Longitudinal dento-skeletal changes in UCLP patients following maxillary distraction osteogenesis using RED system

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1 J Med Dent Sci 2004; 51: Original Article Longitudinal dento-skeletal changes in UCLP patients following maxillary distraction osteogenesis using RED system Eduardo Yugo Suzuki, Nobuyoshi Motohashi and Kimie Ohyama Maxillofacial Orthognathics, Department of Maxillofacial Reconstruction and Function, Division of Maxillofacial/ Neck Reconstruction, Graduate School, Tokyo Medical and Dental University, Tokyo, Japan Longitudinal dento-skeletal changes in unilateral cleft lip and palate (UCLP) patients following maxillary distraction osteogenesis using the rigid external distraction device (RED) were analyzed. Twelve Japanese non-syndromic UCLP patients who underwent maxillary distraction at the mean age of 16.4 years were used as subjects. Serial sets of lateral cephalograms, taken at 4 stages: 1) before osteotomy, 2) immediately after distraction, 3) 6 months and 4) 12 months post-osteotomy, were analyzed. Statistical analyses, including a paired t test, Pearson correlation analysis and stepwise linear regression analysis, were performed to distill characteristic dento-skeletal changes. In accordance with maxillary advancement, significant amounts of up-forward movement of the nasal bone, mandibular rotation and maxillary dental changes were observed. Maxillary dental changes were significantly related to the amount of mandibular rotation and force system of maxillary traction. Significant dento-skeletal relapse was found to occur during the 0-to-6-month follow-up period, but not in the 6-to-12-month follow-up period. Maxillary relapse was significantly related to the amount of maxillary advancement and severity of pre-surgical maxillary hypoplasia, Corresponding Author: Eduardo Yugo Suzuki Maxillofacial Orthognathics, Department of Maxillofacial Reconstruction and Function, Division of Maxillofacial/ Neck Reconstruction, Graduate School, Tokyo Medical and Dental University, 5-45 Yushima 1-Chome, Bunkyo-ku, Tokyo, , Japan Phone: , Fax: yugotmdu@hotmail.com Received November 6; Accepted December 19, 2003 while mandibular relapse was significantly related to maxillary dento-skeletal relapse. Successful clinical application of this procedure therefore requires consideration of both the surrounding dento-skeletal changes and the traction force system. Key words: maxillary distraction osteogenesis, cleft lip and palate, RED system, cephalometric analysis, dento-skeletal changes Introduction Distraction osteogenesis was first described by Codivilla (1905) 1. The technique has been popularized in the field of orthopedic surgery by Ilizarov (1989) 2. In the field of cranio-facial surgery, McCarthy et al. (1992) 3 first applied this procedure to the lengthening of the mandible in a clinical situation. In 1997, Polley and Figueroa 4 developed the rigid external distraction (RED) device for maxillary advancement. The device is fixed to the cranium in order to provide rigid anchorage, and is connected to the maxillary bone via an intraoral appliance. The main advantage this device had, in comparison with other techniques, was the more predictable vertical and horizontal control which gave over the distraction process, consequently facilitating the management of the distracted maxillary bone 5,6. Since then, maxillary distraction osteogenesis has drastically changed the approach taken to the treatment of cleft patients with severe maxillary hypoplasia, and numerous clinical case studies have been reported 7-9.

