Closure of maxillary lateral incisor agenesis space in unilateral cleft lip and palate: a digital model assessment

ABSTRACT Objective: To compare dental positional and gingival parameters of maxillary anterior teeth in unilateral cleft lip and palate (UCLP) after orthodontic treatment with canine substitution due to lateral incisor agenesis. Methods: This split-mouth study comprised 57 subjects with UCLP (31 male, 26 female) and agenesis of maxillary lateral incisor at the cleft side, from a single center. Canine substitution was completed after the secondary alveolar bone graft. Dental models were taken between 2 to 6 months after debonding (mean age: 20.4 years). The following variables were measured in the maxillary anterior teeth: crown height, width, proportion, and symmetry, as well as steps between incisal edges, gingival margins, tooth mesiodistal angulation and labiolingual inclination. Paired t-tests with Bonferroni post-hoc correction was used for comparisons between cleft and non-cleft sides (p<0.05). Results: At the cleft side, canines replacing missing lateral incisors had a higher crown height (0.77mm) and an increased width (0.67mm), and first premolars showed a shorter crown height (1.39mm). Asymmetries were observed in the gingival level of central and lateral incisors, with a greater clinical crown at the cleft side (0.61 and 0.81mm, respectively). Cleft side central incisors were more upright than their contralaterals (2.12º). Conclusions: Maxillary anterior teeth demonstrated positional, size and gingival height differences between cleft and non-cleft side after space closure of maxillary lateral incisor agenesis. Slight asymmetries in tooth position and gingival margin in the maxillary anterior teeth should be expected after orthodontic treatment in UCLP patients.


INTRODUCTION
Cleft lip and palate (CLP) is the most frequent craniofacial anomaly in humans. 1,2 Individuals with CLP often show facial and dental esthetics impairment, resulting in low self-stem and difficulties in social interactions. 3 Craniofacial rehabilitation aims to achieve adequate function and esthetics of the nose, lips and teeth, with the expectation to improve patient's quality of life. 4,5 Individuals with unilateral complete cleft lip and palate (UCLP) often have agenesis of the maxillary lateral incisors in the cleft area. 6,7 The gold standard treatment plan is the mesial movement of maxillary canines after secondary alveolar bone graft (SABG) surgery in order to replace the missing lateral incisor. 8,9 In non-cleft individuals, the orthodontic space closure of missing maxillary lateral incisors can provide excellent esthetics and functional results when multidisciplinary procedures are performed. [10][11][12] The main advantages of space closure include avoiding the use of dental prosthesis and implants, 13,14 and preventing long-term complications in gingival levels. [15][16][17][18] Particularly in individuals with UCLP, there is evidence that orthodontic space closure contributes to the maintenance of the alveolar graft in the cleft area, 19,20 providing improved esthetic outcomes, when compared to cases treated with dental implants or prosthetics in the missing lateral incisor area. 21 Few studies have been conducted in order to assess the anterior dental esthetics of individuals with UCLP. [21][22][23] reported that 13.3% of patients with UCLP considered their smile as esthetically unpleasant after complete dental rehabilitation.
The most common reasons for the dissatisfaction included tooth shape, tooth positioning, tooth contour/color, lip shape and level. 22 Another study in UCLP patients investigated the influence of various dental and surgical treatment options on gingival esthetics and oral health-related quality of life (OHRQoL). The authors concluded that natural teeth integrated into the cleft area showed more adequate esthetics and better quality of life perception. 21 No previous study evaluated the degree of symmetry of maxillary anterior teeth in patients with UCLP after orthodontic treatment with space closure of absent lateral incisors. Thus, the aim of this study was to compare dental position and gingival parameters of maxillary anterior teeth in UCLP patients after orthodontic treatment with canine substitution on the cleft side lateral incisor agenesis. The null hypothesis was that cleft and noncleft sides would demonstrate similar positional and gingival features of anterior teeth after orthodontic treatment.

