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Unexpected complications associated with mandibular fixed retainers: A retrospective study
ORIGINAL ARTICLE
Unexpected complications associated with mandibular fixed retainers: A retrospective study eraa and Ivo Marekb Josef Kuc Prague and Olomouc, Czech Republic
Introduction: The purposes of this retrospective study were to describe the types of unexpected complications associated with mandibular fixed retainers and to assess their prevalences and possible etiologic causes. Methods: A total of 3500 consecutive patients (1423 male, 2077 female) treated with fixed appliances and a mandibular fixed retainer as a part of the retention protocol were screened during the retention period (20082013) for unexpected complications. Thirty-eight subjects (12 male, 26 female; mean age, 20.7 6 8.9 years) with unexpected complications were identified and assigned to the unexpected complications group and compared with a randomly selected control group of 105 subjects (43 men, 62 women; mean age, 29.5 6 9.7 years) without unexpected complications. Relationships between unexpected complications and cephalometric and clinical variables were evaluated. Results: An opposite inclination of the contralateral canines (twist effect) was found in 21 subjects. In 89.5%, the left canines were tipped buccally. A torque difference of 2 adjacent incisors (X effect) was identified in 12 patients. In 5 subjects, nonspecific complications were noted. Subjects in the unexpected complications group were significantly younger at debonding (P 5 0.03) and had higher mandibular plane angles (P \0.0001) and increased pretreatment ventral positions of the mandibular incisors (P 5 0.029). No differences were found between the groups with regard to treatment duration, wire type, failure rate, treatment changes in incisor proclination, or intercanine distance. Conclusions: Unexpected complications of mandibular fixed retainers are relatively rare. Facial divergence was identified as a possible predictor. However, the etiology is most likely multifactorial. Strong asymmetry among the patients with the twist effect suggests that the mechanical properties of retention wires may play a role and should be examined in the future. (Am J Orthod Dentofacial Orthop 2016;149:202-11)
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ong-term stability of orthodontic treatment results is a great challenge in orthodontics. Some authors even consider long-term stability to be a myth.1 To overcome this problem, others have advocated long-term or even lifelong retention as a solution.2-5 Fixed retainers seem to be the best option for longterm maintenance of treatment results, and a growing number of orthodontists use them for this purpose.5,6 a Assistant professor, Department of Orthodontics, First Medical Faculty of Charles University, Prague, Czech Republic; postgraduate student, Department of Orthodontics, Clinic of Dental Medicine, Palacky University, Olomouc, Czech Republic. b Assistant professor, Department of Orthodontics, Clinic of Dental Medicine, Palacky University, Olomouc, Czech Republic; consultant orthodontist, Department of Orthodontics, First Medical Faculty of Charles University, Prague, Czech Republic. All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest, and none were reported. Supported by a research grant from the Ministry of Health of the Czech Republic (IGA MZCR NT14189-3/2013). Address correspondence to: Ivo Marek, Palackeho 12, Olomouc 772 00, Czech Republic; e-mail, [email protected]. Submitted, February 2015; revised and accepted, July 2015. 0889-5406/$36.00 Copyright Ó 2016 by the American Association of Orthodontists. http://dx.doi.org/10.1016/j.ajodo.2015.07.035
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Fixed retainers have been shown to be effective in maintaining an esthetic result in the anterior region without the patient's compliance.7 They have been reported to be safe and predictable,8 and acceptable and compatible with periodontal health.9 However, regular checkups are required, since occasional failures caused by wire fractures or bond failures can occur.10 The reported failure rates of bonded retainers vary widely between 0.1% and 53%.11,12 According to some studies, long-term use of fixed retainers may also be associated with greater plaque and calculus accumulation, which can lead to a higher risk of gingival recession and increased probing depth.13 Unexpected complications may also appear in patients with fixed retainers.7,14,15 These complications were described as unwanted movement of the teeth included in the fixed retainer, even without wire fracture or bond failure. Small spaces between incisors in intact retainer segments,10 unexpected torque changes between the maxillary central incisors,14 torque changes between adjacent mandibular incisors, and opposite inclinations of contralateral mandibular canines have also been reported.7,15 Unexpected complications have been
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estimated to occur in 0.1% to 5% of patients; these are relatively small numbers.5,7,15 However, 50% of these patients may require retreatment.15 In some, the complications can be quite severe, including buccal bone dehiscence.16 Consequently, gingival recessions may occur, posing both health and esthetic problems. In such cases, a demanding orthodontic and reconstructive surgical and periodontal treatment may be necessary. Several causes of unexpected complications in patients with fixed retainers have been suggested, including poor bonding technique and insufficient wire passivity,15,16 instability of multistrand wires,10,17 and wire straightening or wire activation by mechanical trauma.15 Biologic factors, such as forces created by incisor position relapse, have also been proposed in the literature.18 Apart from relapse, increased incisor proclination has also been shown to cause or worsen bone dehiscences of the buccal cortical plate, thus reducing bone support.19,20 With regard to bone support, it has been previously reported that hyperdivergent patients have a higher prevalence of buccal bone dehiscence and fenestrations in the mandibular anterior region even before orthodontic treatment.21,22 We hypothesized that mandibular incisor proclination and increases in intercanine distance during orthodontic treatment may be associated with increased risks of unexpected complications. We also presumed that anatomic conditions related to an increased mandibular plane angle and hyperdivergence may play roles. The purposes of this retrospective study were to describe the types, prevalence, and timing of unexpected complications of mandibular fixed retainers in a group of patients in the retention phase and to identify some possible etiologic factors that were previously suggested in the literature. MATERIAL AND METHODS
A cohort of 3500 consecutive patients (1423 male, 2077 female) fulfilled the following inclusion criteria: (1) mandibular bonded flexible spiral wire fixed retainer in situ; (2) pretreatment (T0) and posttreatment (T1) cephalometric and panoramic radiographs, plaster models, and intraoral photographs; (3) no prosthetic reconstruction in the mandibular anterior region; and (4) no history of periodontal treatment, surgery, or trauma in the mandibular anterior region. They were seen at regular retention visits from January 2, 2008, to November 29, 2013. All patients were of European descent and were treated for various malocclusions with fixed appliances in the private orthodontic practice of the second author (I.M.). They were treated with a 0.022-in slot Roth prescription preadjusted appliance
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(Ortho Organizers, Carlsbad, Calif). In the routine treatment protocol, initial leveling and alignment were performed with round, superelastic, or heat-activated nickel-titanium wires. Space closure was performed using rectangular 0.018 3 0.025-in stainless steel wires. Intramaxillary and intermaxillary elastics were also used during the final stages of treatment. During debonding, all patients received a multistrand flexible spiral wire fixed retainer, either a 0.0215-in gold-plated 5-stranded spiral wire (Penta-One; Gold'n Braces, Palm Harbor, Fla) or a 0.0175-in 6-stranded coaxial wire (Ortho Organizers) bonded to the mandibular incisor region, including both canines and all incisors. All fixed retainers were shaped at chairside and bonded by 1 operator (I.M.) directly on the lingual surfaces of the mandibular anterior teeth using flowable composite (Transbond Supreme LV; 3M Unitek, Monrovia, Calif) according to the method described by Dahl and Zachrisson.10 In addition to a fixed retainer, the patients received removable maxillary and mandibular Hawley retainers or an activator and a maxillary vacuum-formed retainer. They were instructed to adhere to the standard retention protocol for removable retainers as follows: (1) full-time wear for 3 months, (2) nighttime wear only for the rest of the first year, (3) alternating nights for the second year, and (4) twice a week at night for the third year. The patients were also instructed to come at least once a year to have the fixed retainer checked even after they had stopped wearing the removable retainers. The average attendance of patients per year of retention in our study is shown in Figure 1. During the recall visit (T2), the patients were screened for unexpected complications of the mandibular fixed retainer. Written informed consent was obtained from each patient or the parents. The patients were examined, and intraoral photographs and plaster models were made. The prevalence and types of unexpected complications were determined by intraoral examination, and by evaluation and comparison of the study models obtained at T1 and at T2. Unexpected complications were assessed in the mandibular anterior region according to the descriptions reported previously10,15: torque difference (Fig 2, A and B) between 2 adjacent incisors (X effect), increased buccal inclination and opposite inclination (Fig 2, C and D) of the contralateral canines (twist effect), and nonspecific changes such as spacing (Fig 2, E and F). The subjects were divided into 2 groups according to the presence or absence of unexpected complications. The unexpected complications group (UCG) comprised 38 patients with a complication in the mandibular anterior segment. The distributions of unexpected complications among the patients by year in retention and the prevalence rates are shown in Table I and Figure 3.
