| The restorative technique of composite resin inlay/onlay had been developing since the later 1980s. It should overcome the shortcomings of silver amalgam restoration (e.g. unesthetic) and direct composite filling (e.g. polymerization contraction) and come in for a great deal of attention and become popular in most of European countries. Lots of studies reported many clinical observations and related researches; however, the application of composite resin inlay/onlay for children was rarely reported. Meanwhile the steps of light curing, secondary management and bonding, etc. in composite resin inlay/onlay technique have important influence to the clinical restorative performance.This study consists of three parts:Part I Clinical assessments of composite resin inlay/onlay restoration for defected molars in children.According to the including and excluding criteria, 100 teeth of 95 children, aged 4-12 year-old, were selected and randomly assigned to two groups, adopting to the random number table, for direct composite filling and indirect composite inlay/onlay restoration respectively. The marginal integrity, surface texture, contour/abrasion of restoration, integrity of restoration, integrity of tooth, marginal discoloration, gingival index and recurrent caries were directly evaluated by two examiners immediately at baseline and 12 months later respectively, using the modified USPHS criteria. The statistical analysis showed that the surface texture and contour/abrasion of restoration of composite inlay restoration prominently superior to direct composite filling group. The one year follow-up showed that there was no significant statistically difference in the acceptability (A+B) of restoration between the two groups. But indirect composite inlay/onlay restoration exhibited a significant statistically better (P<0.01) at the A degree rate of surface texture and contour/abrasion of restoration than direct composite filling. At the A degree rate of the integrity and marginal discoloration, the difference of the two groups was statistically significant (0.05>P>0.01), except that one direct composite filling failed because of fracture. As to the assessment of other aspects, there was no significant statistically difference.Part II Curing Efficiency of LED LCUs for Dental Composite Resin The study compared the curing efficacy of two kinds of LCUs curing composite resin. Ultralume5 (LED light source, Ultradent Products Inc.) and Optilux 501 (halogen light source, Kerr Company) LCUs and two dental composites (Ultradent and Chrisma, Shade A2) were selected in this study. Samples of 1mm, 1.5mm, 2.0mm and 2.5mm in depth were made with the two kinds of composites, and cured with the two kinds of LCUs for 20s, 40s and 60s respectively, of which the KHN values on the top and bottom were measured with Tukon300 micro-hardness tester. Silicon gel pipes of 8mm in length and 4mm in diameter were filled with the two kinds of composites. And then the depth of cure was measured after curing with two kinds of LCUs respectively for 40s. Results: The multifactor ANOVA showed that the factors ofcuring time, composite and curing mode had a statistically significant influence on the KHN values on the bottom surface of two dental composites. The factor time had the greatest influence (F-ratio=784.4), followed by the factors composite (F-ratio=265.3) and curing mode (F-ratio=22.1), as indicated by the F-ratios. Generally, there was no statistically significant difference in KHN values on the top and bottom of composites cured with the two kinds of LCUs. Ultralume5 LCUs achieved a greater depth of cure than Optilux501 for composite Ultradent, while there was no difference for composite Chrisma of the two LCUs. The present study shows that LED LCUs have a potential to replace halogen LCUs if the composites are selected carefully.Part III The experimental study of adaptation of different adhesive agents with teeth tissue.The study compared the adaptation of duel-cure cement Duo Cement and Panavia F, Adaper Prompt and Primer & Bond NT with tooth tissue. 40 newly extracted cleaned constant teeth were prepared for 3mm in depth and 3mm in diameter cylinder cavities, and then divided into four groups. Group 1 and Group 2 were inlay restoration group bonded with Duo Cement and Panavia F cement; Group 3 and Group 4 were direct resin composite filling group bonded with Adaper Prompt and Primer & Bond NT. The specimens were stored in 37 °C steamed water for 24h and then were split, ultrasonically cleaned, polished, dried and gold-sprayed. The adaptation between restoration materials and dentin or enamel was observed with a scanning electron microscope. The observation showed that there was no gap between composite materials and teeth tissue in four samples of Panavia F group and three samples of Duo Cement group and Adaper group, and there was no gap between composite and enamel in these three groups. There were gaps between enamel and composite in one sample of NT group, while there were gaps between dentin and composite in all groups.Conclusion: Generally, there was no statistically significant difference in the one-year clinical assessments between composite resin inlay/onlay restoration and direct composite filling for children's posterior tooth. There was a trend that the composite resin inlay/onlay restoration was superior to direct filling in contour/abrasion of restoration, surface texture and integrity of restoration. There was no statistically significant difference in curing speed, curing depth and curing efficiency between the LED and halogen LCUs. However, the depth of cure and Knoop hardness test showed that a sufficient curing time and a careful selection of the composite are important factors for the performance of a light cured composite. We should pay much attention to when composite containing co-initiators cured with LED LCUs. But as for other features, LED LCUs have a potential to replace conventional halogen LCUs which are commonly used now. There was no statistically significant difference of adaptation of duel-cure resin cement and Adaper self-etching cement with teeth tissue, the bonding effect of which was superior to Primer & Bond NT.
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