ORIGINAL ARTICLE
Survival analyses of surgical miniscrews as orthodontic anchorage Nita Viwattanatipa,a Sukalya Thanakitcharu,b Akasith Uttraravichien,c and Waranuch Pitiphatd Bangkok, Ubolrajatanee, and Khon-Kaen, Thailand Introduction: The objectives of this study were to determine the survival rate of titanium surgical miniscrews and the clinical parameters that posed the highest risks for failure. Methods: Ninety-seven titanium surgical miniscrews (diameter, 1.2 mm; length, 8-12 mm) were placed in the maxilla of 49 patients, at either a high level (nonkeratinized area) or a medium level (mucogingival junction), with the 1-stage or the 2-stage surgical technique. Survival time, event of each screw (survival or failure), and 7 clinical parameters were gathered for survival analysis. Age and latency factors were analyzed with t tests. Results: The cumulative survival rates were 85% at 6 months and 57% at 1 year. The Kaplan-Meier log rank test indicated significant differences in 3 explanatory variables: surgical stage, level of placement, and tissue response. Cox proportional hazards regression indicated that the 2-stage surgical procedure had a higher risk than the 1 stage. Placement at the high level had a greater risk than placement at the medium level. Inflammatory hypertrophy tissue reaction showed a higher risk than normal or mild inflammation. The t test showed that age and latency period were not significant. Conclusions: Titanium surgical miniscrews can be satisfactorily used as orthodontic anchorage. Controlling some aspects of the surgical protocol could reduce the failure rate. (Am J Orthod Dentofacial Orthop 2009;136:29-36)
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ecently, the paradigm of anchorage control has shifted toward temporary anchorage devices or skeletal anchorage systems. These terms have been used to refer to all implants—retromolar implants, miniscrews, pins, palatal onplants, miniplates, fixation wires.1,2 Skeletal anchorage has become practical after the important study of Bra˚nemark et al,3 and after rigid endosseous (retromolar) implants were used successfully in orthodontics by Roberts et al.4 At present, many case reports and clinical experiments have focused on titanium miniscrews because of their several advantages over conventional implants. Some benefits of titanium miniscrews are smaller size, simpler surgical placement, fewer anatomic limitations, less discomfort for patients, easier removal, and lower costs. Many factors associated with the stability of orthodontic titanium miniscrews have been reported and can be categorized as host factors, miniscrew factors, and treatment
a Associate professor, Department of Orthodontics, Faculty of Dentistry, Mahidol University, Bangkok, Thailand. b Orthodontist, Sarppasitprasong Hospital, Ubolrajatanee, Thailand. c Assistant professor, Department of Oral Maxillofacial Surgery Faculty of Dentistry, Khon-Kaen University, Khon-Kaen, Thailand. d Assistant professor, Department of Dental Public Health, Faculty of Dentistry, Khon-Kaen University, Khon-Kaen, Thailand. The authors report no commercial, proprietary, or financial interest in the products or companies described in this article. Reprint requests to: Nita Viwattanatipa, Department of Orthodontics, Mahidol University, Bangkok 10400, Thailand; e-mail,
[email protected]. Submitted, January 2007; revised and accepted, June 2007. 0889-5406/$36.00 Copyright Ó 2009 by the American Association of Orthodontists. doi:10.1016/j.ajodo.2007.06.018
protocol factors (surgery and orthodontics). Host factors associated with failure of miniscrews are cortical bone thickness,5,6 root proximity,5 maxilla or mandible,7 location of implant placement (anterior or posterior),7 keratinized or nonkeratinized tissue (level of placement),7 vertical skeletal relationship,8 side of placement,9 age,8,9 sex,8,9 oral hygiene,8,9 and inflammation.7-10 Miniscrew factors of type, shape, diameter, and length were evaluated by some authors.7-9 Surgical treatment protocols can include surgical technique,10 angle of miniscrew placement,5 and healing period (latency).8,9 Orthodontic treatment protocols can be related to method of force application and force magnitude.7,9 The 2-stage surgery of conventional implant placement has been a standard procedure for some years. Firstly, the implant must be placed into position, followed by a 4 to 6 month healing period for osseointegration. The second stage involves uncovering the implant and fitting the abutment. Then orthodontic loading can then be applied.4,11 Later, Kanomi,12 who introduced miniscrews for orthodontic anchorage, applied this 2-stage surgical technique for miniscrew placement. He used mini bone screws (length, 6 mm; diameter, 1.2 mm) for fixing bone plates. Since then, device designs and applications have evolved into modern orthodontic miniscrews.13-16 The surgical techniques for miniscrew placement can be categorized into 3 types: (1) the 2-stage (closed) method, in which the flap is sutured over the miniscrew, with a healing period, and, at the second stage, 29
