ORIGINAL ARTICLE
Maxillary changes with bone-borne surgically assisted rapid palatal expansion: A prospective study Karlien Asscherickx,a Elke Govaerts,b Johan Aerts,c and Bart Vande Vannetd Brussels and Veurne, Belgium
Introduction: The aim of this prospective study was to analyze the postexpansion positional changes of the maxillary halves and their initial stability after transpalatal distraction with a bone-borne distractor and standard corticotomies of the anterior, lateral, and median bony supports of the maxilla without pterygomaxillary disjunction. Methods: The sample consisted of 21 patients (15 female, 6 male; mean age, 26 years 5 months). Measurements on the maxillary study casts and the posteroanterior cephalograms were obtained before surgery, at the end of palatal expansion, and 10 weeks later. No orthodontic treatment was initiated during the examination period. Results: After palatal expansion, significantly wider measurements were noted in the canine (35.5%), premolar (26.3%), and molar (17.8%) regions. Angulation changes in the premolar ( 7 ) and molar ( 8 ) segments were observed. No significant changes were seen between the end of palatal expansion and 10 weeks later. Arch perimeter increased by 9.16% between presurgery and 10 weeks after the end of expansion. Conclusions: The results indicated that more expansion was achieved anteriorly, and that there was buccal tipping of the split maxillary halves. Bone-borne surgically assisted rapid palatal expansion can provide significant expansion of the maxilla with an increase in arch perimeter, and it shows initial stability. (Am J Orthod Dentofacial Orthop 2016;149:374-83)
A
n adequate transverse maxillary dimension is a critical component of a stable and functional occlusion.1 A maxilla that is too narrow often creates problems such as tooth crowding, unesthetic buccal corridors, crossbite, and mouth breathing. Rapid palatal expansion is often used for these patients. The aim is to maximize the skeletal effects and minimize the dental effects. Nonsurgical rapid palatal expansion is based on the idea of opening the midpalatal suture with a jackscrew.
a Researcher, Department of Orthodontics and Dentofacial Orthopedics, Vrije Universiteit Brussel, Brussels, Belgium. b Private practice, Veurne, Belgium. c Lecturer, Department of Orthodontics and Dentofacial Orthopedics, Vrije Universiteit Brussel, Brussels, Belgium. d Professor, Department of Orthodontics and Dentofacial Orthopedics, Vrije Universiteit Brussel, Brussels, Belgium. Karlien Asscherickx and Elke Govaerts contributed equally to this article. All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest, and none were reported. Address correspondence to: Karlien Asscherickx, Department of Orthodontics and Dentofacial Orthopedics, Vrije Universiteit Brussel, Laarbeeklaan 109, 1090 Jette, Brussels, Belgium; e-mail, [email protected]. Submitted, November 2014; revised and accepted, August 2015. 0889-5406/$36.00 Copyright Ó 2016 by the American Association of Orthodontists. http://dx.doi.org/10.1016/j.ajodo.2015.08.018
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The devices are tooth-borne. The increase of the transverse dimension of the maxillary arch is achieved by separation of the 2 halves (orthopedic effect) and buccal movement of the posterior teeth and alveolar processes (orthodontic effect). It is important to start expansion before or during the growth spurt because facial suture lines become significantly more interdigitated and become either partially or totally fused with age.2 This procedure is indicated for children and young adolescents.3 Because the points of application of the transverse force are positioned much lower than the centers of resistance of the maxillary halves, there will be segmental buccal tipping of the maxillary halves. The same is true for the anchorage teeth because the point of force application is positioned lower than the center of resistance of the anchorage teeth. In adults or patients who have passed their growth spurt, surgically assisted rapid palatal expansion (SARPE) is indicated. The expansion device can be tooth borne or bone borne. With the tooth-borne appliance, periodontal problems4-6 and problems relating to the orthodontic expansion—eg, tipping and extrusion of the anchorage teeth absorbing the forces—might occur.7 With a boneborne appliance, the points of force application are closer to the centers of resistance of the maxillary halves. No
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Fig 1. Study design. No orthodontic treatment was started before T2. P.A., Posteroanterior cephalogram; S.C., study cast; TPD, transpalatal distraction.
forces need to be applied to individual teeth, and the buccal dentition maintains its original position in the bony segments. Therefore, most of the maxillary expansion is orthopedic and at a mechanically more desired level. Since the teeth are not involved in the appliance, it can be combined with orthodontic treatment.8 Only a few prospective studies have reported on postdistraction changes and stability.9 The objectives of this study were to analyze the postexpansion positional changes of the maxillary halves and to investigate the initial stability of their positions 10 weeks after inserting the blocking screw into the distractor. The null hypotheses were the following: (1) there is no difference in the position of the maxillary halves before and immediately after transpalatal distraction, (2) there is no difference in the position of the maxillary halves immediately after distraction and 10 weeks later, and (3) there is no difference in the position of the maxillary halves before transpalatal distraction and 10 weeks after distraction. MATERIAL AND METHODS
Twenty-one consecutive patients whose treatment plan involved transpalatal distraction were studied prospectively. Maxillary study casts and posteroanterior cephalograms were collected before surgery (T0), at the end of maxillary expansion (T1), and 10 weeks later (T2). Orthodontic alignment of the dental arches was started after the study period. Both dental and skeletal widths were evaluated, as well as buccal tipping. The study design is shown in Figure 1. The clinical trial was carried out at the Department of Maxillofacial Surgery of St John's Hospital, Genk,
Belgium, and included the normal follow-up of patients who received transpalatal distraction, but at standardized time points. Ethical approval from the university was obtained (reference number 2002/109). After we explained the purpose and duration of the study, all subjects signed a written consent form before participating in the study. The inclusion criteria for the patients were (1) need for skeletal bilateral transverse expansion of the maxilla; (2) female patients older than 15 years, and male patients older than 17 years; (3) permanent dentition; (4) no craniofacial congenital anomalies; and (5) no orthodontic appliances used during the study. Over a period of 2 years, 21 patients met the inclusion criteria and volunteered to participate in the study. They ranged in age from 15 years 1 month to 44 years 6 months, with an average age of 26 years 5 months. There were 15 female and 6 male patients. Surgery was performed by the same person for all patients under general anesthesia and nasoendotracheal intubation. The distractor used in this study was a transpalatal distractor (Surgi-Tec, Bruges, Belgium), a boneborne device for surgically assisted rapid maxillary expansion. It was first introduced in 1999 by Mommaerts.10 Standard corticotomies were performed of the anterior, lateral, and median bony supports of the maxilla without pterygomaxillary disjunction. Midpalatal suture separation included loosening and disengagement of the anterior nasal spine and opening of the midpalatal suture between the maxillary central incisors. For mechanical advantage and patient comfort, the transpalatal distractor was placed as high as possible in the palatal vault.11 Abutment plates were inserted, left and right, between the roots of the second premolar
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Fig 3. Transpalatal distractor in situ. Fig 2. Placement of right abutment plate after incision.
