Oral Sciences n3 Original Article Braz J Oral Sci. January/March 2010 - Volume 9, Number 1 Longitudinal study on skeletal changes during and after bionator therapy using metallic implants André da Costa Monini1, Luiz Gonzaga Gandini Júnior2, Lídia Parsekian Martins3, Dirceu Barnabé Raveli3 1 DDS, MS. Graduate student, Department of Orthodontics and Pediatric Dentistry, Araraquara Dental School, São Paulo State University, Brazil 2 DDS, MS, Ph D., Professor, Department of Orthodontics and Pediatric Dentistry, Araraquara Dental School, São Paulo State University, Brazil; Adjunct Clinical Professor, Baylor College of Dentistry, Dallas, TX, USA and Saint Louis University, Saint Louis, MO, USA. 3 DDS, MS, Ph D. Professor, Department of Orthodontics and Pediatric Dentistry, Araraquara Dental School, São Paulo State University, Brazil Correspondence to: Luiz Gonzaga Gandini Júnior Av. Casemiro Perez, 560, Vila Harmonia Araraquara, São Paulo, Brasil. CEP 14802-600 E-mail: luizgandini@uol.com.br Received for publication: November 26, 2009 Accepted: March 8, 2010 Abstract Aim: To demonstrate the magnitude and direction of skeletal changes in the maxilla and mandible during and after the use of bionator, as well as their rotations. Methods: Partial superimposition on the maxilla and mandible on the metallic implants and total superimposition on the cranial base were performed at three periods, T1 before bionator therapy, T2 after bionator therapy, and T3 5.68 years after T2. Results: There was total clockwise maxillary rotation and counterclockwise mandibular rotation, in the North American technique, throughout the study period, as well as extensive remodeling on the condylar region, especially in vertical direction and on the gonial region in horizontal direction. Conclusions: The total maxillary rotation seemed to be significantly affected by therapy than the mandible. There was a clear change in the direction of condylar remodeling compared to the period of bionator therapy and posterior bionator therapy. Considering the entire study period, it was observed that intra-matrix rotation of the maxilla and mandible masked their total rotation, causing minimum changes in the matrix rotation. Keywords: Angle’s class II malocclusion, activator appliances, maxillofacial development. Introduction In the Class II malocclusion, mandibular retrusion seems to be a common characteristic and the major factor contributing to the problem1. Therefore, the best therapeutic approaches should promote forward mandibular positioning. Although these appliances are able to redirect the condylar growth, there is no consensus on their capacity to increase the amount of condylar growth2-7. In the maxilla, these appliances may promote some restriction of sagittal growth3,8. After correction of the distal occlusion, there is a tendency to return to the original condition, both dental and skeletal5-6. Cephalometric studies with superimposition on metallic implants were demonstrated to be the most effective method for longitudinal evaluation of craniofacial growth on cephalograms9-11 and thus are also valid to evaluate the treatment changes. No study has longitudinally analyzed the maxillary and mandibular remodeling in patients submitted to treatment of Class II malocclusion with bionator by partial superimposition on metallic implants. This study evaluated the magnitude and direction of skeletal changes occurring in the maxilla and mandible during and after bionator therapy, as well as their rotations, using lateral cephalograms of patients with metallic implants. Material and methods This study was approved by Research Ethic Committee of the FOAr-UNESP Braz J Oral Sci. 9(1):33-38 34 (no. 0006.0.199.000-07) and informed consent was obtained from the parents of all patients. The treated sample comprised 25 patients who used bionator, who participated in a previous study2. The design and treatment approach is described in the previous study2. All patients presented clinically observed skeletal Class II malocclusion with mandibular retrusion, erupted or erupting maxillary