Trial design and any changes after trial

This study was a split-mouth randomized clinical trial with a 1:1 allocation. The methods were not changed after trial initiation.

Participants, eligibility criteria, and settings

Ethical approval was obtained from institutional review board at King Abdullah University Hospital, Jordanian University of Science and Technology in Irbid, Jordan, with approval number 20150263. This trial was also registered at ClinicalTrials.gov with identifier number NCT02473471 . Participants were recruited from new patients attending the orthodontic department at the Postgraduate Dental Clinics at Jordanian University of Science and Technology. The following inclusion criteria were applied: (1) both male and female subjects, (2) 16 or more years old, (3) Class II Division 1 malocclusion, (4) Class II canine relationship, and (5) average lower facial height and maxillomandibular plane angle. Patients with lower facial height from 53% to 57% (55% ± 2%) and with maxillomandibular plane angles from 23° to 31° (27° ± 4°) were only considered based on Eastman cephalometric standards. The exclusion criteria were (1) diseases and medications that were likely to affect bone biology, (2) poor oral hygiene, (3) low or high angle, (4) previous orthodontic treatment, (5) evidence of bone loss, (6) active periodontal disease, and (7) smoking. Patients were selected according to the inclusion and exclusion criteria during the recruitment time. Subsequently, they were invited to sign a consent form after we clarified the purpose of the intervention and the associated risks and benefits.

Sample size calculation

The sample size was calculated based on a type I error frequency of 5%. According to the power analysis and assuming a large effect size difference between groups (effect size, 0.8), the power analysis showed that 28 subjects per group were needed at a conventional alpha level ( P = 0.05) and desired power (1 – β) of 0.90, yielding a total sample size estimate of 56 subjects. All calculations were performed with the computer application GPOWER.

Randomization (random number generation, allocation concealment, implementation)

The intervention was randomly allocated to either the right or left side with a 1:1 allocation ratio. The randomization was accomplished by using the permuted random block size of 2 with the random generation function in Excel (Microsoft, Redmond, Wash). Subsequently, the random sequences to either the right or left were concealed in opaque envelopes and shuffled before the intervention to increase the unpredictability of the random allocation sequence. Each patient was asked to pick a sealed envelope to assign the surgical intervention to either the right or left side. Allocation concealment was aimed to prevent selection bias and protect the assignment sequence until allocation.

Blinding

Blinding of either patient or clinician was not possible. Blinding was ensured at the measurement stage (data collection), in which the investigator (A.A.) was blinded to where the MOPs were applied by coding all digital models.

Interventions

Orthodontic initial phase

Before the start of orthodontic treatment, the subjects were referred to the periodontal department to check periodontal conditions and for regular oral care. According to the inclusion criteria, all selected patients were diagnosed with a Class II Division 1 malocclusion with a treatment plan including extraction of the maxillary first premolars and fixed orthodontic appliances with maximum anchorage support using miniscrews. The subjects had their orthodontic treatment carried out by the same orthodontic resident (A.A.), using fixed preadjusted edgewise appliances (Gemini brackets, 0.022-in MBT prescription; 3M Unitek, Monrovia, Calif). The standardized bonding method was applied according to the manufacturer’s instruction. Miniscrews were used to prevent unwanted tooth movement of the posterior teeth during canine retraction. Therefore, after initial leveling and alignment, miniscrews (Aarhus System; American Orthodontics, Sheboygan, Wis; 1.5 mm width, 8 mm length) were inserted by an investigator (E.A-M.) between the maxillary first molars and second premolars to be used as direct and indirect anchorage. Direct anchorage was used by applying the force directly from the miniscrews to the canines to prevent mesial movement of posterior teeth during canine retraction. Indirect anchorage was also applied by passively ligating the maxillary second premolars to miniscrews that might prevent mesial movement of the posterior teeth especially at the leveling and alignment stage of the treatment ( Fig 1 ).

MOP protocol.