and the first molar (Fig 2). The distraction module was slightly activated to put the abutment plates in the correct positions against the palatal bone, after which they were fixated with titanium miniscrews. Activation was immediately performed until a diastema of 1 mm occurred between the central incisors (Fig 3). After surgery, the expansion screw was locked passively for 1 week. This latency period is the period from bone division to the onset of traction and is standard procedure.12,13 It is the time allowed for reparative callus formation. The bony segments at both ends of the gap were then progressively distracted over several days, ranging from 8 to 22 days (distraction phase). The expansion module has a color code (3 colors), and patients were instructed to turn it once a day by 120 until the next color appeared, starting 1 week after surgery. One activation of the screw opened the distraction module by 0.33 mm, so the distraction occurred at a rate of 1 mm in 3 days. When distraction is too fast, the collagen fibers might lose contact, and there is no ingrowth of new bone, causing nonunion or malunion. If distraction is too slow, premature consolidation can occur, and the required elongation cannot be obtained. Mean expansion time was 18 days, thus producing a mean expansion of the device of 6 mm. This procedure was continued until both arches were coordinated before surgical correction of the Class II and Class III malocclusions. Once the necessary expansion was achieved, the distractor was turned into a fixed retainer by inserting a blocking screw. The maxilla was not overexpanded, because movements of the bony halves should be stable when the distractor is left in situ passively during the consolidation phase. The distraction module was left in place for a mean retention period of 6 months (minimum, 4 months; maximum, 18 months). No distraction module was removed before the records were taken at T2. Fixed appliance therapy was started after T2 while the distraction
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device was still in situ. Expansion often creates space for the tongue to take a position in the palatal vault and thus prevent relapse. In the studies of Matteini and Mommaerts14 and Zahl and Gerlach,15 it was suggested that overcorrection is not necessary. Satisfactory results and long-term stability after surgically assisted rapid maxillary expansion depend on the orthodontist's ability to obtain a functional and stable occlusion. Casts were made for all patients at T0, T1, and T2. To prevent distortion of the impression, the distraction modules were blocked out with wax before the impressions were taken. Every cast was trimmed with the base parallel to the occlusal plane. Points from which measurements were to be taken were marked with a fine lead pencil to facilitate identification. Once marked, the casts were photographed from an occlusal view with a digital reflex dual CCD camera (Minolta, Osaka, Japan). A camera stand was used to support the casts and hold the camera at a fixed focal length from the occlusal plane of the casts. To provide a scale of distance, a millimeter rule was fixed at the heel of each cast at the level of the occlusal plane. After this procedure, the study casts were reduced on a model trimmer perpendicular to the occlusal plane: first from the front to the cusp tips of the first premolars and then from the back to the level of the mesial cusps of the first molars. These teeth were chosen because they are the anchor teeth in conventional SARPE procedures. Digital photographs were taken again using the standardized protocol as described above. The digital measurements on the photographs of the maxillary models were done with the software package Onyx Ceph (version 2.6.24, release 2.6.52; Image Instruments, Chemnitz, Germany) on a Pentium IV notebook (I power 5000; Packard Bell, Nijmegen, The Netherlands). Metric resolution of the software was 0.17 mm per pixel. The landmarks were marked on the maxillary dental models as described by Adkins et al,16 and the following variables were measured.
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Fig 4. Linear measurements of interdental width on the study casts: C, Most lingual point at the gingival margin of the maxillary canine; P1, most lingual point at the gingival margin of the maxillary first premolar; M, most lingual point at the gingival margin of the maxillary first molar.
1.
2.
In the occlusal plane (linear measurements in millimeters) (Figs 4 and 5): intercanine width (Fig 4); interpremolar width (Fig 4); intermolar width (Fig 4); and arch perimeter, the sum of the lengths of the segments connecting the contact points on the mesial surfaces of the first molars, the contact points on the mesial surfaces of the first premolars, and the contact points on the distal surfaces of the central incisors (Fig 5). In the frontal plane (angular measurements in degrees) (Fig 6): premolar inclination and molar inclination.
Posteroanterior cephalograms were taken of all patients at T0, T1, and T2. All cephalograms were taken at St John's Hospital with the same roentgen equipment and magnification factor. All cephalograms were scanned (cobrascan CX-312T, large-format 12-bit xray digitizer; Radiographic Digital Imaging, Torrance, Calif; www.cobrascan.com) and digitized with an XScan32 software package (Radiographic Digital Imaging). After digitizing, all cephalograms were analyzed using the Onyx Ceph cephalometric software package on the Pentium IV notebook. The following variables were measured parallel to the cranial base reference line, drawn according to the method of Mossaz-Jo€elson and Mossaz17 (Fig 7): medio-orbital width, nasal cavity width, and maxillary width. Statistical analysis
To evaluate possible errors in landmark identification, photographic magnification, and digitization of
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Fig 5. Arch perimeter measurement: Dist I1, Distal surface of the maxillary central incisor; Mes PM1, mesial surface of the maxillary first premolar; Mes M1, mesial surface of the maxillary first molar.
Fig 6. Construction of tangents and angular measurements. Tangents were constructed through the highest points of the mesial and palatal cusps of the first premolars and the mesiobuccal and mesiopalatal cusps of the first molars.
the measurements by the investigator (E.G.), 10 randomly chosen maxillary study casts were photographed and digitized at 1 time. The same 10 study casts were photographed and digitized again after 1 week by the same investigator. Measurements were performed on both sets by the same investigator. On the first set, measurements were also made by a second investigator (B.V.V.). Pearson correlation coefficients were determined for every variable measured on the maxillary casts. The same procedure was used for the posteroanterior cephalograms. Statistical calculations were performed with a software package (SPSS for Windows, version 14.0; SPSS, Chicago, Ill). Significance for all statistical tests was predetermined at P \0.05. Descriptive statistics were determined for each variable at all 3 time points. A longitudinal study was
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Fig 7. Measurements on the posteroanterior cephalograms: Lo, latero-orbital point where the greater wing of the sphenoid bone intersects with the lateral wall of the orbit; CRL, cranial base reference line; Mo, most medial point of the orbital orifice; Ln, most lateral point of the nasal cavity; Mx, point located at the depth of the concavity of the lateral maxillary contour at the junction of the maxilla and the zygomatic buttress.
considered with repeated measurements, in which each variable was observed at 3 time points: T0, T1, and T2 (within-subject factors). Statistical comparisons were made to calculate the changes over time for each variable and test them for statistically significant differences. Statistically significant differences were tested with the parametric 1-way repeated measures analysis of variance test for normal distributions. RESULTS
For each patient, the required amount of expansion on the basis of the treatment plans was achieved. No clinical complications were encountered during the observation period. Figure 8 depicts consecutive models of 1 patient at T0, T1, and T2. All variables at all time points were tested for normal distribution with the Kolmogorov-Smirnov 1-sample test. All variables showed a normal distribution; therefore, parametric tests could be used. For all variables of 10 randomly chosen maxillary casts and posteroanterior cephalograms, intraexaminer repeatability with a Pearson correlation coefficient
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higher than 0.9 and interexaminer repeatability with a Pearson correlation coefficient higher than 0.8 were found. These strong correlations between the first and second measurements made by the investigators (E.G. and B.V.V) indicated that the digitizing process, the identification of the landmarks on the maxillary casts and the posteroanterior cephalograms, and the measurements were done in a reproducible way. Figure 9 shows the differences between the time points of the linear measurements. Figure 10 shows the differences between time points of the angular measurements. The results of the descriptive statistics are given in Table I. Table II shows the pairwise comparisons of T1-T0, T2-T1, and T2-T0. At T1, statistically significant increases were observed in intercanine, interpremolar, and intermolar widths. Between T2 and T1, no significant changes were observed in these parameters. The overall increases in width between T0 and T2 were statistically significant for intercanine, interpremolar, and intermolar widths. The increase in intercanine width was greater than the increase in intermolar width. Arch perimeter showed an increase of 7.8 mm (12.8%) at T1. Arch perimeter showed a statistically significant decrease of 2.4 mm between T1 and T2, a relapse of 28.2% of the originally obtained perimeter increase. The overall increase in arch perimeter at 10 weeks after the maxillary expansion had ceased; it was 6.1 mm, or 9.16%, and statistically significant. Correlations were tested with the bivariate Pearson correlation test for the changes between T0 and T1 in arch perimeter and the increases in intercanine, interpremolar, and intermolar widths between T0 and T1. The predictability of the relationships was moderate, with correlation coefficients of 0.68, 0.60, and 0.56 for intercanine, interpremolar, and intermolar widths, respectively. In the frontal plane, statistically significant mean changes in angulation of the first molar of 8 (buccal crown tipping) and the first premolar of 7 (buccal crown tipping) compared with the original values were observed at T1. At T2, angulation values were still significantly different from those at T0 (buccal tipping was observed). Increases of 0.8 mm in medio-orbital width, 2.7 mm in nasal cavity width, and 4.8 mm in maxillary width between T0 and T1 were found. No parameter, except arch perimeter, had a statistically significant difference between T1 and T2. The null hypothesis that there is no difference in the positions of the maxillary halves before and immediately after transpalatal distraction was rejected.
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Fig 8. Three-dimensional models of a patient at T0, T1, and T2.