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a mucosal punch is made, with a ligature wire tied between miniscrew and bracket6,12; (2) the 1-stage overt (open) method in which the screw head is left exposed above the mucosa13,14; and (3) the 1-stage covert type, in which the ligature wire is tied to the submerged miniscrew head and left extended outward for force application.15 In the last few years, the 1-stage surgical technique hs been advocated by several orthodontists.10,16 However, these surgical techniques are debatable among clinicians, especially oral surgeons and periodontists, who are more acquainted with the well-documented 2-stage surgical procedure. To date, no research has been reported comparing these surgical protocols. Because of the superior features of miniscrews as alternatives for intraoral anchorage, they have become a popular appliance to be studied and used clinically. Unfortunately, clinicians found that some miniscrews failed after placement and during orthodontic treatment. Miniscrew failure factors can be multi-factorial, and the results of clinical research are still controversial. Therefore, more clinical studies are necessary for information about miniscrew applications to achieve more predictable results. The purposes of this study were to explore the clinical performance of surgical miniscrews as orthodontic anchorage by estimation of the overall survival rate and survival characteristics, to evaluate significant factors related to survival of surgical miniscrews and compare survival characteristics of the explanatory factors, and to determine the risk ratio for each explanatory factor related to failure. MATERIAL AND METHODS
The study design and ethical considerations were approved by the Ethical Committee of Khon-Kaen University in Thailand before starting the study. The inclusion criterion was either Class I bimaxillary protrusion or Class II Division 1. The study included 49 patients, 15 to 45 year of age (37 females; mean age, 23.5 years; 12 males; mean age, 22.1 years), and 97 surgical miniscrews. Seventy-three surgical miniscrews were placed in the females and 24 in the males. Most patients required extraction of the first premolars as part of their orthodontic treatment. Surgical miniscrews were placed by oral surgeons. These patients were treated by orthodontic residents at Khon-Kaen University. All miniscrew placement sites were in the maxilla, between the second premolar and the first molar. The sites were located by panoramic radiograph and periapical films. Povidone-iodine 10% (M Dent, Bangkok, Thailand) was applied at the surgical site. After anesthetic infiltration, all miniscrews were placed with the
American Journal of Orthodontics and Dentofacial Orthopedics July 2009
self-tapping procedure on either the buccal or the labial aspect. A small (3 mm) incision line was made at the placement site, and a mucoperiosteal flap was slightly elevated. A 1-mm pilot drilling through cortical and cancellous bone was made by using a low-speed handpiece with normal saline-solution coolant, followed by placement of the miniscrews with a miniature screwdriver. Titanium surgical miniscrews (Osteomed, Dallas, Tex) (diameter, 1.2 mm; length, 8, 10, and 12 mm) were placed at an angle between 50 and 60 from the long axis of the tooth, and the wound was sutured. The surgical procedures were mainly the 2-stage or the 1-stage overt techniques. For the 2-stage procedure, the miniscrew was completely covered with the flap. For the 1-stage procedure, the miniscrew head was intentionally left exposed above the soft tissue by approximately 3 mm. The miniscrews were placed at either a high level (thick nonkeratinized mucosa or infrazygomatic buttress) or a medium level (mucogingival junction). Caution was used to avoid the root apex and the maxillary sinus. The patients were instructed about good oral hygiene. After the surgery, 0.12% chlorhexidine mouthwash, analgesics, and antibiotics were prescribed. The sutures were removed after 7 days. Orthodontic treatment started at various times after the surgery. The latency period ranged from immediate loading to 6 months. For the submerged miniscrews, the covering mucosal tissue had to be removed on the same day as orthodontic force application. This procedure caused no damage to the thin cortical bone of the maxilla. Thereafter, nickel-titanium coil springs were attached with a ligature wire from the miniscrew to the teeth. The orthodontic load applied to the miniscrews was 175 or 200 g. Eighty-seven miniscrews were used for anterior tooth retraction (89.7%), and 10 miniscrews for distalization of the premolars or molars (10.3%). Examples of maxillary anterior retraction and distal molar movement are shown in Figure 1. The mucosal response around the miniscrews was checked after placement at 1 week, 1 month, and each orthodontic visit. Mucosal response was rated by an investigator (N.V.) as normal/ mild inflammation or inflammatory hypertrophy with or without pus. Statistical analysis
Seven clinical characteristics (Table I), the events of the miniscrews, and the survival times were collected for the survival analysis. Survival time was defined as the time from orthodontic force application on the miniscrews to the end of study. The event of each miniscrew was either survival or failure.
