Time-and-motion study on Class II copy-milled ceramic inlays

Objectives: To obtain an estimate of working times of Class II copy-milled ceramic inlays as an indication of their efficiency, and to analyse factors of influence. Methods: In a controlled clinical trial, 173 MO/DO or MOD ceramic inlays of the Celay system were constructed in 101 patients. Treatment was carried out by seven dentists. The inlays were replacements of existing amalgam restorations in both molar and premolar teeth. Net-times needed for the treatment and for the laboratory stage were registered. Variables of influence on the working time were assessed by using ln-working times in ANOVA. Differences of working times were expressed as the relative difference between the upper and lower value of each variable (Δ). Results: The mean clinical treatment time was 67(±22) min. The laboratory stage required 60(±17) min working time. ‘Cavity modification technique’ (composite basing/conventional, Δ=17%), ‘clinical operator’ (seven dentists, Δ=57%), and ‘size of the restoration’ (large/medium, Δ=16%) significantly influenced the clinical treatment time (p<0.001). Although the dentists were familiar with inlay construction, they showed a 25% decrease in working time towards the end of the study. Conclusions: Class II copy-milled ceramic inlays in this time-and-motion study required about 125 min of working time. Working time increased by applying composite basing and making large restorations. The dentist influenced working times, while efficiency increased over time. Dentists needed more laboratory time to produce an inlay than the dental technician.