Cone-Beam Computed Tomographic Comparison of Surgically

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Published by Elsevier Inc on behalf of the American Association of Oral and Maxillofacial. Surgeons. J Oral Maxillofac Surg 73:499-508, 2015. *Private Practice ...
CRANIOMAXILLOFACIAL DEFORMITIES/COSMETIC SURGERY

Cone-Beam Computed Tomographic Comparison of Surgically Assisted Rapid Palatal Expansion and Multipiece Le Fort I Osteotomy William Yao, DDS, MS,* Sona Bekmezian, DDS, MS,y Dan Hardy, DDS, MS,z Harvey W. Kushner, PhD,x Arthur J. Miller, PhD,k John C. Huang, DMD, DMSc,{ and Janice S. Lee, DDS, MD# Purpose:

To examine and compare the skeletal and dental effects of surgically assisted rapid palatal expansion (SARPE) and multipiece Le Fort osteotomy using cone-beam computed tomography (CBCT).

Materials and Methods:

This was a prospective cohort study. Patients underwent SARPE or multipiece Le Fort I osteotomy to address maxillary transverse deficiency. CBCT scans were taken preoperatively, immediately postoperatively or after retention, and at least 6 months postoperatively. Four landmark measurements and ratios of dental-to-skeletal change were used to follow skeletal and dental widths in the posterior and anterior maxillary regions. Wilcoxon signed-rank test and Wilcoxon 2-sample ranksum test were used to compare the landmark measurements and the ratio of dental-to-skeletal change for the 2 surgeries. A P value less than .05 was statistically significant.

Results:

Thirteen patients (mean, 28.3 yr old; 7 women) were enrolled: 9 were treated by multipiece Le Fort I osteotomy and 4 were treated by SARPE. The ratios of dental-to-skeletal expansion in the posterior maxilla for the Le Fort procedure and SARPE were 0.70  0.41 and 25.20  15.8, respectively, and the dental-to-skeletal relapses were 1.17  0.80 and 3.63  3.70, respectively. The ratios of dentalto-skeletal expansion in the anterior maxilla for the Le Fort procedure and SARPE were 0.58  0.38 and 31.80  59.4, respectively, and the dental-to-skeletal relapses were 2.25  3.41 and 4.86  8.10, respectively.

Conclusion:

There was greater correlation between dental and skeletal changes in the multipiece Le Fort procedure, indicating bodily separation of the segments, whereas the SARPE showed noteworthy dental and skeletal tipping. Dental relapse was greater than skeletal relapse for these 2 procedures. Published by Elsevier Inc on behalf of the American Association of Oral and Maxillofacial Surgeons J Oral Maxillofac Surg 73:499-508, 2015

*Private Practice, Saratoga, CA; Former Resident, Division of

This article was prepared while Dr Lee was employed at the

Orthodontics, Department of Orofacial Sciences, University of

University of California, San Francisco. The opinions expressed in

California, San Francisco, CA.

this article are the author’s own and do not reflect the view of the

yResident, Division of Orthodontics, Department of Orofacial

National Institutes of Health, the Department of Health and Human

Sciences, University of California, San Francisco, CA.

Services, or the United States Government.

zResident, Division of Orthodontics, Department of Orofacial

Conflict of Interest Disclosures: None of the authors reported any

Sciences, University of California, San Francisco, CA. xPresident and CEO, Biomedical Computer Research Institute,

disclosures. Address correspondence and reprint requests to Dr Lee: NIDCR/

Philadelphia, PA.

NIH, 10 Center Drive, Building 10, Room 5-2531 (North East

kProfessor, Division of Orthodontics, Department of Orofacial

Atrium), Bethesda, MD 20892-1470; e-mail: [email protected]

Sciences, University of California, San Francisco, CA.

Received February 16 2014

{Private Practice, Moraga, CA; Associate Health Science

Accepted August 19 2014

Professor, Division of Orthodontics, Department of Orofacial

Published by Elsevier Inc on behalf of the American Association of Oral and Maxil-

Sciences, University of California, San Francisco, CA.

lofacial Surgeons 0278-2391/14/01373-1

#Deputy Clinical Director, National Institute of Dental and

http://dx.doi.org/10.1016/j.joms.2014.08.024

Craniofacial Research, National Institutes of Health, Bethesda, MA.

