ORIGINAL ARTICLE

Comparative study of the primary stability of self-drilling and self-tapping orthodontic miniscrews Seil Son,a Mitsuru Motoyoshi,b Yasuki Uchida,c and Noriyoshi Shimizud Tokyo, Japan Introduction: The purpose of this study was to determine the influence of self-tapping and self-drilling placement techniques on the stability of miniscrews. Methods: We included 70 orthodontic patients who received miniscrews (140 screws). Miniscrews measuring 1.6 mm in diameter and 8 mm in length were placed using the self-tapping (35 patients, 70 screws) and self-drilling (35 patients, 70 screws) methods. We examined the success rates, placement torque values, Periotest (Medizintechnik Gulden, Bensheim, Germany) values, rates of root contact, and influence of root contact on mobility. Cone-beam computed tomography was used to evaluate root contact. Miniscrews that endured an orthodontic force for 6 months or more were considered successful. Results: The success rates of the miniscrews were approximately 96% with either placement technique. The placement torques were 7 and 7.5 N cm in the self-tapping and self-drilling miniscrews, respectively (P .0.05). The Periotest values of the self-drilling method were significantly greater than those of the self-tapping method. The Periotest values of the self-drilling miniscrews with root contact were significantly greater than those with no root contact. Conclusions: Both placement techniques showed high stability in the maxillary bone, although the self-drilling miniscrews with root contact had greater mobility. Special attention to root contact further improves the stability of the self-drilling miniscrews. (Am J Orthod Dentofacial Orthop 2014;145:480-5)

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elf-tapping miniscrews have been used as orthodontic anchorage devices.1 This miniscrew requires the preparation of a pilot hole before insertion; this is time-consuming and might result in drill-bit breakage and thermal necrosis of bone.2 On the other hand, the design of self-drilling miniscrews enables them to be inserted without drilling.2-4 Several animal studies have compared the 2 methods. With a dog model, Yadav et al5 demonstrated greater microdamage to the cortical bones of both the maxilla and the mandible using self-drilling compared with self-tapping, but they did not report the failure rate.

From the Department of Orthodontics, School of Dentistry, Nihon University, Tokyo, Japan. a Visiting researcher. b Associate professor, Division of Clinical Research, Dental Research Center. c Assistant professor. d Professor and chair, Division of Clinical Research, Dental Research Center. All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest, and none were reported. Address correspondence to: Mitsuru Motoyoshi, Department of Orthodontics, Nihon University School of Dentistry, 1-8-13 Kanda-Surugadai, Chiyodaku, Tokyo 1018310, Japan; e-mail, [email protected]. Submitted, July 2013; revised and accepted, December 2013. 0889-5406/$36.00 Copyright Ó 2014 by the American Association of Orthodontists. http://dx.doi.org/10.1016/j.ajodo.2013.12.020

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Shank et al6 quantified the bone damage associated with the insertion of both types of miniscrews in dogs and found no difference in the damage parameters in the maxilla, which has similar conditions to human alveolar bone in terms of cortical bone thickness. Gupta et al2 evaluated the stability of self-tapping and self-drilling screws when used as anchorage units for en-masse retraction of maxillary anterior teeth; they demonstrated that both the self-tapping and the self-drilling screws were effective anchorage units. Moreover, they described the advantages of selfdrilling screws, which included decreased operative time, little bone debris, less thermal damage, lower morbidity, and minimal patient discomfort because predrilling is not required. Thus, if both the self-tapping and the self-drilling methods result in placement with equal stability, then the self-drilling method should be preferred because of its clinical advantages. However, Park et al7 stated that self-drilling screws are not recommended for placement in dense and thick cortical bone such as the mandibular molar region; instead, the self-tapping method is preferred to prevent fracture of the screw or the bone. Thus, the self-drilling method might be preferred in thin cortical bone areas such as maxillary alveolar bone in interradicular spaces.

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Placement, removal torque8-10 and the mobility of the screw11 are clinical indices of the stability of miniscrews. Miniscrew stability is thought to be related to overloading,12 inflammation,13 cortical bone thickness and bone density,7 screw design,11,12 and adjacent root proximity.14 Root proximity is an important risk factor because of its relationship with failure.14 Technical biases related to the self-tapping and self-drilling methods might affect root proximity. The aim of this clinical trial was to identify the influences on miniscrew stability of the self-tapping and self-drilling placement techniques. To determine the differences between the self-tapping and selfdrilling methods, we focused on (1) success rate, (2) placement torque, (3) mobility, (4) root contact frequency, and (5) the influence of root contact on mobility. In this study, 70 patients who received miniscrews were randomly selected and evaluated; 35 patients had the self-tapping method, and 35 had the self-drilling method. Placement torque was evaluated using a torque tester, mobility was measured with a Periotest device (Medizintechnik Gulden, Bensheim, Germany), and the placement sites were shown using cone-beam computed tomography (CBCT). MATERIAL AND METHODS