Fig 9. Bar graph depicting means of the linear measurements at the different time points. C, Most lingual point at the gingival margin of the maxillary canine; P1, most lingual point at the gingival margin of the maxillary first premolar; M, most lingual point at the gingival margin of the maxillary first molar; perimeter, distal surface of the maxillary central incisor plus mesial surface of the maxillary first premolar plus mesial surface of the maxillary first molar; Mo, most medial point of the orbital orifice; Ln, most lateral point of the nasal cavity; Mx, point located at the depth of the concavity of the lateral maxillary contour at the junction of the maxilla and the zygomatic buttress. *The mean difference is significant at the 0.05 level.
The null hypothesis that there is no difference in the positions of the maxillary halves immediately after transpalatal distraction and 10 weeks later was accepted for all parameters except arch perimeter. The null hypothesis that there is no difference in the positions of the maxillary halves before transpalatal distraction and 10 weeks after distraction was rejected.
DISCUSSION
SARPE using tooth-borne devices is a standard procedure in treating patients with a narrow maxilla after their growth spurt and has satisfactory results.4,18 Problems related to the mechanical stress on the teeth can be avoided if forces are applied directly to the bone. This study was set up to evaluate the effects and initial stability of bone-borne SARPE by analyzing study
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Fig 10. Bar graph depicting means of the angular measurements at different time points. P-Incl, Premolar inclination; M-Incl, molar inclination. *The mean difference is significant at the 0.05 level.
casts and posteroanterior cephalograms before, immediately after, and 10 weeks after distraction. This study was prospective, but the design has some limitations. There was no control group of untreated patients or a control group of patients treated with SARPE using tooth-borne devices. No significant changes in transverse dimensions can be expected in untreated adults, and therefore a control group of untreated patients was assumed not to be necessary. To divide the group into bone-borne and tooth-borne distractions would have reduced the sample size and made the results less powerful. Data on the effect of toothborne SARPE are available in the literature. Therefore, no control group was included. Another limitation was that only the short-term effect was evaluated, whereas a major issue in orthodontics and orthognathic surgery is stability. In this study, no relapse in the transverse dimensions was found at 10 weeks after the distraction had stopped. The distraction module was still in place at T2; this might have contributed to the stability of the expansion. Further evaluation over a longer time period on the stability of the results and relapse is difficult because of the dental effects of the orthodontic therapy, which is often started approximately 4 months after palatal distraction. Remodeling of the alveolar process due to movement of the teeth by the fixed appliance therapy might influence the width of the maxilla; thus, the net effect of the surgically assisted expansion cannot be determined. For tooth-borne SARPE, relapse is widely recognized but poorly described. Several authors mentioned relapse but did not quantify the amount.19,20 Some recommended overexpanding to counteract the
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relapse effect of buccal tipping of the posterior teeth that takes place during SARPE.18,21 Reported relapses varied from 7%4 to 11.8%22 at the first molar at 6 months and 1 year after surgery. SARPE results in substantial enlargements of the maxillary apical base and the palatal vault, providing space for the tongue, which might contribute to the prevention of relapse.23 No evidencebased protocol is yet available about whether overexpansion is indicated and how long the retention phase should be. A guideline could be to leave the distractor in situ as a retention appliance for at least 6 months after distraction has ceased. This is the time period that the suture needs to be repaired to a normal state after the expansion.24 Since the device is bone borne, orthodontic treatment can be started with the distractor in situ.8 One more limitation of this study was that 3 pairwise comparisons were used, and no correction was applied. Therefore, there is a potential risk of increased type I errors. However, the clinical relevance of the differences between the time points is more important than the statistical significance in this study. The reliability of the measurements on both cephalograms and photographs of the study casts was evaluated, and high intraexaminer reliability was found. Measurements on the cephalograms showed the greatest variations between the first and second measurements, although the differences were within acceptable limits of 0.5 or 10.5 mm. This agrees with other studies.25,26 Although there might be differences in interpretations (landmark identification) and measurement methods between investigators, the fact that the measurements were done by 1 investigator makes the results
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Table I. Descriptive statistics (21 subjects; 15 female,
Table II. Statistical pairwise comparisons between the
6 male)
time points
Variable C-C (mm)
P1-P1 (mm)
M-M (mm)
Perimeter (mm)
P-Incl ( )
M-Incl ( )
Mo-Mo (mm)
Ln-Ln (mm)
Mx-Mx (mm)
Time T0 T1 T2 T0 T1 T2 T0 T1 T2 T0 T1 T2 T0 T1 T2 T0 T1 T2 T0 T1 T2 T0 T1 T2 T0 T1 T2
Mean 20.4 27.0 26.1 23.2 29.3 28.9 29.5 34.8 34.9 67.5 75.4 73.0 198.1 191.5 193.6 155.9 147.7 145.3 21.6 22.4 22.5 30.3 33.0 32.8 55.1 59.9 59.4
SD 2.71 2.77 2.99 2.52 2.79 3.45 3.88 3.69 4.01 6.73 6.27 6.56 12.80 14.68 15.24 15.79 16.51 17.26 1.61 1.45 1.58 2.08 2.55 2.66 3.93 4.14 3.74
Minimum 13 21 20 18 24 24 19 27 26 51.2 61.7 59.6 180.0 167.3 162.4 120.0 104.3 109.8 18.4 19.5 19.5 26.3 27.0 26.3 45.0 47.2 48.2
Maximum 27 32 33 28 34 38 36 43 42 78.5 83.9 82.3 226.0 220.4 219.6 182.0 173.8 171.8 24.5 24.6 24.5 33.4 37.5 37 60.1 66.5 63.3
C, Most lingual point at the gingival margin of the maxillary canine; P1, most lingual point at the gingival margin of the maxillary first premolar; M, most lingual point at the gingival margin of the maxillary first molar; perimeter, distal surface of the maxillary central incisor plus mesial surface of the maxillary first premolar plus mesial surface of the maxillary first molar; P-Incl, premolar inclination; MIncl, molar inclination; Mo, most medial point of the orbital orifice; Ln, most lateral point of the nasal cavity; Mx, point located at the depth of the concavity of the lateral maxillary contour at the junction of the maxilla and the zygomatic buttress.
reliable. If there were a systematic error in identifying landmarks or measuring distances, this would not influence the results of the pairwise comparisons, since the systematic error would occur on the measurements of each time point. According to our results, more expansion was detected anteriorly than posteriorly. All sites of major resistance of the maxilla were released, except the pterygoid plates of the sphenoid bone, which were not disengaged from the tuber maxillae. The new center of resistance was therefore located much more posteriorly than before. This might explain why more anterior and less posterior expansion was accomplished. Similar results were found by Pinto et al9 in 2001. Because of the increased risk of injuring the pterygoid plexus during the osteotomy, many surgeons prefer not to release
Variable C-C (mm)
P1-P1 (mm)
M-M (mm)
Perimeter (mm)
P-Incl ( )
M-Incl ( )
Mo-Mo (mm)
Ln-Ln (mm)
Mx-Mx (mm)
Period T1-T0 T2-T1 T2-T0 T1-T0 T2-T1 T2-T0 T1-T0 T2-T1 T2-T0 T1-T0 T2-T1 T2-T0 T1-T0 T2-T1 T2-T0 T1-T0 T2-T1 T2-T0 T1-T0 T2-T1 T2-T0 T1-T0 T2-T1 T2-T0 T1-T0 T2-T1 T2-T0
Mean difference 6.6* 1.0 5.7* 6.1* 0.4 5.7* 5.2* 0.1 5.4* 7.8* 2.4* 6.1* 6.6* 2.1 4.6* 8.2* 2.4 10.6* 0.8 0.1 0.9* 2.7* 0.2 2.5* 4.8* 0.5 4.3*
SE 0.35 0.38 0.48 0.29 0.36 0.38 0.36 0.35 0.42 0.47 0.39 0.74 1.05 1.32 1.65 1.39 1.52 1.88 0.31 0.17 0.30 0.42 0.22 0.50 0.47 0.23 0.47
Significance 0.00 0.06 0.00 0.00 0.75 0.00 0.00 1.00 0.00 0.00 0.00 0.00 0.00 0.39 0.04 0.00 0.38 0.00 0.05 1.00 0.02 0.00 1.00 0.00 0.00 0.19 0.00
C, Most lingual point at the gingival margin of the maxillary canine; P1, most lingual point at the gingival margin of the maxillary first premolar; M, most lingual point at the gingival margin of the maxillary first molar; perimeter, distal surface of the maxillary central incisor plus mesial surface of the maxillary first premolar plus mesial surface of the maxillary first molar; P-Incl, premolar inclination; MIncl, molar inclination; Mo, most medial point of the orbital orifice; Ln, most lateral point of the nasal cavity; Mx, point located at the depth of the concavity of the lateral maxillary contour at the junction of the maxilla and the zygomatic buttress. *The mean difference is significant at the 0.05 level.