499

500 Rapid palatal expansion with or without surgery is an important treatment tool to treat maxillary transverse deficiency (MTD), which can include a posterior crossbite, an omega-shaped occlusion, and a high palatal vault.1,2 The age of the patient and a fused palatal suture may require the inclusion of surgery in the treatment.3,4 When the MTD exceeds 5 mm, surgical assistance may be necessary for skeletally mature patients.5,6 Surgical options include a multipiece Le Fort osteotomy or a surgically assisted rapid palatal expansion (SARPE).7 Marchetti et al8 examined outcomes between patients receiving a SARPE (n = 10) and those receiving a segmental Le Fort I osteotomy (n = 10) using plaster models to evaluate the adult patient before expansion, immediately after expansion, and 2 years after expansion. The intermolar distance increased by 7 mm with SARPE and then decreased over 2 years by 3 mm (36% relapse), whereas the Le Fort I osteotomy increased the molar distance by 3.8 mm, which then decreased by 0.8 mm (20% relapse) over 2 years. A 2-dimensional study by Chamberland and Proffit9 provided long-term evaluation extending 2 years after SARPE using posteroanterior cephalograms and dental casts. The mean maximum expansion at the first molar was 7.6 mm with a mean relapse of 1.8 mm (24%). They noted that approximately half the expansion was skeletal (46%). Other studies have shown similar results.10-12 Three-dimensional (3D) imaging, particularly with cone-beam computed tomography (CBCT), has provided a new method for assessing the amount of sutural separation and regions of greatest relapse after rapid maxillary expansion. Lagravere et al13,14 used 3D CBCT images to compare transverse, vertical, and anteroposterior changes between a bone-anchored and a traditional tooth-anchored rapid maxillary expansion. The 2 approaches produced similar results, with the greatest changes in the transverse plane and minimal effects in the vertical and anteroposterior dimensions. Garrett et al15 used CBCT to evaluate the effect of rapid maxillary expansion using a Hyrax appliance in children (mean, 13.8 yr old) and found that transverse expansion can occur by separation of the palatal suture (38%), bending or tipping of the palate (13%), and buccal tipping of the dentition (49%). CBCT studies with surface-rendered volumetric images also have shown that palatal expansion is greatest anteriorly and decreases posteriorly.16 The purpose of this study was to examine and compare the dental and skeletal changes between SARPE and multipiece Le Fort I osteotomy to correct maxillary transverse deficiencies using 3D imaging. The specific aim was to determine whether dental and skeletal movements correlate at the time of sur-

SARPE VERSUS LE FORT I OSTEOTOMY BY CBCT

gery and during relapse. The authors hypothesized that the multipiece Le Fort procedure would produce more expansion skeletally than dentally compared with the SARPE approach and that the 2 groups would have more dental relapse than skeletal relapse.

Materials and Methods STUDY DESIGN AND PATIENTS

The authors designed and implemented a prospective longitudinal study. The study population was composed of patients presenting for the evaluation and management of skeletal MTD from August 2008 through August 2010. Patients were included if they were diagnosed with skeletal MTD through clinical examination, cephalograms or CBCT, and diagnostic casts, and required surgical expansion of the maxilla. Patients were excluded if they were missing the required set of CBCT scans, had a craniofacial anomaly that could alter the effects of expansion, or previous surgery. This study was approved by the University of California–San Francisco committee on human research (institutional review board number 10-00564). The authors of this study obtained informed consent from all patients. Patients underwent a 2- or 3-piece Le Fort I osteotomy or a SARPE by the faculty of the department of oral and maxillofacial surgery to correct the MTD. Patients obtained CBCT scans at 3 time points: preoperatively (T0), within 1 month postoperatively (T1), and at least 6 months postoperatively (T2) for patients undergoing a multipiece Le Fort I osteotomy and preoperatively (T0), after expansion in retention (T1), and at least 6 months after expansion (T2) for patients undergoing a SARPE. SURGICAL PROTOCOLS

At the authors’ institution, for skeletally mature patients, the algorithm of treatment includes using nonsurgical orthopedic maxillary expansion for transverse discrepancies up to 3 mm, and surgical assistance for those greater than 3 mm, particularly when a maxillary osteotomy is already part of the overall treatment plan (for other planar discrepancies, ie, vertical or sagittal). For transverse discrepancies from 3 to 6 mm, a 2- or 3-piece Le Fort I osteotomy is considered, whereas a SARPE is considered when the transverse discrepancy is greater than 6 mm owing to the anatomic limitations of expanding the maxilla during a Le Fort I osteotomy and the concern for greater relapse with a Le Fort I osteotomy for larger transverse discrepancies. LE FORT I OSTEOTOMY

All patients received presurgical orthodontic treatment consisting of full-fixed orthodontic appliances.