2 28 E. Y. SUZUKI, N. MOTOHASHI and K. OHYAMA J Med Dent Sci These studies mostly describe maxillary advancement based on the saggital dimension. However, in these studies, retrospective short-term accounts of the procedure s effects on small numbers of heterogeneous patients, from mixed ethnic groups and with variable cleft types, has been the rule 10. The purpose of this study was, therefore, to examine longitudinal dento-skeletal changes in Japanese unilateral cleft lip and palate (UCLP) patients, following maxillary distraction osteogenesis using the RED device. Materials and Methods Twelve non-syndromic Japanese UCLP patients (8 females and 4 males) who underwent maxillary distraction osteogenesis at the Dental Hospital of Tokyo Medical and Dental University were used as subjects. Initial records showed that these subjects had severe maxillary hypoplasia, associated with lingual tipping of the maxillary anterior incisors and remarkable negative anterior overjet. Maxillary advancement (by a mean of 11.8 mm) was performed at the mean age of 16.1 years (subjects ranged from 9.5 to 26.1 years of age), using a RED device (Martin L.P., Jacksonville, FL, USA) in combination with an intraoral splint, fixed onto the maxillary teeth to provide anchorage (Figure 1). This study was designed in accordance with the declaration of Helisink and approved by institutional ethical committee. Fabrication of the intraoral splint and the distraction protocol used with the present subjects both followed the methodology proposed by Figueroa and Polley (1999) 6. After a complete Le Fort I osteotomy followed by maxillary down-fracture, the cranial portion of the Fig. 1. Patient undergoing rigid external distraction (Left), customized intraoral splint (Right) RED device was put in place immediately after surgery using scalp screws. A latency period of 3 to 5 days following the osteotomy was observed before distraction. Distraction was performed at the rate of 1 mm per day. The duration of the activation period was determined clinically and cephalometrically, based on the improvement of the mid-face retrusion and anterior dental cross bite. After the activation was finished, the distraction device was kept in place for 2 to 3 weeks, in order to ensure rigid retention. Subsequently, a facial mask with elastic traction (200 to 300 grams) was used at night for an additional 6 weeks. Cephalometric analysis Dento-skeletal changes were analyzed using serial sets of lateral cephalograms taken in centric occlusion at the following stages: shortly before osteotomy (T1; mean age of 16 years 5 months), immediately after distraction (T2; mean age of 16 years 7 months), 6 months post-osteotomy (T3; mean age of 17 years 0 months) and 12 months post-osteotomy (T4; mean age of 17 years 6 months). Eighteen dento-skeletal anatomical landmarks were digitized, using a digitizer (KD3200: GRAPHTEC), to enable measurements to be made (Figure 2A). A reference system of horizontal and vertical planes was employed; the Frankfort horizontal (FH) plane was used as the x-axis; a line drawn perpendicular to this plane through the sella turcica was used as the y-axis. The subtraction of the x and y values for each landmark at each interval was computed to estimate the horizontal and vertical displacement of the landmarks. To evaluate the direction of displacement in the horizontal dimension, positive and negative values were assigned to indicate forward and backward displacement, respectively. Similarly, positive and negative values were assigned to indicate downward and upward displacement, respectively, in the vertical dimension. Furthermore, the following angular and linear measurements were made in order to evaluate the amount of maxillary dental change and the traction force system used (Fig. 2B): 1) inclination of the maxillary central incisor relative to the palatal plane (U1/PP deg.), 2) vertical distance from the maxillary central incisor edge to the palatal plane (U1/PP mm), 3) inclination of the maxillary first molar relative to the palatal plane (U6/PP deg.), 4) vertical distance of the medial buccal crown top of the maxillary first molar from the palatal plane (U6/PP mm); 5) traction angle relative to the FH plane (a); 6) hook length of the intraoral splint

