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Survival analysis of a miniplate and tube device designed to provide skeletal anchorage
ORIGINAL ARTICLE
Survival analysis of a miniplate and tube device designed to provide skeletal anchorage Shin-Jae Lee,a Lu Lin,b Seong-Hun Kim,c Kyu-Rhim Chung,d and Richard E. Donatellie Seoul and Suwon, Korea, and Gainesville, Fla Introduction: The aim of this prospective cohort study was to compute the clinical survival and complication rates of a miniplate with a tube device (C-tube) used for orthodontic treatment. Methods: From August 2003 to May 2012, 217 patients were recruited. They received 341 C-tube miniplates. Some C-tube miniplates were removed because orthodontic treatment ended. Others remained beyond the study period and were recorded as censored data. Survival was classified as a C-tube miniplate that functioned in the mouth regardless of any complications. Success was defined as survival without complications. From the data, the effects of these clinical variables on the survival of the C-tube miniplates were evaluated: sex, age, jaw, placement sites, oral hygiene, tube clearance, inflammation, miniplate shape, number of screws, and length of the fixation screws. Survival analyses using the Kaplan-Meier method and the Cox proportional hazard model were applied. Results: Of the 341 miniplates, 14 failed, and 32 had complications. Two-year survival and success rates were 0.91 and 0.80, respectively. In terms of the simple ratio statistic, this was equivalent to a success rate of 96%. The status of oral hygiene maintenance and the operators’ experience had significant associations with the complication rates (P \0.001). Conclusions: The C-tube miniplate has an advantage in versatility in terms of force application. When placing a miniplate, the most important factor is maintaining good tissue health by means of good oral hygiene. Even with good hygiene, the doctor’s experience in performing the flap surgery was the second most important factor for success. (Am J Orthod Dentofacial Orthop 2013;144:349-56)
T
he orthodontic miniplate system was initially similar to the maxillofacial plating system,1-4 which evolved to have a specifically modified end to engage orthodontic auxiliaries.5 Recently, orthodontic miniplate systems have become increasingly accepted by a Professor and chair, Department of Orthodontics, School of Dentistry and Dental Research Institute, Seoul National University, Seoul, Korea. b Postgraduate student, Department of Orthodontics, School of Dentistry, Kyung Hee University, Seoul, Korea. c Associate professor and chair, Department of Orthodontics, School of Dentistry, Kyung Hee University, Seoul, Korea. d Professor and chair, Department of Orthodontics, School of Medicine, Ajou University, Suwon, Korea. e Clinical assistant professor, Department of Orthodontics, College of Dentistry, University of Florida, Gainesville, Fla. Shin-Jae Lee and Lu Lin are joint first authors and contributed equally to this work. All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest, and none were reported. Supported by the Basic Science Research Program through the National Research Foundation of Korea funded by the MSIP, Korean government (grants 20120007545 and 2012-0047622). Reprint requests to: Seong-Hun Kim, Department of Orthodontics, Kyung Hee University School of Dentistry, 1 Hoegi-Dong, Dongdaemun-Gu, Seoul 130-701 Korea; e-mail, [email protected]. Submitted, November 2012; revised and accepted, March 2013. 0889-5406/$36.00 Copyright Ó 2013 by the American Association of Orthodontists. http://dx.doi.org/10.1016/j.ajodo.2013.03.026
both patients and clinicians as a safe and effective adjunct for complex orthodontic treatment.6 Some attachments can also be added onto the miniplate. A miniplate with a tube device, such as a C-tube or a Bollard miniplate implant, is an efficient tool for borderline patients who would have been otherwise difficult to treat.7-16 Clinicians are frequently concerned about the ultimate success rate and the risk factors involved in miniplate failures and complications. The most conspicuous findings when comparing miniplates with mini-implants are the better stability and higher success rates of miniplates. Despite their popularity, orthodontic mini-implants have failure rates as high as 10% to 24%.3,17-23 However, miniplate failure rates vary from 1% to 7%.2,6,10,14,23,24 Survival analysis is a systematic statistical method of evaluating the mechanical success or failure of a particular system. Survival analysis has several advantages of measuring a failure pattern over time, especially when those survival data have a principal end point.25-27 Most orthodontic articles have reported simple success or failure rates of mini-implants,2,3,22,24,28 but some have used survival analysis when evaluating mini-implant success or failure.21,27 However, a 349
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Fig 1. The distribution of treatment and follow-up time from August 2003 to May 2012; 341 C-tube miniplates were sorted on the y-axis according to the date of miniplate placement on the x-axis.
