To evaluate the rate of canine retraction and pain perception following micro-osteoperforation – a split-mouth clinical study

The study was a single-centered split-mouth clinical trial. Ethical approval was obtained from IEC (DJC/ IEC/ 2019/21).

The trial was registered at www.ctri.nic.in (CTRI No-CTRI/2022/03/XXXXXX).

The participants were recruited from patients attending the Department of Orthodontics and Dentofacial Orthopaedics, Divya Jyoti College of Dental Science and Research in Uttar Pradesh, India and enrolled after obtaining the necessary informed consent.

The following inclusion criteria were considered for case selection:

The following exclusion criteria were considered:

All patients participating in the study were bonded by a single operator with a pre-adjusted edgewise fixed appliance (Ormco) MBT prescription using an 0.022 × 0.028-inch slot. A standardised six-weekly arch wire sequence was used for alignment, followed by a working arch wire of 0.019 × 0.025-inch stainless steel (G&H, Franklin, Indiana, USA).

Patients were randomly assigned to one of the following groups, Group-I and Group-II, each consisting of 20 patients, who were further subdivided into subgroups A and B consisting of 10 patients, according to the allocation of the test maxillary quadrant. Group-I A and Group-II A were the experimental quadrants in which 3 MOPs and 2 MOPs were performed, respectively, and Group-I B and Group-II B served as control quadrants. Mini-implants of 1.6-mm diameter (FavAnchor, Pitkar Orthotools Pvt Ltd, Pune, India) were buccally placed under local anaesthesia between the first permanent molar and second premolar for anchorage purposes to facilitate canine retraction. The retraction was carried out on the working arch wire using NiTi closed coil springs, delivering a force of 150g on each side. To standardise the amount of the closing force, a Dontrix measurement gauge was used. The retraction immediately commenced after the MOP procedure. Post-operative pain was evaluated for each subject using a visual analogue scale at 24 hrs, 48 hrs and at seven days.

The MOP procedure was performed under topical anaesthesia (2% lidocaine with 1:100,000 epinephrine). MOPs were placed distal to the canines, 2 mm apart and 3 mm in depth (measured using a rubber stopper to standardise the penetration depth), at the coronal, middle and apical regions in a vertical direction using a FavAnchor miniscrew of 1.6 mm diameter and 8 mm length. In Group-I A, three MOPs and in Group-II A, two MOPs were made directly through the buccal mucosa distal to the canine (Fig. 1A and B).

Figure 1.

The primary outcome was to evaluate the rate of space closure in millimeters/month. The MOP procedure was repeated every 30 days until the study period was completed (3 months). Canine retraction was measured on study casts obtained at each time interval and by drawing two perpendicular lines from the mesial point of the 3rd palatal rugae (reference point) and the distal side of the canine to the mid-palatine suture from both sides. With the help of a digital Vernier Calliper, this enabled the determination and comparison of the linear distance (Fig. 2).

Figure 2.

Pain perception was recorded using a 10 mm visual analogue scale (VAS) at three different time intervals, i.e. at 24 hrs, 48 hrs and at the 7th day after MOP. Patients were strictly instructed not to take any analgesics during the study period.

Data collection occurred for 3 months following the start of the mini-implant-facilitated canine movement. A baseline maxillary impression was taken before retraction started (T0). The clinical measurements to evaluate canine retraction were conducted every 30 days (T0, T1, T2 and T3).

Blinding clinicians and subjects was impossible due to the nature of the study. However, the data analyser was blinded regarding the experimental and control groups and the time intervals.

The data for the present study were analysed using the SPSS statistical software, version 23.0 (IBM, Armonk, NY, USA). The intragroup comparison for the different time intervals was conducted using Repeated Measures ANOVA to find differences between the individual time intervals. The level of significance for the present study was set at 5%. The intergroup comparison for the difference in mean scores between two independent groups was performed in the unpaired/independent t-test. The Shapiro–Wilk test was used to investigate the distribution of the data. The G Power Version 3.1.9.6 program was used to determine the power analysis of the study. Based on an 80% power of the study and 5 percent type I error and effect size of 0.90, the sample size was determined to be 15 for each group.

The current study determined that a definite acceleration of tooth movement occurred when a MOP procedure was performed prior to tooth retraction.

