Effect of injectable platelet-rich fibrin on orthodontically induced apical root resorption following non-extraction-based orthodontic treatment in adults: A randomized controlled clinical trial

Abstract

Objective

To investigate the effect of repeated submucosal administration of injectable platelet-rich fibrin in the buccal region of the lower incisors on orthodontically induced apical root resorption in patients with moderate crowding.

Methods

Thirty-six patients (8 males and 28 females; mean age, 20.22 ± 2.55 years) with Class l malocclusion and moderate mandibular incisors crowding (4–6 mm) were included. Participants were randomly assigned to the control or 4-time injectable platelet-rich fibrin group. Fixed orthodontic treatment was performed, and the injection was administered directly after bonding the mandibular brackets during four sessions conducted at 28-day intervals. The orthodontically induced root resorption was assessed using cone-beam computed tomography images by measuring the root length.

Results

All 36 patients completed the orthodontic treatment. The average root resorption of the lower incisors was 0.53 ± 0.09 mm (p < 0.001) and 0.49 ± 0.08 mm (p < 0.001) in the control and experimental groups, respectively. However, no significant difference was observed between the study groups regarding the reduction in tooth length after the orthodontic treatment (mean difference  0.04 mm; p = 0.741).

Conclusion

Herein, repeated administration of injectable platelet-rich fibrin was not effective in decreasing apical root resorption following orthodontic treatment.

Registration: This study was registered in the ClinicalTrials.gov registry (NCT07352241).

Introduction

Teeth crowding is widely recognized as one of the most prevalent forms of malocclusion.^1,2 This condition can adversely affect both the psychosocial and physical aspects of oral health ³ as well as patients’ perceived cognitive abilities. ⁴ Furthermore, it is associated with an increased risk of dental caries, gingivitis, and various other oral health disorders.^5–7 The treatment of crowding may also result in several complications, including orthodontically induced root resorption (OIRR), ⁸ development of white spots on the enamel, ⁸ and poor patient compliance.^9,10

OIRR is a well-recognized and undesirable adverse effect of orthodontic treatment, characterized by the irreversible loss of dental root structure. ¹¹ Although mild root resorption is common and often clinically insignificant, severe forms may compromise tooth longevity and long-term treatment stability. The etiology of OIRR is multifactorial and involves mechanical, biological, and individual susceptibility factors, including force magnitude and duration, treatment time, root morphology, and genetic predisposition. ¹²

From a biological perspective, OIRR is initiated by orthodontic forces that create areas of compression within the periodontal ligament, leading to local hyalinization, sterile inflammation, and activation of clastic cells responsible for cementum and dentin resorption. ¹³ Once cementoblasts are damaged or removed, the root surface becomes susceptible to resorptive activity mediated by odontoclasts and osteoclasts. ¹⁴

In recent years, increasing attention has been directed toward biologically driven approaches aimed at modulating tissue responses during orthodontic treatment to minimize adverse effects such as root resorption. Platelet-rich fibrin (PRF), a second-generation autologous platelet concentrate, has emerged as a promising biomaterial due to its high platelet and leukocyte content and its fibrin matrix, which enables gradual release of multiple growth factors, including platelet-derived growth factor, transforming growth factor-β (TGF-β), vascular endothelial growth factor, and insulin-like growth factor. ¹⁵ However, in 2014, injectable platelet-rich fibrin (i-PRF), which possessed similar qualities, was introduced in France by Choukroun using non-glass tubes and adjusted spin centrifugation forces. ¹⁶ Similar to traditional PRF, i-PRF contains high levels of growth factors, stem cells, leukocytes, and cytokines. ¹⁷

These growth factors play a crucial role in angiogenesis, tissue regeneration, inflammation modulation, and bone remodeling, all of which play central roles in orthodontic tooth movement and periodontal healing.^18,19 Experimental and clinical studies have demonstrated that i-PRF can enhance bone regeneration, accelerate wound healing, and reduce inflammatory responses in various dental and maxillofacial applications.^20,21

