A prospective cohort study on the effects of RME in the mandibular dentition of cleft subjects

Abstract

Purpose

Rapid maxillary expansion (RME) is the most frequent orthopedic procedure in cleft subjects. However, little is known about its effects on the mandible. The aim of this study was to investigate the spontaneous response of the mandibular teeth following RME.

Methods

This prospective cohort study was carried out with a sample of thirty participants with unilateral cleft lip and palate (UCLP), 8–15 years old, who had transverse maxillary deficiency. Two participants were excluded. They were allocated into three groups: G1 (n = 10), G2 (n = 10), and G3 (n = 8). G1 was treated with a Fan-type expander; G2 with an iMini expander; and G3 with a Hyrax expander. Measurements were performed in Cone Beam CT scans obtained before treatment (T1) and 3 months post-expansion (T2). The primary outcomes were buccolingual inclination of mandibular first molars and canines, and intercanine and intermolar width at different levels.

Results

Dental changes were significant (P < 0.05) for intercanine width, increasing in G1 and G2, and for intermolar width, increasing in G2 and G3. There were no significant differences among groups (P > 0.05).

Conclusion

RME in UCLP subjects performed with these expanders may lead to significant spontaneous changes in both anterior and posterior region of the mandible.

1. Introduction

The first report on the rapid maxillary expansion (RME) in orthodontic literature dates back to 1860,¹ however, this technique was only popularized by Haas, about 100 years later.² Along the years, there have been several different modifications to the expander appliance, with different designs achieving different side effects in addition to the expansion accomplished.

Cleft lip and palate (CLP) subjects, commonly present with posterior crossbite and maxillary transversal constriction, showing a further narrowing in the anterior region, making them good candidates for maxillary expansion.³ The biomechanical effects of RME in CLP patients seems to be different from those observed in patients without CLP.^4,5 This phenomenon may occur mainly because these patients present specific and differentiated morphological issues.^6,7 With the expansion in the CLP population having different goals than in noncleft subjects, there are different expander appliances designs looking to achieve a differential expansion in the anterior region.^4,8,9

A series of clinical investigations has been conducted to assess the behavior of the mandibular dentition following RME in noncleft patients.10, 11, 12, 13 In response to changes in the maxillary arch, an increase in intermolar and intercanine width in the mandibular arch was reported. However, the literature lacks data of the mandibular effects of this therapy in CLP patients.

The aim of this study was to evaluate, by means of cone beam computed tomography (CBCT), changes in the position of the mandibular teeth after rapid maxillary expansion in growing unilateral cleft lip and palate (UCLP) subjects, performed with three different types of appliances.

2. Methods

This prospective cohort study was carried out with a sample of 30 UCLP subjects. The elegilbility criteria were: absence of syndrome, no previous orthodontic treatment, erupted permanent first molars, and aged between 8 and 15 years old. All subjects underwent RME due to a severe transverse discrepancy of the maxillary arch. Institutional Review Board of the XXXXXXXXXXXXXXXX approved this study under registration number CAAE - 0145.0.213.000–09, and an informed consent was obtained from all individual participants. This manuscript was written in accordance to Strobe Statements Guidelines and Check-list for reporting of observational studies.

Thirty subjects, 20 males and 10 females, were allocated into three groups according to the type and severity of maxillary atresia. Each group represented a different RME expander: tissue-borne Fan-type expander (G1); Inverted Mini (iMini) expander (G2); and modified Hyrax expander (G3). Cases with maxillary deficiency limited to the anterior area were treat in G1 and G2. Cases with anterior and posterior maxillary deficiency were treated in G3. Each group presented an initial sample size of 10 subjects. No sample size calculation was previously done for this preliminary investigation. The mean age was 11.3 years (8–14.4 years) in G1; 10.5 years (8–14.1 years) in G2; and 10.4 years (7.9–14.8 years) in G3. From the thirty subjects recruited, two were excluded because they received lingual arches for orthodontic interception during the post-expansion period.

