Multifactorial analysis of variables influencing the fracture strength of repair joints for provisional restorative materials using the statistically based Taguchi method

Background/purposeIn this study, we investigated the relative contributions of design factors to the fracture strength of provisional materials after repair.Materials and methodsThe Taguchi method was used to investigate the optimal design with respect to four different design factors: subject material, repair material, repair design, and connector thickness. Each factor was assigned three levels. Using the Taguchi L9 orthogonal array, nine rectangular bar-shaped experimental specimens with different parameter combinations were fabricated (n= 5) and tested with a three-point bending test. The fracture load (in newtons) of each specimen group was recorded. The Taguchi method was employed to identify the significance of each design factor in controlling the fracture strength. The sensitivity of each design parameter was determined using an analysis of variance. Fractographic analysis was performed to identify the adhesive or cohesive failure mode for each specimen.ResultsThe mean effect of the design factors at each level was determined. The subject material, with a contribution percentage of as high as 33.48%, had the most dominant effect on the fracture strength of the repaired provisional restorations, followed by the repair material (31.88%), connector thickness (19.70%), and joint design (14.94%). The strongest subject material was bis-acryl Protemp 3 Garant. The polymethyl methacry late material, Tempron, was the preferred repair material. A 4-mm connector thickness was the best level. A 45º bevel joint was superior to the butt or fiber joint. The predicted fracture strength of the optimum parameter combination (Protemp 3 Garant/45º bevel joint/Tempron/4 mm connector thickness) was 173.34 N. From the fractographic analysis, different bonding abilities between the same and different resin materials were investigated. Fiber joint groups were nearly all in the cohesive mode without complete catastrophic fracture.ConclusionWithin the limitations of this study, these four design factors had different contributions to the fracture strength of repaired provisional restorations. Clinicians must be aware of the sequence of importance in determining better problem-solving methods.