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Fig 1. Average attendance of patients in our study per years in retention.
Of the remaining patients, in whom no unexpected complications were identified, 105 patients were randomly selected to create the control group (CG). Random selection was performed with Excel (Microsoft, Redmond, Wash) using the Rand and Index functions. The sample size was calculated for inclination of the mandibular incisors at a 5 0.05 and a power of 80% to detect a difference of 4 , assuming that the standard deviation was 7.4 . The power analysis showed that 105 patients were needed in the CG. The characteristics of both groups are shown in Table II. Each patient's chart was analyzed to determine the type of retainer wire and rate of wire failure (wire fracture or detachment followed by repair of the fixed retainer), treatment duration (T0-T1), and retention time (T1-T2). Two lateral cephalometric radiographs and plaster models were analyzed of each subject from before treatment (T0) and after treatment (T1) to evaluate the treatment changes (T0-T1) in the inclination and position of mandibular incisors, the mandibular plane angle, and the intercanine distance. Cephalometric radiographs were digitized and traced using software (PC Dent: CompuGroup Medical, Prague, Czech Republic). Plaster model recording of intercanine distance change was performed using a digital caliper (Masel Orthodontics, Carlsbad, Calif), measured with an accuracy of 0.01 mm. The intercanine distance was measured from the middle of the cusp of the mandibular left canine to the middle of the cusp of the mandibular right canine. In the case of an abrasion of a cusp, the middle of the surface was estimated.7 All tracings and evaluations were performed by the same operator (I.M.). A complete list of the variables
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with a detailed description and graphic representation of the cephalometric parameters is given in Figure 4 and Tables II and III. Two weeks after the measurements were taken, the primary investigator remeasured all variables from 20 randomly selected patients to calculate the error of measurement using intraclass correlation coefficients for quantitative variables. The correlation analysis showed the highest r value of 0.997 for intercanine distance and the lowest r value of 0.834 for the position of the mandibular incisor relative to the Point A-pogonion line. Correlations for repeated measurements were statistically significant for all variables at P \0.05. Paired t tests and Bland-Altman plots were also performed to evaluate errors. Both the t tests and the Bland-Altman plots (Fig 5) indicated that the errors were small. The post hoc intraoperator and interoperator agreement for detection of unexpected complications was also determined. Both operators twice within 2 weeks independently evaluated the study models and the photographs of 30 randomly selected subjects at T1 and T2. The Cohen kappa coefficient (k) showed almost perfect agreement (k 5 0.918) for the first operator (J.K.) and perfect agreement (k 5 1.000) for the second operator (I.M.). Almost perfect agreement in the evaluation of unexpected complications was found between the 2 operators (k 5 0.830). Statistical analysis
An exploratory test (Shapiro-Wilk) was performed to assess the normality of the distribution for all quantitative variables. Parametric tests (paired t test, 2-sample
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Fig 2. Clinical examples of unexpected complications of mandibular bonded multistrand retainers on intraoral photographs. Torque difference between 2 adjacent incisors (X effect) from A, frontal and B, occlusals views. Opposite inclination of contralateral canines (twist effect) from C, frontal and D, occlusal views. Nonspecific changes (spacing) from E, frontal and F, occlusal views.
Table I. Numbers of intercepted unexpected compli-
cations and distribution of patients in the sample per years in retention Years in retention 0-1 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10 10-11 11-12
UCG (n 5 38) 6 7 7 5 2 5 2 0 2 1 0 1
Sample (n 5 3500) 710 645 496 381 283 234 177 144 112 113 138 67
t test) were used for the variables when the data had normal distributions. In variables without normal distributions, nonparametric tests (Mann-Whitney U test) were used. Comparisons of the qualitative variables
were performed with the Fisher exact test. A logistic regression analysis (method Enter) was performed with “unexpected complication” as the dependent variable. Sex, age at debonding, failure rate, time of retention, mandibular plane angle, incisor position and inclination, and intercanine distance change were chosen for the independent variables. All statistical analyses were performed using the Statistical Package for the Social Sciences software (version 15; SPSS, Chicago, Ill) at P \0.05. RESULTS
The results are presented in Tables I through V. Of 3500 patients, 38 (1.1%) experienced unexpected complications with the mandibular fixed retainers and were assigned to the UCG. The numbers of unexpected complications and their distributions in time are given in Table I. Twelve patients had an X effect, 21 had a twist effect, and 5 had nonspecific complications.21 As many as
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Fig 3. Prevalence rates of unexpected complications per years in retention.
Table II. Descriptive statistics of the variables and between-group comparisons Variable F (%)/M (%) TT (y) AD (y) AR (y) RT (y) WT (%) FR (%)
UCG (n 5 38) 26 (68%)/12 (32%) 1.9 6 0.7 16.7 6 7.5 20.7 6 8.9 4.0 6 2.8 N 33 (87%) AU 5 (13%) 13 (34.2%)
CG (n 5 105) 61 (58%)/44 (42%) 2.0 6 0.7 20.2 6 9.5 29.5 6 9.7 9.3 6 2.0 N 92 (88%) AU 13 (12%) 43 (41.0%)
P 0.337* 0.270y 0.030y,z \0.0001y,z \0.0001y,z 1.000* 0.562*
F/M, Numbers and percentages of females and males in the groups; TT, treatment time (T0-T1); AD, age at debonding (T1); AR, age at recall (T2) and, in the UCG, also the age of interception of the unexpected complication; RT, retention time (T1-T2); in the UCG, also the time of occurrence of the unexpected complication; WT, wire type (N, 0.0175-in 6-stranded coaxial wire; AU, 5-stranded spiral wire); FR, failure rate, number and percentage of rebondings or repairs of mandibular fixed retainers in the retention period (T1-T2). *Fisher's exact test; yMann-Whitney U test; zstatistically significant differences at P \0.05.
89.5% of the subjects with the twist effect had the left canine inclined in the buccal direction. The distribution of the sexes was not significantly different between groups (P 5 0.337). No significant difference was found between the UCG and the CG in treatment time (P 5 0.270). However, age at debonding (P 5 0.03) and age at recall, and thus retention time, differed significantly between the groups (P \0.0001 for both). The average time of interception of an unexpected complication was 4 6 2.8 years (range, 0.5-12.5 years). An analysis of the UCG per year in retention (Table I) showed that the number of intercepted unexpected complications was highest in the first 5 years after debonding, and then it decreased with time. However, the number of patients attending recall visits also decreased with time (Fig 1; Table I). The estimated prevalence rate
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based on the number of identified unexpected complications and the number of patients at recall per year after debonding show that the rate of complications was increasing with time in the first few years of the retention period. There was no difference between the groups in the distribution of wire type used (P 5 1.000). Failure rates were comparable in the 2 groups (P 5 0.562). Significant differences were found in the pretreatment position of the mandibular incisors relative to the Point A-pogonion line (P 5 0.029) and the mandibular plane angle (P \0.0001). Both values were higher in the UCG compared with the CG at T0. No difference was observed between the groups in the inclination of the mandibular incisors to the mandibular plane (P 5 0.151) or the intercanine distance (P 5 0.065) at T0.
