3. Tooth Morphology

Question 1

How to compare permanent and primary teeth?

Answer 1

• smaller in size for each tooth category
• more bulbous
• more proteins, less mineral so whiter (perm more ivory since transparent enamel shows underlying dentine)
• enamel is thinner and less hard - physically softer - wear/attition happens faster
• less crowded - less interproximal caries
• roots thinner and shorter - molar roots more divergent
• pulp cavities large with thinner dentine - pulp horns higher and close to amelodentinal junction

Question 2

Primary anterior teeth are … than permanent successors due to what?

Answer 2

• plumper
• transverse diameter of crown is greater relative to length

Question 3

Features of the upper right primary central incisor

Answer 3

• similar structure to permanent
• but smaller
• low rounded labial cingulum beside cervical line
• transverse diameter of crown equal to vertical diameter
• lower palatal cingulum and marginal ridges with shallow palatal fossa
• conical root slightly compressed in labio-palatal direction with single root canal (while root often slightly compressed in mesio-distal direction in upper)

Question 4

Upper primary lateral incisors

Answer 4

• similar to upper but less variable, rounded labial cingulum and low lingual cingulum
• resembles upper primary central but smaller and mesial angle more acute and distal angle more rounded
• root is similar to upper primary centrals
• may be difficult to distinguish upper primary lateral from lower of opposite side as both have rounded roots (unlike lower perm)

Question 5

Lower primary central incisors

Answer 5

• centrals are symmetrical and similar to lower perm
• but crown is shorter than perm and has low labial cingulum
• roots are shorter and rounded unlike perm

Question 6

Lower primary lateral incisors

Answer 6

• asymmetrical and similar to lower perm but
• wider and low labial cingulum
• root is rounded (unlike perm)
• if distal incisal angle is markedly rounded, may closely resemble upper primary of opposite side as both have rounded roots
• root is longer than that of lower primary centrals

Question 7

Upper primary canines

Answer 7

• similar to perm
• symmetrical teeth so hard to see what side
• much fatter
• if crown is symmetrical cusp tip often displaced distally (unlike perm)
• low labial cingulum - joins labial ridge (like perm). Lingual surface has low marginal ridges, palatal ridge separates two shallow palatal fossae
• root comparatively long, triangular in cross section, single root canal

Question 8

Lower primary canines

Answer 8

• more slender than upper and asymmetrical crown as cusp tip displaced mesially (like perm, unlike upper)
• mesial slope shorter and more vertical than distal slope
• labial cingulum and root/root canal similar to upper primary

Question 9

Characteristics of both upper and lower primary 1st molars

Answer 9

• crown irregular quadrilateral
• buccal side is wider and palatal is shorter - both are parallel to each other
• mesial surface slopes distally as it passes towards palatal
• buccal cingulum extended mesially to form molar tubercle (on mesio-buccal corner)
• convergence of tip of buccal/palatal cusps towards the midline of crown - reducing occlusal area

Question 10

Cusps and roots of upper primary 1st molar

Answer 10

• 4 cusps (2 buccal, 2 palatal)
• mesio-buccal cusp is largest
• 3 roots (2 buccal, 1 palatal - largest) with 3 root canals similar to perm
• disto-buccal and palatal roots partially fused

Question 11

Lower primary first molar

Answer 11

• crown elongated mesio-distally (compared to upper) - has molar tubercle
• mainly 4 cusps (2 buccal, 2 lingual) where mesial are bigger than distal and buccal bigger than lingual
• ridge of enamel can connect mesial cusps, called transverse ridge and divides central fissure into distal fissure and mesial pit
• like lower perm, 2 roots (mesial and distal) with 2 root canals. mesial root often grooved and its canals may divide into 2
• 2 roots diiverge to accomodate developing lower 1st premolar. Tips of roots sometimes embrace tooth germ

Question 12

Lower primary second molar

Answer 12

• similar to lower 1st but 5 cusps (3 buccal, 2 lingual)
• smaller, narrower, whiter and widely diverging roots
• buccal cingulum more pronounced than 1st and mesial/distal surfaces more convex
• 2 roots (mesial and distal) - mesial root may be grooved dividing root canal in 2
• roots always widely divergent but tips may curve back towards one another at apex embracing tooth germ

Question 13

Primary 1st molars have … and then primary 2nd molars resemble …

Answer 13

• tubercle molar on mesio-buccal corner
• resemble first molars