An operator performed atraumatic extractions of the maxillary first premolars within the same week as miniscrew insertion. After that, leveling and alignment were accomplished until reaching the 0.019 × 0.025-in stainless steel archwire. Maxillary canine retraction was started 6 months after the extractions to ensure complete healing of extraction spaces ( Fig 2 ).

Diagram of time events during the study.

Occlusal interferences can decrease the rate of tooth movement. Therefore, from day 1 and during the weekly follow-up periods, interferences were checked; if present, glass ionomer cement was used on the mandibular molars to raise the bite.

Clinical MOP procedure

MOPs were performed when the canines were ready to be retracted. The patients were asked to rinse their mouth twice with chlorhexidine for 1 minute. Local anesthesia was then given (2% lidocaine with 1:100,000 epinephrine; Septodont, Saint-Maur-des-Fossés, France). MOPs were performed by 1 investigator (A.A.) according to the randomization on either the maxillary right or left canine with the following steps.

• 1.

  A MOP of 1.5 mm width and 3 to 4 mm depth inside the bone was made. MOPs were performed using miniscrews (Aarhus Mini-Implant System, American Orthodontics) of 1.5 mm diameter and 6 mm length at 3 points distal to the canine.

• 2.

  The points of screw insertion were demarcated by bleeding points using a calibrated periodontal probe. One row consisting of 3 holes was made distal to the canine.

• 3.

  For standardization of the protocol, the exact location of screw insertion was determined as the following: the first dot was located 3 mm distal to the canine and 6 mm from the free gingival margin. The second point was marked 5 mm from the first one. The third MOP was marked 5 mm from the second MOP. The net distances between MOPs after insertion of the 1.5-mm diameter miniscrews were 3 mm between each hole, 2 mm from the contact point, and 5 mm from the free gingival margin ( Fig 1 ).

• 4.

  The miniscrew 6 mm long was inserted 3 to 4 mm deep into the bone to account for the thickness of the soft tissue of 2 to 3 mm.

After application of the MOPs, the extraction space was started to be closed using nickel-titanium closed-coil springs connecting the miniscrews between the maxillary second premolar and first molar to the power arm extending from the vertical slot of the maxillary canine bracket (3M Unitek; 9 mm, 150 g) ( Fig 3 ). The force was measured by force gauge (Correx; Dentaurum, Ispringen, Germany) on the day of application to ensure a constant and equal force in all subjects and also between the experimental and control sides.

A, MOPs application; B, 3 MOPs were visible distal to canines; C, canine retraction by NiTi closed coil spring; D and E, occlusal view of canines movement during treatment.

After the intervention, the patients were instructed to take analgesics, such as acetaminophen, only if necessary. Anti-inflammatory NSAIDs were avoided because of their known effect on tooth movement. Maintaining good oral hygiene and using chlorhexidine 0.2%, twice a day for 5 days, were recommended.

Outcomes (primary and secondary) and any changes after trial commencement

Primary outcomes

The rate of tooth movement as the primary outcome was determined by indirect measurement of the study models and direct intraoral measurement.

Alginate impressions were taken every month, and study models were fabricated. The study models were then scanned with Ceramill Map 400 scanner with an accuracy of 0.02 mm (Amann Girrbach, Koblach, Austria) to obtain the 3D model. By using the Ceramill Mind design (computer-aided design) software (Amann Girrbach), 3D model measurements were obtained. The baseline 3D digital model was superimposed on the 3D digital models at the first, second, and third months to determine the anteroposterior displacements of the canines. The stable reference landmark used was the rugae area as recommended in other studies. To superimpose 2 3D digital models, a generic visualization mesh of the following 3D model was added to the baseline model, then performed registration of the selected reference points at the rugae area ( Fig 4 , A and B ). The best-fit matching of the superimposition was evaluated by a color map with a spectrum of colors in which blue represented the best match, and red represented the worst ( Fig 4 , C ). From the buccolingual view, the amount of canine displacement was measured from the middle projection from the distal surface of the maxillary canines in the baseline model to the middle projection from the distal surface of the canines of the superimposed transparent models at months 1, 2, and 3 ( Fig 5 , A ). A reference plane parallel to the bracket slots was used to ensure the standardized orientation of all measurements from the buccal view ( Fig 5 . C ). From the occlusal view, the same point was localized at the middle of the distal surface of the canines to be parallel to the line of the arch anteroposteriorly ( Fig 5 , B ). Additionally, direct measurement of the distance between the canine and second premolar in the patient’s mouth was done every week using a digital caliper (IOS, USA), from the upper mesial wing of the canine bracket to the upper distal wing of the second premolar bracket in both right and left sides parallel to the occlusal plane for a 3-month period.