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Table III. Intergroup comparison of cephalometric
variables and intercanine distances before treatment (2-sample t test) Variable 1/ML ( ) 1/APo (mm) NSML ( ) CC (mm)
UCG (n 5 38) 93.6 6 7.5 2.9 6 2.3 36.4 6 5.2 26.4 6 1.9
CG (n 5 105) 95.5 6 7.5 1.9 6 2.9 31.4 6 6.7 25.6 6 2.3
P 0.151 0.029* \0.0001* 0.065
1/ML, Angle of the mandibular incisors to the mandibular plane; 1/APo, distance of the mandibular incisal edge to the Point A-pogonion line; NSML, mandibular plane angle, angle between the NS line and mandibular plane (ML); CC, intercanine distance, distance of the incisal tips of the mandibular canines. *Statistically significant differences at P \0.05.
DISCUSSION
Fig 4. Linear and angular measurements on cephalometric radiographs: 1/ML, angle of the mandibular incisors to the mandibular plane; 1/APo, distance of the mandibular incisal edge to the Point A-pogonion line; NSML, mandibular plane angle, angle between the NS line and mandibular plane (ML).
The mandibular incisors were significantly proclined during treatment (T0-T1) in both the CG (P 5 0.0005) and the UCG (P \0.0001). However, no significant difference in incisor proclination was identified between the groups (P 5 0.745 and P 5 0.600, respectively). Although no significant change in facial divergence was observed during treatment in the UCG (P 5 0.073), a significant difference was found in the CG (P 5 0.025). However, no significant difference was found between the groups (P 5 0.509). The intercanine distance remained unchanged during treatment in both the UCG (P 5 0.746) and the CG (P 5 0.073), and no difference was found between the groups (P 5 0.326). A logistic regression model (method Enter) showed 2 statistically significant predictors: retention time (odds ratio, 0.442; 95% confidence interval, 0.326-0.599; P \0.0001) and mandibular plane angle at T0 (odds ratio, 1.158; 95% confidence interval, 1.002-1.339; P 5 0.047). A linear regression model of the prevalence rate did not show any statistically significant trend (R2 5 0.29; P 5 0.273).
The primary purposes of this study were to identify unexpected complications associated with mandibular bonded multistranded retainers in a cohort of treated patients and to evaluate the role of selected etiologic factors. The cohort had a 1.1% prevalence rate (n 5 38 patients) of unexpected complications of the mandibular bonded retainers; this is within the range estimated at 0.1% to 5% reported in a survey by Lai et al.5 It is lower than the prevalence rates previously found by Renkema et al7 and Katsaros et al.15 Renkema et al reported a prevalence rate of 2.7% during a 5-year period, and Katsaros et al estimated that approximately 5% of patients might be affected by unexpected complications during a 3-year period. The lower prevalence of unexpected complications may have several causes. First, it may be because the entire orthodontic treatment, fabrication, and delivery of the fixed retainer was performed by 1 experienced operator in a private practice setting. The experience of the operator has been previously questioned as a possible factor influencing the prevalence of common complications associated with bonded retainers.23 In addition, our level of evaluation and sensitivity to the detection of unexpected complications might have influenced our findings. Although we made a detailed comparison of the study models at T1 and T2 as well as the photographs and clinical evaluations, we cannot rule out the possibility that we failed to detect incipient and thus discreet changes in some patients. Also, with respect to the significant dropout rate, there is always the possibility that some patients with an unexpected complication failed to return to our clinic or sought treatment elsewhere. The use of different types of retainer wires may also play a role when our results are compared with other studies. Both Katsaros et al15 and Renkema et al7
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Fig 5. Measurement error evaluation of cephalometric variables with Bland-Altman plots: A, 1/ML; B, 1/APo; C, NSML, and D, intercanine distance.
reported the use of 3-stranded 0.0195-in heat-treated twist wire (Wildcat; GAC International, Bohemia, NY), whereas we predominantly used a 6-stranded 0.0175in coaxial wire (Ortho Organizers), and only a small percentage of patients received wires thicker than the 0.0215-in 5-stranded wire (Penta-One). No significant differences were found between the UCG and the CG in the wire type used, since the 2 groups had the same distribution of both wires. The stability and torsional rigidity of 3-stranded flexible wires have been previously questioned in the literature,10,14,15,18 and the use of thicker 5-stranded wires10 or even rigid rectangular stainless steel wires has been suggested to prevent unexpected posttreatment changes.15 In this regard, the 5-stranded 0.0215-in wire may appear to be a safer alternative. However, unexpected complications were also identified in patients with this wire, although in fewer patients compared with the 0.175-in 6-stranded coaxial wire. Nevertheless, this difference may be accounted for by the uneven distribution of the retainer wires used in our patients, since the 0.175-in 6-stranded coaxial wire was used in most of them.
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In our sample, 12 subjects had a torque change between 2 incisors (X effect), but in 21 subjects, the opposite inclination of the contralateral canines (twist effect) was found, and 5 subjects had a nonspecific complication such as a small space opening or small vertical changes in the position of the incisors. Interestingly, in the patients with a twist effect, as many as 89.5% had the left canine inclined in the buccal direction and the contralateral canine in the lingual direction. In agreement with Katsaros et al,15 we found that this direction of tooth movement did not correlate with the original position of the affected teeth and thus could not be characterized as relapse. This rather striking asymmetry may implicate the direction in which the multistranded wires are wound, resulting in potential instability or unwinding during the retention period. In this study, the average time for unexpected complications to occur was approximately 4 years, with a broad range from a minimum of 6 months to a maximum of 12.5 years during the retention period. Unexpected complications may occur quite soon after debonding as well as after many years of uneventful
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Table IV. Treatment changes (T0-T1) for cephalometric variables and intercanine distances (paired t test) UCG (n 5 38) Variable 1/ML ( ) 1/APo (mm) NSML ( ) CC (mm)
T0 93.6 6 7.5 2.9 6 2.3 36.4 6 5.2 26.4 6 1.9
CG (n 5 105) P 0.0005* 0.0005* 0.073 0.746
T1 97.7 6 7.2 4.7 6 2.5 35.5 6 5.9 26.3 6 2.0
T0 95.5 6 7.5 1.9 6 2.9 31.4 6 6.7 25.6 6 2.3
T1 99.9 6 8.6 4.0 6 3.5 30.7 6 6.6 25.3 6 2.0
P \0.0001* \0.0001* 0.025* 0.073
1/ML, Angle of the mandibular incisors to the mandibular plane; 1/APo, distance of the mandibular incisal edge to the Point A-pogonion line; NSML, mandibular plane angle, angle between the NS line and mandibular plane (ML); CC, intercanine distance, distance of the incisal tips of the mandibular canines. *Statistically significant differences at P \0.05.
Table V. Significance of the intergroup differences (2-
sample t test) Variable 1/ML ( ) 1/APo (mm) NSML ( ) CC (mm)
UCG (n 5 38) 4.1 6 6.6 1.8 6 2.9 0.9 6 3.0 0.1 6 1.4
CG (n 5 105) 4.4 6 7.5 2.1 6 3.5 0.6 6 2.6 0.4 6 2.1
P 0.745 0.600 0.509 0.326
1/ML, Angle of the mandibular incisors to the mandibular plane; 1/APo, distance of the mandibular incisal edge to the Point A-pogonion line; NSML, mandibular plane angle, angle between the NS line and mandibular plane (ML); CC, intercanine distance, distance of the incisal tips of the mandibular canines.
