386 Volume 107 Issue 6

The Journal of Prosthetic Dentistry

387June 2012

Teng et alTeng et al

(Fig. 2B) and provided interlocking bonding for veneering porcelain. SEM analysis demonstrated that the frac-ture of modified zirconia specimens occurred within the veneering porce-lain, leaving a thin layer of veneering porcelain on the zirconia surface (Fig. 4A) where the porcelain infiltrated into the pores of the modified zirco-nia surface and interpenetrated with zirconia particles (Fig. 4B). This find-ing indicated that the weak link in the modified zirconia specimens was in the veneering ceramic rather than in either the zirconia coating itself or its bonding to the zirconia substrate. Meanwhile, on the surfaces of the pol-ished and airborne-particle-abraded zirconia specimens, only limited ve-neering porcelain residues were de-tected (Fig. 3B and C). Thus, it could be concluded that the bond strength of modified zirconia to the veneering porcelain was higher than the bulk strength of the porcelain, which might explain why this group had the high-est SBS value in this study. Because the high bond strength of zirconia to veneering porcelain can reduce the chances of interfacial fracture in all ceramic systems under function,29 it may be expected that the proposed coating technique, which improves the bonding of zirconia to its veneer-ing porcelain, could reduce the risk of failure at their interface.

The limitations of the present study include the following: the lay-ered ceramic specimens did not rep-resent the clinical shape of zirconia restorations; and the effects of aging conditions on the bond quality of zir-conia to veneering porcelain were not evaluated. Therefore, further studies are needed.

CONCLUSIONS

Within the limitations of this study, a porous surface for zirconia ceramic was produced by zirconia powder coating, which significantly improved the zirconia to porcelain bonding as compared with polished surfaces.

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Correspondence author: Dr Xing Liang Department of ProsthodonticsState Key Laboratory of Oral DiseasesWest China Hospital of Stomatology Sichuan University, 14 RenMinNanLu Block 3Chengdu, Sichuan 610041CHINAFax: +86-28-85582167Email: xingliangdent@vip.163.com

Copyright © 2011 by the Editorial Council for The Journal of Prosthetic Dentistry.

Noteworthy Abstracts of the Current Literature

Influence of tray rigidity and impression technique on accuracy of polyvinyl siloxane impressions

Hoyos A, Soderholm KJ.Int J Prosthodont 2011;24:49-54.

Purpose. The aim of this study was to determine how tray rigidity and impression technique affect the accuracy of polyvinyl siloxane impressions.

Materials and methods. Disposable plastic trays and metallic Rim-Lock trays were used in combination with a heavy/light body technique or with two different putty-wash techniques. For each technique-tray combination, 10 impres-sions were made of a master cast with two steel abutments representing the mandibular right first premolar and second molar, between which a steel rod was placed at the ridge level. Each steel abutment had five marks, while the steel rod in between the two abutments had only one mark, which served as a reference point. With a universal mea-suring microscope, the x-, y-, and z-coordinates were recorded for each mark on the master cast and impressions. The distances between the different marks and the reference point on the impressions were calculated and compared with those of the master cast.

Results. All techniques used with the plastic trays had distances that were significantly different from the master cast (P < .05), while for the metal trays, it was only the heavy/light body technique that resulted in distances that were significantly different from the master cast (P < .05).

Conclusion. Plastic trays produced less accurate impressions than metal trays. When metal trays were used, putty-based impressions were dimensionally better than heavy/light body impressions.

Reprinted with permission of Quintessence Publishing.