Influence of irradiation distance on the mechanical performances of resin composites polymerized with high-irradiance light curing units

Soram Oh; Hyun Ju Kim; Hyun-Jung Kim; Sibel A Antonson; Sun-Young Kim

doi:10.1186/s40824-022-00267-5

Influence of irradiation distance on the mechanical performances of resin composites polymerized with high-irradiance light curing units

Biomater Res. 2022 May 20;26(1):18. doi: 10.1186/s40824-022-00267-5.

Authors

Soram Oh^#¹, Hyun Ju Kim^#², Hyun-Jung Kim³, Sibel A Antonson⁴, Sun-Young Kim⁵

Affiliations

¹ Department of Conservative Dentistry, School of Dentistry, Kyung Hee University, 1 Hoe-gi-dong, Dongdaemoon-gu, Seoul, 02447, Korea.
² Department of Periodontics, Seoul National University Dental Hospital, 101 Daehakno, Jongno-gu, Seoul, 03080, Korea.
³ Department of Conservative Dentistry, Kyung Hee University Dental Hospital, 1 Hoe-gi-dong, Dongdaemoon-gu, Seoul, 02447, Korea.
⁴ Department of Oral Science and Translational Research, College of Dental Medicine, Nova Southeastern University, 3200 S. University Dr., Fort Lauderdale, FL, 33328, USA.
⁵ Department of Conservative Dentistry and Dental Research Institute, School of Dentistry, Seoul National University, 101 Daehakno, Jongno-gu, Seoul, 03080, Korea. denkim@snu.ac.kr.

^# Contributed equally.

Abstract

Background: The aim of this study was to evaluate the influence of increased irradiation distance on the flexural strength (FS), dentin micro-shear bond strength (μSBS), and the degree of conversion (DC) of bulk-fill flowable, conventional flowable, and packable resin composites.

Methods: The resin composites tested were Surefil® SDR™ (SDR), Filtek Z350 XT Flowable Restorative A2 shade (Z3F), and Filtek Z350 XT Universal Restorative A2 shade (Z3P). Specimens were cured at four irradiation distances (0, 2, 4, and 8 mm) with an Elipar DeepCure-S LED curing light for 20 s. FS tests were performed (n = 15) using bar-shaped specimens (8 mm × 2 mm × 2 mm) of the resin composites. μSBS tests were performed on the occlusal surfaces of extracted third molars from humans that were ground to expose dentin (n = 15). DC was measured by using Raman spectroscopy on the top and bottom surfaces of disk specimens (2-mm thick) (n = 3). To further investigate whether extended irradiation times could compensate for reduced irradiance, additional Z3P specimens were prepared, which were light-cured at 8-mm distances for 40 and 60 s and subjected to FS tests, μSBS tests, and Raman spectroscopy. Both two-way and one-way ANOVA were used for statistical analyses.

Results: Both FS and DC of Z3P specimens cured at an 8-mm distance were significantly lower than those cured at shorter distances (p < 0.05), whereas the FS and DC of the Z3F and SDR specimens were not significantly influenced by increasing distances. The μSBSs of the three types of resin composites reduced with increasing irradiation distances. The FS, μSBS, and DC of the Z3P specimen light-cured at 8 mm for 40 s were comparable to those of the Z3P specimen cured at 0 mm for 20 s.

Conclusions: Increasing the irradiation distance to 8 mm can have a deleterious influence on mechanical performances, including the FS, DC, and dentin μSBS, of the resin composites polymerized with high-irradiance light curing units.

Keywords: Degree of conversion; Flexural strength; Irradiation distance; Light curing unit; Micro-shear bond strength.