Comparison of second molar protraction using different timing for piezocision application: A randomized clinical trial

ABSTRACT Objective: To compare second molar protraction between early, late and no piezocision groups. Material and Methods: Forty subjects with bilaterally extracted mandibular first molars were selected to participate in the study. Subjects were subdivided into two groups: piezocision and no piezocision. The piezocision group was further subdivided into two subgroups: early piezocision (piezocision performed immediately before second molar protraction) and late piezocision (piezocision performed three months after starting molar protraction). In the no piezocision group, molar protraction was done without surgery. The intervention (piezocision group and timing of piezocision/side within group) was randomly allocated using the permuted random block size of 2, with 1:1 allocation ratio. The amount of second molar protraction, duration of space closure and anterior anchorage loss were measured. A repeated measures analysis of variance was conducted to define the differences between the measured variables at the different time intervals. Differences between groups were assessed using ANOVA test. Results: No difference was detected between early and late piezocision groups in the amount of molar protraction at the end of space closure. Duration of complete space closure was 9 and 10 months in the piezocision and no piezocision groups. Anchorage loss was similar between the three studied groups. Conclusions: Early and late piezocision have similar effect and both increased the amount of second molar protraction temporarily in the first 2-3 months after surgery. Duration of mandibular first molar space closure was reduced by one month when piezocision was applied. Anchorage loss was similar in the three groups.


INTRODUCTION
Fixed appliance orthodontic treatment of moderate to severe malocclusions lasts a mean duration of 18 months. 1 In a systematic review, Mavreas and Athanasiou 2 concluded that the duration of orthodontic treatment is affected by several factors: extraction of teeth, type and severity of malocclusion, timing of treatment and the compliance of the patients. Recently, the acceleration of orthodontic treatment started to gain interest by both patients and orthodontists, especially adult patients, who prefer to complete orthodontic treatment as fast as possible. Also, a shorter treatment duration has the advantage of reducing many side effects associated with fixed orthodontic treatment, such as dental caries, gingival recession and root resorption. 3,4 Piezocision to accelerate tooth movement is a localized piezoelectric alveolar decortication technique that combines buccal microincisions and minimally invasive corticotomies. 5 Although many clinical trials were conducted to evaluate the effect of piezocision on the rate of tooth movement, [6][7][8][9][10][11][12][13][14][15] there is still a controversy regarding the acceleratory effect of piezocision on orthodontic tooth movement. Some studies reported a decrease in treatment duration, ranging from 23% to 59%, in the piezocision groups. 8, [11][12][13] On the other hand, Tunçer et al. 10 reported similar rate and treatment duration between piezocision and control groups. Al-Areqi et al. 15 found that overall second molar protraction was accelerated by only one month. Abu Alhaija ES, Al-Areqi MM, Al Maaitah EF -Comparison of second molar protraction using different timing for piezocision application: A randomized clinical trial 5 Differences in the sample size, piezocision surgical design and location, the tooth to be moved, stage of orthodontic treatment and mechanics used in the aforementioned studies contributed to this inconsistency.
The extraction space of mandibular first molar is considered relatively large. This may affect the archwire sliding during space closure and results in archwire binding, making space closure a more time-consuming procedure. Therefore, the timing for performing piezocision, whether it is before starting space closure or after closing part of the space, may produce different acceleratory effect on mandibular second molar protraction. This has not been investigated so far in orthodontic literature; therefore, the purpose of this randomized clinical trial is to investigate and compare the amount of mandibular second molars protraction when piezocision is performed earlier (immediately before molar protraction, larger extraction space) or later (after three months of molar protraction, shorter extraction space), to find out the proper timing for piezocision procedure. The null hypothesis of no difference in the amount of second molar protraction among early piezocision, late piezocision and control (no piezocision) groups was tested.
Abu Alhaija ES, Al-Areqi MM, Al Maaitah EF -Comparison of second molar protraction using different timing for piezocision application: A randomized clinical trial 6

TRIAL DESIGN
This study was a randomized controlled clinical trial with a 1:1 allocation ratio (piezocision vs. no-piezocision). In the piezocision group, a split-mouth design was utilized, with the timing for piezocision (early or late) randomly assigned to the left or right sides of treated patients. The methods were not changed after trial initiation.

PARTICIPANTS, ELIGIBILITY CRITERIA AND SETTINGS
The study was reviewed and approved by the Institutional Review Board (approval number 28/98/2016) at the University Hospital of Jordan University of Science and Technology (JUST).
This trial was registered at ClinicalTrials.gov with identifier number NCT04338789. The participants for this study were recruited from patients attending orthodontic clinics at the postgraduate dental clinics of JUST. All surgical procedures and orthodontic treatments were undertaken at the postgraduate dental clinics of JUST. The inclusion criteria for this study were: age range from 18 to 30 years, bilaterally extracted mandibular first molars (first molars extracted more than one year ago and with a residual extraction space of more than Subjects were selected based on these inclusion criteria, and were asked to sign a consent form to participate in this study, after clarifying the purpose of the intervention. Initial records (orthopantomogram, lateral cephalogram and alginate impressions) were obtained for all participants. Subjects were referred to the Periodontics department for evaluation of their periodontal health and to have regular oral care thereafter.