retention. Our results are consistent with previous studies, which also reported relatively late onset of similar changes.7,14-16 Katsaros et al15 found unexpected complications after 1 to 2 years of retention, whereas Pazera et al16 reported complications between 2 and 4 years of the retention period. The time factor may also be important when interpreting 2 other possible etiologies. Improper bonding technique and active deflection of the retention wire during insertion have been identified as possible causative factors.15,16 We presumed that this may be true for complications that occur within a few months after bonding of the fixed retainer. Complications arising several years into retention are unlikely to be related to bonding errors. These complications are probably related to wire fatigue and mechanical deformation caused by repeated stress from masticatory forces and hard food particles.15 Sifakakis et al24 showed that even small deflections of the retainer wire can produce forces high enough to cause undesired tooth movement in the retainer segment. The composite resin layer also degrades over time because of mechanical attrition.10 Gradual loss of the composite layer exposes longer segments of the retention wire, rendering it more vulnerable to damage and failure. Because of incisor morphology, bonding the wire in the incisal third could be more
advantageous than bonding in the lower third, since this shortens the exposed wire segments. We expected that the increased failure rate might contribute to the development of unexpected complications. However, no significant difference was found between the 2 groups in this regard, and some of the UCG patients had no history of bond failure or fracture of the retainer wire. The failure rates were considerably higher in both the UCG and the CG (34.2% and 41%, respectively) when compared with the findings of Dahl and Zachrisson.10 The values found in this study were similar Artun et al,25 and to those reported by Renkema et al,7 23 Lie Sam Foek et al. The failure rate was slightly higher in the CG; this might be attributed to a longer observation time compared with the UCG. A significant difference was found between the groups in age at debonding; the average age was significantly lower in the UCG than in the CG. Residual mandibular growth and susceptibility to mandibular incisor crowding are generally more pronounced in younger patients.26,27 However, the regression analysis did not show that age at debonding was a significant predictor. We also evaluated the amounts of mandibular incisor proclination and intercanine distance changes during treatment as possible risk factors in the development of unexpected complications. Before treatment, the mandibular incisors were significantly more procumbent relative to the Point A-pogonion line in the UCG compared with the CG. Significant changes in the proclination of the mandibular incisors relative to the mandibular plane as well as to the Point A-pogonion line were noted during treatment in both groups. Intercanine distance remained fairly consistent during treatment. Neither incisor inclination nor intercanine distance change was a significant predictor in the regression analysis. Nevertheless, incisor proclination may be a risk factor for some patients, depending on local anatomic conditions, especially the buccal cortical plate, because proclination of the mandibular incisors was shown to lead to increased bone loss in some studies.20
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With respect to the mandibular anterior alveolar processes and the buccal cortical plate, facial divergence was evaluated as a potential risk factor in this study. The mandibular plane angle was significantly higher in the UCG than in the CG, and there was a slight but significant decrease in the mandibular plane angle during treatment in the CG. However, these results need to be interpreted with caution because the difference between the groups was relatively small and still within the values of normodivergence. Nevertheless, we presumed that the development and severity of the unexpected complications may depend on the quality and quantity of the surrounding periodontal tissues, especially the buccal cortical plate. Cone-beam computed tomography studies have shown that bone support is often poor even before treatment, and fenestrations or dehiscences are frequently found.19,28 Additionally, it has been shown that a higher mandibular plane angle is often associated with higher and narrower alveolar processes,29,30 with reduced bone thickness and more frequent bone dehiscences and fenestrations of the buccal cortical plate compared with normodivergent patients.22,28 It is likely that the etiology of unexpected complications is multifactorial. Mechanical properties, wire fatigue, or mechanical trauma to the retention wires coupled with anatomic conditions and anteriorly directed forces that influence the anterior segment most likely play a role in the development of unexpected posttreatment changes associated with mandibular fixed retainers. In this regard, long-term retention with bonded retainers is not without risk and should be indicated with caution. Regular checkups are necessary to intercept these complications as soon as possible to minimize any negative side effects. CONCLUSIONS
1.
2.
Unexpected complications of the mandibular bonded multistranded retainers were found in 38 patients (1.1%). Totals of 21 twist effects, 12 X effects, and 5 nonspecific complications were identified. In 89.5% of the patients with a twist effect, a buccal inclination of the mandibular left canine was found. Such a strong asymmetry of canine tipping in these patients suggests that the mechanical properties of retainer wires and their time of use should be examined. Most of the complications were identified within the first 5 to 6 years after placement of the bonded retainer, with the average time of occurrence at 4 years. Based on these results, we presumed that insufficient passivity during bonding of the fixed re-
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3.
4.
5.
tainers does not explain this phenomenon in all patients. The type of multistrand retention wire used or the failure rate of the retention wire does not seem to influence the occurrence of unexpected complications. Subjects with higher mandibular plane angle values were more likely to have an unexpected complication. Incisor proclination alone probably does not play a role in the development of unexpected complications.
REFERENCES 1. Bramante MA. Controversies in orthodontics. Dent Clin North Am 1990;34:91-102. 2. Nanda RS, Nanda SK. Consideration of dentofacial growth in longterm retention and stability: is active retention needed? Am J Orthod Dentofacial Orthop 1992;101:297-302. 3. Pratt MC, Kluemper GT, Hartsfield JK Jr, Fardo D, Nash DA. Evaluation of retention protocols among members of the American Association of Orthodontists in the United States. Am J Orthod Dentofacial Orthop 2011;140:520-6. 4. Little RM, Riedel RA, Artun J. An evaluation of changes in mandibular anterior alignment from 10-20 years post-retention. Am J Orthod 1988;93:423-8. 5. Lai CS, Grossen JM, Renkema AM, Bronkhorst E, Fudalej PS, Katsaros C. Orthodontic retention procedures in Switzerland. Swiss Dent J 2014;124:655-61. 6. Renkema AM, Sips ET, Bronkhorst E, Kuijpers-Jagtman AM. A survey on orthodontic retention precedures in the Netherlands. Eur J Orthod 2009;31:432-7. 7. Renkema AM, Renkema A, Bronkhorst E, Katsaros C. Long-term effectiveness of canine-to-canine bonded flexible spiral wire lingual retainers. Am J Orthod Dentofacial Orthop 2011;139: 614-21. 8. Zachrisson BU. Long-term experience with direct bonded retainers: update and clinical advice. J Clin Orthod 2007;41:728-37. 9. Booth FA, Edelman JM, Proffit WR. Twenty-year follow-up of patients with permanently bonded mandibular canine-to-canine retainers. Am J Orthod Dentofacial Orthop 2008;133:70-6. 10. Dahl EH, Zachrisson BU. Long-term experience with direct bonded lingual retainers. J Clin Orthod 1991;25:619-30. 11. Rogers MB, Andrews LJ. Dependable technique for bonding a 3 3 3 retainer. Am J Orthod Dentofacial Orthop 2004;126: 231-3. 12. St€ ormann I, Ehmer U. A prospective randomized study of different retainer types. J Orofac Orthop 2002;63:42-50. 13. Pandis N, Vlahopoulos K, Madianos P, Eliades T. Long-term periodontal status of patients with mandibular lingual fixed retention. Eur J Orthod 2007;29:471-6. 14. Brenchley ML. A cautionary tale of simplified retention. Br J Orthod 1997;24:113-5. 15. Katsaros C, Livas C, Renkema AM. Unexpected complications of bonded mandibular lingual retainers. Am J Orthod Dentofacial Orthop 2007;132:838-41. 16. Pazera P, Fudalej P, Katsaros C. Severe complication of a bonded mandibular lingual retainer. Am J Orthod Dentofacial Orthop 2012;142:406-9.
