Surface Quality of Direct Composite Resin Restorations Fabricated Using Different Resin Injection Guides

To evaluate the impact of different resin injection guides (RIGs) on the surface roughness (Ra), microhardness (MH), and conversion degree (CD) of direct composite resin restorations.

Disc-shaped specimens (diameter: 4.5 mm, thickness: 2 mm) were fabricated using five molding methods (n = 16 per group): freehand filling (FH), transparent polyester strip (PS), transparent polyvinyl siloxane guide (PVS), flexible resin guide with rigid shell (FR), and rigid resin guide (RG). Surface topography was analyzed using a multi-functional tribometer, and Ra values were calculated. MH was measured with a microhardness tester. CD was determined via Fourier transform infrared spectroscopy. Data were analyzed with ANOVA and post hoc tests.

Significant differences in Ra were found (P < .05), in the order of PS < FH < PVS < FR < RG. The PS, FR, and RG groups showed no significant differences in MH or CD (P > .05), but these values were significantly greater than those in the FH and PVS groups (P < .05). The PVS group had higher MH and CD than the FH group (P < .05).

The use of guides prevents formation of the oxygen inhibition layer, increasing MH and CD by up to 22% compared to the freehand technique. Although all guides increased Ra compared to the polyester strip, the PVS guide produced the smoothest surfaces among the RIGs, albeit with lower MH and CD than the 3D-printed guides (FR, RG).