Root resorption following periodontally accelerated osteogenic orthodontics

INTRODUCTION

Apical root resorption is perceived as an adverse side effect of orthodontic treatment. Ketcham^[1] first described root resorption in 1927, and the topic has been the focus of substantial orthodontic research attention ever since. A question still debated is whether the particular method of orthodontic treatment influences the amount of root shortening observed. Brezniak and Wasserstein^[2,3] presented a comprehensive review of the literature on root resorption and considered several biological, mechanical, and clinical factors. Identified as the most prevalent factors in root resorption were treatment time, magnitude of force delivered, and distance of tooth movement. The authors concluded that the amount of resorption might not be anticipated with certainty based on any of the reported etiologic factors. The present review of the literature will focus on two factors: Treatment time and bone density.

Several investigations have studied the relationship between bone density and apical root resorption, but there is no consensus. Some authors have reported greater resorption of tooth roots moved orthodontically through bone of high density.^[4,5] Goldie and King^[6] observed decreased levels of root surface resorption and enhanced tooth movement in lactating rats fed with a diet deficient in calcium. These authors suggested that increased bone resorption and decreased bone density facilitate remodeling of alveolar bone with minimal effects on the roots. Engström et al.^[7] also studied rats maintained in dietary hypocalcemia and found an increase in root resorption; it was suggested that the increase in root resorption was related to an enhanced alveolar bone turnover. Wainwright^[8] found bone density to be a factor unrelated to root resorption.

Studies regarding the duration of orthodontic treatment and root resorption have yielded contradictory results. Rudolph^[9] showed that the incidence of root resorption increases with each year of treatment. DeShields,^[10] Stenvik and Mjör,^[11] and McFadden et al.^[12] revealed that prolonged treatment time was statistically and significantly correlated to root resorption. In a larger study by Linge and Linge,^[13] treatment time and therapy with a rectangular arch wire and Class II elastics were found to contribute significantly to root resorption. Results reported by Levander and Malmgren^[14] were consistent with Goldson and Henrikson;^[15] both studies found that teeth with irregular root contour or minor root resorption after the initial 6 to 9 months indicated a risk for severe root resorption. Baumrind et al.^[16] concluded that increased length in treatment time in orthodontically treated adults was indirectly associated with the increased root resorption; Baumrind reasoned that the longer patients were in treatment, the further the teeth were displaced. Taithongchai et al.^[17] found a weak but highly significant correlation between treatment time and the amount of apical root resorption. According to this study, treatment time was the best estimator of apical root resorption even though high- and low-risk patients could not be identified. Sameshima and Sinclair^[18,19] found a significant correlation between the duration of treatment and the amount of apical root resorption for maxillary central incisor tooth group. In sharp contrast are the results reported by Phillips,^[20] VonderAhe,^[21] and Mirabella and Artun,^[22] who concluded that root resorption does not increase as a function of treatment time.

Corticotomy (Cort) facilitated orthodontics has been presented as a therapy including rapid tooth movement and significantly reduced treatment time. Kole^[23] and Suya^[24] described Cort as a process of moving blocks of bone rather that moving only teeth themselves. Both authors reported anecdotal findings of little apical root resorption, no loss of tooth vitality, and no pocket formation. These authors surmised that the teeth move faster because the resistance of the cortical bone is reduced by the surgical procedure.

Liou and Huang^[25] reported minimal root resorption in a periodontal ligament technique of rapid canine retraction with a distraction device capable of delivering orthopedic force levels. The canine was distracted immediately following extraction of the first premolars and surgical alteration of the socket adjacent to the canine. Liou averaged 6.5 mm of cuspid retraction in 3.5 weeks and contended that the periodontal ligament re-organized with no adverse sequelae or negative impact on the periodontium in long term.

Frost^[26] introduced the term regional acceleratory phenomenon (RAP) as an account of the normal, local spatiotemporal soft- and hard-tissue healing events subsequent to a noxious stimulus. Tissue turnover is increased and the intensity of its response depends directly on the magnitude and proximity of the stimulus. RAP healing, according to Frost, involved accelerated bone turnover and decreased bone densities (osteopenia). Healing in response to a stimulus occurs 2–10 times faster than it would in normal regeneration processes. The RAP begins within a few days of the injury and typically peaks at 1–2 months, but it can last from 6 to 24 months. Frost^[27] found that when the RAP resolves, the transient osteopenia disappears.

Wilcko et al.^[28] introduced a technique called accelerated osteogenic orthodontics (AOO) or periodontally AOO. Immediately following the placement of active, fixed orthodontic appliances for comprehensive therapy, selective labial and lingual decortication of the alveolar bone housing the teeth is performed. An alloplastic bone graft is applied directly on the bleeding labial and lingual alveolar bone, and the soft tissue flap is closed. Two weeks after the surgery and every 2 weeks thereafter, the orthodontic appliance is reactivated. Wilcko protocol results in decreased treatment time, no loss of tooth vitality, no significant apical root resorption, and no periodontal pocketing. Computed tomography scans suggested that the rapid tooth movement was due to de-mineralization of the alveolar bone surrounding the teeth immediately adjacent to the Cort. This finding strongly suggested that rapid tooth movement was due to a process of alveolar de-mineralization and re-mineralization.^[29]

Compared to orthodontic therapy without Cort, treatment times were found to be 3–4 times more rapid.^[30] Moreover, a significant increase in alveolar bone volume was demonstrated by combining alveolar surgical decortication and alveolar augmentation procedures.^[31,32]

The aim of this study was to compare root resorption of the maxillary central incisor following nonextraction orthodontic therapy, with and without Cort surgery. The null hypotheses tested were no difference in root length immediately following active orthodontic treatment, with and without alveolar decortication therapy.

