General practitioners often report difficulties in creating adequate proximal contacts when placing posterior composite resin restorations. Special matrix systems with separation rings have been introduced to induce separation of teeth to compensate for the thickness of the matrix band and polymerisation shrinkage of the composite resin.

Objectives: To investigate the force delivered by different brands of separation rings, and the influence of repeated loading and cleaning on their resilience.

Methods: Three different types of rings (Composi-Tight, GDS [G]; Palodent, Dentsply [P]; Contact Matrix, Danville Materials [D]) were tested for their opening distance in the un-activated state. Furthermore, the reaction force was measured at a static opening of 5.7 mm. Rings (n=5) were tested according to 6 protocols: 1) negative control; 2) dynamic loading; 3) disinfection at 93șC; 4) sterilisation at 134șC; 5) dynamic loading + disinfection; 6) dynamic loading + sterilisation. Results were statistically analysed using ANOVA and Multiple regression analysis at p<0.05.

Results: All three brands of rings have statistically significant differences in opening [G: 1.18±0.08 mm / P: 1.87±0.20 mm / D: 2.44±0.06 mm] and different separation forces [G: 11.92±0.39 N / P: 20.81±1.13 N / D: 12.55±0.37N] (p<0.01). Repeated loading in absence of disinfection/sterilisation resulted in a statistically significant increase in opening and reduced force (p<0.05). Increase in opening and loss of separation force was statistical significantly reduced by sterilisation (p<0.01), but not by disinfection, for all brands of rings.

Conclusion: Three brands of separation rings for Class II posterior composite resin restorations, showed considerable differences in opening distance and reaction forces. Repeated loading resulted in an enlarged opening and a reduced force for all rings, however, this negative effect was reduced by sterilisation at 134șC.

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