This study included 70 orthodontic patients from 2010 to 2011 who received miniscrews (140 screws) in the maxillary buccal alveolar bone between the second premolar and the first molar. All miniscrews were used as anchors for anterior retraction for first premolar extractions. The subjects were randomly divided into 2 groups: the first group comprised 35 patients (25 female, 10 male; average age, 23.2 6 7.7 years) who had self-tapping for miniscrew placement, and the second group comprised 35 patients (24 female, 11 male; average age, 22.3 6 7.4 years) who had self-drilling. This study was approved by the ethical review board of Nihon University School of Dentistry, Tokyo, Japan, and all patients consented to participate. All patients received miniscrews of the same design, measuring 1.6 mm in diameter and 8 mm in length (ISA self-drill type anchor screw; Biodent, Tokyo, Japan) to prevent any effects of screw design (Fig 1). In the self-tapping group, after administration of local anesthesia, a pilot hole (1.0-mm diameter, 8.0mm length) was drilled using a bone drill under physiologic saline solution flow into the buccal alveolar bone in an area of keratinized gingiva between the second premolar and the first molar of the maxilla. In the self-drilling group, local anesthesia was

Fig 1. The self-drilling miniscrew used in this study: screw thread length, 8 mm; total length, 11 mm; internal diameter, 1.2 mm; external diameter, 1.6 mm.

administered, and the miniscrews were placed with no pilot hole. The sole difference was whether there was a pilot hole, and no punch or incision of the surrounding gingiva was made in either method. To reduce the likelihood of root contact, the miniscrew was placed so that it inclined 45 to 60 vertically with respect to the adjacent tooth axis and was perpendicular horizontally to the bone surface. Examiners (Y.U. and S.S.) measured the maximum placement torque during terminal rotation of all miniscrews using a torque tester (DIS-RL05; nominal accuracy, 60.5%; Sugisaki Meter, Tokyo, Japan) and recorded the mobility (Periotest value) using the Periotest device after placement. Miniscrew mobility has been assessed with the Periotest11 and Osstell devices.15 The Periotest is used to assess the damping capacity, and the Osstell uses resonance frequency. The Osstell instrument requires a

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Fig 2. CBCT cross-sectional images of root contact corresponding to the long axes of the miniscrews: A, no root contact; B, no radiolucency between the screw and the root surface indicates root contact.

SmartPeg attachment containing a magnet. Because SmartPeg modification and the use of miniscrews with inner screw threads would have been difficult in this study, we used the Periotest device. A greater Periotest value indicated more mobility. For each screw, Periotest values were obtained by holding the tip of the handpiece parallel to the bone surface according to the manufacturer's instructions. Each measurement was repeated 3 times, and the average value was calculated. Immediately after placement, an orthodontic force of approximately 2 N was applied to the miniscrews, and CBCT (3D Accuitomo; J. Morita, Kyoto, Japan) imaging for each subject was performed for postplacement diagnosis. All miniscrews were used as anchors for orthodontic treatment at Nihon University School of Dentistry Dental Hospital, Tokyo, Japan. Each patient was prescribed an antibiotic for 3 days after placement to control infection. The following parameters were used for CBCT diagnostic imaging of the placement site: field of view of 60 3 60 mm, voxel size of 0.125 mm3 in super high-resolution mode, x-ray tube voltage of 80 kV, and current of 5.5 mA. A 3-dimensional viewer program (One Volume Viewer, version 1.6.1.13; J. Morita) was used to define the tomographic cross-sections that corresponded to the long axis of the miniscrew and to simultaneously observe cross-sections of the adjacent roots. The distance between the root and the miniscrew was ascertained, and then we judged the root proximity to each miniscrew (Fig 2). Root contact was defined as the absence of radiolucency between the screw and the adjacent root surface. A miniscrew was considered a success when it endured an orthodontic force applied for 6 months or more without clinical mobility. To determine the difference between the self-tapping and self-drilling methods, we compared the success rates, placement torques, Periotest values, rates of root contact, and Periotest values according to root contact.

