Extended orthodontic treatment duration on average 2–3 years^[1-3] poses challenges such as increased risk of dental caries, root resorption, periodontal complications, and reduced patient compliance.^[4-7] As a result, accelerating orthodontic tooth movement (OTM) has become a key area of interest in clinical orthodontics.

Recent findings showed that patients are willing to undergo additional procedures to reduce treatment duration and bear additional costs.^[8] In addition, bone anatomy and cortical bone thickness are also negatively associated with orthodontic treatment duration.^[9] Among the various strategies proposed for this purpose, including pharmacological agents, mechanical stimuli, and surgical methods,^[10-21] micro-osteoperforation (MOP) has emerged as a minimally invasive technique with considerable clinical potential.^[22-24] MOP enhances bone remodeling by inducing the regional acceleratory phenomenon (RAP), which temporarily increases local metabolic activity and facilitates faster tooth movement. This method offers the advantage of being flapless, simple to perform, and well-tolerated by patients. Most MOP techniques utilize mini-screws to create small perforations in the cortical bone. However, the clinical outcomes of MOP may vary depending on the number, location, and frequency of the perforations. While previous studies have confirmed the effectiveness of MOP compared to conventional treatment, few have compared different protocols of MOP using the same instrument, especially under controlled clinical conditions. The speed of tooth movement in more invasive surgeries, such as corticotomy, is higher than MOP, but adverse effects, such as pain, impact on quality of life, and swelling after corticotomy, have been reported to be longer and more severe.^[25]

Therefore, the aim of this randomized clinical trial was to compare two distinct MOP protocols using mini-screws. A standard protocol with four perforations in the center of the extraction site (MOP1), and a modified protocol involving the center of the extraction site, mesial and distal perforations adjacent to the first molar (MOP2) with regard to the rate and pattern of extraction space closure. We also evaluated whether these approaches differ in their effects on posterior versus anterior tooth movement and anchorage preservation.

Thirty patients (11 males, 19 females) participated in the study, randomly assigned to three equal groups: MOP1, MOP2, and a control group, each with 10 patients. All completed the study, and their results were included in the final analysis per the intention-to-treat principle. Tooth movement was assessed on both sides of the maxillary arch.

Thirty-four individuals were assessed for eligibility, with four excluded (one did not meet criteria, three opted out). Thus, 30 patients (11 males, 19 females) were included and randomly assigned to three equal groups: MOP1, MOP2, and control (10 patients each). All participants completed the study and were included in the final analysis based on the intention-to-treat principle. Tooth movement was assessed on both sides of the maxillary arch.

A CONSORT flow diagram illustrating participant progression throughout the trial is presented in Figure 1.

In the present study, the rate of tooth movement was found to be significantly greater in both MOP intervention groups compared to the control group. These findings are consistent with previous research by Alikhani et al., Attri et al., Feizbakhsh et al., Kundi, Singh et al., Kumar et al., Babanouri et al., and Sivarajan et al.^[21,26-32] However, the results differ from those reported by Alkebsi et al., Golshah et al., and Li et al.,^[24,33,34] who observed no significant difference between MOP and control groups when intraoral or extraoral measurements were used. Sivarajan et al.^[26] noted that MOP can significantly accelerate tooth movement statistically, but this may not always be clinically relevant. In contrast, Alikhani and Feizbakhsh et al.^[21,30], found clinically significant improvements in space closure with MOP.

In our study, four MOPs were performed using mini-screws in vertical and horizontal directions. This contrasts with previous studies such as those by Alikhani et al. and Attri et al.,^[21,32] who used three MOPs applied with the PROPEL device, and Feizbakhsh et al.,^[30] who used only two MOPs per quadrant. Given the ease of access and cost-effectiveness of mini-screws, combined with comparable efficacy to PROPEL, they are recommended as a practical tool for clinical MOP applications.

The optimal number of perforations remains controversial. According to Frost’s theory of the RAP, the degree of local inflammation – and thus bone remodeling – is directly related to the extent of surgical injury.^[35] However, Blasi and Pavlin suggested that in areas with limited interradicular space, fewer perforations may suffice.^[36] Subgroup analysis in recent meta-analyses has shown no significant difference between using two or three perforations, suggesting the number should be based on local anatomy and interradicular space.