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Before surgery, a CBCT scan was taken (T0). The surgical technique consisted of lateral maxillary osteotomies from the piriform aperture to the zygomatic buttress with separation along the septum, lateral nasal walls, and pterygomaxillary fissure and complete downfracture of the maxilla. The multipiece osteotomy was performed between the central incisors for a 2-piece procedure or between the canines and first premolars for a 3-piece Le Fort I procedure. A parasagittal osteotomy was made along the palate behind the nasopalatine foramen to complete the multipiece Le Fort I osteotomy. The segments were confirmed to be mobile and separated. Patients obtained maxillary transverse expansion guided by an intraoperative surgical splint. Stabilization of segments was achieved by rigid fixation using 4 titanium plates. The patients were kept in intermaxillary fixation with elastics for 2 to 3 weeks after surgery. Postoperative stabilization of the maxilla included continuous use of an acrylic surgical splint for 6 to 8 weeks. The surgical splints were made using the model surgical technique on a fully adjustable dental articulator. After surgery, a patient returned for a postoperative CBCT scan within 1 month of surgery (T1). A third CBCT scan was taken at least 6 months after surgery (T2). The patient continued with full-fixed orthodontic treatment during this period and was monitored by the department of oral and maxillofacial surgery at follow-up visits. SURGICALLY ASSISTED RAPID MAXILLARY EXPANSION

Patients were fitted with a tooth-borne Hyrax expander before surgery. The expander consisted of an expansion screw with 4 0.05-inch stainless steel arms soldered to 4 stainless steel bands fitted to the maxillary first premolars and first molars. The expander was cemented in place using common light-cured glass ionomer-resin cement. A 0.036-inch stainless steel wire was placed lingual to the dentition to add rigidity and to extend the expansion to include the maxillary canines and second molars when present. A CBCT was taken before surgery (T0). The surgical technique consisted of lateral maxillary osteotomies from the piriform aperture and posterior to the zygomatic buttress with separation of the lateral nasal walls to the descending palatal neurovascular bundle. A midline osteotomy between the central incisors to the posterior nasal spine using 6-mm or spatula osteotomes was performed blindly without downfracture of the maxilla. Intraoperatively, the expansion appliance was activated to achieve a 1- to 2-mm separation at the maxillary central incisors. A latency period of typically 5 days was observed, after which patients were instructed to activate the expansion screw 4 times a day (2 turns in the morning and 2 turns

Table 1. SKELETAL AND DENTOALVEOLAR MEASUREMENTS

Posterior dentoalveolar width

Anterior dentoalveolar width

Posterior skeletal width

Anterior skeletal width

Definition of ratios Expansion (%)

Relapse (%)

Relapse rate (%)

measured from the medial of the left maxillary first molar crown to the medial of the right maxillary first molar crown measured from the medial of the left maxillary canine crown to the medial of the right maxillary canine crown measured from the most posterior point of the greater palatine canal in the axial view at the level of the nasal floor, bilaterally measured from the left recess point to the right recess point of the piriform rim expansion (mm) from T0 to T1 vs presurgical width at T0 relapse (mm) from T1 to T2 vs postexpansion width at T1 relapse (mm) from T1 to T2 vs expansion (mm) from T0 to T1

Abbreviations: T0, preoperatively; T1, immediately postoperatively (Le Fort) or 1 month after expansion (SARPE); T2, at least 6 months postoperatively. Yao et al. SARPE Versus Le Fort I Osteotomy by CBCT. J Oral Maxillofac Surg 2015.

