Summary Background The effect of low-level laser therapy (LLLT) on accelerating orthodontic tooth movement has been extensively studied; however, there is limited knowledge on the use of LLLT on orthodontic root resorption. Objective To investigate the effect of LLLT on orthodontically induced inflammatory root resorption (OIIRR) and to compare the difference between pulsed and continuous LLLT on OIIRR. Trial design Double-blind, single-centre 3-arm parallel split-mouth randomized controlled trial. Participants Twenty adolescent patients who required bilateral maxillary first premolar (MFP) orthodontic extractions were recruited from the Sydney Dental Hospital between October 2014 and December 2014. Intervention All MFPs were tipped buccally for 28 days to induce OIIRR. The experimental premolars (n = 20) received LLLT and the control premolars (n = 20) received placebo-laser on days 0, 1, 2, 3, 7, 14, and 21. Ten experimental premolars received LLLT via continuous delivery and 10 received pulsed delivery. Laser parameter AlGaAs diode laser of 808 nm wavelength, 0.18 W power, 1.6 J per point, and duration of 9s for continuous mode and 4.5 s for pulsed mode. Outcome The difference in root resorption crater volume between LLLT and placebo-laser and continuous or pulsed laser delivery after 28 days. Randomization Randomization was computer-generated, with allocation concealment by opaque sequentially numbered sealed envelopes. Blinding The participants and operator were blinded. Results Eighty-eight patients were screened and 20 patients were randomized. Forty premolars were analysed. LLLT resulted in 23 per cent less root resorption compared to the placebo (P = 0.026). Pulsed laser delivery resulted in 5 per cent less root resorption than continuous; however, this was not statistically significant (P = 0.823). No harm was observed. Conclusion Teeth treated with LLLT had less total root resorption than placebo-laser. Furthermore, there was minimal difference between pulsed or continuous delivery of LLLT. Trial Registration Clinical Trials Registry (ACTRN12616000829415). Protocol The protocol was not published before trial commencement. Introduction Orthodontically induced inflammatory root resorption (OIIRR) is an unavoidable and unpredictable side effect of orthodontic treatment (1, 2). Approximately 90 per cent of patients undergoing orthodontic treatment have some extent of root resorption (3), 32 per cent being moderate (>3 mm resorption) while 5 per cent of the cases manifest as severe resorption (>5 mm resorption) (4). Treatment duration has been associated with increased risk and severity of OIIRR (5, 6); hence, various methods have been trialled in an effort to decrease treatment time. Mechanical vibration (7), corticotomy (8), piezocision (9), as well as several pharmacological agents such as local application of prostaglandins and vitamin D (10) have been proposed as possible methods for accelerating orthodontic tooth movement. Although most were effective, their use may not be clinically feasible due to their invasive nature or side effects (11, 12). In contrast, low-level laser therapy (LLLT) is a non-invasive method with its effects limited to the target tissue (13). Cellular absorption of laser light by the target tissue leads to the activation of intracellular signalling cascades, which increases cellular metabolism, and anti-inflammatory changes (14). Photobiomodulation involving LLLT or light-emitting diodes (LED) therapy has been tested in animal and human studies and it has been proven to stimulate epithelization, vascularization, and collagen synthesis (15). LLLT triggers tissue regeneration by improving cellular differentiation and proliferation, accelerating the clearance of tissue debris, and inducing angiogenesis (16–18). Thereby, LLLT may be beneficial for treating inflammatory processes such as orthodontic root resorption. There is extensive literature on the use of LLLT on accelerating bone remodeling and orthodontic tooth movement as well as reducing orthodontic pain (19–21). Studies have demonstrated that LLLT can enhance bone remodeling in the extraction site and expedite orthodontic tooth movement (21, 22). Some evidence suggests that LLLT are effective in accelerating the rate of orthodontic tooth movement (23–27). Studies have found the rate of orthodontic alignment and space closure was on average 30 per cent faster with LLLT (27–29), thereby significantly reducing the treatment time compared to the control groups (30). However, some studies have failed to detect any significant difference between the rates of orthodontic tooth movement on the irradiated side versus the non-irradiated side (31, 32). There is limited evidence in the orthodontic literature highlighting