Wear of ceramic and titanium ball attachments in subjects with an implant-retained overdenture: a controlled clinical trial.

STATEMENT OF PROBLEM: Loss of retention of implant-retained overdentures due to wear of the patrix or matrix of the attachment system is a common clinical problem. PURPOSE: The purpose of this controlled clinical trial was to compare the wear of ceramic and titanium ball attachments and their corresponding gold matrices after 1 year of clinical function in subjects with implant-retained mandibular overdentures. MATERIAL AND METHODS: Forty subjects who had been treated with a 2-implant-retained overdenture received either 2 ruby ball attachments (20 subjects) or 2 titanium ball attachments (20 subjects). The diameter of the ball attachments and the thickness of the matrix were measured optically before insertion and after 1 year of clinical function. Differences among groups were then compared with the Wilcoxon rank sum test (α=.05). To estimate any correlation between clinical parameters and wear, the Spearman rank test was used. RESULTS: There was no significant difference (P=.73) in the median wear of ball attachments for the titanium group (5.3 µm; median 1.3 µm) and for the ceramic group (1.3 µm; median 1.3 µm). In the ceramic group, a fracture rate of 30% was observed. The mean wear of the matrices in the titanium group was 3.1 µm (median 6.8 µm) and in the ceramic group 2.1 µm (median 3.4 µm), P=.01. No correlation was found between ball attachment wear and matrix insert wear (Spearman rank test). Wear of matrices was weakly correlated with an increase in divergence between implant axes in the sagittal plane (P=-.28 and P=.021). Ball attachment wear was associated with an increase in divergence between matrix axes in the sagittal plane (P=-.34 and P=.047). CONCLUSIONS: Matrices on ceramic ball attachments showed less wear than those placed on titanium ball attachments. However, the use of ruby ball attachments cannot be recommended because of a high fracture rate.

[First clinical experiences with ceramic ball attachments for overdentures]. / Erste klinische Erfahrungen mit Retentionselementen aus Keramik.

In this prospective clinical study on 40 patients with similar clinical conditions (edentulous jaw with 2 interforaminal implants) commercially available ceramic ball attachments (ruby) were compared to commercial titanium ball attachments. The primary aim of the study was to measure the wear of the ball attachments after being 1 year in function. However, in the course of the study already after 7 to 12 months multiple failures with ceramic ball attachments occurred. Twelve (28%) of 43 ceramic ball attachments had to be replaced, mostly because of fractures (8) of the ceramic ball. It seems that ceramic ball attachments of the investigated design are not able to withstand normal intraoral stresses. The short-term susceptibility to fractures didn't allow to examine the ceramic-inherent features such as compressive strength and wear resistance. Furthermore, a secure connection between a titan base and a ceramic ball seems to be challenging. Based on these results, in implant-retained removable prosthesis the use of metal-based retainers is still recommended, although during maintenance a higher wear has to be expected. This wear can be compensated by either activating or changing the matrix or the patrix.