Evaluation of a Method to Determine Wear Resistance of Class I Tooth Restorations during Cyclic Loading

Abstract

The aim of this study was the development of a test regime to determine the wear resistance and predict the clinical performance of conventional glass ionomer cement (GIC) restorations in Class I tooth cavities. Cavities were prepared in excised human teeth and restored using three conventional glass ionomer restorative materials: DeltaFil, Fuji IX GP and Ketac Universal. The restored teeth were mechanically and thermally stressed using a chewing simulator with a maximum number of 1,200,000 load cycles. Besides determining the number of cycles achieved, the abrasion volume after termination of the chewing simulation was calculated using µCT images. All teeth restored with DeltaFil reached 1,200,000 cycles without any restoration failure. Only 37.5% of the restorations each with Ketac Universal and Fuji IX GP were able to achieve the maximum cycle number. A significant lower abrasion volume for restorations with DeltaFil compared to Ketac Universal (p = 0.0099) and Fuji IX GP (p = 0.0005) was found. Laboratory chewing simulations are a useful tool to study basic wear mechanisms in a controlled setting with in-vivo related parameters. DeltaFil shows an improved wear resistance compared to other conventional GICs, indicating the high potential of this material for long-lasting Class I restorations.

Keywords: Class I restoration; chewing simulation; dental restorative material; glass ionomer; wear resistance.

Figure 1

Chewing simulation setup with a restored tooth (DeltaFil—Specimen 4) mounted inside the chamber of the chewing simulator.

Figure 2

Reconstructed µCT images of a restored tooth to calculate the abrasion volume (DeltaFil—Specimen 8). The µCT images were recorded prior to the chewing simulation (a) and after completion of the chewing simulation at 1,200,000 cycles (b).

Figure 3

Cycle number of the restored teeth at termination of the chewing simulation. All teeth restored with DeltaFil reached the maximum number of 1,200,000 cycles. Restorations with DeltaFil lasted significantly longer than restorations with Fuji IX GP (‘*’: p ≤ 0.05). The error bars represent the minimum and maximum values of the measured data.

Figure 4

Abrasion volume of the restored teeth after termination of the chewing simulation. Restorations with DeltaFil resulted in a significantly decreased abrasion volume compared to Ketac Universal and Fuji IX GP (‘*’: p ≤ 0.05; ‘***’: p ≤ 0.001). The error bars represent the minimum and maximum values of the measured data.

Figure 5

High resolution photographs showing the abraded surfaces of the restorations at termination of the chewing simulation. (a) DeltaFil (specimen 5; 1,200,000 cycles), (b) Ketac Universal (specimen 6; 668,629 cycles), (c) Fuji IX GP (specimen 5; 419,892 cycles). Red arrows indicate chipping and embrittlement of the restoration at the dentin interface.

Figure 6

Fracture toughness of the investigated GICs measured using a notchless triangular prism testing rig. The fracture toughness of DeltaFil was significantly higher compared to Ketac Universal and Fuji IX GP (‘*’: p ≤ 0.05). The error bars represent the standard deviations of the measured data.