the pterygoid plates, which are important sites of resistance. When releasing the pterygoid plates from the tuber maxillae, the centers of resistance can be expected to move anteriorly; this will result in a more parallel expansion.14,27 With tooth-borne SARPE, the postexpansion widths of the posterior teeth are greater than those of the anterior teeth, even without pterygoid disjunction.4,28 The reason is the rigid design of the tooth-borne appliance. The design produces, in addition to the desired skeletal expansion, some dental expansion in the posterior region, resulting in dental tipping and buccal movement. Because of the surgical procedure, the new center of resistance in the frontal view is expected to be much lower than before. The point of force application of
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the transverse force with bone-borne anchorage is positioned at a higher level in the palatal vault than with tooth-borne appliances, thus at a more desired level to obtain parallel expansion in the frontal plane.10,11,29 However, in this study, a statistically significant difference was found in tooth angulation before and after expansion, even though the appliance was bone borne. These results correspond with the findings for first premolar tipping of Pinto et al9 using the same bone-borne SARPE device and the same surgical procedure. We assumed that tooth angulation changes resulted from lateral tipping of the split maxillary segments rather than dentoalveolar tipping of the teeth. Postdistractional changes in tooth angulation in the frontal view were also found in previous studies with conventional tooth-borne SARPE.7,21 The buccal tipping in these studies was almost double what we found in this study. In these previous studies with tooth-borne SARPE, the buccal crown tipping of the anchorage teeth must have been a combination of the buccal tipping of the split maxillary segments and the buccal tipping of the anchorage teeth in their alveolar bone. Measurements on posteroanterior cephalograms showed expansion of the maxilla, nasal width, and intraorbital width after distraction. The results should be considered with caution. Errors in landmark identification and measurement and errors associated with the equipment might influence the measurements. Although it showed statistical significance at T2, the increase in medio-orbital width might be due to a measurement error. In this study, expansion of 4.8 mm was measured at the level of the maxilla. This was more than was reported in previous studies when tooth-borne SARPE was used (1.3 mm7 and 3.0 mm19). Landes et al30 found significantly more overall transverse skeletal expansion with bone-borne devices than with tooth-borne devices, when compared with multidetector computed tomography scans 3 months after expansion. This suggests that the use of bone-borne SARPE will initially lead to more skeletal expansion and more translational movement of the maxillary halves than tooth-borne SARPE. In a recent 3-dimensional prospective study on the skeletal effects of SARPE, Nada et al12 found alveolar expansions of 3.6 mm with a bone-borne device and 3.4 mm with a tooth-borne device. Evaluation was done by superimposing 3-dimensional cone-beam computed tomography models before and approximately 22 months after expansion to evaluate the changes in alveolar expansion. Alveolar expansion is the result of both palatal distraction and tooth movements, which might explain why
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no significant difference was found after 22 months between tooth-borne and bone-borne SARPE. Arch perimeter points were chosen on the mesial surfaces of the first premolars and the distal surfaces of the central incisors because the maxillary canines and the lateral incisors were often blocked out labially or palatally. This method with segments underestimates the true arch perimeter. However, within the clinical limitations, the estimated measurements were considered reasonable in evaluating the changes in arch perimeter.9 The change in arch perimeter correlated well with the increases in intercanine, interpremolar, and intermolar widths. Therefore, it could be concluded that transverse width gain leads directly to an increase in arch perimeter, which indicates that transpalatal distraction is useful for the creation of additional arch perimeter space to relieve maxillary tooth crowding. CONCLUSIONS
From these findings, it can be concluded that transpalatal distraction results immediately in increases in interdental, maxillary, and nasal cavity widths, and in an increase in arch perimeter. No statistically significant differences were found between transverse measurements immediately after expansion and 10 weeks later, indicating the initial stability of the expansion when the distractor was left in situ. Transpalatal distraction without pterygoid disjunction results in a nonparallel expansion, with more expansion anteriorly. Transpalatal distraction without pterygoid disjunction results in buccal tipping of the split maxillary halves. ACKNOWLEDGMENTS
We thank Prof Dr Constantinus Politis for the surgical treatments of the patients and the late Prof Dr Leonard Kaufman and Prof Dr Ronald Buyl for help with the statistical analyses of the data. REFERENCES 1. Vanarsdall RL, White RP Jr. Three-dimensional analysis for skeletal problems. Int J Adult Orthod Orthognath Surg 1994;9:159. 2. Chrcanovic BR, Custodio AL. Orthodontic or surgically assisted rapid maxillary expansion. J Oral Maxillofac Surg 2009;13:123-37. 3. Lines PA. Adult rapid maxillary expansion with corticotomy. Am J Orthod 1975;67:44-56. 4. Bays RA, Greco JM. Surgically assisted rapid palatal expansion: an outpatient technique with long-term stability. J Oral Maxillofac Surg 1992;50:110-3. 5. Glassman AS, Nahigian SJ, Medway JM, Aronowitz HL. Conservative surgical orthodontic adult rapid palatal expansion: sixteen cases. Am J Orthod 1984;86:207-13.
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6. Kraut RA. Surgically assisted rapid maxillary expansion by opening the midpalatal suture. J Oral Maxillofac Surg 1984;42:651-5. 7. Byloff FK, Mossaz CF. Skeletal and dental changes following surgically assisted rapid palatal expansion. Eur J Orthod 2004;26: 403-9. 8. Mommaerts MY, vande Vannet B. Dental tours de force 5. Bimaxillary transverse distraction osteogenesis. Ned Tijdschr Tandheelkd 2004;111:40-3. 9. Pinto P, Mommaerts MY, Wreakes G, Jacobs W. Immediate postexpansion changes following the use of the transpalatal distractor. J Oral Maxillofac Surg 2001;59:994-1000. 10. Mommaerts MY. Transpalatal distraction as a method of maxillary expansion. J Oral Maxillofac Surg 1999;37:268-72. 11. Bishara SE, Staley RN. Maxillary expansion: clinical implications. Am J Orthod Dentofacial Orthop 1987;91:3-14. 12. Nada RM, Fudalej PS, Maal TJ, Berge SJ, Mostafa YA, KuijpersJagtman AM. Three-dimensional prospective evaluation of tooth-borne and bone-borne surgically assisted rapid maxillary expansion. J Craniomaxillofac Surg 2012;40:757-62. 13. Koudstaal MJ, Poort LJ, van der Wal KG, Wolvius EB, PrahlAndersen B, Schulten AJ. Surgically assisted rapid maxillary expansion (SARME): a review of the literature. Int J Oral Maxillofac Surg 2005;34:709-14. 14. Matteini C, Mommaerts MY. Posterior transpalatal distraction with pterygoid disjunction: a short-term model study. Am J Orthod Dentofacial Orthop 2001;120:498-502. 15. Zahl C, Gerlach KL. Palatinaldistraktor. Ein innovativer Ansatz f€ ur die Gaumennahterweiterung. Mund Kiefer Gesichts Chir 2002;6: 446-9. 16. Adkins MD, Nanda RS, Currier GF. Arch perimeter changes on rapid palatal expansion. Am J Orthod Dentofacial Orthop 1990;97:194-9. 17. Mossaz-Jo€elson K, Mossaz CF. Slow maxillary expansion: a comparison between banded and bonded appliances. Eur J Orthod 1989;11:67-76. 18. Lehman JA Jr, Haas AJ. Surgical-orthodontic correction of transverse maxillary deficiency. Clin Plast Surg 1989;16:749-55. 19. Berger JL, Pangrazio-Kulbersh V, Borgula T, Kaczynski R. Stability of orthopedic and surgically assisted rapid palatal expansion over time. Am J Orthod Dentofacial Orthop 1998;114:638-45.
