Introduction

One of the major problems with orthodontic therapy is its prolonged duration, which forces patients to select alternate therapy modalities with subpar outcomes and negative side effects. Additionally, it may worsen any unfavorable effects brought on by orthodontic treatment. The frequency of white spot plaques and caries, periodontal issues, soft tissue trauma, and orthodontically driven root resorption are all closely correlated with the length of the therapy. Since the invention of fixed orthodontics, researchers and practitioners have attempted to shorten the length of treatment using various techniques and appliances with varying degrees of success [1, 2]. Self-ligating braces, wires and brackets manufactured to demand, medicines, cell mediator injections, low-level laser and phototherapy are examples of nonsurgical therapies to reduce orthodontic treatment time. Additionally, surgical procedures have been performed to shorten the length of the treatment after speeding up tooth movement. Less invasive surgical procedures include piezocisions, piezopunctures, and micro-osteoperforations, as well as osteotomies and corticotomies surgical procedures with or without bone grafts [3, 4].

MOP, i.e., micro osteotomic perforations, have been utilized to activate the bone's inherent mechanisms, which quicken tooth movement. Orthodontic forces cause the periodontal ligament (PDL) to be under more strain, which causes the intended resorption and deposition of the tooth's surrounding bone. This results in orthodontic tooth movement. To increase the activity of osteoblasts as well as osteoclasts for bone resorption, the PDL stress triggers the release of inflammatory cytokines and other inflammatory mediators [5, 6].

Inflammatory mediators can be elevated by a surgically induced traumatic event, which momentarily increases bone metabolic activity and resorption. This phenomenon of micro orthodontic perforation can be described as the localized acceleratory process, and it may have an impact on how quickly teeth move.  Following surgical procedures like corticotomy, MOP, & corticision, the number of degenerative bone biomarkers such as TNF- and TRAP+ osteoclasts are noticeably increased and is consistent across various interventions [7, 8].  The pace of tooth movement in orthodontic tooth movement has been most significantly and consistently impacted by surgical techniques like corticotomies involving mucoperiosteal flaps and osteotomy surgical techniques.  However, because these procedures are intrusive, unpleasant, and expensive, doctors do not frequently use these traditional surgical techniques. Moreover, an additional specialist doctor will be required to carry out these procedures [9, 10].

In order to address these issues, less invasive surgical techniques such as micro-osteoperforation, piezopuncture and piezocision have been designed. In piezocision, the corticotomies are made through the gingiva, but in corticision, the corticotomies are made through the cortex bone without using mucoperiosteal flaps. Additionally, the micro-osteoperforation technique uses mini-screws or the Propel device to start the bone injury, while piezopuncture uses piezoelectrical equipment with a sharp point to induce some breaches in the cortex [11, 12]. The MOP fixes most issues brought on by conventional surgical procedures. However, unlike other less extensive surgical procedures, it can be carried out by an orthodontist using widely accessible orthodontic tools to quicken tooth movement. It makes difficult orthodontic movements simpler and aids in anchoring adjustment. Although MOP is still a recent technique, there are contradictory findings regarding its positive and negative consequences. This study attempted to integrate these findings and assess how MOP affected the speed of tooth movement. Additionally, it evaluated any negative impacts the intervention might have on the patients receiving it [13, 14].

Basics of MOP

By triggering the production of cytokines that attract osteoclasts to the site of injury and accelerate bone resorption, MOPs cause a decrease in bone density. MOPs are minimally invasive because flap elevation is not needed during the surgery. Micro-osteoperforations (MOPs) are most basically defined as localized trauma to the alveolar bone. Micro-osteoperforations are an ancillary method for speeding the rate of OTM by producing transmucosal osteoperforations in the cortical bone, around the teeth that require movement, according to a group of orthodontists who first presented the technique [15, 16]. They noted more osteoclastic and bone remodeling activity at the perforation sites, and increased tooth mobility in their initial animal investigation of MOPs on rats. Encouraged by these findings, they performed clinical studies on 20 elderly patients having class II division I malocclusion. They saw a rise in the levels of chemokines and cytokines, which are chemical mediators that stimulate osteoclastic activity. They observed that the pace of canine retraction surged 2.3 times following the 28-day testing period, which encouraged them to believe that using MOPs could speed up the entire orthodontic treatment process [17, 18].

