In the all-on-four concept, the positions of both posterior and anterior implants can affect stress distribution. The aim of this study was to examine the effect of the position of anterior implants on stress distribution in the implant, the bone around the implant, and prosthetic components in the resorbed maxilla using the all-on-four concept. All-on-four designs were prepared with three different anterior implant positions in a fully edentulous maxilla. Anterior implants were placed axially in the central incisor area in model 1, in the lateral incisors area in model 2, and in the canine area in model 3, forming three groups. The von Mises and principal stresses in the bone tissue and the von Mises stresses in the implant and prosthetic components were evaluated by three-dimensional finite element analysis. There were more stresses on the cortical bone than cancellous bone. The stresses on the bone tissue and implant components were generally concentrated around the posterior implant, whereas the stresses on the prosthetic components were generally concentrated in the anterior region. Changing the anterior implant positions from the central tooth to the canine tooth reduced the stress on the bone around the implant. The highest von Mises stresses occurred in the prosthetic superstructure in all models, whereas the lowest stresses occurred in the cancellous bone. Changing the position of the anterior implants from the central tooth to the canine area in the maxillary all-on-four concept created a favourable stress distribution.
Purpose: The aim of this study was to examine the effects of various sintering procedures on the color parameters, marginal, and internal fit of zirconia crowns. Materials and Methods: Overall, 60 zirconia crowns were produced using 3 distinct zirconia blocks (Wieland Zenostar, Zirkonzahn Ice Translucent, and Zirkonzahn Prettau). For the sintering procedure of the crowns, six groups were created as follows: Wieland-Standard, Wieland-Speed, Ice-Standard, Ice-Speed, Prettau-Slow, and Prettau-Standard programs. The crowns were assigned into groups ( n = 10 in each group). The color parameters, marginal fit, and internal fit of the crowns were evaluated. The normality of data distribution was evaluated with the Kolmogrov–Smirnov test. Two independent samples t-test and Mann–Whitney U test were used to compare the sintering groups. Results: Acceleration of sintering caused a significant change in the color parameters of the Wieland and Ice groups but not in the Prettau group. In the Wieland group, marginal ( p = .047) and internal ( p = .004) gap values of speed sintering were found to be significantly lower than those in standard sintering. In the Ice group, the marginal gap values of speed sintering were found to be significantly lower than those in standard sintering ( p = .019). In the Prettau group, the marginal gap values of standard sintering were found to be significantly higher ( p = .035) than those in slow sintering. Conclusions: It was concluded that the effects of sintering procedures on color parameters, and internal and marginal fit of zirconia crowns were clinically insignificant. Speed sintering can be recommended for zirconia restorations.
ObjectivesTo analyze the effect of COVID‐19 on early implant failures and identify potential risk factors for early implant failure, concerning patient‐ and implant‐related factors.Materials and MethodsThis retrospective study is based on 1228 patients who received 4841 implants between March 11, 2020, and April 01, 2022, at Erciyes University Faculty of Dentistry. COVID‐19, age and gender of patients, smoking, diabetes, irradiation, chemotherapy, osteoporosis, the implant system, location, and characteristics of implants were recorded. At the implant level, univariate and multivariate generalized estimating equation (GEE) logistic regression was used to examine the effect of explanatory variables on early implant failure.ResultsThe early implant failure rate was 3.1% at the implant level and 10.4% at the patient level. Smokers showed a significantly higher incidence of early implant failures compared to nonsmokers. (odds ratio (OR; 95% CI): 2.140 (1.438–3.184); p < 0.001). Short implants (≤8 mm) had a higher risk of early implant failure than long implants (≥12 mm) (OR (95% CI): 2.089 (1.290–3.382); p = 0.003).ConclusionsCOVID‐19 had no significant effect on early implant failure. Smoking and short implants were associated with a higher risk for early implant failures.
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