Three-dimensional digital superimposition: A, registration of 4 reference points at medial and lateral areas of the third rugae area; B, registration and best-fit matching; C, best-fit color matching with blue as the best match and red as the worst.

Measurement of canine retraction on 3D digital models: A, buccal view of mandibular left canine showing measurement tools on the Ceramill Mind software; B, occlusal view of the canines showing the measurement tool. The canines at baseline model ( yellow ) and in month 3 model ( purple ); C, the reference plane parallel to the bracket slots.

Secondary outcomes

Anchorage loss was measured in the superimposed digital models from the most prominent middle point on the mesial surface of the second premolar of the baseline model to the most prominent middle point on the mesial surface of the second premolar of the superimposed digital model at month 3.

From the buccolingual view, canine tipping was measured in the baseline and month 3 digital models by calculating the difference between the anteroposterior displacements of the canines in the superimposed models from 3 points: the tips of the canines, the most prominent point in the middle of the lateral surfaces, and the middle point at the gingival margin in the lateral surfaces of the canines. From the occlusal view, canine rotation was measured by adding the occlusal transparent plane parallel to the bracket slots of the baseline and third month digital models individually and then moving this plane occlusally with the same orientation to 5 mm from the teeth. Subsequently, an angle between 2 reference lines was drawn in the transparent occlusal plane; 1 line passed through the median raphe, and another line was connected between the mesial and distal contact points of the right and left canines, according to the method of Ziegler and Ingervall. Root resorption was also evaluated, using the periapical radiographs of the canines before retraction and after 3 months. An operator, using the parallax technique, made all digital periapical radiographs with the same x-ray machine (RXDC eXTend; MyRay, Bicocca, Italy), set at 7 mA, 60 kV, and an exposure time of 0.32 seconds. DIGORA Optime digital imaging plate system with its phosphor plate films (Soredex, Tuusula, Finland) was used in this study. Intraoral XCP film holders were used (Dentsply Rinn, York, Pa). Root resorption was measured using DIGORA for Windows software (version 2.8; Soredex). All radiographs were calibrated at 15.63 pixels per millimeter according to the manufacturer’s instruction. Root resorption in millimeters was measured as the difference between root length at baseline and after 3 months. The reference point was the midpoint of the mesial and distal cementoenamel junction. The root length was calculated from the root apex to the midpoint of the cementoenamel junction.

The periodontal index and plaque index were also evaluated clinically in both maxillary canines and second premolars before canine retraction and after 3 months according to the method of Löe. Both pain intensity and interference were evaluated using a visual analog scale (VAS) from 0 to 10 (0, no pain; 10, severe pain). The participants filled out a questionnaire to assess pain intensity immediately, after 1 hour, after 12 hours, and at days 1, 3, 5, and 7 after MOP intervention. Pain interference with daily life was assessed after MOP intervention on days 1, 3, 5, and 7 when patients were asked to provide their ratings of pain during eating, pain that awakened them at night, and the feeling of discomfort and swelling on the surgical side. The VAS was also used to rate the level of satisfaction (0, not satisfied; 10, very satisfied) and easiness of MOP procedure (0, very easy; 10, very complicated). Moreover, the patients were asked whether they were willing to repeat the procedure and recommend it to a friend using categorical data (yes or no). There were no changes to the outcome measures after trial commencement.

Interim analyses and stopping guidelines

Not applicable.

