Conversion degree evaluation of preheated luting materials in indirect restorations

Objectives: Physical and chemical properties of the luting agent are strictly related to conversion degree. Also heating composite materials is reported to improve conversion degree of luting materials. In our study it has been evaluated the curing percentage of a composite material used in normal temperature and after preheating. Methods: Interposing composite restorations of different thickness (2 mm, 3 mm, 4 mm) between curing lamp and cement, we evaluated how, using the same composite shade (A 3.5) and curing modes (40 s, intensity of 1200 mW/cm2, 40 s, intensity of 1200 mW/cm2 and 120 s. intensity of 400 mW/cm2), the temperature of the luting material influences cements conversion. Onlays of different and defined thickness were made in composite material shade A 3.5 and they were cemented into a glass plate with the composite luting material in the two different temperatures (normal and 50) The composite luting materialin two different temperatures (room temperature and 50 oC). Then materials were light cured, with a shielded-all-around tip to induce light reach the cement only through the onlay. Eighteen onlays were divided into 6 groups (n=3). Each sample was examined in three points by Micro-Raman spectrophotometer (DILOR RAMAN HR) to evaluate the polymer conversion degree. Results: The conversion degree of the materials resulted for Venus: modality 40x1200 sec.x mW, 67,70%, 37%, 30% (2mm, 3mm, 4mm respectively). Modality 60x800 sec.x mW, 68,30%,40,90%,34,20% (2mm, 3mm, 4mm respectively). Modality 120x400 sec.x mW, 58,10%,38%,37,10%, (2mm, 3mm, 4mm respectively). For venus preheated: modality 40x1200 sec.x mW, 68,50%,68%,63,40% (2mm, 3mm, 4mm respectively). Modality 60x800 sec.x mW, 66,90%,65,50%,58,80% (2mm, 3mm, 4mm respectively). Modality 120x400 sec.x mW, 67,90%,65,40%,64,80% (2mm, 3mm, 4mm respectively). Conclusions: Restoration thickness influences the conversion rate of the luting agent. Preheated materials increased significantly conversion rates.