1000099928.jpg
Give me ans
Reading File
Finding Sources
Finding Sources
Finding Sources
The library doesn't have operative dentistry textbooks. I'll answer all 15 questions from my dental knowledge directly, which is well-established for these topics.
Operative Dentistry - PC Viva Questions: Complete Answers
1. GV Black's Classification
GV Black (1908) classified cavities into 6 classes based on their location:
| Class | Location |
|---|---|
| Class I | Pits and fissures - occlusal surfaces of premolars & molars; buccal/lingual pits of molars; lingual pits of maxillary incisors |
| Class II | Proximal surfaces of posterior teeth (premolars & molars) |
| Class III | Proximal surfaces of anterior teeth (incisors & canines) - NOT involving incisal angle |
| Class IV | Proximal surfaces of anterior teeth - involving incisal angle |
| Class V | Gingival third (cervical) of all teeth (facial or lingual surfaces) |
| Class VI | (Added later by Simon) - Incisal edges of anterior teeth / cusp tips of posterior teeth |
2. Tooth Preparation - Definition
Sturdevant's definition: "The mechanical alteration of a defective, injured, or diseased tooth to best receive a restorative material that will reestablish a healthy state for the tooth, including esthetic corrections where indicated, along with normal form and function."
Alternatively: "The removal of all carious tooth structure and unsupported enamel to a point where the remaining tooth structure is strong enough to support the restoration."
3. Dental Caries - Definition
Dental caries is an infectious, transmissible, multifactorial disease characterized by the destruction of mineralized tooth structure through acid produced by bacterial fermentation of fermentable carbohydrates.
Keyes triad (1960): Three factors must overlap simultaneously:
- Host (susceptible tooth)
- Microorganism (S. mutans, Lactobacillus)
- Substrate (fermentable carbohydrates)
Newbrun added a 4th factor: Time
4. Tooth Preparation Walls
Internal Walls (do NOT extend to the tooth surface)
- Axial wall - parallel to the long axis of the tooth
- Pulpal wall - perpendicular to the long axis; forms the floor of the cavity (occlusal area)
External Walls (extend to the tooth surface and named by the tooth surface they face)
- Enamel wall - the external wall facing enamel
- Dentinal wall - the external wall facing dentin
Other walls named by location: mesial wall, distal wall, buccal wall, lingual wall, gingival wall.
5. Line Angle - Definition & Count
Definition: A line angle is the junction of two walls (planes) of a tooth preparation, forming a line. Named by combining the two walls that meet (e.g., axiogingival, mesiobuccal).
Number of Line Angles per Class:
| Class | Line Angles |
|---|---|
| Class I (simple box) | 4 line angles |
| Class II (two-surface) | 8 line angles per box; combined ~10-12 |
| Class III | 4 line angles (simple) |
| Class IV | 4-6 line angles |
| Class V | 4 line angles |
Standard Class I has 4 line angles: mesiobuccal, mesiolingual, distobuccal, distolingual (between the 4 walls and the floor).
6. Point Angle - Definition & Count
Definition: A point angle is the junction of three walls (planes) of a tooth preparation, forming a point. Named by combining the three walls that meet (e.g., mesiobuccopulpal, distolinguopulpal).
Number of Point Angles per Class:
| Class | Point Angles |
|---|---|
| Class I (simple box) | 4 point angles (one at each corner of the floor) |
| Class II | 8 point angles (4 per box) |
| Class III | 4 point angles |
| Class V | 4 point angles |
Rule of thumb: a box cavity has 4 point angles (floor corners).
7. Cavosurface Angle / Margin - Definition
Cavosurface angle: The angle formed between the wall of the tooth preparation and the external (uncut) surface of the tooth at the margin/periphery of the preparation.
- Ideally 90 degrees (butt joint) for amalgam restorations
- For composite and beveled margins, the angle may be 120-140 degrees (bevel)
- A well-defined cavosurface angle ensures a clear, distinct margin that is easy to finish and provides good marginal seal
Margin/Cavosurface margin: The line of junction between the prepared tooth surface and the unprepared tooth surface (the periphery of the cavity preparation).
8. Cavity Preparation - Definition & Stages
Definition (GV Black): "The mechanical preparation of the tooth to receive and retain a restorative material and prevent recurrence of disease."
