Introduction
Orthodontic miniscrews have become popular not only because they can provide an absolute form of anchorage, but also because they can reduce the required patient compliance when compared with traditional orthodontic anchorage. The objective of this study was to examine success rates of miniscrews placed by orthodontic residents and to evaluate which factors may affect insertion outcomes.
Methods
The sample consisted of 109 consecutive miniscrews placed in 60 patients (27 males and 33 females). Miniscrews were placed at 4 different insertion sites (anterior palate [n = 31], palatal alveolar process [n = 25], maxillary buccal alveolar process [n = 15], and mandibular buccal alveolar process [n = 38]). Analysis of variance tests were used to evaluate the influence of insertion sites and anchorage type (direct vs indirect) on the success rate.
Results
The overall success rate for miniscrews was 72.5%. The success rate was 83.9% in the anterior palate, 76% in the palatal alveolar process, 60% in the maxillary buccal alveolar process, and 65.8% in the mandibular buccal alveolar process. The success rate was significantly higher in indirect anchorage (84.2%) compared with direct anchorage (58.8%).
Conclusions
Palatal miniscrews were more successful than buccal miniscrews. Indirect anchorage mechanics had a higher success rate than direct anchorage mechanics.
Highlights
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We report a 10-year audit of miniscrew use in a U.S. orthodontic residency program.
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Residents achieved acceptable success rates.
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Anterior palate and palatal alveolar processes were the most successful insertion sites.
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Indirect anchorage was more successful than direct anchorage.
Anchorage control in orthodontic treatment is essential for good treatment outcomes. Orthodontic miniscrews have become very popular not only because they can provide an absolute form of anchorage, but also because they can reduce or eliminate patient compliance when compared with traditional orthodontic anchorage methods. They have become more sophisticated and easy to use compared with the initial attempts using osteosynthesis screws. Currently, miniscrews come in various shapes and sizes, with different head designs allowing the installation of sophisticated biomechanics. , As a result, they have become an integral part of modern orthodontic treatment and are being used in the majority of U.S. orthodontic residencies.
Although multiple studies have reported miniscrew success rates and have made attempts to correlate them to various factors such as insertion torque, jaw, age, or sex, findings are contradictory, and the screws in these studies were typically placed by experts in the field. To date, no study has attempted to evaluate success rates for inexperienced users. The present study, therefore, aimed to evaluate how successful orthodontic miniscrews are being used by residents in a university-based accredited U.S. orthodontic training program.
Material and methods
This study was approved by the Institutional Review Board at Case Western Reserve University. Patient charts for cases using miniscrews in the orthodontic clinic from 2006 to 2016 were examined retrospectively. The sample consisted of 109 consecutively placed miniscrews in 60 patients (27 male and 33 females; average age, 18.5 years; minimum age, 13.3 years; maximum age, 41.9 years). A power analysis determined that the minimum required sample size required was 52. All miniscrews were placed by orthodontic residents under the supervision of a single instructor (S.B.) in the orthodontic clinic at Case Western Reserve University. All miniscrews placed were titanium-alloy tomas SD pins (Dentaurum, Ispringen, Germany) ( Fig 1 ) in 6-mm, 8-mm, and 10-mm length as was determined by local factors, with a universal inner diameter of 1.2 mm and an outer diameter of 1.6 mm. Screws were placed with manual drivers, either straight or contra-angle, depending on the site, and generally without a predrilling procedure, unless the cortical bone at the site was determined to be excessively thick (>1.5 mm). Here, a simple cortical bone perforation was undertaken with a 1 mm diameter round bur and irrigation with sterile saline solution. Insertion sites were categorized into 4 areas: anterior palate (AP) ( Fig 2 ), palatal alveolar process (PP) ( Fig 3 ), maxillary buccal alveolar process (MXP) ( Fig 4 ), and mandibular buccal alveolar process (MDP) ( Fig 5 ). The type of anchorage used was categorized into a direct anchorage and indirect anchorage. The miniscrew is considered to have failed if it becomes loose before achieving the desired treatment goal. The mobility of the screw was determined by visual inspection and manipulation at every appointment. For each patient, the following data were collected: sex, age, site of insertion, date of mini-implant insertion and removal, and type of anchorage used.
Statistical analysis
SPSS statistical software (version 17.0; SPSS Inc, Chicago, Ill) was used for all statistical analyses, and significance levels for all tests were set at a P value of 0.05. Analysis of variance tests were used to evaluate the influence of insertion sites and anchorage type (direct vs indirect) on the success rate with Tukey post-hoc test evaluating further interactions of the different variables.
Results
The overall success rate for miniscrews placed by orthodontic residents was 72.5%. The success rate was 83.9% in the AP, 76% in PP, 60% in the MXP, and 65.8% in MDP ( Table I ). Multiple post-hoc group comparisons showed a significant statistical difference when comparing the AP and PP with the buccal insertions sites. However, there was no statistical difference when comparing the MDP to the MXP ( Table II ).
| Sex | Insertion site | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| AP | PP | MXP | MDP | |||||||||
| S | F | Total | S | F | Total | S | F | Total | S | F | Total | |
| Female | 17 | 1 | 18 | 10 | 3 | 13 | 5 | 6 | 11 | 17 | 6 | 23 |
| Male | 9 | 4 | 13 | 9 | 3 | 12 | 4 | 0 | 4 | 8 | 7 | 15 |
| Total | 26 | 5 | 31 | 19 | 6 | 25 | 9 | 6 | 15 | 25 | 13 | 38 |
| Success rate (%) | 83.9 | 76 | 60 | 65.8 | ||||||||
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