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Fig 1. Orthodontic procedure: A, high-level miniscrew placement for anterior tooth retraction with intrusion; B, maxillary molar distal movement.
Table I.
Event percentages by independent characteristics and results of chi-squared test
Characteristic Sex Male Female Angle classification Class I Class II Class II Division 1 Class II subdivision Quadrant 1 2 Screw length 8 mm 10 mm 12 mm Level of placement High Medium Surgical stage 1 stage 2 stage Tissue response Normal or mild inflammation Inflammatory hypertrophy Total
Survival
Failure
Total
P value
19 (19.6%) 46 (47.4%)
5 (5.2%) 27 (27.8%)
24 (24.7%) 73 (75.3%)
0.14
18 (18.6%) 12 (12.4%) 22 (22.7%) 13 (13.4%)
14 (14.4%) 4 (4.1%) 9 (9.3%) 5 (5.2%)
32 (33.0%) 16 (16.5%) 31 (32.0%) 18 (18.6%)
0.46
33 (34.0%) 32 (33.0%)
19 (19.6%) 13 (13.4)
52 (53.6%) 45 (46.4%)
0.42
10 (10.3%) 46 (47.4%) 9 (9.3%)
5 (5.2%) 13 (13.4%) 14 (14.4%)
15 (15.5%) 59 (60.8%) 23 (23.7%)
\0.01*
28 (28.9%) 37 (38.1%)
25 (25.8%) 7 (7.2%)
53 (54.6%) 44 (45.4%)
\0.01*
45 (46.4%) 20 (20.6%)
7 (7.2%) 25 (25.8%)
52 (53.6%) 45 (46.4%)
\0.001*
62 (63.9%) 3 (3.1%) 65 (67%)
16 (16.5%) 16 (16.5%) 32 (33.0%)
78 (80.4%) 19 (19.6%) 97 (100%)
\0.001*
*Statistical significance at P \0.05.
Survival was reported when the miniscrew functioned throughout the stage of orthodontic use or until the end of the study. No patients withdrew from our study. Failure was defined as remarkable mobility, dislodgement, or infection. The following survival analyses were performed with SPSS software (version 11.5, SPSS, Chicago, Ill). 1.
The life table included probability density (estimated probability of failure in the respective interval, computed per unit of time) and hazard rate (number of failures per time units in the respective interval, divided by the average number of survivors at the midpoint of the interval).
2.
3.
4.
The Kaplan-Meier method was used to estimate survival function and determine the survival rate overall and each potential risk factor. The log-rank test was used to contrast the survival curve difference between subgroups of potential risk factors. Relative risk factors significantly affecting the survival rate were assessed by the Cox proportional hazards regression model.
In addition, the means and standard deviations of patients by age and latency period of the miniscrews were compared between the survival and failure groups by t tests with a P value less than 0.05.
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Table II.