The tissue-borne fan-type expander was made of self-curing acrylic resin, with a hinge in the posterior region and a jackscrew anteriorly (Morelli, Sorocaba, São Paulo, Brazil) (Fig. 1). In contrast, the iMini expander was made only of metal, with a mini screw located in the anterior palatal area (Dynaflex, Saint Ann, Missouri, USA) (Fig. 2). The Hyrax expander was made with a jackscrew (Leone, Florence, Italy) positioned between upper primary molars or bicuspids (Fig. 3). All three appliances were fixed with orthodontic bands in the first permanent molars and bonded with composite in the primary molars or premolars.

Fig. 1.

Fan-type, tissue and tooth-borne expander.

Fig. 2.

IMini, tooth-borne expander.

Fig. 3.

Hyrax, tooth-borne expander.

The protocol for device activation was twice daily, one turn in the morning and one at night, until an overcorrection was obtained. In unusual cases, where the screw reached its expansion limit, the unit was replaced. With the expanders as an exception, no other orthodontic appliances were placed in any case, during the experimental period. A transpalatal arch with anterior extension was used as maxillary retainer after expansion.

CBCT scans were taken in two time points: before the expander placement (T1) and three months post-expansion (T2). This is a routine protocol for orthodontic treatment planning and for post-expansion surgical treatment planning of the alveolar graft in CLP patients. All exams were performed at the same center, by the same technician using an I-CAT scanner (Imaging Sciences International, Hatfield, PA, USA). The scans were acquired at 120 kV, 8 mA, scan time of 40 s, and 0.3-mm voxel dimension.

CBCT images were numerically cataloged and as both T1 and T2 scans were acquired without the expander, the examiner naturally had no access to which group the subject belonged to. No intentional blinding was performed, however. The same examiner carried out all measurements using the Dolphin Imaging software, version 11.7 (Dolphin Imaging & Management Solutions, Chatsworth, CA, USA). The first step in the image manipulation was the orientation of scans into the software. In the sagittal view, the CBCT image was oriented directing the Frankfort plane parallel to the ground. In the frontal view, a line connecting the frontozygomatic sutures was positioned parallel to the ground. In the axial view, a line connecting the crista galli to the landmark Basion was positioned perpendicular to the ground.

2.1. The primary outcomes assessed were

• 1.Buccolingual inclination of the mandibular permanent canines: measured by the angle between the long axis of the tooth (cusp tip to dental apex) and a horizontal line parallel to the mandibular plane (Fig. 4A). This measurement was taken in a paracoronal MPR (multi-planar reconstruction) slice.
• 2.Intercanine width: at crown level, linear measurement between the cusp tip of the mandibular permanent canines; at apex level, linear measurement between the apex of the mandibular permanent canines (Fig. 4B). This measurement was taken in a paracoronal MPR slice.
• 3.Buccolingual inclination of the mandibular first permanent molars: measured by the angle between the long axis of the tooth (mesiolingual cusp tip to mesial root apex) and a horizontal line parallel to the mandibular plane (Fig. 4C). This measurement was taken in a paracoronal MPR slice.
• 4.Intermolar width: at crown level, linear measurement of the shortest distance between the lingual surfaces of the first permanent molars; at apex level, linear measurement defined between the mesial root apex of the first permanent molars (Fig. 4D). This measurement was taken in an axial MPR slice.

Fig. 4.

A. Buccolingual inclination of the mandibular permanent canines; B. intercanine width; C. buccolingual inclination of the mandibular first permanent molars; D. intermolar width.

The secondary outcomes were the skeletal positioning of the mandible in the horizontal (SNB) and vertical (FMA and anterior lower facial height) dimensions.

2.2. Statistical analysis

To determine the intraobserver agreement, 18 scans were randomly selected. The same examiner repeated all linear and angular measurements, after 10-days interval. Intraclass Correlation Coefficient (ICC) was used in order to verify the repeatability of the measurements.

Means and standard deviations were calculated for each variable. After checking normality and homogeneity of the data, the intragroup behavior of linear and angular measurements, as well as the differences between the cleft and noncleft side, was assessed by the paired sample t-test. One-way ANOVA was performed to identify the among-group differences. All statistical analysis was done in the Statistical Package for the Social Sciences (SPSS 20.0, Inc. – Chicago, IL, USA), with a level of significance set at 5%.

