

pulp chamber to prevent perforation through

floor into the furcation area.

Resorption

• Primary teeth – undergo physiologic resorption during shedding of teeth.

• Permanent teeth – physiologic Resorption is absent.

Resorption pattern

• Permanent incisor and canines develop

lingually to primary teeth - resorption of

primary teeth begins in lingual direction.

• Resorption of root of primary molars begins on

inner surface (inter-radicular dentin) because

the early developing bicuspid are found

between them

Revision

• 1. Primary Teeth are known as milk teeth

• They have refractive index similar to that of milk .

• 2. Roots of a primary teeth are

• Flared and slender

Pulp chamber

• Primary teeth –larger in

relation to crown size.

Pulpal outline follows the

DEJ more closely.

• Pulp horns closer to outer

surface.

• Permanent teeth – smaller

in relation to crown size.

Clinical significance

• HIGHER PULP HORNS- care must be taken during

restorative procedures in primary teeth especially over

mesial pulp horns.

• PULPAL FLOOR IS CONCAVE as opposed to

permanent teeth

CELLULARITY

• Primary teeth – high degree of cellularity and

vascularity

• Permanent teeth – less degree of cellularity

and vascularity

Primary teeth - Pulp nerve fibers pass to the

odontoblastic area, where they terminate as

free nerve endings.

Permanent teeth- Nerve fibers terminate

mainly among the odontoblasts and even

beyond the predentin.

Nerve fibers

Bernick S. Innervation of the teeth and periodontium. Dent Clin North Am 1959;

p.503.

• Density of the innervation of the primary tooth

is not as great as that of the permanent tooth

and may be the reason why primary teeth are

less sensitive to operative procedure.

• Neural tissue is the first to degenerate when

root resorption begins, just as it is the last

tissue to mature when the pulp develops.

Clinical significance

• Primary teeth have high potential for repair

as reparative dentin formation is more

More chances of spread of infection –

space involvement (Cellulitis)

Permanent teeth have less potential for repair

Accessory canal

• Primary teeth - floor of pulp chamber is more

porous.

• Accessory canal directly leads to inter-

radicular furcation area.

• Permanent teeth – floor of pulp chamber do

not have many accessory canal.

Accessory (or lateral) canals also occur, located

most commonly in the apical third of the root and in

maxillary and mandibular molars are common in the

furcation area.

Root canals

• Primary teeth – canals are thin tortuous and

have a branching path (ribbon like).

• Permanent teeth – canals are well defined

with less branching.

Clinical implication

• Variation in root canal makes it difficult to

remove necrotic tissue by instrumentation.

Profuse irrigation with 5.25°7% sodium

hypochlorite (NaOC1) is recommended .

Apical foramen

• Primary teeth- apical foramen is enlarged thus having abundant blood supply

• Permanent teeth-

constricted apical foramen thus having reduced blood supply

Enamel • Primary teeth-

Enamel is thinner and has a more consistent depth of about 1mm thickness throughout the crown. The enamel rods at the cervical slopes occlusally from the DEJ. Density of enamel rods is higher in deciduous.

• Permanent teeth –

The enamel is thicker and has a thickness of about 2-3 mm. the enamel rods are oriented gingivally from the DEJ.

Enamel thickness

Direction of enamel rod

Clinical significance

• As enamel rod of primary molars is towards

occlusal surface there is no need for beveling

the gingival seat in primary molars

• Beveling is done in permanent teeth because of

apical or horizontal inclination of enamel rods

in permanent molars

Incremental line

• Primary teeth-

incremental line of

retzius are less

common.

• Permanent teeth -

incremental line of

retzius are more

common

Dentin

• Primary teeth – greater thickness of the

dentinal wall over the occlusal fossa of molars.

• Permanent teeth- lesser thickness of dentin

over the pulpal wall at the occlusal fossa of

molars.

DENTIN

• Primary teeth - dentinal tubule are less

regular. Interglobular dentin is absent.

• Permanent teeth- dentinal tubules are more

regular. Interglobular dentin is present

CLINICAL SIGNIFICANCE

• Thickness of enamel and dentin is thin in

primary teeth so the pulp is proportionately

higher due to this caries can progress to pulp

faster ,

• Etching time in primary teeth is 90-120 sec

whereas in permanent teeth is 30 sec because

more organic matter in enamel of primary teeth

NEONATAL LINE

Primary teeth - present in both enamel and dentin.

Permanent teeth- seen only in 1st

permanent molar as mineralization takes place at birth.

Neonatal line

• Line reflects the abrupt changes in

environment that occur at birth

• Accentuated line of Retzius – enamel

• Accentuated line of contour – dentin

CEMENTUM

PRIMARY TEETH

• Cementum is very thin

and of primary type.

• Secondary cementum is

characteristically absent.

PERMANENT TEETH

• Secondary cementum is

present.

CEMENTODENTINAL JUNCTION

PRIMARY TEETH

• Cementodentinal junction is

scalloped.

PERMANENT TEETH

• Dentin surface upon which

cementum is deposited is

smooth.

CEMENTOENAMEL JUNCTION

CEMENTOENAMEL JUNCTION

• PRIMARY TEETH

• cementum meets

enamel at sharp line

• 2nd common is cementum overlapping the enamel

• Enamel and cementum do not meet is rare

• PERMANENT TEETH

60%- cementum overlaps

the enamel

30%- cementum meets enamel at sharp line

10%- enamel and cementum do not meet.

Question

Enamel of primary teeth is and has more consistent