Interval (mo)
American Journal of Orthodontics and Dentofacial Orthopedics July 2009
Life table of miniscrews Proportion terminating
Cumulative survival rate (%)
Probability density
Hazard rate (%)
.05 .01 .04 .06 .09 .13 .16 .16 .00 .00
95 94 90 85 77 67 57 48 48 48
.026 .006 .018 .026 .037 .052 .052 .045 .000 .000
3 1 2 3 5 7 8 9 0 0
0 2 4 6 8 10 12 14 16 18
Fig 2. The overall survival curve of the miniscrews. RESULTS
The numbers and percentages of miniscrews by their characteristics are shown in Table I. Because of small subgroup sizes, the variables of location and screw diameter were not included in the statistical analysis. Preliminary results with the chi-squared test, with a P value less than 0.05, indicated that 4 clinical parameters—level of miniscrew placement, surgical stage, tissue response, and screw length—appeared to have significant associations on the outcome of the miniscrews (Table I). On the other hand, sex, type of malocclusion, and quadrant of placement had no significant associations with survival or failure of the miniscrews. By using life table analyses, the proportion terminating, the cumulative survival rate, the probability density, and the hazard rate were calculated for all miniscrews during the observation period (Table II). At 6 months, the cumulative survival rate was 85% with the probability of miniscrew failure at 2.6 per 100 miniscrews per month, and the hazard rate was 3%. At 1 year, the cumulative survival rate was 57% with the probability of miniscrew failure at 5.2 per 100 miniscrews per month, and the hazard rate was 8%. The Kaplan-Meier method of calculating overall survival time and survival curves is shown in Figure 2. The median survival time was 15.47 months. The overall survival curve demonstrates gradual reduction of cumulative survival rates of miniscrews across time. According to Table III, the survival rate refers to the percentage of miniscrews surviving to the respective interval. The overall survival rates were 85% at 6 months and 57% at 1 year. For screw length, the survival rates of the 8, 10, and 12 mm miniscrews at 6 months were 71.8%, 88.1%, and 86.4%; these rates at 1 year were 62.9%, 62.6%, and 44.7%, respectively. For surgical stage, the survival rates of the 1-stage group at 6 months and 1 year were 89% and 84%, respectively. The survival rates of the 2-stage group at 6 months and 1 year were
Table III. Log-rank test: comparison of survival curves of miniscrews by factors Survival rate (%) Median survival time (mo) P value
Factor
6 mo
1y
Overall Screw length 8 mm 10 mm 12 mm Surgical stage 1 stage 2 stage Level of placement High Medium Tissue response Normal or mild inflammation Inflammatory hypertrophy
85
57
15.47
—
71.8 88.1 86.4
62.9 62.6 44.7
16 16 13.05
0.15
89 81
84 38
16.6 12.13
0.001*
84 89.2
46 83.1
13.31 16
0.049*
90
67
18
68
28
\0.001*
9.68
*Statistical significance at P \0.05.
81% and 38%, respectively. For level of placement, the survival rates of the high-level group at 6 months and 1 year were 84% and 46%, respectively. The survival rates of the medium-level group at 6 months and 1 year were 89.2% and 83.1%, respectively. For tissue response, the survival rates of the normal or mild inflammation group at 6 months and 1 year were 90% and 67%, respectively. The survival rates of the inflammatory hypertrophy group at 6 months and 1 year were 68% and 28%, respectively. The median survival time is simply explained as the length of time that 50% of the miniscrews still survived. According to Table III, the median survival times for screw lengths of 8, 10, and 12 mm were 16, 16, and 13.05 months, respectively. The median survival time
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Fig 3. Comparison of survival curves between 1-stage and 2-stage surgical techniques (P 5 0.001, log-rank test).
of 2-stage surgery (12.13 months) was less than the 1-stage surgery (16.6 months). The median survival time of high-level placement (13.31 months) was less than medium-level placement (16 months). The median survival time of the inflammatory hypertrophy group (9.68 months) was less than that of the normal or mild inflammation group (18 months). The results of the subgroup comparison were refined by the log-rank test (Table III). Significant differences (P \0.05) were found between the survival curves in 3 variables: surgical stage, level of placement, and tissue response. Figure 3 shows that the cumulative survival rate of the 1-stage group was greater than that of the 2-stage group. Figure 4 shows that the cumulative survival rate plot of the high-level group was lower than that of the medium group. Figure 5 shows that the cumulative survival rate of the normal or mild inflammation group was greater than that of the inflammatory hypertrophy group. The survival-curve comparison between 8-, 10-, and 12-mm screw lengths was not significant. The relationship magnitude among factors and survival times of the miniscrews was analyzed by multivariate analysis. Results of the Cox proportional hazards regression model (Table IV) can be interpreted as follows. 1.
2.
