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Fracture strength of Class 2 amalgams with various cavity-lining materials
A E Palmer1, R D Davis, D F Murchison
181st Dental Squadron/SGD, Keesler AFB, MS 39534, USA.
Operative Dentistry
|May 25, 1999
Summary
The fracture resistance of class 2 amalgam restorations was not significantly affected by the underlying lining material. However, amalgam restorations showed increased fracture resistance after 7 days compared to 1 hour.
Area of Science:
- Dental Materials Science
- Restorative Dentistry
- Biomaterials Engineering
Background:
- Class 2 amalgam restorations are widely used in posterior teeth.
- Lining materials are often placed beneath amalgam to provide insulation or pulpal protection.
- Understanding the effect of liners on restoration integrity is crucial for clinical success.
Purpose of the Study:
- To compare the fracture resistance of class 2 amalgam restorations placed over various lining materials.
- To evaluate the influence of different liner types on the mechanical properties of amalgam restorations.
- To assess the effect of time on the fracture resistance of these restorations.
Main Methods:
- An in vitro study involving 80 maxillary molars with standardized class 2 cavity preparations.
- Lining materials (resin-modified glass-ionomers, polyacid-modified composite resin, conventional glass-ionomers, calcium hydroxide) were placed at 0.5 mm thickness.
- Amalgam was condensed over the liners, and specimens were tested for fracture resistance using an Instron Universal Testing Machine at 1 hour and 7 days.
- Fracture load was applied at a specific angle and location within the restoration.
Main Results:
- No statistically significant differences in fracture resistance were found among the tested lining materials and controls at either time interval.
- A statistically significant increase in fracture resistance was observed between 1-hour and 7-day testing periods.
- Restorations tested at 7 days demonstrated greater resistance to fracture than those tested at 1 hour.
Conclusions:
- The presence of a 0.5 mm thick lining material in the approximal box does not significantly affect the fracture resistance of class 2 amalgam restorations when 3 mm of bulk amalgam remains.
- Amalgam restorations exhibit improved fracture resistance over time (7 days vs. 1 hour).
- Clinical selection of liners beneath amalgam restorations may not be critical for fracture resistance, provided adequate amalgam bulk is present.