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To evaluate measurement error, we randomly selected the CBCT images of 10 subjects and reevaluated their root proximity 2 weeks after the initial evaluations. The chi-square or Fisher exact test was used to compare the results of the self-tapping and self-drilling methods; the Fisher exact test was used when there were more than 20% of cells with an expected value of less than 5 in a contingency table. Analyses were performed using SPSS statistical software (version 16.0; SPSS Japan, Tokyo, Japan), and P \0.05 indicated statistical significance. RESULTS

Miniscrews that endured an orthodontic force for 6 months or more were considered successful. No screws loosened after 6 months or more because these subjects were patients who had been having orthodontic force applied for more than 2 years. To evaluate the root proximity judgment error, the CBCT images of 10 subjects were randomly selected and reevaluated 2 weeks later. There was no difference between the first and the second judgments in these subjects. The success rate of the miniscrews was approximately 96% for either placement technique. The respective success rates of male and female subjects were 95.9% and 95.2% in the self-drilling group, and 96.0% and 95.0% in the self-tapping group (P .0.05). The success rates of the self-tapping and the self-drilling methods in the right side were 94.3% and 91.4%, respectively; the success rates in the left side were 97.1% and 100%, respectively (Table I, P .0.05). The placement torque values of both methods were 7 to 7.5 N cm, with no significant difference (Table II). The Periotest value of the self-drilling method was 3.8, and this value was significantly greater than that of the self-tapping method (Table III). The rate of root contact on the right was 22.9% and that

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Table I. Success rates of self-tapping and self-drilling

methods Self-tapping Right Left Self-drilling Right Left

Success rate (%) 95.7 94.3 97.1 95.7 91.4 100.0

n 67 33 34 67 32 35

Table IV. Rates of root contact for self-tapping and self-drilling methods Rate of root contact (%) 20.0 22.9 17.1 20.0 22.9 17.1

Self-tapping Right Left Self-drilling Right Left

n 14 8 6 14 8 6

Table II. Placement torque values (N cm) for

Table V. Periotest values of miniscrews with and

self-tapping and self-drilling methods

without root contact

Self-tapping Self-drilling

Mean 7.0 7.5

SD 2.1 3.1

Table III. Periotest values of the self-tapping and

self-drilling methods Self-tapping Self-drilling

Mean 1.4 3.8*

SD 3.5 4.0

*P \0.05 (self-tapping vs self-drilling).

on the left was 17.1% (P .0.05), with no significant difference between the 2 methods (Table IV). The Periotest value of the self-drilling miniscrew with root contact was significantly greater than that with no contact (Table V). DISCUSSION

No significant difference was detected in the success rates of the self-tapping and the self-drilling methods. Tachibana et al16 reported that both the self-tapping and the self-drilling placement methods were safe without visible bone damage or screw fracture when the miniscrews were placed into thin cortical bone areas such as maxillary alveolar bone; torque values were within the recommended range (5-10 N cm) for both methods.8,9 The placement torque of the self-tapping method was 7 N cm and that of the self-drilling method was 7.5 N cm (P .0.05); both torque values were within the recommended range. These torque values might have contributed to the increased success rates of both methods in the maxilla. The right side with either method had a lower success rate than did the left side, but the right and left side differences were not statistically significant. Wu et al17 investigated 414 miniscrews and found that the left side had a lower failure rate than the right side. The higher rate of root

No contact Self-tapping Self-drilling

Mean 1.4 3.1*

Contact SD 3.7 3.6

Mean 1.5 6.5*y

SD 2.2 4.6

No contact, Periotest values of miniscrews without root contact; contact, periotest values of miniscrews with root contact. *P \0.05 (self-tapping vs self-drilling); yP \0.05 (no contact vs contact).

contact on the right side might be related to the greater prevalence of right-handed clinicians: surgical access on the right side might be more difficult for a right-handed person; however, future studies with larger samples should be performed. A mobility test device was used in this study to evaluate minuscule mobility of the miniscrews objectively. Several studies have compared the Periotest and Osstell devices, which are the most prevalent mobility test devices18-21 Oh et al18 examined the precision of both devices and stated that both noninvasive diagnostic methods were useful and comparably reliable. In contrast, Lachmann et al21 determined that the Osstell instrument was more precise in their in-vitro study, and this instrument requires a SmartPeg attachment containing a magnet for the measurement of mobility. Because it was difficult to prepare SmartPeg modifications to fit the orthodontic miniscrews, and Inaba22 found a strong correlation between the screw-bone contact condition and the Periotest value, which can be an appropriate index of the screw stability, we used the Periotest device. The self-drilling group showed significantly higher Periotest values than did the self-tapping group, although the screws had no root contact: the self-drilling miniscrews had greater mobility caused by other factors than root contact. However, the greater mobility of the self-drilling method did not affect the success rate. Shank et al6 reported bone damage in the maxilla with a thin cortical bone area. This microdamage

