• The human dentition : upper and lower arches • Heterodont: Different teeth to perform different 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 ENAMEL ERUPTION ROOT CALCIFICATION COMPLETED COMPLETED (WKS IN UTERO)
MAXILLARY
Central 14(13-16) 1 ½ mo 10(8-12)mo 1 ½ yr incisor
Lateral 16(14 ½-16 ½) 2 ½ mo 11(9-13)mo 2 yr incisor
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 CROWN ERUPTION ROOT CALCIFICATION COMPLETED COMPLETED (WKS IN UTERO)
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 CROWN ERUPTION ROOT FORMATION COMPLETED COMPLETED BEGINS
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 AMOUNT ENAMEL ERUPTION ROOT FORMATION OF COMPLETED COMPLETED BEGINS ENAMEL AT BIRTH
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 5-6 yr 10-12 yr 12-13 yr trace 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 he Primary teeth are smaller in all dimensions.
• T he Permanent t eeth are larger in all 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. MESIO DISTAL DIMENSION • Pri mary teeth are wider in their mesiodistal diameter in elationr to their cervico- occlusal height which give cu p appearance to anterior teeth .
Per manent teeth are larger in the ir cervico-occlusal hei ght in relation to the me 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. Mamelons
• Pri m ary teeth have no ma melons .
• Per m anent teeth have ma 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 continuous palatal/lingual and buccal force 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 Nerve fibers
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.
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 PERMANENT TEETH • Cementum is very thin • Secondary cementum is and of primary type. present. • Secondary cementum is characteristically absent. CEMENTODENTINAL JUNCTION
PRIMARY TEETH PERMANENT TEETH • Cementodentinal junction is • Dentin surface upon which scalloped. cementum is deposited is smooth. CEMENTOENAMEL JUNCTION CEMENTOENAMEL JUNCTION
• PRIMARY TEETH • PERMANENT TEETH
• cementum meets 60%- cementum overlaps enamel at sharp line the enamel • 2nd common is 30%- cementum meets cementum overlapping enamel at sharp line the enamel 10%- enamel and • Enamel and cementum cementum do not do not meet is rare meet. Question
Enamel of primary teeth is and has more consistent