Introduction
The purpose of this study was to compare the in-vivo failure rates of single-thread and dual-thread temporary anchorage device (TAD) designs over 18 months.
Methods
Thirty patients with skeletal Class II Division 1 malocclusion requiring anchorage from TADs for retraction of maxillary incisors into the extracted premolar space were recruited in this parallel group, split-mouth, randomized controlled trial. A block randomization sequence was generated with Random Allocation Software (version 2.0; Isfahan, Iran) with the allocations concealed in sequentially numbered, opaque, sealed envelopes. A total of 60 TADs (diameter, 2 mm; length, 10 mm) were placed in the maxillary arches of these patients with random allocation of the 2 types to the left and the right sides in a 1:1 ratio. All TADs were placed between the roots of the second premolar and the first molar and were immediately loaded. Patients were followed for a minimum of 12 months and a maximum of 18 months for the failure of the TADs. Data were analyzed blindly on an intention-to-treat basis.
Results
Four TADs (13.3%) failed in the single-thread group, and 6 TADs (20%) failed in the dual-thread group. The McNemar test showed an insignificant difference ( P = 0.72) between the 2 groups. An odds ratio of 1.6 (95% confidence interval, 0.39-6.97) showed no significant associations among the variables. Most TADs failed in the first month after insertion (50%).
Conclusions
The failure rate of dual-thread TADs compared with single-thread TADs is statistically insignificant when placed in the maxilla for retraction of the anterior segment. Registration: The trial was not registered before commencement. Protocol: The protocol was not published before the trial.
Highlights
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Many temporary anchorage devices (TADs) are available in the orthodontic market.
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There is no sound clinical trial for the evaluation of TADs with and without a microthread.
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Our study suggests an insignificant difference in the survivability of the 2 types of TADs when tested in a split-mouth randomized controlled trial.
Orthodontic miniscrews or temporary anchorage devices (TADs) have been a relatively recent addition to contemporary orthodontics for the provision of anchorage for various tooth movements. Economical cost, ease of insertion and removal, immediate loading, and less cooperation by the patient have made them popular among orthodontists. The stability of the TADs and their ability to take up an orthodontic load is essential for the success of treatment. Prosthetic implants have a low failure rate of less than 10% ; the failure rate for TADs, however, can be 20%. Various designs and modifications by different manufacturers have been suggested to minimize the failure of implants, especially when loaded immediately. These include laser ablation of the coronal part of the implant and reducing the distance between the threads of the implant (pitch) on the coronal part of the implant as in the MicroThread design of ASTRA TECH (Dentsply, York, Pa), along with sand blasting and acid etching of the surface. The microthread design of ASTRA TECH was introduced in 1992. It has been shown that the stresses generated at the cortical bone can be reduced, with less resorption of the marginal bone, by decreasing the pitch of the threads in the cortical area. The above studies were carried out on prosthetic implants, but at this writing no publication was found relating to the clinical performance of dual-thread TADs.
Specific objectives or hypotheses
The aim of our study was to design a dual-thread TAD and compare it clinically with a single-thread TAD in a split-mouth randomized clinical trial.
Material and methods
Trial design and any changes after trial commencement
This was a parallel group, split-mouth, randomized, active controlled trial with a 1:1 allocation ratio. No changes were made after trial commencement.
Participants, eligibility criteria, and settings
For the clinical trial, approval from the ethical committee of Riphah International University was sought. Informed consent from the patients involved in the study was also obtained. Thirty patients were recruited from the university’s Department of Orthodontics. The inclusion criteria were patients with skeletal Class II Division 1 malocclusion with molars in a full-cusp Class II relationship and a normal angle of the maxilla to the mandibular plane (25° ± 5°). The patients required extraction of maxillary first premolars for the retraction of incisal segment. The extractions were done either before the placement of the implant or immediately after the placement. The eligibility criteria also required the patients to be right-handed adolescents with no canine interferences, no bone abnormalities, and no previous placement of TADs ( Fig 1 ).
Interventions
The TADs were made with a titanium-aluminum-vanadium alloy. Both TADs— single thread and dual thread—had the same dimensions; the total length of the TAD was 13 mm and the length of the threaded portion was 10 mm ( Figs 2-4 ). The diameter of the TAD was 2 mm. The tip had a taper of 3° with a vertical channel for self-drilling and self-tapping. The heads of both TADs had an external hexagonal design . The difference in the 2 TADs was in the pitch of the threads: 0.8 mm throughout for the single-thread TAD and for the dual-thread TAD, 0.8 mm for the apical 7.5 mm of the shaft and a 0.25-mm pitch for the coronal 2.5 mm.