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20. Mossaz CF, Byloff FK, Richter M. Unilateral and bilateral corticotomies for correction of maxillary transverse discrepancies. Eur J Orthod 1992;14:110-6. 21. Chung CH, Goldman AM. Dental tipping and rotation immediately after surgically assisted rapid palatal expansion. Eur J Orthod 2003;25:353-8. 22. Pogrel MA, Kaban LB, Vargervik K, Baumrind S. Surgically assisted rapid maxillary expansion in adults. Int J Adult Orthod Orthognath Surg 1992;7:37-41. 23. Wriedt S, Kunkel M, Zentner A, Wahlmann UW. Surgically assisted rapid palatal expansion. An acoustic rhinometric, morphometric and sonographic investigation. J Orofac Orthop 2001;62:107-15. 24. Cleall JF, Bayne DI, Posen JM, Subtelny JD. Expansion of the midpalatal suture in the monkey. Angle Orthod 1965;35:23-35. 25. Major PW, Johnson DE, Hesse KL, Glover KE. Landmark identification error in posterior anterior cephalometrics. Angle Orthod 1994; 64:447-54. 26. Cheung G, Goonewardene MS, Islam SM, Murray K, Koong B. The validity of transverse intermaxillary analysis by traditional PA cephalometry compared with cone-beam computed tomography. Aust Orthod J 2013;29:86-95. 27. Ramieri GA, Spada MC, Austa M, Bianchi SD, Berrone S. Transverse maxillary distraction with a bone-anchored appliance: dentoperiodontal effects and clinical and radiological results. Int J Oral Maxillofac Surg 2005;34:357-63. 28. Str€ omberg C, Holm J. Surgically assisted, rapid maxillary expansion in adults. A retrospective long-term follow-up study. J Craniomaxillofac Surg 1995;23:222-7. 29. Neyt NM, Mommaerts MY, Abeloos JV, De Clercq CA, Neyt LF. Problems, obstacles and complications with transpalatal distraction in non-congenital deformities. J Craniomaxillofac Surg 2002;30:139-43. 30. Landes CA, Laudemann K, Schubel F, Petruchin O, Mack M, Kopp S, et al. Comparison of tooth- and bone-borne devices in surgically assisted rapid maxillary expansion by threedimensional computed tomography monitoring: transverse dental and skeletal maxillary expansion, segmental inclination, dental tipping, and vestibular bone resorption. J Craniofac Surg 2009; 20:1132-41.
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Maxillary changes with bone-borne surgically assisted rapid palatal expansion: A prospective study Karlien Asscherickx,a Elke Govaerts,b Johan Aerts,c and Bart Vande Vannetd Brussels and Veurne, Belgium
Introduction: The aim of this prospective study was to analyze the postexpansion positional changes of the maxillary halves and their initial stability after transpalatal distraction with a bone-borne distractor and standard corticotomies of the anterior, lateral, and median bony supports of the maxilla without pterygomaxillary disjunction. Methods: The sample consisted of 21 patients (15 female, 6 male; mean age, 26 years 5 months). Measurements on the maxillary study casts and the posteroanterior cephalograms were obtained before surgery, at the end of palatal expansion, and 10 weeks later. No orthodontic treatment was initiated during the examination period. Results: After palatal expansion, significantly wider measurements were noted in the canine (35.5%), premolar (26.3%), and molar (17.8%) regions. Angulation changes in the premolar ( 7 ) and molar ( 8 ) segments were observed. No significant changes were seen between the end of palatal expansion and 10 weeks later. Arch perimeter increased by 9.16% between presurgery and 10 weeks after the end of expansion. Conclusions: The results indicated that more expansion was achieved anteriorly, and that there was buccal tipping of the split maxillary halves. Bone-borne surgically assisted rapid palatal expansion can provide significant expansion of the maxilla with an increase in arch perimeter, and it shows initial stability. (Am J Orthod Dentofacial Orthop 2016;149:374-83)
A
n adequate transverse maxillary dimension is a critical component of a stable and functional occlusion.1 A maxilla that is too narrow often creates problems such as tooth crowding, unesthetic buccal corridors, crossbite, and mouth breathing. Rapid palatal expansion is often used for these patients. The aim is to maximize the skeletal effects and minimize the dental effects. Nonsurgical rapid palatal expansion is based on the idea of opening the midpalatal suture with a jackscrew.
a Researcher, Department of Orthodontics and Dentofacial Orthopedics, Vrije Universiteit Brussel, Brussels, Belgium. b Private practice, Veurne, Belgium. c Lecturer, Department of Orthodontics and Dentofacial Orthopedics, Vrije Universiteit Brussel, Brussels, Belgium. d Professor, Department of Orthodontics and Dentofacial Orthopedics, Vrije Universiteit Brussel, Brussels, Belgium. Karlien Asscherickx and Elke Govaerts contributed equally to this article. All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest, and none were reported. Address correspondence to: Karlien Asscherickx, Department of Orthodontics and Dentofacial Orthopedics, Vrije Universiteit Brussel, Laarbeeklaan 109, 1090 Jette, Brussels, Belgium; e-mail, [email protected]. Submitted, November 2014; revised and accepted, August 2015. 0889-5406/$36.00 Copyright Ó 2016 by the American Association of Orthodontists. http://dx.doi.org/10.1016/j.ajodo.2015.08.018
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The devices are tooth-borne. The increase of the transverse dimension of the maxillary arch is achieved by separation of the 2 halves (orthopedic effect) and buccal movement of the posterior teeth and alveolar processes (orthodontic effect). It is important to start expansion before or during the growth spurt because facial suture lines become significantly more interdigitated and become either partially or totally fused with age.2 This procedure is indicated for children and young adolescents.3 Because the points of application of the transverse force are positioned much lower than the centers of resistance of the maxillary halves, there will be segmental buccal tipping of the maxillary halves. The same is true for the anchorage teeth because the point of force application is positioned lower than the center of resistance of the anchorage teeth. In adults or patients who have passed their growth spurt, surgically assisted rapid palatal expansion (SARPE) is indicated. The expansion device can be tooth borne or bone borne. With the tooth-borne appliance, periodontal problems4-6 and problems relating to the orthodontic expansion—eg, tipping and extrusion of the anchorage teeth absorbing the forces—might occur.7 With a boneborne appliance, the points of force application are closer to the centers of resistance of the maxillary halves. No
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Fig 1. Study design. No orthodontic treatment was started before T2. P.A., Posteroanterior cephalogram; S.C., study cast; TPD, transpalatal distraction.
forces need to be applied to individual teeth, and the buccal dentition maintains its original position in the bony segments. Therefore, most of the maxillary expansion is orthopedic and at a mechanically more desired level. Since the teeth are not involved in the appliance, it can be combined with orthodontic treatment.8 Only a few prospective studies have reported on postdistraction changes and stability.9 The objectives of this study were to analyze the postexpansion positional changes of the maxillary halves and to investigate the initial stability of their positions 10 weeks after inserting the blocking screw into the distractor. The null hypotheses were the following: (1) there is no difference in the position of the maxillary halves before and immediately after transpalatal distraction, (2) there is no difference in the position of the maxillary halves immediately after distraction and 10 weeks later, and (3) there is no difference in the position of the maxillary halves before transpalatal distraction and 10 weeks after distraction. MATERIAL AND METHODS
Twenty-one consecutive patients whose treatment plan involved transpalatal distraction were studied prospectively. Maxillary study casts and posteroanterior cephalograms were collected before surgery (T0), at the end of maxillary expansion (T1), and 10 weeks later (T2). Orthodontic alignment of the dental arches was started after the study period. Both dental and skeletal widths were evaluated, as well as buccal tipping. The study design is shown in Figure 1. The clinical trial was carried out at the Department of Maxillofacial Surgery of St John's Hospital, Genk,
Belgium, and included the normal follow-up of patients who received transpalatal distraction, but at standardized time points. Ethical approval from the university was obtained (reference number 2002/109). After we explained the purpose and duration of the study, all subjects signed a written consent form before participating in the study. The inclusion criteria for the patients were (1) need for skeletal bilateral transverse expansion of the maxilla; (2) female patients older than 15 years, and male patients older than 17 years; (3) permanent dentition; (4) no craniofacial congenital anomalies; and (5) no orthodontic appliances used during the study. Over a period of 2 years, 21 patients met the inclusion criteria and volunteered to participate in the study. They ranged in age from 15 years 1 month to 44 years 6 months, with an average age of 26 years 5 months. There were 15 female and 6 male patients. Surgery was performed by the same person for all patients under general anesthesia and nasoendotracheal intubation. The distractor used in this study was a transpalatal distractor (Surgi-Tec, Bruges, Belgium), a boneborne device for surgically assisted rapid maxillary expansion. It was first introduced in 1999 by Mommaerts.10 Standard corticotomies were performed of the anterior, lateral, and median bony supports of the maxilla without pterygomaxillary disjunction. Midpalatal suture separation included loosening and disengagement of the anterior nasal spine and opening of the midpalatal suture between the maxillary central incisors. For mechanical advantage and patient comfort, the transpalatal distractor was placed as high as possible in the palatal vault.11 Abutment plates were inserted, left and right, between the roots of the second premolar
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Fig 3. Transpalatal distractor in situ. Fig 2. Placement of right abutment plate after incision.
