Comparison of Mini-implant-supported Mandibular Canine Retraction with and without Submucosal Injection of Plateletrich Plasma: A Split-mouth Study

INTRODUCTION

We live in an era of escalated self-consciousness, self-awareness, and self-presentation. We are not oblivious to the selfie phenomenon influencing millennials of the time. All of this translates to the heightened sense of self-esteem one seeks in society. Smile esthetics and facial appearance is an important factor in today’s world and demand for orthodontic treatment has been on the rise among adolescents, more so in adults of the present time. With technological advancement came the habit of getting a hold of everything at our fingertips, which to some extent has made all of us impatient or in other words a desire to get a hold on things at the earliest. The field of medicine and dentistry has been no exception to the above mandate. Over the past few decades, countless research has been undertaken on hastening the rate of tooth movement in the field of orthodontics as demand for rapid or shorter treatment timings has been on the rise, especially among adults who seek orthodontic care. Moreover, prolonged treatment time has its own counterproductive effects such as gingival recession, dental caries, root resorption, temporomandibular joint problems, etc. There have been a plethora of techniques for accelerating orthodontic tooth movement (OTM) ranging from surgical to non-surgical methods, of which the surgical techniques have proven to be the most promising. These techniques are based on the principle that when a bone is surgically wounded, an inflammatory cascade is initiated leading to osteoclastogenesis that ultimately accelerates the rate at which tooth moves within the bone (RAP—Regional Acceleratory Phenomenon). But these results do come with a price. In contrast to the noninvasive approaches, they lead to surgical injury to the bone that activates an elevated osteoclastic activity, resorption of the alveolar bone, reduction in alveolar bone density, and squandering of supporting bone of the teeth to be moved. Their disadvantages are that any surgical procedure is not appealing to both the patients and orthodontists and the reduction in alveolar bone volume which ultimately decreases the periodontal support of the target teeth. Other methods to mimic the effects of surgical insults involve the use of local administration of cytokines or hormones, but their clinical feasibility and safety on a systemic level raise many questions. Injection of autologous platelet-rich plasma (PRP) could be a promising substitute for bone surgery.¹ Recently, a novel minimally invasive approach consisting of local administration of PRP at the site of OTM has been developed and tested to reduce the time taken for orthodontic treatment. It has been hypothesized that PRP containing a high concentration of growth factors such as platelet-derived growth factor, transforming growth factor, endothelium growth factor, and the others effectively stimulates the normal healing process and bring about rapid tooth movement mimicking other invasive procedures in bringing about RAP. Thus, this study aims to compare the differences in the rate of individual canine retraction, with and without the administration of autologous PRP.

MATERIALS AND METHODS

The study sample involved individuals who presented to the Orthodontic clinic of JSSDCH as outpatients. Individuals satisfying the inclusion criteria were requested to sign an informed consent form provided they were interested in participation. Ethical clearance was obtained from the institutional ethical committee (JSSDCH IEC Research Protocol No: 20/2018).

RESULTS

The present study was undertaken to measure the differences in the rate of the mandibular canine retraction with and without submucosal administration of PRP with the help of mini-implants as posterior absolute anchorage unit.

The parent sample consisted of 15 patients, out of which 6 were males and 9 were females. The mean age was 21.7 ± 2.52 years. In this split-mouth study, PRP was injected in the attached gingiva and lingual mucosa of canine and extraction site of mandibular first premolar on the PRP side.

The mean time taken for the complete retraction of the canine for the PRP group and the control group was 5.96 ± 0.94 and 7.42 ± 1.12 months, respectively (Table 1 and Fig. 6).

The maximum rate of canine retraction for the PRP group was 1.13 mm/month and for the control group, it was 0.96 mm/month. The minimum rate of canine retraction was 0.65 mm/month for the PRP group and 0.47 mm/month for the control group. The mean rate of canine retraction for the PRP group and control group was 0.87 ± 0.12 and 0.7 ± 0.13 mm/month, respectively. The paired difference observed was 0.17067 mm/month, which was statistically significant (p < 0.001) (Tables 2 and 3, Fig. 6).

The individual canine retraction was found to be 1.24 times accelerated in the PRP group compared to the control group.