and mandibular incisors, deep bite, no missing teeth, absence of crowding, and/or posterior crossbite. The patients also presented four metallic implants placed in the maxilla and three in the mandible, as suggested by Björk12-13. From the original sample of 25 patients, it was possible to obtain long-term cephalograms of 13 patients (Table 1 and 2), nine males and four females with 9.34 years at T1, 11.21 at T2 and 16.89 at T3. Eleven of these patients (84.6%) received complementary treatment with fixed appliance and class II elastics after the bionator therapy. The other patients could not be contacted. Lateral cephalograms were obtained at three periods: T1, at the onset of bionator therapy; T2, at the completion of bionator therapy; and T3, 5.68 years after T2 in the average. The cephalograms were manually traced, the cephalometric points were digitized twice on the software SPSS version 10.0 (SPSS Inc., Chicago, IL, USA) by a single examiner, and the mean of digitizations was used for the cephalometric measurements. The cephalometric points analyzed are described in Table 3. A reference system composed of a horizontal line (HL) and a perpendicular vertical line (PVL) was defined on the cephalogram T1 and transferred to the other cephalograms based on the partial superimposition on maxillary and mandibular metallic implants. Initially, three fiducial points were identified on the tracing T1, the first in front of the maxilla and mandible, the second behind, and the third above this (Figures 1 and 2). The HL and PVL were defined as follows: Horizontal line (HL): line contacting the Anterior Fiducial Point and the Posterior Fiducial Point. The line corresponds to the X axis of the reference system. Perpendicular Vertical Line (PVL): line perpendicular to HL through the Upper Fiducial Point. The line corresponds to the Y axis of the reference system (Figures 1 and 2). Fig. 1. Partial superimposition on the maxilla, transference of the three fiducial points (1, Posterior Fiducial Point-PFP; 2, Anterior Fiducial Point-AFP; 3- Upper Fiducial Point-UFP), and construction of HL(Horizontal Line) and PVL(Posterior Vertical Line). Fig. 2. Partial superimposition on the mandible, transference of the three fiducial points, and construction of HL(Horizontal Line) and PVL(Posterior Vertical Line). Males 9 9.25 1.39 11.08 1.28 16.99 1.62 Females 4 9.55 1.01 11.52 1.7 16.68 2.9 Total 13 9.34 1.25 11.21 1.36 16.89 1.72 S D Mean (years) S D Mean (years) S D Mean (years)nIndividuals T1 T2 T3 Table 1 - Characteristics of the study sample T1 - (treatment onset); T2 - (completion of bionator therapy); T3 - (final evaluation). The changes occurring in cephalometric points during and after treatment were evaluated in relation to the reference system. For example, the horizontal change in the position of the Gonion (Go) was measured parallel to HL, and the vertical change was measured parallel to PVL (Figure 2). Negative values correspond to backward and/or upward displacement. Positive values were assigned to forward and/ or downward displacement. The displacement of all cephalometric points was measured. To enhance the observation of direction of displacement of cephalometric points, each point was followed by a reference. For example, the horizontal displacement of Go is represented by Go H, the vertical displacement of point Go is represented by Go V, and the total displacement of point Go is represented by Go T. The radiographic magnification was corrected using a correction coefficient of 0.91. The total and matrix rotations of the mandible and maxilla11 were defined by the angular change of HL transferred from T1 to the others by total superimposition on the cranial base11 in relation to the implant line (total rotation) and the mandibular and palatal planes (matrix rotation), respectively, Braz J Oral Sci. 9(1):33-38 Longitudinal study on skeletal changes during and after bionator therapy using metallic implants S N A 82.92º 4.0 81.53º 3.9 81.26º 4.4 S N B 76.75º 3.5 77.56º 3.9 78.20º 4.3 A N B 6.17º 1.9 3.96º 2.3 3.05º 2.6 SN GoMe 32.91º 5.3 33.57º 5.9 31.73º 6.4 F M A 23.49º 3.8 23.86o 4.4 22.33º 5.4 SN-ANS-PNS 5.98º 2.7 6.78º 4.2 6.43º 3.5 Mean SD Mean SD Mean SD T1 T2 T3Measurements Table 2 - Sagittal and vertical angular cephalometric measurements. 