Tooth Morphology Lecture Study Notes
TOOTH MORPHOLOGY LECTURE NOTES
LECTURER INFORMATION
Presenter: Dr. C U Okwuosa
Qualifications:
BDS (lb)
M.Sc (lb)
M.Sc (UDU)
MPH (Nig)
Cert. HIV Management (Makerere)
Fellow, International Institute of Africa
Fellow, Society of Specialists
INTRODUCTION
There are certain variations among individual teeth based on various factors:
Racio-ethnicity
Sex
Age
Not every tooth will meet all criteria for identification.
By understanding the characteristics of each tooth, differentiation among teeth and between left and right teeth in any particular group becomes possible.
CLINICAL USES FOR TOOTH MORPHOLOGY
Applications:
Mounting dental radiographs
Assisting in charting mouths with missing teeth and teeth that have “drifted”
Selecting temporary crowns from a box with a variety of shapes
Forming matrix bands before application
ANTERIOR PERMANENT DENTITION
Overview:
Total of 12 anterior teeth in the permanent dentition, 6 per dental arch.
Anterior teeth include:
Central incisors
Lateral incisors
Canines
Arrangement:
Central incisors: Closest to midline
Lateral incisors: Second teeth from midline
Canines: Third teeth from midline
All anterior teeth are succedaneous, replacing primary teeth of the same type.
DIMENSIONS OF TEETH
General Observations:
All permanent teeth are wider buccolingually than mesiodistally, except for maxillary incisors (centrals and laterals) and mandibular molars.
Teeth are wider (MD dimension) on the facial aspect than the lingual aspect, except in maxillary first molars.
Most prominent CEJ curvature is located on the mesial surface, curving toward the incisal/occlusal.
The greatest curvature of the CEJ in the dentition is at the mesial surface of the maxillary central incisor.
SHAPE OF TEETH
Permanent Teeth:
From facial and/or lingual views, all teeth appear trapezoidal.
Anterior Teeth:
Mesial or distal view: triangular
Maxillary Premolars and Molars:
Mesial or distal view: trapezoidal
Mandibular Premolars and Molars:
Mesial and distal view: rhomboidal
PROXIMAL CONTACT AREAS
Importance:
Need to know these contact areas as they are easily identifiable.
Contacts broaden posteriorly.
Board Question Example:
A maxillary premolar has a broader contact on which aspect? Answer: Distal.
CHARACTERISTICS OF PERMANENT ANTERIOR TEETH
All anterior teeth possess a cingulum, a rounded, raised area located on the cervical third of the lingual surface.
The cingulum corresponds to the lingual developmental lobe.
Anterior teeth feature rounded raised surfaces on mesial and distal sides called marginal ridges.
Some anterior teeth have a fossa, which is a wide, shallow depression on the lingual surfaces.
MAXILLARY CENTRAL INCISORS
Anatomic Features:
Maxillary central incisors (#8 and #9) are larger in all dimensions (especially MD) compared to mandibular central incisors.
The labial surfaces are rounded when viewed from the incisal aspect, tapering toward the lingual.
The root is short compared to that of other permanent maxillary teeth.
Prominence of Features:
Lingual surface features, such as marginal ridges, lingual fossa, and cingulum, are more pronounced in maxillary central incisors.
MAXILLARY CENTRAL INCISORS - CONTINUED
Incisal Edges:
Formed at the labioincisal line angle; edges develop from wear.
Also known as the incisal surface or incisal plane.
Newly erupted central and lateral incisors have three mamelons which are rounded enamel extensions on the incisal ridge or edge; these typically undergo attrition shortly after eruption.
MAXILLARY LATERAL INCISORS
Overview:
Maxillary lateral incisors (#7 and #10) are smaller than central incisors in all dimensions but root length.
Eruption occurs after maxillary central incisors.
The lateral incisor has a single root, relatively smooth and straight but may curve slightly to the distal.
MAXILLARY LATERAL INCISORS - CONTINUED
Variation in Form:
Lateral incisors vary in form more than any other tooth in the mouth (except third molars) and are frequently congenitally missing.
The variations pose challenges during preventive, restorative, and orthodontic procedures, often leading to unattractive open contacts called diastemas due to size and position variations.
MANDIBULAR PERMANENT INCISORS
Characteristics:
The smallest teeth of the permanent dentition, highly symmetric.
Central and lateral mandibular incisors resemble each other, with the lateral incisor generally larger.
Supragingival deposits tend to collect in the lingual concavity of the mandibular incisors.
MANDIBULAR CENTRAL INCISORS
Overview:
Mandibular central incisors (#24 and #25) are the smallest and simplest teeth, bilaterally symmetric.