and the first molar (Fig 2). The distraction module was slightly activated to put the abutment plates in the correct positions against the palatal bone, after which they were fixated with titanium miniscrews. Activation was immediately performed until a diastema of 1 mm occurred between the central incisors (Fig 3). After surgery, the expansion screw was locked passively for 1 week. This latency period is the period from bone division to the onset of traction and is standard procedure.12,13 It is the time allowed for reparative callus formation. The bony segments at both ends of the gap were then progressively distracted over several days, ranging from 8 to 22 days (distraction phase). The expansion module has a color code (3 colors), and patients were instructed to turn it once a day by 120 until the next color appeared, starting 1 week after surgery. One activation of the screw opened the distraction module by 0.33 mm, so the distraction occurred at a rate of 1 mm in 3 days. When distraction is too fast, the collagen fibers might lose contact, and there is no ingrowth of new bone, causing nonunion or malunion. If distraction is too slow, premature consolidation can occur, and the required elongation cannot be obtained. Mean expansion time was 18 days, thus producing a mean expansion of the device of 6 mm. This procedure was continued until both arches were coordinated before surgical correction of the Class II and Class III malocclusions. Once the necessary expansion was achieved, the distractor was turned into a fixed retainer by inserting a blocking screw. The maxilla was not overexpanded, because movements of the bony halves should be stable when the distractor is left in situ passively during the consolidation phase. The distraction module was left in place for a mean retention period of 6 months (minimum, 4 months; maximum, 18 months). No distraction module was removed before the records were taken at T2. Fixed appliance therapy was started after T2 while the distraction
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device was still in situ. Expansion often creates space for the tongue to take a position in the palatal vault and thus prevent relapse. In the studies of Matteini and Mommaerts14 and Zahl and Gerlach,15 it was suggested that overcorrection is not necessary. Satisfactory results and long-term stability after surgically assisted rapid maxillary expansion depend on the orthodontist's ability to obtain a functional and stable occlusion. Casts were made for all patients at T0, T1, and T2. To prevent distortion of the impression, the distraction modules were blocked out with wax before the impressions were taken. Every cast was trimmed with the base parallel to the occlusal plane. Points from which measurements were to be taken were marked with a fine lead pencil to facilitate identification. Once marked, the casts were photographed from an occlusal view with a digital reflex dual CCD camera (Minolta, Osaka, Japan). A camera stand was used to support the casts and hold the camera at a fixed focal length from the occlusal plane of the casts. To provide a scale of distance, a millimeter rule was fixed at the heel of each cast at the level of the occlusal plane. After this procedure, the study casts were reduced on a model trimmer perpendicular to the occlusal plane: first from the front to the cusp tips of the first premolars and then from the back to the level of the mesial cusps of the first molars. These teeth were chosen because they are the anchor teeth in conventional SARPE procedures. Digital photographs were taken again using the standardized protocol as described above. The digital measurements on the photographs of the maxillary models were done with the software package Onyx Ceph (version 2.6.24, release 2.6.52; Image Instruments, Chemnitz, Germany) on a Pentium IV notebook (I power 5000; Packard Bell, Nijmegen, The Netherlands). Metric resolution of the software was 0.17 mm per pixel. The landmarks were marked on the maxillary dental models as described by Adkins et al,16 and the following variables were measured.
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Fig 4. Linear measurements of interdental width on the study casts: C, Most lingual point at the gingival margin of the maxillary canine; P1, most lingual point at the gingival margin of the maxillary first premolar; M, most lingual point at the gingival margin of the maxillary first molar.
1.
2.
In the occlusal plane (linear measurements in millimeters) (Figs 4 and 5): intercanine width (Fig 4); interpremolar width (Fig 4); intermolar width (Fig 4); and arch perimeter, the sum of the lengths of the segments connecting the contact points on the mesial surfaces of the first molars, the contact points on the mesial surfaces of the first premolars, and the contact points on the distal surfaces of the central incisors (Fig 5). In the frontal plane (angular measurements in degrees) (Fig 6): premolar inclination and molar inclination.
Posteroanterior cephalograms were taken of all patients at T0, T1, and T2. All cephalograms were taken at St John's Hospital with the same roentgen equipment and magnification factor. All cephalograms were scanned (cobrascan CX-312T, large-format 12-bit xray digitizer; Radiographic Digital Imaging, Torrance, Calif; www.cobrascan.com) and digitized with an XScan32 software package (Radiographic Digital Imaging). After digitizing, all cephalograms were analyzed using the Onyx Ceph cephalometric software package on the Pentium IV notebook. The following variables were measured parallel to the cranial base reference line, drawn according to the method of Mossaz-Jo€elson and Mossaz17 (Fig 7): medio-orbital width, nasal cavity width, and maxillary width. Statistical analysis
To evaluate possible errors in landmark identification, photographic magnification, and digitization of
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Fig 5. Arch perimeter measurement: Dist I1, Distal surface of the maxillary central incisor; Mes PM1, mesial surface of the maxillary first premolar; Mes M1, mesial surface of the maxillary first molar.
Fig 6. Construction of tangents and angular measurements. Tangents were constructed through the highest points of the mesial and palatal cusps of the first premolars and the mesiobuccal and mesiopalatal cusps of the first molars.
the measurements by the investigator (E.G.), 10 randomly chosen maxillary study casts were photographed and digitized at 1 time. The same 10 study casts were photographed and digitized again after 1 week by the same investigator. Measurements were performed on both sets by the same investigator. On the first set, measurements were also made by a second investigator (B.V.V.). Pearson correlation coefficients were determined for every variable measured on the maxillary casts. The same procedure was used for the posteroanterior cephalograms. Statistical calculations were performed with a software package (SPSS for Windows, version 14.0; SPSS, Chicago, Ill). Significance for all statistical tests was predetermined at P \0.05. Descriptive statistics were determined for each variable at all 3 time points. A longitudinal study was
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Fig 7. Measurements on the posteroanterior cephalograms: Lo, latero-orbital point where the greater wing of the sphenoid bone intersects with the lateral wall of the orbit; CRL, cranial base reference line; Mo, most medial point of the orbital orifice; Ln, most lateral point of the nasal cavity; Mx, point located at the depth of the concavity of the lateral maxillary contour at the junction of the maxilla and the zygomatic buttress.
