Introduction
Rapid palatal expansion is a common therapy during orthodontic treatment and could be a preliminary step for correcting different malocclusions; furthermore, this treatment could be necessary at any age. Different anchorage approaches have been proposed to obtain an effective skeletal result, although every device produces both dental and skeletal effects. This study aimed to compare the dentoskeletal effects of a bone-borne palatal expander considering 2 groups of patients of different ages.
Methods
Twenty-four patients consecutively treated were included in the study; patients were divided into 2 groups according to their age: group 1 with age ≤16 years and group 2 patients >16 years. All patients had a preexpansion cone-beam computed tomography scan; a second scan was required at the end of activations. All patients received a bone-borne appliance anchored on 4 miniscrews.
Results
Significant intragroup differences were found for maxillary width and dental diameters. No significant differences were found between groups with regard to longitudinal changes, except for the maxillary right plane.
Conclusions
The use of bone-borne maxillary expansion was effective in generating palatal widening both in growing and young adult patients. No significant skeletal or dental differences were found between groups.
Highlights
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Bone-borne maxillary expansion was generated during palatal widening in adolescent patients.
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Bone-borne expansion was effective and had negligible dental effects.
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No significant skeletal or dental changes were observed between groups.
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Expansion geometry was similar among groups.
Maxillary transversal deficiency is a common problem affecting patients within various individual characteristics ; in fact, a maxillary expansion can be indicated for patients with skeletal Class I, Class II, and Class III malocclusion, and every time the palatal expansion becomes a therapeutic objective, it is well known that such an expansion affects both dental and skeletal components. The standard approach to setting up an orthodontic treatment starts from diagnosis, and through a consistent analysis of treatment objectives, force, and anchorage evaluations lead to the appliance design to obtain these results.
Maxillary expansion with dental support in growing patients can achieve both skeletal and dental movement, whereas the use of such an appliance in adult patients results in prevalent dental shifting. To avoid these undesired side effects, or alternatively, when a skeletal expansion is needed, maxillary expanders anchored on 2 or 4 miniscrews have been proposed. Miniscrews in the palate are considered efficient and safe support in terms of anchorage and success rate.
Miniscrew-supported expansion approaches can include a teeth-bone anchored device (hybrid), , or a completely skeletal anchorage without dental support (bone-borne). , Recently, different studies have been published on the potential of such an approach to obtain substantial skeletal effects in adult patients, but generally, these publications are limited to case reports or series.
A palatine suture maturation criterion has been proposed as a staging method to avoid the side effects of rapid maxillary expansion failure or unnecessary surgically assisted rapid maxillary expansion, and correspondence with cervical vertebral maturation (CVM) stages was investigated as well, showing that earlier CVM stages (cervical stage [CS] 1, CS 2, and CS 3) can be used as reliable indicators for the midpalatal maturational stages A, B, and C, whereas for postpubertal patients (CS 4 and CS 5) an individual assessment of the midpalatal suture with cone-beam computed tomography (CBCT) should be undertaken because fusion of the midpalatal suture already could have occurred partially or totally (stages D and E in midpalatal suture maturation). In the same study, it was found that the CVM method and chronological age were almost equally effective in predicting the midpalatal sutural stages, with the CVM method performing slightly better than chronological age.
The prediction capability of the palatal suture classification for dental and skeletal changes has been recently questioned, and a reliability testing in disagreement with that of the original study was reported. Moreover, the suture evaluation methodology was described as nonintuitive and influenced by the degree of postacquisition image sharpness and clarity.
There are different possible advantages to using a bone-borne device, such as the reduction of root resorption, bony dehiscence, and more physiological suture expansion, as Mosleh et al recently stated.
The present study aimed to compare the dental and skeletal effects of a bone-borne expander applied in 2 groups of consecutively treated patients, divided by chronological age.
Material and methods
This was a retrospective study of consecutively treated patients. The sample included a total of 24 patients, 12 males and 12 females. Patients were divided into 2 groups according to age: group 1 with age ≤16 years and group 2 with age >16 years. According to the age distribution, there were 11 patients in group 1 and 13 patients in group 2. The mean age was 13.9 (standard deviation [SD]) and 20.4 (SD) for groups 1 and 2, respectively.
