Is Pre-warming Capable of Improving Composites Physico-mechanical Properties?

Objectives: The objective of this study was to assess the effects of composite pre-heating on their physical-mechanical properties.

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Methods: A 6x4 factorial design was used having as study factors: 1-Composites in six levels (Admira/ADM, Vitra/VIT, Filtek Supreme/FS, Filtek Supreme Flowable/FSF, Filtek One/FO, Filtek Bulk Fill Flowable/FBF); and 2-temperatures in four levels (Room-temperature/22^oC; 37^oC; 54^oC and 68^oC) using a composite heater. Response variables consisted of: 1-Flexural Resistance/FR (3-point bending test), 2-Degree of Conversion/DC (FTIR), and 3-Color Stability/ΔE (spectrophotometer - immediately after light curing/LC, after seven days; and after one- and three-days artificial aging in water at 50^oC).
All composites were LC for 20s using a 1000mW/cm² LED unit. For FR, eight samples were obtained for each group (2x2x8mm). For ΔE, eight composite disks (6x1mm) were obtained for each group and, for DC, three specimens for each group were packed in contact with the FTIR crystal.
Results: The increase in temperature resulted in similar or enhanced FR results for all composites but VIT and ADM. High-viscosity composites (VIT and FS) showed higher FR than low-viscosity composites (FSF). For bulk-fill composites, FBF and FO showed similar results, but lower than high-viscosity (regular/non-bulk fill) composites. DC were similar (FBF, FS, and FSF) or increased (ADM, FO, VIT) as the temperature increased.
Considering ΔE, all composites showed color stability up to 3 days aging except ADM and FSF. The increase in temperature did not improve ΔE, except for ADM. Comparing the groups, in crescent order of ΔE: FS < VIT < FO < FSF < ADM < FBF. Only VIT and FS showed ΔE≤3.3 (clinical threshold).
Conclusions: The effects of pre-heating are material dependent. Although it seems like some polymers (Ormocer/ADM) are degraded with increased temperature, pre-heated composites can be used for cementation of indirect all ceramic restorations.