the side effects of LLLT. The effect of LLLT on orthodontic root resorption was tested in only two human studies with no adverse outcomes (22, 25). However, a key limitation of these studies was the use of two-dimensional periapical radiographs to quantify root resorption (33). A more accurate method for assessing root resorption is the use of micro-computed tomography (Micro-CT) as it allows three-dimensional identification of resorption craters (34). Specific objectives or hypotheses The aim of this pilot study was to investigate the effect of LLLT on root resorption when 150-g buccal-tipping forces were applied to maxillary first premolars (MFPs) over a 4-week period. A qualitative and quantitative assessment of the degree of root resorption was performed by microcomputed tomography scanning of the extracted premolars. The secondary aim was to investigate the difference between continuous and pulsed laser delivery. Methods Trial design This was a double-blinded, three-arm parallel split-mouth, randomized controlled trial with a 1:1 allocation ratio. Sample The sample consisted of 40 MFPs, which were extracted bilaterally from 20 patients. Twenty consecutive patients (10 males and 10 females) who required the extraction of MFP as part of their orthodontic treatment were recruited from the postgraduate orthodontic clinic at the University of Sydney from October 2014 to December 2014. Patients were selected and enrolled by investigator D.N. according to the following inclusion criteria (35). Patients who required upper first premolar extractions for orthodontic treatment; No previous dental treatment to the upper first premolars assessed via clinical and radiographic examination; No previous reported or observed trauma to the upper first premolars assessed via a trauma history, clinical, and radiographic examination; No previous orthodontic treatment; No past or present signs or symptoms of periodontal disease assessed via clinical and radiographic examination; No significant medical history such as asthma (36); Completed root apexification assess with periapical radiographs. Written informed consent was obtained from the patients and their parents. No changes to methods after trial commencement occurred. Ethical approval was obtained from the human ethics committee at the Royal Prince Alfred Hospital (X14-0200 HREC/14/RPAH/263). Interventions Using a split-mouth study design, each participant had one MFP randomly allocated to receive the LLLT (experimental side) and the contralateral premolar received the placebo-laser (control side). There were a total of 20 experimental premolars and 20 controls. Out of the experimental premolars, 10 received continuous laser delivery and the remainder received pulsed delivery to investigate whether the mode of laser delivery had an effect on orthodontic root resorption. Orthodontic set-up The participants had partial fixed appliances placed bilaterally on the MFPs and first molars. Self-ligating 0.022″ DAMON brackets and tubes were used (Ormco Corporation, Orange, California, USA). Buccal-tipping forces (150 g) were applied to the MFPs using 0.017″ × 0.025″” Beta III Titanium (3M Unitek, Monrovia, California, USA) cantilever springs for 28 days to induce orthodontic root resorption (Figure 1). The force produced by the springs was calibrated to the nearest gram with a strain gauge (Dentaurum, Ispringen, Germany). In addition, occlusal stops (Transbond Plus Light Cure Band Adhesive, 3M Unitek) were placed onto mandibular first molars to prevent occlusal interferences and allow uninhibited tipping of the MFPs during the experiment. Figure 1. View largeDownload slide Orthodontic set-up and location of LLLT or placebo-laser. LLLT, low-level laser therapy. Figure 1. View largeDownload slide Orthodontic set-up and location of LLLT or placebo-laser. LLLT, low-level laser therapy. Laser equipment, application, and dosimetry LLLT was applied to the MFPs for the first 4 days (days 0, 1, 2, and 3) and then weekly (day 7, 14, and 21) during the 28 day experimental period. There were a total of seven laser applications. An 808-nm diode laser (Klas-DX6182, Konftec Corporation, New Taipei City, Taiwan) was utilized in this study. The laser energy was delivered via an 8-mm diameter fibre rod (beam area of 0.5 cm2). The total irradiated surface area was 4 cm2. The continuous and pulsed mode had an average power output of 0.18 W. The pulsed mode was set at 0.36 W and pulsed at 20 Hz (25 ms on/25 ms off, 50% duty cycle).The placebo-laser was created by covering the beam aperture with black absorbent paper to block out the laser beam. The laser and placebo-laser was applied to the mucosal surface along the MFP root at four points on the buccal and four points on the palatal