survival analysis has not yet been used to analyze the long-term success or failure of miniplates. Reports of the success or failure patterns of miniplates over time have been missing from the literature. Even in what has been categorized as clinical success, miniplates sometimes cause complications such as swelling, tissue proliferation, and infection, which can lead to loosening of the miniplate.2,3,23 These adverse complications are not reflected in a simple success or failure rate. A better analysis that distinguishes among simple survival of the miniplate and success with or without various complications would provide valuable guidelines to a clinician wishing to use miniplates and maximize their clinical conditions. The aim of this prospective cohort study was to analyze the clinical survival and success rates without complications of the miniplate and tube device used for orthodontic treatment. MATERIAL AND METHODS
All patients were treated with fixed appliances. The miniplate with a tube device (C-tube; Jin Biomed, Bucheon, Korea) used for this clinical study was composed of a titanium miniplate fixture on the bone side and a welded tube on the oral cavity side. The subjects included 217 patients (137 female, 80 male; average age, 22 years; range, 11-61 years) who had undergone orthodontic treatment with a C-tube miniplate (Fig 1). From August 2003 through May 2012, the subjects were treated at 3 universityaffiliated hospitals by 3 orthodontists, who performed their plate placement surgeries. The institutional review
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board for the protection of human subjects reviewed and approved the research protocol (KHD IRB1208-02). The surgical procedure for placing the C-tube was the following. As a chairside procedure under local anesthesia, all miniplates were placed by 3 orthodontists. After local anesthesia and palpation of the surgical area, a 5-mm vertical incision was made. The periosteum was detached with an elevator. The C-tube miniplate was positioned with the tube-shaped head remaining exposed to the oral cavity and then anchored with 2 to 4 titanium screws (diameter, 1.5 mm; length, 4-6 mm). One or 2 sutures were placed after fixation of the miniplate. More detailed information of the miniplate placement and removal was discussed in previous articles.9,11,12 A total of 341 C-tube miniplates were examined in this study. These clinical variables were investigated: sex, age, jaw, placement sites, oral hygiene, tube clearance, inflammation, miniplate shape, number of screws, and length of screws. The appropriate dimensions of the miniplate (plates with 2, 3, or 4 holes) were selected according to the bone screw length, soft-tissue height, position and shape of adjacent teeth, and placement site in the oral cavity. After a 1- to 2-week period of healing for the device, the tube part was loaded with the desired orthodontic force. We used survival analysis to evaluate the reliability of the C-tube miniplates as anchorage for fixed orthodontic treatment. Survival time was coded by the number of months after placement of the miniplate. Failure was defined when a miniplate
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Fig 2. Failed C tubes: A, 17-year-old adolescent boy, 2 weeks after placement; B, cone-beam computed tomography image shows loose adaptation of the miniplate part of the C tube to the bone surface; C, 14-year-old girl; D, cone-beam computed tomography image shows a loose adaptation of the C tube to the bone surface. Failure was defined as the need for removal of the miniplate because of loosening, loss of attachment, or infection and was coded as event data.
had to be removed because of loosening, loss of attachment, or infection and was coded as event data (Fig 2). For subjects whose follow-up times ended without a failure event, the end status was recorded as “censored” because the actual time to a failure event was considered to be unknown, since the miniplate had not yet failed before the end of orthodontic treatment (Fig 3). To restate, the intact C-tube miniplate that was functioning properly during and beyond the orthodontic treatment period was coded as censored. Complications were coded for tissue irritation, screw loosening, screw fracture, or localized and transient inflammation. Survival was classified as a tube on a miniplate that functioned in the mouth regardless of any of these complications. Success was defined as survival without any complication. Statistical analysis
The Fisher exact test significance and odds ratio statistics were calculated. Kaplan-Meier survival curves were plotted, and the log rank test was used to identify the variables associated with the failures. Prognostic variables were identified with the Cox proportional
hazard model. The R programming language was used for the data analysis.29 A P value less than 0.05 was considered statistically significant. RESULTS
The average follow-up period was 12.9 months (median, 12.7 months) and ranged from 2 weeks to 4.3 years (Fig 1). Table I shows the coded events that occurred in this study. During the study, 14 C-tube miniplates were removed before the end of treatment. Thirty-two plates had complications such as transient abscess, tissue irritation, loosening, or screw fracture. Among the 32 C-tube miniplates with complications, 18 plates were capable of functioning throughout the orthodontic treatment time. Among the investigated clinical variables, sex, age, jaw, placement site, and number of screws had no significant effect on the survival of the tube and the plate. Table II shows the results of conventional ratio tests for the effects of the clinical variables on the complications. Oral hygiene, tissue condition, shape of the miniplate, length of the screws, and operator factor had significant associations with the complication rate. As previously mentioned, the use of survival
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Fig 3. Intact C tubes: A, B, and C functioned properly during and beyond the orthodontic treatment period. D, A cone-beam computed tomography image of an intact C-tube miniplate.
Table I. Sample characteristics in this study Coded events Total Failure Detachment Loosening Abscess Tissue irritation Wrong direction Survival* Complications Loosening (loosened but functioned) Abscess (transient and subsided) Tissue irritation (transient and subsided) Screw fracture (screw removed) Successy
Number of C-tube miniplates 341 14 9 2 1 1 1 327 32 8 1 8 1 309
*Survival equals the total with any complication minus the failures. Success equals the survivals without complications.
