Implant Volume Loss, Misfit, Screw Loosening, and Stress In Custom Titanium and Zirconia Abutments

Abstract

The aim of this study was to verify the effect of the implant volume loss, vertical misfit between abutment and prosthetic platform, prosthetic screw loosening torque, and screw stress distribution in titanium and zirconia abutments. Ten CAD/CAM system custom abutments of each material were milled and attached to the titanium implants. The implant volume loss was evaluated by microtomography, the vertical misfit with optical microscopy, and digital torque wrench measured the prosthetic screw loosening. All experimental analyses were performed before and after mechanical cycle (1,000,000 cycles, 100 N/2 Hz). Virtual models of the structures were created for finite element analysis, and the stress on the screw obtained with von Mises procedure. Data were analyzed using an independent t-test, two-way ANOVA for repeated measures, and Tukey’s HSD test (a=0.05). There was no significant difference in the implant volume loss for the two abutment materials (p=0.662). Titanium abutments provided higher loosening torque values after mechanical cycling (p<0.001). Lesser marginal misfit was obtained with titanium abutments before and after mechanical cycling (p<0.001). The stress distribution on the screw was similar between abutment materials. In conclusion, CAD/CAM custom titanium abutment reduced the marginal misfit and increased the torque maintenance of prosthetic screws when compared to CAD/CAM custom zirconia abutment.

Evaluation of Internal Fit of CAD/CAM Implant Abutments with Hybrid and Internal Hex Connections Using Different Materials

“…Those custom-made CAD/CAM abutments can be either machined from the top down including the implant connection or milled from blocks with pre-machined connections. However, only the former method can be used for the manufacturing of custom-made zirconia abutments 29,37 .…”

“…Customization of abutments can best achieve optimum relation with the gingival tissues and the adjacent teeth where a subgingival margin between 0.5-1 mm is placed 29 . Proper customization can be achieved by CAD/CAM abutments which combine predictable fit and durability that can be gained from stock abutments together with the ability to more of the disadvantages of being too expensive, aggressive, need special equipment or being limited to measuring the marginal gap only [39][40][41][42][43][44][45] .…”

“…This could explain also why the Co-Cr had the highest mean values as Co-Cr is the stiffest material used in this study which may have affected the wear and bending of the drilling instruments 48 . It was reported that stiffness of the abutment material was related to the passivity and preload maintenance 29 . 45 and Sui et al (2014) 50 found a marginal gap of (14.18 μm) and (19.38 μm) at the IAI for milled internal hex zirconia abutments respectively which is comparable to the results obtained by this study (16.3 µm).…”

“…Titanium has been used for custom made abutments. Numerous researchers found it comparable to stock abutments in terms of vertical gap of the IAI [28][29][30] while from the plethora of the esthetic ceramic materials used in the dental field, zirconia has been the mostly used abutment/ crown material in implant prosthodontics due to its biocompatibility, superior strength and good esthetics [31][32][33] .…”

Marginal misfit of heat-pressed milled wax-pattern and CAD/CAM crowns and its effect on stress distribution in implant-supported rehabilitations

“…To avoid bias, the crowns were evaluated exactly in the way they were manufactured, without any kind of adjustment. The measurement was standardized on the center of the buccal, lingual, mesial, and distal faces with a zoom of 550x 24,25 . Four measures were made in each face with a distance of approximately 50 µm between them, and a mean of misfit was obtained for each crown (Figure 1).…”