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INTRODUCTION
Maxillary transverse deficiency is a common orthodontic complication.1 Many maxillary deficiency cases are related to posterior crossbite and crowding of the maxillary arch, which compromise the function of mastication and esthetics.2,3 In 1860, Angell4 was the first to describe maxillary expansion. This procedure gained popularity by Haas5 in 1961. The aim of rapid maxillary expansion (RME) was to produce heavy forces by expanders to obtain maximum skeletal response by opening the mid-palatal suture (MPS) with minimum orthodontic movement.6,7
Nonsurgical treatment of maxillary transverse deficiency before or during puberty has never been a challenge. The main difficulty in dealing with transverse discrepancy is associated with the limited range of tooth movement in transverse dimension, described by Proffit et al.8 as the “transverse envelope of discrepancy.”
The major goal of RME is to increase the width of the maxilla through skeletal expansion of sutures. Bone-borne maxillary expanders promote bi-cortical engagement of the four mini-screws into the cortical bone of the palate.9 It avoids the side effects of tooth-borne expanders, such as alveolar bone resorption, which leads to tooth movement in the same direction.10 Tooth-borne expanders concentrate the force at the dentoalveolar area, which might be iatrogenic to the surrounding periodontal tissue and limit the skeletal effect of the appliance.11
The treatment that affects the biostimulation potency of the laser, which is not accompanied by a local temperature increase in tissues by more than 1°C, is called low-level laser therapy (LLLT). LLLT is noninvasive, nonthermal, painless, and requires a relatively short application time. The procedure is common in orthodontic clinics for reasons such as reducing pain, accelerating tooth movement, and stimulating bone regeneration in the MPS after palatal expansion.12-15
The aim of the current study was to measure the skeletal and dental effects of a miniscrew-assisted expander (Hyrax), six months after expansion, along with LLLT in orthodontic patients with maxillary constriction.
MATERIALS AND METHODS
Trial design
This prospective randomized clinical-controlled trial followed the Consolidated Standards of Reporting Trials guidelines16 for reporting randomized clinical trials (RCTs), allowing a detailed description of the study interventions and assessment methods. This RCT consisted of parallel groups, with a 1:1 allocation ratio.
Participants, eligibility criteria, and settings
The study was conducted at the clinic of the Department of Orthodontics, Faculty of Dentistry, where the subjects were selected and the trial was performed. The study protocol was registered at the Evidence-Based Center and approved by the Research Ethics Committee of the Faculty of Dentistry, Cairo University (IRB no: 16-9-15). All patients were informed of the study, and informed written consent was obtained. The inclusion criteria for this study were female patients with an age range of 10–13 years old with an average growth pattern and an open MPS, which was verified using an occlusal radiograph, and a bilateral posterior crossbite due to apical maxillary deficiency. Good oral hygiene, a healthy periodontal condition, and medically free were the other inclusion criteria. Patients with surgical or other treatments that might affect RME, congenital malformations, previous orthodontic therapy, systematic disease, or active periodontal disease were excluded from this study.
Intervention
Records
Intraoral and extraoral photographs and cone-beam computed tomography (CBCT) images were obtained before treatment (T0) and after 6 months of the retention phase (T1) (Figures 1 and 2).
CBCT images were taken before expansion for proper diagnosis, to determine mini-screw implementation sites, and as the baseline for frequent measurements. Another CBCT image was taken six months after expansion to evaluate dentoskeletal changes after retention.
CBCT images were acquired using a next-generation i-CAT scanner (Henry Schein Dental, Melville, NY, USA). The machine was supplied with an amorphous silicon flat panel sensor with a cesium iodide scintillator, 0.5 mm focal spot size, 14 Bit grey scale resolution, and operating at the following protocol for all the scans of the study: 120 kVp, 37.07 mAs, 0.3 mm voxel size, 17.8 seconds scanning time, and medium diameter field of vision. The Digital Imaging and Communications in Medicine format of the images was processed using InVivo 5.01 Anatomage software (DEXIS, Quakertown, PA, USA).
Bone-borne Hyrax expander
The bone-borne Hyrax expander used in this study was supported by four mini-screws (dimensions 1.5 mm diameter and the length 10 mm with a trans-mucous section of 2 mm) that were placed two on each side, between the first and second premolars, and between the second premolars and first molars (Figure 3).
CBCT images were used to plan the insertion location of the mini-screws in an area of at least 3.5 mm of inter-radicular space to receive the 1.5 mm diameter mini-screw. A rubber base impression was obtained after mini-screw insertion for the Hyrax appliance fabrication. The appliance was soldered into custom-made stainless steel rings that were used to support the appliance on the mini-screw head. Upon delivery, the initial activation of the appliance was four turns.