The risk ratio of the 2-stage procedure was 17.66 times greater than the 1-stage technique, which increased the hazard of failure by 1666%. The risk ratio of high-level placement was 8.63 times greater than medium-level placement, which increased the hazard of failure by 763%.
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Fig 4. Comparison of survival curves between highlevel and medium-level placements (P 5 0.049, logrank test).
Fig 5. Comparison of survival curves between normal or mild inflammation and inflammatory hypertrophy tissue response (P \0.001, log-rank test).
3.
For tissue response (other covariates held constant), the risk ratio of normal or mild inflammation was 3.42 times greater than inflammatory hypertrophy. Therefore, it can be estimated that inflammatory hypertrophy increased the hazard of miniscrew failure by 242%.
Table V shows the descriptive means, standard deviations, 95% confidence intervals, and t test results (P \0.05) for the age and latency period factors. The
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Cox proportional hazards regression model (multivariate)
Table IV.
95% CI Factor Level of placement Medium High Surgical stage 1 stage 2 stage Tissue response Normal or mild inflammation Inflammatory hypertrophy
Exp (B) Risk ratio Lower
Upper
P value
2.16
1 8.63
0.51
145.23
.013*
2.87
1 17.66
1.01
295.02
.046*
7.28
.001*
1 1.23
3.42
1.6
Exp (B), Odds ratio. *Statistical significance at P \0.05.
mean ages were 22.01 6 4.42 years for the survival group and 24.88 6 7.36 years for the failure group. The mean latency periods were 3.20 6 2.32 months for the survival group and 2.78 6 1.71 months for the failure group. No significant difference was found for age and latency period. DISCUSSION
Previous studies showed that surgical miniscrews can sustain orthodontic force as well as a larger diameter implant or miniplate.7,8,18 Because of several advantages of surgical miniscrews, we focused on their effectiveness for orthodontic anchorage. Our research questions for miniscrews were: (1) how consistent was the success of surgical miniscrews subjected to orthodontic force; and (2) what clinical parameters were associated with failure. Most articles reported the success of miniscrews as percentages, simply calculated from the number of successful ones divided by the total number at the end of study. However, we proposed an alternative method for clinical study by using survival analysis. According to Figure 2 and Table II, surgical miniscrews can achieve a satisfactory survival rate of 85% at 6 months, although the rate dropped to 57% at 1 year. The survival rate of miniscrews declined with time after orthodontic force application. The overall 57% survival rate at 1 year in this study was lower than the success percentage reported by Cheng et al7 (89% for a 3-year study period), Miyawaki et al8 (83.9% for a 1-year study period), and Liou et al19 (100% for a 9-month study period). However, in terms of product warranty, this direct comparison of success percentages might be less
informative, because the length of observation time and timing differences of subject recruitment can affect the reported success percentages. In addition, it should not be assumed that survival percentages would be constant across time. Therefore, success percentages might not be sufficient to validate the superiority or inferiority of any type of miniscrew or technique over others. The survival analysis offers more meaningful information than success percentages because it differentiates the probability of failure at a particular interval. It can also assess the dependence of failure time on the independent variables.17 To our knowledge, only 1 study performed survival analysis of miniscrews.7 Observation times varied among the studies. Miniscrew observation times could be classified mainly into 3 periods: latency period, activation period (orthodontic force application), and overall (latency and activation period). Cheng et al7 defined their survival time as the period from implant placement to the end of followup. Bernhart et al18 defined survival time as the orthodontic-force activation period, as our study. Most studies, however, reported the overall period. We observed that the characteristics of miniscrew success or failure were different between the latency period and the activation period. For example, miniscrew placement with 2-stage surgery that were considered normal during the latency period became eventful during the activation period. Therefore, we suggest that future studies of miniscrews should be more attentive to the observation period. The factors associated with miniscrew failure are still controversial. Miyawaki et al,8 using logistic regression analysis, reported 3 significant factors associated with the stability of titanium screws: screw diameter of 1.0 mm or less, inflammation of the periimplant tissues, and high mandibular plane angle (ie, thin cortical bone). Park et al9 reported that mobility, right side of the jaw, and mandible showed significant relative risks. Cheng et al7 reported that anatomic location and placement in nonkeratinized mucosa were the significant factors in survival. By controlling some factors (jaw, location, type of miniscrew, and diameter), we found 3 significant factors associated with failure: surgical stage, level of placement, and tissue response during orthodontic treatment. Surgical placement protocol can strongly affect the stability of miniscrews. Herman et al20 reported that soft-tissue incision before pilot drilling significantly increased stability. However, Kuroda et al21 reported that miniscrews placed without flap surgery had higher success rates. In our study, 2 surgical protocols, 1-stage vs 2-stage surgery were contrasted. According to Table III, the 1-year survival rate of the 1-stage group (84%)
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Table V.