y
analysis, depicted by Kaplan-Meier curves, allows for a more informative analysis of failures and successes, instead of simply reporting the ratios.25-27 The Kaplan-Meier survival curve with the log rank test agreed with the aforementioned ratio test results. In addition, the Kaplan-Meier survival curves showed that the cumulative 2-year survival and success rates were 0.91 and 0.80, respectively. One-year survival
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and success rates were 0.96 and 0.92, respectively (Table III). In terms of the simple and conventional ratio statistic, the overall success rate was 96%, as shown in Table II. To investigate a decisive factor, a regression analysis using the Cox proportional hazard model with multiple predictor variables was applied. This showed that oral hygiene and operator factor were decisive for complications. A conditional inference tree with the survival function estimated by Kaplan-Meier curves is shown for the subgroups of oral hygiene and operators (Fig 4). DISCUSSION
Miniplates can withstand heavier and more dynamic forces than orthodontic mini-implants and provide versatile biomechanics for patients for whom conventional orthodontic treatment is not suitable.11 Previous studies have reported miniplate success rates of 99%,23 97%,3,14 96%,10,24 and 93%,2,6 which are high success rates in contrast to those of mini-implants. A miniplate system not only simplifies the treatment mechanics but also shortens the orthodontic treatment.16,24 Soft-tissue thickness is critical when placing a mini-implant, but it is not important for the placement of miniplates. Even with a less-than-ideal placement, such as root contact or root proximity, the successful
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Table II. Failure rates, complication rates, exact test, and odds ratio statistics by clinical variables Variable Sex Male Female Age (y) \20 .20 Jaw Maxilla Mandible Placement site Anterior Posterior Oral hygiene Good Poor Tube clearance Exposed Covered Tissue condition Good Inflammation Miniplate shape I-bar T-bar Screws (n) 1 or 2 .2 Length of screws (mm) #4 $5 Patient sources and operators A B C
Censored (n)
Failures (n)
Complications (n)y
Total (n)z
122 187
5 9
16 16
203 138
154 155
6 8
13 19
167 174
164 145
7 7
15 17
179 162
87 222
6 8
8 24
95 246
286 23
4 10
12 20
298 43
276 33
11 3
27 5
303 38
254 55
6 8
14 18
268 73
248 61
12 2
20 12
268 73
263 46
13 1
23 9
286 55
161 148
6 8
10 22
171 170
162 92 55
6 6 2
8 12 12
170 104 67
P value* 0.261
Odds ratio (95% CI) 1 0.7 (0.7, 3.4)
0.357 1 1.5 (0.7, 3.3) 0.578 1 1.3 (0.6, 2.9) 0.837 1 1.2 (0.5, 3.2) \0.001 1 20.7 (8.3, 52.0) 0.379 1 1.6 (0.4, 4.5) \0.001 1 5.9 (2.6, 13.7) 0.039 1 2.4 (1.0, 5.6) 0.073 1 2.2 (0.9, 5.4) 0.027 1 2.4 (1.0, 5.8) 0.005 1 2.6 (1.0, 7.7) 4.4 (1.6, 13.1)
*Exact test significance. yThe numbers of failures are included in the numbers of complications. zThe total number sums up the numbers of censored and complications.
Table III. Survival and success rates calculated by the
Kaplan-Meier survival function Year 1 2 3
Survival* rate 0.96 0.91 0.81
Successy rate 0.92 0.80 0.43
*Survival equals the total with any complication minus the failures. y Success equals the survival without complications.
stabilization of miniplates is only minimally affected.3032 Arguably, miniplates might become more increasingly used, since they have the advantage of versatility in terms of the application of forces in different vectors.5 We analyzed 341 miniplates placed in 217 patients over 10 years. The survival rate of these miniplates was excellent, and the complication rate was minimal. The
2-year survival rate of 0.91 is near optimal for the common 1 to 2 years’ worth of orthodontic treatment. In terms of the simple overall success rate, this was a success rate of 96% (Table II), which is similar to the 93% to 99% success rates reported previously.2,6,10,14,23,24 The improved success rate compared with mini-implants is most likely due to use of more than 2 screws to place each miniplate. Unlike individual mini-implants, if 1 screw becomes loose, the remaining screws would still anchor the device. A finite element analysis showed the highest stress and strain values on the inferior screw.33 Although enhanced stability and versatility of the miniplate system is conspicuous, miniplates also sometimes cause soft-tissue swelling and discomfort adjacent to the implantation site. Possible complications are primarily tissue proliferation, which covers the loop of the plate around the miniplate at the transmucosal
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Fig 4. Conditional inference tree with the survival function. Oral hygiene and the doctor’s experience were the most important variables for miniplate survival without complications. Subjects who failed to keep the C-tube area clean appeared to have the worst prognosis, irrespective of the operator factor. Even with good hygiene by the patient, the doctor’s experience was the second most important factor for survival.