SAMPLE SIZE CALCULATION
Sample size was calculated using the G*Power v. 3.1.9 program.
According to the power analysis and assuming a small effect size difference (0.25) between groups, based on a split-mouth study to compare the monthly rate of molar protraction, 15  Assuming an overall attrition rate of 15%, initial recruitment should target a total of 45 molars with 15 molars per group.
Abu Alhaija ES, Al-Areqi MM, Al Maaitah EF -Comparison of second molar protraction using different timing for piezocision application: A randomized clinical trial 8 RANDOMIZATION Random allocation of subjects according to their group (piezocision or no piezocision) was done using the permuted random block size of 2, with a 1:1 allocation ratio, by one dental assistant.
The allocation sequence was concealed from the researcher by sequentially numbered, opaque, sealed and stapled envelopes before the intervention. Patients were asked to pick randomly a sealed envelope that assigned the method of intervention.
In piezocision group, just before mandibular molar protraction, early piezocision was randomly assigned to patients' left or right side by the same dental assistant, with the contralateral side allocated to serve in the other group (late piezocision).
Patients were asked to pick randomly a sealed envelope that assigned the side of intervention (early piezocision).

BLINDING
Blinding of either patient or clinician was not possible.
However, the measurements of the dental casts were performed by one research assistant who was blinded to the type of the intervention used.
Abu Alhaija ES, Al-Areqi MM, Al Maaitah EF -Comparison of second molar protraction using different timing for piezocision application: A randomized clinical trial

Orthodontic intervention
The selected patients had their orthodontic treatment performed by the same orthodontic resident, using fixed pread- wire. Study models were then fabricated. The time points for the protraction rate were; T 0 : baseline measurement before protraction,T 1 : after one month,T 2 : after two months,T 3 : after three months, T 4 : after four months,T 5 : after five months,T 6 : after six months and T 10 : after ten months of molar protraction.

SURGICAL PROCEDURE -PIEZOCISION
All the piezocisions were performed by a single resident in the periodontal clinic. The patients were asked to rinse with 0.2% chlorhexidine gluconate for one minute before being given local anesthesia. Then, 2% lidocaine anesthetic agent was used to perform an infiltration technique mesial and distal to the mandibular first molar extraction space. After that, two incisions were made using a #15 blade, mesial and distal to the extraction space. A piezotome was then inserted into the previously-made incisions and bone cuts were done up to the mucogingival line, at a depth of 3 mm. Piezocision was performed using a Mectron Piezosurgery device (Mectron, Genova, Italy). No sutures or any surgical dressings were placed after.
In Groups 1 and 2, patients were asked to return to the orthodontic clinic, immediately after the piezocision procedure, to attach the NiTi coil spring from the hook of the mandibular permanent second molar to the miniscrew. In Group 3, a NiTi coil spring was attached from the hook of the mandibular perma- » Mandibular second premolar: The distance from the distal surface of the mandibular second premolar at CEJ to the miniscrew, as determined from direct measurement of the study casts.

Treatment duration
Determined in months from the start of mandibular molar protraction until first molar space was almost or completely closed.
Abu Alhaija ES, Al-Areqi MM, Al Maaitah EF -Comparison of second molar protraction using different timing for piezocision application: A randomized clinical trial

METHOD ERROR
Ten subjects were randomly selected, and the study models measurements were done twice with two-week interval.
The Dahlberg formula was used to calculate the standard error of the method. Dahlberg errors were 0.17mm for the amount of molar protraction, 0.21mm for second premolar distal movement, and 0.37 ο for mandibular incisor inclination.  Table 1.

Rate of mandibular molar protraction and anchorage loss
First month after protraction (T 1 in Groups 1 and 3; T 4 in  Abu Alhaija ES, Al-Areqi MM, Al Maaitah EF -Comparison of second molar protraction using different timing for piezocision application: A randomized clinical trial

Amount of mandibular molar protraction
Means, standard deviations, differences between the means and p-values for the rate of second molar protraction and anchorage loss in the studied groups at the different time points are shown in Tables 2, 3 and 4.     In the early and late piezocision groups, the rate of molar protraction was increased in the first two months after performing piezocision, and slowed down afterwards. Molar protraction three months after early piezocision was 3.01 mm, two groups (p > 0.001). Three months after late piezocision, molar protraction was 2.00 mm, 3.43 mm and 1.91 mm in the early, the late and the no piezocision groups, respectively.