Given the dynamic nature of orthodontic force application and the continuous biological remodeling of periodontal tissues, repeated local administration of PRF has been proposed as an effective method for achieving sustained regenerative and anti-inflammatory effects. ²² Repeated injections may help maintain a favorable biological environment via continuous supply of growth factors that promote cementoblast survival, periodontal ligament repair, and controlled bone remodeling, potentially reducing the severity of OIRR.^23,24

However, despite the growing number of studies that have evaluated the effects of administering i-PRF on orthodontic tooth movement,^25–27 limited evidence is available regarding the specific impact of repeated PRF injections on root resorption. Zeitounlouian et al. performed a randomized controlled trial (RCT) to study the effect of i-PRF administration on OIRR of the maxillary canine following first upper premolar extraction. However, the number of injections was limited to two, and the study depended on extraction-based treatment contrary to our study, which depended on non-extraction-based treatment for moderately crowded arches, as severe crowding holds the greatest potential for OIRR incidence. ²² Therefore, further investigation is warranted to clarify its effectiveness, optimal application protocol, and clinical relevance in reducing OIRR during orthodontic treatment. To our knowledge, this study is the first to evaluate the effect of repeated administration of i-PRF on mandibular incisor root resorption associated with orthodontic treatment in patients with a moderately crowded arch.

Materials and methods

Trial design and registration

This single-blind, single-center, two-arm parallel-group randomized controlled clinical trial with a 1:1 allocation ratio was registered in the ClinicalTrials.gov registry (NCT07352241) and adhered to the Consolidated Standards of Reporting Trials (CONSORT) statement guidelines. This trial received approval from the Biomedical Research Ethics Committee of Damascus University (ref no. DN-01102024-329), and no changes were implemented once the trial started.

Sample size calculation

G*Power analysis software was used to estimate the required sample size (G*Power Version 3.1.9.4, Kiel University, Kiel, Germany). Assuming an effect size of 0.672 for the variable (root resorption), according to the study by Zeitounlouian et al., with a power of 95% and a permissible (α) error of 5%, ²² a sample of 32 was required. Four additional participants were added to account for possible dropouts, resulting in a total sample size of 36 (18 per group).

Participants, eligibility criteria, and settings

Ninety-seven patients were assessed for eligibility in this study. Twelve patients declined participation, and 40 were excluded because they did not meet the inclusion criteria; thus, 45 eligible and willing patients were included in the study. Thirty-six patients were randomly recruited between January 2024 and August 2025 from the Department of Orthodontics, Faculty of Dentistry, Damascus University. According to the inclusion criteria, adult patients aged between 17 and 28 years with a Class I malocclusion and moderate crowding (4–6 mm) according to Little’s irregularity index (LII), ²⁸ normal inclination or mild proclination for mandibular incisors, and complete permanent teeth were enrolled in the study. Based on the exclusion criteria, patients who underwent previous orthodontic treatment, had poor oral hygiene, exhibited severe skeletal discrepancy, and had coagulation disorders or were taking anticoagulants were considered ineligible. Each patient was given an information sheet, and written informed consent was obtained from all participants. However, parental/legal guardian informed consent was also obtained when the patient age was <18 years (Figure 1).

Figure 1.

Consolidated Standards of Reporting Trials (CONSORT) flow diagram.

Randomization, allocation concealment, and blinding

Each patient was randomly assigned to one of the two groups using a simple computer randomization technique in a 1:1 allocation ratio. The allocation sequence was concealed in numbered, sealed, and opaque envelopes. For each participant, the envelope was promptly opened immediately after the mandibular arch brackets were bonded. However, single blinding was implemented in this trial during data analysis such that the outcome assessor was unaware of the group to which each participant belonged.

