Effects of different wavelengths of low-level laser therapy on orthodontically induced inflammatory root resorption in rats investigated with micro–computerized tomography

Introduction

The objective of this research was to investigate the effects of different wavelengths low-level laser therapies on orthodontically induced inflammatory root resorption (OIIRR) during orthodontic tooth movement in rats by micro–computerized tomography.

Methods

Forty Wistar albino rats were divided into 5 groups: control group (A), 405-nm laser group (B), 532-nm laser group (C), 650-nm laser group (D), and 940-nm laser group (E). The left side of group A was used as a positive control (A-PC), and the right side of group A was used as a negative control (A-NC) group. In all groups, the maxillary left first molars were moved mesially by 50 g of force for 14 days. The lasers were performed for 9 minutes on the maxillary left first molar tooth. At the end of the experimental period, OIIRR measurements were performed at the mesial and the distal sides along the mesial root of the maxillary first molars.

Results

The root resorption volume was significantly lower in group A-NC than in groups A-PC, B, and D. The percentage of root resorption was significantly lower in group A-NC than in all other groups. The root resorption volume and the percentage of root resorption in groups C, D, and E were significantly lower than group A-PC. The depth and the width of the lacuna and even the number of mesial lacunae were similar between groups. The distal and the total lacunae were significantly lower in group A-NC than in all other groups except group C.

Conclusions

The 532-nm, 650-nm, and 940-nm lasers significantly reduced the volume of OIIRR. In addition, the 532-nm laser reduced the number of lacunae both distally and totally than all the other groups.

Highlights

  • Laser therapies with 532 nm, 650 nm, and 940 nm wavelengths can reduce root resorption.

  • Low-level laser treatments with a wavelength between 660 nm and 905 nm can promote cementum repair.

  • 532-nm laser reduced the number of lacunae than all the other groups.

Obtaining orthodontic tooth movement depends on the rate of bone remodeling. When orthodontic forces are applied, it stimulates remodeling in the cement on the root surface and the adjacent bone. Brudvik and Rygh have shown that the cementum, which is adjacent to the hyalinized (necrotic) regions of the periodontal ligament, is marked by this contact and the destructive cells attack this marked cementum after the periodontal ligament site has been repaired. During the orthodontic tooth movement, the destruction of the cementum and dentin is called orthodontically induced inflammatory root resorption (OIIRR). OIIRR is a common and difficult to avoid side effect of orthodontic treatment. There are many methods used to reduce OIIRR. Most of the methods recommended to prevent or reduce root resorption during orthodontic tooth movement may cause pain and discomfort because of the injection procedure in clinical practice. , Low-level laser treatments (LLLT) have been shown to have biological stimulating effects on bone tissue and wound healing, reduce pain caused by orthodontic force, and accelerate orthodontic tooth movement. In the literature, many studies have reported that LLLT has an inhibitory effect on OIIRR. In these studies, 618 nm, 635 nm, 780 nm, 808 nm, 810 nm, 820 nm, 830 nm, and 940 nm wavelengths of light-emitting diode or laser were used.

The visible spectral range has bands equivalent to 3 primary colors; blue (380-440 nm), green (440-600 nm), and red (600-750 nm); in addition, near-infrared range (750-1100 nm) and short wave infrared range (1550-2400 nm). The laser light penetration and absorption by tissue vary according to the wavelength and the tissue. Because of this, the effects of laser on tissues may change too. In the literature, there is no study investigating which laser of wavelengths used before is more effective on OIIRR. So, in our study, we selected a wavelength from each group (405 nm, 532 nm, 650 nm, and 940 nm) and tried to compare its effects on OIIRR using the same parameters except for wavelengths.

Micro–computerized tomography (microCT) is an x-ray imaging technology used to display mineralized tissues in 3-dimensional high resolution. In the literature, there are studies investigating root resorption with histologic studies, traditional radiographic methods, and cone-beam computed tomography. However, microCT is a successful method that can be used to observe root resorption lacunae in 3-dimensions, both micro and macro.

This study aimed to investigate the effects of different wavelengths of low-level laser therapies (405 nm, 532 nm, 650 nm, and 940 nm) on OIIRR during orthodontic tooth movement in rats by microCT.

Material and methods

The animal experimental protocol used in this study was approved by Erciyes University, Regional Animal Research Ethics Committee. The experimental stages of the study were carried out at Erciyes University Experimental Research Application and Research Center.

Forty 8-week-old Wistar albino rats weighing 140-160 g were divided into 5 groups as the control group (A, n = 8), 405-nm laser group (B, n = 8), 532-nm laser group (C, n = 8), 650-nm laser group (D, n = 8), and 940-nm laser group (E, n = 8) randomly. The left side of the rats in group A was used as a positive control (A-PC, n = 8) and the right side as the negative control group (A-NC, n = 8).

Nickel-titanium closed-coil springs were placed in a position to apply 50 g of force between the maxillary left first molar teeth and the maxillary incisors. No activation was made during the 14-day trial period.