Features:
Small centered cingulum
Subtle lingual fossa and marginal ridges
Crown narrower on lingual surface compared to labial surface
Developmental horizontal lines and depressions are usually faint or absent.
PERMANENT CANINES
General Characteristics:
There are four anterior teeth located at the corners of each quadrant in each dental arch.
Named after the Latin word for dog (canus) due to their resemblance to dog teeth.
Patients often complain about the canines’ slightly deeper yellow color compared to incisors.
Permanent canines are the longest teeth in the dentition.
PERMANENT CANINES - CONTINUED
Root Characteristics:
The root is typically one times the length of the crown, resulting in a significant external bony vertical ridge called the canine eminence.
Patients usually refer to canines as their “eyeteeth.”
MAXILLARY CANINES
Eruption and Features:
Maxillary canines (#6 and #11) typically erupt after mandibular canines, following the maxillary incisors and possibly after premolars.
The cusp tip is sharper on maxillary canines.
The mesial cusp slope is generally shorter than the distal cusp slope, which can change due to attrition.
CLINICAL CONSIDERATIONS WITH MAXILLARY CANINES
Eruption Issues:
Maxillary canines may erupt labially or lingually in relation to surrounding teeth and can fail to erupt fully, becoming impacted.
This situation may arise because the permanent maxillary canines erupt after the maxillary incisors and possibly after the premolars, which can close off arch space.
MANDIBULAR CANINES
Overview and Comparisons:
Mandibular canines (#22 and #27) usually erupt before maxillary canines, after the majority of incisors.
They closely resemble maxillary canines; however, they tend to be narrower labiolingually and mesiodistally than maxillary counterparts.
The lingual surface of a mandibular canine is smoother with less pronounced cingulum and marginal ridges.
POSTERIOR PERMANENT DENTITION
General Traits:
Permanent posterior teeth include premolars and molars.
Each posterior tooth crown has an occlusal surface with two or more cusps, bordered distally and mesially by marginal ridges.
POSTERIOR PERMANENT DENTITION - CONTINUED
Cusp Features:
Each cusp is likened to a mountain with sloping areas or cusp ridges extending down; between the ridges lie sloping areas called inclined cuspal planes.
Defining Depressions:
A fossa is a shallow, wide depression on the occlusal table.
Types of Fossae:
Central fossa: Where cusp ridges converge and grooves meet.
Triangular fossa: Located in the deepest parts of fossae, where developmental pits may occur.
Pits:
Occlusal developmental pits are sharp pinpoint depressions where grooves intersect.
CLINICAL CONSIDERATIONS WITH POSTERIOR TEETH
Caries Concerns:
Permanent posterior teeth have pit and groove patterns susceptible to caries due to plaque retention and thin enamel walls.
When examining these areas, it is important to use an explorer and mirror, and possibly a chemical caries indicator.
Dental Sealants:
Posterior teeth with deep pit and groove patterns should have sealants placed shortly after eruption.
PERMANENT PREMOLARS
Composition:
Eight premolars exist in the permanent dentition, two per quadrant, located posterior to canines and anterior to molars.
Types:
First premolars
Second premolars
MAXILLARY FIRST PREMOLARS
Structural Features:
Maxillary first premolars (#5 and #12) are larger than second premolars, possessing two cusps (buccal and lingual) and two roots (facial and lingual).
Eruption occurs earlier than that of mandibular premolars.
MAXILLARY FIRST PREMOLARS - CONTINUED
Root Characteristics:
Maxillary first premolars have a bifurcated root (each with buccal and lingual roots); some may present fused roots.
Roots are shorter and resemble molar roots.
CLINICAL CONSIDERATIONS WITH FIRST MAXILLARY PREMOLARS
These premolars are often extracted in orthodontics when teeth are crowded to provide space without altering the patient's facial structure.
The slight depression along the root shape increases the risk of periodontal disease, making the first maxillary premolar the favored extraction choice when required.
MAXILLARY SECOND PREMOLARS
Characteristics:
Maxillary second premolars (#4 and #13) typically have two cusps (buccal and lingual) and one root.
DIFFERENCES BETWEEN SECOND AND FIRST PREMOLARS
Cusp Dimensions:
Cusps are more equal in length on the second premolar, with the lingual cusp slightly shorter but not as short as on the first.
Mesiobuccal cusp slope is shorter than the distobuccal slope on the second premolar.
Root and Canal Structures:
Second premolar has one root and one root canal, unlike the first which may exhibit additional structures.
The second is wider buccolingually than mesiodistally.
MANDIBULAR FIRST PREMOLARS
Features:
Mandibular first premolars (#21 and #28) possess a long, well-formed buccal cusp and a small nonfunctional lingual cusp, the latter sometimes equal to the cingulum of some maxillary canines.
