Fracture strength of secondary crown with different taper and thickness in zirconia double crown attachments.

The objective of this study was to clarify the influences of zirconia materials, one-half taper angle, and thickness of the secondary crown on the fracture strength of the secondary crown. For the primary and secondary crowns, Y-TZP and Ce-TZP/Al2O3 were used, respectively. Samples were prepared at one-half taper angles of 2° and 4°, and a secondary crown thickness of 0.5 and 1.0 mm (n=8). Regarding the fracture strength, the secondary crown was restored on the primary crown, all specimens were loaded until fracture using a universal testing machine. The load value added at the time of secondary crown fracture was regarded as fracture strength. Based on the analysis of variance, the fracture strength of Ce-TZP/Al2O3 was significantly higher than that of Y-TZP with regard to the material and that at 1.0-mm thickness was significantly higher than that at 0.5-mm thickness, but the taper angle had no influence.

Influence of the number of insertions and removals of telescopic zirconia/alumina crowns on retentive force and settling.

Telescopic crowns made from zirconia/alumina can be manufactured using computer-aided design/computer-aided manufacturing systems. For their successful clinical use, a suitable retentive force must be maintained over an extended period. However, it is unclear how retentive force and secondary crown settling change after repeated crown insertion and removal. The aim of the present study was to investigate the changes in retentive force and secondary crown settling of telescopic crowns made from zirconia/alumina. Primary crowns with tapers of 2° and 4° were used. Repeated insertion and removal tests were performed for 10,000 cycles at a cyclic load of 50 N. The loads applied when measuring retentive force and settling were 50 and 100 N. The number of insertions and removals had a significant effect on retentive force and settling at both loads (p<0.01). Taper also had a significant effect on retentive force and settling at both loads (p<0.01).

Effects of taper and space settings of telescopic Ce-TZP/A crowns on retentive force and settling.

The aim of this study was to investigate the effect of the taper and space setting of using Ce-TZP/A on retentive force and secondary crown settling. The taper were 2°, 4°, and 6°, and the space settings were 0 and 10 µm. The applied loads were 50 and 100 N. The taper had a significant effect on retentive force and settling at both loads (p<0.05). The space settings did not have a significant effect on retentive force or settling at either load (p<0.05). The taper of the telescopic crowns and the load affected the retentive force and the settling.

Analysis of gaze points for mouth images using an eye tracking system.

PURPOSE: We aimed to clarify whether people stare at non-esthetic restorations by analyzing the gaze point of laypersons looking at mouth images with intraoral non-esthetic restoration. METHODS: The gaze points of 47 laypersons who do not visit dentists were measured using an eye tracker. The stimuli were 18 photographs of mouths with or without a non-esthetic tooth restoration, each randomly shown for 5s. The analysis sites included a tooth with non-esthetic restoration and the same tooth on the opposite side of the mouth. We measured the proportion of participants who first fixated on each analysis site, and total fixation time for each site. RESULTS: In images without non-esthetic restorations, a similar proportion of participants first fixated on each analysis site. However, more participants first fixated on non-esthetic restorations when the images contained them. Total fixation time for each site did not differ significantly between the left and right sides in the images without non-esthetic restoration (P>0.05). Participants fixated on the non-esthetic restoration significantly more in the images containing them (P<0.01). CONCLUSIONS: Within the limitations of this study, the present findings suggest that in photographs of the mouth with non-esthetic restoration on either side, the non-esthetic restoration is first gazed before the opposite side. In addition, the non-esthetic restoration is gazed longer than the opposite side, and there was no major difference in the fixation time regarding the state of non-esthetic restoration.