Orthodontic space opening during adolescence is

ONLINE ONLY Postorthodontic root approximation after opening space for maxillary lateral incisor implants Taylor M. Olsen a and Vincent G. Kokich, Sr b Seattle, Wash Introduction: Orthodontic space opening during adolescence is a common treatment for congenitally missing maxillary lateral incisors. Because of continued facial growth and compensatory tooth eruption, several years can elapse between completion of orthodontic treatment for a teenage patient and implant placement. There are reports that, after successful orthodontic opening of the implant space, the central incisor and canine roots reapproximate during retention and prevent implant placement. Methods: To study this phenomenon, the records of 94 patients with missing maxillary lateral incisors were collected. Periapical and panoramic radiographs were used to measure intercoronal and interradicular distances between the central incisor and the canine adjacent to the missing lateral incisor before and after orthodontic treatment and at implant placement. Results: Although root approximation between the adjacent central incisor and canine during retention did not occur consistently, 11% of the patients experienced relapse significant enough to prevent implant placement. Conclusions: To ensure sufficient space for implant placement, we recommend at least 6.3 mm of intercoronal space and 5.7 mm of interradicular space between the adjacent central incisor and canine. A bonded wire or resin-bonded bridge will help to reduce root approximation that might occur during retention. (Am J Orthod Dentofacial Orthop 2010;137:158.e1-158.e8) Orthodontic space opening during adolescence is a common treatment for congenitally missing maxillary lateral incisors. In these situations, implants are often used to replace the missing tooth to establish ideal esthetics without restoring the adjacent teeth (Fig 1). However, several years can elapse between completion of orthodontic treatment for a teenage patient and implant placement because of continued facial growth and compensatory tooth eruption. 1-3 Since the implant cannot erupt, if it is placed too early, it will appear to submerge vertically as the adjacent teeth continue to erupt. 4-6 It is therefore not uncommon to wait 3 to 5 years after orthodontic treatment before placing a lateral incisor implant. What happens to the positions of the maxillary canine and the central incisor roots during that time? Dickinson 7 reported that, after successful From the Department of Orthodontics, School of Dentistry, University of Washington, Seattle. a Private practice, San Juan Capistrano, Calif; Former resident. b Professor. The authors report no commercial, proprietary, or financial interest in the products or companies described in this article. Reprint requests to: Taylor M. Olsen, Olsen Orthodontics, 31920 Del Obispo St. #265, San Juan Capistrano, CA 92675; e-mail, TaylorOlsenDDS@gmail.com. Submitted, October 2008; revised and accepted, August 2009. 0889-5406/$36.00 Copyright Ó 2010 by the American Association of Orthodontists. doi:10.1016/j.ajodo.2009.08.024 orthodontic opening of the implant space, the central incisor and canine roots reapproximated during retention and prevented implant placement. This problem is frustrating for both the orthodontist and the patient and could require either orthodontic retreatment to facilitate implant placement or the placement of a fixed prosthesis (Fig 2). The literature addressing these issues is limited. To date, no studies have looked at what happens to the space created between maxillary central incisor and canine crowns and roots after orthodontic appliance removal. Seen clinically, do the roots of these teeth exhibit movement or angulation changes into the implant space sufficient to prevent implant placement? The purpose of this study was to evaluate postorthodontic root approximation adjacent to congenitally missing maxillary lateral incisors during retention. MATERIAL AND METHODS Records of 94 patients were collected from various orthodontic, periodontal, and oral surgery practices according to the following criteria: (1) congenitally missing at least 1 maxillary lateral incisor, (2) treated orthodontically to open space for a lateral incisor restoration, (3) not missing an adjacent central incisor or canine, (4) no significant root resorption on the adjacent central incisor or canine, and (5) treatment completed between 1990 and 2008. 158.e1