area, and chronic infection that causes a purulent discharge, closed swelling, and miniplate mobility. Table III shows that the 3-year success rate (survival without complications) drops considerably to 43%. This value was calculated theoretically from the survival function curve. In practice, our orthodontic treatment times would not be 3 years or more. However, the survival analysis function demonstrates that a considerable complication would eventually occur if a miniplate was used for a long term. As shown in Table II, when analyzed using conventional ratio analyses, we found that oral hygiene, tissue condition, shape of the miniplate, length of the screws, and operator factor had significant associations with the rate of complications (Table II). The conventional analysis method incorporates only 1 variable at a time in the analysis. This simple univariate analysis,
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unfortunately, cannot properly control for confounding factors. By controlling for the confounding factors, the Cox proportional hazard regression method is useful. In addition, a conditional inference tree identifies which factor is the most decisive, which factor is the second most decisive, and so on. The multiple regression method with the Cox proportional hazard model showed only 2 factors that significantly affect the survival and success rates: oral hygiene maintenance and the doctor’s experience were the most important variables for miniplate survival (Fig 4). As previously reported, oral hygiene is the most important factor.34 Next, even with good hygiene, the doctor’s experience was the second most significant factor for survival. Although we will not discuss the attributes of the actual operators referenced in Table II, operator A was the most experienced, and operator C was the least experienced
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orthodontist. Since miniplate placement is impossible without surgery, generous surgical access or flap design would have been a critical skill for a successful result. Operator factors that reduce success include contact with the adjacent roots or the cortical bone of the sinus wall, slippage of the screw during driving, or path-ofinsertion angulation errors. A way to minimize these would be the use of a 3-dimensional imaging tool and a virtual model for implant planning measurements.35,36 CONCLUSIONS
1.
2.
Although the C-tube miniplate has an advantage of versatility in terms of force application, when placing the miniplate, the most important factor was an emphasis on good oral hygiene to promote good tissue health. The doctor’s experience might play an important role for the failures and complications when placing a miniplate. Even with good hygienic maintenance, the doctor’s experience in performing the flap surgery was the second most important factor for success.
REFERENCES 1. Umemori M, Sugawara J, Mitani H, Nagasaka H, Kawamura H. Skeletal anchorage system for open-bite correction. Am J Orthod Dentofacial Orthop 1999;115:166-74. 2. Choi BH, Zhu SJ, Kim YH. A clinical evaluation of titanium miniplates as anchors for orthodontic treatment. Am J Orthod Dentofacial Orthop 2005;128:382-4. 3. Miyawaki S, Koyama I, Inoue M, Mishima K, Sugahara T, TakanoYamamoto T. Factors associated with the stability of titanium screws placed in the posterior region for orthodontic anchorage. Am J Orthod Dentofacial Orthop 2003;124:373-8. 4. Chung YK, Lee YJ, Chung KR. The experimental study of early loading on the mini-plate in the beagle dog. Korean J Orthod 2003;33:307-17. 5. Prabhu J, Cousley RR. Current products and practice: bone anchorage devices in orthodontics. J Orthod 2006;33:288-307. 6. Cornelis MA, Scheffler NR, Nyssen-Behets C, De Clerck HJ, Tulloch JF. Patients' and orthodontists' perceptions of miniplates used for temporary skeletal anchorage: a prospective study. Am J Orthod Dentofacial Orthop 2008;133:18-24. 7. Reychler H, Mahy P, Bou Saba S. Alveolar osseous distraction by the combined use of modified miniplates and an orthodontic appliance. A technical note. J Craniomaxillofac Surg 2011;39:124-6. 8. Cornelis MA, De Clerck HJ. Biomechanics of skeletal anchorage. Part 1. Class II extraction treatment. J Clin Orthod 2006;40:261-9. 9. Chung K, Kim SH, Kook Y. C-orthodontic microimplant for distalization of mandibular dentition in Class III correction. Angle Orthod 2005;75:119-28. 10. Cornelis MA, De Clerck HJ. Maxillary molar distalization with miniplates assessed on digital models: a prospective clinical trial. Am J Orthod Dentofacial Orthop 2007;132:373-7. 11. Chung KR, Kim SH, Kang YG, Nelson G. Orthodontic miniplate with tube as an efficient tool for borderline cases. Am J Orthod Dentofacial Orthop 2011;139:551-62.