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Descriptive and t test results for age and latency period 95% CI
Factor Age (y) Latency period (mo)
95% CI
Success (n 5 65) mean (SD)
Lower
Upper
Failure (n 5 32) mean (SD)
Lower
Upper
P value
22.01 (4.42) 3.20 (2.32)
20.92 2.62
23.11 3.78
24.88 (7.36) 2.78 (1.71)
22.22 2.16
27.52 3.40
.05 .37
was significantly higher than the 2-stage group (38%). Although the surgical standard for conventional implants is the 2-stage technique, our evidence shows significantly greater success for surgical miniscrews with the 1-stage technique.3,4 Many studies agree that implant inflammation leads to failure of miniscrews.7,8 We also found that the inflammatory hypertrophy reaction was significantly associated with failure. Inflammatory hypertrophy could be attributed to irritation from stainless steel ligature ties and plaque accumulation. Cheng et al7 reported a 71% failure rate in patients with peri-implant infections. We found a similar failure rate (72% at 1 year) that could probably be due to more miniscrews with the 2-stage surgical procedure. In our study, a significantly lower survival rate was found for surgical miniscrews placed at high levels in the movable nonkeratinized mucosa (infrazygomatic buttress or vestibule area). It was also observed that soft tissues could overgrow, covering the miniscrew head, even over some of the miniscrews that were intentionally placed with 1-stage surgery. Miniscrews that were submerged beneath thick mucosa required softtissue removal to expose the head. The ligature wire tied between the miniscrews and the nickel-titanium spring caused soft-tissue irritation with ensuing risk of inflammatory hypertrophic tissue and infection. Depending on the purpose, high-level placement for correction of vertical malocclusion is sometimes necessary, especially for tooth intrusion or anterior retraction with intrusion. However, clinicians should be aware of possible risks with high-level placement. Moreover, we found that the thicker the nonkeratinized tissue, the greater the severity of the inflammatory hypertrophic tissue response. On the contrary, no miniscrews placed at medium levels had this negative tissue response. The cause of failure at the medium level was dislodgement, indicating insufficient tissueminiscrew retention. According to the Cox proportional hazards regression model (Table IV), the surgical stage was the most significant predictor for miniscrews failure, followed by level of placement and tissue response. However, these 3 variables cannot be taken as the sole predictors because miniscrew failure is multifactorial. Future
studies should include larger sample sizes, and various types and designs of orthodontic miniscrews, surgical protocols, clinician skill levels, and host risk factors (eg, patient’s bone quality, miniscrew surface area, distance from adjacent roots, and so on). Similar to Miyawaki et al8 and Park et al,9 we found no difference in the age factor between the survival and failure groups of miniscrews. Further studies should be carried out with larger sample sizes, including younger and older ages. The latency or healing period for miniscrews as orthodontic anchorage might not be as critical as for conventional implants. From an animal study, the percentage of bone-implant contact of small titanium implants under orthodontic loading showed nonsignificant differences between latency periods at 3, 6, and 12 weeks.22 In agreement with several studies, we found no significant difference in the latency period between the survival and failure groups.8-10 It could be hypothesized from our results that, during the orthodontic force application period, miniscrews that underwent 2-stage surgery and placement at high level are prone to inflammatory tissue hypertrophy, leading to discomfort or infection, and thus failure of the miniscrews. Therefore, the surgical placement protocol is important for the success of surgical miniscrews as orthodontic anchorage. CONCLUSIONS
1.
2.
3.