For safety measures, after applying the appliance to the patient’s palate, it was ligated to the cleats on the lingual surface of the banded upper first molars. Patients were instructed to activate the expansion screw twice daily for the next 15 days of the active expansion phase by verbal explanation and demonstration on the first day of expansion. The patients in the intervention group visited the clinic every day to ensure that they were activating the appliance properly and for LLLT application as per the LLLT protocol of Cepera et al.13 During follow-up, the hyrax was checked to ensure that it was activated twice, as instructed.
After 15 days of expansion, the Hyrax appliance was locked using light-cured composite and was kept in place for the 6 months of retention. During this phase, the patients were asked to visit every three weeks to follow up on their oral hygiene and appliance stability.
LLLT application
In the laser group, low-level laser treatment was performed using Epic 10 Console (Biolase, Foothill Ranch, CA, USA) with an active medium indium gallium arsenide semiconductor diode via the tooth whitening tip (rectangular 35 mm × 8 mm = 2.8 cm2) according to the manufacturer’s instructions using the following parameters: wavelength, 780 nm; power density, 40 mW; energy density, 10 J/cm2; energy per point, 32 J; continuous wave, time, 8 seconds. The energy density used in this study was similar to that used by Cepera et al.13
A dental diode laser was used along with a fully engineered deep tissue hand piece to control important parameters, such as spot size and power intensity. The hand piece was protected using a plastic wrap according to biosafety standards. During laser application, the operator and patient wore filter glasses for a wavelength of 780 nm. Application was performed in points distributed in four application areas around the MPS (Figure 4):
○ Two anterior areas from jackscrew to the canines.
○ Two posterior areas from the jackscrew to the first molars.
LLLT was applied in the following stages, for a total of 11 doses:
○ Day 1 to 5 (first 5 days of expansion).
○ Day 16 to 18 (day 1, 2, and 3 of the retention phase).
○ Day 25 (7 days after the previous dose).
○ Day 32 (7 days after the previous dose).
○ Day 39 (7 days after the previous dose).
The laser group patients received LLLT in the first five days of expansion and the first three days of retention, followed by three separate doses every seven days.
Outcomes
The primary outcome of this RCT was to determine the effect of LLLT on bone-borne rapid palatal expansion (BBE) after six months of retention. This was done by comparing the measurements on the CBCT images at T0 and T1. A total of 48 CBCT images were obtained at the end of this study (24 pre-expansion and 24 post-expansion), upon which the analysis was processed using InVivo 5.01 Anatomage software. A custom analysis of dental and skeletal landmarks, lines, and planes (Table 1) was performed to measure the effect of LLLT on maxillary expansion with and without LLLT after 6 months of retention (Table 2). The CBCT image measurements were transferred into an Excel sheet containing the measurements in rows and the subjects’ names in columns.
Sample size calculation
A study of a continuous response variable from an independent variable was conducted. In a previous study,13 the responses within each subject group were normally distributed, with a standard deviation of 1.6. If the true difference in the means of Groups I and II is 2.2, we will need to study nine Group I subjects and nine Group II subjects to be able to reject the null hypothesis such that the population means of the two groups are equal with a probability (power) of 0.8. The type I error probability associated with this test of null hypothesis was 0.05. Considering the dropout rate, a sample size of 12 per group was appropriate.
In this RCT, the sample comprised of 24 female patients who were randomly divided into two groups: BBE without LLLT (n = 12), and BBE with LLLT (n = 12).
Randomization
Participants were randomly assigned to either the control group (non-laser group) or the experimental group (laser group) at a 1:1 allocation. Sequence generation was performed using computer-generated random numbers in Microsoft Office Excel 2007 (Microsoft, Redmond, WA, USA). Allocation concealment was performed by writing random numbers obtained from the sequence generation on opaque papers, folded four times, and kept in sealed, opaque envelopes in a box with the secretary of the department. After the patient was examined for eligibility, they were sent to the secretary of the department and allowed to choose one of the envelopes to detect the assigned group.
Blinding
The first assessor performing this study assessed the CBCT measurements blindly. The second assessor fed the data into the computer in separate data sheets so that they could analyze the data without having access to the information about the allocation.
Statistical analysis
Data were coded and entered using the statistical package SPSS version 25 (IBM Corp., Armonk, NY, USA). Data were summarized using the mean, standard deviation, median, minimum, and maximum quantitative data. Pre- and post-intervention comparisons in each group were performed using the paired t-test. Comparisons between the two groups regarding quantitative variables were performed using the non-parametric Mann–Whitney test.17 Statistical significance was set at p < 0.05.