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12. Chung KR, Kim YS, Linton JL, Lee YJ. The miniplate with tube for skeletal anchorage. J Clin Orthod 2002;36:407-12. 13. De Clerck HJ, Cornelis MA. Biomechanics of skeletal anchorage. Part 2: Class II nonextraction treatment. J Clin Orthod 2006;40: 290-8. 14. De Clerck EE, Swennen GR. Success rate of miniplate anchorage for bone anchored maxillary protraction. Angle Orthod 2011;81: 1010-3. 15. Ahn HW, Chung KR, Kang SM, Lin L, Nelson G, Kim SH. Correction of dental Class III with posterior open bite by simple biomechanics using an anterior C-tube miniplate. Korean J Orthod 2012;42: 270-8. 16. Chung KR, Jeong DM, Kim SH, Ko YI, Nelson G. En-masse retraction dependent on a temporary skeletal anchorage device without posterior bonding or banding in an adult with severe bidentoalveolar protrusion: seven years posttreatment. Am J Orthod Dentofacial Orthop 2012;141:484-94. 17. Crismani AG, Bertl MH, Celar AG, Bantleon HP, Burstone CJ. Miniscrews in orthodontic treatment: review and analysis of published clinical trials. Am J Orthod Dentofacial Orthop 2010; 137:108-13. 18. Wilmes B, Drescher D, Nienkemper M. A miniplate system for improved stability of skeletal anchorage. J Clin Orthod 2009;43: 494-501. 19. Papageorgiou SN, Zogakis IP, Papadopoulos MA. Failure rates and associated risk factors of orthodontic miniscrew implants: a meta-analysis. Am J Orthod Dentofacial Orthop 2012;142: 577-595.e7. 20. Lim HJ, Eun CS, Cho JH, Lee KH, Hwang HS. Factors associated with initial stability of miniscrews for orthodontic treatment. Am J Orthod Dentofacial Orthop 2009;136:236-42. 21. Antoszewska J, Papadopoulos MA, Park HS, Ludwig B. Five-year experience with orthodontic miniscrew implants: a retrospective investigation of factors influencing success rates. Am J Orthod Dentofacial Orthop 2009;136:158.e1-158.e10. 22. Kuroda S, Sugawara Y, Deguchi T, Kyung HM, TakanoYamamoto T. Clinical use of miniscrew implants as orthodontic anchorage: success rates and postoperative discomfort. Am J Orthod Dentofacial Orthop 2007;131:9-15. 23. Chen YJ, Chang HH, Huang CY, Hung HC, Lai EH, Yao CC. A retrospective analysis of the failure rate of three different orthodontic skeletal anchorage systems. Clin Oral Implants Res 2007;18:768-75. 24. Chen CH, Hsieh CH, Tseng YC, Huang IY, Shen YS, Chen CM. The use of miniplate osteosynthesis for skeletal anchorage. Plast Reconstr Surg 2007;120:232-7. 25. Norman GR, Streiner DL. Biostatistics. The base essentials. St Louis: Mosby; 1996. p. 182-94. 26. Lee ET, Wang JW. Statistical methods for survival data analysis. Hoboken, NJ: Wiley; 2003. p. 1-17. 27. Lee SJ, Ahn SJ, Lee JW, Kim SH, Kim TW. Survival analysis of orthodontic mini-implants. Am J Orthod Dentofacial Orthop 2010;137:194-9. 28. Kim JS, Choi SH, Cha SK, Kim JH, Lee HJ, Yeom SS, et al. Comparison of success rates of orthodontic mini-screws by the insertion method. Korean J Orthod 2012;42:242-8. 29. R Development Core Team. R: a language and environment for statistical computing. Vienna, Austria: R Foundation for Statistical Computing; 2013. 30. Kim GT, Kim SH, Choi YS, Park YJ, Chung KR, Suk KE, et al. Conebeam computed tomography evaluation of orthodontic miniplate anchoring screws in the posterior maxilla. Am J Orthod Dentofacial Orthop 2009;136:628.e1-10.
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31. Kim SH, Kang SM, Choi YS, Kook YA, Chung KR, Huang JC. Conebeam computed tomography evaluation of mini-implants after placement: is root proximity a major risk factor for failure? Am J Orthod Dentofacial Orthop 2010;138:264-76. 32. Kim HS, Lee YJ, Park YG, Chung KR, Kang YG, Choo H, et al. Histologic assessment of the biological effects after speedy surgical orthodontics in a beagle animal model: a preliminary study. Korean J Orthod 2011;41:361-70. 33. Veziroglu F, Uckan S, Ozden UA, Arman A. Stability of zygomatic plate-screw orthodontic anchorage system: a finite element analysis. Angle Orthod 2008;78:902-7.
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34. Daimaruya T, Nagasaka H, Umemori M, Sugawara J, Mitani H. The influences of molar intrusion on the inferior alveolar neurovascular bundle and root using the skeletal anchorage system in dogs. Angle Orthod 2001;71:60-70. 35. Stratemann SA, Huang JC, Maki K, Miller AJ, Hatcher DC. Comparison of cone beam computed tomography imaging with physical measures. Dentomaxillofac Radiol 2008;37:80-93. 36. Suomalainen A, Vehmas T, Kortesniemi M, Robinson S, Peltola J. Accuracy of linear measurements using dental cone beam and conventional multislice computed tomography. Dentomaxillofac Radiol 2008;37:10-7.