considered with repeated measurements, in which each variable was observed at 3 time points: T0, T1, and T2 (within-subject factors). Statistical comparisons were made to calculate the changes over time for each variable and test them for statistically significant differences. Statistically significant differences were tested with the parametric 1-way repeated measures analysis of variance test for normal distributions. RESULTS
For each patient, the required amount of expansion on the basis of the treatment plans was achieved. No clinical complications were encountered during the observation period. Figure 8 depicts consecutive models of 1 patient at T0, T1, and T2. All variables at all time points were tested for normal distribution with the Kolmogorov-Smirnov 1-sample test. All variables showed a normal distribution; therefore, parametric tests could be used. For all variables of 10 randomly chosen maxillary casts and posteroanterior cephalograms, intraexaminer repeatability with a Pearson correlation coefficient
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higher than 0.9 and interexaminer repeatability with a Pearson correlation coefficient higher than 0.8 were found. These strong correlations between the first and second measurements made by the investigators (E.G. and B.V.V) indicated that the digitizing process, the identification of the landmarks on the maxillary casts and the posteroanterior cephalograms, and the measurements were done in a reproducible way. Figure 9 shows the differences between the time points of the linear measurements. Figure 10 shows the differences between time points of the angular measurements. The results of the descriptive statistics are given in Table I. Table II shows the pairwise comparisons of T1-T0, T2-T1, and T2-T0. At T1, statistically significant increases were observed in intercanine, interpremolar, and intermolar widths. Between T2 and T1, no significant changes were observed in these parameters. The overall increases in width between T0 and T2 were statistically significant for intercanine, interpremolar, and intermolar widths. The increase in intercanine width was greater than the increase in intermolar width. Arch perimeter showed an increase of 7.8 mm (12.8%) at T1. Arch perimeter showed a statistically significant decrease of 2.4 mm between T1 and T2, a relapse of 28.2% of the originally obtained perimeter increase. The overall increase in arch perimeter at 10 weeks after the maxillary expansion had ceased; it was 6.1 mm, or 9.16%, and statistically significant. Correlations were tested with the bivariate Pearson correlation test for the changes between T0 and T1 in arch perimeter and the increases in intercanine, interpremolar, and intermolar widths between T0 and T1. The predictability of the relationships was moderate, with correlation coefficients of 0.68, 0.60, and 0.56 for intercanine, interpremolar, and intermolar widths, respectively. In the frontal plane, statistically significant mean changes in angulation of the first molar of 8 (buccal crown tipping) and the first premolar of 7 (buccal crown tipping) compared with the original values were observed at T1. At T2, angulation values were still significantly different from those at T0 (buccal tipping was observed). Increases of 0.8 mm in medio-orbital width, 2.7 mm in nasal cavity width, and 4.8 mm in maxillary width between T0 and T1 were found. No parameter, except arch perimeter, had a statistically significant difference between T1 and T2. The null hypothesis that there is no difference in the positions of the maxillary halves before and immediately after transpalatal distraction was rejected.
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Fig 8. Three-dimensional models of a patient at T0, T1, and T2.
Fig 9. Bar graph depicting means of the linear measurements at the different time points. C, Most lingual point at the gingival margin of the maxillary canine; P1, most lingual point at the gingival margin of the maxillary first premolar; M, most lingual point at the gingival margin of the maxillary first molar; perimeter, distal surface of the maxillary central incisor plus mesial surface of the maxillary first premolar plus mesial surface of the maxillary first molar; Mo, most medial point of the orbital orifice; Ln, most lateral point of the nasal cavity; Mx, point located at the depth of the concavity of the lateral maxillary contour at the junction of the maxilla and the zygomatic buttress. *The mean difference is significant at the 0.05 level.
The null hypothesis that there is no difference in the positions of the maxillary halves immediately after transpalatal distraction and 10 weeks later was accepted for all parameters except arch perimeter. The null hypothesis that there is no difference in the positions of the maxillary halves before transpalatal distraction and 10 weeks after distraction was rejected.
DISCUSSION
SARPE using tooth-borne devices is a standard procedure in treating patients with a narrow maxilla after their growth spurt and has satisfactory results.4,18 Problems related to the mechanical stress on the teeth can be avoided if forces are applied directly to the bone. This study was set up to evaluate the effects and initial stability of bone-borne SARPE by analyzing study
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Fig 10. Bar graph depicting means of the angular measurements at different time points. P-Incl, Premolar inclination; M-Incl, molar inclination. *The mean difference is significant at the 0.05 level.
casts and posteroanterior cephalograms before, immediately after, and 10 weeks after distraction. This study was prospective, but the design has some limitations. There was no control group of untreated patients or a control group of patients treated with SARPE using tooth-borne devices. No significant changes in transverse dimensions can be expected in untreated adults, and therefore a control group of untreated patients was assumed not to be necessary. To divide the group into bone-borne and tooth-borne distractions would have reduced the sample size and made the results less powerful. Data on the effect of toothborne SARPE are available in the literature. Therefore, no control group was included. Another limitation was that only the short-term effect was evaluated, whereas a major issue in orthodontics and orthognathic surgery is stability. In this study, no relapse in the transverse dimensions was found at 10 weeks after the distraction had stopped. The distraction module was still in place at T2; this might have contributed to the stability of the expansion. Further evaluation over a longer time period on the stability of the results and relapse is difficult because of the dental effects of the orthodontic therapy, which is often started approximately 4 months after palatal distraction. Remodeling of the alveolar process due to movement of the teeth by the fixed appliance therapy might influence the width of the maxilla; thus, the net effect of the surgically assisted expansion cannot be determined. For tooth-borne SARPE, relapse is widely recognized but poorly described. Several authors mentioned relapse but did not quantify the amount.19,20 Some recommended overexpanding to counteract the
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relapse effect of buccal tipping of the posterior teeth that takes place during SARPE.18,21 Reported relapses varied from 7%4 to 11.8%22 at the first molar at 6 months and 1 year after surgery. SARPE results in substantial enlargements of the maxillary apical base and the palatal vault, providing space for the tongue, which might contribute to the prevention of relapse.23 No evidencebased protocol is yet available about whether overexpansion is indicated and how long the retention phase should be. A guideline could be to leave the distractor in situ as a retention appliance for at least 6 months after distraction has ceased. This is the time period that the suture needs to be repaired to a normal state after the expansion.24 Since the device is bone borne, orthodontic treatment can be started with the distractor in situ.8 One more limitation of this study was that 3 pairwise comparisons were used, and no correction was applied. Therefore, there is a potential risk of increased type I errors. However, the clinical relevance of the differences between the time points is more important than the statistical significance in this study. The reliability of the measurements on both cephalograms and photographs of the study casts was evaluated, and high intraexaminer reliability was found. Measurements on the cephalograms showed the greatest variations between the first and second measurements, although the differences were within acceptable limits of 0.5 or 10.5 mm. This agrees with other studies.25,26 Although there might be differences in interpretations (landmark identification) and measurement methods between investigators, the fact that the measurements were done by 1 investigator makes the results
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Table I. Descriptive statistics (21 subjects; 15 female,
Table II. Statistical pairwise comparisons between the
6 male)
time points
Variable C-C (mm)
P1-P1 (mm)
M-M (mm)
Perimeter (mm)
P-Incl ( )
M-Incl ( )
Mo-Mo (mm)
Ln-Ln (mm)
Mx-Mx (mm)
Time T0 T1 T2 T0 T1 T2 T0 T1 T2 T0 T1 T2 T0 T1 T2 T0 T1 T2 T0 T1 T2 T0 T1 T2 T0 T1 T2
Mean 20.4 27.0 26.1 23.2 29.3 28.9 29.5 34.8 34.9 67.5 75.4 73.0 198.1 191.5 193.6 155.9 147.7 145.3 21.6 22.4 22.5 30.3 33.0 32.8 55.1 59.9 59.4
SD 2.71 2.77 2.99 2.52 2.79 3.45 3.88 3.69 4.01 6.73 6.27 6.56 12.80 14.68 15.24 15.79 16.51 17.26 1.61 1.45 1.58 2.08 2.55 2.66 3.93 4.14 3.74
Minimum 13 21 20 18 24 24 19 27 26 51.2 61.7 59.6 180.0 167.3 162.4 120.0 104.3 109.8 18.4 19.5 19.5 26.3 27.0 26.3 45.0 47.2 48.2
Maximum 27 32 33 28 34 38 36 43 42 78.5 83.9 82.3 226.0 220.4 219.6 182.0 173.8 171.8 24.5 24.6 24.5 33.4 37.5 37 60.1 66.5 63.3
C, Most lingual point at the gingival margin of the maxillary canine; P1, most lingual point at the gingival margin of the maxillary first premolar; M, most lingual point at the gingival margin of the maxillary first molar; perimeter, distal surface of the maxillary central incisor plus mesial surface of the maxillary first premolar plus mesial surface of the maxillary first molar; P-Incl, premolar inclination; MIncl, molar inclination; Mo, most medial point of the orbital orifice; Ln, most lateral point of the nasal cavity; Mx, point located at the depth of the concavity of the lateral maxillary contour at the junction of the maxilla and the zygomatic buttress.
