Reduktion der Spannungsentwicklung von Kompositfüllungen durch neue Methoden der Steuerung der Lichtpolymerisation

Objectives: The polymerization shrinkage stress of various filling methods was examined by means of a photo-elastic investigation. Using a flowable bulk-fill composite (x-tra base/VOCO), the bulk- and incremental technique were compared with two new methods. The aim of this study was to develope new filling methods to reduce shrinkage stress without any additional time requirement. Methods: The two new methods are based on the use of a special curing light with two different wavelenghts, which allows the activation of two photoinitiators of different concentration with a time delay and thus leads first to a pre-gelation and then to final curing. In the first new method, bulk-fillings with this mixture were pre-cured and then final cured. In the second new method, a stress breaking layer was applied and pre-cured. Before the stress breaking layer is final cured, the rest of the cavity is filled and final cured. Class-I-Cavities (5x5x5 mm) in Araldit-B epoxy resin plates (35x35x5mm) were pretreated with Al2O3-particles (∅110 µm) and Adhese Universal (Ivoclar Vivadent) to ensure bonding of resin composites. All cavities were filled up to 4 mm. Polymerization stress data (MPa) 1000 s post exposure were calculated based on the diameter of the isochromatic rings using ImageJ and extrapolated in Excel. The statistical analysis of the obtained data was carried out with the Mann-Whitney U-test (p<0.05). Results: After 1000s the following mean stress values and standard deviations were obtained: bulk: 12.84 ± 0.61 MPa; incremental: 7.49 ± 0.60 MPa; first new method: 7.84 ± 0.41 MPa; second new method: 5.24 ± 0.64 MPa. Conclusions: Both new methods and the incremental-technique showed significantly less polymerization shrinkage stress than the bulk-technique. There was no significant difference between the incremental technique and the first new method, but the incremental technique needed a higher expenditure of time. The second new method significantly showed the lowest stress values. The new methods are promising but still in the beginning and therefore require technical refinement. They should be further improved, investigated and applied in practice.