American Journal of Orthodontics and Dentofacial Orthopedics
Survival analysis of a miniplate and tube device designed to provide skeletal anchorage Shin-Jae Lee,a Lu Lin,b Seong-Hun Kim,c Kyu-Rhim Chung,d and Richard E. Donatellie Seoul and Suwon, Korea, and Gainesville, Fla Introduction: The aim of this prospective cohort study was to compute the clinical survival and complication rates of a miniplate with a tube device (C-tube) used for orthodontic treatment. Methods: From August 2003 to May 2012, 217 patients were recruited. They received 341 C-tube miniplates. Some C-tube miniplates were removed because orthodontic treatment ended. Others remained beyond the study period and were recorded as censored data. Survival was classified as a C-tube miniplate that functioned in the mouth regardless of any complications. Success was defined as survival without complications. From the data, the effects of these clinical variables on the survival of the C-tube miniplates were evaluated: sex, age, jaw, placement sites, oral hygiene, tube clearance, inflammation, miniplate shape, number of screws, and length of the fixation screws. Survival analyses using the Kaplan-Meier method and the Cox proportional hazard model were applied. Results: Of the 341 miniplates, 14 failed, and 32 had complications. Two-year survival and success rates were 0.91 and 0.80, respectively. In terms of the simple ratio statistic, this was equivalent to a success rate of 96%. The status of oral hygiene maintenance and the operators’ experience had significant associations with the complication rates (P \0.001). Conclusions: The C-tube miniplate has an advantage in versatility in terms of force application. When placing a miniplate, the most important factor is maintaining good tissue health by means of good oral hygiene. Even with good hygiene, the doctor’s experience in performing the flap surgery was the second most important factor for success. (Am J Orthod Dentofacial Orthop 2013;144:349-56)
T
he orthodontic miniplate system was initially similar to the maxillofacial plating system,1-4 which evolved to have a specifically modified end to engage orthodontic auxiliaries.5 Recently, orthodontic miniplate systems have become increasingly accepted by a Professor and chair, Department of Orthodontics, School of Dentistry and Dental Research Institute, Seoul National University, Seoul, Korea. b Postgraduate student, Department of Orthodontics, School of Dentistry, Kyung Hee University, Seoul, Korea. c Associate professor and chair, Department of Orthodontics, School of Dentistry, Kyung Hee University, Seoul, Korea. d Professor and chair, Department of Orthodontics, School of Medicine, Ajou University, Suwon, Korea. e Clinical assistant professor, Department of Orthodontics, College of Dentistry, University of Florida, Gainesville, Fla. Shin-Jae Lee and Lu Lin are joint first authors and contributed equally to this work. All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest, and none were reported. Supported by the Basic Science Research Program through the National Research Foundation of Korea funded by the MSIP, Korean government (grants 20120007545 and 2012-0047622). Reprint requests to: Seong-Hun Kim, Department of Orthodontics, Kyung Hee University School of Dentistry, 1 Hoegi-Dong, Dongdaemun-Gu, Seoul 130-701 Korea; e-mail, [email protected]. Submitted, November 2012; revised and accepted, March 2013. 0889-5406/$36.00 Copyright Ó 2013 by the American Association of Orthodontists. http://dx.doi.org/10.1016/j.ajodo.2013.03.026
both patients and clinicians as a safe and effective adjunct for complex orthodontic treatment.6 Some attachments can also be added onto the miniplate. A miniplate with a tube device, such as a C-tube or a Bollard miniplate implant, is an efficient tool for borderline patients who would have been otherwise difficult to treat.7-16 Clinicians are frequently concerned about the ultimate success rate and the risk factors involved in miniplate failures and complications. The most conspicuous findings when comparing miniplates with mini-implants are the better stability and higher success rates of miniplates. Despite their popularity, orthodontic mini-implants have failure rates as high as 10% to 24%.3,17-23 However, miniplate failure rates vary from 1% to 7%.2,6,10,14,23,24 Survival analysis is a systematic statistical method of evaluating the mechanical success or failure of a particular system. Survival analysis has several advantages of measuring a failure pattern over time, especially when those survival data have a principal end point.25-27 Most orthodontic articles have reported simple success or failure rates of mini-implants,2,3,22,24,28 but some have used survival analysis when evaluating mini-implant success or failure.21,27 However, a 349
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Fig 1. The distribution of treatment and follow-up time from August 2003 to May 2012; 341 C-tube miniplates were sorted on the y-axis according to the date of miniplate placement on the x-axis.
survival analysis has not yet been used to analyze the long-term success or failure of miniplates. Reports of the success or failure patterns of miniplates over time have been missing from the literature. Even in what has been categorized as clinical success, miniplates sometimes cause complications such as swelling, tissue proliferation, and infection, which can lead to loosening of the miniplate.2,3,23 These adverse complications are not reflected in a simple success or failure rate. A better analysis that distinguishes among simple survival of the miniplate and success with or without various complications would provide valuable guidelines to a clinician wishing to use miniplates and maximize their clinical conditions. The aim of this prospective cohort study was to analyze the clinical survival and success rates without complications of the miniplate and tube device used for orthodontic treatment. MATERIAL AND METHODS
All patients were treated with fixed appliances. The miniplate with a tube device (C-tube; Jin Biomed, Bucheon, Korea) used for this clinical study was composed of a titanium miniplate fixture on the bone side and a welded tube on the oral cavity side. The subjects included 217 patients (137 female, 80 male; average age, 22 years; range, 11-61 years) who had undergone orthodontic treatment with a C-tube miniplate (Fig 1). From August 2003 through May 2012, the subjects were treated at 3 universityaffiliated hospitals by 3 orthodontists, who performed their plate placement surgeries. The institutional review
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board for the protection of human subjects reviewed and approved the research protocol (KHD IRB1208-02). The surgical procedure for placing the C-tube was the following. As a chairside procedure under local anesthesia, all miniplates were placed by 3 orthodontists. After local anesthesia and palpation of the surgical area, a 5-mm vertical incision was made. The periosteum was detached with an elevator. The C-tube miniplate was positioned with the tube-shaped head remaining exposed to the oral cavity and then anchored with 2 to 4 titanium screws (diameter, 1.5 mm; length, 4-6 mm). One or 2 sutures were placed after fixation of the miniplate. More detailed information of the miniplate placement and removal was discussed in previous articles.9,11,12 A total of 341 C-tube miniplates were examined in this study. These clinical variables were investigated: sex, age, jaw, placement sites, oral hygiene, tube clearance, inflammation, miniplate shape, number of screws, and length of screws. The appropriate dimensions of the miniplate (plates with 2, 3, or 4 holes) were selected according to the bone screw length, soft-tissue height, position and shape of adjacent teeth, and placement site in the oral cavity. After a 1- to 2-week period of healing for the device, the tube part was loaded with the desired orthodontic force. We used survival analysis to evaluate the reliability of the C-tube miniplates as anchorage for fixed orthodontic treatment. Survival time was coded by the number of months after placement of the miniplate. Failure was defined when a miniplate
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Fig 2. Failed C tubes: A, 17-year-old adolescent boy, 2 weeks after placement; B, cone-beam computed tomography image shows loose adaptation of the miniplate part of the C tube to the bone surface; C, 14-year-old girl; D, cone-beam computed tomography image shows a loose adaptation of the C tube to the bone surface. Failure was defined as the need for removal of the miniplate because of loosening, loss of attachment, or infection and was coded as event data.