The cumulative survival rates were 85% at 6 months and 57% at 1 year for titanium surgical miniscrews (diameter, 1.2 mm; length, 8-12 mm) placed in the maxilla. Comparison of survival characteristics indicated significant differences in 3 explanatory variables: surgical stage, level of miniscrew placement, and tissue response. The relative risk factors assessed by Cox proportional hazards regression indicated that the 2-stage surgical procedure was the most significant predictor for failure, followed by miniscrew placement at a high level (nonkeratinized mucosa) and the inflammatory hypertrophy tissue response during orthodontic force application.
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We thank Keith Godfrey, Pattaramon Rattanaphan, Pornpaka Thongdee, Montein Manosudprasit, and the orthodontic residences of Khon-Kaen University for their assistance with this project. REFERENCES 1. Mah J, Bergstrand F. Temporary anchorage devices: a status report. J Clin Orthod 2005;39:132-6. 2. Cope J. Temporary anchorage devices in orthodontics: a paradigm shift. Semin Orthod 2005;11:3-9. 3. Bra˚nemark PI, Breine U, Hallen O. Repair of defects in mandible. Scand J Plast Reconstr Surg 1970;4:100-8. 4. Roberts WE, Smith RK, Zilberman Y. Osseous adaptation to continuous loading of rigid endosseous implants. Am J Orthod 1984; 86:95-111. 5. Deguchi T, Nasu M, Murakami K, Yabuuchi T, Kamioka H, Yamamoto T. Quantitative evaluation of cortical bone thickness with computed tomographic scanning for orthodontic implants. Am J Orthod Dentofacial Orthop 2006;129:721.e7-12. 6. Costa A, Pasta G, Bergamaschi G. Intraoral hard and soft tissue depths for temporary anchorage devices. Semin Orthod 2005; 11:10-5. 7. Cheng SJC, Tseng IY, Lee JJ, Kok SH. A prospective study of the risk factors associated with failure of mini-implants used for orthodontic anchorage. Int J Oral Maxillofac Implants 2004;19: 100-6. 8. Miyawaki S, Koyama I, Inoue M. 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. 9. Park HS, Jeong SH, Kwon OW. Factors affecting the clinical success of screw implants used as orthodontic anchorage. Am J Orthod Dentofacial Orthop 2006;130:18-25.
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10. Herman R, Cope J. Miniscrew implants: IMTEC mini ortho implants. Semin Orthod 2005;11:32-9. 11. Thilander B. Implant anchorage in orthodontic treatment. In: Higuchi K, editor. Orthodontic applications of osseointegrated implants. Chicago: Quintessence; 2000. p. 71-87. 12. Kanomi R. Mini-implant for orthodontic anchorage. J Clin Orthod 1997;31:763-7. 13. Park HS. The skeletal cortical anchorage using titanium microscrew implants. Korea J Orthod 1999;29:699-706. 14. Kyung HE, Park HS, Bae SM. Development of orthodontic microimplants for intraoral anchorage. J Clin Orthod 2003;37:321-8. 15. Park HS, Kyung HE, Sung JH. A simple method of molar uprighting with micro-implant anchorage. J Clin Orthod 2002;36:592-6. 16. Melsen B, Verna C. Miniscrew implants: the Aarhus anchorage system. Semin Orthod 2005;11:24-31. 17. Gonzalez RH. Survival/failure analysis. Available at: http:// userwww.sfsu.edu/efc/classes/biol1710/survival/surv-anal.htm. Accessed October 15, 2006. 18. Bernhart T, Freudenthaler JW, Dortbudak O, Bantleon HP, Watzek G. Short epithetic implants for orthodontic anchorage in the paramedian region of the palate—a clinical study. Clin Oral Implants Res 2001;12:624-31. 19. Liou EJW, Pai BCJ, Lin JCY. Do miniscrews remain stationary under orthodontic forces? Am J Orthod Dentofacial Orthop 2004;126:42-7. 20. Herman R, Currier F, Miyake A. Mini-implant anchorage for maxillary canine retraction: a pilot study. Am J Orthod Dentofacial Orthop 2006;130:228-35. 21. Kuroda S, Sugawara Y, Deguchi T, Kyung HM, Yamamoto T. Clinical use of miniscrew implants as orthodontic anchorage: success rates and postoperative discomfort. Am J Orthod Dentofacial Orthop 2007;131:9-15. 22. Deguchi T, Yamamoto T, Konomi R. The use of small titanium screws for orthodontic anchorage. J Dent Res 2003;82:377-81.
