Microtomographical Evaluation of Porosity Formation in Composite Restorations

Objective s:  To evaluate the porosity formation within a composite restoration when a composite (Filtek Supreme, 3M/ESPE) is placed incrementally or in bulk into a proximal-box preparation with or without light curing of a flowable-composite liner (Esthet-X Flow, Dentsply).  Methods:   Class 2 slot preparations were prepared on a proximal surface of mounted extracted human third molars.  The occlusal and proximal surfaces were flattened slightly to allow for a standardized 5-mm occlusal-gingival, 4-mm buccal-lingual and 2-mm axial slot preparation.  A bonding agent (Optibond FL, Kerr) was placed and light cured (Bluephase 16i, Ivoclar).  Ten teeth per each of four groups were restored: 1) 1-mm uncured flowable composite (snowplow technique) followed by two, 2-mm, 20-sec-cured incremental placements of composite; 2) 1-mm uncured flowable composite (snowplow technique) followed by 40-sec curing of bulk-placed composite; 3) 1-mm, 20-sec-cured flowable composite followed by two, 2-mm, 20-sec-cured incremental placements of composite; 4) 1-mm, 20-sec-cured flowable composite followed by 40-sec curing of bulk-placed composite.  After 24-hour storage in distilled water (37°C) the specimens were scanned with a microtomography unit (Skyscan) and analyzed to determine the percent porosity within the composite resins.  Scans were limited to a standardized central area spanning the length and width of the composite but short of the marginal areas.  Data were analyzed with a two-way ANOVA (alpha=0.05). Results: Significant differences were found between groups based on restorative composite placement (p<0.001) or flowable technique (p<0.05) with no significant interaction (p=0.56).  Conclusion s:  Bulk filling the restorative composite into the proximal box preparations resulted in significantly less porosity formation compared to incremental filling.  The snowplow technique (uncured flowable) resulted in significantly less porosity than the placement of a cured flowable increment.  The least amount of porosity was created within the proximal composite when the flowable composite was uncured and the restorative composite was placed in bulk.

	Mean Percent Porosity (st dev) Restorative Composite Placement Flowable Technique Cured Uncured Incremental 1.24 (0.75) 0.82 (0.64) Bulk 0.34 (0.19) 0.11 (0.08)