Clinical interventions

After undergoing radiographic and clinical examinations, patients who met the inclusion criteria were randomly and equally enrolled in one of two treatment groups. All 36 patients were treated with a conventional fixed orthodontic appliance. A pre-adjusted edgewise appliance (MBT prescription) with a 0.022-inch bracket slot (Pinnacle™, Ortho Technology®, Florida, USA) was used for all patients, and brackets were bonded to both maxillary and mandibular arches. Directly after bonding the orthodontic appliance, a 0.012-inch nickel–titanium (NiTi) archwire was placed for patients in both treatment groups. The following archwire sequence was followed during the dental arch alignment stage: 0.012, 0.014, 0.016, 0.016 × 0.022, 0.017 ×0.025, and 0.019 × 0.025-inch NiTi wires, followed by 0.019 × 0.025-inch stainless steel (SS) wire (American Orthodontics, Sheboygan, WI, USA). Patients were monitored biweekly, and interproximal reduction (IPR) was frequently performed using metal abrasion strips (Double-Sided Interproximal Diamond Strips, Ortho Technology Inc., West Columbia, SC, USA). The amount of IPR needed was carefully assessed prior to the orthodontic treatment based on each patient’s specific needs. This was evaluated based on the initial proclination of the lower incisors, anterior Bolton’s analysis, and primary LII value. The required amount of IPR was then documented in the patient’s file, and IPR was conducted gradually over the treatment appointments. The archwire was replaced with a second one when it became neutral or near neutral. However, once the ability for full engagement of 0.019 × 0.025-inch SS wire into bracket slots with LII equaled zero, the mandibular alignment stage was considered achieved. Regarding i-PRF preparation, 10-mL venous blood samples were collected from the patients and placed into plastic tubes which did not contain any anticoagulant. The samples were then centrifuged using an electric centrifuge (HETTICH-Zentrifugen EBA20, Typ 2002, BJ 2011, Tuttlingen, Germany) at 700 r/min for 3 min. This process produced 2 mL of i-PRF, which was transferred to a marked 3-mL syringe using a 27-gauge needle (Sterile disposable Hypodermic needle, Kohope Medical, Shanghai, China) (Figure 2). At this moment, i-PRF became ready for submucosal injection preceded by bilateral incisive nerve block with lidocaine (2%) and epinephrine (1/80,000) (Figure 3). However, saline serum was injected in the control group to avoid any acupuncture effect due to the injection process.

Figure 2.

Injectable platelet-rich fibrin (i-PRF) preparation using an electric centrifuge.

Figure 3.

Administration of the injectable platelet-rich fibrin (i-PRF) submucosally in the buccal region of the mandibular incisors.

Experimental group: i-PRF injection group

i-PRF administration was performed over four sessions at 28-day intervals. The injection was administered submucosally in the buccal region of the lower incisors with 2 mL of i-PRF during every session (0.5 mL for each incisor).

Control group: Traditional treatment group

Saline serum was injected during the four sessions at 28-day intervals at the same volume and region as in the experimental group.

Outcome measures

Cone-beam computed tomography (CBCT) images were obtained before (T0) and after achieving the alignment stage (T1). OIRR was assessed by comparing the difference in the full linear length of each incisor (incisal edge to the apex) between T0 and T1. The sagittal plane was used for these measurements (Figure 4). ²⁹

Figure 4.

Buccolingual section of incisor CBCT scan demonstrating measurement of the entire tooth length. CBCT: cone-beam computed tomography.

The X-ray device, VATECH® (Pax-i3D Green. Seoul, Korea), was used, with 0.12 mm voxel size and 17 × 23 cm field of view for 12 s. Patients were positioned with their Frankfort plane parallel to the floor, and Ez-3D plus software (Seoul, Korea) was utilized to view and read the CBCT images in multiplanar reconstruction mode that contained four different views, including sagittal, coronal, axial, and three-dimensional (3D). To achieve consistent and reproducible measurements, all scans were systematically aligned with the different sections. In the axial plane, the intersection between the x and y axes was positioned at the center of the buccolingual axis of each incisor’s pulp chamber. In the coronal plane, the x-axis passed through the mesiodistal cementoenamel junction (CEJ) of each incisor. In the sagittal plane, the x-axis passed through the buccolingual CEJ of each incisor, and the y-axis was parallel to the long axis of the incisor root.

