This single-centered, parallel-groups trial aimed to evaluate the efficacy of traditional corticotomy vs flapless corticotomy in accelerating en-masse retraction. In addition, to assess the skeletal, dental, and soft-tissue variables, as well as the external apical root resorption (EARR) of the maxillary anterior teeth.
Forty patients with Class II Division 1 malocclusion aged >18 years at the beginning of treatment, requiring maxillary first premolar extractions, were randomly distributed into 2 groups (n = 20 each): 1 group was treated using traditional corticotomy, and the other group was treated with flapless corticotomy in en-masse retraction with anchorage based on miniscrews placed between maxillary second premolars and first molars bilaterally. Randomization was implemented with a computer-generated list of random numbers; allocation was concealed in sequentially numbered, opaque, sealed envelopes. The study was single-blinded (outcomes’ assessor). The primary outcome was the en-masse retraction duration. Secondary outcomes were the skeletal, dental, and soft-tissue changes on lateral cephalometric and the EARR of maxillary anterior teeth on digital panoramic radiographs.
The en-masse retraction duration in the flapless corticotomy group was longer than the traditional corticotomy group. The average retraction duration was 4.04 ± 1.10 months for the flapless corticotomy group and 3.75 ± 2.14 months for the traditional corticotomy group, with no significant difference between the 2 groups (95% confidence interval [CI], −0.81 to 1.39; P = 0.59). No significant differences were observed between the 2 groups regarding changes in several lateral cephalometric variables (eg, SNA angle [95% CI, −2.55° to 1.66°; P = 0.67], SN-U1 angle [95% CI, −1.70° to 1.32°; P = 0.80], and UL-E [95% CI: −1.33 to 1.00 mm; P = 0.78]) or in the amount of EARR in the maxillary anterior teeth ( P = 0.31). The proportion of the observed EARR ranged from 1% to 6% of root length in both corticotomy groups. No serious harms were observed in both groups.
No significant differences between the flapless and traditional corticotomies were found in terms of the skeletal, dental, and soft-tissue variables as well as in the amount of EARR. Corticotomy-assisted en-masse retraction led to improvements in skeletal structures and facial profile and resulted in sufficient retraction of maxillary anterior teeth, slight distal movement of maxillary first molars, and an intrusion movement for both anterior and posterior teeth. Both corticotomy techniques did not cause significant EARR.
The protocol was not published before the trial commencement.
This trial aimed to compare the treatment outcomes of 2 corticotomy techniques.
No significant difference was found in en-masse retraction times for 2 techniques.
Both corticotomy techniques improved skeletal, dental, and soft-tissue measurements.
Neither technique caused any significant root resorption.
The retraction of maxillary anterior teeth is an important phase in the orthodontic treatment of patients with Class II Division 1 malocclusion when premolar extraction is performed, and a camouflage treatment is indicated. Several studies have shown that the en-masse retraction technique is preferable to the 2-step retraction technique because of several practical benefits, especially the reduction of orthodontic treatment time. Sliding mechanics is a commonly used method for the en-masse retraction, and this is often supported by miniscrews for extra anchorage. ,
Prolonged treatment time is one of the most important challenges in daily practice because of the multiple side effects of lengthy treatments, such as dental caries, periodontal diseases, and root resorption. External apical root resorption (EARR) is defined as a physiological and pathologic process that exhibits a loss of cementum and/or root dentin causing shortness in the root. Because most of the damages affecting the root surface are irreversible when extending into dentin, determining the risk factors of root resorption and finding methods to avoid such complications are very important to orthodontists. The etiologic factors for EARR are complex and multiple and include a mixture of mechanical factors and individual biologic variability. EARR begins between 2 and 5 weeks after the beginning of orthodontic treatment, but it takes 3-4 months to become detectable on the radiographs.
Several therapeutic procedures have been introduced to reduce orthodontic treatment duration, such as surgical interventions. It has been suggested to elevate flaps and perform corticotomy using surgical burs. Although traditional corticotomy proved to be effective in accelerating different types of tooth movement, it has been considered aggressive. Hence, minimally invasive surgical techniques that may offer similar clinical efficacy with the least possible trauma have been proposed, and such procedures have been labeled “flapless corticotomies,” (ie, surgical interventions without flap elevation).