158.e2 Olsen and Kokich American Journal of Orthodontics and Dentofacial Orthopedics February 2010 Fig 1. A, This patient was congenitally missing her maxillary right lateral incisor, and the space was opened orthodontically for a single-tooth implant. B, The anterior periapical radiographs of the implant site showed that the roots were far enough apart for C and D, implant placement and restoration of the missing tooth. Fig 2. A, This patient was congenitally missing her maxillary right lateral incisor, and the space was opened orthodontically for a single-tooth implant. B, However, the central incisor and canine roots were close together. C, A resin-bonded Maryland bridge was used D, to fill the space for the missing lateral incisor. These 94 subjects had 142 missing lateral incisors. Of them, 80 patients (121 missing lateral incisors) were consecutively treated in 1 periodontal practice. Although all available radiographs were collected, unfortunately, not all patients had a complete set of radiographs at all 3 time points. Periapical and panoramic radiographs were collected and used to measure the distance between the central incisor and canine adjacent to the missing lateral incisor. Periapical radiographs were taken with the parallel technique, which reduces some potential errors inherent in a radiographic study when compared with

American Journal of Orthodontics and Dentofacial Orthopedics Olsen and Kokich 158.e3 Volume 137, Number 2 other radiographic techniques. Because the entire consecutive sample was taken from 1 periodontal practice, we were confident that the measurements could be readily compared between patients. The radiographs were scanned, imported, and analyzed with Scion Image, a public domain Java image-processing program developed at the US National Institutes of Health and available on the Internet at http://www.scioncorp.com/ pages/scion_image_windows.htm. All measurements were made to the nearest 0.01 mm. Corrections for radiographic magnification at different time points and between different types of radiographs were made by comparing the mesiodistal width of a reference tooth (the adjacent canine) measured at the cementoenamel junction (CEJ). The following time points were used: T1, before orthodontic treatment; T2, after orthodontic treatment; and T3, before implant placement. One examiner (T.M.O.) evaluated the space between the central incisor and the canine at each time point. The following measurements were made. 1. Intercoronal distance: the distance between the adjacent central incisor and canine crowns, measured at the CEJ. 2. Interradicular distance: the distance between the adjacent central incisor and canine roots at their nearest proximity. 3. Reference: the mesiodistal width of the adjacent canine measured at the CEJ. The interradicular measurements were made at the point of closest proximity between the adjacent central incisor and canine roots. This measurement was made from the corresponding adjacent lamina dura to minimize any changes from root resorption. To ensure examiner reliability, the primary author (T.M.O.) repeated and recorded complete T2 and T3 measurements for 10 randomly selected patients 1 month after the T1 measurements. Statistical analysis The intercoronal and interradicular distances were measured at T1, T2, and T3 on both the panoramic and periapical radiographs. We compared the intercoronal and interradicular measurements at T2 and T3 using a paired t test. The 95% CI was calculated when assessing the incidence of dental movement significant enough to prevent implant placement. Because some patients were missing both lateral incisors, these teeth could not be considered independent. Generalized estimating equations were used to account for this lack of independence when calculating the 95% CI for overall missing lateral incisors. The sample was divided into 2 groups for further analysis. In the adequate space group, intercoronal and interradicular distances at T3 were judged by the surgeon to be sufficient for placing a dental implant. In the inadequate space group, intercoronal or interradicular distances at T3 were judged by the surgeon to be insufficient for placing a dental implant. Intercoronal and interradicular distance changes in the adequate space vs the inadequate space groups were compared by averaging the measurement changes in all patients between T2 and T3. We compared the measurement changes in each group, as well as differences based on age at T2 and sex, using independent sample t tests. Fisher exact tests were used to assess the association between implant placement success and the method of retention. All analyses were performed with SPSS software (version 16.0, SPSS, Chicago, Ill) with a significance level of 0.05. The examiner s reliability was assessed by computing intraclass correlation coefficients (Pearson s r) for repeated measurements. These measurements were highly repeatable, with coefficients of 0.97 and 0.98 for the intercoronal and interradicular measurements, respectively. Furthermore, the mean errors for intercoronal and interradicular measurements computed with Dahlberg s formula were 0.10 and 0.11 mm, respectively. 