Statistical analyses

Statistical analyses were performed using the Statistical Package for Social Sciences (SPSS®) software (version 26.0, IBM corporation, Armonk, NY). Since all the variables were normally distributed according to the Shapiro–Wilk test, parametric statistics were applied. Independent sample t-test was utilized to compare the results between the two groups. The level of significance was set at 5%.

Error of the method and reliability assessment

The main investigator (M.I.I.) re-performed the OIRR measurements of 18 randomly chosen CBCT images 28 days after the first evaluation. Intraclass correlation coefficients (ICCs) were applied to assess the intra-examiner reliability of the root resorption parameters (random error), and paired sample t-tests were employed to identify any systematic errors.

Results

Thirty-six patients (8 males and 28 females, mean age: 20.22 ± 2.55 years) were included in this study, and no dropouts occurred in either group. There were no significant differences in the sex distribution, LII values, patient age, and L1.Go-Me angle between the two groups (p = 0.328, 0.146, 0.496, and 0.675, respectively). Basic characteristics of the enrolled patients are presented in Table 1. The ICCs were >0.990, indicating a high level of reliability among examiners. Paired sample t-test demonstrated no significant differences between the first and second measurements of the tooth length values (p > 0.05), reflecting nonsignificant systematic errors.

Table 1.

Basic sample characteristics (sex, age, Little’s index value, and L1.Go-Me angle).

Variable		Control group(n = 18)	4-time injection group (n = 18)	p-valuec
Sex	Male	5 (27.8%)	3 (38.8%)	0.328 a
	Female	13 (72.2%)	15 (61.2%)
Age	Mean ± SD	20.11 ± 2.72	20.38 ± 2.19	0.496b
Little’s index	Mean ± SD	4.94 ± 0.61	4.80 ± 0.75	0.146b
L1.Go-Me (baseline)	Mean ± SD	91.19 ± 1.44	90.69 ± 2.95	0.675b

^achi-square test; ^bindependent sample t-test; ^cSignificance level: < 0.05; L1.Go-Me: The angle between the lower incisor and mandibular plane.

Concerning OIRR, no significant differences were observed between the two groups at baseline (p = 0.532). Intra-group comparisons exhibited a statistically significant decrease in the tooth length in both groups after the orthodontic treatment (control group: MD = 0.53 mm, p < 0.001 and experimental group: MD = 0.49 mm, p < 0.001). However, there were no statistically significant differences in the changes in root length between the groups (MD = 0.04 mm, p = 0.741) (Table 2).

Table 2.

Descriptive statistics of the tooth length values at baseline, changes in the parameters T0–T1 (in mm) of the two groups, and results of the significance test.

Time point/interval	Group	Mean/MD	SD	p-valuec
T0	Control	22.19	1.29	0.955 a
	4-time injection	22.32	1.69
T0–T1 (Intra-group)	Control	−0.53	0.09	0 < 0.001b
	4-time injection	−0.49	0.08	0 < 0.001b
T0–T1 (Intergroup)	Control/4-time injection	−0.04	0.09	0.741 a
			0.08

^aIndependent sample t-test; ^bpaired sample t-test; ^cSignificance level: <0.05; MD: mean difference.

Discussion

In recent years, there has been a growing interest in the utilization of platelet concentrations to enhance tissue healing and regeneration across various medical and dental fields. These include bone regeneration, ²¹ wound healing after gingivectomy and gingivoplasty operations, ³⁰ minimization of discomfort and enhancement of healing at palatal donor sites, ³¹ and effective reduction of inflammatory responses in a wide range of dental and maxillofacial applications.^32,33 To our knowledge, the current study is the first two-arm clinical RCT to evaluate the effect of repeated administration of i-PRF on potential external apical root resorption after orthodontic therapy in non-extraction-based treatments for moderately crowded mandibular arches. A previous study has demonstrated that i-PRF gradually releases high concentrations of growth factors for 7–14 days post injection. ³⁴ Therefore, in this study, i-PRF was administered four times to ensure sustained release of these growth factors during orthodontic therapy. In the control group, saline serum was injected repeatedly at the same volume as the i-PRF used in the intervention groups. This was done to eliminate any acupuncture effects from the injection process that could activate the regional acceleratory phenomenon and stimulate stem cells in the area, similar to observations in previous studies.^25,35