The recent systematic review by Khlef et al indicated that there was a lack of scientific evidence on the effectiveness of flapless corticotomy performed by piezosurgery in accelerating the en-masse retraction of the maxillary 6 anterior teeth. There is only 1 randomized controlled trial by Tunçer et al, which found no significant difference between the flapless corticotomy group (FCG) of patients and the control group in terms of en-masse retraction duration ( P = 0.96). The mean retraction duration in the FCG was 9.33 ± 4.10 months compared with 9.27 ± 2.55 months in the control group. This finding contradicts many previous studies that have indicated that flapless corticotomy accelerates the orthodontic movement, such as canine retraction , and leveling and alignment , ; therefore, more investigation is required in this aspect.
To the best of our knowledge, there is no clinical trial comparing the flapless corticotomy with the traditional corticotomy associated with the en-masse retraction of maxillary anterior teeth in terms of speed, dentoalveolar, skeletal, and soft-tissue changes, and EARR.
The objectives of this randomized controlled trial were (1) to investigate the effectiveness of traditional corticotomy and flapless corticotomy performed by piezosurgery in accelerating the en-masse retraction of maxillary anterior teeth, (2) to compare the 2 corticotomy techniques in terms of the skeletal, dental, and soft-tissue changes, and (3) to assess the amount of EARR at the 6 maxillary anterior teeth using digital panoramic radiographs.
Material and methods
Trial design, registration, and any changes after trial commencement
This study was a single-centered, 2-arm parallel-group randomized controlled clinical trial. It was registered at ClinicalTrials.gov database (Identifier: NCT03279042 ) and was funded by the University of Damascus Dental School Postgraduate Research Budget (Ref no. 84194725390DEN). There were no changes after trial commencement.
Participants, eligibility criteria, and settings
Forty adult patients (36 female, 4 male) were recruited from the Department of Orthodontics, University of Damascus Dental School, Damascus University, Damascus, Syria, from September 2016 to December 2016. The recruitment process began after obtaining formal approval from the Local Ethics Committee at the University of Damascus Dental School, Syria (Ref no. UDDS-401-07092016/SRC-2831). Patients’ allocation and follow-up are given in Figure 1 . The patients were equally and randomly divided into 2 groups: FCG (n = 20) and traditional corticotomy group (TCG) (n = 20). All patients fulfilled the following criteria: (1) age range between 18 and 30 years, (2) Class II Division 1 malocclusion requiring maxillary first premolars extraction, (3) mild to moderate skeletal Class II malocclusion, (4) overjet >5 mm and <10 mm, (5) normal or excessive anterior facial height, (6) no or mild crowding (tooth size–arch length discrepancy ≤3 mm), (7) completion permanent dentition (regardless of third molars), (8) no previous orthodontic treatment history, (9) no systematic diseases or drug use that would affect bone and tooth movement rate, and (10) good oral hygiene and healthy periodontium.
The eligible patients were informed in detail about the procedures of the study and were asked whether they wanted to participate in the study. Information sheets were distributed to all patients, and informed consent was obtained from all patients before recruitment. No changes in the methods were made after trial commencement occurred.
Leveling and alignment
The orthodontic treatment was conducted by the principal investigator (H.N.K) under the supervision of one of the coauthors (M.Y.H) at the Orthodontic Department of Damascus University Dental School. The extraction of first premolars was performed for all patients at the beginning of the treatment, in order not to disturb the results of the applied corticotomy. All patients were treated with 0.022 × 0.028-in brackets (Votion, Ortho Technology, Tampa, Fla). After the extraction of premolars and application of brackets, self-drilling titanium miniscrews (diameter, 1.6 mm; length, 8 mm; 3S screw, Hubit, Seoul, Korea) were applied. After the administration of local anesthesia, the miniscrews were inserted between the roots of maxillary second premolars and first molars bilaterally, at approximately 8-10 mm above the archwires at the mucogingival junction. Next, they were checked for primary stability. Both the maxillary second premolar and first molar were linked to the miniscrew with ligature wire to ensure that no mesial movement of the posterior segments might occur during the leveling and alignment phase. A periapical radiograph was taken to ensure the integrity of the miniscrew relationship with the adjacent structures.
