Effect of maxillary distraction osteogenesis and LeFort-1 advancement orthognathic surgery on soft-tissue thickness and anterior soft-tissue to hard-tissue movement ratios among patients with complete unilateral cleft lip and palate

INTRODUCTION

Midface hypoplasia, impaired growth, and a collapsed maxillary dental arch are some of the cardinal features of patients with cleft lip and palate (CL±P) anomaly. Conventional orthopedic/orthodontic approaches to treatments are sometimes successful in achieving stable occlusal relationships. However, sometimes they often fall short of expectations with respect to facial balance and esthetics. About one-quarter of patients with CL±P develop maxillary hypoplasia that cannot be corrected by orthodontic or orthopedic treatment alone and require orthosurgical intervention.^[1]

The restoration of facial balance and occlusion in severe skeletal discrepancy due to hypoplastic maxilla requires LeFort 1 advancement. In CL±P patients, due to the postoperative difficulties caused by the palatal scar contracture, maxillary advancement of >5–6 mm requires distraction osteogenesis for stable results.^[2-4]

Distraction osteogenesis technique has the advantage that allows a more gradual adaptation of surrounding soft-tissue drape and the palatal scar tissue, whereas this change is more acute in osteotomy cases, resulting in muscle imbalance and contractures.^[5] When gradual distraction forces are applied across the osteotomy site, not only does the callus elongates, but also the soft tissues grow in response to mechanical stress. Not mere stretching, but hyperplasia of soft tissue occurs, and this is termed as Distraction Histogenesis, and the outcome achieved with this treatment modality is believed to be more stable than LeFort-1 maxillary advancement.^[6]

The soft-tissue morphology and underlying hard tissue are closely related, and it is the soft-tissue profile of the patient that dictates the limits and esthetic outcomes of the treatment.^[7] The soft-tissue thickness in patients with unilateral cleft lip and/or palate (UCLP) has been evaluated using cone-beam computed tomography^[8] and lateral cephalogram.^[9]

Ewing and Ross^[9] found that soft-tissue changes following LeFort-1 maxillary advancement surgery in patients with UCLP were highly correlated with horizontal movement of the underlying skeletal bases with minimal changes in mandibular soft-tissue thickness. A systematic review conducted by Cheung and Chua^[10] (2006) concluded that there were no significant changes in soft-tissue thickness of patients with UCLP who underwent maxillary osteotomies.

A significant number of patients with CL±P anomalies are treated with an interdisciplinary approach for the comprehensive cleft care in our center. There is controversy between the results of the previous studies regarding the effect of maxillary advancement on lip thickness. Furthermore, due to the difference in the mechanism of maxillary advancement using single-stage advancement and distraction, there may be differences in the soft-tissues changes in the two procedures. Thus, it is important to study the effects of the two procedures for future treatment planning.

Hence, the purpose of this study was to compare the soft-tissue thickness and anterior soft-tissue to hard-tissue movement ratios in patients with UCLP following maxillary distraction osteogenesis using a rigid external distractor device and maxillary advancement at LeFort I level.

MATERIAL AND METHODS

This retrospective study was conducted following the guidelines of the Declaration of Helsinki for medical protocol and ethics and approved by the Institutional Ethics Committee (NK/6890/MDS/775). A prior sample size was calculated using G* Power statistical software based on the study of Chua and Cheung^[11] at alpha (α) value of 0.05, power of 90%, and 95% confidence interval. Power analysis showed a minimum of eight patients was required in each group.

A sample of 20 patients with complete UCLP with ten patients in each group were categorized into two groups. Group 1 comprised of seven male and three female patients with a mean age of 16.9 ± 3.11 years who underwent maxillary distraction osteogenesis at LeFort 1 level using Rigid External Distraction (RED) device; Group 2 comprised five males and five females with a mean age of 20 ± 4.29 years who underwent LeFort-1 maxillary advancement. The surgical procedures for all the subjects were performed by a single maxillofacial surgeon under general anesthesia. CL±P closure all the patients were done at the same institute, though the surgeons were different, following the same protocol.

The patients with a pre-surgical negative overjet of ≥5 mm were treated by maxillary distraction osteogenesis, while a negative overjet of <5 mm was managed with maxillary advancement orthognathic surgery. Non-syndromic patients with complete UCLP anomalies who underwent either maxillary distraction osteogenesis using a rigid external distraction device or maxillary advancement orthognathic surgery and skeletal class III pattern due to maxillary hypoplasia were included in the study. The growth completion in all the patients was assessed using the cervical vertebrae maturation index (CS 6) on lateral cephalogram.^[12] All the patients received isolated maxillary surgery only. Those with bilateral CL±P, isolated clefts of the palate or lip, craniofacial syndromes, and faulty or incomplete records were excluded from the study. The lateral cephalograms were taken before surgery (T0) and at six-month (T1) post-surgery were assessed with manual tracing.

The investigator was calibrated for registration, landmark identification, and measurement of soft-tissue thickness on lateral cephalogram. The intraexaminer reliability was assessed by repeating the measurement of selected parameters on 10% of all the lateral cephalograms selected randomly after an interval of three weeks. The value of intra class correlation (ICC) ranged from 0.938 to 0.999, which indicated an excellent reliability between 1^st and 2^nd measurements.

