Randmorphologie und Dichtheit von Kompositfüllungen bei Verwendung von experimentellen internen Lichtleitern in Klasse-II-Kavitäten

Aim of the study: The aim of this study was to examine the marginal behaviour of class II double surface fillings. The newly constructed light inserts were used for the initial curing of the fillings. The intention was to discover whether these exert a positive influence on the quality of the filling margin and whether this influence is a result of the volume reduction of the composite or a result of the direction of the light into the depths of the cavity. Fillings in incremental layer technique served as a positive control group while fillings done with a single increment (bulk method) were used as a negative control group. Material & Method: A total of n=60 human molars were prepared using rotating and ultrasonic instruments to get class-II cavities so that the cervical margin was in dentine. The teeth were divided to groups of 15 each. Two groups were filled by using an internal light conductor. In one of these groups the light conductor was used inactive wich means just as an classical insert. The group for positive control was filled by using the established increment technique, eight increments at least. The negative group was treated with just a single increment (bulk-filling). First replicas were manufactured for examination under electron scanning microscope. After subjection to alternating mechanical and thermal stress, replicas of the teeth were made once again. A quantitative analysis of the replica margins under the electron scanning microscope and with a 200-fold magnification was carried out using the method described by Roulet. In order to facilitate dye penetration the teeth were then placed at room temperature for 24 hours in 0,1% watery methylene blue solution.The teeth were divided into mesio-distal direction, so that the penetration depth on four measuring points each could be analysed. Results: All groups showed a considerable difference at the margin analysis for the margin integrity before and after thermocycling. This was significant for the variance analysis (p<0.05), which means that already the matter of being stressed reveals a difference before and after thermocycling. As expected were the results for criteria D adhesive failure in reverse.The control group with activated light insert achieved perfect margins of over 80% in the enamel, a significantly better result (p=0.05) than the other test groups and a comparable result in the dentine (not significantly different, p=0.05) to the positive control group (increment method). The results of the dye penetration also reveal the same tendency. Whereas the results of the positive control group and the activated light insert are comparable at the occlusal measuring point, it was possible to find a clearly better result for the activated light insert at the approximal measuring point. In all the tests the results for the activated light insert are significantly better than those for the non-activated light insert where the entry of the polymerization light is external. These results show that the type of light introduction has a significant effect (p=0.05). Conclusions:It was possible to demonstrate that better or equally satisfactory results in comparison to the positive control group were achieved by using the light insert. If the extra work involved in the layering technique in relation to the necessary polymerization time required for each insert is taken into consideration, then the light insert appears to be an interesting and less time- consuming alternative to the layering technique. Since this experimental study with dental cavities was performed in vitro, further tests will be necessary to prove the clinical viability and effectiveness of fillings done with light inserts.