in the evening, 0.25 mm per turn). Patients were monitored weekly until the desired expansion was achieved. The expansion device was kept in place for approximately 3 times the duration of the activation period and until full-fixed orthodontic brackets were bonded and orthodontic treatment was initiated on the maxillary teeth. When expansion was complete, a CBCT scan was taken during the retention period (T1). The patient returned for a third scan 6 months beyond the retention period (T2). CONE-BEAM COMPUTED TOMOGRAPHY

A Hitachi CB MercuRay (Hitachi Medical Corporation, Tokyo, Japan) was used for all patient scans. The machine was set to capture images at the manufacturer’s recommended settings of 15 mA and 120 kVp. All patients were positioned in an upright seated position,

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SARPE VERSUS LE FORT I OSTEOTOMY BY CBCT

FIGURE 1. A-C, Multiplanar views of the greater palatine canals and measurements made at the level of the nasal floor and point of exit. Yao et al. SARPE Versus Le Fort I Osteotomy by CBCT. J Oral Maxillofac Surg 2015.

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FIGURE 2. A, Sagittal view depicting identification of the furcation of the maxillary first molar and height of contour. B, Axial view showing measurement of intermolar width. Yao et al. SARPE Versus Le Fort I Osteotomy by CBCT. J Oral Maxillofac Surg 2015.

with their head stabilized against a headrest. The technician ensured that the scan was generated in a natural head position by having the patient look into his or her own eyes in a mirror directly in front of the machine. Patients were asked to close their teeth into occlusion and hold their breath with their tongue to the palate. Table 2. PATIENT DATA

Patient data for Le Fort I group 1 2 3 4 5 6 7 8 9 F/M Patient data for SARPE group 1 2 3 4 F/M

Gender

Age at Surgery (yr)

F M F F F M M M M 4/5

18.3 43.8 19.3 34.2 18.9 45.3 34.7 17.1 23.8 avg, 28.4

F M F F 3/1

18.5 18.1 17.0 23.2 avg, 19.2

Abbreviations: avg, average; F, female; M, male; SARPE, surgically assisted rapid palatal expansion. Yao et al. SARPE Versus Le Fort I Osteotomy by CBCT. J Oral Maxillofac Surg 2015.

EVALUATING SKELETAL AND DENTAL EXPANSION AND RELAPSE

From a pilot study, 2 skeletal measurements and 2 dental measurements were selected to be used in this study to represent transverse skeletal changes and transverse intra-arch dental changes owing to their ease of identification and reproducibility (Table 1). The skeletal measurements chosen were the greater palatine superior intercanal width in the axial view to represent the posterior width of the maxilla (posterior skeletal; Fig 1) and the piriform base width to represent the anterior width (anterior skeletal). The dental measurements selected were the intermolar width of the first molar to represent posterior dental change (Fig 2) and the intercanine width to represent anterior dental change. Although these dental landmarks have been used extensively in previous studies to represent maxillary width changes, their use in a 3D CBCT analysis was confirmed statistically for use in the present study. STATISTICAL ANALYSIS

In this study, the predictor variable was the operation to manage the transverse discrepancy and is a binary variable grouped as SARPE versus multipiece Le Fort I osteotomy. The primary outcome variables were changes in 2 skeletal and dental measurements over time. Age and gender were not evaluated as separate variables. A Wilcoxon signed-rank test was used to evaluate the statistical significance of the reported outcome values. A Wilcoxon 2-sample rank-sum test was used to compare the ratio of dentoalveolar-to-skeletal change in the Le Fort and SARPE groups. All statistical analysis was

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SARPE VERSUS LE FORT I OSTEOTOMY BY CBCT

FIGURE 3. A, Posterior and B, anterior skeletal changes in the SARPE and Le Fort groups compared at T0, T1, and T2. D, difference; SARPE, surgically assisted rapid palatal expansion; T0, preoperatively; T1, immediately postoperatively (Le Fort) or 1 month after expansion (SARPE); T2, at least 6 months postoperatively. Yao et al. SARPE Versus Le Fort I Osteotomy by CBCT. J Oral Maxillofac Surg 2015.

performed by 1 author (H.W.K.) using the SAS system (SAS Institute, Cary, NC). A P value less than .05 was considered statistically significant.