had to be removed because of loosening, loss of attachment, or infection and was coded as event data (Fig 2). For subjects whose follow-up times ended without a failure event, the end status was recorded as “censored” because the actual time to a failure event was considered to be unknown, since the miniplate had not yet failed before the end of orthodontic treatment (Fig 3). To restate, the intact C-tube miniplate that was functioning properly during and beyond the orthodontic treatment period was coded as censored. Complications were coded for tissue irritation, screw loosening, screw fracture, or localized and transient inflammation. Survival was classified as a tube on a miniplate that functioned in the mouth regardless of any of these complications. Success was defined as survival without any complication. Statistical analysis
The Fisher exact test significance and odds ratio statistics were calculated. Kaplan-Meier survival curves were plotted, and the log rank test was used to identify the variables associated with the failures. Prognostic variables were identified with the Cox proportional
hazard model. The R programming language was used for the data analysis.29 A P value less than 0.05 was considered statistically significant. RESULTS
The average follow-up period was 12.9 months (median, 12.7 months) and ranged from 2 weeks to 4.3 years (Fig 1). Table I shows the coded events that occurred in this study. During the study, 14 C-tube miniplates were removed before the end of treatment. Thirty-two plates had complications such as transient abscess, tissue irritation, loosening, or screw fracture. Among the 32 C-tube miniplates with complications, 18 plates were capable of functioning throughout the orthodontic treatment time. Among the investigated clinical variables, sex, age, jaw, placement site, and number of screws had no significant effect on the survival of the tube and the plate. Table II shows the results of conventional ratio tests for the effects of the clinical variables on the complications. Oral hygiene, tissue condition, shape of the miniplate, length of the screws, and operator factor had significant associations with the complication rate. As previously mentioned, the use of survival
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Fig 3. Intact C tubes: A, B, and C functioned properly during and beyond the orthodontic treatment period. D, A cone-beam computed tomography image of an intact C-tube miniplate.
Table I. Sample characteristics in this study Coded events Total Failure Detachment Loosening Abscess Tissue irritation Wrong direction Survival* Complications Loosening (loosened but functioned) Abscess (transient and subsided) Tissue irritation (transient and subsided) Screw fracture (screw removed) Successy
Number of C-tube miniplates 341 14 9 2 1 1 1 327 32 8 1 8 1 309
*Survival equals the total with any complication minus the failures. Success equals the survivals without complications.
y
analysis, depicted by Kaplan-Meier curves, allows for a more informative analysis of failures and successes, instead of simply reporting the ratios.25-27 The Kaplan-Meier survival curve with the log rank test agreed with the aforementioned ratio test results. In addition, the Kaplan-Meier survival curves showed that the cumulative 2-year survival and success rates were 0.91 and 0.80, respectively. One-year survival
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and success rates were 0.96 and 0.92, respectively (Table III). In terms of the simple and conventional ratio statistic, the overall success rate was 96%, as shown in Table II. To investigate a decisive factor, a regression analysis using the Cox proportional hazard model with multiple predictor variables was applied. This showed that oral hygiene and operator factor were decisive for complications. A conditional inference tree with the survival function estimated by Kaplan-Meier curves is shown for the subgroups of oral hygiene and operators (Fig 4). DISCUSSION
Miniplates can withstand heavier and more dynamic forces than orthodontic mini-implants and provide versatile biomechanics for patients for whom conventional orthodontic treatment is not suitable.11 Previous studies have reported miniplate success rates of 99%,23 97%,3,14 96%,10,24 and 93%,2,6 which are high success rates in contrast to those of mini-implants. A miniplate system not only simplifies the treatment mechanics but also shortens the orthodontic treatment.16,24 Soft-tissue thickness is critical when placing a mini-implant, but it is not important for the placement of miniplates. Even with a less-than-ideal placement, such as root contact or root proximity, the successful
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Table II. Failure rates, complication rates, exact test, and odds ratio statistics by clinical variables Variable Sex Male Female Age (y) \20 .20 Jaw Maxilla Mandible Placement site Anterior Posterior Oral hygiene Good Poor Tube clearance Exposed Covered Tissue condition Good Inflammation Miniplate shape I-bar T-bar Screws (n) 1 or 2 .2 Length of screws (mm) #4 $5 Patient sources and operators A B C
Censored (n)
Failures (n)
Complications (n)y
Total (n)z
122 187
5 9
16 16
203 138
154 155
6 8
13 19
167 174
164 145
7 7
15 17
179 162
87 222
6 8
8 24
95 246
286 23
4 10
12 20
298 43
276 33
11 3
27 5
303 38
254 55
6 8
14 18
268 73
248 61
12 2
20 12
268 73
263 46
13 1
23 9
286 55
161 148
6 8
10 22
171 170
162 92 55
6 6 2
8 12 12
170 104 67
P value* 0.261
Odds ratio (95% CI) 1 0.7 (0.7, 3.4)
0.357 1 1.5 (0.7, 3.3) 0.578 1 1.3 (0.6, 2.9) 0.837 1 1.2 (0.5, 3.2) \0.001 1 20.7 (8.3, 52.0) 0.379 1 1.6 (0.4, 4.5) \0.001 1 5.9 (2.6, 13.7) 0.039 1 2.4 (1.0, 5.6) 0.073 1 2.2 (0.9, 5.4) 0.027 1 2.4 (1.0, 5.8) 0.005 1 2.6 (1.0, 7.7) 4.4 (1.6, 13.1)
*Exact test significance. yThe numbers of failures are included in the numbers of complications. zThe total number sums up the numbers of censored and complications.
