Le Fort I osteotomies using Bio-Oss ®Collagen to promote bony union: a prospective clinical split-mouth study

Abstract

The purpose of this study was to evaluate whether a bone substitute can be used to promote bony union in patients undergoing maxillary advancement after Le Fort l osteotomy. Nine patients were treated bilaterally with Le Fort I osteotomies and maxillary advancements of 5 mm or less. In each patient, one gap was grafted with the bone substitute Bio-Oss ® Collagen (BOC). The contralateral site was left empty and served as control. After 6 months there were still empty gaps in the control sites of three patients, while in the grafted sites all gaps were completely filled with bone. The histomorphometric analysis performed with biopsies from the region of the original gap showed a similar amount of new bone in both groups, however, in the test group the mean overall amount of the mineralized fraction was higher compared to the control group (test site 65.0 ± 6.2%, control site 38.9 ± 32.6%). The bone substitute seemed to be a suitable material to promote bony union in Le Fort I osteotomies. Further studies are needed to analyse whether this technique is efficient in preventing relapse and promoting bony union in larger advancements.

Advancement of the maxilla by Le Fort I osteotomy has become a standard procedure to re-establish facial function and aesthetics, correct skeletal occlusal discrepancies and manage obstructive sleep apnoea. Definitive correction of these anomalies entails long-term stability of skeletal changes. Despite the use of rigid internal fixation with plates and screws, the attainment of three-dimensional skeletal stability remains a problem in the postoperative period. Indeed, the stability of the osteosynthesis may be inadequate if the size of the defect between the advanced inferior segment and the superior segment is wide enough to involve fibrotic tissue rather than robust bone along the osteosynthesis line. In this context, initial resistance to relapse is only exerted by this fibrotic scar and the plate and screw itself. The greater the maxillary advancement, the greater the risk of relapse.

In order to promote the bony union of the void and to reduce this relapse risk, bone grafts were introduced. Autogenous bone harvesting implies a second surgical site, thereby increasing morbidity and prolonging surgical time. Mouldable osteoconductive bone substitutes offer an excellent alternative to autogenous bone grafting by accelerating complete reossification of the inter-osteotomy gaps without increasing morbidity, surgical time and costs.

A bone substitute prepared from bovine bone (Bio-Oss ® Collagen (BOC), Geistlich Pharma AG, Wolhusen, Switzerland) was introduced several years ago to regenerate bone defects and was tested extensively for various indications in oral and maxillofacial surgery. It is available in granules, as a block or as a collagen block consisting of granules embedded in a spongy-like collagen structure. This collagen block can be easily conformed into the desired shape and effectively adheres to bony structures when wet. Bone cells penetrate the Bio-Oss structure through its interconnecting pores and form vital bone layers on the inert scaffold. Contrary to autogenous bone grafts, which show a 40% volume loss at 180 days due to resorption, Bio-Oss volume remains relatively stable (loss of approximately 15% at 90 and 180 days) and histological analysis does not show any signs of resorption. Initial volume reduction can be explained by shrinkage of the connective tissue and its remodelling process to native bone.

The purpose of this study was to evaluate clinically and histologically whether the bone substitute BOC could be a suitable treatment option to promote bony union in comparison to the non-grafted site in patients undergoing maxillary advancement with Le Fort l osteotomy. Owing to ethical reasons related to not placing a graft in the control side based on the split-mouth design of the study, only patients in whom maxillary advancement was 5 mm or less were included, since in these patients relapses in the non-grafted sites were not expected.

Materials and methods

Nine patients (5 men; 4 women) requiring a Le Fort I osteotomy with maxillary advancement ≤5 mm for correction of a maxillofacial deformity were prospectively recruited for this study. The mean age at the time of surgery was 20 ± 2.7 years. All patients gave their written informed consent to participate. The study was approved by the Ethical Committee of the Canton Aargau.

Le Fort l osteotomies were performed under general anaesthesia according to the standardized procedure. In brief, a vestibular incision was performed exposing the Le Fort l plane. The lateral wall of the sinus and the lateral nasal wall were cut bilaterally and the nasal septum was sectioned. Pterygomaxillary separation was performed using a curved osteotome. In the region of the zygomatic buttress, a chisel was placed in order to downfracture and pull down the maxillary fragment. After exposure of the posterior wall of the sinus, maxillary tuberosity and pterygoid process, the maxillary segments were pulled down and advanced. Small bone pieces and surplus parts of the sinus membranes were removed. Any interference between the posterior part of the maxilla and the pterygoid processes was eliminated with a piezoelectric saw (Piezosurgery ® 3, mectron s.p.a, Carasco, Italy). Care was taken not to damage the descending palatal artery. The maxillary segment was repositioned according to the pre-planned position using a wafer and fixed with 2.0 locking plates and screws (Synthes AG, Waldenburg, Switzerland).