35 Cephalometric Points Description 1. PFP Posterior fiducial point 2. AFP Anterior fiducial point 3. UFP Upper fiducial point 4. PNS (Posterior nasal spine) Most posterior point of the posterior nasal spine 5. ANS (Anterior nasal spine) Most anterior point of the anterior nasal spine 6. A (Subspinale) Most posterior point on the maxillary anterior concavity 7. B (Supramentale) Most anterior point on the mandibular anterior concavity 8. Pg (Pogonion) Most anterior point on the anterior symphyseal contour 9. Gn (Gnathion) Most anterior and inferior point on the anterior symphyseal contour 10. Me (Menton) Most inferior point on the symphyseal contour 11. Ag (Antegonial) Most superior point on the antegonial champher 12. InfGo (Inferior Gonion) Most inferior point of the gonial angle 13. Go (Gonion) Most posterior and inferior point of the gonial angle 14. PostGo (Posterior Gonion) Most posterior point of the gonial angle 15. Ar (Articulare) Intersection between the posterior cranial base and the posterior condylar surface 16. Co (Condylion) Most posterior and superior point of the mandibular condyle 17. CoSup (Superior Condylion) Most superior point of the mandibular condyle Table 3 - Digitized cephalometric points. in the North American technique. The intra-matrix rotation11 (remodeling) was determined by the angular change in the implant line in relation to the mandibular and palatal planes, respectively. For the total and matrix rotation, positive values indicated clockwise rotation and negative values represented counterclockwise rotation. Concerning the intra-matrix rotation, positive values indicated that the mandibular or palatal plane exhibited clockwise rotation in relation to the implant line, whereas negative values indicated counterclockwise rotation. Statistical Analysis The mean and standard deviation were calculated for each variable. All the variables submitted a normality test (skewness and kurtosis) and showed normal distribution. The differences among the three periods (T2–T1, T3–T2, and T3– T1) were calculated and the one-sample t-test was used to evaluate the significance of changes in those differences. The significance level was set at 5%. All calculations were performed using SPSS for Windows (version 10.0,SPSS Inc., Chicago, IL, USA.). To evaluate the error in the location of cephalometric points and digitization procedures, all tracings were redigitized after 2 weeks by the same examiner. The casual method error (Dahlberg formula) did not exceed 0.33º or 0.88mm. The paired t-test (systematic errors) revealed statistically significant systematic error for only 5 of the 112 measurements performed (PostGo V at T1 and T2, Me V at T3, InfGo H at T3, and PNS V at T1). The variation of all measurements was between -0.17 and 0.34 mm for linear measurements and -0.13º and 0.03º for angular measurements. Results Superimposition on the maxilla During bionator therapy, only the PNS exhibited significant change in horizontal direction (mean = -1.52 mm; p = 0.006). Evaluation of the total displacement revealed that all points exhibited statistically significant change. After bionator therapy, point A presented significant vertical change (mean 1.78 mm; p=0.007) and the PNS in the horizontal direction (mean -2.65 mm; p=0.000). Observation of the entire study period revealed significant horizontal change in ANS and PNS and significant vertical change in point A (Figure 3 and Table 4). PNS V 0.42 (0.9) 0.142 n 0.48 (1.8) 0.354 n 0.91 (1.8) 0.097 n ANS V -0.10 (1.4) 0.806 n 0.51 (1.4) 0.233 n 0.41 (1.4) 0.320 n A V -0.06 (1.2) 0.863 n 1.78 (1.9) 0.007* 1.72 (2.0) 0.011* PNS H -1.52 (1.6) 0.006 * -2.65 (1.3) 0.000 * -4.18 (2.0) 0.000* ANS H 0.41 (1.8) 0.435 n 1.28 (2.9) 0.136 n 1.70 (2.5) 0.035 * A H -0.24 (0.7) 0.292n -0.23 (1.1) 0.493 n -0.47 (1.4) 0.249 n PNS T 2.10 (1.2) 0.000 * 3.20 (1.3) 0.000 * 4.77 (1.6) 0.000 * ANS T 1.82 (1.4) 0.001 * 2.88 (1.9) 0.000 * 2.95 (1.5) 0.000 * A T 1.33 (0.6) 0.000 * 2.23 (1.8) 0.001 * 2.70 (1.3) 0.000 * Table 4 - Maxillary growth (vertical, horizontal and total) and remodeling (in mm). * = statistically significant values (p < 0.05); n = non statistically significant values. Mean (SD) “p” Mean (SD) “p” Mean (SD) “p” T2 - T1 T3-T2 T3-T1Variable Braz J Oral Sci. 9(1):33-38 Longitudinal study on skeletal changes during and after bionator therapy using metallic implants Fig. 3. Maxillary remodeling between T1 and T2 (upper data) and between T2 and T3 (lower data). The horizontal/vertical components are proportional in scale. Each square represents 0.5 mm. 36 Fig. 4. Condylar remodeling between T1 and T2 (upper data) and between T2 and T3 (lower data). The horizontal/vertical components are proportional in scale. Each square represents 1 mm. Fig. 5. Remodeling of the gonial angle between T1 and T2 (upper data) and between T2 and T3 (lower data). Horizontal/vertical components are proportional in scale. Each square represents 1 mm. B V 0.09 (1.3) 0.807 n -1.40 (2.1) 0.038 * -1.30 (2.0) 0.045 * Pg V 0.85 (1.3) 0.038 * 0.45 (1.7) 0.376 n 1.31 (2.0) 0.043 * Gn V 0.47 (1.1) 0.169 n 0.97 (1.3) 0.019 * 1.45 (1.6) 0.008 * Me V 0.23 (0.8) 0.329 n 1.36 (0.8) 0.000 * 1.60 (1.1) 0.000 * A Go V -2.68 (2.5) 0.003 * -2.68 (1.8) 0.000 * -5.37 (2.1) 0.000 * Inf Go V -2.96 (3.0) 0.004 * -4.06 (1.9) 0.000 * -7.03 (3.4) 0.000 * Go V -3.32 (4.5) 0.022 * -6.34 (2.5) 0.000 * -9.67 (5.7) 0.000 * Post Go V -3.20 (5.1) 0.044 * -9.19 (3.7) 0.000 * -12.39 (6.4) 0.000 * Ar V -5.71 (2.4) 0.000 * -13.28 (3.1)0.000* -18.99 (3.6) 0.000 * Co V -5.77 (3.4) 0.000 * -14.22 (4.5)0.000* -20.00 (4.0)0.000 * Co Sup V -5.48 (3.1) 0.000 * -14.13 (4.0) 0.000* -19.62 (3.6)0.000 * B H 0.12 (0.4) 0.329 n 0.06 (0.6) 0.705 n 0.19 (0.6) 0.279 n Pg H -0.46 (0.9) 0.096 n -0.29 (0.6) 0.145 n -0.76 (1.2) 0.046 * Gn H -0.49 (1.2) 0.169 n -0.39(0.8) 0.112 n -0.89 (1.6) 0.083 n Me H -0.26 (1.2) 0.468 n -0.69 (1.0) 0.031 n -0.96 (1.8) 0.089 n A Go H -3.57 (2.6) 0.000 * -3.96 (2.7) 0.000 * -7.55 (1.8) 0.000 * Inf Go H -3.17 (3.0) 0.002 * -5.32 (1.7) 0.000 * -8.50 (2.3) 0.000 * Go H -2.10 (2.1) 0.005 * -6.02 (1.6) 0.000 * -8.12 (1.7) 0.000 * Post Go H -1.71 (1.6) 0.003 * -5.09 (1.6) 0.000 * -6.81 (1.5) 0.000 * Ar H -1.42 (2.2) 0.039 * -0.56 (2.2) 0.386 n -1.99 (3.7) 0.080 n Co H -1.06 (2.8) 0.201 n 0.71 (2.9) 0.405 n -0.35 (4.9) 0.802 n Co Sup H -1.23 (2.9) 0.160 n 1.24 (2.9) 0.150 n 0.01 (4.7) 0.993 n B T 1.19 (0.7) 0.000 * 1.92 (1.7) 0.002 * 1.84 (1.7) 0.002 * Pg T 1.40 (1.2) 0.001 * 1.57 (1.1) 0.000 * 2.08 (1.9) 0.002 * Gn T 1.50 (0.9) 0.000 * 1.52 (1.0) 0.000 * 2.32 (1.7) 0.000 * Me T 1.19 (0.9) 0.001 * 1.81 (0.9) 0.000 * 2.44 (1.4) 0.000 * A Go T 4.81 (3.2) 0.000 * 4.91 (3.1) 0.000 * 9.37 (2.4) 0.000 * Inf Go T 4.87 (3.5) 0.000 * 6.85 (2.0) 0.000 * 11.21 (3.6) 0.000 * Go T 4.94 (3.9) 0.001 * 8.93 (2.3) 0.000* 12.97 (5.1) 0.000 * Post Go T 5.26 (3.6) 0.000 * 10.69 (3.4) 0.000 * 14.63 (5.3) 0.000 * Ar T 6.31 (2.3) 0.000 * 13.44 (3.2) 0.000 * 19.41 (3.7) 0.000 * Co T 6.56 (3.2) 0.000 * 14.54 (4.4) 0.000 * 20.52 (4.3) 0.000 * Co Sup T 6.37 (2.9) 0.000 * 14.52 (3.8) 0.000 * 20.11 (3.8) 0.000 * Mean (SD) “p” Mean (SD) “p” Mean (SD) “p” T2 - T1 T3-T2 T3-T1Variable Table 5 - Mandibular growth (vertical, horizontal and total) and remodeling (in mm). * = statistically significant values (p < 0.05); n = non statistically significant values. Superimposition on the mandible During the bionator treatment period, there was statistically significant vertical change in the following cephalometric points: Pg, Ag, InfGo, Go, PostGo, Ar, Co, and CoSup. In the horizontal direction, the following cephalometric points presented a statistically significant change: Ag, InfGo, Go, PostGo, and Ar. After bionator therapy, statistically significant vertical change was observed for the cephalometric points Ag, InfGo, Go, PostGo, Ar, Co, CoSup, Me, Gn, and point B. In the horizontal direction, only the points related to the gonial angle exhibited significant change. No significant