MATERIALS AND METHODS

Periapical radiographic technique

Periapical radiographs were examined for the pretreatment (T1) and posttreatment (T2) study periods for all subjects. The study comprised 54 subjects, which included 107 permanent right and left maxillary central incisors. Each periapical was mounted in a 2 × 2 slides holder and projected onto a wall using a Kodak carousel projector to enlarge the image exactly 8 times the actual size. The projected image of the maxillary central incisors was then traced on a piece of 8.5 × 14 inch white paper with a 2HB lead pencil and appropriately labeled.

Apical root resorption was evaluated utilizing the total tooth length technique described by Mirabella (1995), Lee (1999), and Sameshima (2001a, 2001b). Tooth length was measured from the incisal edge to the root apex along the long axis of the tooth. The amount of root resorption was calculated in millimeters based upon the difference in overall tooth length from pretreatment to posttreatment. A digital vernier caliper (Mitutoyo Mfg. Co., Ltd., Japan) was used to record the tooth length to the nearest 10^th of a millimeter [Figure 1].

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Figure 1

Calculation of apical root resorption was based on the following computation: TLF = TL1–TL2; where, TLF = Tooth length final, TL1 = Pretreatment tooth length, and TL2 = Posttreatment tooth length

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Cephalometric technique

Lateral cephalometric radiographs were examined for the pretreatment (T1) and posttreatment (T2) study periods for all subjects. Each lateral cephalogram was traced on frosted acetate by the investigator, and the most anteriorly positioned central incisor was used in the analysis. The following five cephalometric measurements were made for the purpose of relating the amount of root resorption to the amount of linear and angular change in the axial inclination of the maxillary central incisors: SNA, U1-Sn, U1-NA, U1-NA, and U1-PP [Figure 2].

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Figure 2

Cephalometric angular and linear measurements used in the study. A: SNA (°), B: U1-SN (°), C: U1-NA (°), D: U1-NA (mm), E: U1-PP (°)

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RESULTS

DISCUSSION

This study was conducted to compare root resorption of the maxillary central incisors following nonextraction orthodontic therapy with and without alveolar Cort surgery. In the present study, the permanent maxillary central incisor was selected because this tooth group is one of the most commonly resorbed groups during orthodontic treatment.^[20,33,34] Moreover, the maxillary central incisor typically has formed roots completely by the start of fixed, orthodontic treatment.

The amount of root resorption was measured by subtracting each tooth length measurement at T2 from the corresponding measurement at T1. Mirabella and Artun^[22] suggested this technique for calculating the amount of root resorption and consider it more valid when compared with the technique proposed by Linge and Linge,^[13] in which T2 is adjusted by correcting for any change in the crown length from T1 to T2. Mirabella pointed out that with the Linge technique, the estimate for apical root resorption is reduced and a greater number of teeth showed root elongation. They suggested that a crown reduction will cause an overestimation of the root resorption when using their methods, but this overestimation will be considerably smaller than the corresponding amount of underestimation calculated with the Linge method. Results of the present study were similar to the previous investigations regarding random root elongation.^{[17-19,22,35,36]} Because of overall errors in collecting data and methodology (e.g., tracing error, magnification, etc.,) a few maxillary central incisors demonstrated some elongation from T1 to T2 while most teeth showed resorption.

Because most of the radiographic records were obtained from the same radiographic facility in each group and were made using that same paralleling technique, errors as a result of variations in radiographic projection and enlargement are likely to be small and randomly distributed in the samples.

Mirabella and Artun^[22] also suggested that the incisal edge and apex could be identified with a higher degree of accuracy than the cemento-enamel junction. These findings are in agreement with the results found by Sameshima and Sinclair.^[18,19]

Results in relation to cephalometric study variables indicated that SNA was significantly larger (84.0° vs. 79.4°,P = 0.001) in the Conv sample representing a more prognathic position. Effects of therapy on study variable SNA was significant in the two nonextraction groups. SNA significantly decreased from 83.9° to 82.9° in Conv whereas SNA significantly increased in Cort from 79.4° to 80.0°. There was no significant difference in posttreatment SNA between the two groups (80.2° vs. 82.9°,P > 0.05); the increase in Cort SNA was logically due to the alveolar augmentation grafting.

CONCLUSIONS

This study was conducted to compare root resorption of the maxillary central incisors following nonextraction orthodontic therapy with and without alveolar Cort surgery. The most important results of this investigation were as follows:

• Root resorption was statistically greater (1.1 mm,P = 0.03) in Conv than in Cort

• Statistically significant (P ≤ 0.007) root resorption was demonstrated in both study groups as a consequence of therapy; however, the amount of root resorption was not clinically significant, i.e., 0.3 and 0.7 mm

• Point A, represented by the cephalometric measurement SNA, decreased significantly in Conv, but increased significantly in Cort because A-point was supplemented with alveolar graft augmentation

• Cort treatment time was 2.7 times more rapid than Conv treatment time

• Based on the conditions of this study, it may be concluded that Cort-facilitated nonextraction orthodontic therapy results in less root resorption and enhanced alveolar support within a significantly reduced clinical service delivery time frame. Rapid orthodontic treatment and reduced apical root resorption are probably due to the transient osteopenia induced by the Cort surgery and inspired by RAP.