3 DENTO-SKELETAL CHANGES IN UCLP FOLLOWING DOG 29 period. Fig. 2A. Dento-skeletal cephalometric landmarks and reference planes. Abbreviations: 1. Sella (S), 2. Nasion (N), 3.Porion (Po), 4. Orbitale (Or), 5. Rhinion (Rhi), 6. Anterior nasal spine (ANS), 7. Point A (A), 8. Upper incisal edge (U1), 9. Apex of upper incisor (U1r), 10. Midpoint of upper first molar crown (U6), 11. Midpoint of upper first molar apex (U6c), 12. Posterior nasal spine (PNS), 13. Lower incisal edge (L1), 14. Lower incisor apex (L1r), 15. Point B (B), 16. Pogonion (Pog), 17. Menton (Me), 18. Gonion (Go) Fig. 2B. Measurements for dental change and traction force system. Inclination of the maxillary central incisor relative to the palatal plane (U1/PP deg.), Vertical destance of the maxillary central incisor edge from the palatal plane (U1/PP mm), Inclination of the maxillary first molar relative to the palatal plane (U6/PP deg.), Vertical distance of the medial buccal crown top of maxillary first molar from the palatal plane (U6/PP mm), Traction angle relative to FH plane (a) and Hook length of the intraoral splint (h). (h). The error associated with the method was computed using all 48 lateral cephalograms, in order to examine measurement reliability. Each cephalogram was traced and digitized twice, with a 3-week interval between the two repetitions. Analysis of the mean differences between duplicate measurements of the variables, using a paired t test, showed no significant systematic errors (p 0.05). Statistical analysis 1. Characteristic dento-skeletal changes A paired t test was used to assess the significance of the amount of two-dimensional displacement demonstrated by all dento-skeletal landmarks during the following 3 periods: 1) the distraction period (T1 vs. T2); 2) the short-term follow-up period (T2 vs. T3); and 3) the long-term follow-up period (T3 vs. T4). The individual variation of the representative skeletal landmarks, including the nasal bone (Rhi), the maxilla (point A) and the mandible (Pog), as well as of the angular and linear dental measurements, was also examined in each 2. Relationship between dento-skeletal changes in the maxilla and the mandible The relationship between dento-skeletal changes in the maxilla and in the mandible was examined after both the distraction and the short-term follow-up periods. First, stepwise linear regression analysis was performed, in order to identify significant maxillary changes which could be used to describe mandibular changes. The analysis used dento-skeletal maxillary variables (point A and U1) as explanatory variables, and mandibular variables (Pog and L1) as response variables (F value is more than 5.0). Subsequently, Pearson correlation coefficients were computed between a significant pair of dento-skeletal variables of the maxilla and mandible. 3. Effect of the traction force system on dentoskeletal change The effects that the traction force system had, in terms of the dento-skeletal changes arising from maxillary advancement, were also examined. Pearson correlation coefficients were computed for the relationships between the traction force system (including traction angle and the external hook length of the intraoral splint) and the dento-skeletal changes observed in both the maxilla and the mandible during the distraction period. 4. Factors affecting post-surgical maxillary stability In order to identify factors that could affect post-surgical maxillary stability, Pearson correlation coefficients were computed for relationships between maxillary changes in the short-term follow-up period and factors which could, potentially, have an influence (such as the pre-surgical maxillary hypoplasia evaluated using Coben 11 analysis, the amount of surgical maxillary movement and the age of the subject). The statistical analyses were performed using the software Stat View 4.5 (Abacus Concepts) on a personal computer system. Results 1. Characteristic dento-skeletal changes The absolute mean values calculated for the horizontal and vertical changes observed in each landmark in each period are shown in Table 1. Significant twodimensional displacement of all dento-skeletal land-

4 30 E. Y. SUZUKI, N. MOTOHASHI and K. OHYAMA J Med Dent Sci Table 1. Two-dimensional displacement of dento-skeletal landmarks during distraction, short-term follow-up and long-term follow-up periods. marks was observed in the distraction and short-term follow-up periods, but displacement was not significant in the long-term follow-up period (Table 1). Comparisons made by superimposing cephalograms demonstrated characteristic displacement of each skeletal landmark, such as Rhi, Point A and Pog, in both the distraction and short-term follow-up periods (Fig. 3). In the distraction period, Rhi moved to up-forward in all subjects. Point A moved to forward in all subjects, with upward movement being observed in 6 of the subjects and downward movement in the other 6. Pog moved to down-backward in 8 subjects and up-forward in 4 subjects. In the short-term follow-up period, a significant relapse was observed to occur in each skeletal landmark. Rhi moved to down-backward in 8 subjects, and to down-forward in 4 subjects. Point A moved to backward, with upward movement in 5 of the subjects and downward movement in the other 7. Pog moved to upforward in 9 subjects and down-backward in 3 subjects. Significant dental changes occurring in the maxilla in the distraction and short-term follow-up periods are summarized in Table 2. In the distraction period, the maxillary incisor showed lingual inclination in 8 subjects and labial inclination in 4 subjects with significant extrusion. The maxillary molar showed significant distal inclination, with intrusion in 6 subjects and extrusion in 6 subjects. In the short-term follow-up period, significant dental relapse was found. The maxillary incisor showed lingual inclination in 3 subjects and labial inclination in 9 subjects with a significant intrusion. The maxillary molar showed significant mesial inclination, with intrusion in 9 subjects and extrusion in 3 subjects. Fig. 3. Individual variations of skeletal landmarks during distraction period (straight line) and short-term follow-up period (dotted line). 