Of the various surgical methods, micro-osteoperforation is a minimally invasive technique. The concept is similar to other surgical procedures in which damaging or traumatising the cortical alveolar bone causes a localised inflammatory response, thereby increasing bone turnover and the rate of tooth movement. MOPs cause bone injury leading to cytokine release, to accelerate bone turnover and decrease regional bone density via an iatrogenic inflammatory cascade. This phenomenon is known as a regional acceleratory phenomenon described by Frost.⁵ Technological advances such as PROPEL (Ossining, NY, USA) were introduced to meet this demand but came with a high cost coupled with problems of availability. However, Cheung et al.,¹³ Aksakalli et al.,¹⁴ and Haliloglu-Ozkan et al.¹⁶ reported that mini-screw facilitated micro-osteoperforation can satisfactorily serve as a minimally invasive method with an economic advantage.

In a consideration of the economic benefits, a mini-screw was used for carrying out the MOP procedure in the present study. Lesaffre et al.⁸ elaborated that the attractiveness of the split-mouth design removed all components related to variations between subjects by making within-patient comparisons rather than between-patient comparisons. Pandis et al.¹⁰ explained that a key advantage of this study design is the smaller sample size required compared with a parallel-group design. Evidence from the literature indicates that numerous studies using a split-mouth study design have been conducted.^{11,14,15,17,21} Hence, the current study followed a split-mouth design.

A flapless MOP procedure using a mini-implant was performed in the designated maxillary quadrant of each patient in both groups (Group I and Group II) at T0, T1 and T2 following the method recommended by Jaiswal et al.²² Jaiswal et al. suggested that a two-time MOP intervention was more effective than a one-time MOP procedure in accelerating tooth movement. In addition, Bavikati et al.²³ concluded that for enhanced efficiency, MOPs should be repeated every 6-8 weeks. However, Teixeira et al.,⁹ Alikhani et al.¹¹ and Alansari et al.¹² conducted MOPs at the initial time point based on the findings of Frost⁶ in that the effect of a regional acceleratory phenomenon peaks at 1 to 2 months and subsequently subsides. Similar to Aksakalli et al.,¹⁴ the current research applied three MOPs distal to the canines using mini-screws of 8 mm in length and 1.6 mm in diameter, with each perforation 3 mm deep and calibrated by a rubber stopper. Sangsuwon et al.⁵ indicated that MOPs should be applied close to the target teeth and far from the anchor teeth to obtain maximum effect. Therefore, the MOPs were applied at the distal margin of the canine. Similar to the study by Haliloglu-Ozkan et al.¹⁶ and Alkebsi et al.,¹⁷ the current research individualised canine retraction using a 150 gm pre-calibrated NiTi closed coil spring.

An accurate measurement of space closure would validate the rate of tooth movement and provide insight into the efficacy of micro-osteoperforation. Since Almeida et al.⁷ concluded that landmarks on the palatal raphe and palatal rugae may be considered stable reference points. Canine retraction was measured using traditional cast methods at each time interval. The linear distance was compared and determined by drawing two perpendicular lines from the mesial point of the third rugae (reference point) and the distal side of the canine to the mid-palatine suture with the help of a digital Vernier calliper. Alikhani et al.¹¹ measured tooth movement on casts by drawing a line that divided the lateral incisor and the canine into equal halves. Haliloglu-Ozkan et al.¹⁶ used the canine cusp tip and second bicuspid cusp tip as references for superimposition on digital models, and by comparing the initial and the final outcome. In the current study, the primary outcome showed that there was a significant increase in the rate of canine retraction on the 3MOP side compared to the control side at all-time intervals in group I, which is similar to the results described by Alikhani et al.,¹¹ Attri et al.,¹⁸ Sivarajan et al.,¹⁹ and Aboalnaga et al.²⁰

There was no significant difference in the rate of canine retraction in group II between the 2MOPs and the control side. This result may be due to the lesser amount of bone injury (less trauma), which led to a reduced tissue strain level and less cell activity level by osteoblasts and osteoclasts (i.e. less inflammatory response). As Frost⁶ suggested, increased bone injury led to cytokine release which accelerated bone turnover. In the present study, the rate of canine retraction was significantly higher following the 3MOP procedure in comparison with the 2MOP procedure. This finding may be due to the more significant surgical trauma, which generated a higher rate of inflammatory response and osteoclast activity which, in turn, increased the rate of tooth movement as suggested by Frost.⁶ In addition, Jaiswal et al.²² and Bavikati et al.²³ concluded that, for enhanced efficiency, MOPs should be repeated every 6-8 weeks.

In the present study, inflammatory markers were not assessed and the follow-up period did not continue until complete canine retraction. The sample size was likely too small for accurate pain assessment. Therefore, these factors were considered limitations of the study.

Further studies involving a larger sample size with different age and population groups segregated into different growth patterns by including the mandibular quadrants would provide further insight.

The present study’s findings suggest that the MOP procedure is a safe and minimally invasive chairside technique.

The 3 MOPs procedure showed more effective and faster tooth movement than the 2 MOPs.