Comparison of fit accuracy and torque maintenance of zirconia and titanium abutments for internal tri-channel and external-hex implant connections

PURPOSE: This in vitro study aimed to evaluate the effect of implant connection design (external vs. internal) on the fit discrepancy and torque loss of zirconia and titanium abutments. MATERIALS AND METHODS: Two regular platform dental implants, one with external connection (Brånemark, Nobel Biocare AB) and the other with internal connection (Noble Replace, Nobel Biocare AB), were selected. Seven titanium and seven customized zirconia abutments were used for each connection design. Measurements of geometry, marginal discrepancy, and rotational freedom were done using video measuring machine. To measure the torque loss, each abutment was torqued to 35 Ncm and then opened by means of a digital torque wrench. Data were analyzed with two-way ANOVA and t-test at α=0.05 of significance. RESULTS: There were significant differences in the geometrical measurements and rotational freedom between abutments of two connection groups (P<.001). Also, the results showed significant differences between titanium abutments of internal and external connection implants in terms of rotational freedom (P<.001). Not only customized internal abutments but also customized external abutments did not have the exact geometry of prefabricated abutments (P<.001). However, neither connection type (P=.15) nor abutment material (P=.38) affected torque loss. CONCLUSION: Abutments with internal connection showed less rotational freedom. However, better marginal fit was observed in externally connected abutments. Also, customized abutments with either connection could not duplicate the exact geometry of their corresponding prefabricated abutment. However, neither abutment connection nor material affected torque loss values.

[Accuracy of implant transfer with open-tray and closed-tray impression techniques and surface detail reproduction of the tooth during impression]

Accurate recording of implant location is required to achieve passive fit and have the implants without stress concentration. The aim of this in-vitro study was to evaluate the dimensional and angular accuracy of open-tray and closed-tray impression techniques using polyether impression material and also to assess the surface detail reproduction of the tooth while impression making. One reference metal model with 2 implants [Implantium] on the position of the maxillary second premolar and first molar and one molar tooth for evaluation of surface details was prepared. 27 polyether impressions of these models were made [9 using open-tray, 9 using closed-tray techniques and 9 were made just of the surface of the teeth without any implants]. Impressions were poured with ADA type IV stone. Coordinate Measuring Machine was used for measuring the dimensional accuracy and video measuring machine for surface detail reproduction. All of these measurements were compared with the measurements on the reference model. Data were analyzed by and compared by T-test and One-way ANOVA. There was a significant statistical difference between open-tray and closed-tray techniques [P<0.001]. There was no significant difference in the surface detail reproduction of open-tray and Closed-tray techniques and impression making with or without the implants [P>0.05]. The accuracy of open-tray impression technique was more than closed-tray technique. The surface detail reproduction of the tooth was not affected by impression technique

effect of porcelain veneer and liner usage on microtensile bond strength of cercon zirconia ceramics

Bond strength between veneers ceramic any zirconia framework is the weakest component in the layered structure. This bond was sensitive to the liner application and type of veneer ceramic. This study examined the core-veneer microtensile bond strength of a CAD/CAM [computer aided design/computer assisted manufactured] zirconia ceramic by comparing two ceramic veneers with and without liners. Disc-shaped [19.4x3.5mm] specimens were fabricated using CAD/CAM zirconia core materials [Cercon]. Half of the discs were left white and the others were colored with an A2 liner. The specimens were veneered with Ceram Kiss or Zirkonzahn ICE veneering ceramics [3.5 mm]. The discs were then cut into microbars [CC, ZC, CW, ZW] and the microtensile strength of the core-veneer bond was calculated. The specimens were analyzed by SEM and the data were compared using one-way ANOVA and Post hoc tests. The type of veneering ceramic [Ceram Kiss] and liner application [coloring] significantly affected the core-veneer microtensile bond strength [P<0.0001]. The Zirkonzahn layer [ZC, ZW] did not show significant differences [P=0.08]. Careful selection of veneering ceramics and liner applications can be recommended as they have significant roles in microtensile bond strength of core veneered restorations