8 The standard errors of the mean difference of repeated measurements were 0.04 and 0.05 mm, respectively. RESULTS Many orthodontists use panoramic radiographs to assess root proximity and end-of-treatment results. In part because of reported distortion in panoramic radiographs, many surgeons use periapical radiographs to measure the distance between roots. 9-11 To elucidate potential differences between these 2 types of radiographs, we compared the distances measured on both the periapical and panoramic radiographs that were taken on the same day intercoronal and interradicular distances between the central incisor and the canine, and mesiodistal width of the reference tooth (canine) measured at the CEJ. We then assessed the magnification of these 57 pairs of panoramic and periapical radiographs. The mean ratios of the intercoronal, interradicular, and reference teeth were 1.12, 1.21, and 1.08, respectively (Table I). This variation in magnification between 8% and 21% at different locations on the radiographs shows the distortions in panoramic radiographs. At T3, the surgeon s assessment for fixture placement was based primarily on the space available

158.e4 Olsen and Kokich American Journal of Orthodontics and Dentofacial Orthopedics February 2010 Table I. Magnification: panoramic to periapical measurement ratios Intercoronal Interradicular Reference Mean ratio 1.12 1.21 1.08 SD.11.12.09 Range.85-1.40.92-1.51.9-1.32 Table II. Adequacy of space for implant placement at T3 for the total sample Patients Missing lateral incisors n % n % Adequate space 78 83.0 117 82.4 Inadequate space 16 17.0 25 17.6 Total (n) 94 142 Table III. Adequacy of space for implant placement at T3 for the consecutive sample Patients Missing lateral incisors n % n % Adequate space 71 88.8 107 88.4 Inadequate space 9 11.3 14 11.6 Total (n) 80 121 Table IV. Average interdental changes, T2 to T3 (42 patients, 63 missing lateral incisors) Intercoronal Interradicular Mean 0.09 mm 0.04 mm SD 0.51 mm 0.52 mm 95% CI 0.04-0.22 0.17-0.10 P value 0.17 0.60 between the CEJ and the roots of the adjacent teeth and on the size of the implant. At this assessment, 16 patients (with 25 missing lateral incisors) of the total sample of 94 patients (with 142 missing lateral incisors) had inadequate space between the central incisor and the canine to permit implant placement. These patients composed the inadequate space group (Table II). To establish the incidence of postorthodontic dental movement sufficient to prevent implant placement, we evaluated 80 patients (with 121 missing lateral incisors) who were treated consecutively in 1 periodontal office. Of this sample, 9 patients had inadequate space for an implant at T3. They were missing a total of 14 lateral incisors of a possible 121. That is, 11.3% of the patients (95% CI, 4.3%-18.2%) and 11.6% of the missing lateral incisors (95% CI, 5.9%-21.3%) had enough change in root angulation of the adjacent teeth to prevent implant placement (Table III). Of the total sample, 42 patients (with 63 missing laterals) had periapical radiographs available at T2 and T3. This sample had a mean of 14 months between T2 and T3 (range, 1-58 months). Patients with only a short time between T2 and T3 were included because some had sufficient root movement to inhibit implant placement in only 2 months. Practicing orthodontists will attest that when retainers are not worn, relapse can occur quickly; practitioners should be aware that root movement and clinical crown movement can occur rapidly. It would be wise to consider this when determining the timing of orthodontic treatment and implant placement. To assess dental movement during the retention period, the changes in intercoronal and interradicular distances between the adjacent central incisor and the canine were analyzed. Each measurement was scaled to the overall average magnification (1.02 times), determined by comparing the reference canine