Soft-tissue thickness^[13] was calculated from hard tissue to corresponding soft-tissue landmarks, as shown in [Figure 1]. The changes in sagittal and vertical positions of the landmarks were assessed as perpendicular distances with respect to the horizontal reference line and vertical reference line reference planes at time interval (T0-T1), as shown in [Figure 2a and b]. Correlation between the anterior movement ratio of soft-tissue and hard-tissue landmarks was derived and compared between Group 1 and Group 2 patients.

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Figure 1:

Cephalometric landmarks and various soft-tissue thickness measurements; 1: Glabella-Soft-tissue glabella, 2: Nasion-Soft-tissue Nasion, 3: Rhinion-soft-tissue rhinion, 4: Orbitale to Soft-tissue Orbitale, 5: Point A-Subnasale, 6: Prosthion-Labrale Superius, 7: Upper incisor tip-Stomion, 8: Infradentale-Labrale Inferius, 9: Point B-Labiomentale, 10: Pogonion to soft-tissue Pogonion. Green dots: Hard tissue landmarks Red dots: Soft tissue Landmarks.

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Figure 2:

(a) Horizontal distance from vertical reference line to hard-tissue (Green dot) and soft-tissue (Red dot) landmarks: Horizontal distance from VRL to: 1: Pronasale (Point located on a tangent drawn perpendicular to HRL from Pn to avoid overlapping of 1 and 2), 2: Cheek point, 3: Subnasale, 4: Point A, 5: Labrale superius, 6: Stomion, 7: Upper incisor tip, 8: Labrale inferius, 9: Labiomentale, 10: Point B, 11: Pogonion, 12: Soft-tissue Pogonion. (b): Vertical distance from HRL to hard-tissue (Green dot) and soft-tissue (Red dot) landmarks: Vertical distance from HRL to: 1: Pronasale, 2: Labrale Inferius, 3: Soft-tissue Pogonion, 4: Labrale superius, 5: Labiomentale, 6: Subnasale, 7: Stomion, 8: Cheekpoint, 9: Pogonion, 10: Point B, 11: Upper incisor tip, 12: Point A, VRL: Vertical reference line, HRL: Horizontal reference line.

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RESULTS

The pre-surgical comparison of skeletal dysplasia (Wits appraisal) and overjet between Group 1 and Group 2 was statistically significant; however, the differences among various soft-tissue thickness parameters were statistically insignificant [Table 1]. In Group 1, soft-tissue thickness decreased (T0-T1) significant at subnasale, labrale superius, stomion, and labrale inferius (P < 0.05). Group 2 also showed significant decrease in soft-tissue thickness at subnasale, labrale inferius, and stomion (P < 0.05). The intergroup comparison showed a significantly greater decrease in soft-tissue thickness in Group 1 at labrale superius, stomion, and labrale inferius [Table 2].

Comparison of sagittal movement of various hard- and soft-tissue landmarks in Group 1 and Group 2 is shown in [Table 3]. The intragroup mean maxillary advancement in Group 1 and Group 2 was statistically significant at point A and upper incisal edge (P < 0.01). The intergroup comparison showed significantly greater maxillary advancement in Group 1 at Point A and upper incisal edge (P < 0.01). Group 1 showed greater advancements at Subnasale (P < 0.05), Labrale Superius, and Stomion (P < 0.01) as compared to Group 2. Downward displacement of Point A (P < 0.01), pogonion (Pog), labrale inferius, labiomentale, and soft-tissue pogonion (P < 0.05) was also greater in Group 1 when compared to Group 2 [Table 4].

The sagittal change in the hard-tissue parameters at dA, dU1, dB, and dPog was found to be positive and strongly correlated with the respective soft-tissue parameters except dC for Group 1 and dSn and dPog’ in Group 2 [Table 5]. In Group 1, a statistically highly significant strong positive correlation was found between vertical change in dU1 to soft-tissue dLs and dStms. In Group 2, change in hard-tissue point A was positively correlated with soft-tissue point dC and dStms and dU1 with dLs and dStm [Table 6].

DISCUSSION

The treatment modality for maxillary retrognathism in adult patients with CL±P is based on the extent of the deformity, degree of desirable jaw movement, and anticipated soft-tissue changes following surgical intervention.^[14] Traditional orthodontic and or orthopedic approaches, such as Facemask therapy to treat these patients in growing stage, often fall short of expectations with respect to facial balance and esthetics, despite obtaining a stable occlusal relationship.

In the present study, there was a significant difference of 5.80 mm in maxillary advancement between Group 1 and Group 2 as measured at Point A (U1), and the results were similar to the previous study by Markose et al.^[15] and Chua and Cheung.^[11]

CONCLUSION

1. In both groups, soft-tissue thickness was significantly reduced at subnasale, stomion, and labrale inferius (lower lip); however, reduction in thickness was not significant at labrale superius after LeFort 1 advancement surgery.

2. The sagittal movement of all soft-tissue landmarks strongly correlated with movement of the corresponding hard-tissue landmarks in both Group 1 and Group 2.

3. A marked positive and strong correlation was found between labrale superius and stomion points to the downward movement of the upper incisal edge in both Group 1 and Group 2.

4. There was significant soft-tissue lengthening at subnasale and the upper lip following maxillary distraction in Group 1.