10.4 Cavity Classification & Cavity Preparation Terminology
Key Takeaways
Under G.V. Black's classification, Class II lesions involve proximal surfaces of premolars and molars, while Class III and IV involve proximal surfaces of incisors and canines.
A Class IV lesion includes the incisal angle of an anterior tooth, whereas a Class III lesion leaves the incisal angle intact.
Class V lesions are in the gingival third of the facial or lingual surface of any tooth, and Class VI lesions involve incisal edges or cusp tips.
A line angle is where two preparation walls meet and a point angle is where three meet; the pulpal wall is perpendicular, and the axial wall parallel, to the tooth's long axis.
Black's preparation steps are outline, resistance, retention and convenience form, then removal of remaining caries, finishing the walls and cleaning the preparation.
10.4 Cavity Classification & Cavity Preparation Terminology
Quick Answer: Competencies 5.7.1 and 5.7.2 require you to classify lesions and restorations, and to use cavity preparation terminology correctly. Under G.V. Black's classification:
- Class I: pits and fissures
- Class II: proximal surfaces of premolars and molars
- Class III: proximal surfaces of incisors and canines, not including the incisal angle
- Class IV: proximal surfaces of incisors and canines including the incisal angle
- Class V: gingival third of facial or lingual surfaces
- Class VI (added later): incisal edges and cusp tips.
Preparations have walls (pulpal, axial, gingival and external walls named for the tooth surface), line angles (two walls meeting), point angles (three walls) and a cavosurface margin. Black's steps include outline, resistance, retention and convenience form.
1. G.V. Black's Classification
| Class | Location of the lesion or restoration | Typical teeth / examples | Chartable surfaces |
|---|---|---|---|
| Class I | Pits and fissures: occlusal surfaces of premolars and molars, buccal and lingual pits of molars, lingual pits of maxillary incisors | Occlusal of 46 (O); lingual pit of 12 (L) | O, B pit, L pit |
| Class II | Proximal surfaces of premolars and molars | MO on 25; DO on 36; MOD on 16 | M and/or D, usually with O |
| Class III | Proximal surfaces of incisors and canines, incisal angle intact | Distal of 21; mesial of 33 | M or D (often with F or L access) |
| Class IV | Proximal surfaces of incisors and canines involving the incisal angle | Fractured mesioincisal corner of 11 | MI or DI |
| Class V | Gingival (cervical) third of the facial or lingual surface of any tooth (smooth surface, not a pit) | Cervical caries or abfraction on the buccal of 44 | F (B) or L |
| Class VI | Incisal edges of anterior teeth and cusp tips of posterior teeth (wear or developmental defects) | Worn cusp tip of 26 | I or cusp tip |
Naming by number of surfaces:
- A simple cavity involves one surface (O, F).
- A compound cavity involves two surfaces (MO, DO, DL).
- A complex cavity involves three or more surfaces (MOD, MODBL).
Surfaces are written in the order mesial or distal first, then occlusal or incisal, then facial or lingual (for example, MOD, DOL). Combined with FDI notation, an example chart entry is "36 MOD composite". The same letters are used when charting existing restorations (Domain 4).
2. Walls, Angles and Margins
| Term | Definition | Example |
|---|---|---|
| Pulpal wall (floor) | Internal wall perpendicular to the long axis of the tooth, over the pulp | The floor of a Class I occlusal preparation |
| Axial wall | Internal wall parallel to the long axis of the tooth | The inner wall of a Class II proximal box, or the inner wall of a Class V preparation |
| Gingival wall (seat) | The floor of a proximal box, nearest the gingiva | Where the matrix band and wedge must seal (section 10.3) |
| External (surrounding) walls | Walls named for the tooth surface they are next to: mesial, distal, buccal/facial, lingual | Buccal wall of a Class I preparation |
| Line angle | The line where two walls meet, named by combining the walls (with "-o-" joining them) | Axiopulpal, distopulpal, axiogingival line angles |
| Point angle | The point where three walls meet | Axio-bucco-gingival point angle |
| Cavosurface margin | The junction of a preparation wall with the outer surface of the tooth | Where restorative material must seal; may be bevelled for composite |
| Isthmus | The narrow connection between the occlusal portion and the proximal box of a Class II preparation | A common fracture site in amalgam restorations |
3. Principles of Cavity Preparation (Black's Steps)
- Outline form: the shape and extent of the preparation at the tooth surface. It is determined by the extent of the caries and, today, by the principle of conserving tooth structure.
