Chapter 6: Primary (and Mixed) Dentition

I. Background Information Definitions Dental Formulae Functions of the Primary Dentition

A. Definitions Primary (or deciduous) dentition Permanent (or secondary or adult) dentition

Primary Dentition: Location and Universal Identification with Letters

B. Dental Formulae for Primary Dentition Is a Ratio of the Number of Each Tooth Class per Maxillary Quadrant Over Mandibular Quadrant. Note: No Primary Premolars Incisors = 2/2 Canines = 1/1 Molars = 2/2

Dental Formulae for Secondary (Adult) Dentition Is a Ratio of the Number of Each Tooth Class per Maxillary Quadrant Over Mandibular Quadrant Succedaneous teeth Incisors = 2/2 (same as primary) Canines = 1/1 (same as primary) Premolars = 2/2 (replace primary molars) Molars = 3/3 (erupt distal to spaces filled with primary teeth so are not succedaneous)

C. Functions of Primary Dentition Chewing (mastication) Support for lips and cheeks Formulation of speech Maintain arch space and room for secondary teeth

Adult Tooth Crowding Due to Premature Primary Tooth Loss Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins

II. Developmental Data for Primary and Secondary Teeth Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Important times for eruption Crown and root development

A. Tooth Eruption Times (Approximate) Birth to 6 or 8 months: no teeth erupted Primary teeth erupt from 6 months–2 years All 20 primary teeth present from 2–6 years Mixed dentition from 6–12 years Only adult teeth after 12 years Last permanent teeth erupt (third molars) = late teens/early 20s

B. Crown and Root Development (Primary Teeth) Primary crowns begin to form at 6 months in utero Crowns complete (about 10 months after beginning) Root formation takes place during eruption process and emergence Roots complete (1½–3 years after emergence) Exfoliation and replacement with permanent (succedaneous) teeth (6–12 years)

Crown and Root Development (Secondary Teeth) Secondary crowns begin to form/calcify (beginning at birth for first molars through 8–10 years for beginning third molars) Crowns complete calcification about 3 (to 4+) years prior to eruption Roots complete (about 3 years after emergence)

Order of Emergence of Primary Teeth (Between 6 Months and 2 Years) First: Mandibular central incisor (6 months) Second: other incisors (maxillary lateral incisors last) Third: First molars Fourth: Canines Fifth: Second molars (at about 2 years)

Model Depicting 3-Year-Old (Note Tooth Crowns Forming in Jaw Bones)

Order of Emergence of Secondary Teeth (Between 6 Years and Late Teens/Early 20s) First: First molars followed closely by mandibular central incisors (6 years) Next: Other incisors (7–9 years) Then: Mandibular canines (9 years) Premolars (10–12 years) Maxillary canines (12 years) Second molars (12 years) Third molars (late teens)

Model of 9-Year-Old (Note: Adult Incisors and First Molars Have Erupted)

8-Year-Old (Adult Canines and Premolars Have Not Yet Erupted) Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins

III. Dentition Traits of All Primary Teeth (Compared to Secondary) Smaller than secondary tooth of same name Marked cementoenamel junction (CEJ) constriction and cervical crown bulges Relatively long roots compared to crowns More wear since less mineralized

Dentition Traits of All Primary Teeth (Compared to Secondary [cont.]) Thinner enamel and dentin layers Whiter Fewer anomalies

Prominent cervical ridges Prominent lingual cingula Dentition Traits of Anterior Primary Teeth (Compared to Secondary [cont.]) Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Anteriors: Prominent cervical ridges Prominent lingual cingula No labial depressions, mamelons, or perikymata Anterior roots: thin mesiodistally Anterior roots bend labially in apical third

Dentition Traits of Primary Molars (Compared to Secondary) Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Prominent mesial cervical ridge (bulges) with exaggerated cervical line curve apically on facial Crowns taper narrower toward occlusal with narrow occlusal table Wide mesiodistally versus occlusogingivally

Primary Molars (Compared to Secondary [cont.]) Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Shallow occlusal anatomy: few grooves or depressions Second molars are larger than firsts Enamel rods slope occlusally near CEJ

Primary Molar Roots (Compared to Secondary) Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Root furcations are near crown (small root trunks) Roots thin and slender Roots diverge considerably (to make room for forming adult premolars within the jaw bones)

IV. Class and Type Traits of Primary Teeth Primary Incisor Traits (Central and Lateral) Primary Canine Traits Primary Molar Traits (First and Second)

A. Primary Incisor Traits Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins

1. Incisors: Labial View Outline: All are longer incisocervically than mesiodistally EXCEPT that maxillary central incisor is wider mesiodistally (otherwise similar to secondary incisors)

Incisors: Labial View [cont.] Smooth surfaces, minimal depressions Roots relatively much longer than crowns (before resorption) compared to secondary

2. Incisors: Lingual View Prominent, large cingula Marginal ridges most prominent on maxillary central incisors; mandibular lingual anatomy less distinct