In each patient, the inter-osteotomy gap was grafted with BOC on one side ( Fig. 1 ). The material (500 mg blocks) was moistened with sterile saline solution, conformed into the desired shape and applied with direct contact to the bony walls along the osteotomy line ( Fig. 2 ). The contralateral site was left ungrafted and served as a control. After a healing period of at least 6 months, the operated site was re-exposed under local anaesthesia and a biopsy from the region of the original gap was obtained bilaterally. Concomitantly with sample taking and although only about 10% of operated patients require osteosynthesis material removal after Le Fort I osteotomy, all hardware material was prophylactically removed. In case the bony void was not closed at that time, it was grafted with BOC. The results of bone formation were rated subjectively by the surgeon according to a visual analogue scale (VAS) ranging from 1 (bad) to 10 (excellent). At the end of the 1-year observation period, a radiographic control was performed in all patients (orthopantomography and tele-radiography, or cone-beam computed tomography (CBCT)).

Fig. 1
A Bio-Oss ® Collagen block is positioned in the gap in between the two plates.

Fig. 2
The Bio-Oss ® Collagen block has been moulded to fill the gap.

Histological processing

Bone biopsies were fixed in 4% formalin for 48 h, dehydrated in serial steps of ethanol (70%, 80%, 90%, 100%) remaining for 1 day in each of the ethanolic solutions, and then defatted for 1 day in xylene (Merck, Darmstadt, Germany). Specimens were infiltrated, embedded and polymerized in Technovit 9100 (Heraeus Kulzer, Wehrheim, Germany) according to the manufacturer’s instructions. After polymerization, samples were cut into 300 μm sections using a low-speed rotary diamond saw Microslice™ (Metals Research, Cambridge, UK). The sections were mounted onto opaque acrylic slides (Maertin, Freiburg, Germany) and ground to a final thickness of approximately 60 μm on a rotating grinding plate (Stuers, Ballerup, Denmark). Specimens were stained with azure II and pararosaniline (Merck, Darmstadt, Germany).

Histomorphometric analysis

Imaging was performed with an Axio Imager M1 microscope equipped with a digital AxioCam HRc (Carl Zeiss, Göttingen, Germany). Histomorphometrical analysis was achieved with analySIS FIVE – software (Soft Imaging System, Münster, Germany).

Results

In all nine patients, maxillary advancement by Le Fort I osteotomy proved an effective procedure to achieve the pre-planned occlusal and aesthetic change. Healing occurred uneventfully and results remained clinically stable at the 1-year follow-up (mean 383.2 days, range 367–412 days). The second surgery was performed an average of 206.56 days after the first procedure (range 174–251 days). When re-opening the sites, the control sites of three patients still presented empty gaps ( Fig. 3 ). Bony bridges were visible only at the location of the plates. In contrast, on the grafted sites, all gaps were completely filled with hard tissue ( Fig. 4 ). On VAS evaluation, test sites achieved a mean score of 9.7 ± 0.7, while control sites achieved 1.5 ± 1.5. Radiographic analysis corroborated the clinical findings ( Figs. 5 and 6 ). While some empty gaps bridged with soft tissue could be detected in control sites, test sites were filled with a thick bone-like structure, suggesting that early ossification was in progress probably due to the presence of BOC.

Fig. 3
Control site 6 months after surgery. A residual empty gap can be seen.

Fig. 4
Grafted test site 6 months after surgery: the former gap is completely filled with hard tissue.

Fig. 5
CBCT: the test site is filled with a thick bony structure.

Fig. 6
CBCT: the control site shows empty gaps bridged with soft tissue.

Histomorphometrically, the amount of new bone was similar in both groups ( Table 1 ), but the test group had a higher mineralized fraction and a lower soft tissue percentage in comparison to the control group.

Table 1
Histomorphometric results (mean ± standard deviation).
Test site Control site
% Bone 39.9 ± 15.6 38.9 ± 32.6
% Bone substitute 25.1 ± 10.8
% Soft tissue 35.0 ± 6.2 61.1 ± 32.6

Histological evaluation of the test sites demonstrated thick structures of mineralized tissue ( Fig. 7 ). The new bone presented predominantly with a lamellar, compact structure ( Fig. 8 ). The presence of active osteoblasts indicated on-going bone formation ( Fig. 9 ). Most bone substitute particles were completely integrated into the new bone forming solid hard tissue trabeculae. The tissue was well vascularized and showed no signs of inflammation.

Jan 24, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Le Fort I osteotomies using Bio-Oss ®Collagen to promote bony union: a prospective clinical split-mouth study
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