- Resistance form: the shape that helps the tooth and the restoration withstand chewing forces without fracturing. Examples include flat floors, rounded internal angles and adequate thickness of material.
- Retention form: features that keep the restoration from dislodging. Examples include converging walls or undercuts for amalgam, retention grooves or slots, pins in extensive preparations, and micromechanical bonding for composite.
- Convenience form: modifications that give the operator access and visibility, for example widening for instrument access.
- Removal of remaining carious dentin: with spoon excavators or slow-speed round burs. In deep lesions the dentist may leave some affected dentin over the pulp (indirect pulp capping; section 10.1).
- Finishing the enamel walls and margins: smoothing and, where indicated, bevelling the margins.
- Cleaning (debridement) of the preparation: rinsing and drying before liners, bases, adhesives or restorative material are placed.
Black's original rule of "extension for prevention" extended outlines into self-cleansing areas. Minimally invasive dentistry has largely replaced it, using conservative outlines, adhesive materials and sealants. Examples are slot (box-only) preparations, preventive resin restorations and conservative Class V preparations.
4. Instruments Associated with Cavity Preparation
Rotary cutting instruments (burs)
| Bur shape | Common numbers | Use |
|---|---|---|
| Round | #¼, #½, #1, #2, #4, #6, #8 | Initial entry, removing caries, retention points |
| Inverted cone | #33½, #34, #35, #37 | Undercuts, flattening floors |
| Straight fissure (plain / cross-cut) | #56–#58 / #556–#558 | Extending outlines, walls |
| Tapered fissure (plain / cross-cut) | #169–#171 / #699–#703 | Walls that converge; crown preparation |
| Pear | #330–#333, #245 | Class I and II amalgam preparations (rounded internal angles) |
| Diamond and finishing burs | Various shapes and grits | Bevelling, crown preparation, finishing composites |
Shank types: friction-grip (FG) for high-speed handpieces; latch-type for low-speed contra-angles; straight for low-speed straight handpieces and lab work.
Hand cutting instruments
- Spoon excavators: remove soft carious dentin and temporary material.
- Enamel hatchets and chisels (straight, Wedelstaedt, binangle): cleave unsupported enamel and plane walls. Chisels are used with a push stroke.
- Hoes: plane floors and walls with a pull stroke.
- Gingival margin trimmers (GMT) (paired mesial and distal): bevel and smooth the gingival margin of Class II boxes.
5. Why the Assistant Needs This Vocabulary
- Anticipating the tray: a Class II preparation calls for a matrix, wedges, a burnisher and the proximal-box instruments. A Class V preparation may need a gingival retraction cord or a cervical clamp (#212). A Class IV preparation needs a clear strip or a crown form and a shade guide.
- Charting and progress notes: "Class II DO amalgam on 25" must match the surfaces charted and the procedure codes billed.
- Communicating with the operator: for example, "Axial wall depth looks close to the pulp. Would you like a liner?" Using the correct terms keeps chairside communication fast and accurate.
Caries on the distal surface of tooth 22 has spread to involve the incisal angle. How is this lesion classified?
Class VI
Class III
Class II
Class IV
In a Class II preparation, which wall forms the floor of the proximal box nearest the gingiva?
Axial wall (inner)
Gingival wall (seat)
Distal external wall
Pulpal wall (floor)
Which principle of cavity preparation refers to grooves, undercuts or converging walls that keep the restoration from being dislodged?
Retention form
Outline form
Convenience form
Resistance form
Which type of bur shank is used in a high-speed handpiece?
Latch-type
Friction-grip (FG)
Straight (long) shank
Mandrel-mounted
Sections you finish are checked off in the contents.