How does MOP work

By triggering Frost's (1983) "Regional Acceleratory Phenomenon" (RAP), which describes the amplification of the alveolar bone's regenerative process in response to unpleasant stimuli, MOPs increase the rate of bone resorption. The localized trauma caused by MOPs leads to transient osteopenia. As a result, tooth movement is expedited through the perforated alveolus since it has less bone resistance [19, 20]. The rise in local pro-inflammatory chemical mediators, such as chemokines and cytokines, is the cause of the temporary osteopenia seen after the activation of RAP. Increased bone turnover and decreased resistance to tooth movement arise from these chemical mediators penetrating the alveolus around the MOPs and activating osteoclastic activity. Using the prostaglandin E2 or the RANK/RANKL pathway, chemokines recruit osteoclast precursor cells and cytokines and trigger the differentiation of adult osteoclasts from the precursor cells [21-25].

Higher osteoclast activity, a higher rate of resorption, and a resulting decrease in bone density are brought on by the increased release of these substances. MOP can be employed in clinical situations where dense cortical bone restrains the orthodontic results since the activated osteoclasts temporarily reduce bone density. According to a study, MOPs cause the periodontal ligament cells to undergo apoptosis and activate the pathways that cause cell proliferation. In response to orthodontic stresses, the aforementioned physiologic processes quicken tooth movement [26-29].

Any orthodontic appliance not limited to fixed appliances, removable appliances, transparent aligners, etc., can be complemented by MOP. The osteoclasts are activated by chemical mediators such as CCL 3, CCL 5, and IL 8 released in response to tooth movement. Proteins specifically from the cytokine family are also secreted in addition to chemokines. Macrophages and cells generate these pro-inflammatory cytokines in the periodontium, including fibroblasts, endothelial cells, and osteoblasts [19, 30, 31]. They amplify or maintain the inflammatory response while triggering bone resorption. Chemokines from the surrounding blood arteries invade the alveolus during orthodontic tooth movement and develop into macrophages or osteoclasts. One chemokine is Monocyte Chemoattractant Proteins (MCP-1), also known as Chemokine Ligand (CCl-2). In a split-mouth investigation studies evaluated the bone structures at the sites after performing surgical insults on the bone surrounding the maxillary second premolars [32-34]. They concluded that more surgical insults result in a lesser maturity of the bone surrounding the teeth being moved, less bone quantity, poorer bone density, increased osteoclastic activity, and faster orthodontic tooth movement. Applying orthodontic forces during tooth movement triggers an array of chemical reactions linked to aseptic inflammation. According to the events' sequelae, orthodontic tooth movement is a "periodontal phenomenon" accompanied by a considerable rise in leucocyte concentration in the alveolar bone [35-38].

How the procedure of MOP carried out clinically

The treatment is most typically performed on the buccal cortex. Radiographs can be used to assess the quality of the bone, the position of nearby important structures, the width of the interradicular bone, and other factors. Before beginning MOP, informed consent should be acquired. To rule out the possibility of postoperative adverse effects, the practitioner should thoroughly review the patient's medical and dental histories. The site should be as close to the target teeth as possible, away from the anchor teeth, in the associated gingiva, and up to 1mm superior to the mucogingival junction to maximize the effects of MOP. Planning extractions closure to MOP procedures may have an additional impact on the action of MOPs because tooth extraction also activates RAP [39-41]. MOP should be positioned more apically and, if possible, oriented apically for root position modifications like incursion and/or torque correction so that it may be applied through the associated gingiva. The doctor can still access the apical tissues.

Which instruments are used in carrying out MOP

The MOP tool introduced by Propel INC, is a portable disposable used to administer tiny osteoperforations. The device has a 1.5mm width and a depth that can be adjusted between 3,5 and 7mm. Even if the Propel device was created specifically for MOPs, it is not yet a part of clinical practice. Nevertheless, an increasing number of researchers are experimenting with mini-implants for the same reason. Propel INC has been used in investigations by several other researchers [18, 42].

Mini-implants have recently been used in scientific experiments, and comparable outcomes have been noted. MOPs have been successfully implanted using self-drilling mini-implants with a thickness range of 1.2 mm to 1.8 mm. Any armamentarium that causes the desired thickness and depth is favored since biochemical and molecular events are thought to occur consistently regardless of the instrument utilized as long as the depth and design are followed [24, 43].

What care should be taken post-operatively after MOP

A recent mouse study found a vitamin E-enriched diet to have a favorable impact on the rate of OTM. Therefore, additional research may determine whether vitamin E supplementation could be utilized in conjunction with MOPs for greater success. To preserve periodontal health, patients should be instructed to gargle with 0.2 percent Chlorhexidine (CHX) mouthwash twice daily for five days.  Regular mouthwashes and saltwater rinses can be used in place of chlorhexidine mouthwash if patients have satisfactory periodontal health. Following the first day of the procedure, it was reported that there was little to no pain or discomfort, for which analgesics are unnecessary [44, 45]. But because every person experiences pain differently, acetaminophen is the go-to analgesic. Because they are known to slow the pace of OTM, analgesics such Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) were contraindicated.

