Introduction
The objective of this study was to evaluate whether the success or failure of miniscrew-assisted rapid palatal expansion (MARPE) in patients with advanced bone maturation could be related to factors such as midpalatal suture density (MPSD), midpalatal maturation stage (MPSM), midpalatal bone thickness (MBTh), palatal length (PL), expander screw position (ESP), and patient’s age.
Methods
Cone-beam computed tomography scans of 25 patients of both sexes, aged 15-37 years (23 ± 7.2), presenting transverse maxillary deficiency and complete skeletal maturation (cervical vertebral maturation stage 5) treated using MARPE were evaluated. The success of MARPE was confirmed by the midpalatal suture opening and failure when no opening or limited separation of midpalatal suture occurred. Data were analyzed using t test for independent samples for differences in the variables of success and failure cases and the Pearson correlation test to evaluate the relation of the success and age, ESP, MPSD, MPSM, PL, and MBTh.
Results
Age, MPSM, and MBTh at 12 mm and 16 mm presented statistically significant results ( P <0.05). The older the patient with advanced bone maturation, the lower the success rates of MARPE (94.1%, 90%, and 76% for 25, 30, and 37 years, respectively). The ESP had similar averages in cases of success (15.34 mm) and failure (13.51 mm). There was no correlation between ESP, MPSD, MPSM, or PL and MARPE success.
Conclusions
MARPE success was related to age and a greater MBTh at 12 mm and 16 mm.
Highlights
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The success rate of midpalatal suture opening with MARPE decreases with age.
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The MARPE success rate is 94.1% up to age 25 years, decreasing to 76% at age 37 years.
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Greater midpalatal bone thickness is found 12-16 mm behind the incisor foramen.
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Bone thickness is a factor in the success of midpalatal suture opening with MARPE.
Rapid maxillary expansion (RME) is the standard treatment method for patients presenting transverse deficiency of the maxillary bone. In this treatment modality, expanders are used to apply lateral forces to the teeth, which increases the perimeter of the arch and disarticulates the midpalatal suture (MPS). Later, a reorganization at the suture occurs by connective tissue repair and bone formation. ,
Previous studies have shown that about 10% of the total population and 30% of adult orthodontic patients have some transverse maxillary deficiency related to a posterior crossbite. MPS disarticulation can be easily achieved in young children; meanwhile, in adult patients, this suture presents increasingly complex interdigitation, which makes it more challenging to split. Both midpalatal and circummaxillary sutures initiate the ossification process approximately in late adolescence and become more rigid with advancing age. , When performing maxillary expansion in patients with more advanced bone maturation, widening of the maxillary width tends to result in greater alveolar bone flexion and dental inclination. In addition, associated undesirable effects may include buccal alveolar fenestrations, no MPS split, alveolar bending, extrusion of posterior teeth, pain, instability, and root resorption.
Miniscrew-assisted rapid palatal expander (MARPE) technique reported by Lee et al emerged as a clinically effective and stable approach for nonsurgical correction of transverse discrepancy in adult patients. , Clinical studies have been demonstrating successful results using MARPE in adults. , However, in some patients with MARPE, orthopedic maxillary expansion may not occur. It is still unclear the reasons related to MARPE failure, but differences in calcification patterns of the MPS and craniofacial architecture (higher resistance) may play a role as contributing factors. ,
A retrospective clinical study by Choi et al showed as age increases, the amount of dentoalveolar expansion tended to be greater in relation to the orthopedic effects of maxillary expansion. The authors stated that, in older patients, the rigidity of the craniofacial skeleton could limit the skeletal effects of MARPE. Therefore, the predictability of success should be well explained to the patient because MARPE is still susceptible to failure.
In clinical practice, it is difficult to predict the success of MARPE in adult patients. A method to maximize the effects of the MARPE technique in clinical situations has not been fully studied. In this sense, it seems relevant to study the factors that may be associated with the success or failure of the MPS opening in these patients to better predict the outcome of the expansion procedure.
This research aimed to evaluate whether the success or failure of MARPE in patients with advanced bone maturation is related to factors such as midpalatal bone density (MPSD), maturation stage (MPSM), palatal length (PL), bone thickness (MBTh), expander screw position (ESP), and patient’s age.