3. Results

The intraobserver agreement was very high, with the ICC ranging from 0.971 to 0.998. The primary outcomes were analyzed as follows:

3.1. Intragroup changes

Statistical analysis of dental changes in the interval T1-T2, for all three groups, is presented in Table 1. There was a statistically significant increase of the mandibular intercanine width at crown level (P < 0.05) in the Fan-type (0.5 mm) and iMini (0.9 mm) groups. In the mandibular intermolar width at crown level, the iMini and Hyrax increased by 0.7 mm on average (P < 0.05). There were no statistically significant changes in the mandibular intercanine and intermolar width in Hyrax and Fan-type groups, respectively (P > 0.05).

Table 1.

Intragroup changes of mandibular measurements (T1 to T2).

OUTCOMES	T1		T2		Difference	P value (t-test)
	Mean ± SD	Range	Mean ± SD	Range
Fan-type expander (n = 10)
Cleft side canine inclination (°)	97.1 ± 3.8	91.2–101.1	96.8 ± 3.8	91–103.2	−0.4	0.705
Noncleft side canine inclination (°)	98.2 ± 4.6	90–105.4	99.8 ± 6.4	91.8–110.1	1.6	0.171
Intercanine width – crown (mm)	26.9 ± 1.7	24.7–30.3	27.4 ± 2	25.4–31.8	0.5	0.019*
Intercanine width – apex (mm)	21.8 ± 2.5	18.6–25.2	21.9 ± 3.1	18.5–26.2	0.1	0.766
Cleft side molar inclination (°)	67.9 ± 7.5	53.8–79.5	70.5 ± 6	62.3–79.6	2.6	0.098
Noncleft side molar inclination (°)	69 ± 5.5	58.4–76.8	71.4 ± 3.9	64–78.9	2.4	0.093
Intermolar width – crown (mm)	33 ± 2.4	28.7–36.1	33.3 ± 1.9	30.2–35.7	0.3	0.219
Intermolar width – apex (mm)	49.2 ± 1.8	45.9–51.9	49 ± 2.1	46.9–52	−0.2	0.388
Inverted mini expander (n = 10)
Cleft side canine inclination (°)	98.1 ± 10.6	79.6–112.8	98.7 ± 7.8	87.3–112.3	2.6	0.109
Noncleft side canine inclination (°)	97.6 ± 6.9	80.7–103.3	97.6 ± 8.1	79–105.6	0	0.978
Intercanine width – crown (mm)	25.1 ± 4.7	14.2–28.9	25.9 ± 4.5	15.9–30.4	0.9	0.002**
Intercanine width – apex (mm)	20.3 ± 3.8	17.4–26.8	20.4 ± 4.1	17.2–27.7	0.1	0.573
Cleft side molar inclination (°)	65.3 ± 4.8	59.7–75.4	66.7 ± 4.5	61.6–76.6	1.4	0.033*
Nonleft side molar inclination (°)	67.7 ± 4.7	60.6–74.7	71.2 ± 3.7	65.1–74.6	3.5	0.001**
Intermolar width – crown (mm)	33.5 ± 2.9	29.6–38.3	34.3 ± 2.7	30.7–39.2	0.7	0.000***
Intermolar width – apex (mm)	51 ± 3.2	46.7–55.9	50.7 ± 3.4	44.9–55.8	−0.3	0.248
Hyrax-type expander (n = 8)
Cleft side canine inclination (°)	95.5 ± 9.2	80.1–105.8	97.1 ± 8	84–107	1.6	0.116
Noncleft side canine inclination (°)	94.9 ± 7.9	84.9–102.8	97 ± 7.6	85.4–104.7	2.1	0.143
Intercanine width – crown (mm)	25.9 ± 3.8	19.4–31.1	26.1 ± 3.5	20.2–30.8	0.2	0.398
Intercanine width – apex (mm)	21.7 ± 3	18.4–27.2	21.6 ± 3.1	18.5–27.5	−0.1	0.346
Cleft side molar inclination (°)	61.6 ± 3.4	54.7–65.3	64.6 ± 4.5	58.3–72.8	3	0.048*
Noncleft side molar inclination (°)	64.9 ± 6.3	56.9–75.3	69.5 ± 5.2	63.6–77.3	4.6	0.002**
Intermolar width – crown (mm)	31.4 ± 3.2	25.8–34.5	32.1 ± 2.6	27.3–34.9	0.7	0.049*
Intermolar width – apex (mm)	49.5 ± 2.6	44.7–52	49 ± 3	43.9–52.4	−0.6	0.036*