In terms of malocclusion types, all participants in our study presented with Class I malocclusion requiring bilateral extraction of maxillary first premolars. Prior studies varied in this regard: Alikhani et al.,^[21] Alkebsi et al.,^[24] Golshah et al.,^[34] and Kundi^[28] focused on Class II div. 1, whereas Feizbakhsh et al.^[30] studied Class I bimaxillary protrusion, and Shrestha Singh and Babanouri et al.^[31] included both Class I and II. Some researchers, such as Dudic et al. and Haralur et al., have suggested that malocclusion type and interarch interference may affect tooth movement rate.^[37,38] However, a direct and consistent relationship between malocclusion type and tooth movement has not been conclusively established.

Our research is distinct because it uses en masse retraction with NiTi coil springs, unlike previous studies that relied on canine retraction with mini-screws between the second premolar and first molar, which could skew results due to their closeness to the perforation site.^[21,24,30] In addition, tools like elastomeric chains and MBT tie-backs in other studies may introduce variability from inconsistent force application.^[26,32]

Age is another well-documented factor influencing the rate of OTM. Studies have shown that younger patients undergoing active growth exhibit faster tooth movement than adults.^[24,37] To control for this variable, we limited our sample to individuals aged 17–30 years, with a mean age of 23.47 ± 3.02 years, similar to other studies on MOP efficacy.

Our study tracked participants for 12 weeks, administering MOP three times at monthly intervals. In contrast, most previous studies, including those by Alikhani, Attri, Feizbakhsh, and Kundi et al.,^{[21,28,30,32]} only evaluated outcomes up to 4 weeks post-MOP, limiting their long-term analysis. Blasi and Pavlin^[36] highlighted the necessity of MOP every 4 weeks for effectiveness. Although Alkebsi et al.^[24] monitored patients for 12 weeks, they only applied MOP once, which may account for their ambiguous results. Similarly, Sivarajan et al.^[26] found no significant benefit in increasing MOP frequency, as their assessment was restricted to a single endpoint without considering monthly variations.

Some trials also failed to demonstrate clinical significance. For example, Jiaojiao Li et al.^[33] applied MOPs with a 5 mm depth twice over 12 weeks, but observed no significant improvement in premolar space closure. Similarly, Amin Golshah et al.^[34] reported no significant differences in canine retraction over 5 months but did find reduced canine tipping in the MOP group. Importantly, gender had no effect on outcomes in that study.

Prashant Kumar et al.^[29] demonstrated that MOP significantly accelerated OTM during both intervention (T0–T2) and postintervention (T2–T4) phases over 4 months. Shrestha Singh et al.^[27] also found a twofold increase in canine retraction on the MOP side versus control after 56 days, though no difference was found between MOP1 and MOP2 groups. In MOP1 patients received 3 buccal MOPs on the experimental side and in MOP2, Patients received 3 buccal MOPs + 3 palatal MOPs on the experimental side. Babanouri et al. observed a trend toward faster movement with MOP, although results did not reach statistical significance.^[31]

Study limitations include individual variability in biological response to MOP and potential side effects such as pain or inflammation. The procedure requires specialized equipment and time, increasing cost and limiting accessibility. Generalizability is restricted due to the exclusion of patients with systemic conditions or poor bone quality. Recruitment from a single center may have introduced selection bias, and investigator blinding was not feasible. In addition, the small sample size and short follow-up may have limited the ability to detect subtle treatment differences.

The findings of this study are most applicable to young adult patients aged 17–30 years with Class I malocclusion requiring bilateral premolar extraction. Generalizability to other malocclusion types, age groups such as adolescents or older adults, or individuals with poor bone quality is uncertain. As the study was conducted at a single academic center using mini-screws, replication in varied clinical settings with different levels of practitioner expertise and equipment is necessary. Furthermore, the use of en masse retraction with NiTi coil springs may limit applicability to practices using different mechanics.

This study demonstrated that MOP significantly enhances the rate of OTM. After 3 months, both MOP1 and MOP2 groups achieved approximately 0.9 mm more space closure than controls, with no clinically meaningful difference between them. MOP also reduced tipping of adjacent teeth, with mean angular changes of −6.59° ± 0.9° in the control group, −3.03° ± 0.51° in MOP1, and −2.91° ± 0.64° in MOP2, indicating the most favorable control of tipping in the MOP2 group. Anterior teeth consistently showed greater movement across all groups. Although MOP is generally safe and effective, its use should be tailored to each patient, considering potential risks alongside the anticipated benefits.