INTRODUCTION

The literature describing characteristics of rotation of the maxillary central incisors in repaired complete unilateral cleft lip and palate (UCLP) is sparse.^1–9 While there has recently been an increased emphasis on evaluating cleft-side maxillary central incisor rotations in UCLP, most studies describe incisor rotation qualitatively, with a wide range in frequency from 42.7%⁴ to 83.6%,⁶ and the magnitude of rotation has rarely been described (Table 1). The pattern and magnitude of rotation of permanent maxillary first molars has largely been ignored in the published literature.

Table 1.  Studies in the Published Literature, Containing Data of Rotations of Permanent Maxillary Central Incisors in Unilateral Cleft Lip and Palate (UCLP)

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Severe rotation of maxillary central incisors can have serious consequences (Figure 1) and can lead to visible stigmata of the cleft lip deformity (Figure 2). Children affected by clefts with visible anomalies are more dissatisfied with their facial appearance than those without them.^10,11 Negative impacts and stigmatizing consequences of facial defects on the self-concept of children as young as 7 years have been documented,¹² making them vulnerable to teasing at school, which can persist throughout their teenage years.¹¹

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This study aimed to explore comprehensively the rotational features of the permanent maxillary central incisor and molar in the mixed dentition in repaired complete UCLP to better understand the basis of these aberrations. The permanent maxillary central incisors and permanent first molars were evaluated on the cleft and noncleft sides to study differences in the patterns, frequencies and magnitudes of their rotations, and further analyzed to study if these rotations were affected when some teeth in their vicinity were absent.

MATERIALS AND METHODS

Following Research Ethics Board approval, a retrospective chart review was undertaken to select patients with nonsyndromic complete UCLP who had received all of their lip and palate reparative surgeries at The Hospital for Sick Children, Toronto, Ontario, Canada. Orthodontic records, which are routinely taken at the center for all patients prior to beginning orthodontic preparation for alveolar bone grafting (ABG), were screened to include study models of patients who had not received any prior orthodontic treatment and had at least one permanent maxillary central incisor and one permanent maxillary first molar fully erupted. Further inclusion criteria required that none of the subjects had mandibular skeletal or dental asymmetry, which was verified from chart notes and photographs. A pair of dividers was used to measure linear distances from the mesial-cervical margin of the mandibular central incisors to the mesial contact points of each mandibular permanent first molar. Models in which the difference was less than 1 mm were selected. No other exclusion criteria were applied.

Longitudinal radiographic records and dental charts were studied to record tooth agenesis, as well as teeth that were lost after eruption, near the permanent central incisors and first molars. To study if the permanent maxillary central incisors and first molar rotations were affected when some teeth in their vicinity were absent, keeping in perspective the age at which this study was conducted, the presence or absence of a permanent tooth (lateral incisor or supernumerary permanent tooth) distal to the maxillary central incisor in the greater hemimaxilloalveolar segment was documented. For the permanent maxillary first molar, the absence of one or more deciduous buccal segment teeth (ie, deciduous canines and deciduous molars) or premolars was recorded. This absence could have resulted from premature loss of deciduous teeth and/or agenesis of permanent teeth.

Applying these criteria, the included sample comprised dental models of 74 children (53 male, 21 female) born with complete UCLP (30 right, 44 left). The mean age at which the models had been taken was 8.9 ± 1.0 years. All primary lip and palate surgeries had been conducted by any of the hospital's five staff surgeons. Lip repair techniques included the Millard, Tennison, or Fisher anatomic subunit techniques. Palate repair techniques included the von Langenbeck, Wardill-Killner pushback, or hybrid techniques. These surgical techniques are commonly followed around the world and therefore represented typical surgical treatment in UCLP. Ten percent of the sample had received secondary surgical procedures such as rhinoplasty, pharyngoplasty, and, rarely, redo palatoplasty prior to model acquisition.

A line was drawn using a 0.5-mm-thick pencil connecting the buccal groove of each mandibular permanent first molar to the bucco-occlusal surface of its opposing permanent maxillary first molar, in occlusion. The maxillary model was then mounted on a stand, and standardized occlusal photographs of the maxillary dental arch were acquired parallel to the occlusal plane using a 12.3-megapixel digital single lens reflex camera with a 90-mm macro lens, set at ISO 200, 1/30 second at f13, and the resolution set at 4,032 × 3,024 pixels. Each image was calibrated using a 10-mm plastic scale placed at the correct depth of field and parallel to the camera lens. Images were processed using Photoshop CS4 and Adobe Illustrator 4 (Adobe Systems Inc, San Jose, Calif). A horizontal construct (hc) was drawn connecting the right and left marks that had been made on the bucco-occlusal surface of the maxillary molars prior to photographing the models. A perpendicular line drawn at the midpoint of this horizontal construct was referred to as the midsagittal construct (msc) of the maxillary arch (Figure 3).