CBCT was used to determine root resorption of the mandibular incisors in patients from each study group. This imaging modality was selected because root resorption represents a 3D lesion that may not be fully detected using conventional radiographic techniques. ²⁹ In addition, the ability to consistently orient imaging planes and extract reproducible two-dimensional sections in the axial, coronal, and sagittal planes minimizes assessment errors that may arise from changes in tooth position following orthodontic treatment. CBCT also eliminates the problem of anatomical structure superimposition and allows accurate, highly reproducible evaluation of the extent of root structure loss. ³⁶ Root resorption was quantified by measuring the total tooth length (in millimeter) from the root apex to the incisal edge of the mandibular incisor before and after treatment. A systematic review by Samandara et al. has reported no statistically significant differences between assessment of root resorption based on the total tooth length versus that using root length alone, indicating that both methods are reliable for evaluating root resorption. ²⁹ Total tooth length measurement was adopted in the present study because identifying the incisor length is easier and more reliable than locating the CEJ.

Herein, there was a statistically significant decrease in the incisors’ root length following non-extraction orthodontic treatment in both groups. This result is in line with previous reports; Yu et al. have reported that orthodontic treatment was associated with incisor root resorption of 0.36 ± 0.25 mm after 7 months of treatment in their patients. ³⁷ Casrto et al. also demonstrated lower incisors root resorption of 0.51 ± 0.34 mm after orthodontic treatment. ³⁸ Similar results were reported in the meta-analysis conducted by Deng et al. who found that the non-extraction-based orthodontic treatment yielded 0.35 ± 0.37 mm root resorption of the anterior mandibular teeth. ³⁹ However, a comparison of the two groups revealed no significant differences. Root resorption is a complex phenomenon influenced by various factors, including the magnitude and duration of orthodontic forces, tooth type, and individual biological variability. ⁴⁰ This suggests that i-PRF does not impact the biological mechanisms associated with OIRR. This result may be attributed to the inability of i-PRF to affect or modulate the activity of odontoclasts and cementoclasts, which are responsible for apical root resorption. Additionally, i-PRF may not alter local signaling pathways, such as receptor activator of nuclear factor kappa-B (RANK)/receptor activator of nuclear factor kappa-B ligand (RANKL)/osteoprotegerin (OPG) that play crucial roles in the root resorption process.^41,42 This result was consistent with that reported by Zeitounlouian et al. in their RCT, according to which, there was no significant difference in root resorption between the control and i-PRF injection groups. ²²

Although i-PRF is known for its potential to enhance bone and soft tissue healing, its effect on root resorption appears limited, likely due to the multifactorial nature of root resorption. Unfortunately, few studies have investigated the effect of i-PRF on root resorption following orthodontic treatment, and well-designed RCTs should be performed in the future to reach an evidence-based decision.

The present study has certain limitations. First, it was a single-blind trial wherein blinding was only applied during data analysis. This may have increased the risk of detection bias. Second, the study focused solely on the lower arch and did not include the upper arch. Third, patient-reported outcomes such as satisfaction, discomfort, and pain were not measured and compared between treatment groups. Fourth, treatment duration, which impacts OIRR, was not measured or compared between the groups. In the future, RCTs involving various malocclusion types should be conducted to reach evidence-based decisions concerning the effects of i-PRF on orthodontic outcomes.

Conclusion

Considering the limitations of this study, the findings indicate that i-PFR is not an effective method for preventing apical root resorption following non-extraction-based orthodontic treatment, suggesting that its routine use for this purpose does not provide any clinical benefits. However, further well-designed studies with larger sample sizes and longer follow-up duration are needed to confirm and validate these findings.

Data availability

The data used in this study will be shared upon reasonable request to the corresponding author.

Declaration of conflicting interests

The authors declare that there are no competing interests to declare.

Ethics approval

This trial was approved by the Biomedical Research Ethics Committee of Damascus University (DN-01102024-329).