surface. The application points aimed to cover the periodontal fibers and alveolar process around the first premolar teeth (Figure 1). The laser was applied at the following points: Apex; Middle third (centre of the root); Cervical third (mesial); and Cervical third (distal). The laser tip was held perpendicularly contacting the gingival mucosa during the laser irradiation. The irradiation time for continuous laser was 9 seconds per point and the pulsed laser was 4.5 second per point. The energy dose was 1.6 J per point. Operator D.N. conducted all laser applications. The same laser procedure was repeated on the control premolar, but with the placebo-laser. During laser application, eye protection of the patient, operator, and dental assistants were assured by wearing laser safety glasses. Beam profile and power density verification Prior to the commencement of the study, the beam profile, power density of the laser system, and the power detector (Molectron detector, Power max 600, Portland, USA) were verified, recorded, and calibrated at the Physics Department, Optical Unit, University of Macquarie. The Molectron power meter confirmed the average power output before each laser application. Specimen collection At the end of the 28-day experimental period, the partial fixed appliances and occlusal stops were removed. The MFPs were extracted atraumatically by operator (D.N.) and stored separately in sterilized de-ionized water (Milli-Q®, Millipor, Bedford, Massachusetts, USA). An ultrasonic bath was used for 10 minutes to allow the removal of soft tissue and periodontal fragments from the root surface. Any residual periodontium was carefully removed with damp gauze. Disinfection was achieved by placing the teeth into 70 per cent Isopropyl Alcohol for 30 minutes, followed by bench drying at room temperature (23°C ± 2°C) for at least 48 hours. Outcomes and sample analysis The primary outcome was to measure the difference in root resorption crater volume between LLLT and placebo-laser. The samples were scanned with SkyScan 1172 desktop X-ray micro-tomograph system (SkyScan, Aartselaar, Belgium). Teeth were individually scanned from the cementoenamel junction (CEJ) to the root apex. Specimens were scanned 180 degree around the vertical axis, with image resolution set at 17.6 µm. Specifically designed software, NRecon (version 220.127.116.11, Skyscan, Aartselaar, Belgium), reconstructed the image data from the SkyScan. This program utilized a modified Feldkamp cone-beam algorithm (37) to produce slice-by-slice axial reconstruction. The settings for NRecon were standardized for all of the images. The reconstructed slices were saved in 16-bit tagged image file format (TIFF) format. Root resorption crater analysis was performed using the imaging software program Fiji (version: 2.0.0-rc-15/1.49k, http://imagej.net/Contributors), along with a custom macro Enigma (38). Each image slice needed to be converted to a binary image (black and white) prior to calculation (Figure 2). All of the axial slices of the image stack for each specimen were manually examined for resorption craters. Figure 2. View largeDownload slide Binary axial image slice of root specimen. Figure 2. View largeDownload slide Binary axial image slice of root specimen. Once a crater was identified, the crater was selected with a clipping tool and duplicated into its own image sequence to allow Enigma to calculate the individual volume of each crater in cubic millimetres. All measurements were carried out by one investigator (D.N.) to reduce error and bias. The craters were grouped (1) according to their location on the root surface e.g. buccal, palatal, mesial, or distal and (2) according to their location in the vertical plane e.g. apical, middle, or cervical. The vertical plane was determined by measuring the total length of the root from the CEJ to the apex and dividing it into equal thirds. Total root resorption volume was also recorded for each tooth. For 3-dimensional image reconstruction, Avizo Fire (version 8.1.0. Konrad-Zuse-Zentrum-Berlin (ZIB), FEI, SAS) was used to create and view selected specimens (Figure 3). Figure 3. View largeDownload slide 3D reconstruction of LLLT and placebo-laser specimen showing root resorption craters. LLLT, low-level laser therapy. Figure 3. View largeDownload slide 3D reconstruction of LLLT and placebo-laser specimen showing root resorption craters. LLLT, low-level laser therapy. Sample size calculation The sample size was calculated based on previous root resorption studies with similar study designs (39, 40). The split-mouth design was chosen to improve the power of the study. Ideally, an a priori sample size calculation would have allowed the study to have a sufficient sample size to achieve adequate