2. Relationship between dento-skeletal changes in the maxilla and the mandible (Table 3) Stepwise linear regression analysis resulted in the selection of only one variable vertical change of the maxillary incisor (U1y) as a valid parameter for explaining vertical and horizontal dento-skeletal changes in the mandible in the distraction period (Table 3). U1y was significantly correlated with each of the following: L1x, L1y, Pogx and Pogy. With regard to the short-term follow-up period, both vertical and horizontal changes of the maxillary incisor (U1y and U1x) were selected as valid parameters for explaining vertical and horizontal dento-skeletal changes in the mandible (Table 3). U1y was significantly correlated with L1y, Pogx and Pogy, while U1x was significantly correlated with L1x and Pogx. 3. Effect of traction force system on dento-skeletal change (Table 4) The length of the external hook was significantly correlated with maxillary dental changes (U1/PP deg. and U6/PP mm; Table 4). Traction angle was significantly correlated not only with maxillary dental changes (U1/PP mm and U6/PP deg.), but also with dentoskeletal changes of the maxilla and mandible (U1y, L1x, L1y, Bx, By, Pogx, Pogy, Mex, Mey). 4. Factors affecting post-surgical maxillary stability Significant pairs of two-dimensional maxillary displacement in the short-term follow-up period and fac-

5 DENTO-SKELETAL CHANGES IN UCLP FOLLOWING DOG 31 Table 2. Change of dental measurements during distraction and short-term follow-up periods Table 4. Coefficient correlations between dento-skeletal changes and traction force system Table 3. Stepwise linear regression analysis and significant corrilation coefficients between dento-skeletal variables of the maxilla and mandible during distraction and short-term follow-up periods Table 5. Factors affecting post-surgical maxillary stability tors affecting maxillary stability are summarized in Table 5. The displacement of Ay which occurred in the short-term follow-up period (maxillary vertical relapse) was significantly correlated with the displacement of Ay in the distraction period (amount of surgical maxillary vertical movement). On the other hand, the displacement of Ax which occurred in the short-term follow-up period (maxillary horizontal relapse) was significantly correlated with the severity of the pre-surgical maxillary hypoplasia (Ptm-A and ANS-1). No significant correlation was found with the age of subjects. Discussion Characteristic dento-skeletal changes Since Polley and Figueroa 4 developed the RED system for maxillary advancement, numerous clinical case studies have been reported. However, the number of quantitative statistical studies is limited, and the dento-skeletal changes associated with maxillary advancement have therefore remained unknown. The present study revealed characteristic dento-skeletal changes, as well as stability, in the nasal bone, maxilla and mandible in the distraction and follow-up periods. During the distraction period, a significant two-dimensional dento-skeletal change was observed. During the short-term follow-up period (0-6 months after surgery), however, a significant dento-skeletal relapse was found to occur, though no significant change occurred during the long-term follow-up period (6-12 months after surgery), suggesting dento-skeletal stability occurs 6 months after surgery. Moreover, different dento-skeletal changes occurred in different facial components during the distraction period and the first 6-month follow-up period. In the case of the nasal bone, significant up-forward movement of the nasal tip was observed in the distraction period. This was followed by a significant downbackward relapse during the short-term follow-up period. Similar changes in the nasal bone have been reported following maxillary advancement involving Le Fort I osteotomy 12, but post-surgical stability has not been reported. Neither changes in, nor the stability of, the nasal bone following maxillary distraction osteogenesis have been analyzed quantitatively. In the maxilla, a large amount of horizontal advancement, together with some upward and downward movement, was achieved during the distraction period; however, a significant relapse was observed in both the vertical and horizontal dimensions during the