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17. Zachrisson BU. Third generation mandibular bonded lingual 3-3 retainer. J Clin Orthod 1995;29:39-48. 18. Pizzaro K, Jones ML. Crown inclination relapse with multiflex retainers. J Clin Orthod 1992;26:780-2. 19. Nahm KY, Kang JH, Moon SC, Choi YS, Kook YA, Kim SH, et al. Alveolar bone loss around incisors in Class I bidentoalveolar protrusion patients: a retrospective three-dimensional cone beam CT study. Dentomaxillofac Radiol 2012;41:481-8. 20. Kim Y, Park JU, Kook YA. Alveolar bone loss around incisors in surgical skeletal class III patients. A retrospective 3-D CBCT study. Angle Orthod 2009;79:676-82. 21. Enhos S, Uysal T, Yagci A, Veli _I, Ucar FI, Ozer T. Dehiscence and fenestration in patients with different vertical growth patterns assessed with cone-beam computed tomography. Angle Orthod 2012;82:868-74. 22. Swasty D, Lee J, Huang JC, Maki K, Gansky SA, Hatcher D, et al. Cross-sectional human mandibular morphology as assessed in vivo by cone-beam computed tomography in patient with different vertical facial dimensions. Am J Orthod Dentofacial Orthop 2011;139(Suppl):e377-89. 23. Lie Sam Foek DJ, Ozcan M, Verkerke GJ, Sandham A, Dijkstra PU. Survival of flexible, braided, bonded stainless steel lingual retainers: a historic cohort study. Eur J Orthod 2008;30:199-204.
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24. Sifakakis I, Pandis N, Eliades T, Makou M, Katsaros C, Bourauel C. In-vitro assessment of the forces generated by lingual fixed retainers. Am J Orthod Dentofacial Orthop 2011;139:44-8. 25. Artun J, Spadafora AT, Shapiro PA. A three year follow-up study of various types of orthodontic canine-to-canine retainers. Eur J Orthod 1997;5:501-9. 26. Richardson ME. Late lower arch crowding: facial growth or forward drift? Eur J Orthod 1979;1:219-25. 27. Richardson ME. Late lower arch crowding in relation to skeletal and dental morphology and growth changes. Br J Orthod 1996; 23:249-54. 28. Yagci A, Veli I, Uysal T, Ucar FI, Ozer T, Enhos S. Dehiscence and fenestration in skeletal Class I, II, and III malocclusions assessed with cone-beam computed tomography. Angle Orthod 2012;82: 67-74. 29. Kuitert R, Beckmann S, van Loenen M, Tuinzing B, Zentnere A. Dentoalveolar compensation in subjects with vertical skeletal dysplasia. Am J Orthod Dentofacial Orthop 2006;129:649-57. 30. Kucera J, Marek I, Tycova H, Baccetti T. Molar height and dentoalveolar compensation in adult subjects with skeletal open bite. Angle Orthod 2011;81:564-9.
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Unexpected complications associated with mandibular fixed retainers: A retrospective study eraa and Ivo Marekb Josef Kuc Prague and Olomouc, Czech Republic
Introduction: The purposes of this retrospective study were to describe the types of unexpected complications associated with mandibular fixed retainers and to assess their prevalences and possible etiologic causes. Methods: A total of 3500 consecutive patients (1423 male, 2077 female) treated with fixed appliances and a mandibular fixed retainer as a part of the retention protocol were screened during the retention period (20082013) for unexpected complications. Thirty-eight subjects (12 male, 26 female; mean age, 20.7 6 8.9 years) with unexpected complications were identified and assigned to the unexpected complications group and compared with a randomly selected control group of 105 subjects (43 men, 62 women; mean age, 29.5 6 9.7 years) without unexpected complications. Relationships between unexpected complications and cephalometric and clinical variables were evaluated. Results: An opposite inclination of the contralateral canines (twist effect) was found in 21 subjects. In 89.5%, the left canines were tipped buccally. A torque difference of 2 adjacent incisors (X effect) was identified in 12 patients. In 5 subjects, nonspecific complications were noted. Subjects in the unexpected complications group were significantly younger at debonding (P 5 0.03) and had higher mandibular plane angles (P \0.0001) and increased pretreatment ventral positions of the mandibular incisors (P 5 0.029). No differences were found between the groups with regard to treatment duration, wire type, failure rate, treatment changes in incisor proclination, or intercanine distance. Conclusions: Unexpected complications of mandibular fixed retainers are relatively rare. Facial divergence was identified as a possible predictor. However, the etiology is most likely multifactorial. Strong asymmetry among the patients with the twist effect suggests that the mechanical properties of retention wires may play a role and should be examined in the future. (Am J Orthod Dentofacial Orthop 2016;149:202-11)
L
ong-term stability of orthodontic treatment results is a great challenge in orthodontics. Some authors even consider long-term stability to be a myth.1 To overcome this problem, others have advocated long-term or even lifelong retention as a solution.2-5 Fixed retainers seem to be the best option for longterm maintenance of treatment results, and a growing number of orthodontists use them for this purpose.5,6 a Assistant professor, Department of Orthodontics, First Medical Faculty of Charles University, Prague, Czech Republic; postgraduate student, Department of Orthodontics, Clinic of Dental Medicine, Palacky University, Olomouc, Czech Republic. b Assistant professor, Department of Orthodontics, Clinic of Dental Medicine, Palacky University, Olomouc, Czech Republic; consultant orthodontist, Department of Orthodontics, First Medical Faculty of Charles University, Prague, Czech Republic. All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest, and none were reported. Supported by a research grant from the Ministry of Health of the Czech Republic (IGA MZCR NT14189-3/2013). Address correspondence to: Ivo Marek, Palackeho 12, Olomouc 772 00, Czech Republic; e-mail, [email protected]. Submitted, February 2015; revised and accepted, July 2015. 0889-5406/$36.00 Copyright Ó 2016 by the American Association of Orthodontists. http://dx.doi.org/10.1016/j.ajodo.2015.07.035
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Fixed retainers have been shown to be effective in maintaining an esthetic result in the anterior region without the patient's compliance.7 They have been reported to be safe and predictable,8 and acceptable and compatible with periodontal health.9 However, regular checkups are required, since occasional failures caused by wire fractures or bond failures can occur.10 The reported failure rates of bonded retainers vary widely between 0.1% and 53%.11,12 According to some studies, long-term use of fixed retainers may also be associated with greater plaque and calculus accumulation, which can lead to a higher risk of gingival recession and increased probing depth.13 Unexpected complications may also appear in patients with fixed retainers.7,14,15 These complications were described as unwanted movement of the teeth included in the fixed retainer, even without wire fracture or bond failure. Small spaces between incisors in intact retainer segments,10 unexpected torque changes between the maxillary central incisors,14 torque changes between adjacent mandibular incisors, and opposite inclinations of contralateral mandibular canines have also been reported.7,15 Unexpected complications have been
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estimated to occur in 0.1% to 5% of patients; these are relatively small numbers.5,7,15 However, 50% of these patients may require retreatment.15 In some, the complications can be quite severe, including buccal bone dehiscence.16 Consequently, gingival recessions may occur, posing both health and esthetic problems. In such cases, a demanding orthodontic and reconstructive surgical and periodontal treatment may be necessary. Several causes of unexpected complications in patients with fixed retainers have been suggested, including poor bonding technique and insufficient wire passivity,15,16 instability of multistrand wires,10,17 and wire straightening or wire activation by mechanical trauma.15 Biologic factors, such as forces created by incisor position relapse, have also been proposed in the literature.18 Apart from relapse, increased incisor proclination has also been shown to cause or worsen bone dehiscences of the buccal cortical plate, thus reducing bone support.19,20 With regard to bone support, it has been previously reported that hyperdivergent patients have a higher prevalence of buccal bone dehiscence and fenestrations in the mandibular anterior region even before orthodontic treatment.21,22 We hypothesized that mandibular incisor proclination and increases in intercanine distance during orthodontic treatment may be associated with increased risks of unexpected complications. We also presumed that anatomic conditions related to an increased mandibular plane angle and hyperdivergence may play roles. The purposes of this retrospective study were to describe the types, prevalence, and timing of unexpected complications of mandibular fixed retainers in a group of patients in the retention phase and to identify some possible etiologic factors that were previously suggested in the literature. MATERIAL AND METHODS
