The development of submucosal injection of platelet rich plasma for accelerating orthodontic tooth movement and preserving pressure side alveolar bone

INTRODUCTION

Several noninvasive or invasive techniques have been proposed clinically or experimentally for accelerating orthodontic tooth movement. The noninvasive techniques include the biomechanical approach such as the self-ligation brackets,^[1-6] the physiological approach such as the direct electric current stimulation,^[7-9] low dose laser therapy,^[10-17] vibration,^[18-22] or photobiomodulation,^[23,24] and the pharmacological approach such as the injection of prostaglandin^[25-27] or relaxin.^[28-32]

Vibration or photobiomodulation is among the latest noninvasive developments that could be the most feasible and practical methods for accelerating orthodontic tooth movement, but they still need more experimental and clinical studies to prove their clinical effectiveness.^[33,34] Currently, the surgical-assisted approaches have been proved experimentally and clinically to be the most effective technique in accelerating orthodontic tooth movement.^[35] These invasive techniques include the rapid canine retraction through distraction of periodontal ligament,^[36-40] rapid canine retraction through distraction of dentoalveolus,^[41-43] periodontally accelerated osteogenic orthodontics (PAOO),^[44,45] corticision,^[46] orthognathic surgery,^[47] piezocision,^[48,49] piezopuncture,^[50] and micro-osteoperforation.^[51] In comparison to the noninvasive approaches, they all have surgical insults to the bone that trigger a higher osteoclastic activity, resorption of the alveolar bone, decrease of the alveolar bone density, and loss of alveolar bone of the target teeth.^[44-51] Their disadvantages are the surgery is not friendly to both of the patients and orthodontists, and the loss of alveolar bone that undermines the periodontal support of the target teeth.

It is, therefore, the PAOO included the bone allograft materials to expand the alveolar bone volume to compensate the extensive loss of alveolar bone after the corticotomy, and the other surgical-assisted techniques tried to reduce the surgery from a radical and extensive surgical insult toward a conservative and limited surgical insult. This could be elucidated sequentially by the change of surgical technique of bone insult from an extensive insult of bone through flap surgery in PAOO to a flapless and moderate insult of bone in corticision or piezocision, and then toward a minimal insult of bone in piezopuncture or micro-osteoperforation.

However, the effect of a minimal insult is not equal to that of an extensive insult. It has been revealed experimentally that the intensity and extensity of accelerating tooth movement depend on the intensity and extensity of the surgical insult.^[52] The bigger the intensity and extensity the surgical insult the higher the intensity and extensity of the acceleration. In other words, a minimal insult of bone might not be able to trigger a strong and long lasting effect on accelerating orthodontic tooth movement. To simulate the effects of surgical insult without surgery, the local injection of cytokines or hormone could be a substitute for the surgical insults,^[25-27] but it is not practical clinically due to its systemic effects and the need of frequent injections. Injection of autologous platelet rich plasma (PRP) could be a better substitute for bone surgery.

THE PLATELET RICH PLASMA

Platelets are one of the initiators both in the soft and hard tissue wound healing processes. Platelets contain growth factors such as the platelet-derived growth factor, transforming growth factor, endothelium growth factor, and the others. These growth factors are critical in the regulation and stimulation of the wound healing process, and they play an important role in regulating cellular processes such as mitogenesis, chemotaxis, differentiation, and metabolism.^[53] Peripheral blood contains 94% of red blood cells (RBCs), 6% of platelets, and <1% of white blood cells (WBCs), while PRP contains 5% of RBCs, 1% of WBC, and 94% of platelets. PRP has been applied in dentistry for its capability of enhancing osseointegration of a dental implant and augmentation of alveolar bone height in maxillary sinus lift.^[54-60]

In contrast to the other medical professions, the PRP in dentistry is always prepared by mixing with calcium chloride (CaCl₂) and thrombin to coagulate the platelets into a gel form and activate the containing growth factors before being applied to the region of interest through a full thickness flap operation. The CaCl₂ and thrombin initiate a burst release and activation of all the growth factors of PRP all at once. It is, therefore, the duration of action of PRP is short. On the other hand, the flap surgery is invasive in nature and causes the regional acceleratory phenomenon that induces a severe alveolar bone resorption and, therefore, might diminish some of the osteogenic effects of PRP. However, due to its gel form, flap operation, and short duration of action, this preparation for PRP is not suitable for orthodontic purposes.

