A predictive formula of the contraction stress in restorative and luting materials attending to free and adhered surfaces, volume and deformation

Objectives: To find a predictive formula of stress, considering the surfaces (free, adhered) involved, the volume and characteristics of material and the deformation of the measuring system. Materials and methods: 231 samples of five chemically cured restoratives (Silar (SIL, 23), Clearfil F2 (CLE, 39), P10 (P10, 33), Concise (CON, 30), Isopast (ISO, 28)) and four luting (3M Experimental 241 (EXM, 20), Variolink II (VAR, 13), Vitremer LC (VTM, 20) and Dyract Cem (DYR, 25)) materials were allowed to polymerize until they reached a maximum tension (Tmax, 25 min) between six pairs (empty set 5.81, 8.5, 11.26, 12.42, 17.02, 23.14 mm) of polished metallic discs (range of distances: 0.02–5.9 mm) mounted in a tension machine. The deformation of the measuring system was measured for the recorded forces. Results: A descriptive non-linear formula Tmax=KVol−3.267FS3.283AS0.642Def0.561 was found that individualizes the materialʹs characteristics (K) that considers volume (Vol), free (FS) and adhered (AS) surfaces and deformation (Def) of the system for each force. This formula renders good correlation (material K (r2 coefficient)): SIL 0.9998 (0.995), CLE 1.0062 (0.989), P10 1.0224 (0.990), CON 0.9908 (0.992), ISO 0.9648 (0.974), EXM 1.0083 (0.991), VAR 0.9777 (0.996), VTM 0.9925 (0.993), DYR 0.9971 (0.997) between actual Tmax and calculated Tension. There are statistically significant differences (p=0.002) between K values of both (restorative and luting) groups. Significance: Predictive parameters have influence in a different way to what is actually considered, if the system is allowed to have deformation, as occurs naturally and volume and materialʹs characteristics are considered.