7.1 Dental Anatomy: Tooth Notation, Permanent Tooth Morphology and Identification
Key Takeaways
In FDI notation the first digit is the quadrant (1-4 permanent, 5-8 primary, starting upper right and moving clockwise) and the second digit the tooth, so 36 is the permanent mandibular left first molar and 85 the primary mandibular right second molar.
The maxillary first premolar usually has two roots and a mesial crown concavity, while the mandibular first premolar has a small, non-functional lingual cusp and a mesiolingual groove.
The maxillary first molar has an oblique ridge and often a cusp of Carabelli; the mandibular first molar has five cusps and two roots, and mandibular second molars have four cusps in a cross-shaped groove pattern.
Facial heights of contour lie in the cervical third of all teeth; lingual heights of contour lie in the cervical third of anterior teeth and the middle third of posterior teeth.
The curve of Spee is the anteroposterior curve of the mandibular occlusal plane and the curve of Wilson is the mediolateral curve formed by the lingual inclination of mandibular molars.
The blueprint asks candidates to identify and describe tooth morphology, analyze occlusion, and apply anatomical and occlusal principles to restorations. Every SDLE vignette uses FDI notation, so misreading a tooth number can turn a correct clinical judgment into a wrong answer.
Tooth Numbering Systems
| System | Permanent teeth | Primary teeth | Example: permanent mandibular left first molar |
|---|---|---|---|
| FDI (two-digit, ISO 3950) | Quadrants 1-4, teeth 1-8 from the midline | Quadrants 5-8, teeth 1-5 | 36 |
| Universal (ADA) | 1-32, starting at the maxillary right third molar | Letters A-T | 19 |
| Palmer | Quadrant symbol with numbers 1-8 | Quadrant symbol with letters A-E | Lower-left bracket with 6 |
FDI quadrants run clockwise from the patient's upper right: 1 upper right, 2 upper left, 3 lower left, 4 lower right; primary quadrants are 5, 6, 7, 8 in the same order. Tooth 18 is the maxillary right third molar, 23 the maxillary left canine, 41 the mandibular right central incisor, 55 the primary maxillary right second molar.
Identifying Permanent Teeth
| Tooth | Key identifying features |
|---|---|
| Maxillary central incisor | Widest incisor; mesioincisal angle sharper than distoincisal; prominent cingulum and marginal ridges |
| Maxillary lateral incisor | Smaller, most variable shape; peg laterals and congenital absence are common; lingual pit may harbor caries |
| Mandibular incisors | Smallest teeth; central is bilaterally symmetrical; roots flattened mesiodistally (two canals occur) |
| Canines | Longest roots; maxillary canine has a cusp tip with a longer distal ridge; key to canine guidance |
| Maxillary first premolar | Usually two roots (buccal and palatal); mesial crown concavity and mesial root depression; buccal cusp longer |
| Maxillary second premolar | Usually one root; cusps more equal in height |
| Mandibular first premolar | Small non-functional lingual cusp, mesiolingual groove, crown tilted lingually |
| Mandibular second premolar | Often three cusps (Y-shaped groove pattern) or two cusps (U or H pattern) |
| Maxillary first molar | Three roots (palatal longest); oblique ridge joining mesiolingual and distobuccal cusps; cusp of Carabelli on the mesiolingual cusp |
| Maxillary second molar | Smaller, roots closer together; Carabelli trait absent |
| Mandibular first molar | Five cusps (three buccal, two lingual), two roots (mesial and distal), distal cusp smallest |
| Mandibular second molar | Four cusps with a cross-shaped (+) groove pattern; roots closer together |
| Third molars | Most variable; frequently impacted or congenitally missing |
Contact Areas, Embrasures and Heights of Contour
- Proximal contacts are near the incisal third in anterior teeth and move cervically toward the posterior; in molars they sit at the junction of the occlusal and middle thirds (or in the middle third for maxillary molar distal contacts). Restorations that misplace contacts trap food and harm the papilla.
- Embrasures (occlusal, facial, lingual and gingival) give spillways for food and space for the papilla; the gingival embrasure must not be overfilled by restorations.
- Height of contour: facial surfaces of all teeth in the cervical third; lingual surfaces in the cervical third for anterior teeth (cingulum) and in the middle third for posterior teeth. Over-contouring crowns at these areas promotes plaque accumulation; correct contours deflect food and protect the gingiva.
Occlusal Anatomy and Curves
- Supporting (centric holding) cusps: maxillary palatal cusps and mandibular buccal cusps; they maintain the vertical dimension.
- Non-supporting (shearing) cusps: maxillary buccal and mandibular lingual cusps.
- Curve of Spee: the anteroposterior curve of the mandibular occlusal plane from the canine cusp tip along the buccal cusps.
- Curve of Wilson: the mediolateral curve produced by the lingual inclination of the mandibular posterior teeth.
- Bonwill triangle: an equilateral triangle of about 10 cm (4 inches) between the condyles and the mandibular incisor contact point; the Balkwill angle between the Bonwill triangle and the occlusal plane averages about 26 degrees.
- Compensating curves in complete dentures reproduce these curves to keep balance in excursions.
Permanent Eruption Sequence and Root Counts
The usual permanent eruption order is first molars and mandibular central incisors (about 6-7 years), incisors (7-8 years), mandibular canines and first premolars (9-11 years), maxillary premolars and canines (10-12 years), second molars (11-13 years) and third molars (17-21 years). Typical root and canal counts that guide endodontics and extraction:
| Tooth | Usual roots | Notes |
|---|---|---|
| Maxillary incisors and canine | 1 | Canine root is the longest |
| Maxillary first premolar | 2 | Buccal and palatal roots |
| Maxillary molars | 3 | Mesiobuccal root often has a second canal (MB2) |
| Mandibular incisors | 1 | Second (lingual) canal is common |
| Mandibular premolars | 1 | First premolar may divide into two canals |
| Mandibular molars | 2 | Mesial root has two canals; distal one or two |
Clinical Application
- Waxing and carving restorations reproduce cusp heights, fossae and marginal ridges so contacts fall on cusp tips and marginal ridges rather than on inclines.
- Root morphology guides treatment: the mesial concavity of the maxillary first premolar makes strip perforations and periodontal pockets more likely, and the furcation entrances of molars are close to the cementoenamel junction.
- Tooth form influences gingival form: triangular crowns with long contacts produce tall papillae; long proximal contacts help close black triangles.
Exam Traps
- Tooth 46 is the mandibular right first molar, not the maxillary right.
- The two-rooted premolar in most SDLE questions is the maxillary first premolar.
- The cusp of Carabelli is on the mesiolingual (mesiopalatal) cusp of the maxillary first molar.
A vignette describes a carious lesion on tooth 26. Which tooth is this in FDI notation?
The permanent mandibular left second premolar in the lower arch
The permanent maxillary left first molar (upper left quadrant)
The permanent maxillary right first molar on the opposite side
The primary maxillary left second molar in a mixed dentition
A single extracted premolar has two roots, a mesial concavity on the crown that continues onto the root trunk, and a buccal cusp longer than the palatal cusp. Which tooth is it?
A mandibular second premolar with a Y-shaped groove
A maxillary second premolar with two cusps of nearly equal height
A mandibular first premolar with a mesiolingual groove
A maxillary first premolar with a mesial crown concavity
Where is the height of contour on the lingual surface of a maxillary first molar?
In the cervical third, as on all lingual surfaces
At the cementoenamel junction of the palatal root
In the middle third of the lingual crown surface
In the occlusal third at the marginal ridges
Sections you finish are checked off in the contents.