3. Incisors: Proximal Views Quite wide labiolingually in cervical third Cervical line (CEJ) same shape as secondary: curve greater on mesial All roots bend facially in apical third Maxillary incisor roots also bend lingually in cervical half

4. Incisors: Incisal View Maxillary central is much wider mesiodistally than faciolingually compared to maxillary lateral Mandibular incisors: mesiodistal almost = faciolingual

B. Primary Canines: Traits Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins

1. Primary Canine: Labial View Outline: maxillary = about as wide and long; mandibular = like secondary: longer incisocervically than mesiodistally Cervical lines: similar to secondary Roots taper to blunt apex

Primary Canine: Labial View (Maxillary) Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Contact areas: UNIQUE: mesial contact of maxillary canine crown more cervical than distal (only other tooth is mandibular first premolar)

Primary Canine: Labial View (Maxillary [cont.]) Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Cusp ridges Maxillary = pointed and UNIQUE: mesial cusp ridges longer than distal (only other tooth like this is secondary maxillary first premolar)

Primary Canine: Labial View (Mandibular) Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Cusp ridges Mandibular = also quite pointed but similar to secondary canine: mesial cusp ridges shorter than distal

2. Primary Canine: Lingual View Maxillary ridges Cingulum and marginal ridges more prominent Lingual ridge with mesial and distal fossae (similar to secondary) Mandibular ridges Faint ridges

3. Primary Canine: Proximal Views Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Outline: Cervical third even thicker than primary incisor Pronounced labial and lingual cervical bulges with pronounced concave “S” shape on maxillary canines

Primary Canine: Proximal Views [cont.] Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Maxillary cusp tips positioned labial to root axis, but mandibular = lingual (as in secondary) Cervical lines (CEJ) similar to secondary: more curve on mesial Roots: roots bent labially in apical third

4. Primary Canines: Incisal View Maxillary canine wider mesiodistally than faciolingually (less so on mandibular) Mandibular canine outlines are diamond shaped from incisal

C. Primary Molar Traits Both types of maxillary molars have three roots (mesiobuccal, distobuccal, and palatal) Mandibular molars have two (mesial and distal)

Primary Molar Traits [cont.] All are wider mesiodistally than premolars that will replace them

Primary Molar Traits [cont.] All have prominent buccal bulges (mesiobuccal)

Primary Molar Traits [cont.] Cervical lines curve apically in mesial half of buccal surface

Primary Second Molar Traits Primary second molars resemble secondary first molars

Primary Second Molar Traits [cont.] Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Primary second molars resemble the adjacent secondary first molar in that arch just distal to them after age 6 Primary second molars are smaller than permanent first molars

Primary Maxillary Second Molar (Type Traits) Crown similar to secondary maxillary first molar but smaller Four cusps plus Carabelli Oblique ridge Mesiobuccal cusp is almost equal to mesiolingual cusp (while mesiolingual cusp is largest on permanent first molars)

Primary Mandibular Second Molar (Type Traits) Crown similar to secondary mandibular first molar but smaller Five cusps: three buccal (mesiobuccal, distobuccal, distal) and two lingual (mesiolingual and distolingual)

Primary Mandibular Second Molar (Type Traits [cont.]) Crown similar to secondary mandibular first molar but smaller However, distobuccal cusp is widest and mesiobuccal and distal cusps are almost same size (while distal cusp is smallest on permanent first molars)

Primary First Molar Traits Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Primary First Molar Traits Primary first molar crowns are unique in shape Occlusal view of a primary maxillary first molar somewhat resembles a maxillary premolar Primary mandibular first molars resemble no other tooth Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins

Primary Maxillary First Molar (Type Traits) Crown from occlusal view is similar to maxillary premolar (two prominent cusps = mesiobuccal and mesiolingual) but also very small distobuccal and distolingual cusps (as on secondary molars) Crowns are slightly wider faciolingually than mesiodistally

Primary Maxillary First Molar (Type traits [cont.]) But from buccal: are wider than high (similar to secondary molars) Occlusal grooves may form “H” pattern

Primary Mandibular First Molar (Type Traits) Crown resembles no other tooth Four cusps (mesiobuccal, distobuccal, mesiolingual, distolingual) Wider mesiobuccally than high occlusocervically Very prominent mesiobuccal cervical ridge or bulge with more apical cervical line in mesial half of buccal surface

Primary Mandibular First Molar (Type Traits [cont.]) Prominent mesial transverse ridge and mesial marginal ridge Prominent mesiolingual cusp Occlusal table wider buccolingually in distal half

Groove Patterns of All Primary Molars Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins

V. Pulp Cavities of Primary Teeth Pulps are relatively larger in proportion to tooth than secondary pulps Molar pulp chambers are located mostly in crown (due to short root trunk) Narrow pulp horns located beneath cusps Pulp size makes it easier to expose during tooth preparation

Estimate the Dental Age

Estimate the Dental Age Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins

Estimate the Dental Age

Identify the Teeth in this Mixed Dentition