A biomechanical model for a new incremental technique for tooth restoration.

The objective of this study is to introduce a modified incremental technique that leads to improved marginal adaptation and to develop a mathematical model that explains the results obtained. The technique proposed is a two-step incremental technique that reduces volume of a resin that is polymerized at each step and eliminates the central point in resin, so that the stresses are additionally reduced. In the first step, the resin is placed in the cylindrical cavity with a conical dental instrument embedded in the middle of restoration. After polymerization, the conical dental instrument is removed and the conical hole is filled with the second layer of composite and polymerized. This technique is a variant of a method where singular stress point is eliminated. We modified the previous technique by introducing a conical dental instrument into the centre of the cavity. The procedure proposed was compared with the bulk and horizontal layer incremental technique. This study confirmed that the incremental type placement technique used here has better marginal adaptation than bulk technique and horizontal two-layer incremental technique although it has larger C-factor in the first step than the two-layer incremental technique. Thus, the elimination of the central point of restoration leads to better marginal adaptation. Conical shape of the cavity that is filled in the second step makes this technique easy to apply in clinical conditions. A mathematical model describing stresses in the restoration shows stress reduction as a consequence of applying the procedure proposed.