Bone-anchored maxillary protraction therapy in patients with unilateral complete cleft lip and palate: 3-dimensional assessment of maxillary effects

Introduction

The aim of this study was to 3-dimensionally assess the treatment outcomes of bone-anchored maxillary protraction (BAMP) in patients with unilateral cleft lip and palate.

Methods

The cleft group comprised 24 patients with unilateral cleft lip and palate and Class III malocclusion with mean initial and final ages of 11.8 and 13.2 years, respectively. The noncleft group comprised 24 noncleft patients with Class III malocclusion with mean initial and final ages of 11.9 and 12.9 years, respectively. Cone-beam computed tomography examinations were performed before and after BAMP therapy in both groups and superimposed at the cranial base. Three-dimensional displacements of maxillary landmarks were quantified and visualized with color-coded maps and semitransparent superimpositions. The t test corrected for multiple testing (Holm-Bonferroni method), and the paired t test was used for statistical comparison between groups and sides, respectively ( P <0.05).

Results

BAMP produced anterior (1.66 mm) and inferior (1.21 mm) maxillary displacements in the cleft group with no significant differences compared with the noncleft group. The maxillary first molars of the cleft group showed significantly greater medial displacement than did those in the noncleft group. The zygoma showed significantly greater lateral displacement at the cleft side compared with the noncleft side.

Conclusions

BAMP caused similar amounts of maxillary protraction in patients with and without unilateral cleft lip and palatem with discrete differences between the cleft side and the noncleft side.

Highlights

  • BAMP outcomes were assessed 3-dimensionally in patients with cleft lip and palate.

  • BAMP caused a symmetric maxillary protraction in patients with cleft lip and palate.

  • BAMP is a promising treatment to reduce the need for orthognathic surgery.

In patients with complete cleft lip and palate, maxillary growth is often compromised by the restrictive forces from the lip and palate repair. In unoperated patients with unilateral complete cleft lip and palate (UCLP), the maxilla is intrinsically retruded. Such maxillary retrusion is often more severe in operated patients, where the maxillary anteroposterior position decreases on average by 5.4° from 5 to 18 years of age. As a result, patients with cleft lip and palate often show a Class III skeletal pattern associated with anterior crossbite. The GOSLON index is a “reliable, robust, and simple mean” to assess the dental arch relationship for patients with UCLP, with scores from 1 to 5. Scores 1 and 2 represent, respectively, excellent and good dental arch relationships, requiring simple or no orthodontic treatment; score 3 describes a fair dental relationship, requiring a more complex orthodontic treatment, such as maxillary expansion and protraction to compensate for the sagittal and transversal discrepancies; and scores 4 and 5 show poor dental arch relationships and often need orthognathic surgery correction. An intercenter study showed that between 6 and 12 years of age, approximately 35% of the patients were classified as GOSLON index 3, 30% as GOSLON index 4, and only 6% as GOSLON index 5.

For years, the most common therapy for a maxillary deficiency in patients with complete cleft lip and palate with a mild discrepancy consisted of rapid maxillary expansion followed by facemask therapy for maxillary protraction. Over the past decade, new treatment protocols have been proposed aiming to control dental compensations and increase the amount of skeletal maxillary protraction with a facemask. Bone anchorage has also been used to substitute conventional dental anchorage for maxillary protraction with a facemask in patients with clefts.

Recent studies have shown marked skeletal changes after bone-anchored maxillary protraction (BAMP) in noncleft Class III patients. Therefore, the purpose of this study was to 3-dimensionally assess maxillary changes with BAMP therapy in patients with UCLP. The null hypothesis was that no differences are observed for maxillary outcomes in patients with UCLP compared with noncleft subjects.

Material and methods

Institutional research ethics committee approval was obtained from the University of Michigan. The sample size calculation was based on preliminary statistics including the first 10 patients of the experimental group. For a standard deviation of 1.49 mm and a minimal intergroup difference of 1.5 mm to be detected, a sample of 17 patients was required to provide statistical power of 80% with an alpha of 0.05.

The cleft group (CG) consisted of 24 patients with UCLP and maxillary retrusion, treated consecutively at the Hospital for Rehabilitation of Craniofacial Anomalies, University of São Paulo. The CG was prospectively treated, and the inclusion criteria were age between 10 and 13 years old, clinical presence of the mandibular permanent canines, secondary alveolar bone graft at least 3 months before the miniplates were installed, and maxillary deficiency varying from moderate to severe (GOSLON index, 3-5). The exclusion criteria were patients with syndromes and bad initial oral hygiene. The comparison noncleft group (NCG) consisted of secondary data analysis of 25 Class III patients without cleft lip and palate, consecutively treated with BAMP therapy in a private practice in Brussels, Belgium. The samples are described in Table I .

