Primary Dentition

Primary Dentition Properties

• Primary Dentition Definition

  • The first set of teeth in humans, known as primary dentition.

  • Typically will be shed and replaced by permanent dentition.

  • Total Count of Primary Teeth: 20 primary teeth in total when the primary dentition period is completed, which is 10 per dental arch.

  • Primary teeth include various types: incisors, canines, and molars.

Universal and International Numbering Systems of Primary Dentition

• Universal Numbering System

  • Teeth are designated by capital letters A through T.

• International Numbering System

  • Utilizes digits 5 through 8 for the first of two digits (to denote quadrant in a clockwise manner).

  • Utilizes digits 1 through 5 for the second digit (numbering starts at midline for each tooth).

Eruption and Replacement of Primary Teeth

• Replacement Process

  • Primary molars are replaced by permanent premolars.

  • No premolars exist in the primary dentition.

  • Permanent molars erupt distally to the primary second molars.

Mineralization of Primary Teeth

• Mineralization Timeline

  • Begins in utero between 13 to 16 weeks.

  • By 18 to 20 weeks prenatally, all primary teeth commence mineralization.

  • At birth, typically, there are no primary teeth visible in the oral cavity.

• Eruption Timeline

  • First eruption of a primary tooth (mandibular central incisor) occurs on average between 6 to 10 months.

  • Subsequent eruption of the remaining primary dentition follows.

Duration of Primary Dentition Development

• Completion Timeline

  • Primary dentition completes within 2 to 3 years, starting from initial mineralization of mandibular central incisors and concluding with root formation of maxillary second molar.

  • Notable variations of 6 months earlier or later are considered normal.

  • Early or late dental emergence may necessitate inquiry into dental history.

Importance of Eruption Sequence

• Eruption Dates vs. Sequence

  • Eruption dates may vary greatly among children; thus, the eruption sequence holds more significance.

  • The sequence follows a general uniform pattern.

  • Specific tooth types erupt in pairs; noted asymmetry may require a radiograph.

  • Observations indicate that young women typically shed their primary teeth earlier than young men.

Interproximal Spaces in Primary Dentition

• Presence of Interproximal Spaces

  • Most child patients exhibit interproximal spaces between primary teeth, essential for future alignment of larger permanent dentition.

  • Notable large spaces are identified as primate spaces, often found between:

  • Primary maxillary lateral incisor and canine.

  • Primary mandibular canine and first molar.

Comparison of Primary and Permanent Dentition

• Size and Structure Differences

  • Primary teeth are generally smaller than permanent teeth; not merely scaled-down versions.

  • Key differences in structure include:

  • Crown Structure

  • Shorter crown in relation to overall tooth length.

  • Crowns appear bulbous due to narrower dimensions at the CEJ (Cementoenamel Junction).

  • Occlusal tables narrower compared to permanent teeth.

  • Prominent cervical ridge on both labial and lingual surfaces of anterior teeth and buccal surfaces of molars compared to permanent.

  • Contacts are broader and flatter.

  • Roots Structure

  • Roots are narrower and longer in proportion to crown length.

  • There exists a smaller crown-to-root ratio in primary teeth when compared to permanent counterparts.

  • Molar roots flare more as they approach the apex, with larger apical foramina.

  • Potential partial resorption of roots as teeth shed can be observed radiographically.

• Pulp Cavity in Primary Teeth

  • Pulp chambers and pulp horns are larger relative to those in permanent dentition; specifically larger mesial pulp horns in molars.

  • Each cusp typically has a pulp horn beneath it, with horns positioned closer to the outer surface.

• Dentin and Enamel Characteristics

  • Dentin is thinner than that found in permanent dentition.

  • Enamel is also thinner but has a consistent thickness overlaying the crown's dentin.

  • Primary teeth display a whiter tone of enamel due to increased opacity, which affects the underlying yellow dentin’s visibility.

Importance of Primary Dentition

• The primary dentition is often underestimated by parents and caregivers due to beliefs about their temporality. However:

  • A person utilizes permanent teeth 91% of their lifetime and only 6% with primary teeth.