They are smaller and shorter than the second premolars.
MANDIBULAR SECOND PREMOLARS
Types:
Mandibular second premolars (#20 and #29) erupt distal to the first premolars and replace primary mandibular second molars.
Forms include:
Three-cusp type (tricuspidate)
Two-cusp type (bicuspidate)
PERMANENT MOLARS
General Overview:
There are 12 molars in total, with three in each quadrant of the permanent dentition.
Molar crowns typically include four or five short, blunt cusps.
Each molar possess two or three roots supporting the larger crown.
PERMANENT MOLARS - CONTINUED
The term molar derives from the Latin term for “grinding.”
Types of Molars:
First molars
Second molars
Third molars (commonly referred to as wisdom teeth, as they erupt last)
MAXILLARY MOLARS
Eruption and Structure:
Usually the first permanent teeth to erupt in the maxillary arch with four major cusps (two buccal, two lingual).
Each has three well-separated and developed roots, hence termed trifurcated.
MAXILLARY FIRST MOLARS
Key Characteristics:
Maxillary first molars (#3 and #14) are the inaugural permanent teeth in the maxillary arch, erupting distal to primary maxillary second molars.
They are nonsuccedaneous and the largest tooth in the maxillary arch, comprising five developmental lobes (two buccal, three lingual).
The fifth cusp, known as the cusp of Carabelli, is notable.
MAXILLARY FIRST MOLARS - CONTINUED
Additional features and clinical considerations relate to the morphology, eruption, and function in occlusion.
MAXILLARY SECOND MOLARS
Structure:
The crown is smaller than that of the first molar, generally with four cusps.
Lacks the fifth cusp and features three roots, smaller than those of the first molar.
Buccal groove is located farther distally compared to the first molar.
MAXILLARY SECOND MOLARS - CONTINUED
Mesiobuccal cusp is longer with a less sharp cusp tip compared to the distobuccal cusp.
MAXILLARY THIRD MOLARS
Eruption and Features:
Maxillary third molars (#1 and #16) exhibit considerable size and contour differences.
Generally smaller crown, shorter roots likely to fuse into a single, tapered root.
Often termed the wisdom tooth as it erupts last.
CLINICAL CONSIDERATIONS WITH MAXILLARY MOLARS
Sinus and Pain Associations:
Roots of maxillary molars may penetrate the sinus, leading to confusion between sinus infection pain and dental pain.
Permanent maxillary third molars may become impacted within the alveolar bone.
Loss of maxillary first molar can lead to tipping and drifting of the second molar into the space, causing chewing difficulties and increased periodontal disease risk.
MANDIBULAR MOLARS
Eruption Timing:
Erupt 6 months to 1 year earlier than corresponding maxillary molars.
Crows display four to five major cusps, with two lingual cusps of equal width.
All mandibular molars are wider mesiodistally than buccolingually, akin to anterior teeth.
MANDIBULAR MOLARS - CONTINUED
Each molar possesses two well-developed roots: mesial and distal.
A tooth with two roots is referred to as bifurcated.
MANDIBULAR FIRST MOLARS
Time of Eruption:
Erupt between six and seven years of age, typically the first permanent teeth to erupt.
The mesial and distal roots are larger and more divergent than those of the second molar, with a mesial root potentially exhibiting both buccal and lingual branches.
MANDIBULAR FIRST MOLARS - CONTINUED
MANDIBULAR SECOND MOLARS
Eruption Age:
Erupt between 11 and 12 years of age, positioned distal to the permanent first molars, and are nonsuccedaneous.
Crown is slightly smaller than first molar in all dimensions featuring four well-developed cusps.
MANDIBULAR SECOND MOLARS - CONTINUED
MANDIBULAR THIRD MOLARS
Variability in Shape:
Characteristics are similar to maxillary third molars, with significant variation in shape, often smaller than the second molar.
Usually consists of four developmental lobes and typically has two fused, shorter roots compared to mandibular second molars.
CLINICAL CONSIDERATIONS WITH MANDIBULAR MOLARS
Oral Hygiene Challenges:
Positioning oral evacuators can be difficult due to lingual inclination of molar crowns, leading to hygiene issues, particularly missing cleaning in the lingual gingiva.
THE PRIMARY DENTITION
Overview:
Comprises 20 primary teeth (10 per arch), including incisors, canines, and molars.
Primary teeth are numbered A through T using the Universal Tooth Numbering System.
Generally smaller and whiter enamel compared to permanent teeth; crowns are short in relation to total length, with narrower crowns at the CEJ.
THE PRIMARY DENTITION - CONTINUED
Pulp chambers and horns are relatively large compared to permanent teeth, with a thicker layer of dentin.