Results Thirteen patients (7 female, 6 male) were recruited for the study from the department of oral and maxillofacial surgery (Table 2). Nine patients (4 female, 5 male) underwent a multipiece Le Fort I osteotomy and 4 patients (3 female, 1 male) underwent a SARPE. The mean age for the Le Fort group was 28.4 years (17.1 to 45.3 yr). The mean age for the SARPE group was

19.2 years (17.0 to 23.2 yr). No surgical or orthodontic complications occurred during the study period. The average intervals from T0 to surgery, surgery to T1, and T1 to T2 for the Le Fort group were 9, 13, and 243 days, respectively. The average intervals from T0 to surgery, postexpansion to T1, and T1 to T2 for the SARPE group were 77, 13, and 243 days, respectively. The average expansion duration for the SARPE was 28.5 days. SKELETAL CHANGES IN LE FORT AND SARPE GROUPS

All patients showed an increase in posterior and anterior skeletal width from T0 to T1 (Fig 3). The Le

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Table 3. SUMMARY OF WIDTH CHANGES IN GROUP WITH LE FORT I OSTEOTOMY

Mean Expansion Posterior skeletal change

absolute (mm) relative expansion (%)

P Value 3.43  1.24 11.57  4.31

z z

Anterior skeletal change

absolute (mm) relative expansion (%)

1.94  0.93 9.95  5.01

z

Intermolar width

absolute (mm) relative expansion (%)

2.17  0.90 6.76  2.98

z

1.01  0.68 4.44  3.30

y

Intercanine width

absolute (mm) relative expansion (%)

z

z

y

Mean Relapse absolute (mm) relative relapse (%) relapse rate (%) absolute (mm) relative relapse (%) relapse rate (%) absolute (mm) relative relapse (%) relapse rate (%) absolute (mm) relative relapse (%) relapse rate (%)

P Value z

0.86  0.42 2.57  1.16 26.0  13.3 0.55  0.55 2.51  2.54 24.6  16.1 0.77  0.38 2.25  1.13 37.9  13.2 0.39  0.24 1.60  1.01 43.0  21.8

z z

* * y z z z y y y

* Statistically significant at P < .05. y Statistically significant at P < .005. z Statistically significant at P < .0005. Yao et al. SARPE Versus Le Fort I Osteotomy by CBCT. J Oral Maxillofac Surg 2015.

Fort group had a mean posterior expansion of 3.43  1.24 mm (P < .0005; 11.6  4.3%; Table 3). There was greater variation in the amount of expansion in the anterior maxilla compared with the posterior maxilla. The Le Fort group had a mean anterior expansion of 1.94  0.93 mm (P < .0005; 10.0  5.0%). The SARPE group had a mean posterior expansion of 0.50  0.24 mm (P < .05; 1.7  0.8%; Table 4) and a mean anterior expansion of 2.25  1.79 mm (10.2  7.7%), although this expansion was not statistically meaningful. From T1 to T2, the Le Fort group had a mean posterior relapse of 0.86  0.42 mm (P < .0005; 2.6  1.2%) and showed a mean anterior relapse of 0.55 

0.55 mm (P < .05; 2.5  2.5%) in skeletal width. From T1 to T2, the SARPE group had a mean increase in posterior skeletal width of 0.80  0.54 mm (2.7  1.9%) and had an anterior skeletal relapse of 0.74  0.63 mm (2.9  2.3%); however, these changes were not statistically meaningful. DENTAL CHANGES IN LE FORT AND SARPE GROUPS

The Le Fort group showed a mean increase of 2.17  0.90 mm (P < .0005; 6.8  3.0%) at the molars and a mean increase of 1.01  0.68 mm (P < .005; 4.4  3.3%) at the canines from T0 to T1 (Fig 4, Table 3).

Table 4. SUMMARY OF WIDTH CHANGES IN GROUP WITH SURGICALLY ASSISTED RAPID PALATAL EXPANSION

Mean Expansion

P Value

Mean Relapse absolute (mm) relative relapse (%) relapse rate (%) absolute (mm) relative relapse (%) relapse rate (%) absolute (mm) relative relapse (%) relapse rate (%) absolute (mm) relative relapse (%) relapse rate (%)

Posterior skeletal change

absolute (mm) relative expansion (%)

0.50  0.24 1.71  0.82

* *

Anterior skeletal change

absolute (mm) relative expansion (%)

2.25  1.79 10.2  7.71

NS NS

Intermolar width

absolute (mm) relative expansion (%)

10.0  1.40 35.7  8.39

z

Intercanine width

absolute (mm) relative expansion (%)

5.33  2.42 28.6  17.7

* *

y

Abbreviation: NS, not statistically significant. * Statistically significant at P < .05. y Statistically significant at P < .005. z Statistically significant at P < .0005. Yao et al. SARPE Versus Le Fort I Osteotomy by CBCT. J Oral Maxillofac Surg 2015.

