Clinical aspects of Amalgam
The manipulation and the clinical aspects of silver amalgam are dealt in this section covering the procedures involved, precautions and the possible causes for defective restorations.
1. What are the primary resistance features provided when a proximal box is prepared?
- Flat gingival wall, perpendicular to the forces directed to the long axis of the tooth
- Rounded or bevelled axio pulpal line angle
- Bevelling the gingival margin
- Reverse curve at the junction of the occlusal step and the proximal box
- Providing enough thickness of the material
Ref: Theodore.M.Roberson,Harald.O.Heymann,Edward.J.SwiftJR.Sturdevant's Art and Science of Operative Dentistry.Mosby publications;676
2. What is pre carve burnishing?
It is a form of condensation in which the tooth preparations are overfilled with amalgam and this overpacked amalgam is burnished immediately with a large burnisher, using heavy strokes mesiodistally and faciolingually. This ensures a good condensation at the margins and produces denser amalgam at the margins. A large headed burnisher is used for maximum effectiveness so that in the final strokes, the cusp slopes are contacted and not the margins.
Ref: Theodore.M.Roberson,Harald.O.Heymann,Edward.J.SwiftJR.Sturdevant's Art and Science of Operative Dentistry.Mosby publications;2002;683
3. What are Amalgam Blues or what is the reason for darkening of tooth structure adjacent to an amalgam restoration?
Amalgam blues are dark discolouration seen in the tooth structure adjacent to amalgam restoration. They mimick secondary caries. It is caused by the gradual diffusion of metallic ions from amalgam restoration into the dentin or by light passing through the transluscent, thin enamel that is reflected from the underlying amalgam. When a cement liner or a base is placed when such restorations are replaced, this appearance is decreased. Other than esthetics concern, it does not warrant replacement of such amalgam restorations.
Ref: Theodore.M.Roberson,Harald.O.Heymann,Edward.J.SwiftJR.Sturdevant's Art and Science of Operative Dentistry.Mosby publications;2002;297,409
4. What is an Automatrix?
It is a retainerless matrix with 4 types of bands that are designed to fit all the teeth,regardless of the circumference. It is indicated for extensive class II preparations. A main disadvantage of this matrix is that since they are not precontoured, physiologic contours are difficult to be developed. The advantages include convenience, improved visibility since it is retainerless and decreased application time.
Ref: Theodore.M.Roberson,Harald.O.Heymann,Edward.J.SwiftJR.Sturdevant's Art and Science of Operative Dentistry.Mosby publications;2002;788
5. What are the factors that dictate the outline form for an amalgam restoration?
The factors that dictate the initial extension of an amalgam cavity are:
- Extension of caries
- Extent of the pit and fissure
- Preparation form requirements of amalgam
- The need for adequate access
- Already existing restorations.
Ref: Theodore.M.Roberson,Harald.O.Heymann,Edward.J.SwiftJR.Sturdevant's Art and Science of Operative Dentistry.Mosby publications;2002;660
6. What is a 90 degree Butt joint for amalgam restorations?
The junction between the cavity wall and the external tooth surface is called the cavo surface margin. The enamel at the cavosurface margin should be 90degree or greater. Otherwise ,it will be subject to fracture. For enamel strength, the marginal enamel rods should be supported by sound dentin. So the walls prepared should result in 90 degree enamel walls that meet the placed amalgam at a butt joint.
Ref: Theodore.M.Roberson,Harald.O.Heymann,Edward.J.SwiftJR.Sturdevant's Art and Science of Operative Dentistry.Mosby publications;2002;661
7. What is a matrix?
A matrix is a rigid material which restores anatomic contours and the contact areas and prevents gingival excess.
Ref: Theodore.M.Roberson,Harald.O.Heymann,Edward.J.SwiftJR.Sturdevant's Art and Science of Operative Dentistry.Mosby publications;2002;718
8. What are the objectives for extension of proximal margins in a class II cavity preparation?
- The extension proximally should include all caries,faults or existing restorative material
- Create 90 degree cavosurface margins
- Establish a clearance of not more than 0.5 mm with the adjacent tooth facially, lingually,and gingivally.
Ref: Theodore.M.Roberson,Harald.O.Heymann,Edward.J.SwiftJR.Sturdevant's Art and Science of Operative Dentistry.Mosby publications;2002;699
9. What are the retentive features in a cavity for amalgam?
The retentive features are:
- Inverted truncated cone shape of the cavity with a slight occlusal convergence or vertical walls near parallel to each other.
- Dovetail preparation.
- Secondary retentive features like locks, grooves and pins
- Bonding of amalgam to the tooth
Ref: Theodore.M.Roberson,Harald.O.Heymann,Edward.J.SwiftJR.Sturdevant's Art and Science of Operative Dentistry.Mosby publications;2002;662
10. What are the resistance features included in a cavity for amalgam restoration?
The resistance features are:
- 90 degree cavosurface margins.
- Uniform and adequate thickness of amalgam
- Preserving cusps and marginal ridges
- Flat floors
- Rounded line and point angles
Ref: Theodore.M.Roberson,Harald.O.Heymann,Edward.J.SwiftJR.Sturdevant's Art and Science of Operative Dentistry.Mosby publications;2002; 662
11. What are the clinical indications for direct amalgam restorations?
The indications are:
- moderate to large class I and class II restorations
- class V restorations (not esthetically critical)
- Temporary caries control restorations
- as foundation restorations
Ref: Theodore.M.Roberson,Harald.O.Heymann,Edward.J.SwiftJR.Sturdevant's Art and Science of Operative Dentistry.Mosby publications;2002; 657
12. What are the basic requirements for a tooth preparation to receive an amalgam restoration?
The tooth preparation should have:
- A uniform minimum thickness of 1 - 1.5 mm for strength
- A 90 degree butt joint at the cavo surface margin
- mechanical retentive features
Ref: Theodore.M.Roberson,Harald.O.Heymann,Edward.J.SwiftJR.Sturdevant's Art and Science of Operative Dentistry.Mosby publications;2002;655
13. When is an amalgam restoration carved?
After completion of condensation, the amalgam can be carved when it is hard enough to resist the carving instrument. A ringing sound should be heard while carving. Starting to carve early may pull the amalgam from the margins.
Ref: Science of Dental Materials, Skinner, Prism books private limited,9th Edn,337
14. Why does pain occur in a tooth restored with amalgam, after 10-12 days of restoring?
This pain that is experienced after 10-12 days of restoring with amalgam is due to the delayed expansion which wedges the restoration against the cavity walls and a pressure results in the pulp chamber. It has to be removed, otherwise expansion continues and a protruded restoration results leading to fracture and marginal defects.
Ref: Science of Dental Materials, Skinner, Prism books private limited,9th Edn,338,339
15. What is Ditching of amalgam?
When unsupported amalgam is left at the margins of the cavity, amalgam remains very thin in those areas which can break and form a ditch. Also, the unsupported enamel may breakdown creating marginal defect inviting secondary caries. This is called as ditching of amalgam.
Ref: Science of Dental Materials, Skinner, Prism books private limited,9th Edn,344