A suitable PRP for orthodontic purposes should be injectable and has a long lasting effect. To develop an injectable PRP with a prolong effect on the target tissue, a simple approach is to prepare the PRP without mixing with CaCl₂ and thrombin, so that it could be maintained in a liquid form and be injectable.

THE PREPARATION OF PLATELET RICH PLASMA FOR ORTHODONTIC PURPOSES

The autologous PRP should be prepared under aseptic processing procedures [Figure 1].

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Figure 1

The preparation of platelet rich plasma. (1a-c): The blood sample is first centrifuged under 1000 rpm for 12 min and separated into the red blood cells at the bottom, the buffy coat (platelets) in the middle, and the platelet poor plasma at the top. (2a-c): The buffy coat and platelet poor plasma are pipetted and collected with care, and centrifuged again under 3000 rpm for 8 min. (3a-c): After the second centrifugation, the platelet poor plasma is removed until 4 ml remained and then the remaining platelet poor plasma is mixed with the buffy coat to become platelet rich plasma.

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• A volume of 60 ml of whole blood is drawn from the medial cubital vein of a patient using three 30 ml syringes that each contained 3 ml of 10% sodium citrate solution as an anticoagulant. Heparin is not recommended for using as the anticoagulant due to its systemic effects and inducing alveolar bone resorption. One ml of the blood is used for checking the platelet counts.

• The remaining 59 ml of whole blood is first centrifuged under 1000 rpm for 12 min at room temperature. The blood is then separated into its 3 basic components as the RBCs at the bottom, the buffy coat (platelets) in the middle, and the platelet poor plasma (PPP) at the top.

• The RBCs is discarded, and the remaining buffy coat and PPP are collected and centrifuged again under 3000 rpm for 8 min. After the second centrifugation, the PPP is removed until 4 ml remained and then the remaining PPP is mixed with the buffy coat to become PRP. One ml of the PRP is analyzed for its platelet count.

Under such a preparation, the PRP contains anticoagulant, high concentration of platelets, and a few of RBCs and WBCs, and it has to be injected shortly after its preparation.

THE SUBMUCOSAL INJECTION OF PLATELET RICH PLASMA FOR ORTHODONTIC PURPOSES

The PRP together with the containing anticoagulant is injected submucosally. Due to the presence of anticoagulant, we surmised that after injection of PRP, only part of the platelets adhere and aggregate little by little on the surfaces of collagen fibers, the intrinsic and extrinsic pathways of hemostasis initiate to generate thrombin gradually, platelet clots lay down little by little above the periosteum, and then the growth factors release and infiltrate little by little into the periosteum and alveolar bone. The procedures of injection are summarized as follows [Figure 2]:

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Figure 2

The platelet rich plasma is injected through the attached gingivae into oral mucosa to avoid leakage using a 27-gauge dental needle. (a): The submucosal injection of platelet rich plasma for the anterior teeth. (b): The submucosal injection of platelet rich plasma for the posterior teeth.

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• Before the injection of PRP, local anesthesia (Xylocaine) should be injected at the target sites for the pain control.

• For each target site, 0.7 ml of PRP could be injected. It is better to inject through the attached gingivae into the oral mucosa using a 27-gauge dental needle to avoid leakage of the PRP.

• It is a submucosal injection rather than a sub-periosteal injection. It is just similar to the injection of local anesthesia, and it has no certain injection pattern.

• Acetaminophen (500 mg) could be prescribed for the postinjection pain control. Nonsteroidal anti-inflammatory drug will neutralize the effects PRP and is not appropriated for the postinjection pain control.

Eighty-five percent of the patients reported 6–12 h of acceptable postinjection discomfort including intraoral mucosal swelling, itching sensation and mild to moderate pain, but 15% of the patients reported severe pain. The intensity of postinjection discomfort varies with the concentration of PRP. It has been observed clinically that the higher the concentration of PRP the more the postinjection discomfort.