Leveling and alignment were performed with the following archwires sequences: 0.014-in nickel-titanium (NiTi), 0.016-in NiTi, 0.016 × 0.022-in NiTi, 0.017 × 0.025-in NiTi, 0.019 × 0.025-in NiTi, 0.019 × 0.025-in stainless steel (SS). To ensure the completion of the leveling and alignment phase, the last SS archwire was left for 3 weeks before starting the retraction process.
After completion of the leveling and alignment phase, panoramic radiographs were taken to evaluate the paralleling of the maxillary anterior teeth roots and to assess the amount of root resorption on the 6 maxillary anterior teeth. Metal determinants were applied to the maxillary first molar to assess the horizontal movement of the first molars on the lateral cephalograms.
All patients were asked to rinse with 0.12% chlorhexidine gluconate for 1 minute immediately before the surgical intervention; next, regional anesthesia was injected in the infraorbital foramen and incisive foramen (2% lidocaine HCl with 1:80,000 epinephrine). After finishing the corticotomy, the surgical area was covered by a piece of iodoform gauze. The patients underwent the following postsurgical regimen: (1) taking antibiotic tablets (1000 mg Augmentin: 875 mg amoxicillin and 125 mg clavulanate potassium) 1 tablet twice a day for 1 week, (2) maintaining good oral hygiene, (3) putting ice packs on for the first 6-8 hours after corticotomy, (4) avoid smoking completely during the first week after corticotomy, (5) eating soft food in the first few days after corticotomy, and (6) taking 500 mg acetaminophen (Panadol) only if necessary. Nonsteroidal antiinflammatory drugs were forbidden in order to avoid overlapping with the regional acceleratory phenomenon (RAP).
Flapless corticotomy group
The flapless corticotomy was performed by the principal investigator (H.N.K) under the supervision of one of the coauthors (O.H) at the Oral and Maxillofacial Surgery Department of University of Damascus Dental School. After regional anesthesia, vertical soft-tissue incisions were made on the buccal and palatal gingiva. Two incisions were made between the maxillary canines and second premolars, and 1 incision was made between the roots of the 6 maxillary anterior teeth by using a blade holder no. 3 and blade no. 15. These incisions started 4 mm apical to the interdental papilla to avoid any further gingival recessions and were 5 mm long. Next, a piezosurgery knife (BS1, Implant Center 2; Satelec, Viry-Châtillon, France) associated with an irrigation solution pump (80 ml/m) was inserted to perform the cortical alveolar incisions with 8 mm long and 3 mm deep, which were confirmed by the millimetric signs on the piezosurgery knife. No subsequent sutures were required because soft-tissue incisions were limited to the attached gingiva, and no periosteum dissection was performed ( Figs 2 , A and B ).
Traditional corticotomy group
The traditional corticotomy was performed by an experienced surgeon (N.Y) under the supervision of the coauthor (O.H) in the same department. After regional anesthesia, a full-thickness mucoperiosteal flap was elevated, including the interdental papilla, and extended from the distal side of the second premolar on the right side to the same position on the left side without making any vertical releasing incisions. The full-thickness flap was raised by the mucoperiosteal elevator, extending to 3 mm above the root apices, from the buccal and palatal sides, except the incisal papilla region, where the incision was made around it with a “U” or “V” shape to avoid causing injury in the neurovascular structures. After this, 2 vertical cortical alveolar incisions in the place of first premolar extraction and 1 vertical incision between the roots of maxillary anterior teeth were made by the piezosurgery knife (BS1). The vertical incisions were joined by a horizontal incision using the piezosurgery knives (BS2L and BS2R). The depth of the corticotomy was 3 mm, with vertical incisions starting 2-3 mm apical to the alveolar crest. The cortical alveolar incisions extended beyond the root apices with a distance of 3 mm, to protect the blood flow to the teeth when performing the horizontal incision ( Figs 3 , A and B ). After that, the area was well-washed with a physiological serum to remove the osteoporosis and blood clots. The flap was repositioned, and the surgical suturing was performed using a nonabsorbent 3-0 black silk with the interrupted technique ( Fig 3 , C ). Sutures were removed 7 days after corticotomy.