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in the bone might cause mobility of miniscrews placed with the self-drilling method; however, a Periotest value of approximately 4 is acceptable mobility to prevent loosening of the miniscrews. One fifth of the miniscrews contacted the roots of the adjacent teeth, with no difference between the self-tapping and self-drilling methods. Kim et al23 reported a higher rate of root contact than in our study; 30% of the miniscrews contacted adjacent roots, whereas Min et al24 reported a lower rate of root contact, at 9.3%. The probability of root contact is influenced by miniscrew diameter; Kim et al used miniscrews with a diameter of 1.8 mm, and Min et al used miniscrews with a diameter of 1.2 mm. We used miniscrews with an intermediate diameter. The Periotest values of the miniscrews with self-drilling placement showed a significant difference according to root proximity. The mobility of the self-drilling miniscrews with root contact was significantly greater than that of those without root contact, whereas self-tapping miniscrews were stable regardless of root proximity. The self-tapping method involves drilling a pilot hole in the bone; this might create a concavity on the root surface in cases of root contact; this concavity might buffer the shock caused by root contact. This is merely an assumption, but it might reduce the adverse effects on the mobility of the miniscrews. Thus, root damage from predrilling might be overlooked, although it is recommended to immediately remove a miniscrew after root contact to allow for reparative cementum. Kuroda et al14 investigated the correlation between failure of self-tapping miniscrews and root proximity and concluded that root proximity is a factor for miniscrew failure in the mandible, and Watanabe et al25 verified this in their study using CBCT. However, they found no significant correlation between root proximity and miniscrew failure in the maxilla, perhaps due to the small number of subjects in their study. We believe that the reason for the nonsignificant correlation in the maxilla could be the buffer effect associated with predrilling. To avoid root contact, Watanabe et al recommended the use of CBCT for diagnosis and evaluation of miniscrew placement, and we support their recommendation. CONCLUSIONS

1.

We do not recommend the self-tapping method over the self-drilling method in maxillary alveolar bone because both placement techniques had high success rates.

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2.

3.

4.

The self-drilling miniscrews showed greater mobility than did the self-tapping miniscrews, although this difference did not influence the success rate of the self-drilling method. Special attention to root proximity is recommended because miniscrews with root contact had significantly greater mobility when placed with the self-drilling method compared with the self-tapping method. With self-tapping miniscrews, root contact can be overlooked because it did not affect the high mobility in the self-tapping group.

ACKNOWLEDGMENTS

We thank the staff of the Department of Radiology of Nihon University School of Dentistry for their assistance with the CBCT. REFERENCES 1. Kanomi R. Mini-implant for orthodontic anchorage. J Clin Orthod 1997;31:763-7. 2. Gupta N, Kotrashetti SM, Naik V. A comparative clinical study between self tapping and drill free screws as a source of rigid orthodontic anchorage. J Maxillofac Oral Surg 2012;11:29-33. 3. Heidemann W, Gerlach KL. Clinical applications of drill free screws in maxillofacial surgery. J Craniomaxillofac Surg 1999; 27:252-5. 4. Heidemann W, Gerlach KL, Gr€ obel KH, K€ ollner HG. Drill free screws: a new form of osteosynthesis screws. J Craniomaxillofac Surg 1998;26:163-8. 5. Yadav S, Upadhyay M, Liu S, Roberts E, Neace WP, Nanda R. Microdamage of the cortical bone during mini-implant insertion with self-drilling and self-tapping techniques: a randomized controlled trial. Am J Orthod Dentofacial Orthop 2012;141: 538-46. 6. Shank SB, Beck FM, D'Atri AM, Huja SS. Bone damage associated with orthodontic placement of miniscrew implants in an animal model. Am J Orthod Dentofacial Orthop 2012;141: 412-8. 7. Park HS, Lee YJ, Jeong SH, Kwon TG. Density of the alveolar and basal bones of the maxilla and the mandible. Am J Orthod Dentofacial Orthop 2008;133:30-7. 8. Motoyoshi M, Hirabayashi M, Uemura M, Shimizu N. Recommended placement torque when tightening an orthodontic mini-implant. Clin Oral Implants Res 2006;17:109-14. 9. Motoyoshi M, Yoshida T, Ono A, Shimizu N. Effect of cortical bone thickness and implant placement torque on stability of orthodontic mini-implants. Int J Oral Maxillofac Implants 2007; 22:779-84. 10. Motoyoshi M, Uemura M, Ono A, Okazaki K, Shigeeda T, Shimizu N. Factors affecting the long-term stability of orthodontic mini-implants. Am J Orthod Dentofacial Orthop 2010;137: 588.e1-5. 11. Uemura M, Motoyoshi M, Yano S, Sakaguchi M, Igarashi Y, Shimizu N. Orthodontic mini-implant stability and the ratio of pilot hole implant diameter. Eur J Orthod 2012;34:52-6.

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Comparative study of the primary stability of self-drilling and self-tapping orthodontic miniscrews.

The purpose of this study was to determine the influence of self-tapping and self-drilling placement techniques on the stability of miniscrews...
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