power. This was not possible since this was a pilot study, and there were no previous studies that could provide data on the expected magnitude of change or standard deviations needed for a power analysis. Hence, this pilot study aims to provide adequate information to carry out sample size calculation for future studies investigating a similar topic. Interim analyses and stopping guidelines Not applicable. Randomization (random number generation, allocation concealment, implementation) Randomization, allocation, concealment, blinding, and laser set-up was implemented by one investigator (A.K.C.). Randomization was accomplished using a remote computerized random number generator. Each patient was randomly allocated either the right or left MFP to be the experimental laser side and the contralateral premolar acted as the control side. Additionally, patients were randomized in a 1:1 ratio to either 808-nm continuous or pulsed laser delivery. Randomization was accomplished with random permuted blocks of 10 patients with allocation concealed in sequentially numbered, opaque, sealed envelopes. One investigator (A.K.C.) generated the random allocation sequence and assigned the participants to intervention. Blinding This was a double-blind trial, both the experimental laser and the placebo-laser beams were invisible to the naked eye, and at 808 nm there was negligible glow from the laser; hence, both the participants and operator (D.N.) were blinded during this trial. The outcome assessor was only unblinded after the teeth were scanned, root resorptions craters counted, and the data had been collected and verified. Statistical analysis (primary outcomes, subgroup analysis) The SPSS statistics program (version 23; IBM Corporation, USA) was used for statistical analysis and P <0.05 was considered statistically significant. Paired t tests were used to determine whether there were any significant differences in the data between the laser and the placebo. This included comparing the total resorption crater volume per tooth, per root surface (buccal, palatal, mesial, and distal) and per vertical third (cervical, middle, and apical). The root resorption data were analysed using a general linear model (univariate analysis of variance) for each variable, the fixed factors were the intervention (laser or placebo) or delivery mode (continuous or pulsed) and the random factor was the participant. Linear regression models were also performed to determine the relationship between the amount of root resorption and the improvement due to laser. This was conducted for each tooth overall, then for each surface and height component. The assumptions for such analyses (normality of residuals and lack of pattern in residuals) were checked and were reasonable. Results Participant flow (include flow diagram, early stopping, and time periods) All 20 patients (10 males—mean age (16.4 ± 1.3years) and 10 females (16.7 ± 1.1 years)) completed the study (Figure 4) with all 40 premolars being deemed eligible for assessment and inclusion in the study. Patient recruitment commenced in October 2014 and ended in December 2014. The trial period was set at 28 days (so that root resorption could be initiated and was still ethically acceptable). Figure 4. View largeDownload slide CONSORT flow chart showing patient flow during the trial. LLLT, low-level laser therapy. Figure 4. View largeDownload slide CONSORT flow chart showing patient flow during the trial. LLLT, low-level laser therapy. Baseline data At baseline, information regarding age and sex was collected. Baseline characteristics were similar in both groups. Numbers analyzed for each outcome, estimation and precision, subgroup analyses Laser versus placebo-laser Overall, less root resorption was seen on the LLLT teeth than on the control teeth. For the total volume of root resorption craters per tooth, the LLLT teeth averaged 0.381 mm3, and the placebo teeth averaged 0.495 mm3. This resulted in the LLLT treatment producing an average 0.114 mm3 (23%) less root resorption than the placebo. This difference was statistically significant (P = 0.026; Figure 5). Figure 5. View largeDownload slide LLLT reduced total root resorption by 23 per cent compared to the placebo-laser. LLLT, low-level laser therapy. Figure 5. View largeDownload slide LLLT reduced total root resorption by 23 per cent compared to the placebo-laser. LLLT, low-level laser therapy. Root resorption data were also assessed in terms of distribution on the various surfaces of each tooth. LLLT resulted in less root resorption on all surfaces (buccal, palatal, mesial, and distal; Table 1) and vertical thirds (cervical, middle, and apical; Table 1) compared to the control. However, these results were not statistically