Paired “t” test. SD, standard deviation. *p < 0.05; **p < 0.01; ***p < 0.001.

Regarding dental tipping, there were no differences in canine buccolingual inclination for all groups (P > 0.05). However, a statistically significant increase in the molar buccolingual inclination was observed in the Hyrax and iMini groups (P < 0.05).

3.2. Intergroup changes

One-way ANOVA showed no statistically significant differences among the Fan-type, iMini, and Hyrax groups in all the analyzed variables (P > 0.05) (Table 2).

Table 2.

Comparison of T2-T1 changes between the three groups.

OUTCOMES	Fan-type (n = 10)		Inverted mini (n = 10)		Hyrax-type (n = 8)		ANOVA P value
	Mean	SD	Mean	SD	Mean	SD
Anterior region
Cleft side canine inclination (°)	−0.4	3.1	2.6	4.1	1.6	2.1	0.179
Noncleft side canine inclination (°)	1.6	3.2	0	2.4	2.1	2.9	0.336
Intercanine width – crown (mm)	0.5	0.5	0.9	0.5	0.2	0.6	0.079
Intercanine width – apex (mm)	0.1	0.9	0.1	0.5	0.1	0.3	0.756
Posterior region
Cleft side molar inclination (°)	2.6	4.4	1.4	1.7	3	3.6	0.579
Noncleft side molar inclination (°)	2.4	4.1	3.5	2.5	4.6	4.5	0.481
Intermolar width – crown (mm)	0.3	0.8	0.7	0.4	0.7	0.8	0.376
Intermolar width – apex (mm)	−0.2	0.6	−0.3	0.7	−0.6	0.6	0.368

One-way ANOVA. SD, standard deviation.

3.3. Cleft vs noncleft side

The comparison of the mandibular changes related to the cleft side was performed for each group. No influence of the cleft was found on any of the studied variables after RME (P > 0.05) (Table 3).

Table 3.

Comparison of dental inclinations changes in relation to the cleft side.

OUTCOMES	Cleft Side		Noncleft Side		P value (t-test)
	Mean	SD	Mean	SD
Fan-type (n = 10)
Canine inclination (°)	−0.4	3.1	1.6	3.2	0.158
Molar inclination (°)	2.6	4.4	2.4	4.1	0.910
Inverted mini (n = 10)
Canine inclination (°)	2.6	4.1	0	2.4	0.286
Molar inclination (°)	1.4	1.7	3.5	2.5	0.079
Hyrax-type (n = 8)
Canine inclination (°)	1.6	2.1	2.1	3	0.642
Molar inclination (°)	3	3.6	4.6	4.5	0.525

Paired “t” test. SD, standard deviation.

4. Discussion

The impact of RME on the craniofacial complex has been widely studied,^5,12,14,15 but there is little data published on a cleft sample.^16,17 RME is the most frequent orthopedic procedure in CLP subjects. This manuscript is reporting one of its important effects, that is the spontaneous dental changes that occurs in the opposite arch. It is part of the results of a comprehensive prospective cohort study designed to investigate RME in this population.^4,18

The homogeneity of the sample is a basic condition for conducting studies on this topic. Only participants with unilateral cleft lip and palate could be enrolled. Another precaution was in regard to the age difference, which could affect dentoalveolar and skeletal responses.^14,19 Therefore, it was determined a range of 8–15 years old in an attempt to decrease the chances of a selection bias. However, it should be mentioned that individuals growth potential varied substantially (cervical maturation stage from CS1 to CS4), but with a homogenous distribution among groups.