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Permanent maxillary central incisor rotation was measured as the internal angle between the mesial and distal line angles of its incisal edge and the msc (Figure 3). Based on whether the measured angle was greater than, equal to, or less than 90°, patterns of incisor rotation were recorded as distolabial, no rotation, or distopalatal, respectively. Permanent maxillary first molar rotation was measured as the internal angle formed between a tangent connecting its mesiobuccal and distobuccal cusps and the hc (Figure 3). Patterns of molar rotation were categorized as mesiobuccal, no rotation, or mesiopalatal, based on this angle in relation to 90°. One investigator completed all measurements.

Intraexaminer reliability was assessed by intraclass correlation coefficient analysis and Dahlberg's formula applied to repeated measurements made by the same investigator, 45 days apart. Descriptive statistics, paired t-tests, and Wilcoxon signed-rank tests were used as indicated to compare differences between the cleft and noncleft sides using paired measurements. Independent samples t-tests were conducted to compare the magnitude of the permanent central incisor and first molar rotation with and without the absence of a permanent tooth or one or more buccal segment teeth on the cleft and noncleft sides. The significance level for statistical tests was set at 5%.

RESULTS

Reliability tests showed excellent repeatability with small method errors (Table 2). Maxillary central incisor rotations on the cleft side were significantly greater than on the noncleft side, and this was also seen in molar rotations (Table 3). Most of the cleft side central incisors were rotated distolabially, while most of the noncleft side central incisors were rotated distopalatally (Table 4). Among subjects in whom incisor rotation was observed, a permanent tooth was absent distal to the cleft side maxillary central incisor in the greater hemimaxilloalveolar segment in 85.71% cases but in only 5.48% of cases on the noncleft side. A greater proportion of the cleft side central incisors were rotated distopalatally when a permanent tooth was present distal to them in the greater hemimaxilloalveolar segment than when it was absent (Table 5).

Table 2.  Repeatability of Measurements

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Table 3.  Magnitudes of Permanent Maxillary Central Incisor and First Molar Rotations

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Table 4.  Patterns and Magnitudes of Permanent Maxillary Central Incisor and First Molar Rotations^a

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Table 5.  Patterns and Magnitudes of Permanent Maxillary Central Incisor Rotations in the Presence or Absence of Permanent Teeth Distal to the Central Incisor in the Greater Hemimaxilloalveolar Segment^a

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The frequency of absence of buccal segment teeth was greater on the cleft side than on the noncleft side (Table 6). On average, 0.66 (0.39 deciduous, 0.27 permanent) teeth were not present in the buccal segment on the cleft side, and 0.58 (0.42 deciduous, 0.16 permanent) teeth were not present in the buccal segment on the noncleft side. The frequency of maxillary second premolar agenesis was 22.97% on the cleft side and 12.16% on the noncleft side. All except two permanent maxillary first molars were rotated mesiopalatally on both the cleft and noncleft sides. The magnitude of rotation of the permanent maxillary first molar was greater when one or more deciduous and/or permanent buccal segment teeth were not present (Table 6).

Table 6.  Patterns and Magnitudes of Permanent Maxillary First Molar Rotations in the Presence or Absence of Buccal Segment Teeth Mesial to the Permanent First Molars^a

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DISCUSSION

The aim of this study was to study comprehensively the incisor and molar rotations that are frequently seen in the mixed dentition in UCLP but have not been well elucidated in the literature. A systematic, qualitative, and quantitative analysis of these rotations in UCLP has not been reported previously (Table 1). To facilitate such an appraisal, a coordinate system was developed for maxillary arch analysis using digital image processing software, which facilitated making the desired measurements. This method was described previously.¹³ This system was required because of the lack of a reliable midline in the maxillary model due to the palate repair scar and the fact that the molar relationship was frequently different between the cleft and noncleft sides.¹³ This precluded using an intermolar line as a basis for the analysis. While an analysis based on craniofacial computed tomography (CT)¹⁴ or cone-beam CT could be more precise, it would have involved a significant amount of additional radiation. The system used in the current study did not involve such radiation exposure and allowed use of existing pretreatment models and records that were collected for a reasonably large number of children before pre-ABG orthodontic preparation as a part of the cleft team's routine protocol. CT scans were not available for these subjects.

The findings in this study were similar to those of Jabbari et al.⁸ and Chang et al.,⁹ and the frequency of the cleft side maxillary central incisor rotation found was in agreement with the findings of Pegelow et al.⁶ but were greater than that reported by Lai et al.,⁵ Tortora et al.,⁴ and Eslami et al.⁷ (Table 1). In the current study, the most frequent rotational pattern of cleft side central incisors was distolabial (77.14%), with the palatal surface rotated toward the cleft and a large magnitude of rotation (121.09° ± 24.50°). Conversely, 82.19% of the noncleft incisors were rotated distopalatally, also with the palatal surfaces turned toward the cleft, and the magnitude of rotation was smaller (71.98° ± 12.75°).