significant. Table 1. Total root resorption per tooth surface/vertical third (mm3) between Laser and Placebo. Treat Mean Std. error 95% Confidence interval P value Lower bound Upper bound Buccal Laser 0.069 0.014 0.039 0.098 Placebo 0.104 0.014 0.075 0.134 0.091 Palatal Laser 0.026 0.014 −0.003 0.056 Placebo 0.038 0.014 0.008 0.068 0.568 Mesial Laser 0.180 0.023 0.131 0.228 Placebo 0.242 0.023 0.194 0.29 0.072 Distal Laser 0.106 0.025 0.054 0.158 Placebo 0.111 0.025 0.059 0.163 0.89 Cervical Laser 0.215 0.023 0.166 0.264 Placebo 0.218 0.023 0.17 0.267 0.916 Middle Laser 0.143 0.031 0.079 0.208 Placebo 0.221 0.031 0.156 0.286 0.092 Apical Laser 0.022 0.013 −0.005 0.049 Placebo 0.056 0.013 0.029 0.083 0.082 Treat Mean Std. error 95% Confidence interval P value Lower bound Upper bound Buccal Laser 0.069 0.014 0.039 0.098 Placebo 0.104 0.014 0.075 0.134 0.091 Palatal Laser 0.026 0.014 −0.003 0.056 Placebo 0.038 0.014 0.008 0.068 0.568 Mesial Laser 0.180 0.023 0.131 0.228 Placebo 0.242 0.023 0.194 0.29 0.072 Distal Laser 0.106 0.025 0.054 0.158 Placebo 0.111 0.025 0.059 0.163 0.89 Cervical Laser 0.215 0.023 0.166 0.264 Placebo 0.218 0.023 0.17 0.267 0.916 Middle Laser 0.143 0.031 0.079 0.208 Placebo 0.221 0.031 0.156 0.286 0.092 Apical Laser 0.022 0.013 −0.005 0.049 Placebo 0.056 0.013 0.029 0.083 0.082 View Large Table 1. Total root resorption per tooth surface/vertical third (mm3) between Laser and Placebo. Treat Mean Std. error 95% Confidence interval P value Lower bound Upper bound Buccal Laser 0.069 0.014 0.039 0.098 Placebo 0.104 0.014 0.075 0.134 0.091 Palatal Laser 0.026 0.014 −0.003 0.056 Placebo 0.038 0.014 0.008 0.068 0.568 Mesial Laser 0.180 0.023 0.131 0.228 Placebo 0.242 0.023 0.194 0.29 0.072 Distal Laser 0.106 0.025 0.054 0.158 Placebo 0.111 0.025 0.059 0.163 0.89 Cervical Laser 0.215 0.023 0.166 0.264 Placebo 0.218 0.023 0.17 0.267 0.916 Middle Laser 0.143 0.031 0.079 0.208 Placebo 0.221 0.031 0.156 0.286 0.092 Apical Laser 0.022 0.013 −0.005 0.049 Placebo 0.056 0.013 0.029 0.083 0.082 Treat Mean Std. error 95% Confidence interval P value Lower bound Upper bound Buccal Laser 0.069 0.014 0.039 0.098 Placebo 0.104 0.014 0.075 0.134 0.091 Palatal Laser 0.026 0.014 −0.003 0.056 Placebo 0.038 0.014 0.008 0.068 0.568 Mesial Laser 0.180 0.023 0.131 0.228 Placebo 0.242 0.023 0.194 0.29 0.072 Distal Laser 0.106 0.025 0.054 0.158 Placebo 0.111 0.025 0.059 0.163 0.89 Cervical Laser 0.215 0.023 0.166 0.264 Placebo 0.218 0.023 0.17 0.267 0.916 Middle Laser 0.143 0.031 0.079 0.208 Placebo 0.221 0.031 0.156 0.286 0.092 Apical Laser 0.022 0.013 −0.005 0.049 Placebo 0.056 0.013 0.029 0.083 0.082 View Large A regression analysis was conducted to compare the amount of root resorption experienced by the placebo teeth and the reduction in root resorption as a result of LLLT (placebo-laser volume − laser volume), revealing a significant relationship (P = 0.004; Tables 2 and 3). The results demonstrated that the amount of improvement seemed to be positively linearly related to the underlying amount of resorption. Thereby, a greater underlying amount of resorption correlated with a greater preventative effect or a greater reduction of resorption with laser treatment. The relationship was significant in all situations except for the mesial surface and cervical height. The amount of improvement is total improvement (Itot) = root resorption volume under placebo − root resorption volume under LLLT. The underlying amount of root resorption is measured by total root resorption under placebo-laser (Ptot). For the overall tooth, the regression equation for total tooth improvement (Itot) in terms of underlying amount of resorption (Ptot) was Itot = −0.11 + 0.45 Ptot with P = 0.004 and R-sq = 0.37 (Table 3). This indicates that a subject with one higher unit of underlying root resorption (as measured on the placebo side) would experience a 0.45 extra amount of benefit of laser treatment. Table 2. General linear model (univariate analysis of variance). Model Sum of squares df Mean square F Sig Regression 0.317 1 0.317 10.578 0.004 Residual 0.539 18 0.030 Total 0.856 19 Model Sum of squares df Mean square F Sig Regression 0.317 1 0.317 10.578 0.004 Residual 0.539 18 0.030 Total 0.856 19 View Large Table 2. General linear model (univariate analysis of variance). Model Sum of squares df Mean square F Sig Regression 0.317 1 0.317 10.578 0.004 Residual 0.539 18 0.030 Total 0.856 19 Model Sum of squares df Mean square F Sig Regression 0.317 1 0.317 10.578 0.004 Residual 0.539 18 0.030 Total 0.856 19 View Large Table 3. Regression analysis—comparing overall placebo-laser and overall improvement with laser. Coefficients Model Unstandardized coefficients Standardized coefficients t Sig. B Std. error Beta (Constant) −0.109 0.079 −1.381 