Statistical analysis (primary and secondary outcomes, subgroup analyses)

Statistical analysis was accomplished using the SPSS software (version 20.0; IBM, Armonk, NY). Probability values equal or less than 0.05 were considered significant. Independent sample t tests were calculated to analyze the results of the primary outcome and the secondary outcomes to compare the difference between the MOP and control sides. Additionally, pair T-test were performed to compare the amount of root resorption before and after 3 months in the MOP and control sides separately. The chi-square test was used for analysis of categorical data including the willingness to repeat the procedure and recommend it to a friend. Descriptive statistics were used to describe the satisfaction and ease of the procedure.

The reliability coefficient (Cronbach alpha) was used to evaluate the reliability of measurements of the primary outcome. One examiner made all measurements, and all subjects were randomly selected. Six 3D superimposed digital models were chosen randomly. Superimpositions on the rugae area and canine displacement were measured twice within a 2-week interval. The reliability coefficient (Cronbach alpha) was 0.95, showing excellent superimposition and measurement agreement.

For intraoral measurements, intraexaminer reliability was done in the mandibular arch after reaching the 0.019 × 0.025-in stainless steel archwire and after the teeth were in a passive state; there were no extractions in the mandibular arch. Six subjects were selected randomly, and measurements were made twice with a 2-week interval. Measurements were done from the upper mesial wings of the mandibular canine bracket to the upper distal wing of the mandibular second premolar bracket. The reliability coefficient (Cronbach alpha) was 1.00, indicating excellent measurement agreement.

Trial design and any changes after trial

This study was a split-mouth randomized clinical trial with a 1:1 allocation. The methods were not changed after trial initiation.

Participants, eligibility criteria, and settings

Ethical approval was obtained from institutional review board at King Abdullah University Hospital, Jordanian University of Science and Technology in Irbid, Jordan, with approval number 20150263. This trial was also registered at ClinicalTrials.gov with identifier number NCT02473471 . Participants were recruited from new patients attending the orthodontic department at the Postgraduate Dental Clinics at Jordanian University of Science and Technology. The following inclusion criteria were applied: (1) both male and female subjects, (2) 16 or more years old, (3) Class II Division 1 malocclusion, (4) Class II canine relationship, and (5) average lower facial height and maxillomandibular plane angle. Patients with lower facial height from 53% to 57% (55% ± 2%) and with maxillomandibular plane angles from 23° to 31° (27° ± 4°) were only considered based on Eastman cephalometric standards. The exclusion criteria were (1) diseases and medications that were likely to affect bone biology, (2) poor oral hygiene, (3) low or high angle, (4) previous orthodontic treatment, (5) evidence of bone loss, (6) active periodontal disease, and (7) smoking. Patients were selected according to the inclusion and exclusion criteria during the recruitment time. Subsequently, they were invited to sign a consent form after we clarified the purpose of the intervention and the associated risks and benefits.

Sample size calculation

The sample size was calculated based on a type I error frequency of 5%. According to the power analysis and assuming a large effect size difference between groups (effect size, 0.8), the power analysis showed that 28 subjects per group were needed at a conventional alpha level ( P = 0.05) and desired power (1 – β) of 0.90, yielding a total sample size estimate of 56 subjects. All calculations were performed with the computer application GPOWER.

Randomization (random number generation, allocation concealment, implementation)

The intervention was randomly allocated to either the right or left side with a 1:1 allocation ratio. The randomization was accomplished by using the permuted random block size of 2 with the random generation function in Excel (Microsoft, Redmond, Wash). Subsequently, the random sequences to either the right or left were concealed in opaque envelopes and shuffled before the intervention to increase the unpredictability of the random allocation sequence. Each patient was asked to pick a sealed envelope to assign the surgical intervention to either the right or left side. Allocation concealment was aimed to prevent selection bias and protect the assignment sequence until allocation.

Blinding

Blinding of either patient or clinician was not possible. Blinding was ensured at the measurement stage (data collection), in which the investigator (A.A.) was blinded to where the MOPs were applied by coding all digital models.