THE CLINICAL APPLICATIONS FOR PLATELET RICH PLASMA SUBMUCOSAL INJECTION

The injection of PRP could be applied for accelerating orthodontic tooth alignment and leveling in anterior crowding [Figure 3], and space closure in en masse anterior retraction [Figure 3] or molar protraction [Figure 4]. It could also be used for preserving the pressure side alveolar bone of en masse anterior retraction.

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Figure 3

The platelet rich plasma application for accelerating the alignment of anterior crowding and space closure in a case treated with upper and lower premolar extraction. (1a-e): The first platelet rich plasma injection in the upper and lower anterior teeth. (2a-e): 3 months after the first platelet rich plasma injection. (3a-e): 6 months after the first platelet rich plasma application and the second boost of platelet rich plasma injection. (4a-e): The extraction space was closed 3 months after the second boost of platelet rich plasma injection.

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Figure 4

The platelet rich plasma application for upper and lower molars protraction with temporary anchorage devices. (1a-e): The first application of platelet rich plasma at the #36, 46, and #16. (2a-e): The upper space was closed 6 months after the first platelet rich plasma injection, and the second platelet rich plasma was injected for the further space closure in the lower. (3a-e): The lower space was closed 2 months after the second injection of platelet rich plasma.

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• The target sites of injection are the labial and lingual/palatal sides of the anterior teeth when the purpose of injection is to accelerate the alignment and leveling.

• The target site is the lingual/palatal side of anterior teeth when the purpose is to accelerate anterior retraction or to preserve the pressure side alveolar bone.

• The target sites could be the buccal, lingual/palatal, and mesial sides of the posterior teeth when the purpose is to accelerate the protraction of posterior teeth or preserve the alveolar bone of the protracted posterior teeth.

THE DOSAGE AND EFFECTS OF SUBMUCOSAL INJECTION OF PLATELET RICH PLASMA

A single injection of PRP lasts for 5–6 months clinically. It has been observed clinically that the fastest rate of acceleration is during the second to fourth month after the injection. The applied regimen for different purposes is summarized:

• Single injection of PRP in the beginning of treatment for the purpose of alignment and leveling.

• One injection of PRP in the beginning and another boost of injection 6 months after the first injection for the purpose of anterior retraction.

• One injection of PRP in the beginning and another boost of injection 6 months after the first injection for the purpose of protraction of posterior teeth.

Our clinical data revealed that the submucosal injection of PRP accelerated orthodontic tooth alignment and decreased the alveolar bone loss on the pressure side of orthodontic tooth movement. The injection of PRP accelerated the mandibular or maxillary anterior teeth alignment 1.7 folds in average (range from 1.3 to 2.1 folds), and the acceleration was dose-dependent when the PRP fold (platelet count in PRP/platelet count in blood) was <12.5. The optimal PRP fold for a more than 2-fold of acceleration of orthodontic alignment was found to be 9.5 to 12.5 folds.

On the other hand, the submucosal injection of PRP in the pressure side of en masse anterior retraction decreased 71–77% of alveolar bone loss, and this was PRP dose-dependent. The pressure side was found having no alveolar bone loss when the PRP fold was higher than 11.0.

In summary, the optimal PRP fold for a higher than 2-fold acceleration of orthodontic tooth movement and no pressure side alveolar bone loss is 11.0–12.5.

THE PREPARATION OF OPTIMAL PLATELET RICH PLASMA DOSAGE

The easiest way to prepare an 11.0–12.5 folds of PRP is to dilute a known high concentration PRP with certain amount of PPP. The high concentration PRP could be prepared by removing most of the PPP without disturbing the buffy coat at the bottom after the second centrifuge. For example, we could prepare 1.0 ml of 22 folds of high concentration PRP and then dilute with 1.0 ml of PPP to obtain 2.0 ml of 11.0 folds of PRP.

CONCLUSIONS

The submucosal injection of PRP is a clinically feasible and effective technique to accelerate orthodontic tooth movement and at the same time, preserve the alveolar bone on the pressure side of orthodontic tooth movement, and the optimal dose of PRP for the best clinical performance is 11.0–12.5 folds.