0.184 Placebo-laser total 0.451 0.139 0.608 3.252 0.004 Coefficients Model Unstandardized coefficients Standardized coefficients t Sig. B Std. error Beta (Constant) −0.109 0.079 −1.381 0.184 Placebo-laser total 0.451 0.139 0.608 3.252 0.004 View Large Table 3. Regression analysis—comparing overall placebo-laser and overall improvement with laser. Coefficients Model Unstandardized coefficients Standardized coefficients t Sig. B Std. error Beta (Constant) −0.109 0.079 −1.381 0.184 Placebo-laser total 0.451 0.139 0.608 3.252 0.004 Coefficients Model Unstandardized coefficients Standardized coefficients t Sig. B Std. error Beta (Constant) −0.109 0.079 −1.381 0.184 Placebo-laser total 0.451 0.139 0.608 3.252 0.004 View Large The root resorption crater volumes of 10 randomly selected teeth were measured again to determine the overall standard error of the measurements and the coefficient of variance. Continuous versus pulsed laser The pulsed laser group had 5 per cent less root resorption than the continuous laser group, but this was not statistically significant (P = 0.823). The continuous laser resulted in a mean root resorption volume of 0.45 mm3 and the pulsed laser group had a slightly lower mean root resorption crater volume of 0.426 mm3. Harms No harm was observed during this study. Laser safety protocol was adhered to during the study with the use of laser safety eyewear to protect the eyes of the operator, participant, and auxiliary staff. Discussion Main findings in the context of the existing evidence, interpretation The effect of photobiomodulation on OIIRR has been investigated in previous animal and human studies (21, 22, 25, 31, 41–43). The general consensus from the limited human studies in the literature indicated that LLLT did not result in more root resorption than conventional orthodontic treatment (22, 25). However, the accuracy of these human studies is questionable as root resorption was examined using periapical radiographs therefore only advanced root resorption and apical root loss would be detected (33). Cone-beam computed tomographs have been reported to allow better detection of root resorption than two-dimensional films (44). This pilot double-blind clinical trial is the first study to use Micro-CT to examine the use of LLLT on the root resorption process. It was possible to obtain detailed information about the root resorption crater volumetric dimensions by extracting the MFPs, such detailed analysis would not have been possible if the teeth remained in-situ and examined with conventional two-dimensional radiographic methods. This is one of the first human studies to report a statistically significant decrease in root resorption with the use of LLLT. The specific laser protocol was derived from literature with the aim of instigating the biostimulatory and/or bioinhibitory benefits of LLLT to minimize root resorption (45, 46). LLLT was applied daily at the beginning of buccal force application because cells are more readily influenced by LLLT at the initial stages of a biological response (47, 48). LLLT was applied seven times during the 28-day experimental period as multiple applications of LLLT have been demonstrated to produce a greater response than a single dose (49, 50). The energy density used in this study fall into the range of 0.5 to 4 J/cm2, which is considered to be the most effective in triggering tissue biological response (51). It is unclear whether the reduction in root resorption on the laser side is the result of the preventative effect of LLLT or whether it is due to its reparative potential. One suggested mechanism may be that LLLT accelerates the overall cellular response of target tissues involved in the inflammatory process of orthodontic tooth movement by increasing both osteoblastic and osteoclastic activity in the short term but reducing the overall amount of osteoclasts in the long term to minimize root resorption (41, 52). Histologically, LLLT has been shown to induce osteoblast proliferation, whilst diminishing osteoclasts (41, 52). Another hypothesis may involve the reparative effect of LLLT on root resorption. Studies have shown that LLLT stimulates cementoblast and fibroblast proliferation and enhances the reparative process (53–55), through secondary cementum formation (56), new capillary formation and reduction of osteoclastic activity secondary to RANKL/OPG ratio reduction (53). In the present study, the laser delivery mode was also investigated. The pulsed laser tended to result in a less root resorption (5% less) compared to the continuous delivery; however, this was not statistically significant (P = 0.828). This result may be due to the small sample size or there may be no difference between modes of operation on OIIRR. Therefore, future