A cohort of 3500 consecutive patients (1423 male, 2077 female) fulfilled the following inclusion criteria: (1) mandibular bonded flexible spiral wire fixed retainer in situ; (2) pretreatment (T0) and posttreatment (T1) cephalometric and panoramic radiographs, plaster models, and intraoral photographs; (3) no prosthetic reconstruction in the mandibular anterior region; and (4) no history of periodontal treatment, surgery, or trauma in the mandibular anterior region. They were seen at regular retention visits from January 2, 2008, to November 29, 2013. All patients were of European descent and were treated for various malocclusions with fixed appliances in the private orthodontic practice of the second author (I.M.). They were treated with a 0.022-in slot Roth prescription preadjusted appliance
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(Ortho Organizers, Carlsbad, Calif). In the routine treatment protocol, initial leveling and alignment were performed with round, superelastic, or heat-activated nickel-titanium wires. Space closure was performed using rectangular 0.018 3 0.025-in stainless steel wires. Intramaxillary and intermaxillary elastics were also used during the final stages of treatment. During debonding, all patients received a multistrand flexible spiral wire fixed retainer, either a 0.0215-in gold-plated 5-stranded spiral wire (Penta-One; Gold'n Braces, Palm Harbor, Fla) or a 0.0175-in 6-stranded coaxial wire (Ortho Organizers) bonded to the mandibular incisor region, including both canines and all incisors. All fixed retainers were shaped at chairside and bonded by 1 operator (I.M.) directly on the lingual surfaces of the mandibular anterior teeth using flowable composite (Transbond Supreme LV; 3M Unitek, Monrovia, Calif) according to the method described by Dahl and Zachrisson.10 In addition to a fixed retainer, the patients received removable maxillary and mandibular Hawley retainers or an activator and a maxillary vacuum-formed retainer. They were instructed to adhere to the standard retention protocol for removable retainers as follows: (1) full-time wear for 3 months, (2) nighttime wear only for the rest of the first year, (3) alternating nights for the second year, and (4) twice a week at night for the third year. The patients were also instructed to come at least once a year to have the fixed retainer checked even after they had stopped wearing the removable retainers. The average attendance of patients per year of retention in our study is shown in Figure 1. During the recall visit (T2), the patients were screened for unexpected complications of the mandibular fixed retainer. Written informed consent was obtained from each patient or the parents. The patients were examined, and intraoral photographs and plaster models were made. The prevalence and types of unexpected complications were determined by intraoral examination, and by evaluation and comparison of the study models obtained at T1 and at T2. Unexpected complications were assessed in the mandibular anterior region according to the descriptions reported previously10,15: torque difference (Fig 2, A and B) between 2 adjacent incisors (X effect), increased buccal inclination and opposite inclination (Fig 2, C and D) of the contralateral canines (twist effect), and nonspecific changes such as spacing (Fig 2, E and F). The subjects were divided into 2 groups according to the presence or absence of unexpected complications. The unexpected complications group (UCG) comprised 38 patients with a complication in the mandibular anterior segment. The distributions of unexpected complications among the patients by year in retention and the prevalence rates are shown in Table I and Figure 3.
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Fig 1. Average attendance of patients in our study per years in retention.
Of the remaining patients, in whom no unexpected complications were identified, 105 patients were randomly selected to create the control group (CG). Random selection was performed with Excel (Microsoft, Redmond, Wash) using the Rand and Index functions. The sample size was calculated for inclination of the mandibular incisors at a 5 0.05 and a power of 80% to detect a difference of 4 , assuming that the standard deviation was 7.4 . The power analysis showed that 105 patients were needed in the CG. The characteristics of both groups are shown in Table II. Each patient's chart was analyzed to determine the type of retainer wire and rate of wire failure (wire fracture or detachment followed by repair of the fixed retainer), treatment duration (T0-T1), and retention time (T1-T2). Two lateral cephalometric radiographs and plaster models were analyzed of each subject from before treatment (T0) and after treatment (T1) to evaluate the treatment changes (T0-T1) in the inclination and position of mandibular incisors, the mandibular plane angle, and the intercanine distance. Cephalometric radiographs were digitized and traced using software (PC Dent: CompuGroup Medical, Prague, Czech Republic). Plaster model recording of intercanine distance change was performed using a digital caliper (Masel Orthodontics, Carlsbad, Calif), measured with an accuracy of 0.01 mm. The intercanine distance was measured from the middle of the cusp of the mandibular left canine to the middle of the cusp of the mandibular right canine. In the case of an abrasion of a cusp, the middle of the surface was estimated.7 All tracings and evaluations were performed by the same operator (I.M.). A complete list of the variables
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with a detailed description and graphic representation of the cephalometric parameters is given in Figure 4 and Tables II and III. Two weeks after the measurements were taken, the primary investigator remeasured all variables from 20 randomly selected patients to calculate the error of measurement using intraclass correlation coefficients for quantitative variables. The correlation analysis showed the highest r value of 0.997 for intercanine distance and the lowest r value of 0.834 for the position of the mandibular incisor relative to the Point A-pogonion line. Correlations for repeated measurements were statistically significant for all variables at P \0.05. Paired t tests and Bland-Altman plots were also performed to evaluate errors. Both the t tests and the Bland-Altman plots (Fig 5) indicated that the errors were small. The post hoc intraoperator and interoperator agreement for detection of unexpected complications was also determined. Both operators twice within 2 weeks independently evaluated the study models and the photographs of 30 randomly selected subjects at T1 and T2. The Cohen kappa coefficient (k) showed almost perfect agreement (k 5 0.918) for the first operator (J.K.) and perfect agreement (k 5 1.000) for the second operator (I.M.). Almost perfect agreement in the evaluation of unexpected complications was found between the 2 operators (k 5 0.830). Statistical analysis
An exploratory test (Shapiro-Wilk) was performed to assess the normality of the distribution for all quantitative variables. Parametric tests (paired t test, 2-sample
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Fig 2. Clinical examples of unexpected complications of mandibular bonded multistrand retainers on intraoral photographs. Torque difference between 2 adjacent incisors (X effect) from A, frontal and B, occlusals views. Opposite inclination of contralateral canines (twist effect) from C, frontal and D, occlusal views. Nonspecific changes (spacing) from E, frontal and F, occlusal views.
Table I. Numbers of intercepted unexpected compli-
cations and distribution of patients in the sample per years in retention Years in retention 0-1 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10 10-11 11-12
UCG (n 5 38) 6 7 7 5 2 5 2 0 2 1 0 1
Sample (n 5 3500) 710 645 496 381 283 234 177 144 112 113 138 67
t test) were used for the variables when the data had normal distributions. In variables without normal distributions, nonparametric tests (Mann-Whitney U test) were used. Comparisons of the qualitative variables
were performed with the Fisher exact test. A logistic regression analysis (method Enter) was performed with “unexpected complication” as the dependent variable. Sex, age at debonding, failure rate, time of retention, mandibular plane angle, incisor position and inclination, and intercanine distance change were chosen for the independent variables. All statistical analyses were performed using the Statistical Package for the Social Sciences software (version 15; SPSS, Chicago, Ill) at P \0.05. RESULTS
The results are presented in Tables I through V. Of 3500 patients, 38 (1.1%) experienced unexpected complications with the mandibular fixed retainers and were assigned to the UCG. The numbers of unexpected complications and their distributions in time are given in Table I. Twelve patients had an X effect, 21 had a twist effect, and 5 had nonspecific complications.21 As many as
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Fig 3. Prevalence rates of unexpected complications per years in retention.