All TADs were placed by the same operator (O.K.D.), who was right handed. Periapical radiographs of the area where the TADs were supposed to be placed were taken before and after the procedure to assess the space between the roots and any contacts with the roots of adjacent teeth, respectively. The TADs were at an angulation of approximately 45° to the long axis of the tooth just occlusal to the mucogingival junction as recommended by Kim et al. Patients were advised to apply 0.25% chlorhexidine gel on and around the TADs at least 3 times a day. After placement of the TAD, the first premolars, if not extracted previously, were extracted, and the TAD was directly loaded with a 300-g nickel-titanium coil spring (Ortho-Care, Saltaire, United Kingdom) with the spring extended between the TAD and the hook of the canine bracket of the corresponding side. The incisors and the canines were joined with steel ligature, and en-masse retraction was performed.
Outcomes (primary and secondary) and any changes after trial commencement
The primary outcome was the failure of the TAD; this was defined as loosening of the TAD so that it could not bear the loading forces of the retraction spring. The data were recorded at monthly intervals, until either the orthodontic treatment was completed or the TAD needed removal because of treatment completion or failure. No changes to methods after trial commencement occurred.
Sample size calculation
No sample size calculation was carried out before the study.
Interim analysis and stopping guidelines
Not applicable.
Randomization (random number generation, allocation concealment, implementation)
In this split-mouth study, only patients who required bilateral maxillary implants were included. A total of 60 TADs were placed, with each patient receiving 2 different types of TADs. The TADs in the maxillary arches were randomly allocated by Random Allocation Software (version 2.0; Isfahan, Iran) in a 1:1 distribution to the left and right sides in equal numbers. After the random sequence generation, the allocation of the random numbers for each patient was sealed in an opaque envelope. Before placing the implants, the envelope was opened to reveal the type of TAD to be placed on either side of the maxillary arch of that patient. The random number generation, allocation, concealment, and implementation were performed by the department manager, who had no financial, research, or publishing interest in this study.
Blinding
Blinding was applied to the assessment of the outcome. Due to the differences in the head design and the threads, blinding of the patient and the operator was impossible.
Statistical analysis (primary and secondary outcomes, subgroup analyses)
Statistical analyses were performed using SPSS software for Windows (version 20; IBM, Armonk, NY). TAD survival rates were evaluated with the Kaplan-Meier test ( Fig 5 ). Differences in the survival curves were evaluated with the Breslow (generalized Wilcoxon) test. Differences between the groups were assessed using the McNemar test with chi-square or Fisher exact statistics. In addition, odds ratios with 95% confidence intervals were calculated on the basis of the McNemar test, which uses discordant pairs for the odds ratio. The level of significance was set at P = 0.05 or less.
Material and methods
Trial design and any changes after trial commencement
This was a parallel group, split-mouth, randomized, active controlled trial with a 1:1 allocation ratio. No changes were made after trial commencement.
Participants, eligibility criteria, and settings
For the clinical trial, approval from the ethical committee of Riphah International University was sought. Informed consent from the patients involved in the study was also obtained. Thirty patients were recruited from the university’s Department of Orthodontics. The inclusion criteria were patients with skeletal Class II Division 1 malocclusion with molars in a full-cusp Class II relationship and a normal angle of the maxilla to the mandibular plane (25° ± 5°). The patients required extraction of maxillary first premolars for the retraction of incisal segment. The extractions were done either before the placement of the implant or immediately after the placement. The eligibility criteria also required the patients to be right-handed adolescents with no canine interferences, no bone abnormalities, and no previous placement of TADs ( Fig 1 ).
Interventions
The TADs were made with a titanium-aluminum-vanadium alloy. Both TADs— single thread and dual thread—had the same dimensions; the total length of the TAD was 13 mm and the length of the threaded portion was 10 mm ( Figs 2-4 ). The diameter of the TAD was 2 mm. The tip had a taper of 3° with a vertical channel for self-drilling and self-tapping. The heads of both TADs had an external hexagonal design . The difference in the 2 TADs was in the pitch of the threads: 0.8 mm throughout for the single-thread TAD and for the dual-thread TAD, 0.8 mm for the apical 7.5 mm of the shaft and a 0.25-mm pitch for the coronal 2.5 mm.