measurements at T2 and T3. Although an average magnification does not rule out possible individual magnification error, it levels the field statistically and allows for proper statistical analysis. Overall, the intercoronal distance changed an average of 0.09 mm (95% CI, 0.04-0.22). The interradicular distance changed an average of 0.04 mm (95% CI, 0.17-0.10). Neither change was statistically significant (intercoronal: P 5 0.17; interradicular: P 5 0.60) (Table IV). Positive change indicates an increase in distance, and negative change indicates a decrease in distance. The average interdental changes indicate that, in this sample, the adjacent central incisor and canine crowns or roots did not reapproximate during retention; ie, angulation changes during retention is not a universal phenomenon. We analyzed the adequate space and inadequate space groups to elucidate factors that affected the maintenance of adequate space for implant placement. At T2, the average intercoronal space between the central incisor and the canine in the adequate space group was 6.31 mm (95% CI, 6.17-6.46; range 5.25-7.56). The average interradicular space between these teeth was 5.74 mm (95% CI, 5.56-5.93; range, 4.06-7.12) (Table V). At T3, the average intercoronal space between the central incisor and the canine in the adequate space group was 6.33 mm (95% CI, 6.21-6.45; range, 4.91-7.71). The average interradicular space between these

American Journal of Orthodontics and Dentofacial Orthopedics Olsen and Kokich 158.e5 Volume 137, Number 2 Table V. Interdental space: adequate space vs inadequate space at T2 and T3 (66 patients, 101 missing lateral incisors) T2 T3 Intercoronal Interradicular Intercoronal Interradicular Adequate space 6.31 mm 5.74 mm 6.33 mm* 5.62 mm* Inadequate space 6.23 mm 4.97 mm 5.53 mm* 3.94 mm* P value of difference 0.65 0.012 0.014 0.0003 *Statistically significant, P \0.02. Table VI. Method of orthodontic retention Adequate space Inadequate space Total Patients Lateral incisors Patients Lateral incisors Patients Lateral incisors Hawley 45 66 8 13 53 79 Vacuum formed 7 12 4 5 11 17 Fixed wire 10 17 0 0 10 17 Bonded tooth 4 6 0 0 4 6 Table VII. Adequate space vs inadequate space groups based on method of retention (78 patients, 119 missing lateral incisors) Patients Lateral incisors Adequate space Inadequate space Adequate space Inadequate space Removable 52 12 78* 18* Fixed 14 0 23* 0* Fisher s exact test 0.11 0.022 *Statistically significant, P \0.03. teeth was 5.62 mm (95% CI, 5.46-5.77; range, 3.73-6.96) (Table V). At T3, the average intercoronal space between the central incisor and canine in the inadequate space group was 5.53 mm (95% CI, 5.04-6.01; range, 4.62-6.51). The average interradicular space between the roots of these teeth was 3.94 mm (95% CI, 3.42-4.46; range, 2.88-4.66). The mean difference of the intercoronal and interradicular spaces in the adequate space group vs the inadequate space group at T3 was statistically significant (intercoronal: P 5 0.014; interradicular: P 5 0.0003) (Table V). At T2, the average intercoronal space in the inadequate space group was 6.23 mm (95% CI, 5.92-6.53; range, 5.93-6.45). The average interradicular space was 4.97 mm (95% CI, 4.69-5.26; range, 4.75-5.25) (Table V). Two methods of orthodontic retention for this sample were used: removable and fixed. The removable group included Hawley and vacuum-formed retainers. The fixed group included a bonded lingual wire between the central incisors or a lateral incisor pontic bonded to the adjacent teeth (Table VI). In the removable group, 12 of 64 patients (18 of 96 missing lateral incisors) were judged to have inadequate space at implant placement (P 5 0.11). Alternatively, in the fixed group, none of the 14 patients (with 23 missing lateral incisors) were judged to have inadequate space at implant placement (P 5 0.022) (Table VII). Because of lack of power, statistics were not performed for the retention methods. The difference in age at T2 was compared in the adequate space vs inadequate space groups. The average age of the adequate space group was 21.2 years (n 5 78; median, 17.6 years; range, 13.2-59.3 years; 95% CI, 20.7-21.7). The average age of the inadequate space group was 16.0 years (n 5 16; median, 15.7 years; range, 12.8-20.2 years; 95% CI, 15.4-16.6). This difference was statistically significant, P \0.0001 (Table VIII). In the total sample of 94 patients, there was no statistically significant difference in the occurrence of inadequate space at T3 in the sexes (Table IX).

