Randomized clinical trial of orthodontic treatment efficiency with self-ligating and conventional fixed orthodontic appliances


Our objective was to test the hypotheses that treatment with 2 fixed orthodontic appliances (SmartClip and Victory; 3M Unitek, Monrovia, Calif) would result in no difference in (1) the duration of orthodontic treatment or (2) the number of visits required.


Sixty-six consecutive patients were randomly allocated to treatment with a self-ligating bracket system (SmartClip) or a conventional appliance (Victory). The duration of treatment and the number of visits required in addition to the initial and final peer assessment rating (PAR) scores were recorded. The number of teeth extracted during treatment and the frequency of mechanical eruption of canines were also noted. Analyses of covariance were used to assess the influence of bracket type on treatment durations, visits required, and percentage PAR score reductions.


Fifty-four (81.8%) participants completed the study. The duration of treatment was 3 months greater in the group treated with SmartClip. However, bracket type had no statistical influence on treatment duration ( P = 0.076), total visits required ( P = 0.184), or percentage PAR score reduction ( P = 0.255).


Neither hypothesis could be rejected. Bracket type did not influence the duration of treatment or the number of visits required. The percentages of PAR score reductions were also unaffected by the choice of appliance.

Orthodontic treatment involving fixed appliances is typically completed in 15 to 24 months, with tooth movement relying on gradual bone turnover and periodontal adaptation in response to applied forces. Treatment time is influenced by various factors including patient compliance, occlusal features (eg, Class II molar relationship and impacted teeth), and treatment protocol, with extraction-based treatment and treatment involving molar-relationship correction more prolonged. The possibility that a bracket system might influence treatment duration has been advanced, but it remains unsubstantiated by prospective evidence. However, a development of this nature would be of obvious value to both patient and clinician by reducing time commitments and limiting associated biologic risks.

Self-ligating brackets have a built-in mechanism to close off the edgewise slot—usually a gate or clip securing the archwire. Many advantages of self-ligating bracket systems have been claimed, including reduced friction, less discomfort, more efficient tooth movement and sliding mechanics, less chair-side time, and reduced biohostability. However, perhaps the most compelling potential advantage is less overall treatment time; a reduction of up to 7 months was confirmed in retrospective studies with similar occlusal results obtained using the peer assessment rating (PAR) index.

Prospective research in this area has been confined to surrogate measures of treatment duration—eg, efficiency of initial alignment and space closure. Generally, these studies are incompatible with the claims that self-ligating appliances produce more efficient treatment. However, these studies did not consider the entire duration of orthodontic treatment. The purpose of this prospective study was to compare the efficiency of orthodontic treatment with SmartClip self-ligating brackets and Victory conventional twin brackets (both, 3M Unitek, Monrovia, Calif).

Material and methods

Ethical approval for the study was obtained from the South East Research Ethics Committee (06/MRE01/36, April 2006). The study was based in the Kent and Canterbury Hospital, Canterbury, and the Royal London Dental Institute, London, United Kingdom, with subjects recruited after their recall from the orthodontic treatment waiting lists in preparation for active therapy from May to September 2006.

The methodology was partially outlined elsewhere. Based on a retrospective power analysis, a total of 66 patients were required to demonstrate a clinically meaningful difference of 4 months in treatment duration between the appliance systems with a power of 80% and an α of 0.05, assuming a noncompletion rate of 30%. An unstratified subject allocation sequence was performed using a computer-generated randomization program. The subjects were between 11 and 21 years of age, required treatment with fixed appliances on a nonextraction basis in the mandibular arch, were in the permanent dentition, had mild mandibular incisor crowding, and had study models taken not more than 1 month before placement of the mandibular appliance. Patients were excluded if they had previous orthodontic treatment, had a complex medical history and were taking medications, had cleft lip and palate or other craniofacial anomalies, failed to attend more than 2 appointments, had 3 or more appliance breakages, were undergoing combined orthodontic-surgical treatment or correction of molar relationships, or had hypodontia in the mandibular arch other than third molars.

Two operators (P.S.F. and A.T.D.) treated the participants with both appliances; the vast majority were treated by an orthodontic resident (P.S.F.) who was equally experienced with the 2 appliances. The subjects were randomized to treatment with either a self-ligating (Smart Clip) or a conventional preadjusted edgewise system (Victory) with MBT values for tip and torque and a 0.022-in slot. All subjects followed a predetermined archwire sequence during arch levelling and alignment: 0.016-in nickel-titanium (NiTi), 0.017 × 0.025-in NiTi, 0.019 × 0.025-in NiTi, and 0.019 × 0.025-in stainless steel. Appliances were routinely adjusted at intervals of 8 weeks until the working archwire was passive; however, the 0.017 × 0.025-in NiTi wire was in situ for 6 weeks. Thereafter, treatment mechanics and archwire choices were governed by clinical requirements. Shorter interappointment intervals were used during the finishing stages. The operator was not blinded to appliance type during treatment.

Routine reference models were taken before and after treatment; all models were scored independently by an orthodontic technician. Treatment duration was measured in months from initial placement of the preadjusted edgewise appliances to their removal; the total number of appointments was also recorded. Potential confounding variables, including mechanical eruption of teeth and requirement for extractions, were noted.

Statistical analysis

Descriptive and analytical statistical analyses were performed with SPSS software (release 13.0, SPSS for Windows, SPSS, Chicago, Ill). The 2 groups were tested for differences in their baseline characteristics. Analysis of covariance (ANCOVA) was used to compare the treatment effects of the bracket systems while accounting for baseline differences and confounding continuous variables, including the number of canines mechanically erupted during treatment and the number of maxillary arch extractions undertaken. The level of statistical significance was set at P <0.05.


Sixty-six subjects were recruited for the study from May to September 2006. Overall, 54 subjects (81.8%) completed the study; those who failed to complete treatment were omitted from the analysis ( Fig ). Baseline demographic and clinical characteristics for both groups are summarized in Table I .

CONSORT flow diagram for subjects through the study.

Table I
Demographic baseline characteristics and clinical features of the sample
Variable Victory group SmartClip group Overall sample
Age (y) 15.48 (2.38) 16.11 (2.74) 15.81 (2.58)
Male 7 (26.9%) 11 (39.3%) 18 (33.3%)
Female 19 (73.1%) 17 (60.7%) 36 (66.7%)
Total 26 (78.8%) 28 (84.8%) 54 (81.8%)
Malocclusion type (n)
Class I 13 (50%) 10 (35.7%) 23 (42.5%)
Class II Division 2 5 (19.2%) 7 (25%) 12 (22.2%)
Class II Division 1 5 (19.2%) 9 (32.1%) 14 (25.9%)
Class III 3 (11.5%) 2 (7.1%) 5 (9.3%)
Patients having maxillary arch extractions (total) 6 (12) 9 (17) 15 (29)
Ectopic maxillary canines (total) 3 (4) 5 (7) 8 (11)

Mean (SD).

Frequency (%).

The mean duration of orthodontic treatment was 19.92 months overall: 18.32 months in the Victory group and 21.41 months in the SmartClip group. A mean of 15.7 visits was required for those treated with Victory, with 2 additional visits for the SmartClip group. The mean pretreatment and posttreatment PAR scores are given in Table II .

Apr 14, 2017 | Posted by in Orthodontics | Comments Off on Randomized clinical trial of orthodontic treatment efficiency with self-ligating and conventional fixed orthodontic appliances
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