Three-dimensional evaluation of dentopalatal changes after rapid maxillary expansion in growing children

Introduction

In growing children with transverse malocclusion problems, various types of rapid maxillary expanders (RMEs) have been effectively used in skeletal and dental expansions. We evaluated 3-dimensional dentopalatal changes in growing children who underwent maxillary expansion using RMEs and bonded RMEs.

Methods

We investigated dentopalatal changes in 20 patients treated with bonded RMEs, 19 with RMEs, and 38 control patients. Dental plaster models before and after expansion were scanned 3-dimensionally and superimposed to evaluate transverse expansion, expansion ratio, angular expansion, and palatal expansion height ratio.

Results

Using bonded RMEs, similar anterior and posterior dental expansions were achieved with an efficiency of 69%-76% (expansion ratio), and palatal soft-tissue expansion occurred more apically in the posterior area (palatal expansion height ratio, 1.00) than in the anterior area (palatal expansion height ratio, 0.64). Using RMEs, a larger posterior dental expansion was achieved, with an efficiency of 106%-117% (expansion ratio), than anterior dental expansion (55%-60%), and palatal soft-tissue expansion occurred more apically in the posterior area (palatal expansion height ratio, 0.99) than anterior area (palatal expansion height ratio, 0.23).

Conclusions

Dental expansions in the anterior and posterior areas were similar using bonded RMEs, whereas the posterior dental expansions were larger than those of the anterior area using RMEs. The entire palatal soft-tissue slope expanded in the posterior area, whereas the occlusal part expanded in the anterior area using RMEs and bonded RMEs.

Highlights

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Three-dimensional evaluation of dentopalatal changes were achieved using bonded rapid maxillary expanders (RMEs) and RMEs.
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Bonded RMEs achieved similar anterior and posterior dental expansions.
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RMEs achieved a larger posterior than anterior dental expansion.
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The entire palatal soft-tissue slope expanded in the posterior area.

After the report on maxillary expansion by Angell, the expansion appliance manufactured by Haas has been used in orthodontics. Maxillary expansion appliances alleviate dental crowding, correct posterior crossbite, and expand maxilla width when narrower than the mandible. Since the initial use of maxillary expansion, orthodontists have been investigating the use of various anchorages, including dentition, palatal soft tissue, and temporary skeletal anchorage devices, to effectively treat transverse discrepancy and minimize side effects, such as buccal crown tipping of posterior teeth or buccal alveolar bone loss. ^,

In growing children with transverse malocclusion, various rapid maxillary expanders (RMEs) have been widely studied and effectively used in both skeletal and dental expansions. Tooth-borne (Hyrax-type) and tissue-borne (Haas-type) appliances have been commonly used to induce maxillary skeletal and dental expansions. Garib et al and Weissheimer et al reported that Haas-type expanders induced larger buccal molar inclination, whereas Oliveira et al suggested that Haas-type expanders achieved larger orthopedic expansion of the maxilla. Furthermore, different effects of band type and bonded RMEs have been reported. Kiliç et al and Olmez et al demonstrated larger dentoalveolar tipping after using band-type RMEs than that observed after using bonded RMEs. Sarver and Johnston showed that the bonded RME reduced the extrusion of posterior teeth. However, Asanza et al reported no significant difference in dental tipping between the 2 RMEs.

Changes in the teeth and periodontal tissue during maxillary expansion have been primarily observed in previous studies. Furthermore, to evaluate the skeletal changes of the maxilla, including midpalatal suture opening and morphologic changes of the palatal vault in growing children, cone-beam computed tomography (CBCT) is used periodically.

However, with 3-dimensional (3D) study model scanning and analysis programs, it is possible to detect changes in dentition and maxillary skeletal changes. As tooth movement affects the remodeling of the periodontal tissue, including the alveolar bone, opening the midpalatal suture and subsequent maxillary expansion would alter the shape of the palatal soft tissue. Recent advances in 3D technologies can provide information that could not be observed using previous methods, such as posteroanterior cephalogram or dental plaster model analyses. Moreover, 3D model scanning has excellent precision and reproducibility and provides information on various sections to show the changes, such as remodeling or expansion patterns in both the teeth and palatal soft tissue.