158.e6 Olsen and Kokich American Journal of Orthodontics and Dentofacial Orthopedics February 2010 Table VIII. Average age at T2 (94 patients) DISCUSSION Adequate space Inadequate space Average (y) 21.2 16.0 Range (y) 13.2-59.3 12.8-20.2 95% CI 20.7-21.7 15.4-16.6 P value of difference \0.0001 Table IX. Adequate space vs inadequate space groups based on sex (94 patients, 142 missing lateral incisors) Patients Lateral incisors Male Female Male Female Adequate space 14 64 20 97 Inadequate space 2 14 4 21 Inadequate space 13% 18% 17% 18% P value 0.60 0.89 Although orthodontists often use panoramic radiographs to assess pretreatment dentitions and posttreatment results, considerable distortion in panoramic radiographs has been reported, especially in the canine and premolar regions. 9-11 For this reason, surgeons typically use periapical radiographs to assess intercoronal and interradicular spaces for implant placement. To emphasize the potential distortion inherent in panoramic radiographs when assessing for implant placement, we compared the distances measured on panoramic and periapical radiographs at the end of orthodontic treatment and found significant magnification variations averaging from 8% to 21% at different locations on the panoramic radiographs. This tendency for enlargement and alteration in magnification on panoramic radiographs emphasizes the importance of using periapical radiographs to evaluate the adequacy of space for implant placement. Orthodontists in private practice who rely on panoramic radiographs after orthodontic treatment to determine the space for implants will consistently overestimate the available space because of magnification. Therefore, we recommend that orthodontists and surgeons use periapical radiographs to assess the space between the central incisor and the canine before removing the orthodontic appliances. Whereas the amount of space necessary for missing lateral incisor restorations is ultimately determined by esthetics, the size of available implant fixtures must also be considered. To provide implant space guidelines for orthodontic practitioners specifically with regard to minimizing the risk of root angulation changes that can inhibit implant placement, we analyzed the adequate space group at T2 and T3. At T2, the average intercoronal space between the adjacent central incisor and the canine was 6.3 mm; the average interradicular space was 5.7 mm. At T3, these measurements remained relatively constant (intercoronal, 6.3 mm; interradicular, 5.6 mm). We also analyzed the intercoronal and interradicular spaces in the inadequate space group at T3. Although the average intercoronal space was sufficient (5.53 mm), the average interradicular space was considered inadequate for implant placement (3.94 mm). So, we could divide the postorthodontic results into 3 general groups: adequate space.5.5 mm; marginal space.4.0 mm but \5.5 mm; and inadequate space \4.0 mm. With today s implant technology, assuming a 3.25-mm lateral incisor implant, most surgeons would probably be comfortable placing a maxillary lateral incisor implant in a patient with an interradicular space greater than 5.5 mm, leaving at least 1 mm of alveolar bone on either side of the implant. If the interradicular space were less than 4.0 mm, many surgeons would suggest orthodontic retreatment. Therefore, speaking specifically to minimizing the risk of root movement during retention that would impede implant placement, we recommend leaving extra space for the surgeon ie, a minimum of 6.3 mm between the crowns and 5.7 mm between the roots. This correlates well with the space traditionally suggested for implant placement of 1 mm on either side of the implant. Keeping future implant placement in mind, we suggest that orthodontists adhere to these guidelines to reduce the risk of future orthodontic retreatment. A few patients in this sample had inadequate space for implant placement and required orthodontic retreatment to move the central incisor and the canine apart. So we hypothesized that all patients might experience some approximation between the crowns and roots of the canine and the central incisor adjacent to the edentulous space. We measured and compared the intercoronal and interradicular distances between the central incisors and the canines at T2 to those measured at T3. There was no statistically significant difference between the spaces at T2 and T3. Therefore, whereas root convergence occurred in a few patients, generally, the roots remained the same distance apart as measured at the end of orthodontic treatment. Although approximation of adjacent teeth was not observed consistently, some patients had postorthodontic tooth movement that prevented implant placement. Perhaps this tendency would be prevented if fixed retainers were used after orthodontic treatment. We compared the adequate and inadequate space groups by the method of postorthodontic retention. When fixed retainers were used, implant space remained adequate,