studies with larger sample sizes comparing the difference between pulsed and continuous laser may be useful. However, these results corroborate with other LLLT studies, which demonstrate that pulsed modes solicit a greater biostimulatory response than its continuous wave counterpart (57, 58). Limitations One of the limitations of the present study may be the relatively small sample size. However, the sample size of 20 patients (n = 40 premolars) proved to be adequate to detect a significant difference for the primary outcome. The main comparison between LLLT and placebo-laser did in fact reach statistical significance with a P value of 0.026. The main cited disadvantage of split-mouth studies is the possible crossover effect; however, the laser is aimed at a targeted area on the desired tissue and acts locally on the target tissue. Therefore, the effect of LLLT is site specific and the crossover effect would be minimal (13). For both groups, root resorption was seen on the buccal and palatal surfaces, in particular, the buccal-cervical and palatal-apical regions; this was similar to previous studies that examined buccal-tipping forces and root resorption (12, 40, 59). Resorption was also present on the mesial and distal surfaces. It was likely that a mesial, distal, or rotational component of force was imparted on the maxillary premolars during tipping. This could be explained by the simple cantilever design of the buccal beta-titanium alloy springs, and the relative position and rotation of the MFPs in relation to the dental arch. Generalizability The generalizability of the observed results may be limited because this research was undertaken in a single center by one clinician (D.N.). In addition, there is considerable individual variation in root resorption susceptibility. The root resorption process seems to vary between individuals and even within the same individual; thus, the results may not be generalizable to everyone. The buccal-tipping force of 150 g was chosen as a clinically relevant force that was ‘intermediate’ when compared to ‘light’ and ‘heavy’ forces established in previous studies (40, 59). A 4-week experimental period has been proven to be sufficient for detectable root resorption craters to form (3), while remaining ethical and practical for the participants. However, this study design only reflects the initial response of the root surfaces to force and LLLT application and the results should further be verified with patients undergoing a full course of orthodontics treatment. The results of this study was based on the use of an 808-nm diode laser; therefore, results may not be applicable to other wavelengths or types of lasers. Conclusions The duration of the study was 4 weeks; hence, results and conclusion should be interpreted with caution. LLLT seems promising in preventing or reducing orthodontic root resorption during the initial stages of orthodontic force application. There was significantly less root resorption crater volume on the laser side compared to the placebo-laser side, indicating either possible prevention or induction of root repair in patients susceptible to root resorption. There was no significant difference between the continuous or pulsed mode of LLLT delivery. However, further research is required with patients undergoing a full course of orthodontic treatment and LLLT application. Funding This work was supported by the Australian Society of Orthodontist Foundation for Research and Education (ASOFRE) for their generous research funding. Conflict of Interest None to declare. Acknowledgements The authors acknowledge the facilities, and the scientific and technical assistance, of the Australian Microscopy and Microanalysis Research Facility (ACMMRF) at the Sydney Microscopy and Microanalysis Unit, The University of Sydney. References 1. Brezniak , N. and Wasserstein , A . ( 2002 ) Orthodontically induced inflammatory root resorption. Part I: the basic science aspects . The Angle Orthodontist , 72 , 175 – 179 . 2. Remington , D.N. , Joondeph , D.R. , Artun , J. , Riedel , R.A. and Chapko , M.K . ( 1989 ) Long-term evaluation of root resorption occurring during orthodontic treatment . American Journal of Orthodontics and dentofacial Orthopedics , 96 , 43 – 46 . Google Scholar CrossRef Search ADS 3. Kurol , J. , Owman-Moll , P. and Lundgren , D . 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Published by Oxford University Press on behalf of the European Orthodontic Society. All rights reserved. For permissions, please email: email@example.com This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices)
The European Journal of Orthodontics – Oxford University Press
Published: Sep 7, 2017
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