Measuring dental inclinations requires specific points in the tooth surface to be located, including points inside the alveolar socket. Therefore, some studies have used CBCT images for this purpose.^4,19,20 It has several advantages for quantitative assessments in studies of the craniofacial complex.²¹ This is especially true when measurements are performed in MPR images, instead of 3D volumetric rendering, which may decrease reliability and accuracy of linear measurements.^22,23

The results of this study showed significant changes in the mandibular molar, for both buccolingual inclination and intermolar distance. However, these findings were statistically significant only for the iMini and Hyrax groups. There was a mean increase of 0.7 mm in the intermolar distance, that based on our results could be attributed to a significant buccal inclination movement of the mandibular molars. We believe that the premature occlusal contacts, between the palatal cusps of the upper teeth and the lower buccal cusps, generated by maxillary expansion are responsible for such changes in the mandibular dentition. Conversely, the mandibular molar measurements for the Fan-type group showed no significant changes. Probably because this appliance achieves a smaller expansion on the maxillary molar region,⁴ so it does not stimulate the buccal movement of the mandibular molars. In contrast, the intercanine width in Fan-type group showed a statistically significant increase (0.5 mm), which may indicate that the lower teeth tend to follow the movement of the correspondent upper teeth during a RME. However, no significant increase in mandibular canines inclinations was found, what is supposedly related with the absence of occlusal contact in this region.

To our knowledge, no study has been published on the spontaneous mandibular dental changes following RME in a cleft population. Studies with noncleft subjects have shown a slight increase in mandibular intercanine (0.3 mm–1.1 mm) and intermolar (1 mm–2.1 mm) width, using conventional expanders.^{10,11,13,24,25} Additionally, the results for intermolar width were stable in long-term evaluations.^11,13 We have only assessed the short-term effects of RME, with 3 months of post-expansion period. Therefore, a long-term evaluation is necessary to obtain a better understanding of the stability of this procedure in the mandibular arch of CLP subjects. Ideally, it should be done with digital study models superimpositions, as there is no ethical reason for a third CBCT acquisition.

Considering the buccolingual inclination changes of the mandibular teeth after RME, we found no difference between cleft and noncleft sides. This behavior was similar to the maxillary teeth that also showed no difference in dental tipping between both sides.⁴

The vertical and horizontal skeletal measurements of the mandible were also considered in our study. For this purpose, a lateral cephalometric image derived from CBCT was used. Some authors have suggested this protocol to be superior when compared to the conventional lateral radiograph.^26,27 There was a significant trend of mandibular clockwise rotation after RME in all three groups (P < 0.05). The Fan-type group showed a mean increase of 0.7° in FMA, followed by 0.8° in iMini group, and 1.1° in Hyrax group. It is very likely that despite being statistically significant, in a clinical standpoint these findings are not relevant. Our data also showed a statistically significant increase in lower facial height of 1.8 mm in Fan-type group, 2.4 mm in iMini group, and 1.7 mm in Hyrax group. There were no significant anteroposterior changes (SNB) in either group. In noncleft subjects studies, a similar trend was found regarding the mandibular positioning, in both vertical and anteroposterior dimensions.^14,28 In fact, all findings considered to be skeletal, the authors believe that is a response to occlusal changes, and this is why we kept it apart from our main results. Therefore, it is important that further studies be carried out in long-term in order to verify whether these changes are transient or not.

Finally, besides the short interval of follow up between measurements, the sample size may also be considered a limitation of the present study. This is particularly true for the intergroup analysis, which the null hypothesis could erroneously be accepted (type II error). Although it does not invalidate the overall results, the absence of differences among appliances should be interpreted and considered with caution.

5. Conclusion

• •iMini and Fan-type RME appliances led to an increase in the mandibular intercanine width.
• •iMini and Hyrax RME appliances led to a significant increase in the mandibular intermolar width.
• •No difference was found between the cleft vs noncleft side in all analyzed variables.

Funding

None.

Ethical approval

All procedures performed were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

Informed consent

Informed consent was obtained from all individual participants included in the study.

Declaration of competing interest

The authors declare that they have no conflict of interest.