How many times should the MOP be carried out to achieve the desired results

According to clinical studies conducted on animals, the rise in pro-inflammatory chemical markers lasts only 14 to 28 days. It was seen that the levels of pro-inflammatory chemical markers decreased to the baseline after this time. Researchers recommended that MOPs be repeated every 28 days until the intended outcome was attained as a result of this. It is more cost-effective because a doctor does not need a larger inventory. After all, the process can be done with microscrews [46-49].

Alikhani and colleagues compared the effects of one, three, and four micro osteoperforations on the acceleration of OTM. They concluded that while a single MOP was ineffective in producing the desired results, three to four MOPs produced the best results [10]. Feizbakhsh and colleagues discovered that even 2 MOPs were sufficient to produce the desired effects. Consequently, there were typically 2-4 perforations per site, spaced 2 mm apart in the vertical direction [20, 50-53].

What should be the depth up to which penetration should be carried out

Feizbakhsh and associates found that even two MOPs were enough to achieve the required results. As a result, each site usually had 2-4 perforations that were 2 mm apart in the vertical direction [20].

Conditions where MOP can be applied

MOPs are recommended for accelerating tooth movement, facilitating root movement, the dental expansion that is symmetrical and asymmetrical, translating teeth into spaces lacking in structure, like old extraction spaces, and reducing root resorption brought on by orthodontic movements. According to previous research on orthodontic patients, age has an impact on bone quality, density, and metabolism. Therefore, to reduce confounding factors, most studies have concentrated on the 18–45 age group. When using MOPs for canine retraction, most studies have had beneficial results [52, 53].

In cases of open bite, it has been proved that the use of MOPs for molar intrusion without needing auxiliaries. The author showed that three-dimensional molar control prevented clockwise mandibular rotation in the repair of hyper-divergent patients with clear aligner therapy by combining clear aligners with selected micro osteoperforations in lateral and posterior locations [54-57].

Conditions where MOP should be avoided

Patients with widespread periodontitis with gingival and bone involvement should not undergo this surgery. Cardiovascular issues like angina pectoris, myocardial infarction, etc., pulmonary issues like chronic obstructive pulmonary disease, severe asthma, etc., renal issues like dialysis and transplant, hepatic issues resulting in impaired liver function, endocrine issues like diabetes mellitus, adrenal insufficiency, hyperthyroidism, etc., and hematological issues are just a few of the conditions that put a patient at high risk. Without previous medical approval, this treatment should not be performed on patients with systemic diseases who are high-risk candidates for infection and septicaemia [58-62].

Patient compliance regarding MOPs

Although MOPs are considered invasive operations, the absence of bone augmentation, corticotomy incisions, or flap elevation makes them more patient-friendly. According to documented patient instances, the patient did not experience pain or discomfort beyond the first 24 hours, which increased patient acceptance of the surgery and their willingness to have it repeated more than once. After the damage brought on by osteoperforations, it has been. discovered that MOPs had a stronger impact on oral health-related quality of life (OHRQoL) [20, 63-66]. It was reported that MOPs mostly affected psychological discomfort and that these effects persisted for up to 3 days post-procedure. MOPs have also been the subject of several systematic reviews. The research does not appear to corroborate the assertions of statistically significant acceleration of tooth movement, according to studies by Fu et al., and Sivaranjan et al. [28, 29].

Canine retraction acceleration of 0.45mm/month was statistically significant but not clinically relevant, according to Shahabee et al.'s systematic review [24]. Given that the average premolar extraction space is 7.1mm, an acceleration of 0.45mm might reduce the length of the entire treatment by about 2 months. Furthermore, the rate of acceleration during en-masse retraction can be decreased, which raises the question of whether the repeated damage to the alveolar bone and its adverse effects are justified [11-12, 67-69].

Table 1. Details of systematic reviews on MOPs

Impact of MOPs on the Orthodontic tooth movement

Surgical guides are necessary to help the doctor prevent mistakes because the procedure's success depends on the accuracy of the perforation and location. There has not been much research done in this area recently. In a study using cadaver mandibles, it was found that using surgical guides that were 3D printed avoided root penetration on either side of the hole, thus lowering the possibility of adverse effects [70-73]. In their work, Alkasaby et al. successfully used a 3D-printed MOP surgical guide [13].

