Next, concerning the types of abutments used with cement-retained prostheses (Q4) (Figure 1), CAD/CAM abutments accounted for about one third of the total (titanium, 19.7%; zirconia, 12.1%), and custom UCLA-type abutments made from cast gold alloy accounted for about the same proportion. It is likely that this breakdown is because, in many cases, implant systems using fabricated crowns are not supported by CAD/CAM abutments. CAD/CAM system use is also subject to numerous limitations because of the licensing process imposed by the Ministry of Health, Labour and Welfare (MHLW) in Japan, which is strict when compared with its constituents in other countries. The questionnaire also indicated that titanium two-piece abutments (preparable type) are used in about the same proportion; 28% of the time. This reflects such factors as efforts to keep laboratory costs down and to shorten delivery time frames, in addition to the above reasons.

Concerning the types of prostheses used in the anterior region (i.e., veneering materials), the questionnaire indicated a trend toward selection of roughly the same materials for both single crowns and bridges (Q5) (Figure 2). As a rule, porcelain fused to metal (PFM) crowns accounted for 43.7% of the total, but selection of metal-free restorations using zirconia has been increasing in recent years, reaching approximately 27.1%. Incidentally, veneering porcelain was also used as the veneer material for zirconia copings. The questionnaire also indicated that while highly filled indirect composites such as Estenia (Kuraray, Osaka, Japan) were used 21.3% of the time, primarily for facing crowns, these materials were used infrequently for jacket crowns (2.4%). There is a low risk of facing damage and chipping for prostheses in the anterior region. Nonetheless, the questionnaire revealed the unexpected result that indirect composite facing crowns accounted for 21.3% of the total. This may be because there are many indirect composite resins (Estenia, Ceramage, etc.) available in Japan, and crowns and bridges in the anterior region (natural abutment teeth) are covered by certain types of insurance in the country (National Health Insurance and Social Insurance), with the result that Japanese dentists are familiar with these materials and use them frequently. Consequently, it can be surmised that using these materials in implant prostheses is more common than in Europe and the USA. However, no survey of prosthesis selection has yet been carried out, and future research on that subject is expected.