change was revealed in a horizontal direction only for the points B, Gn, Me, Ar, Co, and CoSup during observation of the entire study period (Figures 4 and 5 and Table 5). Maxillary and mandibular rotation: Table 6 shows that during the period of bionator therapy, only the total mandibular rotation presented significant change (mean = -1.74º; p = 0.047). After bionator therapy, the total mandibular rotation (mean= -3.96º; p= 0.004) and mandibular intra-matrix rotation (mean= 2.78º; p=0.004) exhibited significant change. During the study period, no significant change was observed in matrix rotations for both the maxilla and the mandible. Discussion Despite the small sample size and lack of control group, this study may be considered of interest to the scientific community because of the presence of metallic implants and longitudinal follow-up of the same patients. This allowed a detailed analysis of maxillary and mandibular growth in patients with Class II malocclusion submitted to orthopedic treatment using the Balters functional appliance. Braz J Oral Sci. 9(1):33-38 Longitudinal study on skeletal changes during and after bionator therapy using metallic implants 37 Matrix Maxilla 0.29 (1.8) 0.583n 0.20 (2.2) 0.753n 0.49 (2.7) 0.524n Matrix Mandible 0.04 (2.3) 0.950n -1.21 (3.3) 0.213n -1.17 (3.2) 0.214n Total Maxilla 1.36 (2.5) 0.075n 1.49 (4.2) 0.225n 2.85 (4.6) 0.045* Total Mandible -1.74 (2.8) 0.047* -3.96 (3.9) 0.004* -5.7 (4.9) 0.001* Intra-matrix Maxilla -1.30 (3.5) 0.208n -1.17 (3.9) 0.307n -2.47 (3.8) 0.038* Intra-matrix Mandible 1.79 (4.6) 0.189n 2.78 (2.8) 0.004* 4.57 (5.2) 0.008* Mean (SD) “p” Mean (SD) “p” Mean (SD) “p” T2 - T1 T3-T2 T3-T1 Variable Table 6 . Maxillary and mandibular rotation. * = statistically significant values (p < 0.05); n = non statistically significant values. There was progressive closure of the angle of the mandibular implant line (counterclockwise rotation), that is, the total mandibular rotation 9,11,14-15. In addition to the treatment period, there was counterclockwise rotation throughout the study period. Araújo et al.2 demonstrated that the bionator was able to inhibit the total counterclockwise mandibular rotation. The rotation observed in the present study (1.74º) was smaller than that observed by Araújo et al. 2 (2.53º) in the control group and higher than the counterclockwise rotation of only 0.17º of the treated group. This confirmed that the appliance has the same influence, that is, inhibiting the total counterclockwise mandibular rotation6,16. Björk and Skieller11 published a case treated with headgear and observed inhibition of counterclockwise mandibular rotation during treatment, which returned after treatment. This is in agreement with the results of Melsen17 using the same appliance, and Pancherz et al.6 using the Herbst appliance. The difference in the quantity of rotation between this study and the findings of Araújo et al.2 may be explained by the longer treatment period of this study, that is, 2 years compared to 1 year. Moreover, as the need of utilization of the appliance is reduced, its influence is also reduced, allowing the natural rotation expected by growth to occur. The 5.7º mandibular rotation evaluated from T1-T3 was greater than that reported by Buschang and Gandini Jr14, and Kim and Nielsen18, 2º to 3.3º and 3.5º, respectively. This is smaller than the values observed by Lavergne and Gasson19, 12.8º, Björk and Skieller11, 8.6º, and very close to the value observed by Lee et al. 20, 5.8º. This could probably be because of the longer follow-up period of this study when compared to other studies that had follow-up periods of 7 years14 and 5 years18. However, it is shorter than the 12-year follow-up by Lavergne and Gasson19 and 15-year follow-up by Björk and Skieller 11, and similar to that of Lee et al. 20 Several studies9,14,16,19,21 have revealed that patients with greater counterclockwise rotation exhibit more vertical condylar growth. Analysis of the rotation occurring per year reveals a mean of 0.77o/year, close to the values observed by other authors11,16,20-22 (Table 7), demonstrating that the influence of bionator is reduced with time. In the maxilla, the total rotation occurred in clockwise direction and in lower intensity. The most variable behavior of maxillary rotation, which may occur in two directions and in lower intensity compared to the mandibular rotation, is reported in the literature10,15,23 and agrees with the present findings, revealing a variation of -4.6º to 10.8º. The results of this study also revealed clockwise maxillary rotation during and after bionator therapy, which was greater during treatment, 0.8º/year, than after treatment, 0.23º/year. The total counterclockwise maxillary rotation is the most common9- 10,15,24 and the clockwise rotation might be an outcome of treatment using headgear17 and the activator7. Clockwise maxillary rotation was also observed after bionator therapy, considering that these patients received fixed appliances and used Class II elastics at some period, the influence of the entire Class II mechanics on the total clockwise maxillary rotation may be inferred as Melsen17 observed inversion in the direction of total maxillary rotation after treatment of the Class II malocclusion. Table 8 demonstrates that the smaller total maxillary rotations are related to studies whose samples also included treated patients, highlighting the influence of the mechanotherapy for Class II malocclusion in most cases, thus promoting clockwise maxillary rotation. Solow and Iseri24 observed 2.5º of posterior maxillary intra-matrix rotation from 8 to 15 years. This study also observed nearly 2.5º rotation in the anterior direction, probably as a remodeling to compensate for the total clockwise rotation occurring as a result of treatment10,12,23. As previously mentioned in the literature9-12,16, because there is total counterclockwise rotation and the matrix rotation is very subtle, there is remodeling of the mandibular base and palatal plane to compensate for the rotation. The maxilla exhibited clockwise total and matrix rotation, and remodeling occurred more by vertical displacement of the PNS, compared with the ANS. This is in agreement with the treated group of Baumrind et al.25, suggesting that the orthodontic treatment may interfere with the maxillary remodeling, as untreated groups24-25 present greater vertical displacement of the ANS than of the PNS. The final outcome was an increase in the maxillary matrix rotation of only 0.5º in the present study and 1º in the study of Solow and Iseri24, revealing minimum Braz J Oral Sci. 9(1):33-38 Longitudinal study on skeletal changes during and after bionator therapy using metallic implants º Gu, McNamara21 I and II A 20 -0.78º 9 -15.6 Lavergne, Gasson19 several A 26 -1.07º 7-19 Araújo et al.2 II T 14 -0.17º 9.5-10.5 Araújo et al.2 II U T 11 -2.53º 9-10 Gasson, Lavergne15,22 several A 22 -0.81º 7-16 Björk, Skieller9 I, II and III U T 21 -1º 6-year follow up Björk, Skieller11 I U T 9 -0.78º 4 -19.7 Lee et al.20 several A 28 -0.74º 8.5-16.2 Odegaard 16 several A 25 -0.78º 2.5-year follow up Present study II T 13 -0.77º 9.34-16.89 *T= treated patients; UT= untreated patients; A=both; + indicates clockwise rotation / - indicates counterclockwise rotation. Table 7. Yearly changes in the mandibular total rotation in studies on metallic implants – available data. Authorsreference Type of malocclusion Patients* n Degrees/ year Interval in years Gasson, Lavergne15,22 several A 22 -0.21º 7-16 Solow, Iseri24 several U T 14 -0.38º 8.5-12.5 Björk, Skieller9 I, II and III U T 19 -0.42º 6-year follow up Björk, Skieller11 I U T 9 -0.41º 10 -19.7 Doppel et al.23 I, II and III A 50 -0.13º 12-16 Present study II T 13 +0.36º 9.34-16.89 Authorsreference Type of malocclusion Patients* n Degrees/ year Interval in years * T = treated patients; UT = untreated patients; A = both; + indicates clockwise rotation / - indicates counterclockwise rotation. Table 8. Yearly changes in the maxillary total rotation in studies on metallic implants – available data. 38 change in the palatal plane angle, in agreement with other authors12,15,23, as also