6 32 E. Y. SUZUKI, N. MOTOHASHI and K. OHYAMA J Med Dent Sci first 6-month follow-up period. The mean relapse ratio for the maxilla was 22.3% in the horizontal dimension and 53.7% in the vertical dimension. It has been suggested that relapse of a maxilla advanced by distraction osteogenesis is minimal 4-9, despite a lack of quantitative analysis. However, Ko et al. 7, using the same distraction protocol as used in the present study, reported a significant maxillary horizontal relapse (mean relapse ratio of 12.6%) from 4 to 12 months after surgery. The difference between the horizontal maxillary relapse reported by Ko et al. 7 and that reported by the present study might be due to differences in the homogeneity of the subjects and the length and timing of the post-operative follow-up period. On the other hand, no quantitative study has been made of maxillary vertical relapse following distraction osteogenesis, though maxillary vertical relapse following Le Fort I osteotomy has been reported in several studies 13,14. In the mandible, significant mandibular rotation was observed in accordance with maxillary advancement. Mandibular clockwise rotation has been previously reported 5-7 ; however, the direction of rotation was not uniform in the present study. During the distraction period, 8 subjects demonstrated mandibular clockwise rotation and 4 subjects counter-clockwise rotation. During the first 6-month follow-up period, a significant relapse of the mandible (including clockwise and counter-clockwise rotation) was observed. Mandibular relapse has only been reported by Ko et al. 7, who observed significant mandibular counter-clockwise rotation from 4 to 12 months after surgery. The occurrence of maxillary dental change during the distraction period, particularly that of the maxillary incisor, has caused controversy. Swennen et al. 15, using a protraction facial mask, and Krimmel et al. 9, using a RED device, reported some labial tipping on the maxillary incisor. However, Figueroa and Polley 6, using a RED device with a specially customized intraoral splint, reported no significant inclination of the maxillary incisor. In the present study, using the same distraction protocol and intraoral splint as were proposed by Figueroa and Polley 6, significant maxillary dental change (such as elongation and lingual tipping of the incisor as well as elongation and distal tipping of the molar) was observed in accordance with maxillary advancement. On the other hand, maxillary dental changes in the follow-up period have not been reported, though significant relapse was observed both in the incisor and molar during the 6 month follow-up period. Relationship between dento-skeletal changes of the maxilla and mandible Until now, no quantitative analysis had been performed to examine the effects that dento-skeletal changes of the maxilla have on the mandible following maxillary distraction osteogenesis. The present study identifies the existence of a significant relationship between dento-skeletal changes which occur in the maxilla and mandible during the distraction and followup periods. As a result of stepwise linear regression analysis, the vertical change that occurred in the maxillary incisor during the distraction period was identified as a valid parameter for explaining the dento-skeletal changes that occurred in the mandible. The high correlation coefficients obtained suggest that the vertical positional change of the maxillary incisor could determine the direction of the mandibular rotation. Since the direction of the mandibular rotation has a great influence on the improvement of any skeletal discrepancy, consideration of the movement of the maxillary incisor will be needed in the treatment plan when using this procedure. Furthermore, in the 6-month follow-up period, the results of stepwise linear regression analysis indicated that both horizontal and vertical changes in the maxillary incisor can be used as a valid parameter in predicting the dento-skeletal changes of the mandible. This suggests that two-dimensional dento-skeletal relapse of the maxilla could have great influence on the relapse of the mandible. Effect of traction force system on dento-skeletal changes In the RED system, since traction forces are transmitted to the maxillary bone through dental anchorage (including the maxillary incisor and molar), it has been suggested that dental changes occur as a result of maxillary advancement (dental compensation 15,16 ). However, quantitative evaluation of the effects of the traction force system on this dental compensation has never been conducted. The present study revealed that the traction force system could play an important role not only with regard to dental compensation, but also with regard to the dento-skeletal changes occurring in the maxilla and mandible. The external hook length of the intraoral splint was significantly correlated with the lingual tipping of the maxillary incisor and with elongation of the maxillary molar, while the traction angle was significantly correlated with the dento-skeletal changes occurring in the maxilla and mandible. Clinically, dental compensation is not desirable because of unsatisfactory bone movement and the

