3D comparison of dental arch stability in patients with and without cleft lip and palate after orthodontic/rehabilitative treatment

Abstract This study aimed to compare the linear dimensions of the dental arches of adult patients with complete unilateral cleft lip and palate (UCLP) after orthodontic and prosthetic treatment with fixed partial dentures (FPD) to patients without clefts, using 3D technology. This retrospective longitudinal study sample consisted of 35 subjects divided into two groups. Included in this sample were 15 complete UCLP individuals who had received orthodontic treatment before rehabilitation with a fixed partial denture (FG), as well as 20 patients without cleft as control group (CG). All patients were aged between 18 and 30 years. Digital dental casts were obtained in two stages: (T1) end of orthodontic treatment and (T2) one year after prosthetic rehabilitation (FG); and (T1) end of orthodontic treatment and (T2) one year after removal of the orthodontic appliance (CG). Intercanine, interfirst premolar and intermolar distances, and incisor-molar length were obtained. A precalibrated and trained examiner performed the assessments. Intergroup differences between T2 and T1 were compared between the groups using the t test or Mann-Whitney test with a significance level of 5% (p<0.05). The intercanine distance variation (T2-T1) showed statistical difference (p=0.005) increasing in the FG group and decreasing in the CG group. In the interfirst premolar distance variation, FG decreased, while CG increased with statistically significant difference (p=0.008). The intercanine distance of individuals with cleft showed stability, while that of the CG had no stability. The CG showed stability in the interfirst premolar distance, while FG had no stability. These findings showed that the FPD is capable of restricting orthodontic results, leading to a stabilization of the dental arches.


Introduction
Cleft lip and palate (CLP) is the most prevalent congenital malformation (1 in every 500 to 700 births per year) and is considered a public health burden according to the World Health Organization. 1 Oral clefts may involve the lip, alveolus and palate, and occur up to the 12 th week of intrauterine life. 1 An early diagnosis may occur during pregnancy after ultrasound examination, 2 but rehabilitative treatment starts immediately after birth with primary surgeries generally being performed up to the age of 12 months.
Although primary surgeries correct aesthetics and function, they can have deleterious effects on maxillary growth. [3][4][5][6][7][8] For the success of rehabilitative treatment, study model dental casts should be obtained for diagnosis, planning and monitoring morphological information.
These become part of the patient's dental record, which should be systematically maintained from birth through all phases of treatment 9 to enable the longitudinal evaluation of rehabilitative treatment. 10 Despite the valuable information obtained with study casts, comparative studies must deal with the inconvenience of transporting the casts. Such challenges have led to alternative methods for morphological evaluation of anatomic structures. Thus, the three-dimensional (3D) analysis of the dental arches is a significant shift in data collection, [10][11][12][13][14][15] showing several advantages. 11,12,[15][16][17][18] Studies comparing measurements on digital dental images and on study dental casts concluded that 3D images are clinically acceptable and reproducible. [16][17][18] Professionals must be aware of dimensional changes in the dental arches of individuals with cleft lip and palate because these alterations influence the outcomes of the rehabilitative process, 19 which aims not only to anatomically and functionally rehabilitate, but also to restablish the social acceptance of the individual. 20 Studies on the evaluation of the dental arch dimensions of individuals with CLP after orthodontics and on the stability achieved after prosthetic treatment are lacking. Therefore, this study aimed to compare the linear dimensions of the dental arches of patients with complete unilateral cleft lip and palate (UCLP) after orthodontic and prosthetic treatment with a fixed partial denture with the dimensions of patients without cleft lip and palate immediately after orthodontics and one year after removal of the orthodontic appliance.
The hypothesis was that no stability of the dental arches would be observed in non-cleft patients after orthodontic treatment, as well as for cleft patients after orthodontic and prosthetic treatment. The information provided will aid in a better understanding of the factors interfering in the stability of the dental arches of individuals with complete UCLP, mainly the definitive outcome of rehabilitative treatment.
All patients (CG and FG) received similar orthodontic treatment, and rapid maxillary expansion to correct and align the maxillary arch. When the orthodontic appliance was removed, the patient wore a Hawley appliance while waiting for prosthetic treatment.
The evaluation was performed on 3D images of the maxillary dental cast obtained at the following time

Digitation of casts
The dental casts obtained from the files of both institutions were digitized with a laser scanner

Obtaining measurements
A set of landmarks was identified on the 3D images of dental arches to obtain the linear measurements ( Figures 1 and 2). All measurements were performed point-by-point with the software tool: intercanine distance, 4,21 interfirst premolar distance, 8 intermolar distance, and total length of the dental arch from the incisor to the molar line. 21,22 The variation of the distances between the study time points was obtained by the difference between values at T2 and values at T1 (Δ). This difference was considered for the statistical analysis of dental arch stability.

Statistical analysis
All statistical tests were performed with statistical software (Statistica for Windows -Version 7.0 -StatSoft, TIBCO Software, Palo Alto, CA, USA). To analyze the intra-rater error, the sample was measured again 15 days after the first evaluation. To calculate the systematic error, the paired t test was used. The random error was determined by using the Dahlberg formula. 23 The Shapiro-Wilk test was applied to verify data normality. Accordingly, the t test was used to test differences during the analyzed time points in dental arch measurements with a normal distribution, while the Mann-Whitney was used for those with a nonnormal distribution. All tests were set at a 5% level of significance. Mean and standard deviation were reported for normally distributed data, while median and interquartile range were reported for not-normally distributed data.

Error of method
The intra-rater reproducibility was verified with the paired t test and the Dahlberg formula between the measurements performed by the same examiner (JTC) within the 15-day interval. Tables 1 and 2 show the inter group comparisons for each period (T1 and T2) of the evaluated groups and observe the main alterations in the studied     (Table 3). Both groups showed a reduction in the intermolar distances (MM'), without statistically significant differences between groups (p>0.05) ( Table 3). Both groups showed an increase in the incisor-molar length (IM), without statistically significant differences between groups (p=0.375) ( Table 3).

Discussion
The Class III malocclusion pattern is the most In this study, the linear distances between the canines in CG and GF in T1 were significantly different, being shorter in GF relative to CG (p=0.003). As orthodontics does not always restore the canine to its original position in the dental arch, taking it to the lateral incisor position instead, it is possible to have different measures between groups in T1 (Table   1). Throughout the linear measurements, we were sometimes able to observe the canine in the lateral incisor area, and this condition may have led to the observed statistical alterations. This bias could be eliminated by excluding all patients who presented the canine out of its correct position in the dental arch.
At T2, the intercanine distances of the CG decreased and those of the FG increased ( Table 2).
The difference (ΔC) also showed the same behavior (Table 3) Professionals must be aware that treatment is not finished with the fixed partial denture installation.
Periodic follow-up appointments are necessary and should include occlusion assessments, since dental alterations may occur over time. In the long term, alterations to the dental arches may not significantly alter the aesthetic outcome, but they may directly influence the necessity of occlusal adjustments due to the lack of dental arch stability. This would explain the

Conclusion
The intercanine distance was stable in the FG and unstable in the CG, showing that the fixed partial denture is capable of restraining orthodontic outcomes; The interfirst premolar distance was unstable in the fixed partial denture group and stable in the control group; The intermolar distances values of both groups showed reduction after treatment; The incisor-molar line length was stable for both groups because the maxillo-mandibular discrepancy is maintained from childhood to adulthood in individuals with cleft lip and palate.
The present findings showed that the FPD is capable of containing orthodontic results, leading to a stabilization of the dental arches.