Material and methods
The sample used for this retrospective controlled study included cone-beam computed tomography (CBCT) scans of 25 patients aged between 15 and 37 years (mean, 23 ± 7.02), treated with MARPE. Table I shows the sample distribution.
| Treatment effect | Sex | Age | MPSM stage | MIF | PP | AP | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| n | Mean | SD | Min | Max | B | C | D | E | Mean | SE | Mean | SE | Mean | SE | ||
| Success | Male | 7 | 15 | 26 | 2 | 1 | 1 | 3 | ||||||||
| Female | 12 | 15 | 34 | 1 | 4 | 3 | 4 | |||||||||
| Both | 19 | 20.6 | 5.32 a | 15 | 34 | 3 | 5 | 4 | 7 | 2.83 a | 0.27 | 2.70 a | 0.20 | 3.47 a | 0.33 | |
| Failure | Male | 1 | 31 | 31 | 1 | |||||||||||
| Female | 5 | 17 | 37 | 2 | 3 | |||||||||||
| Both | 6 | 30.6 | 7.42 b | 15 | 34 | 2 | 4 | 0.47 b | 0.16 | 0.61 b | 0.20 | 0.71 b | 0.24 | |||
The inclusion criteria were CBCT’s before (T0) and after maxillary expansion (T1) of subjects presenting transverse maxillary deficiency with unilateral or bilateral posterior crossbite (a difference greater than 5 mm between the transverse distance of the palatal cusps of the maxillary first molars and the transverse distance of the first mandibular molars central sulcus) with complete skeletal maturation confirmed by examination of the cervical vertebrae. All subjects were in cervical vertebral maturation stage 5 of Hassel and Farman’s analysis modified by Baccetti, Franchi, and McNamara. Patients with previous orthodontic treatment, cleft lip and palate, and syndromic conditions were excluded. Four patients that met the inclusion criteria (success cases) were excluded because the MARPE appliance was in place on the initial tomographic evaluation, restricting the visualization of bone structures for measurements.
Patients were treated by RME using a hybrid expander device supported by 4 orthodontic miniscrews inserted paramedian to the MPS and attached to the molars (PecLab, Belo Horizonte, Minas Gerais, Brazil) ( Fig 1 ). MARPE positioning and miniscrew sizes were planned using initial CBCT images (T0), considering the bone thickness and the available palate space to accommodate the expander device.
All miniscrews were inserted manually with a manual contra-angle driver (PecLab). To measure the insertion torque, a torque wrench was used. All steps were performed by the same clinician (C.B.O.).
The activation protocol was two-fourth turn immediately after MARPE placement and two-fourth turn daily on the following days (one-fourth in the morning and one-fourth at night), varying from 14 to 18 days until full correction was achieved. After expansion, the expander screw was locked and kept in place, without activation, for the following 4 months.
CBCT scans before (T0) and after (T1) expansion were taken using the i-CAT Next Generation scanner (Imaging Sciences International, Hatfield, Pa) at these settings: 36 mA, 120 kV, exposure time of 7 seconds, voxel size of 0.25 mm, axial slice thickness of 0.5 mm, and scanning area of 23 × 17 cm. Data were exported in the digital image and communication in medicine format. All CBCTs were taken before bonding brackets or any other apparatus.
The success of the orthopedic expansion of the maxilla with MARPE was confirmed by the opening of the medial palatine suture observed by the separation of the two halves of the palatine process confirmed in the tomographic examination after the activation period. Treatment failure was defined when the separation of the MPS was not observed in the tomographic examination. In patients in which moderate MPS separation was observed anteriorly but the posterior portion of the palate did not show significant changes (≤ 1.0 mm), it was considered a limited result and included as a failure of the technique. Maxillary changes were obtained by the difference of the linear measurements achieved (T1 − T0). The images were oriented as Figure 2 , A-C, and the measure was made in axial slice (MIF, the measurement between infraorbital foramen; PP, lateral walls between the greater palatine foramina; AP, lateral walls of the incisive foramen). The measurements ( Table I ) were used to separate the samples by success and failure because the expansion values of success were statistically higher than failure.
Initial examinations (T0) of each patient were used to evaluate the MPSD ratio. CBCT images were oriented using Dolphin 3D software (Dolphin Imaging and Management Solutions, Chatsworth, Calif) to adjust the palatal plane in the sagittal and frontal views to yield an axial slice through the center and parallel to the hard palate.
After orientation, the scans were exported and saved in digital image and communication in medicine format. After that, gray density measurements were performed using Mimics software (version 21.0; Materialise, Leuven, Belgium), with a cut thickness of 0.5 mm. Average gray density values were determined following the protocol previously described in the study of Grünheid et al. Regions of the suture (GDs), soft palate (GDsp), and palatal process of the maxilla (GDppm) were defined ( Fig 2 ), and average gray density values were used to calculate the MPSD ratio by the following equation.
MPSDratio=GDs−GDspGDppm−GDsp
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