7 DENTO-SKELETAL CHANGES IN UCLP FOLLOWING DOG 33 difficulty inherent in obtaining the ideal 1:1 (device:skeletal advancement) ratio due to undesirable dental movement 17. Moreover, unstable results are expected, due to the high probability of dental relapse 9. Instead of a tooth-borne distraction device (involving a dental anchorage system such as the RED device), a bone-borne distraction device (skeletal anchorage system) has been suggested for use in applying force to the maxilla, in order to avoid dental compensation 8,18. In the skeletal anchorage system, however, additional surgical interventions (in comparison with the dental anchorage system) would be needed for the placement and removal of the device. Accordingly, it was suggested that dental anchorage with greater reinforcement would be desirable, in order to reduce dental compensation associated with this procedure. Factors affecting post-surgical maxillary stability No quantitative analysis regarding factors affecting maxillary stability after distraction had previously been performed. In the present study, Pearson correlation analysis was performed, in order to identify the factors that affect two-dimensional maxillary stability. In the vertical dimension, maxillary relapse was significantly correlated with the amount of surgical maxillary movement. It was suggested that the more the maxilla was moved downwards, the more it relapsed upwards in the follow-up period. Similar findings have been reported after Le Fort I osteotomies 13,14,19. On the other hand, maxillary horizontal relapse was significantly correlated with the degree of pre-surgical maxillary hypoplasia. A high relapse ratio for the maxilla might be expected in cases with severe maxillary hypoplasia. This is because the severity of maxillary hypoplasia is strongly related to scar tissue and soft tissue tension that have been suggested as the principal factors causing maxillary horizontal relapse after Le Fort I osteotomies 19. Acknowledgements The authors would like to thank to Dr. Masaomi Kusayama for his invaluable assistance. 2. Ilizarov G A. The tension-stress effect on the genesis and growth of tissues. Part I. The influence of stability of fixation and soft tissue preservation. Clin Orthop 1989;238: McCarthy JG, Schreiber JS, Karp NS, et al. Lengthening of the human mandible by gradual distraction. Plast Reconstr Surg 1992;89: Polley JW, Figueroa AA. Management of severe maxillary deficiency in childhood and adolescence through distraction osteogenesis with an external, adjustable, rigid distraction device. J Craniofac Surg 1997;8: Polley JW, Figueroa AA. Rigid external distraction: Application in cleft maxillary deformities. Plast Reconstr Surg 1998;102: Figueroa AA, Polley JW. Management of severe cleft maxillary deficiency with distraction osteogenesis: procedure and results. Am J Orthod Dentofacial Orthop 1999;115: Ko EW, Figueroa AA, Polley JW. Soft tissue profile changes after maxillary advancement with distraction osteogenesis by use of a rigid external distraction device: A 1-year follow-up. J Oral Maxillofac Surg 2000;58: Swennen G, Dujardin T, Goris A, et al. Maxillary distraction osteogenesis: A method with skeletal anchorage. J Craniofac Surg 2000;11: Krimmel M, Cornelius C P, Roser M, et al. External distraction of the maxilla in patients with craniofacial dysplasia. J Craniofac Surg 2001;12: Shaw WC, Mandall NA, Mattich CR. Ethical and scientific decision making in distraction osteogenesis. Cleft Palate Craniofac J 2002;39: Coben SE. Growth and Class II treatment. Am J Orthod 1966;52: Mcfarlane RB, Frydman WL, McCabe SB, et al. Identification of nasal morphology features that indicate susceptibility to nasal tip deflection with the Le Fort I osteotomy. Am J Orthod Dentofac Orthop 1995;107: Proffit WR, Phillips C, Prewitt JW, et al. Stability after surgicalorthodontic correction of skeletal Class III malocclusion. II. Maxillary advancement. Int J Adult Orthod Orthognath Surg 1991;6: Arpornmaeklong P, Heggie AA, Shand JM. A comparison of the stability of single-piece and segmental Le Fort I maxillary advancements. J Craniofac Surg 2003;14: Swennen G, Colle F, De Mey A, et al. Maxillary distraction in cleft lip palate patients: a review of six cases. J Craniofac Surg 1999;5: Swennen G, Figueroa AA, Schierle H, et al. Maxillary distraction osteogenesis: A two-dimensional mathematical model. J Craniofac Surg 2000;11: Block MS, Cervini D, Chang A, et al. Anterior maxillary advancement using a tooth-supported distraction osteogenesis. J Oral Maxillofac Surg 1995; 53: Smalley WM, Shapiro PA, Hoi TH, et al. Osteointegrated titanium implants for maxillofacial protraction in monkeys. Am J Orthod Dentofac Orthop 1988;94: Hochban W, Ganss C, Austermann KH. Long-term results after maxillary advancement in patients with clefts. Cleft Palate Craniofac J 1993;30: References 1. Codivilla A. On the means of lengthening in the lower limbs, the muscles and tissues which are shortened through deformity. Am J Orthop Surg 1905;2: