The biggest problem in the orthodontic process is the pain and the long duration of treatment, which is also generally divided into 2 phases, namely the orthodontic tooth movement (OTM) and the retention phase. In recent decades, low-level-laser therapy has gained attention because it is non-invasive, inexpensive, relieves pain and has no significant adverse effects. Low-level-laser therapy (LLLT) has been proved to effectively induce and accelerate the remodeling process of alveolar bone by increasing the number of osteoblasts and osteoclasts. Therefore, LLLT is widely used in OTM to accelerate tooth displacement, but there are few studies and limited evidence on the stability whether it can strengthen and shorten the retention stage to avoid relapse. Thus, the purpose of this study is to investigate the stability after orthodontic treatment by observing the substantial influence of low-level-laser as during retention phase.

Research Question(s)

1. Does the low-level laser treatment can enhance stability and shorten retention time after orthodontic treatment or not will be demonstrated through 3 aspects：

1. The Incisor Irregularities Index between laser and control group after application of LLLT at debond (0), 6 and 12 months of retention
2. The interarch dimension: intercanine width, intermolar width, interpremolar width, arch length between laser and control group after application of LLLT at debond (0), 6 and 12 months of retention
3. The overjet and overbite between laser and control group after application of LLLT at debond (0), 6 and 12 months of retention

Objective

General:

The goal of this study is to investigate the stability in retention phase after application of LLLT during leveling and alignment with fixed appliances.

Specific:

1. To compare the Incisor Irregularities Index between laser and control group after application of LLLT at debond (0), 6 and 12 months of retention
2. To compare the interarch dimension: intercanine width, intermolar width, interpremolar width, arch length between laser and control group after application of LLLT at debond (0), 6 and 12 months of retention To compare the overjet and overbite between laser and control group after application of LLLT at debond (0), 6 and 12 months of retention

This is a continuation study from the previous approved project entitle "The Effect of low level laser therapy on orthodontic tooth movement using conventional and self-ligating brackets in extractions cases: A randomised clinical trial and 3D evaluation via CBCT and digital dental model approaches" with ethical approval no ( USM/JEPeM/17070339). Previous studies used an in-vivo study, designed as randomised clinical trial for patients under treatment with fixed orthodontic brackets in Orthodontic Specialist Clinic at Hospital Universiti Sains Malaysia.

The current study was designed to observe the effect of laser irradiation (LLLT) during retention period at debond (0), 6 and 12 months of retention phases. The laser (LLLT dose) was applied only during active orthodontic treatment (levelling and alignment stage) in previous study. Patients will not receive any more doses of LLLT during retention phases at debond (0), 6 and 12 months.

All participants (control group and experimental group) from the previous studies will be included and enrolled in this current study after receiving the consent from patients. Among them, those who received LLLT in the previous study will be enrolled in the Retention Laser Group (LG) and those who did not receive LLLT will be in the Retention Control Group (CG) for the current study. The smaller the variation in tooth alignment between LG and CG, the better the retention stability.

In this current study, Little's Irregularity Index (LII), overjet, overbite, arch length, intermolar and intercuspid widths will be used as indicators for the stability assessment.

Study population The same participants from project entitle "The Effect of low level laser therapy on orthodontic tooth movement using conventional and self-ligating brackets in extractions cases: A randomised clinical trial and 3D evaluation via CBCT and digital dental model approaches" with ethical approval no (USM/JEPeM/17070339) treated at Specialist Orthodontic Clinic, Hospital Universiti Sains Malaysia will be recruited for this current study.

Sampling method and subject recruitment Patients who meet the inclusion and exclusion criteria and ready to debond will be invited to participate in this current trial. The orthodontist will have provided patients (≥18years) with verbal and written information about the study protocol in order to obtain the consent.

This study is a continuation of a previous research project as stated in the study design section where the sampling method used was simple random sampling. Previous research project was conducted in the Specialist Orthodontic Clinic, School of Dental Sciences, Hospital USM. A total of thirty-two patients were randomised using the online free randomisation software (http://www.randomization.com). The software automatically generated the randomisation plan where the number of patients were balanced in each group (1:1). Thus, the subjects were recruited in each group blindly following the randomisation plan. A total of sixteen patients were included in LLLT and non-LLLT groups, respectively. During the follow up, none of the patients were discontinued from each group. Therefore, a total of thirty-two patients will selected for the current study, those who received LLLT in the previous study will be enrolled in the Retention Laser Group (LG) and those who did not receive LLLT will be in the Retention Control Group (CG).

Operational definition

Study variables:

Independent variable is Retention laser group (LG), Retention control group (CG) and difference stages which is debond (0), 6 months and 12 months.

Dependent variable is LII index, arch lengh, intercanin length, intermolar width, overjet and overbite.

1. Little's Irregularity Index (LII, mm) A modification of Little's technique (Little, 1975), the sum of the distances between the anatomic contact points from the mesial of the left canine to the mesial of the right canine.
2. Arch length (left, mm) The distance between the incisal contact point of the central incisors to the mesial contact point of the left first permanent molar.
3. Arch length (right, mm) The distance between the incisal contact point of the central incisors to the mesial contact point of the right first permanent molar.
4. Arch length (total, mm) The sum of arch length (left) and arch length (right).
5. Intercanine width ICW, mm) The distance between the cusp tips of the permanent canines. In case of tooth abrasion, the midpoint of the plateau was used.
6. Intermolar width (IMW, mm) The distance between the mesiobuccal cusp tips of the left and right first permanent molars. In case of tooth abrasion, the midpoint of the plateau.
7. Overjet (OJ, mm) The distance of the most labial maxillary central incisor to the labial surface of the mandibular central incisor.
8. Overbite (OB, mm) The mean overlaps of the maxillary to the mandibular central incisors.

Data collection method and Research tools

1 Application of laser in the previous study. A Ga-Al-As diode laser (Ilase, USA) with a wavelength of 940 nm has been used in the previous study, operating in continuous wavelength (CW) mode. The fiber diameter of the laser beam is 0.04 cm2 (Figure 1.1). The tip of the optical fiber is kept in contact with the mucosa during irradiation. The laser was irradiated to five points on each dental site (Figure 1.2). The points are: two points in the mesial and distal apical regions, one point approximately in the middle of the cervical part of the incisor and canine (Figure 1.3). The conventional irradiation point is at the labial side of the maxillary and mandibular dental arches. The laser parameters that have been used in previous study are shown in (Table 1). The procedure was performed in an isolated room where the patient, the operator and the dental assistant wear the protective glasses. The energy density calculated on each tooth was calculated using the following equation: Energy density = laser output power x Sec / diameter in cm2.

Table 1: The laser parameter used in previous study:

Laser type: Ga-Al-As Wavelength: 940 nm Emission type : Continuous Irradiation dosage/per tooth: 75J/cm2 Application technique: Direct contact with the mucosa Exposure time per point: 6 second Laser classification: 3B Laser application time: Once in a month (4-week intervals) for the maxilla and mandibular incisors and canines Output: 100Mw Diameter of the optical fiber: 0.04 cm2

2. Specific operations for Retention Laser group (LG) and Retention Control group (CG) (1:1) After finishing the active orthodontic treatment and the patients ready for debonding (removal of braces), all participants from both groups LG and CG will be issues and wear the same type of retainer which is Vacuum formed retainer (VFR) during the retention phase. At debond (0), 6 and 12 months of retention phases, all patients will not receive any more doses of laser. All patients from both groups will be instructed to wear the retainer following the same regime as usual practice. Patients need to wear the VFR retainer for full time (24 hours daily) for 12 months of debonding and only remove the retainer during eating and brushing.

The VFR will be fabricated from copolyester material (Transparent Copyplast C, size 1.0x125mm) following the manufacture's instructions. It will be heated for 90 seconds then cool for 150 seconds with 0.5mm thickness after thermoformed. The retainer will be trimmed to provide 1-2 mm buccal and 3-4mm lingual extension past the gingival margins. All occlusal surfaces will be covered up to and included the most distal teeth.

3. Study model preparation and collections Alginate impression at debond (0) and after 6 and 12 months of retention after debonding will be obtained from participants. Then the dental cast will be fabricated using dental stone to produce a study model.

The series of the study models collected from patients according to intervention time will be scanned individually using scanner machine (Next Engine) to produce the 3D model for the measurements of the variables.

The Next Engine 3D laser scanner (Next Engine Inc, Canada) will be used to analyze the pre-and post-dental models for both groups for transverse dental changes and irregularities index.

The computer, scanner, and auto-drive are all included in the 3D scanner equipment. The gripper arm, platter pad, and platter shaft make up the auto drive. A platter pad may be used to carry the cast, and a gripper arm can be used to secure it. The platter pad screw can also be used to adjust the cast up, down, right, and left. The gripper arm is moved up and down by a screw. The scanner and the auto-drive are connected by a USB connection. Another USB cord connects the scanner to the computer. Scanning can be divided into three categories: scan family, placement, and divisions. To scan the cast from every angle, select the 360-degree scan option from the panel. The next-generation 3D laser scanner can detect an object's length, width, and depth by triangulating distances between the reflecting aser beam and the scanned cast surface.

The following engine, the 3D laser scanner, uses a Class II laser gamma of 685 nm at 25 mW, with a beam-spread angle (2 Theta) of 21 horizontally and 0.1 vertically, an object-to-scanner distance of 0.3 m, a field of view of 70 mm, and a scanning time of 30 seconds. For its 3D data, the scanner uses a one-half-inch frame transfer charged coupled device (CCD) with 380,000 pixels, as well as a color CCD with a similar specification. The output data from the scanner is 200 x 200 x 256 for 3D and 400 x 400 for color data. The device weighs one kilogram in total.

All scanned data coordinates (in x, y, and z) are imported in DXF format into ScanStudio HD software to be measured. Spatial linear measurements are taken using a digital caliper (computer mouse) that is accurate to 0.5 mm, and the average value is used.

Blinding

The clinician and researcher will be blinding because both groups use the same type of retainers and the impression will be taken at the same time frame. Furthermore, no more laser dose will be given during the retention period.

Questionnaires A set of questionnaires will be distributed to the participants at the end of the final data collections at 12 months of retention phase to assess the patients' compliances. The questionnaires used for this study was adapted from the questionnaire used by Ab Rahman et al with permission. The questionnaires will be available in both languages; English and Malay and the version will be given according to participant preference in term of language.

Community sensitivities and benefits If the result from this current study shows the LG group proven to have a better stability during the retention phase, some suggestions can be provided to the orthodontists/clinician such as to use the LLLT during the active orthodontic treatment not only to shorten the treatment duration and reduce the pain during active treatment but the laser also can obtained more stability after debonding. Another advantages, the duration/ regime to wear the retainer can be shorten to avoid burden of the patients in wearing the retainer.

Data analysis Descriptive statistics will be calculated for each measurement (mean, median, standard deviation, and Inter-Quartile Range). The amount of relapse will be described by comparing the measurements at the time of debonding (T1), after 6 months (T2), and after 12 months (T3) of wear of the retainer. Data were analysed using Statistical Package for the Social Sciences (SPSS) version 26. One-way repeated measure ANOVA will be used to compare the Incisor Irregularities Index between laser and control group after application of LLLT at debond (0), 6 and 12 months of retention (Objective 1). Two-way repeated measure ANOVA will be used to compare the interarch dimension: intercanine width, intermolar width, interpremolar width, arch length, overjet and overbite between laser and control group after application of LLLT at debond (0), 6 and 12 months of retention (Objective 2 and Objective 3). The level of significance for the statistical analysis is set at 0.05.

Inclusion Criteria:

• 1.Patient treated with laser and non-laser application during orthodontic treatment as in previous study
• 2.The patient presents with mild to moderate crowding malocclusion with extraction of all 1st premolars and using conventional brackets
• 3.The treatment of fixed appliances involving both arches
• 4. Patients wearing vacuum formed retainers.
• 5. Patients are compliance towards retainer wear with no history of retainer lost
• 6. All permanent teeth erupted except for third molars.

Exclusion Criteria:

• 1.Age less than 18 years old
• 2.Active caries and Periodontal disease
• 3.Use any long-term use of analgesics or drugs that affect the function of the central nervous system.
• 4. Non-compliance patients in term of wearing retainers

Withdrawal criteria:

• 1.Any patient who would like to withdraw from the experiment can do without their treatment being compromised.
• 2.Patients who do not comply with the retainer requirements during the retention phase will be considered an automatic withdrawal from the research and their data will not be accepted.