Therefore, this study aimed to evaluate and compare the dentopalatal expansions of different positions in 3D-scanned dental models using 2 RME types, bonded and band-type RME, in growing children.

Material and methods

This is a retrospective study conducted after review and approval by Gangnam Severance Hospital Institutional Review Board (no. 3-2017-0320).

Initially, 146 patients who had visited the Department of Orthodontics, Gangnam Severance Dental Hospital, between 2012 and 2018 and received maxillary expansion treatment using either RME (79 patients) or bonded RME (67 patients) were enrolled. RME was selected because of dental crowding and transverse discrepancy, including posterior crossbite. RME and bonded RME were allocated according to the eruption state of the maxillary first premolars. Patients who satisfied the following conditions were included in the expansion groups: (1) availability of dental plaster models before (T1) and after maxillary expansion (T2), (2) no appliance detachment or breakage during treatment, (3) no defects or interference from inflammation-related edema with the measurement of the plaster model, (4) no specific systemic disease or jaw deformity, (5) no prior experience of orthodontic treatment, and (6) no changes in crown morphology (eg, because of a prosthesis or trauma).

A total of 39 subjects were finally included in the RME group: 20 patients (4 males, 16 females; median age, 8.71 years) for the bonded RME group and 19 patients (10 males, 9 females; median age 11.63 years) for the RME group.

A Biederman-type expander was used in the RME group to band the first premolars and molars bilaterally. For bonded RME, the same expander type was used with occlusal bite blocks of 1-3 mm thickness to cover the bilateral posterior teeth ( Fig 1 ). For both RME and bonded RME groups, the patients were instructed to turn the expander by one-quarter of a turn per day. The expansion was performed until the palatal cusps of the maxillary posterior teeth did not move beyond the buccal cusps of the mandibular posterior teeth using RMEs. Using bonded RMEs, the expansion continued until the entire palatal cusps in the bite-block maintained the occlusal contact with the mandibular buccal cusp. The articulating paper was used to check the occlusal contact in the bonded RME group.

To evaluate chronological changes by normal growth, we enrolled 2 control groups from the archives of Institute of Craniofacial Deformity, College of Dentistry, Yonsei University based on the same criteria. The control group had no orthodontic treatment history, and plaster dental models were collected yearly. Control group 1 (n = 19; 6 boys and 13 girls; median age, 9.0 years) was selected to match the age of the bonded RME group, whereas control group 2 (n = 19; 9 boys and 10 girls; median age, 12.0 years) was selected to match the age of the RME group. The characteristics of the RME and control groups are summarized in Table I .

Table I

Demographic features of maxillary expansion and control groups

Variables	Bonded RME (n = 20)	Control 1 (n = 19)	P value	RME (n = 19)	Control 2 (n = 19)	P value
Sex			0.408			0.746
Male	4 (20.0)	6 (31.6)		10 (52.6)	9 (47.4)
Female	16 (80.0)	13 (68.4)		9 (47.4)	10 (52.6)
Age (y)
T1	8.71 (6.33-10.75)	9.00 (6.00-10.00)	0.718	11.63 (8.92-13.67)	12.00 (10.00-14.00)	0.967
T2	10.09 (7.08-11.66)	10.00 (7.00-11.00)	0.654	12.50 (10.17-14.83)	13.00 (11.00-15.00)	0.901
T2 − T1	1.13 (0.25-1.91)	1.00	0.613	1.08 (0.42-1.42)	1.00	0.607
ANB (°)
T1	0.28 (−2.21 to 5.01)	2.75 (0.70-5.80)	<0.001 ^∗∗∗	2.28 (−1.99 to 5.96)	4.20 (1.95-5.98)	<0.05 ^∗
T2	1.38 (−2.83 to 3.24)	3.50 (0.90-6.60)	<0.001 ^∗∗∗	2.72 (−0.75 to 5.66)	4.48 (1.65-6.29)	<0.05 ^∗
T2 − T1	0.56 (−3.50 to 3.22)	0.25 (−2.30 to 3.60)	0.988	0.20 (−1.61 to 4.86)	0.01 (−1.36 to 1.60)	0.977
Mp-SN (°)
T1	36.13 (29.10-41.74)	37.50 (30.00-41.70)	0.784	37.33 (31.51-41.47)	35.68 (32.80-39.90)	0.284
T2	37.58 (28.66-41.35)	36.80 (31.00-41.80)	0.791	38.44 (30.72-44.20)	35.98 (31.39-42.60)	0.223
T2 − T1	0.14 (−3.89 to 3.29)	−0.20 (−3.60 to 3.00)	0.355	0.88 (−2.20 to 2.73)	0.10 (−2.19 to 2.70)	0.370

