Er:YAG laser-induced damage to a dental composite in simulated clinical scenarios for inadvertent irradiation: an in vitro study

Heike Rudolph,Carmen U. Schmid,Rolf Diebolder,Katharina Kuhn,Ralph G. Luthardt

doi:10.1007/s10103-021-03348-4

Abstract

Inadvertent Er:YAG laser irradiation occurs in dentistry and may harm restorative materials in teeth. The aim of this in vitro study was to quantify Er:YAG laser-induced damage to a nanohybrid composite in simulated clinical scenarios for inadvertent direct and indirect (reflection) laser irradiation. The simulation was performed by varying the output energy (OE;direct˃indirect) reaching the specimen and the operating distance (OD;direct˂indirect). Composite specimens were irradiated by an Er:YAG laser. The ablation threshold was determined and clinically relevant parameters were applied (n = 6 for each OE/OD combination) for direct (OE: 570 mJ/OD: 10 mm, OE: 190 mJ/OD: 10 mm) and indirect irradiation (OE: 466 mJ/OD: 15 mm, OE: 57 mJ/OD: 15 mm, OE: 155 mJ/OD: 15 mm, OE: 19 mJ/OD: 15 mm). The extent of damage in the form of craters was evaluated using a laser scanning microscope (LSM) and a conventional light microscope (LM). The ablation threshold was determined to be 2.6 J/cm2. The crater diameter showed the highest value (LM: 1075 ± 18 µm/LSM: 1082 ± 17 µm) for indirect irradiation (reflectant:dental mirror) (OE: 466 mJ/OD: 15 mm). The crater depth showed the highest and comparable value for direct (OE: 570 mJ/OD: 10 mm; LSM: 89 ± 2 µm) and indirect irradiation (OE: 466 mJ/OD: 15 mm; LSM: 90 ± 4 µm). For each OD, the crater diameter, depth, and volume increased with higher laser fluence. However, the OD—and thus the laser spot diameter—also had an enlarging effect. Thus, indirect irradiation (reflectant:dental mirror) with only 47% of the laser fluence of direct irradiation led to a larger diameter and a comparable depth. The three-dimensional extent of the crater was large enough to cause roughening, which may lead to plaque accumulation and encourage caries, gingivitis, and periodontitis under clinical conditions. Clinicians should be aware that reflected irradiation can still create such craters.

Highlights

Non-target tissues can be damaged by inadvertent laser irradiation during dental laser application, which is repeatedly addressed in publications on laser safety [1,2,3]
Further nanohybrid composite specimens made of the same material were irradiated using the same Er:YAG laser and handpiece with clinically relevant laser parameters varying in operating distance and output energy, which simulated clinical scenarios for inadvertent laser irradiation
This results from the fact that the larger laser spot diameter proved to have an enlarging effect on the ablation crater diameter and depth

Summary

Introduction

Non-target tissues can be damaged by inadvertent laser irradiation during dental laser application, which is repeatedly addressed in publications on laser safety [1,2,3]. In addition to non-target tissues outside the mouth (e.g., eye), intraoral structures can be affected. The extent of Er:YAG laser-induced ablation has been investigated for several intraoral structures. The range of ablation thresholds for the Er:YAG laser is 3.9–11 J/cm for enamel [13,14,15] and 2.7–4 J/cm for dentin [15, 16]. The values for the ablation thresholds (2.6–4.7 J/cm2) for four representatives of the composite material class

Methods

Results

Discussion

Conclusion