  • Primary dentition serves essential functions, such as:

  • Aesthetics.

  • Mastication (chewing).

  • Speech for 5 to 12 years.

  • Maintaining eruption arch space for the permanents that will replace primary teeth.

Homecare for Primary Dentition

• Monitoring & Support

  • Supervision of dental care should start as soon as the first primary tooth erupts to prevent premature loss.

  • Children typically need assistance with brushing until about 7 years of age.

Endodontic Complications in Primary Dentition

• The thinner nature of enamel and dentin in primary teeth increases the risk of endodontic complications.

• Larger pulp chambers and pulp horns raise the likelihood of pulp exposure during cavity preparations.

Early Childhood Caries (ECC)

• Etiological Factors

  • Extended nighttime baby bottle use with cavity-causing beverages or sugar-laden pacifiers is associated with early childhood caries, commonly referred to as baby bottle tooth decay (ECC).

First Dental Appointment Guidelines

• Timing for First Visit

  • A child's first dental appointment should occur within 6 months following the eruption of the first primary tooth but no later than 12 months of age.

  • This aims to equip supervising adults with information to foster preventive behaviors and allay concerns about the child's teeth.

Importance of Early Dental Care

• Early dental visits are crucial not only for maintaining primary dentition health but also for evaluating potential needs for interceptive orthodontic therapy.

Staining of Primary Teeth

• Extrinsic Staining

  • Extensive extrinsic staining on primary teeth can be attributed to the Nasmyth membrane.

Primary Incisors: General Features

• Number and Types

  • Each dental arch has four primary incisors:

  • Two types: central incisor and lateral incisor.

  • Resembles permanent successors but has exceptions including a more prominent cervical ridge on labial and lingual surfaces.

  • Primary incisors hold similar arch position, function, and general shape as their permanent counterparts and serve as such for approximately 5 years.

  • Primary anterior teeth have a narrower mesiodistal (MD) width compared to permanent successors, allowing for arch leeway space.

Attrition in Primary Incisors

• Common Observations

  • Dental professionals may observe extensive wear of the incisal ridges in primary incisors due to bruxism and the potential formation of an end-to-end bite between arches.

Characteristics of Primary Maxillary Central Incisor (E and F)

• Labial Aspect

  • Crown is wider mesiodistally than incisogingivally, differing from the permanent central incisor.

  • Mesial and distal outlines are more rounded due to cervical constriction.

  • No mamelons present; labial surface is smooth, with no evident pits or developmental depressions.

  • Lingual surface features more prominent cingulum and marginal ridges compared to its permanent successor; the lingual fossa is deeper.

• Proximal Surfaces

  • Both proximal surfaces appear similar, with the short crown and wide labiolingual measurement making it appear thick at the incisal third.

• Cementoenamel Junction (CEJ)

  • The CEJ curves distinctly toward the incisal, though less than on the permanent incisor.

• Root Characteristics

  • Single root, round in shape, tapers evenly to the apex; longer in relation to crown length than the permanent central incisor.

Characteristics of Primary Maxillary Lateral Incisor (D and G)

• General Features

  • Crown resembles the central incisor but is smaller across all dimensions.

  • Incisor length is longer incisogingivally than mesiodistally, contrary to the central incisor.

  • Incisal angles are more rounded compared to central incisors.

• Root Characteristics

  • Similar to central incisor but longer in relation to the crown’s proportions, with a sharper apex.

Characteristics of Primary Mandibular Central Incisor (O and P)

• Shape and Symmetry

  • Crown resembles the primary mandibular lateral incisor more than other primary or permanent maxillary incisors.

  • Symmetrical appearance, similar to its permanent successor.

• Lingual Surface Features

  • Smooth appearance, tapering towards the prominent cingulum, with less pronounced marginal ridges and shallow lingual fossa.

• Root Characteristics

  • Features a single, long, and slender root with rounded labial and lingual surfaces and slightly flattened proximal surfaces.

Characteristics of Primary Mandibular Lateral Incisor (N and Q)

• Crown Dimensions and Features

  • Crown shares form similarities with the central incisor but is wider and longer.