DISCUSSION

Out of the many detrimental factors hampering a person to smile, a major one is a malocclusion. The WHO estimates that malocclusion is one among the three most prevalent oral health problems, the others being dental caries and periodontal diseases.² As a result, the demand for orthodontic treatment is on the rise especially among adults and so is for shorter treatment duration. It appears there is no common consensus regarding overall orthodontic treatment duration. A recent systematic review revealed average treatment duration of 2 years (19.9 months). However, a wide range of treatment durations (14–33 months) were reported in the orthodontic literature.³

But the interesting fact is that when patients (adults, adolescents) and parents were asked about how long they would like treatment to last, 40.8% of adolescent patients answered less than 6 months, while 33.2% of them answered between 6 months and 12 months whereas, among adult patients, 42.9% answered between 6 months and 12 months, while 26.5% answered between 12 months and 18 months.⁴ This shows that not only will shorter treatment duration translate to better patient compliance and satisfaction but also reported to have a fewer incidence of iatrogenic factors like dental caries, gingival recession, and root resorption among many.⁵

The RAP was described first by Harold Frost as “a tissue reaction to different noxious stimuli that leads to recruitment of BMUs (basic multicellular units) that works overtime by which tissue regenerates faster than normal in a regional regeneration/remodeling process”.⁶ It is a heightened reaction that varies directly in duration, size, and intensity depending on the intensity of the stimulus, and is regarded a physiological “emergency” process that ultimately hastens the healing responses. The extent of RAP response is based on the character of tissue and mostly persists for nearly 4 months in human bone. This event brings about bone turnover 10–50 times faster than usual. Surgical techniques, such as corticotomies, piezocision, etc., that make use of the above phenomenon have been tried and tested and have proven to be quite successful in accelerating the rate of OTM. But these at the end of the day have their own degree of invasiveness and discomfort and would not be a patient’s as well as a clinician’s go-to choice at any point in time. This is where the quest for minimally invasive techniques to accelerate OTM gains its significance. In fact, a study conducted by Uribe et al. in 2014 points outpatients preferred minimally invasive techniques over traditional surgical methods as adjuncts to reduce orthodontic treatment time.⁴

Recently, a new technique has been proposed and tested where autologous PRP has been locally administered at the site of OTM as a means to accelerate the rate of tooth movement. It has been hypothesized that PRP can simulate the effects induced by the surgical therapy without having the disadvantage of invasiveness or aggressiveness as the case with the various surgical approaches.¹

Platelet-rich plasma is essentially an increased concentration of autologous platelets suspended in a small amount of plasma after centrifugation.⁷ Basically, the patient’s blood is collected and centrifuged at varying speeds until it separates into three layers: PPP, PRP, and red blood cells. Usually, two spins are used. The first spin (“Hard spin”) separates the PPP from the red fraction and PRP. The second spin (“Soft spin”) separates the red fraction from the PRP. The material with the highest specific gravity (PRP) will be deposited at the bottom of the tube. The whole process takes approximately 20 minutes and produces a platelet concentration of 3–5× that of native plasma.⁸

According to Liou, “single injection of PRP activity lasts for 5–6 months clinically and the fastest rate of acceleration is during the second to fourth month after the injection. According to his study, single injection of PRP in the beginning of treatment for the purpose of alignment and levelling is sufficient”.¹ Same dosage pattern and injection technique was followed as described by Liou in his study.

In the present study, PRP was injected in the attached gingiva and lingual mucosa of the canine and first premolar extraction site on the experimental side of the mandibular arch. To make sure that an identical amount of retraction forces are utilized for the canine retraction, the retraction auxiliary used in both the experimental and control side was nickel titanium closed coil springs (9 mm length) with TAD heads extending from the posterior implant head (placed between mandibular 1st molar and 2nd premolar) and the canine bracket power arm. A 100–150 g force is traditionally used in single canine retraction, therefore for the present study a 150 g force was employed that was measured using a Dontrix gauge.⁹

In the present study, microimplants were utilized to retract the mandibular canines instead of taking anchorage from the posterior molar teeth which made sure that there was absolutely no amount of anchorage loss that could have occurred or in other words the complete space gained by extraction of 1st bicuspid was utilized absolutely for canine retraction and did not result in mesial movement of the molar.

CONCLUSION

Within the constraints of the current study, it can be deduced that:

Submucosal injection of autologous PRP is an innovative, comfortable, safe, and minimally invasive method to accelerate tooth movement during orthodontic treatment. A 1.24 folds acceleration of tooth movement was found between the PRP and control group during canine retraction. More studies on the effect of PRP administration on the rate of tooth movement at different intervals of the canine retraction process warrant further investigations.

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