Table II. Descriptive statistics of the variables and between-group comparisons Variable F (%)/M (%) TT (y) AD (y) AR (y) RT (y) WT (%) FR (%)
UCG (n 5 38) 26 (68%)/12 (32%) 1.9 6 0.7 16.7 6 7.5 20.7 6 8.9 4.0 6 2.8 N 33 (87%) AU 5 (13%) 13 (34.2%)
CG (n 5 105) 61 (58%)/44 (42%) 2.0 6 0.7 20.2 6 9.5 29.5 6 9.7 9.3 6 2.0 N 92 (88%) AU 13 (12%) 43 (41.0%)
P 0.337* 0.270y 0.030y,z \0.0001y,z \0.0001y,z 1.000* 0.562*
F/M, Numbers and percentages of females and males in the groups; TT, treatment time (T0-T1); AD, age at debonding (T1); AR, age at recall (T2) and, in the UCG, also the age of interception of the unexpected complication; RT, retention time (T1-T2); in the UCG, also the time of occurrence of the unexpected complication; WT, wire type (N, 0.0175-in 6-stranded coaxial wire; AU, 5-stranded spiral wire); FR, failure rate, number and percentage of rebondings or repairs of mandibular fixed retainers in the retention period (T1-T2). *Fisher's exact test; yMann-Whitney U test; zstatistically significant differences at P \0.05.
89.5% of the subjects with the twist effect had the left canine inclined in the buccal direction. The distribution of the sexes was not significantly different between groups (P 5 0.337). No significant difference was found between the UCG and the CG in treatment time (P 5 0.270). However, age at debonding (P 5 0.03) and age at recall, and thus retention time, differed significantly between the groups (P \0.0001 for both). The average time of interception of an unexpected complication was 4 6 2.8 years (range, 0.5-12.5 years). An analysis of the UCG per year in retention (Table I) showed that the number of intercepted unexpected complications was highest in the first 5 years after debonding, and then it decreased with time. However, the number of patients attending recall visits also decreased with time (Fig 1; Table I). The estimated prevalence rate
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based on the number of identified unexpected complications and the number of patients at recall per year after debonding show that the rate of complications was increasing with time in the first few years of the retention period. There was no difference between the groups in the distribution of wire type used (P 5 1.000). Failure rates were comparable in the 2 groups (P 5 0.562). Significant differences were found in the pretreatment position of the mandibular incisors relative to the Point A-pogonion line (P 5 0.029) and the mandibular plane angle (P \0.0001). Both values were higher in the UCG compared with the CG at T0. No difference was observed between the groups in the inclination of the mandibular incisors to the mandibular plane (P 5 0.151) or the intercanine distance (P 5 0.065) at T0.
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Table III. Intergroup comparison of cephalometric
variables and intercanine distances before treatment (2-sample t test) Variable 1/ML ( ) 1/APo (mm) NSML ( ) CC (mm)
UCG (n 5 38) 93.6 6 7.5 2.9 6 2.3 36.4 6 5.2 26.4 6 1.9
CG (n 5 105) 95.5 6 7.5 1.9 6 2.9 31.4 6 6.7 25.6 6 2.3
P 0.151 0.029* \0.0001* 0.065
1/ML, Angle of the mandibular incisors to the mandibular plane; 1/APo, distance of the mandibular incisal edge to the Point A-pogonion line; NSML, mandibular plane angle, angle between the NS line and mandibular plane (ML); CC, intercanine distance, distance of the incisal tips of the mandibular canines. *Statistically significant differences at P \0.05.
DISCUSSION
Fig 4. Linear and angular measurements on cephalometric radiographs: 1/ML, angle of the mandibular incisors to the mandibular plane; 1/APo, distance of the mandibular incisal edge to the Point A-pogonion line; NSML, mandibular plane angle, angle between the NS line and mandibular plane (ML).
The mandibular incisors were significantly proclined during treatment (T0-T1) in both the CG (P 5 0.0005) and the UCG (P \0.0001). However, no significant difference in incisor proclination was identified between the groups (P 5 0.745 and P 5 0.600, respectively). Although no significant change in facial divergence was observed during treatment in the UCG (P 5 0.073), a significant difference was found in the CG (P 5 0.025). However, no significant difference was found between the groups (P 5 0.509). The intercanine distance remained unchanged during treatment in both the UCG (P 5 0.746) and the CG (P 5 0.073), and no difference was found between the groups (P 5 0.326). A logistic regression model (method Enter) showed 2 statistically significant predictors: retention time (odds ratio, 0.442; 95% confidence interval, 0.326-0.599; P \0.0001) and mandibular plane angle at T0 (odds ratio, 1.158; 95% confidence interval, 1.002-1.339; P 5 0.047). A linear regression model of the prevalence rate did not show any statistically significant trend (R2 5 0.29; P 5 0.273).
The primary purposes of this study were to identify unexpected complications associated with mandibular bonded multistranded retainers in a cohort of treated patients and to evaluate the role of selected etiologic factors. The cohort had a 1.1% prevalence rate (n 5 38 patients) of unexpected complications of the mandibular bonded retainers; this is within the range estimated at 0.1% to 5% reported in a survey by Lai et al.5 It is lower than the prevalence rates previously found by Renkema et al7 and Katsaros et al.15 Renkema et al reported a prevalence rate of 2.7% during a 5-year period, and Katsaros et al estimated that approximately 5% of patients might be affected by unexpected complications during a 3-year period. The lower prevalence of unexpected complications may have several causes. First, it may be because the entire orthodontic treatment, fabrication, and delivery of the fixed retainer was performed by 1 experienced operator in a private practice setting. The experience of the operator has been previously questioned as a possible factor influencing the prevalence of common complications associated with bonded retainers.23 In addition, our level of evaluation and sensitivity to the detection of unexpected complications might have influenced our findings. Although we made a detailed comparison of the study models at T1 and T2 as well as the photographs and clinical evaluations, we cannot rule out the possibility that we failed to detect incipient and thus discreet changes in some patients. Also, with respect to the significant dropout rate, there is always the possibility that some patients with an unexpected complication failed to return to our clinic or sought treatment elsewhere. The use of different types of retainer wires may also play a role when our results are compared with other studies. Both Katsaros et al15 and Renkema et al7
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Fig 5. Measurement error evaluation of cephalometric variables with Bland-Altman plots: A, 1/ML; B, 1/APo; C, NSML, and D, intercanine distance.
reported the use of 3-stranded 0.0195-in heat-treated twist wire (Wildcat; GAC International, Bohemia, NY), whereas we predominantly used a 6-stranded 0.0175in coaxial wire (Ortho Organizers), and only a small percentage of patients received wires thicker than the 0.0215-in 5-stranded wire (Penta-One). No significant differences were found between the UCG and the CG in the wire type used, since the 2 groups had the same distribution of both wires. The stability and torsional rigidity of 3-stranded flexible wires have been previously questioned in the literature,10,14,15,18 and the use of thicker 5-stranded wires10 or even rigid rectangular stainless steel wires has been suggested to prevent unexpected posttreatment changes.15 In this regard, the 5-stranded 0.0215-in wire may appear to be a safer alternative. However, unexpected complications were also identified in patients with this wire, although in fewer patients compared with the 0.175-in 6-stranded coaxial wire. Nevertheless, this difference may be accounted for by the uneven distribution of the retainer wires used in our patients, since the 0.175-in 6-stranded coaxial wire was used in most of them.
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In our sample, 12 subjects had a torque change between 2 incisors (X effect), but in 21 subjects, the opposite inclination of the contralateral canines (twist effect) was found, and 5 subjects had a nonspecific complication such as a small space opening or small vertical changes in the position of the incisors. Interestingly, in the patients with a twist effect, as many as 89.5% had the left canine inclined in the buccal direction and the contralateral canine in the lingual direction. In agreement with Katsaros et al,15 we found that this direction of tooth movement did not correlate with the original position of the affected teeth and thus could not be characterized as relapse. This rather striking asymmetry may implicate the direction in which the multistranded wires are wound, resulting in potential instability or unwinding during the retention period. In this study, the average time for unexpected complications to occur was approximately 4 years, with a broad range from a minimum of 6 months to a maximum of 12.5 years during the retention period. Unexpected complications may occur quite soon after debonding as well as after many years of uneventful
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Table IV. Treatment changes (T0-T1) for cephalometric variables and intercanine distances (paired t test) UCG (n 5 38) Variable 1/ML ( ) 1/APo (mm) NSML ( ) CC (mm)
T0 93.6 6 7.5 2.9 6 2.3 36.4 6 5.2 26.4 6 1.9
CG (n 5 105) P 0.0005* 0.0005* 0.073 0.746
T1 97.7 6 7.2 4.7 6 2.5 35.5 6 5.9 26.3 6 2.0
T0 95.5 6 7.5 1.9 6 2.9 31.4 6 6.7 25.6 6 2.3
T1 99.9 6 8.6 4.0 6 3.5 30.7 6 6.6 25.3 6 2.0
P \0.0001* \0.0001* 0.025* 0.073
1/ML, Angle of the mandibular incisors to the mandibular plane; 1/APo, distance of the mandibular incisal edge to the Point A-pogonion line; NSML, mandibular plane angle, angle between the NS line and mandibular plane (ML); CC, intercanine distance, distance of the incisal tips of the mandibular canines. *Statistically significant differences at P \0.05.