  • Incisal ridge slopes distally, with a more rounded distoincisal angle and distal margin.

• Incisal Aspect

  • Asymmetrical from the incisal perspective as the cingulum is offset to the distal, similar to its permanent successor.

• Root Characteristics

  • The root may display a distal curvature in the apical third with a distal longitudinal groove.

General Features of Primary Canines

• Total Count

  • Four primary canines exist: two in each dental arch, one per quadrant.

• Structural Features

  • They mainly resemble the outline of permanent successors, yet present with a more prominent cervical ridge on both labial and lingual surfaces.

Characteristics of Primary Maxillary Canine (C and H)

• Crown Aspects

  • The crown possesses a longer, sharper cusp than the permanent successor when first erupted.

  • Outlines are rounder, significantly overhanging the cervical line.

• Lingual Surface

  • Contains a well-developed cingulum, lingual ridge, and marginal ridges; the lingual ridge connects the cingulum to the cusp tip.

  • Features shallow mesial and distal fossae.

• Root Features

  • Root is significantly long (approximately twice the crown length) and slender, inclined distally.

Characteristics of Primary Mandibular Canine (M and R)

• Size and Shape Comparison

  • Crown resembles primary maxillary canine but is smaller in labiolingual dimension.

• Lingual Surface

  • Exhibits a smoother texture than the primary maxillary canine and contains a shallow lingual fossa.

• Root Characteristics

  • Long and narrow root, approximating twice the crown length, though shorter and more tapered than the primary maxillary canine's root.

General Features of Primary Molars

• Total Count

  • Eight primary molars consisting of both first and second molars, one of each type found in each quadrant.

• Replacement Dynamics

  • Primary molars are replaced by permanent premolars.

• Unique Features

  • None of the primary first molars resemble any tooth in either dentition.

  • The second molar crown resembles first molars in the permanent dentition, which erupt posteriorly.

  • Molars shorter occlusally than mesiodistally with prominent cervical ridges on buccal surfaces.

Characteristics of Primary Maxillary First Molar (B and I)

• Crown Shape

  • No other tooth in either dentition resembles this crown shape.

  • Mesial and distal outlines are rounded with constriction at the CEJ.

• Occlusal Features

  • Possessing 4 cusps (MB, ML, DB, DL) with variability in size; mesial cusps are larger while distal may be smaller or absent.

  • An H-shaped groove pattern appears on the occlusal table with prominent transverse ridges.

• Root Structure

  • Short root trunk with thinner, greater flare compared to the permanent molars’ roots; MB root wider buccolingually than the DB root, while the lingual root is the longest and most divergent.

Characteristics of Primary Maxillary Second Molar (A and J)

• Size Comparison

  • This molar is larger than the primary maxillary first molar.

  • Closely resembles the permanent maxillary first molar in form but is smaller in dimensions.

  • Often includes a cusp of Carabelli (a minor fifth cusp).

Characteristics of Primary Mandibular First Molar (L and S)

• Unique Crown Features

  • Displays a crown unlike any other tooth in both dentitions.

  • Prominent buccal cervical ridge located on the mesial half of the buccal surface.

• Occlusal Features

  • Contains four cusps where mesial cusps are larger; a transverse ridge spans between MB and ML cusps.

• Root Characteristics

  • Two roots positioned similarly to those of other primary or permanent mandibular molars.

Characteristics of Primary Mandibular Second Molar (K and T)

• Overall Dimensions

  • Larger than the primary mandibular first molar.

  • Closely resembles the permanent mandibular first molar in form.

  • Displays an oval occlusal shape with three buccal cusps that are nearly equal in size.

Mixed Dentition Period

• Children may not notice when the permanent first molars of either arch erupt as they appear similar to the larger primary second molars in adjacent positions.

Additional Information on Primary Dentition

• Extraction Considerations

  • Greater root spread in primary molars, along with their narrow shape and lack of root trunk, can make them susceptible to fracture during extraction.

  • Shedding primary teeth is an intermittent process; sometimes loose primary teeth may tighten.

  • Extraction procedures should always be approached with caution due to the young patient population.