MATERIAL AND METHODS
This split-mouth study was approved by the Institutional Review For measuring dental crown width and height, dental models were laterally rotated, in order to observe each tooth in a frontal perspective (Fig 2). For the other measurements, the models were fixed in the anterior frontal perspective, except for the crown inclination, which was measured from a distal view of each tooth crown. 24 The width dimension of the crown was considered the greatest distance between the mesial and distal contact points of each tooth. 25 The crown height was measured from the gingival zenith to the incisal edge. 25 The ratio between width and height was calculated. Teeth were measured twice by one investigator, with a minimal interval of three weeks. Intra-rater agreement was assessed using intraclass correlation coefficients (ICC). Clinical relevance was considered when statistical differences were greater than 0.5mm or 1 degree.

Mean differences between the linear and angular measurements
were smaller than 0.5 mm and 1 o , respectively.  A clinically significant asymmetry was observed for the gingival levels, which were more apically displaced in the cleft side for the central (+0.62mm) and lateral incisors (+0.81mm) ( Table 1).
A slight asymmetry was also observed for the incisal edge level of central incisor and canines, which were less extruded at the cleft side, without clinical relevance ( Table 1).

DISCUSSION
This is the first study analyzing the magnitude of asymmetries between cleft and noncleft side after comprehensive orthodontic treatment in patients with complete unilateral cleft lip and palate. The cleft side has limitations for orthodontic finishing including the frequent prevalence of missing lateral incisors, the alveolar bone defect and the scars and fibrosis of the reconstructive plastic surgeries. The method of measuring digital dental models showed an adequate reproducibility. The angular measurements showed slightly less agreement than linear measurements, and these results are in accordance to previous studies. 26,27 Digital dental models were previously validated to quantitative measurements. [28][29][30][31] An increased width for canines replacing lateral incisors on the cleft side was found, compared to the non-cleft side lateral incisor (Fig 4). A difficulty in achieving an acceptable esthetic  Canine width on the cleft side can be reduced with interproximal enamel reduction to improve final esthetic results. [10][11][12]32 However, there is a limit for interproximal reduction, to avoid dentin exposure. A previous study demonstrated that narrow canines were preferred in the position of lateral incisors. 33 No mesiodistal tooth size asymmetries were found for the max- In cases of missing lateral incisors followed by canine substitution in patients without oral clefts, premolar intrusion and canine extrusion can produce adequate gingival margin. [10][11][12][13][14][15] Previous studies in noncleft patients recommended the protocol of extrusion of maxillary canines and intrusion of the first premolars for space closure of lateral incisor agenesis for remodeling of the gingival margin, achieving an adequate esthetical outcome. 11,15,40,41 Although first premolars were slightly intruded and the canines extruded at the cleft side for improving the gingival margin, clinically relevant asymmetries between cleft and non-cleft side were still present after the orthodontic treatment. Crown heights were greater for U2 and smaller for U3 on the cleft side, in comparison to noncleft side (Fig 4). These differences were also reflected on the width/height ratio, gingival contour, gingival step and incisal step. The presence of asymmetries in dental and/or gingival margin might negatively influence the smile esthetics in patients with a high smile line. 42,43 Additionally, incisal reduction of canines and augmentation of the first premolars was previously recommended. 12 In the present study, an asymmetrical gingival level between cleft and non-cleft sides corroborated previous studies. 22,23,44 At the cleft side, the central incisor showed a more apical displaced gingival margin (Figs 4B and 4C). The central incisor on the cleft side is usually severely rotate in UCLP before treatment. Orthodontic rotation of central incisors might produce buccal bone dehiscence. [44][45][46] Furthermore, the flaps performed during secondary bone graft surgery may precipitate gingival recession in areas with buccal bone dehiscence. [44][45][46] Canine replacing the lateral incisor on the cleft side showed an apical displaced gingival margin of 0.8mm, compared to non-cleft side (Fig 4). Canines replacing lateral incisors on the cleft side should be extruded by bonding the bracket toward cervical or using step downs associated with incisal reduction in cases where the exposure during the smile is evident.
Central incisors at the cleft side were more mesiodistally upright, when compared to the contralateral teeth ( Fig 4C). » Cleft side central incisors were more upright than contralaterals.