Ross and Johnston² suggested that postsurgical scar tissue induced the periodontal ligament to pull anterior teeth backward and rotated toward the palate. Ishikawa et al.¹⁵ described that the lingual inclination of the dentoalveolar process on the cleft side was a result of periosteal denudation of the bone and its scar tissue. Smahel et al.³ suggested that rotation of incisors could be a result of a lack of space at the end of the alveolar segment and might be associated with other factors such as absence of the lateral incisor and an anomaly of the dental anlage.

It may be hypothesized that the rotation patterns of both cleft and noncleft side central incisors can be explained by scar tissue from the repair of the anterior palate, with scar contracture potentially pulling the periodontal apparatus of these teeth, contributing to the characteristic direction of rotation. However, there are additional factors that contribute. Because of the frequently missing cleft side lateral incisor, the stabilizing effect of a normal transseptal fiber relationship between the central and lateral incisors is lacking on the cleft side, making single-rooted central incisors more prone to severe rotation on the cleft side. In this study, a permanent tooth distal to the cleft side central incisor in the greater hemimaxilloalveolar segment was absent in 85.71% subjects in whom rotation of the cleft side central incisor was measured. Of these, 78.33% had distolabial rotation of the cleft side central incisors, 6.67% had no rotation, and 15.00% had distopalatal rotation. In comparison, of the subjects who had a permanent tooth present distal to the cleft side central incisor, 30.00% showed distopalatal rotation of the central incisor and 70.00% showed distolabial rotation. Direction notwithstanding, the magnitude of rotation was greater when a permanent tooth was present distal to the cleft side central incisor in the hemimaxilloalveolar segment (Table 5). Lai et al.⁵ also found a greater chance of rotation of the maxillary central incisor when a permanent lateral incisor was present mesial to the cleft.⁵ These results highlight the contribution of crowding at the terminal end of the alveolar segment.

It may be further hypothesized that the cleft side central incisor is rotated more severely because it comes under the additional influence of asymmetric muscular contraction and pull on the greater hemimaxilloalveolar segment toward the noncleft side. Until ABG has been performed, the maxillary alveolus is discontinuous. The central incisor is the terminal tooth in the greater segment, which itself is tethered to the lip musculature by the mucosa and maxillary frenum. Studies on lip muscle and facial animation in children with clefts have described significant asymmetry in movements on the cleft and noncleft sides in the unrepaired state during infancy¹⁶ and asymmetrically restricted lateral movements in the long term¹⁷ due to the surgical scar. Ultrasound elastography has also revealed asymmetric muscular strain,¹⁸ with greater strain on the noncleft side. Although the repaired cleft lip exerts a constraining effect on the dentition, the terminal end of the greater hemimaxilloalveolus can receive an asymmetric muscular pull in many cases. This asymmetric muscular pull is seen in infancy prior to lip repair and likely manifests to a varying extent on the dental lamina and the dental arch, prior to ABG. Furthermore, distolabial rotation of the cleft side central incisor has also been reported in unoperated clefts¹⁹ and clefts of the lip only,⁶ which implicates asymmetric muscle pull as an additional factor that can influence maxillary incisor rotation patterns (Figure 4).

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Longitudinal studies on patterns and severities of rotation of maxillary incisors after their emergence are required to better elicit how these factors play a role in incisor positions. It is important to recognize that rotation of central incisors occurs frequently in UCLP and should be corrected when severe to prevent deleterious events such as trauma (Figure 1). A severely rotated maxillary central incisor is visible in the smile, drawing attention to the repaired cleft lip (Figure 2), and it can have unfavorable effects at a vulnerable age of psychological development of a child. If there is sufficient bone support for the cleft side incisor, correcting or reducing the severity of rotation before the ABG reduces treatment requirements after the surgery and allows better oral hygiene. These corrections facilitate better treatment outcomes of ABG.^8,9

Permanent maxillary first molar rotation in UCLP has been ignored in the literature. The nearly 7.5° greater magnitude of mesiopalatal rotation of the permanent maxillary first molar on the cleft side could have been associated with several factors, including scar contracture and missing teeth in the buccal segments, and can explain the greater frequency of Class II molar relationship seen on the cleft side in the mixed dentition.^13,20 The average number of buccal quadrant teeth that were absent and the frequency of second premolar agenesis were greater on the cleft side. The magnitude of mesiopalatal rotation of the permanent maxillary first molar on the noncleft side was significantly greater (P<.05) when one or more deciduous and/or permanent buccal segment teeth were not present (Table 6). These results highlight the association of maxillary molar rotation with the absence of teeth in their vicinity. These results also underscore the importance of preventing tooth loss in the buccal segments in the mixed dentition in UCLP.

CONCLUSIONS

• Distolabial rotation of the cleft side permanent maxillary central incisor and distopalatal rotation of the noncleft side central incisor were the most frequent incisor rotation presentations in the mixed dentition in UCLP.

• The magnitude of mesiopalatal rotation of the permanent maxillary first molar was greater on the cleft side than on the noncleft side.

• Crowding of anterior teeth in the greater segment was associated with greater magnitude of rotation of the cleft side permanent central incisor.

• Absence of one or more buccal segment teeth was associated with greater magnitude of rotation of the molar.