Comparative evaluation of fracture resistance and failure modes in endodontically treated molars restored with zirconia endocrown and onlays.

INTRODUCTION: Developments in dental materials, CAD/CAM technologies and adhesive dentistry have improved the application of conservative restorations such as endocrowns and onlays. Among ceramics, zirconia has properties such as high strength, transformation toughening, chemical and structural durability, and biocompatibility, which enable zirconia to be used in the posterior area. AIM: This study is a comparative evaluation of fracture resistance and failure modes in endodontically treated molars restored with zirconia endocrown and onlays. MATERIALS AND METHODS: This study was performed on 20 human mandibular first molars with similar dimensions. After root canal treatment, the samples were divided into two groups: endocrowns and onlays (n=10). Restorations were made using a CAD-CAM milling machine with zirconia CAD blocks and, after cementation, subjected to 10,000 thermocycling and 500,000 fatigue cycle procedures, respectively. Each specimen was placed on a Universal Testing Machine and subjected to axial compressive force applied at a crosshead speed of 0.5 mm/min. The mean loads of failure of each group were statistically compared using the Student t-test. Chi-square tests were used to compare frequencies of failure modes among groups. RESULTS: Fracture resistance showed a statistically significant difference between endocrown (5374.6810±670.03445 N) and onlay (3312.5000±804.01428 N) (p<0.001). No statistically significant difference was detected in the distribution of failure types among the groups (p>0.05). CONCLUSIONS: The fracture resistance of endocrown is substantially higher than that of onlay, and failure type does not differ in both restorations. Zirconia is a reliable material to use in conservative restorations.

The effect of dynamic loading on bacterial microleakage of the dental implant fixture-abutment interface: An in vitro study.

Aim: Bacterial micro leakage at implant-abutment interface under functional loading is an important factor, may lead to crestal bone loss and affect the long term success of dental implants. Due to the limited studies about the implant systems with a connection of Slip joint design, this study aimed to evaluate the effect of dynamic loading on bacterial leakage at the implant-abutment interface with slip joint connection. Settings and Design: In vitro- comparative study. Materials and Methods: A total of 20 implants and abutments with slip joint connections (Tapered Screw-Vent, 3.7 mm ×10 mm, Zimmer Dental, USA) was examined and depends on using functional loading were divided into two groups; loaded and unloaded. Initially, 10 µl of Brain Heart Infusion (BHI) culture broth was pipetted to the internal lumen of each implant, then the abutments were tightened to the fixtures and crowns were cemented. In the unloaded group, samples were immersed in E-Coli suspension for 5 days. In the loaded group, samples were immersed in microbial suspension under 500000 cycles using a cyclic load device. Following disconnection of fixtures and abutments, microbial samples were taken from the internal lumen of implants and colonies were counted. Data were analyzed using. Statistical Analysis Used: Mann-Whitney statistical test, SPSS version 24. Results: The mean rate of micro leakage in unloaded and loaded groups was 4000 CFU/ml and 27000 ± 31640 CFU/ml respectively. Bacterial colonies grew in 10% of unloaded samples and 50% of loaded samples. This difference was statistically significant. (P < 0.05). Conclusions: Microbial micro leakage at the implant-abutment interface with slip joint design increased significantly after functional loading.

In Vitro Bacterial Leakage at the Implant-Abutment Connection of Two Dental Implant Systems with Internal Connection.