Patients were treated from April 2018 to April 2020. Ethical committee approval was obtained by Genova University. The inclusion criteria were as follows: no systemic disease, no previous orthodontic treatment, no alteration of bone metabolism or use of drugs altering the bone metabolism, transverse maxillary deficiency with unilateral or bilateral posterior crossbite (10 unilateral crossbite, 6 bilateral crossbite, and 8 maxillary transversal deficiency without dental crossbite), permanent dentition including second molar eruption, no surgical or other treatment that might influence the rapid maxillary expansion outcome during the expansion period.
All patients underwent an orthodontic therapy in which the first step was a maxillary expansion, and a preinsertion CBCT scan was obtained. A second CBCT was required at the end of the activations.
To achieve the best miniscrew position in terms of bone quantity and considering the device design, digital insertion planning was performed. Intraoral scans were superimposed with the initial CBCT using a specific Dolphin software module (3-dimensional module; Dolphin Imaging & Management Solutions, Chatsworth, Calif), overlapping the model’s details to the dental-skeletal profile of the CBCT itself. The device used for the expansion includes 4 miniscrews: 2 in the anterior area of the palate, at the third ruga level, and 2 other miniscrews inserted between the second premolar and the first molar area, where the root distance is more favorable, approximately at a distance of 6-8 mm from the alveolar crest ( Fig 1 ).
If anatomic conditions prevented such an ideal position, an alternative extraradicular site was selected at the level of the second premolar between the nasal and sinus cortical.
All virtual insertion planning had the objective of obtaining a bicorticalism, exploiting the greatest bone availability, thus choosing the corresponding correct miniscrew length. Miniscrews used in the present study varied between 9 mm and 15 mm in length, while the diameter was 2 mm for all patients (Spider Screw; HDC, Thiene, Italy).
For each patient, 2 insertion guides were designed and 3-dimensionally printed (Form 2; Formlabs, Sommerville, Mass), including 2 sleeves each in a cross position, each guide allowing the insertion of 2 miniscrews ( Fig 2 ).
After a chlorhexidine gluconate oral rinse, a preliminary guide fitting check was performed, and thereafter, local anesthesia was applied in correspondence with the palatal insertion sites.
To improve procedure precision and surgery ergonomics, guides were fixed to the teeth using a fluid resin (trial gel; Dentsply GAC International, Islandia, NY); all the miniscrew insertions were preceded by pilot drill use for a cortical perforation. A dedicated pickup instrument was used to attain the correct depth stop indication planned with the digital insertion procedure. All screws were inserted with an insertion torque that was comprised between 15 and 30 Ncm using a low-speed handpiece. After the guide removal, the palatal surface was cleaned with a physiological solution, and the bone-borne expander was inserted. The insertion of a 4 miniscrew expander device can be difficult because of the different screw axis insertions (3 different axes) and because of the undercut generated by the posterior screws; the bone-borne expander was set with 0.8 mm expansion already inserted. The device was then completely closed, fit to the anterior screws, and reactivated until a complete passiveness of the structure was attained on all the screws. Thereafter, the fixation screws were screwed to the skeletal anchorage devices.
The activation protocol was 2 turns per day until reaching the desired expansion. The device remained for another 12 months after the end of the expansion for all patients ( Fig 3 ).
Data were analyzed by ITK-SNAP. To set an identical reference plane in the T1 and T2 stages, the CBCT images were oriented along the palatal suture (x-plane), parallel to the palatal plane (y-plane), and tangent to the nasal floor (z-plane).
The size of the CBCT (the number of cuts on the x-, y-, z-axes) and the volume of the voxels were changed to obtain isotropic voxels in all the examined CBCTs. The SlicerCMF4-1 program was used, and data were loaded in the Guys Imaging Processing Laboratory format. Using the downsize image–spacing function, voxels were set to the same size in the x-, y-, and z-axes.
All measurements were performed on the maxillary first premolar and molar area. Data acquisition and analysis were blinded with respect to the groups’ age.
Maxillary width was evaluated with linear measurements at different levels: nasal floor and hard palate ( Fig 4 , A ).
Nasal floor (NF) indicates the maxillary width tangent to the nasal floor at its most inferior level.
Hard palate (HP) indicates the maxillary width tangent to the hard palate at the most inferior level.
Maxillary plane (MP) indicates a segment connecting the most lateral point of the maxillary bone and the point where the cortex of the bone that forms the floor of the nasal cavities meets the maxillary sinus.
