Fracture resistance of prepared teeth restored with bonded inlay restorations

https://doi.org/10.1016/S0022-3913(03)00173-2Get rights and content

Abstract

Statement of problem

Tooth preparation weakens the remaining tooth structure.

Purpose

This study attempted to measure and compare the strength of intact, prepared, and restored human maxillary premolars.

Material and methods

Fifty intact, noncarious human maxillary premolars were divided into 5 groups of 10 and were mounted with their roots imbedded in autopolymerized acrylic. In the first group, the teeth were intact with no preparation. In the other 4 groups, Class II MOD preparations were made with a water-cooled high-speed hand piece. In 1 group, the cavity preparations were restored with bonded CAD/CAM ceramic inlays. In 2 groups, the preparations were restored with bonded CAD/CAM composite inlays (acid etched or air particle abraded). In the final group, the teeth were prepared but unrestored. Specimens were tested individually in a universal testing machine, in which a 4.82-mm-diameter steel sphere plunger was mounted in the crosshead moving at 0.5 mm/min. The plunger contacted the facial and lingual triangular ridges beyond the margins of the restorations. Peak load to fracture (N) was measured for each specimen. Means were calculated and analyzed with analysis of variance (P≤.05).

Results

MOD preparations weakened the teeth by approximately 59%. Restoring the teeth with ceramic or composite inlays did not significantly strengthen the teeth under this testing system. Of the restored teeth, those restored with indirect composite inlays cemented following manufacturer’s recommendations had the highest fracture resistance.

Conclusion

Within the limitations of this study, under static compression load testing, bonded inlay restorations did not strengthen maxillary premolars with large MOD preparations.

Section snippets

Selection and preparation of teeth

Fifty recently extracted human premolar teeth were immersed in 0.5% chloramine solution for disinfection and stored for 1 week in distilled water before the experiment was begun. Any calculus and soft tissue deposits were removed from the selected teeth by use of a hand scaler (Gracey curette SG 17/18; Hu-Friedy, Chicago, Ill.). The teeth were mounted with their roots imbedded in autopolymerized acrylic blocks with the cementoenamel junction (CEJ) 2 mm above the surface of the acrylic resin

Results

The mean peak fracture load (N) for each group is reported in Table II. Analysis of the results revealed that prepared maxillary premolars with large MOD lose 59% of their strength when tested occlusally with a compressive load. Intact teeth were more resistant to fracture than prepared but unrestored teeth (P<.0001) and all restored groups (P<.0001). Restored teeth were not more resistant to fracture than prepared but unrestored teeth (P>.05), but the average strength for each group restored

Discussion

Preparing maxillary premolars with large and deep MOD preparations weakened the teeth by 59%. In a recent study, Cotert et al20 confirmed the weakening effect of preparation and that there is partial reinforcement when teeth are restored with acid etching, bonding agents, and different types of restorations. In this study, the restored teeth showed a slight increase in fracture resistance varying between 4% and 15% when compared with unrestored teeth, but bonded ceramic and composite inlays did

Conclusions

Within the limitations of this study, the results suggest that the use of large MOD preparations severely weakens maxillary premolars. Under compressive load testing, composite and ceramic bonded inlay restorations do not restore the original strength of the teeth. Clinical extrapolation of these experimental results must be made carefully, since at this time no experimental method truly imitates the conditions under which the teeth function in the oral environment.

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