Tooth Separation And Proximal Contact Strengths Of Posterior Composite Restorations C. E. Dörfer*, P. Macke, H. J. Staehle (Poliklinik Für Zahnerhaltungskunde, Universitätsklinikum Heidelberg) The objective of the investigation is to evaluate the correlationship between the amount of tooth separation (TS) and the proximal contact strength (PCS) of directly inserted class II-composite res-torations.   Materials and methods: Mesio-occlusal cavities (extension of the proximal box: 5.0±0.5 mm (oro-vestibular), 5.0±0.5mm (apico-coronal)) were prepared into artificial first lower molars. The teeth were mounted into a mandibular mannequin model, the socket of which was sectioned between the second premolar and the first molar and reassembled with an orthodontic screw, al-lowing reproducible tooth separation and repositioning. Prior to the placement of the composite, the teeth were separated either for 0, 40, 70, 100, 130 or 160µm. Per group 7 composite restorations were placed, using a biconcave translucent matrix (70µm thick). After finishing the restoration, the teeth were brought back into their original position. PCS were measured by removing a thin metal band from the proximal contact area of the repositioned and restored teeth. The frictional forces were taken as PCS. After testing the data for normal distribution, means and standard deviations were calculated per group. Differences between groups were tested for statistical significance with ANOVA followed by the post hoc Bonferroni-test. A regression analysis was performed to proof the relationship between TS and PCS. Significance level was set at p=0.05.   Results: The results are listed in table 1. The correlation between TS and PCS was described best by a compound regression model with an exponential function at the beginning. By extrapolating the data, the original PCS would have been achieved at a TS of approximately 120µm.   Conclusion: To achieve the original PCS after reconstruction the amount of tooth separation should be about 1.7times the thickness of the matrix band.   Tab. 1 Proximal contact strengths (PCS, [N]) at different amounts of tooth seperation (TS, [µm]). Mean values and standard deviations are listed.   TS [µm] 0 40 70 100 130 160 p (ANOVA) original PCS [N] 0.06 ±0,03 0.14 ±0.20 0.55 ±0.29 1.25 ±0.37 2.26 ±0.14 2.65 ±0.23 <0.0005 1.75 ±0.62