All evaluations were carried out at the height of the furcation of the first molar in the coronal slice.
The inclination of the alveolar process was evaluated observing the angle between the tangent to the palatal side of alveolar bone, NF plane (medial angle), and MP plane (lateral angle; Fig 4 , B ).
The tooth inclination ( Fig 5 , A ) was evaluated by analyzing the angle formed by the dental axis (line passing through the palatal mesial cusp and palatal root apex), NF plane (medial angle), and MP plane (lateral angle).
The vertical dental height was evaluated by measuring the distance between the MP and MV cusps and the NF plane ( Fig 5 , B ).
Periodontal evaluations and buccal bone width on both sides were evaluated on the coronal slices at the height of the MV root of the first molar ( Fig 6 , A ):
Taking a 0.3 mm apical from the cementoenamel junction (CEJ) on MV root and calculating the distance from the vestibular alveolar bone at this level.
Taking a 0.6 mm apical from the CEJ on MV root and calculating the distance from the vestibular alveolar bone at this level.
The transverse dental distance was measured at the tooth apex, CEJ, and crown level ( Fig 6 , B ). The transverse distance was evaluated, measuring the distance (1) between palatal root apices, (2) between palatal root CEJ, and (3) between palatal cusps.
These measures were also checked in the axial slices. All evaluations were carried out at the height of the furcation of the first molar in the coronal slice. The bispinal distances were measured in axial view, only at T1 ( Fig 7 ).
Anterior: at the most anterior point where the cortices are visible; half: between 5′ and 6′; posterior: in the most posterior point where the cortices are visible.
Statistical analysis
Continuous variables are presented as means ± SD and medians with interquartile range, whereas categorical variables are given as a number and/or percentage of subjects. All the baseline differences between groups were tested by the Student t test or Mann-Whitney U test. Intragroup differences over time were tested by the paired t test or Wilcoxon signed rank test. To investigate the association of differences over time with groups, the Student t test and Mann-Whitney U test were performed again. Differences with a P <0.05 were selected as significant. Data were acquired and analyzed in the R (version 3.4.4; The R foundation, The R project for statistical computing. http://www-R-project.org ) software environment. ,
Results
The sample included in the final analysis comprised 22 patients. The mean age was 17.50 years. The minimum age was 11 years, and the maximum age was 29 years. The demographic and clinical characteristics of groups are shown in Table I .
| Group 1 (≤16 y) | Group 2 (>16 y) | Row total | |
|---|---|---|---|
| No. of patients | 11 | 13 | 24 |
| Sex | |||
| Female | 7 | 5 | 12 |
| Male | 4 | 8 | 12 |
| Age (y) | 13.96 ± 1.82 | 20.43 ± 3.81 | 17.47 ± 4.55 |
| CVM stage | |||
| CS 2 | 2 | 0 | 2 |
| CS 3 | 1 | 0 | 1 |
| CS 4 | 7 | 1 | 8 |
| CS 5 | 1 | 11 | 12 |
| CS 6 | 0 | 1 | 1 |
| Palatine suture maturation | |||
| Stage B | 1 | 0 | 1 |
| Stage C | 10 | 5 | 15 |
| Stage D | 0 | 8 | 8 |
| Mean screw nominal expansion (mm) | 8.56 ± 1.67 | 7.78 ± 3.73 | 8.12 ± 2.98 |
| Activation days | 20.40 ± 3.63 | 19.73 ± 3.41 | 20.05 ± 3.44 |
The mean amount of activation of the expansion screw was 8.12 ± 2.98 mm (range, 0-10.30 mm). And the duration of the expansion ranged from 12 to 24 days.
Two patients (17 and 18 years old) out of 24 did not show any suture expansion, indicating a success rate of 91.7%. After a week of activations, miniscrews and expansions screws showed a migration into palatal mucosa generating decubitus, and the removal of the appliance was consequently necessary.
Differences analysis at baseline between groups are shown in Table II ; no significant differences were found except for the transverse distance of the first molar at the apex level ( P = 0.007). Significant intragroup differences over time were found for the tooth axis to NF and the vertical dental height at the vestibular cusp of the right first molar in group B ( P = 0.028 and P = 0.029, respectively) and for buccal bone width at 6 mm of the left first molar in group B ( P = 0.032). Significant differences over time were found in each group for maxillary width and dental diameters ( P < 0.01 in all patients for both groups; Table III ).