Table III. Survival and success rates calculated by the
Kaplan-Meier survival function Year 1 2 3
Survival* rate 0.96 0.91 0.81
Successy rate 0.92 0.80 0.43
*Survival equals the total with any complication minus the failures. y Success equals the survival without complications.
stabilization of miniplates is only minimally affected.3032 Arguably, miniplates might become more increasingly used, since they have the advantage of versatility in terms of the application of forces in different vectors.5 We analyzed 341 miniplates placed in 217 patients over 10 years. The survival rate of these miniplates was excellent, and the complication rate was minimal. The
2-year survival rate of 0.91 is near optimal for the common 1 to 2 years’ worth of orthodontic treatment. In terms of the simple overall success rate, this was a success rate of 96% (Table II), which is similar to the 93% to 99% success rates reported previously.2,6,10,14,23,24 The improved success rate compared with mini-implants is most likely due to use of more than 2 screws to place each miniplate. Unlike individual mini-implants, if 1 screw becomes loose, the remaining screws would still anchor the device. A finite element analysis showed the highest stress and strain values on the inferior screw.33 Although enhanced stability and versatility of the miniplate system is conspicuous, miniplates also sometimes cause soft-tissue swelling and discomfort adjacent to the implantation site. Possible complications are primarily tissue proliferation, which covers the loop of the plate around the miniplate at the transmucosal
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Fig 4. Conditional inference tree with the survival function. Oral hygiene and the doctor’s experience were the most important variables for miniplate survival without complications. Subjects who failed to keep the C-tube area clean appeared to have the worst prognosis, irrespective of the operator factor. Even with good hygiene by the patient, the doctor’s experience was the second most important factor for survival.
area, and chronic infection that causes a purulent discharge, closed swelling, and miniplate mobility. Table III shows that the 3-year success rate (survival without complications) drops considerably to 43%. This value was calculated theoretically from the survival function curve. In practice, our orthodontic treatment times would not be 3 years or more. However, the survival analysis function demonstrates that a considerable complication would eventually occur if a miniplate was used for a long term. As shown in Table II, when analyzed using conventional ratio analyses, we found that oral hygiene, tissue condition, shape of the miniplate, length of the screws, and operator factor had significant associations with the rate of complications (Table II). The conventional analysis method incorporates only 1 variable at a time in the analysis. This simple univariate analysis,
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unfortunately, cannot properly control for confounding factors. By controlling for the confounding factors, the Cox proportional hazard regression method is useful. In addition, a conditional inference tree identifies which factor is the most decisive, which factor is the second most decisive, and so on. The multiple regression method with the Cox proportional hazard model showed only 2 factors that significantly affect the survival and success rates: oral hygiene maintenance and the doctor’s experience were the most important variables for miniplate survival (Fig 4). As previously reported, oral hygiene is the most important factor.34 Next, even with good hygiene, the doctor’s experience was the second most significant factor for survival. Although we will not discuss the attributes of the actual operators referenced in Table II, operator A was the most experienced, and operator C was the least experienced
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orthodontist. Since miniplate placement is impossible without surgery, generous surgical access or flap design would have been a critical skill for a successful result. Operator factors that reduce success include contact with the adjacent roots or the cortical bone of the sinus wall, slippage of the screw during driving, or path-ofinsertion angulation errors. A way to minimize these would be the use of a 3-dimensional imaging tool and a virtual model for implant planning measurements.35,36 CONCLUSIONS
1.
2.
Although the C-tube miniplate has an advantage of versatility in terms of force application, when placing the miniplate, the most important factor was an emphasis on good oral hygiene to promote good tissue health. The doctor’s experience might play an important role for the failures and complications when placing a miniplate. Even with good hygienic maintenance, the doctor’s experience in performing the flap surgery was the second most important factor for success.
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