Wearing behaviors of a hybrid composite resin for crown and bridge

Influence of cleaning methods after 3D printing on two-body wear and fracture load of resin-based temporary crown and bridge material

OBJECTIVES

To investigate the impact of different cleaning methods on the fracture load and two-body wear of additively manufactured three-unit fixed dental prostheses (FDP) for long-term temporary use, compared to the respective outcomes of milled provisional PMMA FDPs.

MATERIALS AND METHODS

Shape congruent three-unit FDPs were 3D printed using three different resin-based materials [FPT, GCT, NMF] or milled [TEL] (N = 48, n = 16 per group). After printing, the FDPs were cleaned using: Isopropanol (ISO), Yellow Magic 7 (YEL), or centrifugal force (CEN). Chewing simulation was carried out with a vertical load of 50 N (480,000 × 5 °C/55 °C). Two-body wear and fracture load were measured. Data were analyzed using global univariate ANOVA with partial eta squared, Kruskal-Wallis H, Mann-Whitney U, and Spearman's rho test (p < 0.05).

RESULTS

TEL showed less wear resistance than FPT (p = 0.001) for all cleaning methods tested. Concerning vertical material loss, NMF and GCT were in the same range of value (p = 0.419-0.997), except within FDPs cleaned in ISO (p = 0.021). FPT showed no impact of cleaning method on wear resistance (p = 0.219-0.692). TEL (p < 0.001) showed the highest and FPT (p < 0.001) the lowest fracture load. Regarding the cleaning methods, specimens treated with ISO showed lower fracture load than specimens cleaned with CEN (p = 0.044) or YEL (p = 0.036).

CONCLUSIONS

The material selection and the cleaning method can have an impact on two-body wear and fracture load results.

CLINICAL RELEVANCE

Printed restorations showed superior two-body wear resistance compared to milled FDPs but lower fracture load values. Regarding cleaning methods, ISO showed a negative effect on fracture load compared to the other methods tested.

Clinical wear of posterior metal-free polymer crowns. One-year results from a randomized clinical trial

OBJECTIVES

The purpose of this randomized clinical trial was to evaluate the clinical wear behavior of posterior, metal-free polymer crowns, with and without a glass-fiber framework, and to compare it with that of metal-ceramic crowns.

METHODS

Eighty single crowns manufactured from a newly designed polymer composite were set in posterior teeth. Half of these received a glass-fiber framework (group 1) whereas half were prepared without framework stabilization (group 2). All polymer crowns were adhesively luted with resin cement. As the control group, 40 conventional metal-ceramic crowns were inserted with hybrid cement. Wear was measured, by use of gypsum replicas, at baseline and after 12 months, by use of a 3D laser scanner. Statistical analysis was performed using mixed-effects regression model analyses.

RESULTS

The mean total wear of posterior single crowns was -8.1 microm (+/-9.7 microm) in group 1, -7.0 microm (+/-9.1 microm) in group 2, and -3.4 microm (+/-6.3 microm) in the control group. Statistical analysis revealed wear behavior was significantly different from the control group for group 1 (p=0.014) and group 2 (p<0.01). No significant difference was detected between groups 1 and 2. Age, gender, and opposing teeth had no significant effect on wear behavior.

CONCLUSIONS

Within a 12-month observation period mean total wear of posterior polymer crowns with and without a glass-fiber framework was significantly greater than for metal-ceramic crowns. The selection of restorative materials should be based on knowledge of clinical wear in order to preserve occlusal stability.

Effects of Occlusal and Brushing Forces on Wear of Composite Resins

Effects of occlusal and brushing forces on the wear of composite resins were investigated using three different wear tests: simulated occlusal wear test, toothbrush wear test, and combined wear test which carried out toothbrush wear test and occlusal wear test alternately. Test specimens were prepared from four commercial composite resins. Worn volume and maximum worn depth were measured under different occlusal forces (40 N and 80 N) and brushing forces (1.5 N and 3 N) in the three wear tests. Worn surfaces were observed using a SEM. In all the three wear tests, both higher occlusal and brushing forces resulted in significantly greater worn volume and higher maximum worn depth. The effects of occlusal force on worn volume and maximum worn depth varied with different composites, indicating that the four tested composites showed different wear behaviors under different occlusal forces and brushing forces. It was suggested that their different wear behaviors most probably stemmed from the differences in their filler systems.