Table I
Sample description
Group n (cleft side right/left) Male/female Mean (SD) age at T1 CBCT Mean (SD) age at T2 CBCT Wits appraisal mean (SD)
CG 24 (6/18) 17/7 11.8 y (±9 mo) 13.2 y (±8 mo) −7.13 mm (3.13)
NCG 24 10/15 11.9 y (±14 mo) 12.9 y (±16 mo) −4.8 mm (2.8)

In the CG, miniplates were installed bilaterally at least 3 months after the secondary alveolar bone graft procedure using recombinant human bone morphogenetic protein-2 (Medtronic; Fridley, Minnesota); 3 months was the mean time for new bone formation in the cleft region. Maxillary miniplates were installed in the infrazygomatic crest, and mandibular miniplates were installed between the permanent lateral incisor and the canine, as described by de Clerck et al ( Fig 1 ). Three weeks after the miniplates were placed, the patients were instructed to wear the intermaxillary elastics (G&H Orthodontics, Franklin, Ind) full time, connecting the maxillary and mandibular miniplates. When decomposed, the force vector would not only have anterior and inferior directions, but also a lateral direction because the distance between the right and left miniplates was greater in the maxilla than in the mandible, showing a lateral component in the posterior region of the maxilla, where the miniplates were installed. The force of the elastics was measured bilaterally and started with 75 g in each side in the first month, 150 g in the second month, and 250 g from the third month to the end of active treatment, similar to the protocol previously described for patients without oral clefts. The patients were instructed to wear the elastics 24 hours per day and replace them twice a day: early morning and night. Elastics were worn during meals. No facemask was used during BAMP treatment.

Fig 1
Anterior and lateral intraoral photos of the installation of intermaxillary elastics in a patient in the CG.

Cone-beam computed tomography (CBCT) examinations were obtained before (T1) and after (T2) treatment with intervals of 18 and 12 months for the CG and the NCG, respectively. In the CG, 2 patients were lost during the follow-up because of treatment interruption, 1 patient was excluded due to maxillary miniplate instability and recurrent bad oral hygiene, and 1 patient was excluded due to movement artifacts during the CBCT examination. The study sample consisted then of 20 patients in the CG. One patient was excluded from the NCG for missing CBCT data.

Three-dimensional surface models were created from the DICOM files in 6 steps.

  • 1.

    Create a volumetric label map: using ITK-SNAP, an open-source software (version 2.4.0; www.itksnap.org ), the cranial base and the maxilla were segmented for the T1 and T2 scans.

  • 2.

    Create a virtual 3-dimensional (3D) surface model: using 3D Slicer (version 4.4; www.slicer.org ), another open-source software, the virtual 3D surface models were created from the T1 and T2 volumetric label maps.

  • 3.

    Head orientation: the 3D coordinate system of the 3D Slicer was kept fixed to be used as a reference to consistently orient the 3D models of all patients. Using axial, coronal, and sagittal views of the 3D models, the T1 model was moved to match the midsagittal plane (defined by glabella, crista galli, and basion) vertically and coincident to the sagittal plane of the 3D coordinate system. The Frankfort horizontal plane was oriented to match the axial plane, and the horizontal infraorbitale (most inferior point of the left and right orbitals) line was oriented to be coincident to the coronal plane.

  • 4.

    Three-dimensional cranial base superimposition: the 3D superimposition registered in the cranial base was performed in 2 steps. Using 3D Slicer, the T2 scan was manually approximated to the T1 oriented scan, and using the anterior cranial fossa label map as a best fit reference, a fully automated voxel-based registration was performed in 3D Slicer. The matrix generated from the registration of T2 over T1 was applied to the T2 scan, volumetric label map, and 3D surface model also in 3D Slicer.

  • 5.

    Landmark identification: landmarks were placed at the T1 and T2 surface models using the Q3DC tool in the 3D Slicer software as shown in Table II and Figure 2 .

    Table II
    Description of the landmarks
    Maxillary central incisor Landmark placed at the center of the clinical crown of the noncleft side maxillary central incisor (CG) or the right central incisor (NCG).
    A-point (A) Landmark placed at the most posterior point of the concavity of the anterior region of the maxilla, as in the cephalometric analysis; it should be seen in both left and right views.
    Orbitale (Or) Landmarks placed at the most inferior point of the left and right orbitals.
    Infraorbital foramen (IOF) Landmarks placed at the entrance of the right and left infraorbital foramina.
    Zygomatic (Zyg) Landmarks placed in the most inferior portion of the inferior border of the right and left zygomatic bones.
    Maxillary permanent first molar (U6) Landmarks placed at the buccal-mesial occlusal cusp of the right and left permanent first molars.

    Fig 2
    Landmarks placed in the 3D surface model: (1) A-point (A); (2) center of the central incisor on the noncleft side or the right central incisor of the NCG (U1); (3) and (4) right and left infraorbitale points (Or); (5) and (6) right and left infraorbital foramina (IOF); (7) and (8) right and left inferior points of the zygomatic bone (Zyg); (9) and (10) mesial buccal cusps of the permanent first molar on the right and left sides (U6).
  • 6.

