The evaluation of flexural strength of inlay-retained-dentures constructed with different brand monolithic zirconia materials

The purpose of this study is to evaluate the flexural strength of inlay-retained dentures produced from three different brands of monolithic zirconia material, based on two different types of preparation and with and without thermal cycling applications. A model was created that mimics the lack of right and left mandibular first molar in order to be used to make the cavity preparations. On one side of the model a tube shaped cavity and on the other side a box shaped cavity was prepared. Seventy-two epoxy resin model was prepared using addition-type silicon impression material by putty-wash technique. Twenty-four inlay-retained bridge restorations from each monolithic zirconia material [Zirconia Prettau (Zirkonzahn, Italy), Katana Zirconia (Noritake, Japan) and Copran Z-i monolith (White Peaks, Germany)] were fabricated (manufactured) for each preparation type. Each restoration was cemented to its own epoxy model with the dual-cure adhesive resin cement according to the manufacturers' instructions. Half of each group was applied to thermal cycles (10,000 cycles, 5-55oC). Samples were subjected to the flexural strength test by a universal tester with a crosshead speed of 0.5mm / min. The obtained data were uploaded to SPSS program and analyzed statistically. Fracture zones were examined by SEM and to examine the structural changes, DTA (Differential Thermal Analysis) was applied to a sample from each group. There were no statistically significant difference between the flexural strengths of all brands with both cavity designs and pre and post-thermal cycles (p≥0.05). However, SEM and DTA results showed that there were some changes in the structure of monolithic zirconia after aging 1 year. In all groups, there was no significant difference in the stability of restoration between the two cavity types (p≥0.05). There was no statistically significant difference in terms of the strength of each brand in the same cavity design (p≥0.05). The restorations of the brands used in the study for two kinds of cavity preparation were found to be suitable for use in a single posterior tooth loss.