Ch. 18 Primary Dentition

Primary dentition

The first set of teeth, also called baby, milk, or temporary teeth. They eventually shed and are replaced by permanent teeth.

Number of primary teeth

20 total, with 10 teeth in each arch.

Primary tooth types

Incisors, canines, and molars. Primary dentition has no premolars.

Universal numbering system for primary teeth

Capital letters A–T.

Primary tooth mineralization

Begins in utero around 13–16 weeks. All primary teeth have begun development by 18–20 weeks prenatal.

Primary teeth at birth

Usually not visible at birth.

First primary tooth to erupt

The mandibular central incisor, around 6–10 months.

Primary tooth eruption sequence

The order teeth erupt is more important than exact eruption dates. Eruption should generally be symmetrical.

What should be done if primary teeth erupt asymmetrically?

A radiograph may be needed to investigate the asymmetry.

Primary teeth eruption and gender

Girls tend to mature faster than boys.

Completion of primary tooth eruption

All primary teeth are usually erupted by 33 months.

Completion of primary tooth root formation

Approximately 18 months to 3 years.

Leeway spaces / interproximal spaces

Spaces between primary teeth that help accommodate the larger permanent teeth.

Primate spaces

Spaces located distal to the primary canines.

Primary teeth compared with permanent teeth

Primary teeth are smaller overall, have shorter crowns relative to total length, and have narrower crowns at the CEJ.

Primary tooth roots

Roots are narrower and longer relative to the crown. Primary molar roots flare widely.

Primary tooth pulp

Primary teeth have larger pulp chambers and pulp horns, especially the mesial pulp horns of molars.

Primary tooth enamel and dentin

Enamel and dentin are thinner than in permanent teeth, allowing decay to progress rapidly toward the pulp.

Why are primary teeth whiter than permanent teeth?

Their enamel is more opaque and hides the yellow color of the underlying dentin.

Primary tooth root resorption

Roots begin resorbing approximately three years after eruption as the teeth prepare to shed.

Importance of primary teeth

They are important for esthetics, mastication, speech, and maintaining space for permanent teeth.

Succedaneous teeth

Permanent teeth that replace primary teeth.

Primary tooth decay and pulp exposure

Thin enamel and dentin combined with large pulp chambers make primary teeth vulnerable to rapid decay and pulp exposure.

Pulpotomy and pulpectomy

Procedures that may be used when decay or injury affects the pulp of a primary tooth.

First dental examination

Should occur by 12 months of age.

Nasmyth membrane / dental cuticle

A membrane on newly erupted enamel that can collect food debris and cause extrinsic staining.

Extrinsic staining of primary teeth

May be associated with the Nasmyth membrane and food debris; selective polishing may be used.

Primary incisors

There are four incisors per arch, with central and lateral incisors in each quadrant.

Primary incisors compared with permanent incisors

They resemble their permanent successors in position, function, and general shape, but are narrower mesiodistally.

Primary maxillary central incisors (E/F)

Erupt around 8–12 months. Their facial crown is wider mesiodistally than incisocervically, unlike permanent maxillary central incisors.

Primary maxillary central incisor characteristics

No mamelons, lingual pits, or usually developmental depressions; prominent cingulum and marginal ridges; deep lingual fossa.

Primary maxillary central incisor root

Single, round, tapering root approximately twice the crown length.

Primary maxillary lateral incisors (D/G)

Erupt around 9–13 months and are much smaller than primary maxillary central incisors.

Primary maxillary lateral incisor characteristics

The crown is longer incisocervically than mesiodistally; incisal angles are more rounded.

Primary maxillary lateral incisor root

Similar to the central incisor root but longer relative to the crown, with a sharper apex.

Primary mandibular central incisors (O/P)

Erupt around 6–10 months and are symmetrical.

Primary mandibular central incisor characteristics

The lingual surface tapers to a prominent cingulum with a shallow lingual fossa.