Table 2. Details of research conducted in animals on MOPs

Studies on MOPs have shown both conclusive and inconclusive results. Tables 1 and 2 provide a succinct summary of the change observed with MOPs and indicate if they were clinically relevant. Several studies have supported the idea that MOPs can double the rate of orthodontic tooth movement. Adult patients have a higher incidence of the atrophic ridge. External root resorption occurs more frequently and for longer periods when teeth are moving through atrophic ridges. A study detected a 1.8 times increase in OTM across the atrophic ridge with osteoperforations in a study that looked at the impact of osteoperforations on the atrophic ridge of beagle dogs. However, there was no appreciable increase in bone volume. Therefore, since more adult patients choose orthodontic treatment, extensive research is needed to understand how MOPs affect tooth movement across atrophic ridges [10, 78-81].

Long-term stability has not been the focus of much research. According to Reitan, remodeling of gingival fibers has taken 232 days and is supported by animal experiments on dogs. Due to insufficient time for gingival fiber remodeling, the acceleration of OTM may jeopardize the durability and retention of the results. Post retention follow-up is required to evaluate the long-term retention of the effects of rapid orthodontics. Bacteremia is a serious concern in any process when an instrument comes into contact with blood. This has been declared as fact for various surgical operations like the implantation and removal of molar bands, piezocision, etc. [15, 74, 82-84].

Despite being flapless, the MOP method still entails piercing the gingiva and making alveolar holes, which increases the risk of temporary bacteremia. Azeem et al., however, observed a low rate of these side effects (3.3 percent). Since there has not been much information reported on bacteremia linked to MOPs, doctors should use caution when applying the same. It is challenging to objectively assess the mean orthodontic tooth movement due to the lack of standardization of the device or wire used for retraction [18]. Alikhani et al. retracted the teeth more by tipping them than by moving the body, using a 0.16x0.022-inch wire in a 0.022-inch slot [14]. This could result in a false-positive test that shows faster tooth movement [15, 75-77, 81].

Studies with 0.019x0.025 inch SS wires reduced tooth tilting and provided a more accurate assessment of tooth movement. Alkebsi et al. found that anchorage loss was lower at MOP sites (0.39mm) than at control sites (0.36mm) but that the difference was statistically insignificant, making it impossible to accurately assess anchorage loss in the current literature because canine retraction places less stress on anchor units than end mass retraction [13]. According to the results of another investigation, anchoring loss is not statistically significantly impacted by MOPs [85].

Root resorption in MOP patients has to be studied more in-depth. In a study by Chan et al., greater root resorption of the maxillary first premolar at the location of MOPs was seen after applying a buccal tipping force of 150g for 28 days. According to the authors, when the bone turnover rate increases due to the perforation injuries to the alveolus, the worsening of root resorption near MOPs may subsequently impact the increase in osteoclastic activity [19]. However, according to other studies, MOPs did not raise the prevalence of root resorption. Significant root resorption was seen, and it was more pronounced on the control site than on the MOP side, according to Alkebsi et al. [13].

This is consistent with the results of Tsai et al., who found that the control group experienced statistically significantly more root resorption than the MOP group [30]. According to Alkasaby et al., MOP increased OIIRR for the mesiobuccal roots that were farther away from the MOP site and decreased orthodontically induced inflammatory root resorption (OIIRR) for the neighboring distobuccal roots through a decrease in the density of the surrounding alveolus [31]. Animal studies have also demonstrated full healing with minor root surface damage caused by mini-implants, resulting in normal periodontal structure. Continuous cementum repair occurs on the root surface at the injury site when mini-implants are placed and withdrawn immediately [86].

Therefore, it is wise to evaluate both the MOPs' action and the supporting periodontium's response before starting the process. Even in cases with an enhanced bone density that offers more resistance to orthodontic tooth movement, a decrease in the pace of tooth movement enables the clinician to minimize the overall treatment period for patients. According to studies, several therapeutic techniques, such as fixed mechanotherapy, detachable appliance therapy, molar distalization, and clear aligner therapy, can be complemented by MOP [87].

The tendency for a collection of teeth connected by a wire to distribute stresses equally is a significant problem in split-mouth investigations. Therefore, it is impossible to avoid force dispersal to adequately assess how the dental unit will respond to force applied, even if RAP remains confined to the point of application. For prolonged RAP benefits, it is necessary to repeat the MOP procedure until the desired results are obtained, according to previous clinical trials on animals that have shown that the concentration of chemical mediators or pro-inflammatory markers persist for 2-4 weeks, after which there is a gradual return to baseline levels. Further research is required to determine patient acceptance of MOP repetition until space closure is achieved.

Table 3. Details of studies carried out in humans concerned with MOPs