P Value 0.80  0.54 2.71  1.90 146.9  81.8 0.74  0.63 2.93  2.29 32.5  32.5 1.86  1.75 4.81  4.51 18.4  16.4 0.56  0.38 2.26  1.64 12.7  12.7

NS NS * NS NS z

NS NS NS NS NS NS

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FIGURE 4. A, Intermolar and B, intercanine width changes in the SARPE and Le Fort groups compared at T0, T1, and T2. D, difference; SARPE, surgically assisted rapid palatal expansion; T0, preoperatively; T1, immediately postoperatively (Le Fort) or 1 month after expansion (SARPE); T2, at least 6 months postoperatively. Yao et al. SARPE Versus Le Fort I Osteotomy by CBCT. J Oral Maxillofac Surg 2015.

The SARPE group showed a significantly greater amount of dental expansion, with a mean increase of 10.0  1.40 mm (P < .0005; 35.7  8.4%) at the molars and a mean increase of 5.33  2.42 mm (P < .05; 28.6  17.7%) at the canines from T0 to T1 (Table 4). From T1 to T2, the Le Fort group showed a mean dental relapse of 0.77  0.38 mm (P < .0005; 2.25  1.13%) at the molars and a relapse of 0.39  0.24 mm (P < .005; 1.6  1.0%) at the canines. In the SARPE group, there was a mean relapse of 1.86  1.75 mm (not statistically different; 4.8  4.5%) at the molars and a relapse of 0.56  0.38 mm (not statistically different; 2.3  1.6 %) at the canines.

DENTAL AND SKELETAL EXPANSION AT SURGERY

In the posterior maxilla, the Le Fort group had a ratio of dental expansion to skeletal expansion of 0.70  0.41, indicating slightly greater skeletal change than dental change during surgical expansion (Table 5). The SARPE group had a ratio of 25.20  15.8, indicating significantly more dental expansion than skeletal expansion in the posterior maxilla after distraction was completed. This ratio was significantly greater than in the Le Fort group (P < .05). In the anterior maxilla, the Le Fort group had a ratio of dental expansion to skeletal expansion of 0.58  0.38, indicating approximately twice as much skeletal change

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Table 5. RATIO OF DENTAL-TO-SKELETAL CHANGE

Le Fort

SARPE

In the posterior maxilla 0.70  0.41 25.20  15.8 Dental expansion vs skeletal expansion 1.17  0.80 3.63  3.0 Dental relapse vs skeletal relapse In anterior maxilla Dental 0.58  0.38 31.80  59.4 expansion vs skeletal expansion Dental relapse 2.25  3.41 4.86  8.10 vs skeletal relapse

P Value

*

*

*

NS

Note: Values are presented as mean  standard deviation. Abbreviations: NS, not statistically significant; SARPE, surgically assisted rapid palatal expansion. * Statistically significant at P < .05. Yao et al. SARPE Versus Le Fort I Osteotomy by CBCT. J Oral Maxillofac Surg 2015.

than dental change. In the SARPE group, this ratio was 31.80  59.4, indicating significantly more dental change. This ratio was statistically significantly greater than in the Le Fort group (P < .05). DENTAL AND SKELETAL RELAPSE OVER TIME

The ratios of dental relapse to skeletal relapse in the posterior and anterior maxilla also were analyzed (Table 5). In the posterior maxilla, the Le Fort group had a ratio of dental-to-skeletal relapse of 1.17  0.80, indicating nearly equal relapse of the teeth and maxillary segments. The SARPE group had a ratio of 3.63  3.70, indicating a greater dental relapse than skeletal relapse. This negative ratio in the SARPE group was due to an increase (rather than relapse) in width from T1 to T2. The ratios of relapse were statistically significant (P < .05). In the anterior maxilla, the Le Fort group had a ratio of dental-to-skeletal relapse of 2.25  3.41, indicating more dental relapse than skeletal relapse. In the SARPE group, the ratio of dental-toskeletal relapse in the anterior maxilla was 4.86  8.10, also indicating more relapse in the dentition compared with the maxillary segments. The ratios of relapse between the 2 procedures for the anterior maxilla were not statistically different.