Objectives: Bacterial leakage at the implant-abutment interface is one of the main causes of peri-implant inflammation. One of the factors that influences bacterial leakage is the structural design of the interface. Considering the limited studies that have examined slip-joint connections, a comparative study of bacterial leakage was performed on two different systems namely Zimmer (Tapered Screw-Vent, Zimmer Dental) with slip-joint connection and Argon (Konus K3pro, Argon Implants) with conical connection. Materials and Methods: Twenty-two implants were selected in 2 groups (11 Zimmer with slip-joint connection, and 11 Argon with conical connection) with similar platforms. Escherichia coli (E. coli) suspension (2 µL) was pipetted into the internal lumen of implants. The abutments were screwed onto the implants with a closing torque of 30 Ncm. The assemblies were placed in culture broth for 6, 24, 48 and 72 h, and 7 and 14 days. The colonies were counted and analyzed by the Mann-Whitney test (a=0.05). Results: Microleakage was observed in 20% of the samples of conical connection group after 6 h to 2 days, and in 50% of the samples in slip-joint connection group after 3 to 7 days. There was a significant difference in bacterial leakage rate between the two implant groups (P<0.001) but no significant difference was seen in bacterial leakage over time (P>0.05). Conclusion: Type of connection had a significant effect on bacterial leakage, but the rate of bacterial leakage did not significantly change over time.

Five year clinical outcomes and survival of chairside CAD/CAM ceramic laminate veneers - a retrospective study.

PURPOSE: The aim of this clinical study was to compare the survival, modified California Dental Association (CDA) criteria, and periodontal parameters of laminate veneers made with Empress CAD and emax CAD over 60 months. METHODS: One hundred and ninety seven ceramic laminate veneers were placed in 71 patients in a private practice. The restorations were made using CEREC AC Bluecam with Empress CAD and emax CAD blocks. Modified CDA guidelines were used to evaluate clinical performance of the restorations. Gingival and plaque indices, probing pocket depth, and bleeding on probing were also recorded. Patient's satisfaction was assessed using visual analogue scale. Kaplan-Meier and Log rank test were used to analyze survival probability and success rate of the restorations. CDA rating of Empress CAD and emax CAD was compared with Log rank test (α=0.05). RESULTS: The survival rates of ceramic Empress CAD and emax CAD laminate veneers were 97.8 % and 100 % respectively (p=0.13). The success rate of these veneers was 92.4 % for Empress CAD and 100 % for emax CAD (p<0.05). Two Empress CAD laminate veneer failed because of fracture. Other restorations had very good or good CDA scores after 5 years. The periodontal parameters were not significantly different between first and fifth years except plaque index. The mean score of patients' satisfaction was 95.5±8.4. CONCLUSIONS: Chair-side computer-aided design/computer-aided manufacturing ceramic laminate veneers were clinically successful restorations with mean survival rate of 99.0 % and success rate of 96.4 % after 5 years.

Clinical performance of CEREC AC Bluecam conservative ceramic restorations after five years--A retrospective study.

OBJECTIVES: The aim of this study was to assess the clinical performance of CAD/CAM partial coverage posterior restorations made by CEREC AC Bluecam system after 5 years. METHODS: 159 ceramic partial coverage posterior restorations were placed in 109 patients in a private practice. The restorations were made using CEREC AC Bluecam with CEREC Blocs or Empress CAD blocks. The clinical performance of the restorations was evaluated with modified California Dental Association (CDA) guidelines, gingival and plaque indices, probing pocket depth, and bleeding on probing in a period of 5 years. Patients' satisfaction was assessed using visual analogue scale. The Kaplan-Meier method was used to analyze survival probability of the restorations (α=0.05). RESULTS: The restorations included 102CEREC Blocs and 57 Empress CAD. The survival rates of CEREC Blocs and Empress CAD blocks were 96.0% and 94.6%, respectively (P=0.67). A total of 7 (4.5%) failures were found. The failures were not significantly influenced by restoration size, type and position of teeth. The ceramic fracture was significantly more in nonvital teeth (P=0.04). The periodontal parameters were not significantly different between the restored and control teeth except plaque index. The mean score of patients' satisfaction was 94.4 ± 8.1. CONCLUSIONS: Chair-side CEREC AC ceramic partial coverage posterior restorations were clinically successful restorations with mean survival rate of 95.5% after 5 years. CLINICAL SIGNIFICANCE: Conservative chair-side CAD/CAM ceramic restorations with less reduction of tooth structure can be a successful restorative method with acceptable survival rate and patient's satisfaction.