Reliability and Failure Modes of a Hybrid Ceramic Abutment Prototype

Purpose

A ceramic and metal abutment prototype was fatigue tested to determine the probability of survival at various loads.

Materials and Methods

Lithium disilicate CAD‐milled abutments (n = 24) were cemented to titanium sleeve inserts and then screw attached to titanium fixtures. The assembly was then embedded at a 30° angle in polymethylmethacrylate. Each (n = 24) was restored with a resin‐cemented machined lithium disilicate all‐ceramic central incisor crown. Single load (lingual‐incisal contact) to failure was determined for three specimens. Fatigue testing (n = 21) was conducted employing the step‐stress method with lingual mouth motion loading. Failures were recorded, and reliability calculations were performed using proprietary software. Probability Weibull curves were calculated with 90% confidence bounds. Fracture modes were classified with a stereomicroscope, and representative samples imaged with scanning electron microscopy.

Results

Fatigue results indicated that the limiting factor in the current design is the fatigue strength of the abutment screw, where screw fracture often leads to failure of the abutment metal sleeve and/or cracking in the implant fixture. Reliability for completion of a mission at 200 N load for 50K cycles was 0.38 (0.52% to 0.25 90% CI) and for 100K cycles was only 0.12 (0.26 to 0.05)—only 12% predicted to survive. These results are similar to those from previous studies on metal to metal abutment/fixture systems where screw failure is a limitation. No ceramic crown or ceramic abutment initiated fractures occurred, supporting the research hypothesis. The limiting factor in performance was the screw failure in the metal‐to‐metal connection between the prototyped abutment and the fixture, indicating that this configuration should function clinically with no abutment ceramic complications.

Conclusion

The combined ceramic with titanium sleeve abutment prototype performance was limited by the fatigue degradation of the abutment screw. In fatigue, no ceramic crown or ceramic abutment components failed, supporting the research hypothesis with a reliability similar to that of all‐metal abutment fixture systems. A lithium disilcate abutment with a Ti alloy sleeve in combination with an all‐ceramic crown should be expected to function clinically in a satisfactory manner.     

Multifunctional Guide for Implant Placement,Impressions, and an Occlusal Index for Fixed Complete Dentures

This article proposes an approach to simplify the steps and reduce fabrication time for fixed implant‐supported complete dentures. A multifunctional guide can function as a surgical template during implant placement and provides a framework for the definitive impression and occlusal registration. It therefore enables immediate or early loading of dental implants in full‐arch rehabilitations.     

Color in Zirconia‐Based Restorations and Related Factors: A Literature Review

Zirconia ceramic is a popular trend in esthetic and restorative dentistry. Computer‐aided design/computer‐aided manufacturing (CAD/CAM) systems have been well developed to fabricate zirconia frameworks and restorations with acceptable mechanical properties. Zirconia ceramics have excellent optical characteristics; however, achieving optimal esthetic outcomes with zirconia‐based restorations is still challenging due to multiple effective factors on the final color. These factors are different layers of a zirconia‐based restoration and its underlying structures including: dental substrate, cement, zirconia coping, veneering ceramic, and glaze. Moreover, the laboratory procedure of these restorations’ fabrication is another effective factor on the resultant color. Unpredictable esthetic results may be obtained without estimation of the role of each factor and its effect on the final color. This review discussed the color aspect of zirconia‐based restorations according to these factors and based on the literature. In the past decade, investigators have been concerned with the shade reproduction with zirconia‐based restorations; however, there are no sufficient clinical guidelines on how to reproduce the appearance of natural teeth with these restorations. Zirconia‐based restorations have presented a new chance for accomplishing optimum esthetics. Nonetheless further investigations are needed on these restorations to establish clinical guidelines on esthetics.     

Differences in Lip Support with and without Labial Flanges in a Maxillary Edentulous Population – Part 3: Unblinded and Discriminatory Subjective Analysis

Purpose

To study the subjective differences in direct lip support assessments and to determine if dentists and laypeople are able to discern and correctly identify direct changes in lip support between flange and flangeless dentures.

Materials and Methods

A random sample of 20 maxillary edentulous patients described in part 2 of the study was used for analysis. A total of 60 judges comprising 15 general dentists, 15 prosthodontists, and 30 laypeople, the majority of who were distinct from part 2 of the study, were recruited. All images used in this study were cropped at the infraorbital level and converted to black and white tone, to encourage the judges to focus on lip support. The judges were un‐blinded to the study objectives and told what to look for, and were asked to rate the lip support of each of the 80 images on a 100 mm visual analog scale (VAS). The judges then took a discriminatory sensory analysis test (triangle test) where they were required to correctly identify the image with a flangeless denture out of a set of 3 images. Both the VAS and triangle test ratings were conducted twice in a random order, and mean ratings were used for all analyses.

Results

The overall VAS ratings of lip support for images with flangeless dentures were slightly lower compared to images with labial flanges, and this difference was statistically significant (p < 0.0001). This was true for both profile and frontal images. However, the magnitude of these differences was too small (no greater than 5 mm on a 100‐mm scale) to be clinically significant or meaningful. The differences in VAS ratings were not significant between the judges. For the triangle test, judges overall correctly identified the flangeless denture image in 55% of frontal image sets and 60% of profile image sets. The difference in correct identification rate between frontal and profile images was statistically significant (p < 0.0001). For frontal and profile images, prosthodontists had the highest correct identification rate (61% and 69%), followed by general dentists (53% and 68%) and by laypeople (53% and 50%). The difference in correct identification rate was statistically significant between various judges (p = 0.012). For all judges, the likelihood of correctly identifying images with flangeless dentures was significantly greater than 1/3, which was the minimum chance for correct identification (p < 0.0001).

Conclusions

Removal of a labial flange in a maxillary denture resulted in slightly lower ratings of lip support compared to images with a labial flange, but the differences were clinically insignificant. When judges were forced to look for differences, flangeless dentures were detected more often in profile images. Prosthodontists detected the flangeless dentures more often than general dentists and laypeople.