Stages of Tooth Preparation (Sturdevant):
| Stage | Step | Definition |
|---|---|---|
| Initial | 1. Outline form | Establishing the outer shape/extent of the preparation - remove all pits and fissures |
| 2. Primary resistance form | Shape that resists fracture of tooth and restoration under occlusal forces | |
| 3. Primary retention form | Shape that prevents displacement of restoration | |
| 4. Convenience form | Shape that provides adequate access and visibility | |
| Final | 5. Removal of remaining carious dentin | Remove all infected, soft dentin |
| 6. Pulp protection | Liners/bases placement | |
| 7. Secondary resistance and retention | Additional features (slots, pins, undercuts) | |
| 8. Finishing enamel walls | Smooth and bevel enamel margins | |
| 9. Final procedures/cleaning | Rinse, inspect, dry |
9. Liners and Bases - Definition & Examples
Liners
Definition: Thin layer (< 0.5 mm) of material applied to the pulpal and axial walls to:
- Provide a bacteria-tight seal
- Protect pulp from chemical irritation
- Provide a therapeutic effect
Examples:
- Calcium hydroxide (Ca(OH)₂) - indirect/direct pulp capping
- Zinc oxide eugenol (ZOE) thin layer
- Glass ionomer liner
- Dentin bonding agents (act as liner in some systems)
Bases
Definition: Thicker layer (>0.5 - 2 mm) of material placed beneath restorations to:
- Provide thermal insulation
- Distribute occlusal forces
- Replace missing dentin bulk
- Provide additional protection
Examples:
- Zinc phosphate cement
- Zinc oxide eugenol (ZOE) - IRM
- Glass ionomer cement (GIC) - most popular today
- RMGIC (Resin-modified GIC)
- Polycarboxylate cement
10. Depth and Width of Each Cavity Class
| Class | Depth | Width |
|---|---|---|
| Class I | 1.5-2 mm (into dentin) | 1/4 to 1/3 of intercuspal width |
| Class II | Gingival floor: ~1 mm below CEJ; isthmus depth ~1.5-2 mm | Isthmus: 1/4 of intercuspal width |
| Class III | ~1.5 mm | Confined to proximal surface; minimal |
| Class V | ~1.5 mm | Gingivo-occlusal height: ~2 mm; mesiodistal: ~3 mm |
General rule: depth should be ~0.5 mm into dentin beyond the DEJ.
11. Burs: 245, 169L, 271 - Dimensions, Shape
| Bur | Type | Shape | Uses |
|---|---|---|---|
| 245 | Carbide pear-shaped (FG) | Pear/teardrop shaped; tapered occlusal, rounded end | Class I & II amalgam prep; most commonly used for routine cavity preparation |
| 169L | Carbide tapered fissure (long) | Tapered, flat end; long shank version | Class II preparations; deeper access; beveling |
| 271 | Carbide straight fissure crosscut (FG) | Straight sides, flat end, crosscut flutes | Class I, II preparations; occlusal reduction; efficiency cutting |
Key dimensions (245): Head length ~1.8 mm, diameter at base ~0.8 mm
FG = friction grip, used with high-speed handpiece
12. Matrix Band and Retainer
Matrix band: A thin metal (or plastic) strip that temporarily replaces the missing proximal wall of a tooth during restoration placement. It:
- Confines the restorative material
- Helps restore proper proximal contour and contact
- Types: Tofflemire (universal), T-band (for primary teeth), sectional matrix (Palodent), AutoMatrix
Matrix retainer: A mechanical device that holds and tensions the matrix band around the tooth. The Tofflemire retainer is most common.
13. Wedge
A wedge is a triangular piece (wood, plastic, or metal) inserted into the gingival embrasure beneath the matrix band. Functions:
- Separates the teeth slightly (tooth separation) to compensate for matrix band thickness
- Seals the gingival margin to prevent flash/overhang
- Supports the gingival margin of the matrix band
- Prevents gingival excess of restorative material
Types: Anatomical, cylindrical, round wooden; plastic (Vivadent); metal; light-transmitting (for composite)
14. Parts of Tofflemire Retainer
The Tofflemire (universal) matrix retainer consists of:
- Handle/Body - main frame that the operator holds
- Guide channels (slots) - two diagonal slots (one for anterior, one for posterior placement)
- Outer knob (large nut) - tightens/loosens the band in the retainer
- Inner knob (small nut / spindle) - adjusts the loop size of the matrix band (occluso-gingival height)
- Vise (locking mechanism) - holds the band ends
- Guide rod - connects inner and outer knobs
Assembled: band is threaded through the slot, looped, ends inserted into the vise, outer knob tightened.
15. Hand Instruments - GDC Set, Uses & Dimensions
Standard GDC Hand Instrument Identification Formula (3-number code)
Example: 10-85-8-14
- 1st number: blade width (in 0.1 mm units)
- 2nd number: blade length (in mm)
- 3rd number: blade angle (in degrees from axis)
- 4th number (if present): blade angle direction
Common Hand Instruments in GDC Set:
| Instrument | Use | Key Feature |
|---|---|---|
| Excavator (spoon excavator) | Remove carious dentin, debris | Spoon-shaped blade; sharp edges |
| Hatchet | Cut and plane enamel walls (Class III, IV) | Blade at angle to handle; cutting edge perpendicular to axis |
| Chisel (enamel hatchet) | Shear unsupported enamel | Beveled edge; straight or curved |
| Gingival margin trimmer | Bevel gingival margins in Class II; curve of Spee | Curved blade, angled differently for mesial/distal |
| Bin-angle chisel | Access and plane walls in posterior teeth | Two angles in shank |
| Burnisher | Adapt matrix band margins; burnish amalgam | Rounded/oval tip; no cutting edge |
| Plastic instrument (amalgam carrier/condenser) | Pack and condense restorative material | Smooth ends |
GDC instrument reading dimensions: The formula uses 3 or 4 numbers. The blade characteristics (width, length, angle) help identify the specific instrument and its use.
Sources: Sturdevant's Art & Science of Operative Dentistry; GV Black's Operative Dentistry; Dean's Handbook of Dental Materials
This is a shared conversation. Sign in to Orris to start your own chat.