American Journal of Orthodontics and Dentofacial Orthopedics Olsen and Kokich 158.e7 Volume 137, Number 2 and placement was always successful. However, removable retainers did not consistently maintain the space. Since younger orthodontic patients often require a longer retention period to permit completion of facial growth, we recommend fixed retention with a bonded wire or resin-bonded bridge to maintain adjacent tooth and root positions. What mechanism could cause approximation of the roots of the central incisor and the canine after orthodontic treatment? If a patient were using a removable retainer after orthodontic treatment, the pontic would maintain the space between the central incisor and the canine crowns. It is possible that, when the retainer is out of the mouth, the adjacent central incisor and the canine could move toward one another (ie, relapse). When the patient replaces the retainer, the pontic would exert a force between the crowns of the central incisor and the canine, occlusal to the center of resistance of each of these teeth. Therefore, although the crowns are pushed back apart, the roots could approximate slightly. Repeated occurrence of this phenomenon with time could account for the changes in angulation of the roots in some patients in the inadequate space group. Another possible explanation for changes in root position could be continued vertical growth. Patients with missing maxillary lateral incisors often receive orthodontic treatment during early adolescence. Since implant placement must be delayed until the cessation of vertical facial growth, it is possible that vertical growth of the mandible and compensatory eruption of the teeth could alter the position of the tooth roots. 1-3 To test this hypothesis, we compared the amount of interdental change between the sexes. Since boys have longer periods of facial growth, we expected to observe more approximation of tooth roots in the male subjects compared with the female subjects. However, we found no sex differences in the amount of space across the roots of the teeth at T3. We also compared the average age at T2 for patients with adequate space compared with those with inadequate space for the implant. Those who ultimately had inadequate space finished orthodontic treatment at an average age of 16, whereas those who maintained adequate space finished orthodontic treatment at an average age of 21. This age discrepancy points to a possible role of vertical facial growth in the observed root approximation. Together, these findings suggest that continued vertical growth and eruption of the central incisor and the canine might cause approximation of the roots of these teeth with time, but further elucidation would require additional research. This study had some limitations. First, a retrospective study by nature has limitations such as selection bias and the inability to oversee record taking. Next, although the radiographic technique was controlled for as much as possible (especially in the consecutive sample), radiographs are not a perfect representation of reality. Also, radiographic measurements were not scaled to the models or the size of the actual teeth to account for individual radiograph magnification. In future studies, we suggest including measurements of the reference teeth (models) to scale radiographs to actual size. Although a prospective study on this topic would be ideal, this is a difficult sample to collect because this is a relatively rare condition that would require consecutive records over many years. Because there is no previous research on this subject for comparison, this study will help to offer practitioners guidelines for treatment goals and act as a springboard for future research, ideally a prospective study. CONCLUSIONS Based on our sample and methods, the following conclusions can be made. 1. Although root approximation between the adjacent central incisor and the canine during retention did not occur consistently, 11% of the patients experienced relapse significant enough to prevent implant placement. 2. To ensure sufficient space for implant placement, we recommend at least 6.3 mm of intercoronal space and 5.7 mm of interradicular space between the adjacent central incisor and the canine. 3. A bonded wire or resin-bonded bridge helps to reduce any root approximation during retention. 4. Panoramic radiographs overestimate the intercoronal and interradicular spaces between the central incisor and the canine 5. We recommend taking a periapical radiograph near the end of orthodontic treatment to ensure sufficient space for future implant placement. REFERENCES 1. Thilander B, Persson M, Adolfsson U. Roentgen-cephalometric standards for a Swedish population. A longitudinal study between the ages of 5 and 31 years. Eur J Orthod 2005;27:370-89. 2. Thilander B, Odman J, Grondahl K, Lekholm U. Aspects on osseointegrated implants inserted in growing jaws. A biometric and radiographic study in the young pig. Eur J Orthod 1992;14:99-109. 3. Fudalej P, Kokich VG, Leroux B. Determining the cessation of vertical growth of the craniofacial structures to facilitate placement of single-tooth implants. Am J Orthod Dentofacial Orthop 2007;131(Suppl):S59-67. 4. Thilander B, Odman J, Grondahl K, Friberg B. Osseointegrated implants in adolescents. An alternative in replacing missing teeth? Eur J Orthod 1994;16:84-95. 5. Spear F, Mathews D, Kokich V. Interdisciplinary management of single-tooth implants. Semin Orthod 1997;3:45-72.

158.e8 Olsen and Kokich American Journal of Orthodontics and Dentofacial Orthopedics February 2010 6. Thilander B, Odman J, Jemt T. Single implants in the upper incisor region and their relationship to the adjacent teeth. An 8 year follow-up study. Clin Oral Implants Res 1999;10:346-55. 7. Dickinson G. Space for missing maxillary lateral incisors orthodontic perceptions. Ann R Australas Coll Dent Surg 2000;15: 127-31. 8. Dahlberg G. Statistical methods for medical and biological students. New York: Interscience Publications; 1940. 9. Samawi SS, Burke PH. Angular distortion in the orthopantomogram. Br J Orthod 1984;11:100-7. 10. Peck JL, Sameshima GT, Miller A, Worth P, Hatcher DC. Mesiodistal root angulation using panoramic and cone beam CT. Angle Orthod 2007;77:206-13. 11. Owens AM, Johal A. Near-end of treatment panoramic radiograph in the assessment of mesiodistal root angulation. Angle Orthod 2008;78:475-81.