29 - Anatomical + Physiological differences between primary + permanent dentition

Question 1

Size + form

Answer 1

Crowns ⇢ 1° < P

Crowns of incisors + canines larger than 1° ones

1° teeth resemble P teeth

Incisors ⇢ both have single roots + incisal edge

Canines ⇢ both have single roots + single cusps

1° bear no resemblance to succeeding premolars

Crowns of P molars > 1° molars

Question 2

Crowns

Answer 2

1 ° teeth have a shorter crown

1° crowns bluish-white, P = yellowish ⇢ thinner enamel of 1° teeth

Occlusal table of 1° molars narrower than permanent molars

1° teeth more constricted in cervical portion of crown

1° teeth have pronounced cervical ridge

Enamel + dentin layers thinner in 1° ⇢ enamel equally thick in all areas of crown 1mm

Enamel rods in gingival ⅓ extend in slightly occlusal direction from DEJ in 1° but continue apically in permanent

Contact areas of 1° molars are broad + flat

mineral content in 1° < P

Lighter colour of 1° teeth

Crowns in 1° more square, P=rectangular crowns

Question 3

Pulp

Answer 3

Pulp of 1° tooth > P in relation to crown size

Pulp horns of 1° teeth closer to outer surface of tooth

Mandibular molar pulp chambers > maxillary molar in 1° tooth

Form of pulp chamber of 1° tooth follows surface of the crown

Histologically there is very little difference between pulp of 1° tooth and that of a young permanent tooth

Question 4

Root

Answer 4

Roots of 1° < Root of P

Root of 1° anterior teeth narrower mesio-distally than P anterior teeth

Roots of posterior 1° > in relation to crown size

Roots of 1° molar flare MORE as they approach apex ⇢ afford necessary room for development of tooth buds

Curved roots + thin walls = more difficult to access root canals in 1° molars

Question 5

Tooth structure

Answer 5

1° has thinner enamel + dentin ⇢ enamel equally thick in all parts of the crown

Permanent teeth have thicker + better mineralised enamel + dentin

Enamel in P teeth thickest in cusps zone, thinner in lateral areas of crown + thinnest in cervical zone + in fissure

Question 6

Arch shape

Answer 6

Arch shape is similar om anterior portion of both dentitions

Permanent dentition extends further distally

Succession of 1° incisors w/larger P incisors = incisor liability

Difference in mesial distal-dimension between 1° molars + P premolars = Lee way space