Table V. Significance of the intergroup differences (2-
sample t test) Variable 1/ML ( ) 1/APo (mm) NSML ( ) CC (mm)
UCG (n 5 38) 4.1 6 6.6 1.8 6 2.9 0.9 6 3.0 0.1 6 1.4
CG (n 5 105) 4.4 6 7.5 2.1 6 3.5 0.6 6 2.6 0.4 6 2.1
P 0.745 0.600 0.509 0.326
1/ML, Angle of the mandibular incisors to the mandibular plane; 1/APo, distance of the mandibular incisal edge to the Point A-pogonion line; NSML, mandibular plane angle, angle between the NS line and mandibular plane (ML); CC, intercanine distance, distance of the incisal tips of the mandibular canines.
retention. Our results are consistent with previous studies, which also reported relatively late onset of similar changes.7,14-16 Katsaros et al15 found unexpected complications after 1 to 2 years of retention, whereas Pazera et al16 reported complications between 2 and 4 years of the retention period. The time factor may also be important when interpreting 2 other possible etiologies. Improper bonding technique and active deflection of the retention wire during insertion have been identified as possible causative factors.15,16 We presumed that this may be true for complications that occur within a few months after bonding of the fixed retainer. Complications arising several years into retention are unlikely to be related to bonding errors. These complications are probably related to wire fatigue and mechanical deformation caused by repeated stress from masticatory forces and hard food particles.15 Sifakakis et al24 showed that even small deflections of the retainer wire can produce forces high enough to cause undesired tooth movement in the retainer segment. The composite resin layer also degrades over time because of mechanical attrition.10 Gradual loss of the composite layer exposes longer segments of the retention wire, rendering it more vulnerable to damage and failure. Because of incisor morphology, bonding the wire in the incisal third could be more
advantageous than bonding in the lower third, since this shortens the exposed wire segments. We expected that the increased failure rate might contribute to the development of unexpected complications. However, no significant difference was found between the 2 groups in this regard, and some of the UCG patients had no history of bond failure or fracture of the retainer wire. The failure rates were considerably higher in both the UCG and the CG (34.2% and 41%, respectively) when compared with the findings of Dahl and Zachrisson.10 The values found in this study were similar Artun et al,25 and to those reported by Renkema et al,7 23 Lie Sam Foek et al. The failure rate was slightly higher in the CG; this might be attributed to a longer observation time compared with the UCG. A significant difference was found between the groups in age at debonding; the average age was significantly lower in the UCG than in the CG. Residual mandibular growth and susceptibility to mandibular incisor crowding are generally more pronounced in younger patients.26,27 However, the regression analysis did not show that age at debonding was a significant predictor. We also evaluated the amounts of mandibular incisor proclination and intercanine distance changes during treatment as possible risk factors in the development of unexpected complications. Before treatment, the mandibular incisors were significantly more procumbent relative to the Point A-pogonion line in the UCG compared with the CG. Significant changes in the proclination of the mandibular incisors relative to the mandibular plane as well as to the Point A-pogonion line were noted during treatment in both groups. Intercanine distance remained fairly consistent during treatment. Neither incisor inclination nor intercanine distance change was a significant predictor in the regression analysis. Nevertheless, incisor proclination may be a risk factor for some patients, depending on local anatomic conditions, especially the buccal cortical plate, because proclination of the mandibular incisors was shown to lead to increased bone loss in some studies.20
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With respect to the mandibular anterior alveolar processes and the buccal cortical plate, facial divergence was evaluated as a potential risk factor in this study. The mandibular plane angle was significantly higher in the UCG than in the CG, and there was a slight but significant decrease in the mandibular plane angle during treatment in the CG. However, these results need to be interpreted with caution because the difference between the groups was relatively small and still within the values of normodivergence. Nevertheless, we presumed that the development and severity of the unexpected complications may depend on the quality and quantity of the surrounding periodontal tissues, especially the buccal cortical plate. Cone-beam computed tomography studies have shown that bone support is often poor even before treatment, and fenestrations or dehiscences are frequently found.19,28 Additionally, it has been shown that a higher mandibular plane angle is often associated with higher and narrower alveolar processes,29,30 with reduced bone thickness and more frequent bone dehiscences and fenestrations of the buccal cortical plate compared with normodivergent patients.22,28 It is likely that the etiology of unexpected complications is multifactorial. Mechanical properties, wire fatigue, or mechanical trauma to the retention wires coupled with anatomic conditions and anteriorly directed forces that influence the anterior segment most likely play a role in the development of unexpected posttreatment changes associated with mandibular fixed retainers. In this regard, long-term retention with bonded retainers is not without risk and should be indicated with caution. Regular checkups are necessary to intercept these complications as soon as possible to minimize any negative side effects. CONCLUSIONS
1.
2.
Unexpected complications of the mandibular bonded multistranded retainers were found in 38 patients (1.1%). Totals of 21 twist effects, 12 X effects, and 5 nonspecific complications were identified. In 89.5% of the patients with a twist effect, a buccal inclination of the mandibular left canine was found. Such a strong asymmetry of canine tipping in these patients suggests that the mechanical properties of retainer wires and their time of use should be examined. Most of the complications were identified within the first 5 to 6 years after placement of the bonded retainer, with the average time of occurrence at 4 years. Based on these results, we presumed that insufficient passivity during bonding of the fixed re-
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3.
4.
5.
tainers does not explain this phenomenon in all patients. The type of multistrand retention wire used or the failure rate of the retention wire does not seem to influence the occurrence of unexpected complications. Subjects with higher mandibular plane angle values were more likely to have an unexpected complication. Incisor proclination alone probably does not play a role in the development of unexpected complications.
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24. Sifakakis I, Pandis N, Eliades T, Makou M, Katsaros C, Bourauel C. In-vitro assessment of the forces generated by lingual fixed retainers. Am J Orthod Dentofacial Orthop 2011;139:44-8. 25. Artun J, Spadafora AT, Shapiro PA. A three year follow-up study of various types of orthodontic canine-to-canine retainers. Eur J Orthod 1997;5:501-9. 26. Richardson ME. Late lower arch crowding: facial growth or forward drift? Eur J Orthod 1979;1:219-25. 27. Richardson ME. Late lower arch crowding in relation to skeletal and dental morphology and growth changes. Br J Orthod 1996; 23:249-54. 28. Yagci A, Veli I, Uysal T, Ucar FI, Ozer T, Enhos S. Dehiscence and fenestration in skeletal Class I, II, and III malocclusions assessed with cone-beam computed tomography. Angle Orthod 2012;82: 67-74. 29. Kuitert R, Beckmann S, van Loenen M, Tuinzing B, Zentnere A. Dentoalveolar compensation in subjects with vertical skeletal dysplasia. Am J Orthod Dentofacial Orthop 2006;129:649-57. 30. Kucera J, Marek I, Tycova H, Baccetti T. Molar height and dentoalveolar compensation in adult subjects with skeletal open bite. Angle Orthod 2011;81:564-9.
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