En-masse retraction in proper
The en-masse retraction was initiated after 4 days of performing the corticotomy; 0.019 × 0.025-in SS archwires with 8-to-10-mm long soldered hooks distal to the lateral incisors were placed for all patients, and NiTi closed coil springs (NT3 closed coil, American Orthodontics, Sheboygan, Wis) with a length of 9 mm were stretched from the soldered hooks to the miniscrews and applied 250 g of force per side. The generated force was checked using a force gauge (040-711-00; Dentaurum, Ispringen, Germany).
The patients’ follow-up appointments were every 2 weeks in order to take the maximum advantages of the RAP. At each appointment, the force was calibrated and readjusted when necessary. The endpoint of the observation period was the session when canines reached Class Ι relationship with normal overjet and overbite.
Outcomes (primary and secondary) and any changes after trial commencement
The primary outcome was the duration of en-masse retraction in both corticotomy techniques. It was calculated from the first day on which NiTi springs were applied until the canines reached Class Ι relationship with normal overjet and overbite.
The secondary outcomes were the skeletal, dental, and soft-tissue changes. They were assessed on the lateral cephalograms, which were digitally traced and measured using Viewbox (version 18.104.22.168; dHAL Software, Kifissia, Greece). The definitions of the angular and linear measurements are given in Supplementary Table I .
The EARR was assessed on the digital panoramic radiographs by using the ImageJ program (NIH and LOCI, Madison, Wis). The mesial and distal cementoenamel-junction (CEJ) points were connected by a straight line. The length of the root and crown was measured by drawing a vertical line extended from the root apex to the CEJ line, and another vertical line extended from the midincisal edge to the CEJ line. Any difference in magnification can be measured by the fixed length of the crown between successive radiographs. This method was established by Linge and Linge and has been described by several studies. , No changes to the study design were made after commencement.
Sample size calculation
The sample size was calculated using Minitab (version 17; Minitab, LLC, State College, Pa). The intended statistical test was the 2-sample t test. The number of patients required for each group was 20 patients depending on the following assumptions: a minimal of 40% reduction of the en-masse retraction time (ie, 5.61 months vs 9.33 months for the en-masse retraction time) was considered clinically important (on the basis of Tunçer et al ); a standard deviation of 4.1 (on the basis of the same study); the alpha level was set at 5%; power was set at 80%; 2-tailed tests. No precautions were made to increase the number of patients in case of dropouts.
Interim analyses and stopping guidelines
Randomization and allocation concealment
Simple randomization was conducted by one of the academic staff (not involved in the study) using computer-generated random numbers with an allocation ratio of 1:1. The allocation sequence was concealed using sequentially numbered, opaque, sealed envelopes, which were opened only after the completion of the leveling and alignment phase.
Blinding either the investigator performing the clinical procedures (H.N.K) or patients was not possible; however, blinding was applied only for the outcomes’ assessor.
Two statistical packages were used for data analysis: Minitab and SPSS program (version 21; IBM, Armonk, NY). Anderson-Darling Normality tests were used to test the normality of distributions. Two-sample t tests were used to compare the treatment duration and cephalometric variables between the 2 groups. Mann-Whitney U test was used to compare the amount of EARR between the 2 groups. Fisher exact tests were used to detect significant differences between the 2 groups regarding the proportions of maxillary anterior teeth exposed to EARR.
The error of the method
Twenty lateral cephalometric radiographs were randomly chosen and reanalyzed after a 4-week interval. The interclass correlation coefficients were used to determine the intraexaminer reliability for measurements (random error), whereas paired-sample t tests were used to find out any systematic error.
Patient recruitment started in September 2016 and ended in December 2016. Forty patients were enrolled (36 female and 4 male), 20 patients in each group, and no patient was lost to follow-up in both groups, as mentioned in Figure 1 .
The baseline sample characteristics at the beginning of the treatment are given in Table I .