Mandibular magnetic distractor: preclinical validation.

The feasibility of magnetic activation for mandibular distraction has been demonstrated previously. In this study, we developed a biocompatible device to evaluate the feasibility of distraction in cadaveric subjects and the functionality of the device in bench tests. To confirm, considering the dimension of the distractor, that the torque applied on the internal magnet would be sufficient to activate distraction osteogenesis we measured, for different distances, the transmitted torque between a magnet (internal and external). We evaluated the friction force of the device, and the resilience of the magnet to the sterilisation process. To confirm the feasibility of distraction with this device, we proceeded to cadaveric tests, and evaluated the satisfaction of four surgeons. The force applied to the moving plate was greater than 50 Newtons (N) with a friction coefficient of η=0.2. We determined a friction torque of 65.10-3 N.mm in the distractor mechanism and demonstrated that sterilisation did not alter the magnet. Mandibular distraction had been successfully achieved in cadaveric trials, and surgeons were satisfied. This new device could be implanted in human subjects, for clinical assay, after approval by the regulatory agencies. The use of this fully internalised device should improve patients' comfort.

Sagittal split ramus osteotomy-related biomechanical properties.

Sagittal split ramus osteotomy (SSRO) is one of the most common maxillofacial operations, and the technique relies on a directed fracture involving different biomechanical variables. The aim of this study was to find out the biomechanical characteristics involved during each step of sagittal split osteotomy. We sampled eight fully dentate human mandibles and used the right side for hardness tests and the left side for a traction-to-fracture test within an unfinished SSRO. Right sides were sampled in five parts underlying the corticotomy course and tested with a hardness testing automatic machine. The mean hardness measures ranked to 21.5HV (Hardness Vickers Unit): 17.8HV; 27.4HV; 22.7HV; 28.7HV; for the lingual, diagonal, vestibular, full ramus, and full body samples, respectively. Left sides were cut using Epker's technique, and split with an electromechanical testing machine. The higher values reached before fracture in the traction-to-fracture tests ranked to 99.1N/6.7mm; 137.2N/10.8mm; 36.2N/4.2mm; 93.0N/7.3mm; 74.0N/8.1mm; 78.1N/4.5mm; 90.9N/10.6mm; and 64.7N/4.1mm, respectively, for specimens I, II, III, IV, V, VI, VII and VIII. This study provides to our knowledge the first biomechanical characteristics of SSRO and proposes a reproducible method for evaluation.

Maxillary shape after primary cleft closure and before alveolar bone graft in two different management protocols: A comparative morphometric study.

AIM AND SCOPE: Result assessment in cleft surgery is a technical challenge and requires the development of dedicated morphometric tools. Two cohorts of patients managed according to two different protocols were assessed at similar ages and their palatal shape was compared using geometric morphometrics. MATERIAL AND METHODS: Ten patients (protocol No. 1) benefited from early lip closure (1-3 months) and secondary combined soft and hard palate closure (6-9 months); 11 patients (protocol No. 2) benefited from later combined lip and soft palate closure (6 months) followed by hard palate closure (18 months). Cone-Beam Computed Tomography (CBCT) images were acquired at 5 years of age and palatal shapes were compared between protocols No. 1 and No. 2 using geometric morphometrics. RESULTS: Protocols No. 1 and No. 2 had a significantly different timing in their surgical steps but were assessed at a similar age (5 years). The inter-canine distance was significantly narrower in protocol No. 1. Geometric morphometrics showed that the premaxillary region was located more inferiorly in protocol No. 1. CONCLUSION: Functional approaches to cleft surgery (protocol No. 2) allow obtaining larger inter-canine distances and more anatomical premaxillary positions at 5 years of age when compared to protocols involving early lip closure (protocol No. 1). This is the first study comparing the intermediate results of two cleft management protocols using 3D CBCT data and geometric morphometrics. Similar assessments at the end of puberty are required in order to compare the long-term benefits of functional protocols.