reliable. If there were a systematic error in identifying landmarks or measuring distances, this would not influence the results of the pairwise comparisons, since the systematic error would occur on the measurements of each time point. According to our results, more expansion was detected anteriorly than posteriorly. All sites of major resistance of the maxilla were released, except the pterygoid plates of the sphenoid bone, which were not disengaged from the tuber maxillae. The new center of resistance was therefore located much more posteriorly than before. This might explain why more anterior and less posterior expansion was accomplished. Similar results were found by Pinto et al9 in 2001. Because of the increased risk of injuring the pterygoid plexus during the osteotomy, many surgeons prefer not to release
Variable C-C (mm)
P1-P1 (mm)
M-M (mm)
Perimeter (mm)
P-Incl ( )
M-Incl ( )
Mo-Mo (mm)
Ln-Ln (mm)
Mx-Mx (mm)
Period T1-T0 T2-T1 T2-T0 T1-T0 T2-T1 T2-T0 T1-T0 T2-T1 T2-T0 T1-T0 T2-T1 T2-T0 T1-T0 T2-T1 T2-T0 T1-T0 T2-T1 T2-T0 T1-T0 T2-T1 T2-T0 T1-T0 T2-T1 T2-T0 T1-T0 T2-T1 T2-T0
Mean difference 6.6* 1.0 5.7* 6.1* 0.4 5.7* 5.2* 0.1 5.4* 7.8* 2.4* 6.1* 6.6* 2.1 4.6* 8.2* 2.4 10.6* 0.8 0.1 0.9* 2.7* 0.2 2.5* 4.8* 0.5 4.3*
SE 0.35 0.38 0.48 0.29 0.36 0.38 0.36 0.35 0.42 0.47 0.39 0.74 1.05 1.32 1.65 1.39 1.52 1.88 0.31 0.17 0.30 0.42 0.22 0.50 0.47 0.23 0.47
Significance 0.00 0.06 0.00 0.00 0.75 0.00 0.00 1.00 0.00 0.00 0.00 0.00 0.00 0.39 0.04 0.00 0.38 0.00 0.05 1.00 0.02 0.00 1.00 0.00 0.00 0.19 0.00
C, Most lingual point at the gingival margin of the maxillary canine; P1, most lingual point at the gingival margin of the maxillary first premolar; M, most lingual point at the gingival margin of the maxillary first molar; perimeter, distal surface of the maxillary central incisor plus mesial surface of the maxillary first premolar plus mesial surface of the maxillary first molar; P-Incl, premolar inclination; MIncl, molar inclination; Mo, most medial point of the orbital orifice; Ln, most lateral point of the nasal cavity; Mx, point located at the depth of the concavity of the lateral maxillary contour at the junction of the maxilla and the zygomatic buttress. *The mean difference is significant at the 0.05 level.
the pterygoid plates, which are important sites of resistance. When releasing the pterygoid plates from the tuber maxillae, the centers of resistance can be expected to move anteriorly; this will result in a more parallel expansion.14,27 With tooth-borne SARPE, the postexpansion widths of the posterior teeth are greater than those of the anterior teeth, even without pterygoid disjunction.4,28 The reason is the rigid design of the tooth-borne appliance. The design produces, in addition to the desired skeletal expansion, some dental expansion in the posterior region, resulting in dental tipping and buccal movement. Because of the surgical procedure, the new center of resistance in the frontal view is expected to be much lower than before. The point of force application of
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the transverse force with bone-borne anchorage is positioned at a higher level in the palatal vault than with tooth-borne appliances, thus at a more desired level to obtain parallel expansion in the frontal plane.10,11,29 However, in this study, a statistically significant difference was found in tooth angulation before and after expansion, even though the appliance was bone borne. These results correspond with the findings for first premolar tipping of Pinto et al9 using the same bone-borne SARPE device and the same surgical procedure. We assumed that tooth angulation changes resulted from lateral tipping of the split maxillary segments rather than dentoalveolar tipping of the teeth. Postdistractional changes in tooth angulation in the frontal view were also found in previous studies with conventional tooth-borne SARPE.7,21 The buccal tipping in these studies was almost double what we found in this study. In these previous studies with tooth-borne SARPE, the buccal crown tipping of the anchorage teeth must have been a combination of the buccal tipping of the split maxillary segments and the buccal tipping of the anchorage teeth in their alveolar bone. Measurements on posteroanterior cephalograms showed expansion of the maxilla, nasal width, and intraorbital width after distraction. The results should be considered with caution. Errors in landmark identification and measurement and errors associated with the equipment might influence the measurements. Although it showed statistical significance at T2, the increase in medio-orbital width might be due to a measurement error. In this study, expansion of 4.8 mm was measured at the level of the maxilla. This was more than was reported in previous studies when tooth-borne SARPE was used (1.3 mm7 and 3.0 mm19). Landes et al30 found significantly more overall transverse skeletal expansion with bone-borne devices than with tooth-borne devices, when compared with multidetector computed tomography scans 3 months after expansion. This suggests that the use of bone-borne SARPE will initially lead to more skeletal expansion and more translational movement of the maxillary halves than tooth-borne SARPE. In a recent 3-dimensional prospective study on the skeletal effects of SARPE, Nada et al12 found alveolar expansions of 3.6 mm with a bone-borne device and 3.4 mm with a tooth-borne device. Evaluation was done by superimposing 3-dimensional cone-beam computed tomography models before and approximately 22 months after expansion to evaluate the changes in alveolar expansion. Alveolar expansion is the result of both palatal distraction and tooth movements, which might explain why
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no significant difference was found after 22 months between tooth-borne and bone-borne SARPE. Arch perimeter points were chosen on the mesial surfaces of the first premolars and the distal surfaces of the central incisors because the maxillary canines and the lateral incisors were often blocked out labially or palatally. This method with segments underestimates the true arch perimeter. However, within the clinical limitations, the estimated measurements were considered reasonable in evaluating the changes in arch perimeter.9 The change in arch perimeter correlated well with the increases in intercanine, interpremolar, and intermolar widths. Therefore, it could be concluded that transverse width gain leads directly to an increase in arch perimeter, which indicates that transpalatal distraction is useful for the creation of additional arch perimeter space to relieve maxillary tooth crowding. CONCLUSIONS
From these findings, it can be concluded that transpalatal distraction results immediately in increases in interdental, maxillary, and nasal cavity widths, and in an increase in arch perimeter. No statistically significant differences were found between transverse measurements immediately after expansion and 10 weeks later, indicating the initial stability of the expansion when the distractor was left in situ. Transpalatal distraction without pterygoid disjunction results in a nonparallel expansion, with more expansion anteriorly. Transpalatal distraction without pterygoid disjunction results in buccal tipping of the split maxillary halves. ACKNOWLEDGMENTS
We thank Prof Dr Constantinus Politis for the surgical treatments of the patients and the late Prof Dr Leonard Kaufman and Prof Dr Ronald Buyl for help with the statistical analyses of the data. REFERENCES 1. Vanarsdall RL, White RP Jr. Three-dimensional analysis for skeletal problems. Int J Adult Orthod Orthognath Surg 1994;9:159. 2. Chrcanovic BR, Custodio AL. Orthodontic or surgically assisted rapid maxillary expansion. J Oral Maxillofac Surg 2009;13:123-37. 3. Lines PA. Adult rapid maxillary expansion with corticotomy. Am J Orthod 1975;67:44-56. 4. Bays RA, Greco JM. Surgically assisted rapid palatal expansion: an outpatient technique with long-term stability. J Oral Maxillofac Surg 1992;50:110-3. 5. Glassman AS, Nahigian SJ, Medway JM, Aronowitz HL. Conservative surgical orthodontic adult rapid palatal expansion: sixteen cases. Am J Orthod 1984;86:207-13.
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