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Abstract

Background/purpose: The durability of clear aligner attachments is closely related to the polymerization and surface hardness of resin composites, which may be affected by extended light-curing distance during clinical procedures. This study aimed to evaluate the effects of different light-curing times at a 10 mm distance on the surface hardness and polymerization efficiency of conventional and bulk-fill resin composites.

Materials and methods: A total of 120 disk-shaped specimens (5 mm diameter, 2 mm thickness) were fabricated from six resin composites (two conventional and four bulk-fill). Specimens were light-cured for 20, 30, or 40 seconds using a low-intensity LED curing unit positioned 10 mm from the surface. Knoop microhardness numbers (KHNs) were measured on top and bottom surfaces after 24-hour storage. The Knoop hardness ratio (%KHR) was calculated to assess depth of cure. Statistical analysis was performed using one-way ANOVA and independent t-tests (α = 0.05).

Results: Increasing curing time significantly improved surface hardness and %KHR across all materials. Bulk-fill composites achieved the clinically acceptable 80% KHR threshold after 30 seconds, whereas conventional composites did not reach this level even at 40 seconds. No significant differences were observed between polystyrene (PS) and polyurethane (PU) template groups.

Conclusion: A curing time of 30 seconds is sufficient for bulk-fill composites, while conventional composites require at least 40 seconds to achieve adequate polymerization under a 10 mm curing distance.

Publication Date

2026

Received Date

Apr 5 2026

Accepted Date

May 13 2026

Final Revision Date

May 12 2026

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