Date Published: December 3, 2015
Publisher: Taylor & Francis
Author(s): Nuri Murat Ersoy, Hasan Murat Aydoğdu, Beyza Ünalan Değirmenci, Neslihan Çökük, Müjde Sevimay.
Objective: This study investigated the effect of different sintering temperatures and times on the flexural strength and grain size of zirconia.
Zirconia is used for dental restoratives, such as crowns, bridges, implant fixtures and implant abutments  due to its suitable properties for dental prostheses.[2–4] The excellent mechanical properties of zirconia are attributed to the stress-induced transformation toughening mechanism, similar to that encountered in quenched steel.[5–7] Zirconia fixed partial dentures are used to replace posterior teeth because of the high flexural strength and fracture toughness of zirconia, which is used as the framework material.[8–10] Fractures of zirconia frameworks have rarely been reported.[11–15] In contrast, chipping of the veneering ceramic is a frequent complication.[11–15] From a clinical point of view, the stability of the system consisting of both the zirconia framework and the veneering ceramic is important.
Sixty zirconium oxide and 60 highly translucent zirconium oxide bar specimens (In-Coris ZI and In-Coris TZI, Sirona Dental Systems GmbH, Bensheim, Germany) were cut using a low speed diamond saw (Isomet 1000, Buehler, IL). Then, the ZI and TZI specimens were randomly divided into three subgroups (with each group containing n = 20 samples) according to the sintering time and temperature. The employed parameters belong to fixed program numbers 1 – superspeed for groups C and F; 2 – speed for groups B and E; 5 – classic for groups A and D of the sintering furnace (inFire HTC Speed, Sirona, Bensheim Germany). The test groups are listed below.
The mean flexural strength values (MPa) and standard deviations for each group are presented in Table 2.
Table 2.Mean and standard deviations (SD) values of all tested groups.GroupMean (MPa)sdGroup A700.3a125.3Group B662.1a77.8Group C871.8b108.8Group D579.7a140.6Group E622.3a82.7Group F904.2b115.7Letters rendered in superscripts represent a significant difference.
The 1580 °C–10 min sintering program (C and F groups) led to the highest flexural strength values for both materials. For groups A, B, D and E, the sintering temperature and time combinations did not have a significant effect on the flexural strength of zirconia. Hence, the null hypothesis is rejected.
Based on the results obtained in this study, the following conclusions can be drawn.Zirconia samples tested showed the highest flexural strength when sintering was carried out at 1580 °C for 10 min.All experimented sintering parameters have provided full sinterization for green zirconia.