Intercenter comparison of slow and rapid maxillary expansion in unilateral complete cleft lip and palate

ABSTRACT Objective: The aim of this study was to compare the occlusal changes of rapid maxillary expansion (RME) and slow maxillary expansion (SME) in patients with unilateral complete cleft lip and palate (UCLP), by means of digital dental models. Methods: Group RME was composed by 22 patients (13 males and 9 females), with mean age of 9.9 years, treated with rapid maxillary expansion with Hyrax appliance in Center 1. Group SME was composed by 29 patients (14 females and 15 males), with mean age of 10.7 years, treated with slow maxillary expansion with quad-helix appliance in Center 2. Digital dental models of the maxillary dental arch were obtained immediately pre-expansion (T1) and 6-month post-expansion (T2). Transversal distances, arch perimeter, arch length, palatal depth, palatal volume and posterior tooth inclination were digitally measured. Interphase and intergroup comparisons were performed with paired t-test and independent t-test, respectively. Results: Intercanine expansion was 4 to 5mm in both groups, and increase in the intercanine distance was similar for both groups. RME group showed a greater increase in arch distances at the region of permanent premolar and molars, compared to SME group. Arch perimeter increase was greater for RME group, compared to SME. No differences were found for arch length, palatal depth, palatal volume and posterior tooth buccal tipping. Conclusion: RME and SME produced similar dentoalveolar outcomes, with greater amount of expansion on RME group.

Palavras-chave: Fissura palatina. Fissura de lábio. Técnica de expansão palatina. commonly present with significant constriction of the maxillary dental arch due to collapse of the maxillary segments and to plastic surgery fibrosis. [1][2][3] Before the secondary alveolar bone graft procedure at the late mixed dentition, maxillary expansion is often required to improve the arch form, align the maxillary segments 3 and correct the posterior crossbite frequently found in patients with complete cleft lip and palate. 1,4 Maxillary expansion can be achieved with rapid (RME) or slow expansion (SME). Brunetto et al 5 compared the effects of slow and rapid maxillary expansion in noncleft patients using Haas-type palatal expanders, by means of cone-beam computerized tomography (CBCT). They concluded that both protocols had similar transversal increase and lead to buccal bone plate height and thickness decrease. Rapid maxillary expansion produced increased molar inclination.
A previous study comparing slow and rapid maxillary expansion, in a sample including both unilateral and bilateral cleft lip and palate, found no differences for rapid and slow maxillary expansion. 6 In patients with bilateral complete cleft lip and palate, Almeida et al 7 observed similar transversal changes of maxillary basal bone using RME and SME. Medeiros Alves et al 8 found similar dentoalveolar outcomes using slow and rapid  band. The usual time for expansion was three months. Digital dental models were obtained immediately pre-expansion (T1) and 3 months after the bone graft, when the appliance was removed (T2) (Fig 1). The dental models were scanned with a 3Shape R700 3D laser scanner (3Shape A/S, Copenhagen, Denmark), and the digital model was saved in .STL format.     The palatal volume was measured before and after maxillary expansion using the Appliance Designer software (3Shape A/S, Copenhagen, Denmark) and the VistaDent 3D software (Dentsply, New York). In the Appliance Designer, a volumetric image of the palate was created considering as posterior limit a plane tangent to the distal aspect of first maxillary molars and, as the lateral limits, the midpoint of the lingual aspect of each maxillary tooth at the level of the gingival margin (Fig 7).

MATERIAL AND METHODS
This image was exported to VistaDent 3D software (Dentsply, EUA, New York), in which volume calculation was performed.

ERROR STUDY
The same examiner remeasured fifty percent of the sample after a 30-day interval. The random errors were calculated according to Dahlberg's formula (Se 2 =Σd 2 /2n), 12 where Se 2 is the error variance and 'd' is the difference between two determinations of the same variable, and the systematic errors were evaluated with dependent t-tests, at p<0.05. 13 Ayub

RESULTS
The random error varied from 0.26mm to 85.52mm. No significant systematic error was found.
Comparing the initial features of the two study groups, there was no statistically differences between groups (Table 1).
Intergroup comparisons showed differences to interpremolar and intermolar transversal distances that were greater for RME group compared to SME group (Table 2). Arch perimeter showed a greater increase for RME group compared to SME group. Table 1: Comparison of starting forms between the Slow (SME) and Rapid Maxillary Expansion (RME) groups.

DISCUSSION
Based on random and systematic error analysis, the intraexaminer reproducibility was adequate. Digital dental models have been shown to be an accurate and precise method for evaluating study model dimensions. 14,15 Previous studies demonstrated lead to different initial maxillary morphology. 17,18 In the present study, groups had similar features (Table 1).
Intergroup comparisons showed differences only for arch distance increase of posterior teeth (premolars and molars) and for arch perimeter, which was greater for RME (Table 2).
Hyrax expander presents a screw with parallel opening that could not produce differential expansion. In both groups, the correction of intercanine distance was the reference for the amount of expansion, so models in the RME had the posterior region often over-expanded. When considering slow maxillary expansion effects (  17,18,19 Another study 8 also found that slow maxillary expansion produced greater intercanine distance increases, when compared with intermolar distance increases, due to its differential expansion potential. No statistically difference between RME and SME was found when evaluated posterior tooth inclinations (Table 2). These results are in agreement with others. 6,8 Previous studies also found similar molar tipping for Hyrax and quad-helix appliances both in patients with UCLP and BCLP. 3,18 On the other hand, Brunetto et al 5 found a greater buccal inclinations of posterior teeth for RME, compared to SME, in noncleft patients.
The presence of the cleft may decrease the resistance to the lateral movement of the maxillary segments. 8 Future studies with CBCT should be conducted to verify differences between SME and RME for the proportion of skeletal and dental effects.

CONCLUSION
Dentoalveolar effects of SME and RME in patients with UCLP were similar, with greater amount of expansion on RME group.