RESULTS
Participant flow, dropouts, and numbers analyzed (Figure 5)
In the non-laser group, 12 patients underwent bone-borne palatal expansion without LLLT. Fourteen participants were initially assigned to the laser group. One patient was excluded because she was not able to visit the clinic regularly for LLLT. Another patient was lost because the Hyrax screw was blocked during the first week of treatment and was delivered a week later to continue the expansion phase after replacing the Hyrax appliance. The records of all 12 participants in the laser group were analyzed.
Recruitment
The first patient was treated on October 13th, 2016, while the last patient was treated on April 6th, 2018. All patients included in this study were followed up for 6 months.
Data baseline
Each group consisted of 12 female patients with bilateral skeletal posterior crossbite.
Outcomes and estimation
General clinical findings
Patients in both groups experienced a significant amount of palatal expansion. A diastema was observed in the midline between the central incisors on the fourth day of expansion. The diastema was approximately 2–4 mm in both groups on the 15th day of expansion. The midline diastema closed during the first 14 days of the retention phase, with central incisor tipping. Crowding relief in the upper arch was also evident by the end of the retention phase after diastema closure due to widening of the upper arch (Figures 1 and 2).
Post-retention CBCT measurements
CBCT measurements were performed after 6 months to evaluate the effect of LLLT on dental and skeletal retention within each group and between both groups (Tables 3 and 4).
According to the post-retention measurements of the transverse skeletal changes in the maxilla and circummaxillary structures in the non-laser group, the nasal and maxillary widths were significantly increased, and no statistically significant changes were observed in the other transverse skeletal measurements. In the laser group, the mean and standard deviation values of the nasal, maxillary, and left maxillary-mandibular widths were significantly increased, with no statistically significant change in the rest of the transverse skeletal measurements. There was no statistically significant difference in the transverse skeletal linear measurements between the two groups.
Regarding the post-retention vertical skeletal linear measurements, a statistically significant increase in the total facial height was found in both groups. However, in the non-laser group, the increase was due to a statistically significant increase in the lower facial height. In contrast, in the laser group, the increase was due to a statistically significant increase in middle facial height.
In the post-retention vertical skeletal angular measurements, no statistically significant difference was observed in the non-laser group. In the laser group, the angle between the mandibular line and the maxillary plane and Frankfort horizontal plane was significantly decreased. The angle between the mandibular line and Frankfurt horizontal plane was significantly different between the two groups.
There was no statistically significant change in the anteroposterior skeletal angular measurements after the retention phase in the non-laser group. In the laser group, the Sella-Nasion-Point A (SNA) and Point A-Nasion- Point B (ANB) angles were significantly increased after expansion, with no statistically significant change in the Sella-Nasion-Point B (SNB) angle. There was no statistically significant difference in the anteroposterior skeletal angular measurements between the two groups.
In the post-retention transverse dento-alveolar linear changes (inter-dental widths), all measurements in the non-laser group were significantly increased, except for the apical inter-premolar and apical inter-incisor widths. In the laser group, all dentoalveolar linear measurements significantly increased. The interpremolar apical distance was significantly increased in the laser group, and no statistically significant difference was observed in the other transverse dentoalveolar linear measurements between the two groups.
According to the transverse dental angular changes (buccolingual dental inclination) and vertical dental changes of the upper first permanent molar, there was no statistically significant change in any of the measurements after expansion treatment within each group or when comparing the differences between the groups.
Harm
Participants who were not committed to oral hygiene instructions in both groups experienced moderate to severe palatal mucosal inflammation. Three patients experienced palatal overgrowth of the screws and part of the appliance arm during the expansion phase. Inflammation receded during the retention phase after strictly following the oral hygiene instructions and finally diminished a few days after the appliance and mini-screws were removed.
DISCUSSION
Several reports and trials11,18,19 have shown the clinical success of BBE; however, this is one of the first RCT to assess the effects of LLLT on BBE. LLLT is a noninvasive, nonthermal, and painless procedure that requires a relatively short application time. Owing to its biostimulatory effect, it is believed that LLLT accelerates the opening and bone regeneration and healing of the MPS in RME procedures by stimulating collagen synthesis, a basic component of the osteoid matrix.20-22 To test whether this positive effect of LLLT on bone regeneration extended to influence the quality of expansion, rendering it more skeletal in nature, application of LLLT to a bone-anchored hyrax was presented. Similar to the Beiderman23 hygienic appliance, the expansion appliance used in this study lacked acrylic palatal coverage, preventing any inference with laser application along the MPS. This is in addition to the ease of maintaining oral hygiene and being better tolerated by patients.