MANDIBULAR INCISORS INCLINATION
Significant differences were detected between the late piezocision group and the other two groups (p > 0.001).
Six months after initial space closure, the amount of molar protraction was 5.02 mm, 5.52 mm and 3.83 mm in Groups 1, 2 and 3, respectively. Significant differences were detected between the three studied groups (p > 0.001). However, near to the end of space closure (10 months), no difference was detected between early and late piezocision groups regarding the amount of molar protraction (p > 0.05).

ANCHORAGE LOSS
In piezocision groups, mandibular incisors proclined by 2.33 ο , whereas in no piezocision group, mandibular incisors pro- Duration of mandibular first molar space closure (Table 3) was   9.33 months, 9.26 months and 10.17 months in the early, the late and the no piezocision groups, respectively. Although treatment duration in the no piezocision group was one month more than the piezocision groups, the differences were statistically significant (p < 0.01). However, duration of first molar space closure was similar in the early and late piezocision groups (p > 0.05).

HARMS
No negative outcomes were reported by any patient during the trial.

DISCUSSION
In orthodontic literature, there is conflicting evidence regarding the effect of inter-brackets distance on frictional forces during space closure. Some investigators reported that an increased inter-brackets width during space closure allow a greater tipping, which could lead to increased angle interface between the archwire and the bracket floor, resulting in a greater binding incidence, 16 while others stated that resistance to sliding is inversely proportional to inter-brackets distance. 17,18 During mandibular second molar protraction, first molar extraction space will be large initially and will be reduced during subsequent space closure.
To our knowledge, no study investigated the effect of inter-brackets distance on the rate of tooth movement, therefore, the present randomized controlled clinical study was conducted.
A split-mouth design was adopted in this study to reduce the biological variability between the subjects 19 in which piezocision was applied, according to the technique described by Dibart et al. 5 In the current study, 3-mm vertical cuts in the buccal side of alveolar ridge were performed. The cuts were deeper than the traditional circumscribed corticotomy, which involves 2-mm vertical and horizontal cuts in the cortical bone circumscribing the teeth to be moved, to ensure blade access to the cortical bone. 5 Space closure was carried out on a rigid rectangular SS archwire to achieve maximum amount of bodily movement. 20 However, mesial tipping of mandibular second molars may still occur due to the play between archwire and molar tube. A closed NiTi coil spring was used to achieve molar protraction, since it provides constant force, when compared to an elastomeric chain, 21 and provides a more predictable amount of force.
The current trial demonstrated a significant increase in the rate of mandibular molar protraction in patients who received piezocision, compared to no piezocision group, which lasted for 2 to 3 months in the early and late groups, respectively. Up to 1-mm increase in the rate of molar protraction was found in the current study, which was less than that reported in previous trials. This may be related to different factors, such as: the structure of mandibular bone, compared to maxillary bone; molar protraction through old extraction space, compared to retraction of canine to the recently extracted first premolar space. Charavet et al. 14 reported that piezocision is more effective in the maxilla than in the mandible.
In the current study, the rate of molar protraction was almost similar whether the inter-brackets distance was small or large.
In both early and late piezocision groups, tooth movement was accelerated temporarily for two months by a comparable amount.
Abu Alhaija ES, Al-Areqi MM, Al Maaitah EF -Comparison of second molar protraction using different timing for piezocision application: A randomized clinical trial 23 The findings of the current study was in disagreement with previous studies that suggested inter-brackets width affects frictional resistance. Some studies reported that reduced inter-brackets distance produced greater frictional resistance, 17,18,23 and others suggested that as the inter-brackets distance reduces, friction reduces, due to reduction in tipping. 24,25 The findings of the current study may be related to the other variables affecting force delivery during molar protraction. Nanda 26 stated that a large inter-brackets distance reduces the load/deflection rate and helps deliver constant force magnitude, providing better directional control of the tooth movement.
Although the rate of mandibular second molar protraction was slightly higher in the late piezocision group, compared to the early one, the duration of space closure in both piezocision groups was similar at the end of treatment, and was faster in both piezocision groups, compared to no piezocision group.
This finding was in agreement with previous studies 8,11,12-14 that reported reduction in treatment time up to 59% by piezocision, and in disagreement with others that reported no difference in treatment time. 9,10 Even though the rate of molar protraction was increased following early and late piezocision groups, the net reduction in space closure duration was less than one month. This was in agreement with Tunçer et al., 10  These two opposite forces may have masked anchorage loss.
Although temporary anchorage devices (TADs) have been proved to be effective in providing absolute anchorage during second molar protraction, 27 it has been reported that they do not remain absolutely stationary throughout orthodontic loading. 28