observed in Table 2. The results demonstrate nearly 4.6º of opening of the angle between the implant line and the mandibular base. This intra-matrix rotation occurred because of upward remodeling of the gonial angle and downward displacement of the Me, as presented in Table 5. During the treatment period, the mandibular matrix rotation remained unchanged (0.04º) and during the second period there was a slight closure (-1.21º), also identified by reduction in the angles SNGoMe and FMA (Table 2). Throughout the study period and also during the treatment, there was extensive backward and upward remodeling of the gonial region, especially of the Go and PostGo points, agreeing with previous reports.11-14,21,26 Figure 5 reveals that this region did not exhibit changes in the direction of growth between the study periods, maybe because it is less susceptible to the environment14. At the symphyseal region, there was apposition on the lower part and upward repositioning of point B and downward repositioning of points Pg, Gn, and Me, in agreement with other studies14,26. In the horizontal direction, there was stability of cephalometric points at the Me region, agreeing with the studies of Björk11,13. The condylar region exhibited the greatest vertical changes in the mandible14,26. During the treatment period, there was backward condylar growth2-6,8. After bionator therapy, the condylar growth was redirected in anterior direction, returning almost totally to the initial anteroposterior condylar positioning. Studies11-13,26 revealed that the condyle presents upward and forward growth of nearly 6o in relation to the mandibular posterior border in untreated patients and forward growth of 10º in patients with total counterclockwise mandibular rotation. This information suggests that the backward growth obtained by treatment might be statistically significant when compared with a control group. Some of the patients in the present sample were followed for 1 year without treatment in a previous study2 and presented anterior condylar growth during this period. After use of the bionator, Faltin et al.4 demonstrated stability of condylar redirectioning in patients treated during the peak growth spurt. The results of this study do not support these findings3-4, probably because they were treated before the peak growth. However, the results agree with other studies5-6. The posterior displacement of point A observed in this study was nearly 0.5mm, probably because of the natural resorption occurring on the maxillary anterior region24-25 combined with the Class II mechanics employed25. In the vertical direction, the differences occurred because of the intra-matrix rotation, which presented a different direction in this study compared to earlier reports. Concerning the PNS point, the authors observed downward and backward displacement24. The PNS always presents backward growth, both in the treated and untreated groups, and also exhibits greater displacement of the ANS, which is the primary mechanism of maxillary growth25. In conclusion, the total maxillary rotation seemed to be significantly affected by therapy than the mandible. There was a clear change in the direction of condylar remodeling compared to the period of bionator therapy and posterior bionator therapy. Considering the entire study period, it was observed that intra- matrix rotation of the maxilla and mandible masked their total rotation, causing minimum changes in the matrix rotation. References 1. McNamara Jr JA. Components of Class II malocclusion in children 8-10 years of age. Angle Orthod. 1981; 51: 177-202. 2. Araújo AM, Buschang PH, Melo ACM. Adaptive condylar growth and mandibular remodelling changes with Bionator therapy -an implant study. Eur J Orthod. 2004; 26: 515-22. 3. Croft RS, Buschang PH, English JD, Meyer R. A cephalometric and tomographic evaluation of Herbst treatment in the mixed dentition. Am J Orthod Dentofacial Orthop. 1999; 116: 435-43. 4. Faltin Jr K, Faltin RM, Baccetti T, Franchi L, Ghiozzi B, McNamara Jr JA. 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