    Quantitative measurements: 3D linear distances and the amount of directional changes in each plane of 3D space (x, y, and z: respectively the mediolateral, anteroposterior, and superoinferior axes) were measured between corresponding coordinates of landmarks placed in the T1 and registered T2 surface models. Anterior, inferior, and lateral displacements were considered positive values; posterior, superior, and medial displacements were considered negative values. Color-coded surface distance maps and semitransparent superimpositions were used to visually demonstrate the overall maxillary changes in the CG.

Statistical analysis

Intraclass correlation coefficients (ICC) with a confidence level of 95% were used in 10 patients randomly selected from both group to assess the reproducibility of the x, y, and z coordinates of the landmarks placed at T1 and T2.

The statistical analysis was performed with the SPSS Statistical Software Package (version 21.0; IBM, Armonk, NY). Average values from the right and left sides were determined for all bilateral anatomic points. All variables showed normal distributions with the Kolmogorov-Smirnov test. Intergroup comparisons were performed with independent t tests corrected for multiple testing (Holm-Bonferroni method). The comparison between cleft and noncleft sides was performed using dependent t tests. The level of significance was set at 0.05.

Results

Very good intraexaminer agreement was observed. The ICC result for each variable is shown in Table III .

Table III
Intraexaminer results from the ICC test
x y z 3D
U1 0.97 1.00 0.77 0.95
A 0.80 0.96 0.98 0.94
Or.R 0.99 0.87 0.79 0.82
Or.L 0.86 0.82 0.91 0.83
IOF.R 0.87 0.92 0.83 0.95
IOF.L 0.90 0.85 0.93 0.89
Zyg.R 0.76 0.87 0.94 0.84
Zyg.L 0.78 0.83 0.96 0.89
U6.R 0.92 0.89 0.96 0.97
U6.L 0.91 0.94 0.86 0.92
3D , 3-dimensional; R , right; L , left.

The mean values, standard deviations, and statistical comparisons between the CG and NCG are given in Tables IV and V . A statistically significant difference between the CG and the NCG was found only for the first molar: the CG showed a medial displacement of 0.10 mm (0.76), and the NCG showed a lateral displacement of −0.76 mm (0.83) ( Table IV ).

Table IV
Descriptive (means and standard deviations) and statistical analyses of the comparison between the CG and the NCG
Landmarks Medial-lateral plane (x) (mm) Anteroposterior plane (y) (mm) Superior-inferior plane (z) (mm) Total linear displacement (3D) (mm)
CG group NCG group CG group NCG group CG group NCG group CG group NCG group
Mean (SD) Mean (SD) Mean (SD) Mean (SD) Mean (SD) Mean (SD) Mean (SD) Mean (SD)
Central incisor −0.48 (1.50) −0.28 (1.10) 2.98 (2.11) 3.50 (2.18) 0.84 (1.52) 1.76 (1.32) 3.89 (1.85) 4.50 (1.62)
P = 0.627 P = 0.437 P = 0.043 P = 0.266
A-point −0.36 (1.07) −0.32 (1.19) 1.66 (1.54) 2.37 (1.83) 1.21 (1.64) 0.63 (1.43) 2.61 (1.89) 3.20 (1.59)
P = 0.906 P = 0.173 P = 0.220 P = 0.283
Orbitale 0.45 (0.54) 0.38 (0.58) 1.30 (0.67) 1.36 (0.98) 0.56 (0.67) 0.34 (0.81) 1.77 (0.83) 1.83 (0.96)
P = 0.670 P = 0.817 P = 0.338 P = 0.806
Infraorbitale foramen 0.17 (0.72) −0.20 (0.75) 1.70 (1.20) 1.44 (1.24) 0.69 (0.91) 0.58 (1.03) 2.47 (0.99) 2.24 (1.10)
P = 0.085 P = 0.408 P = 0.809 P = 0.436
Zygomatic 0.41 (0.79) 0.55 (0.81) 1.63 (0.93) 1.77 (1.21) 1.38 (1.24) 1.27 (1.05) 2.61 (1.06) 2.76 (0.95)
P = 0.573 P = 0.661 P = 0.761 P = 0.639
First molar −0.76 (0.83) 0.10 (0.76) 3.21 (1.63) 3.27 (1.71) 2.08 (1.41) 2.26 (1.09) 4.31 (1.65) 4.41 (1.38)
P = 0.001 P = 0.904 P = 0.628 P = 0.840
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Dec 19, 2018 | Posted by in Orthodontics | Comments Off on Bone-anchored maxillary protraction therapy in patients with unilateral complete cleft lip and palate: 3-dimensional assessment of maxillary effects
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