Interventions

Orthodontic initial phase

Before the start of orthodontic treatment, the subjects were referred to the periodontal department to check periodontal conditions and for regular oral care. According to the inclusion criteria, all selected patients were diagnosed with a Class II Division 1 malocclusion with a treatment plan including extraction of the maxillary first premolars and fixed orthodontic appliances with maximum anchorage support using miniscrews. The subjects had their orthodontic treatment carried out by the same orthodontic resident (A.A.), using fixed preadjusted edgewise appliances (Gemini brackets, 0.022-in MBT prescription; 3M Unitek, Monrovia, Calif). The standardized bonding method was applied according to the manufacturer’s instruction. Miniscrews were used to prevent unwanted tooth movement of the posterior teeth during canine retraction. Therefore, after initial leveling and alignment, miniscrews (Aarhus System; American Orthodontics, Sheboygan, Wis; 1.5 mm width, 8 mm length) were inserted by an investigator (E.A-M.) between the maxillary first molars and second premolars to be used as direct and indirect anchorage. Direct anchorage was used by applying the force directly from the miniscrews to the canines to prevent mesial movement of posterior teeth during canine retraction. Indirect anchorage was also applied by passively ligating the maxillary second premolars to miniscrews that might prevent mesial movement of the posterior teeth especially at the leveling and alignment stage of the treatment ( Fig 1 ).

MOP protocol.

An operator performed atraumatic extractions of the maxillary first premolars within the same week as miniscrew insertion. After that, leveling and alignment were accomplished until reaching the 0.019 × 0.025-in stainless steel archwire. Maxillary canine retraction was started 6 months after the extractions to ensure complete healing of extraction spaces ( Fig 2 ).

Diagram of time events during the study.

Occlusal interferences can decrease the rate of tooth movement. Therefore, from day 1 and during the weekly follow-up periods, interferences were checked; if present, glass ionomer cement was used on the mandibular molars to raise the bite.

Clinical MOP procedure

MOPs were performed when the canines were ready to be retracted. The patients were asked to rinse their mouth twice with chlorhexidine for 1 minute. Local anesthesia was then given (2% lidocaine with 1:100,000 epinephrine; Septodont, Saint-Maur-des-Fossés, France). MOPs were performed by 1 investigator (A.A.) according to the randomization on either the maxillary right or left canine with the following steps.

• 1.

  A MOP of 1.5 mm width and 3 to 4 mm depth inside the bone was made. MOPs were performed using miniscrews (Aarhus Mini-Implant System, American Orthodontics) of 1.5 mm diameter and 6 mm length at 3 points distal to the canine.

• 2.

  The points of screw insertion were demarcated by bleeding points using a calibrated periodontal probe. One row consisting of 3 holes was made distal to the canine.

• 3.

  For standardization of the protocol, the exact location of screw insertion was determined as the following: the first dot was located 3 mm distal to the canine and 6 mm from the free gingival margin. The second point was marked 5 mm from the first one. The third MOP was marked 5 mm from the second MOP. The net distances between MOPs after insertion of the 1.5-mm diameter miniscrews were 3 mm between each hole, 2 mm from the contact point, and 5 mm from the free gingival margin ( Fig 1 ).

• 4.

  The miniscrew 6 mm long was inserted 3 to 4 mm deep into the bone to account for the thickness of the soft tissue of 2 to 3 mm.

After application of the MOPs, the extraction space was started to be closed using nickel-titanium closed-coil springs connecting the miniscrews between the maxillary second premolar and first molar to the power arm extending from the vertical slot of the maxillary canine bracket (3M Unitek; 9 mm, 150 g) ( Fig 3 ). The force was measured by force gauge (Correx; Dentaurum, Ispringen, Germany) on the day of application to ensure a constant and equal force in all subjects and also between the experimental and control sides.

A, MOPs application; B, 3 MOPs were visible distal to canines; C, canine retraction by NiTi closed coil spring; D and E, occlusal view of canines movement during treatment.

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