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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 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.

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Objectives : To investigate the short term effects of gamma-irradiation and conventional freezing on the hardness of human dentine. Methods : Twenty-one dentine disks were produced by transverse sectioning 21 sound extracted human permanent molar teeth. The 2.1 mm thick disks were wet polished using 4000 grit polishing paper. Three lines were drawn dividing each disk into six symmetrical areas. Seven disks were randomly assigned for freezing in water at −18°C for 12 days; seven were exposed to a single dose of 25.2 kGy gamma radiation in water; seven were kept in water at 20°C for 12 days (control). Before treatment, three Vicker’s indentations at a load of 30 kg and a dwelling time of 20 s were made in one half of each disk, at equal distances from its edge and centre. Using light microscopy and image analysis software, the indentation diagonals were measured 4 h after preparation. Vicker’s hardness values (VHN=kg/mm 2 ) were calculated for each indentation. Following the treatment, VHNs were calculated again, for three symmetrical indentations in the second half of each disk. A statistical analysis was performed using the Wilcoxon rank sum test. Results : The frozen group showed no changes following the treatment (VHN=58±6 before vs. 57±6 after). The irradiation and control groups showed some hardening (VHN=53±7 vs. 59±8; 57±3 vs. 63±6, respectively), however all values were within the normal variation. Conclusion : Both conventional freezing at −18°C for 12 days in water, and a single gamma-irradiation dose of 25.2 kGy in water, appeared to have no short term effects on the hardness of human coronal dentine.

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Objective : This preliminary study aimed to find out whether it is possible to produce a well fitting Class II inlay from an extracted tooth using a copy-milling technique. Methods : Two pairs of matching sound extracted permanent molar teeth were used. The molars were matched for mesio-distal size of the tooth crown and the convexity of the approximal surfaces. One tooth of each pair was assigned to be the ‘donor’ tooth, the other tooth being the ‘host’. MO inlay preparations were made in the host teeth. These were restored with the milled ‘Natural Inlays’ produced from the donor teeth using the CELAY system. The restored host teeth were sliced and examined using light-microscopy. Results : The specimens showed the desired location of enamel and dentine, and a clinically acceptable fit. Conclusion : This study has shown that by using the CELAY milling machine it is possible to ‘recycle’ extracted teeth for the production of dental restorations.

Objectives: Bases are used in restorative dentistry for several reasons (i.e. isolation, elimination of undercuts, etc). Glass ionomers are the standard materials used as bases for porcelain inlays, despite the disadvantages of their mechanical properties. An alternative basing material is composite: a generous layer of posterior composite is cured and shaped in the cavity before an impression is taken. The composite basing technique has several clinical advantages. The aim of this study was to investigate the effect of the thickness of a composite base on the bulk fracture resistance of industrial porcelain, and to describe the procedure. Methods: Fifteen porcelain (P) and 15 composite (C) bars, 1-, 2-, and 3-mm thick were joined to form 15 C/P bars, all 4-mm thick. Three groups were created: C 1 mm/P 3 mm (group 1), C 2 mm/P 2 mm (group 2), and C 3 mm/P 1 mm (group 3). The pairs were joined using Twinlook cement, subjected to a three-point bending test and loaded to fracture. The beam theory was used to support and explain the results. Results: The fracture load means were: group 1, 197.7 ± 18.7 N; group 2, 234.3 ± 63.3 N, group 3, 336.3 ± 31.3 N. Group 3 was significantly stronger than group 1 (P = 0.01) and group 2 (P = 0.03). Groups 1 and 2 were not statistically different. Conclusion: Composite basing is a tissue conserving method which may significantly increase the resistance to bulk fracture of adhesive porcelain inlays.