Note. Data are presented as n (%) and median (range); Chi-square tests were used to compare gender between groups, whereas Mann-Whitney U tests were used to compare age, ANB, and Mp-SN between groups.

∗ P <0.05.

∗∗∗ P <0.001.

Impressions were taken as a regular procedure at T1 and T2 to evaluate the degree of expansion. The dental models at T2 were fabricated after the appliance removal and 3-6 months of maintenance after the expansion had been completed. In case of severe gingival swelling at T2, the patient was recalled 1 week later to confirm the subsidence of the swelling and take the impression.

The dental models at T1 and T2 were scanned using a 3D model scanner (Freedom HD; DOF, Irvine, Calif). The 3D digital models at T1 and T2 were superimposed (Rapidform2006; Inus, Seoul, South Korea) on the basis of the medial parts of the anterior third palatal rugae and the median raphe, which are known to be stable structures ( Fig 2 ). ^,

For measurements, we defined bilateral landmarks on the digital model at T1 and T2: the cusp tip of the (deciduous) canine (C3 _R and C3 _L ); the most prominent point of the palatal gingival margin of the (deciduous) canine (G3 _R and G3 _L ); mesiopalatal cusp of the first molar (C6 _R and C6 _L ); the point in which the palatal groove of the first molar met the gingival margin (G6 _R and G6 _L ); and estimated center of resistance of the first molar, which was located 5 mm below the G6 point (P6 _R and P6 _L ). The line connecting G6 _R and G6 _L was registered as the x-axis, and the midpoint was defined as (0, 0, 0). The line connecting (0, 0, 0) with the gingival embrasure between the maxillary central incisors was the y-axis, and the other axis was the z-axis. The plane containing the x- and y-axes were defined as the horizontal reference plane, whereas the planes perpendicular to the horizontal reference plane and including the G3 and G6 points were defined as the anterior and posterior vertical planes, respectively ( Fig 3 ).

The transverse expansion was assessed for the canine and first molar by measuring the distance between the right and left sides: C3 _R -C3 _L , G3 _R -G3 _L , C6 _R -C6 _L , G6 _R -G6 _L , and P6 _R -P6 _L ( Fig 4 ).

The expansion ratios were defined as the relative amount of transverse expansion of the teeth (C3 _R -C3 _L , G3 _R -G3 _L , C6 _R -C6 _L , and G6 _R -G6 _L ) and palatal soft tissue (P6 _R -P6 _L ) to assume the total expansion amount of the bonded RME or RME appliance as 1. For example, if the maxillary first molars showed 4.0 mm expansion on the cusp tips with 5.0 mm of the appliances, the expansion ratio would be 0.8. To verify the amount of appliance expansion, the numbers of screw turnings were counted by reverse turning the jackscrew after appliance removal.

In the anterior and posterior vertical plane before expansion, the apex of the palatal vault was defined as Aa and Ap, respectively. The angle connecting the bilateral landmarks (C3, G3, C6, G6, and P6) to the apex of the palatal vault was measured, and the angular expansion was defined as the differences between T1 and T2 for each landmark ( Fig 5 ).

The palatal expansion height ratio indicates the inflection point on the palatal soft tissue. On the posterior vertical plane, the outline of the palate was drawn at T1 and T2 ( Fig 6 ). The intersection points of the 2 outlines were defined as the posterior palatal expansion points, in which changes in the palatal soft tissue were observed. The same procedure was performed for the anterior vertical plane, and the intersection point was defined as the anterior palatal expansion point.