Discussion Direct comparison of absolute expansion in the Le Fort group versus the SARPE group is difficult owing to the inherent differences in the indications for

selecting one procedure over the other. For these reasons, ratios of dental expansion to skeletal expansion were used to contrast the relative changes in the 2 procedures as opposed to absolute descriptions. It was clear from the results that skeletal expansion at the time of surgery was achieved with the multipiece Le Fort osteotomy, whereas dental expansion was considerably greater in the SARPE procedure. In fact, there appeared to be little skeletal expansion at the designated landmarks with the SARPE, indicating important skeletal tipping of the maxillary segments with the landmarks being near the fulcrum points. It is important to note that tooth-borne, and not palatal boneborne, Hyrax devices were used in this study. The bone-borne devices may allow for greater skeletal expansion rather than dental expansion. The findings in the SARPE group are consistent with the results in previous studies, which have shown that the maxilla expands in a hinge-like fashion, with more expansion occurring anteriorly.17,18 Comparison of dental and skeletal changes using SARPE with and without pterygomaxillary disjunction showed some differences, but usually less than 1 mm between the 2 approaches.19 The SARPE procedure in the present study did not include separation at the pterygomaxillary junction, potentially limiting the posterior expansion. Interestingly, the authors observed initial restriction in the posterior region. However, by the follow-up CBCT (T2), there was continued posterior skeletal expansion. This has not been previously reported. In contrast to the SARPE, the multipiece Le Fort osteotomy showed greater posterior skeletal and dental expansion compared with the anterior region. Overall, the SARPE group exhibited more change at the level of the dentition than the skeletal landmarks during expansion and relapse, with an important differential occurring during expansion. The Le Fort group showed more skeletal change during expansion and more dental change during relapse, but the differences between the dental changes and skeletal changes were not as dramatic as the differences seen in the SARPE group. The findings in relapse are generally consistent with trends presented in the previous literature, with considerably more relapse occurring dentally.9,12,17,19,20 Using the 3D CBCT modality, the authors have defined a new method to assess changes in the maxilla using the greater palatine canal at the level of the nasal floor to view the posterior skeletal width and the width of the base of the piriform aperture for the anterior skeletal width. These 2 landmarks were highly reproducible and readily identifiable.7,21,22 From this study, the authors were able to appreciate the landmarks in various planar views that were reproducible and recommend scan orientation confirmation for CBCT

508 studies. CBCT imaging has allowed for analysis with 1 modality versus using plain radiographs with or without dental models for comparable analysis.23 In conclusion, 2 procedures were compared using newly defined landmarks evaluated on CBCT images. The multipiece Le Fort procedure produced more expansion skeletally than dentally, with a posterior and an anterior ratio of dental to skeletal expansion of 0.70 and 0.58, respectively. However, with the ratio closer to 1, the dental and skeletal changes correlated more closely with each other and represent bodily separation of the right and left segments. In contrast, with the SARPE procedure, considerably more expansion occurred dentally than skeletally, with a posterior and an anterior ratio of dental to skeletal expansion of 25.19 and 31.80, respectively. Thus, the dental and skeletal changes had very little correlation with each other and suggest significant dental and skeletal tipping rather than true bodily separation of the segments. In the 2 groups, relapse was more dental than skeletal, with the SARPE group showing a higher ratio of dental-to-skeletal relapse. Thus, the authors’ hypothesis that the multipiece Le Fort procedure would produce more expansion skeletally than dentally compared with the SARPE approach and that the 2 groups would have more dental relapse than skeletal relapse was proved to be true. Future studies will focus on further analysis of these 2 groups to determine the clinical impact of the degree of expansion on the surrounding alveolar bone and the degree of relapse on the stability of the occlusion. Long-term follow-up using this new 3D technique and landmarks will provide greater understanding of the natural progression after these 2 types of surgery.

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