Except for the control group, the other groups were treated with LLLT (mesial, buccal, and palatal sides) on the maxillary left first molar tooth. Laser modules with output energy of 100 mW were applied in contact with approximately 1 cm 2 area. Lasers performed for 3 minutes on each surface, for a total of 9 minutes (total dose, 54 J/cm 2 ), and process was repeated 7 times in 48-hour intervals starting from the first day. ,

Apparatus placement and laser applications were performed under general anesthesia (ketamine HCl [1.0 mg/kg; Alfamine, Egevet, Turkey] and xylazine HCl [0.5 mg/kg; Rompun, Bayer, Leverkusen, Germany]). At the end of the experimental period, the rats were killed with high-dose anesthetic agents.

The half maxillary segments, including the molar teeth of the subjects, were dissected. These samples were scanned using with the microCT device of Erciyes University Faculty of Dentistry Research Laboratory (SkyScan 1272; Bruker, Kontich, Belgium) with an x-ray, source potential of 80 kV, amperage of 125 μA, power of 10 W through 360° of a rotation and a rotation step of 0.4° at 9× magnification and at a resolution 9 μm. In the conversion of the data obtained from the samples scanned by microCT, NRecon (version 1.6.3, SkyScan; Bruker) and CTAn software (version 1.18, SkyScan; Bruker) were used. Images were reconstructed with NRecon software using 35 section hardening correction, resulting in an average of 160 coronal sections for each sample. Serial sagittal and coronal sections were obtained such that the maxilla included all of the molar teeth crown and roots with CTAn software. To ensure that the experiment was blinded, the staff who made measurements were not informed. To assess measurement reproducibility, we repeated the measurements for 20 randomly selected samples (half of the total number of samples) 15 days after all measurements were completed. The standard deviation was within 1%.

OIIRR measurements were performed on the coronal plane sections at the mesial and distal sides along the mesial root of the maxillary first molar. The outer and inner borders of the mesial root were determined from the cementoenamel junction to the root apex. The resorption sites were marked to maintain the root boundaries ( Fig 1 , A ). Resorption lacunae on the root surface were counted. The width and depth measurements of the largest lacuna were performed ( Figs 1 , B and C ). Because of the density difference, both the root resorption volume and the total root volume were obtained separately. We called the ratio of the root resorption volume to the total root volume as a percentage of root resorption, and we used this parameter in our comparison. The root resorption volume (RRV) and the percentage of root resorption (PRR) were calculated with CTAn software ( Fig 1 , D ).

Fig 1
Demonstration of microCT measurements: A, schematic view of the completion of the outer boundary of the root in the resorption area; B, schematic view of lacuna depth measurement; C, schematic view of lacuna width measurement; D, schematic view of root borders in coronal section; E, demonstration of tooth movement and root resorption in the transaxial section; F, Transaxial image of the negative control group.

Statistical analysis

Stata software (version 15; StataCorp, College Station, Tex) was used for the statistical analysis of all data. The normality of data distribution was determined with the Kolmogorov-Smirnov test. The resorption volume data were not distributed normally; therefore, the Shapiro-Wilk test was used. The intergroup comparisons were performed for normally distributed parameters using the 1-way analysis of variance test, and for nonnormally distributed parameters, the Kruskal-Wallis test was used. The statistical test was determined as significant at P <0.05.

Results

Experimental orthodontic tooth movement was achieved successfully in all groups ( Fig 1 , E and F ). RRV was significantly lower in group A-NC than in group A-PC ( P <0.001), group B ( P = 0.005), and group D ( P = 0.014). In addition, RRV in group A-NC was less than in group C and group E, but there was no significant difference. RRVs in group C ( P = 0.013), group D ( P = 0.020), and group E ( P = 0.007) were significantly lower than that in group A-PC ( Table I ) ( Fig 2 , A ).

Table I
Comparison of the RRV (mm 3 ) and PRR (%)
Group/variable A-NC A-PC B C D E P value
Mean SD Mean SD Mean SD Mean SD Mean SD Mean SD
RRV 0.0009 0.0006 0.0089 0.0043 0.0063 0.0054 0.0025 0.0021 0.0027 0.0013 0.0026 0.0020 0.001
PRR 0.1085 0.0699 1.1603 0.5710 0.7787 0.6485 0.3299 0.2720 0.3186 0.1528 0.3160 0.2088 <0.001

Pairwise comparisons: P values
Group/variable A-NC/A-PC A-NC/B A-NC/C A-NC/D A-NC/E A-PC/B A-PC/C A-PC/D A-PC/E B/C B/D B/E C/D C/E D/E
RRV <0.001 0.005 0.077 0.014 0.077 0.270 0.013 0.020 0.007 0.157 0.317 0.195 0.465 0.873 1.000
PRR <0.001 0.004 0.034 0.014 0.045 0.171 0.013 0.014 0.007 0.239 0.257 0.157 0.584 0.749 1.000
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Feb 28, 2021 | Posted by in Orthodontics | Comments Off on Effects of different wavelengths of low-level laser therapy on orthodontically induced inflammatory root resorption in rats investigated with micro–computerized tomography
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