Since a greater response to RME has been reported in younger subjects,19,24,25 pre-pubertal and circumpubertal patients were recruited for this study to improve the prognosis of expansion. Female patients were chosen to exclude any gender variability, in addition to their cooperation and high motivation for treatment.26 CBCT was used to allow 3-dimensional evaluation of the skeletal and dental effects of LLLT on expansion. Pretreatment and post-expansion CBCT images after 6 months of retention were collected to minimize radiation exposure.27
Following the laser protocol used by Cepera et al.,13 the results of this trial showed that BBE alone was able to laterally displace the maxillary halves as much as BBE with laser. There was an increase of nearly 2 mm in the maxillary width in both groups, with no effect on facial width. This indicates that the effect of BBE was strongest near the MPS in both groups and diminished as we advanced upward. In agreement with our findings, Lin et al.18 measured the transverse skeletal maxillary changes over three levels and reported that BBE increased almost twice as much at the skeletal level than the hyrax group, with the least increase at the nasal floor and the greatest increase below the hard palate by 5 mm. Mosleh et al.28 reported a similar increase (2.2 mm) in the interjugal width of adolescents following BBE. Regarding the effect of LLLT, Cepera et al.13 used occlusal radiographs to compare bone density, and concluded that LLLT improved MPS opening and accelerated bone regeneration and healing. Ferreira et al.14 used a different LLLT protocol and revealed a higher optimal bone density in the laser group, postulating that LLLT had a positive influence on bone regeneration by accelerating the repair process.
Because the nasal floor is a reflection of the palatal vault, the nasal floor and cavity are highly affected by the expansion forces. A significant increase in the nasal width of 2.7 mm (± 2.32 mm) in the laser group and 1.72 mm (± 1.47 mm) in the non-laser group was detected. The higher measurement in the laser group, although statistically insignificant, could suggest greater expansion or better retention of expansion. Following expansion and throughout the retention period, all mouth-breathing patients in both groups reported improvement and ease of nasal breathing. These findings agree with those of Bicakci et al.,29 who reported an increase in the minimum cross-sectional area of the nose following conventional rapid palatal expander in pre- and postpubertal subjects. Bazargani et al.30 reported a significantly higher nasal airway flow and lower nasal airway resistance following BBE.
No significant differences were found between the two groups in either the vertical or anteroposterior measurements, despite the significant increase in the upper anterior facial height, SNA, and ANB measurements within the LLLT group. This modest increase agrees with previous trials28,31 and may be secondary to the biostimulatory and remodeling effects of the laser on the anterior maxilla, resulting in a clinically and statistically insignificant maxillary anterior and downward displacement.5,32
A statistically significant increase in the SNA and ANB angles within the laser group was found due to LLLT treatment at the beginning of the expansion phase, which reached its peak effect in the first 2 days of radiation, significantly stimulated bone regeneration of the MPS during expansion and increased the rate of bone remodeling and retention, as in previous studies.33,34 The post-retention CBCT indicated that LLLT reduced the relapse and kept the maxilla in its forward position, while there was no statistically significant increase in the same angles in the control group.
With all the statistically significant increased transverse dental measurements in both the laser and non-laser groups, together with the unchanged posterior teeth inclination in both groups, the findings indicate an optimum skeletal expansion accompanied by bodily movement of the molars with no buccal rolling in both groups. Mosleh et al.28 reported similar results with apical and coronal inter-molar widths of 3.5 ± 1 and 3.9 2.1, respectively, after 15 days of expansion. An increase was noted in the apical inter-molar, inter-premolar, inter-canine and inter-incisor measurement in this study of 3.63 ± 1.16, 3.28 ± 1.9, 3.4 ± 1.93, and 2.2 ± 1.18 mm, respectively, in the laser group and 3 ± 0.86, 1.89 ± 1.48, 3.14 ± 1.72 and 2.62 ± 3.62 mm, respectively, in the non-laser group. The measurements were more increased and closer in number within the laser group, which might suggest a more parallel sutural opening. The only difference between the two groups was significant premolar tipping in the non-laser group, with clinical insignificance.
CONCLUSIONS
These results suggest that the parameters and protocol used for LLLT did not clinically affect the efficiency of BBE in prepubertal and pubertal patients. There were no differences in the amount or quality of skeletal and dental expansion in the transverse, anteroposterior, and vertical dimensions.
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