Enamel is relatively thin.
GENERAL CHARACTERISTICS OF PRIMARY TEETH
Smaller size
Whiter color
Less mineralized, prone to wear
Significant attrition occurs due to jaw growth.
Attrition is a natural occurrence and not a dentition-specific trait.
GENERAL CHARACTERISTICS OF PRIMARY TEETH - CONTINUED
Shorter crowns relative to roots
Thinner enamel + dentin
Proportionally larger pulp chambers
Consistent shape
Crown appears bulbous (labial/buccal cingula).
CLINICAL CONSIDERATIONS WITH PRIMARY TEETH
Misunderstanding by parents about the importance of primary teeth; hold space for erupting permanent teeth.
Thinner enamel and dentin result in rapid decay progression to pulp, potentially causing tooth loss.
Early dental care and education are crucial for preserving primary dentition.
PRIMARY INCISORS
Labial Surface Features:
Smooth surface, no depression; lacks mamelons on the incisal edge, a key trait.
Prominent cervical ridges on facial surfaces.
Cingulum occupies 1/3 of cervical to incisal third, roots are long and bend labially in apical third to half.
PRIMARY INCISORS - LABIAL ASPECT
Proportional Features:
Primary maxillary central incisors are wider MD than inciso-cervically, a unique distinction.
Crown narrows near CEJ, prominent cervical ridges on both labial and lingual surfaces.
Primary maxillary central incisor symmetry differs from primary lateral incisor; format shows longer than wider.
PRIMARY INCISORS - ROOT TO CROWN PROPORTION
Roots of primary incisors are significantly longer compared to crown length (approximately twice the crown length), with maxillary lateral incisor roots being even longer.
PRIMARY INCISORS - OUTLINE SHAPE OF CROWNS
Features of primary maxillary central incisor:
Flat incisal edge
Round distoincisal angle
Flat mesial side; mesial and distal margins overhang root profile
No grooves, depressions, or lobes.
PRIMARY MAXILLARY INCISORS
Crown Dimensions:
The crown of primary maxillary central incisor (E and F) is wider mesiodistally than incisocervically.
Unique in either dentition; no mamelons noted, with more pronounced cingulum and marginal ridges versus permanent successors.
Presence of deeper lingual fossa.
PRIMARY MAXILLARY LATERAL INCISORS
Size and Features:
Crown similar to central incisor but smaller in all dimensions; incisal angles rounder.
The lateral root is proportionally longer than its crown, with a sharper apex.
PRIMARY MANDIBULAR CENTRAL INCISORS
Characteristics:
Crown resembles primary mandibular lateral incisor more than its permanent central successor; symmetric with less constriction at CEJ compared to primary maxillary incisor.
Lingual surface appears smooth, tapering toward the prominent cingulum.
PRIMARY MANDIBULAR LATERAL INCISORS
Structural Features:
Crown form parallels that of central incisor but is wider and longer.
Incisal edge slopes distally, with more rounded distoincisal angle.
Root may curve distally in apical third with a longitudinal groove.
PRIMARY CANINES
Overview of Primary Canines:
Four primary canines exist, two in each dental arch.
Differences from permanent successors include:
Primary maxillary canine (C and H) has a longer and sharper cusp initially than its permanent successor.
Mesial and distal outlines of primary maxillary canine are rounder.
PRIMARY MANDIBULAR CANINES
Comparison with Maxillary Canine:
Resembles primary maxillary canine but smaller labiolinguistically.
Distal cusp slope is longer than mesial cusp slope; features a shallow lingual fossa.
PRIMARY MOLARS
Uniqueness of Primary Maxillary First Molar:
Crown shape does not resemble any tooth in either dentition.
Height of contour on buccal surface located at cervical third; on lingual, at middle third.
Has three roots, thinner with greater flare than permanent maxillary first molar, with the lingual root largest and most divergent.
PRIMARY MAXILLARY SECOND MOLARS
Size and Crown Characteristics:
Larger than the primary maxillary first molar; closely resembles the form of the permanent maxillary first molar but smaller.
Commonly possesses a minor fifth cusp, the cusp of Carabelli.
PRIMARY MANDIBULAR FIRST MOLARS
Distinct Crown Features:
Crown unique compared to other teeth, with height of contour on buccal at cervical third and lingual at middle third.
Contains four cusps, larger mesial cusps, typically with two roots similar to other primary and permanent mandibular molars.
PRIMARY MANDIBULAR SECOND MOLARS
Size Characteristics and Features:
Larger than the primary mandibular first molar, it has five cusps, resembling permanent mandibular first molar.
Three buccal cusps are nearly equal in size, maintaining an overall oval occlusal shape.