Primary mandibular central incisor root

Approximately twice the crown length; facial and lingual surfaces are rounded, while proximal surfaces are slightly flattened.

Primary mandibular lateral incisors (N/Q)

Erupt around 10–16 months and are slightly larger than primary mandibular central incisors.

Primary mandibular lateral incisor characteristics

The incisal ridge slopes distally; the distal margin and distoincisal angle are rounded; the cingulum is offset distally.

Primary mandibular lateral incisor root

Approximately twice the crown length; may curve distally near the apex and usually has a distal longitudinal groove.

Primary canines

There are four primary canines, one in each quadrant. They generally resemble permanent canines.

Primary maxillary canines (C/H)

Erupt around 16–22 months.

Primary maxillary canine characteristics

The newly erupted cusp is longer and sharper than the permanent successor; prominent cingulum, lingual ridge, and marginal ridges divide the lingual surface into two shallow fossae.

Primary maxillary canine root

Approximately twice the crown length, slender, and inclined distally.

Primary mandibular canines (M/R)

Erupt around 17–23 months.

Primary mandibular canine characteristics

Similar to the maxillary primary canine but much smaller faciolingually, with a smoother lingual surface and shallow fossa.

Primary mandibular canine root

Long and narrow, nearly twice the crown length, shorter and more tapered than the maxillary primary canine.

Primary molars

There are eight primary molars, two in each quadrant. They are replaced by permanent premolars.

Primary molar similarities

The primary second molars resemble permanent first molars in the same arch. Primary first molars do not resemble other teeth.

Primary molar crown characteristics

Crowns are shorter occlusocervically than mesiodistally, have prominent buccal cervical ridges, and narrower occlusal tables buccolingually.

Primary molar roots

Roots flare beyond the crown outlines to make room for developing premolars. They have short root trunks and branch near the crown base.

Primary maxillary first molars (B/I)

Erupt around 13–19 months and have a crown unlike any other molar.

Primary maxillary first molar cusps

Usually four cusps: mesiobuccal, mesiolingual, distobuccal, and distolingual. The distolingual cusp may be absent.

Primary maxillary first molar occlusal features

H-shaped groove and three fossae: central, mesial triangular, and distal triangular.

Primary maxillary first molar roots

Three thin, widely flared roots. The lingual root is longest and most divergent; the mesiobuccal root is wider buccolingually than the distobuccal root.

Primary maxillary second molars (A/J)

The slide lists eruption as 25–23 months. They are larger than primary maxillary first molars and resemble permanent maxillary first molars, but are smaller.

Cusp of Carabelli

A minor fifth cusp that is usually present on the primary maxillary second molar.

Primary mandibular first molars (L/S)

Erupt around 14–18 months and have a crown unlike any other tooth.

Primary mandibular first molar characteristics

Prominent buccal cervical ridge on the mesial half; four cusps, with the mesial cusp larger; long, pointed mesiolingual cusp.

Primary mandibular first molar transverse ridge

A ridge connecting the mesiobuccal and mesiolingual cusps.

Primary mandibular first molar roots

Two roots positioned similarly to other mandibular molars.

Primary mandibular second molars (K/T)

Erupt around 23–31 months and are larger than primary mandibular first molars.

Primary mandibular second molar characteristics

Resemble permanent mandibular first molars; have three nearly equal buccal cusps and an oval occlusal shape.

Clinical importance of primary second molars

Adults may mistake erupting permanent first molars for primary second molars because they look similar. Permanent first molars may benefit from sealants.

Mixed dentition

Stage when primary and permanent teeth are present together.

Mixed dentition age ranges shown in slides

Approximately 6–7, 7–8, and 10–12 years.

Primary teeth erupted by 33 months

All primary teeth are usually erupted by 33 months.

Tooth distal to the primary maxillary second molar in a 7-year-old

Permanent maxillary first molar.

Age when primary maxillary incisors, canines, molars, permanent mandibular incisors, and permanent first molars are present

Approximately 5–7 years.