The effect of fixation plate use on bone healing during the reconstruction of mandibular defects

Use of customized 3-dimensional printed mandibular prostheses with a dental implant pressure-reducing device in mandibular body defect: A finite element study performing multiresponse surface methodology

Background/purpose

Segmental body defects of the mandible result in the complete loss of the affected region. In our previous study, we investigated the clinical applicability of a customized mandible prosthesis (CMP) with a pressure-reducing device (PRD) in an animal study. In this study, we further incorporated dental implants into the CMP and explored the use of dental implant PRD (iPRD) designs.

Materials and methods

By employing a finite element analysis approach, we created 4 types of CMP: CMP, CMP with iPRD, CMP-PRD, and CMP-PRD with iPRD. We developed 2 parameters for the iPRD: cone length (CL) in the upper part and spring pitch (SP) in the lower part. Using the response surface methodology (RSM), we determined the most suitable structural assignment for the iPRD.

Results

Our results indicate that CMP-PRD had the highest von Mises stress value for the entire assembly (1076.26 MPa). For retentive screws and abutments, CMP with iPRD had the highest von Mises stress value (319.97 and 452.78 MPa, respectively). CMP-PRD had the highest principal stress (131.66 MPa) in the anterior mandible. The iPRD reduced principal stress in both the anterior and posterior mandible. Using the RSM, we generated 25 groups for comparison to achieve the most favorable results for the iPRD and we might suggest the CL to 12 mm and the SP to 0.4 mm in the further clinical trials.

Conclusion

Use of the PRD and iPRD in CMP may resolve the challenges associated with CMP, thereby promoting its usage in clinical practice.

Total mandible and bilateral TMJ reconstruction combining a customized jaw implant with a free fibular flap: a case report and literature review

BACKGROUND

The need for whole mandibular bone reconstruction and bilateral joint replacement is fortunately rare, but it is an extremely challenging topic in maxillofacial surgery, due to its functional implications. CAD-CAM techniques development has opened new broad horizons in the surgical planning of complex maxillofacial reconstructions, in terms of accuracy, predictability, and functional cosmetic results. The review of the literature has revealed a small number of scientific reports on total mandibulectomy including the condyles, with only eleven cases from 1980. Most of the works describe reconstructions secondary to dysplastic or inflammatory diseases affecting the lower jaw. The aim of this work, reporting a rare case of massive fibrous dysplasia of the whole mandible, is to share our experience in the management of extended mandibular and bilateral joint reconstruction, using porous titanium patient-specific implants.

CASE PRESENTATION

The authors present a 20-year-old male patient suffering from massive bone fibrous dysplasia of the mandible. The mandibular body and both the rami and the condylar processes had been involved, causing severe functional impairment, tooth loss, and facial deformation. The young patient, after repeated ineffective conservative surgical treatments, has required a biarticular mandibular replacement. Using virtual surgical planning (VSP) software, the authors, in collaboration with medical engineers, have created a custom-made original titanium porous mandibular implant, suspended from a bilateral artificial temporomandibular joint. The mandibular titanium implant body has been specifically designed to support soft tissues and to fix, in the alveolar region, a free fibular bone graft, for delayed dental implant prosthetic rehabilitation.

CONCLUSION

The surgical and technical details, as well as the new trends in mandibular reconstructions using porous titanium implants, are reported, and discussed, reviewing literature reports on this topic. Satisfactory functional and cosmetic restorative results have been obtained, and no major complications have occurred. The patient, currently in the 18^th month clinical and radiological follow-up, has recently completed the functional restoration program by an implant-supported full-arch dental prosthesis.

The Use of Customized Three-Dimensionally Printed Mandible Prostheses with a Pressure-Reducing Device: A Finite Element Analysis in Different Chewing Positions, Biomechanical Testing, and In Vivo Animal Study Using Lanyu Pigs

Segmental bony defects of the mandible constitute a complete loss of the regional part of the mandible. Although several types of customized three-dimension-printed mandible prostheses (CMPs) have been developed, this technique has yet to be widely used. We used CMP with a pressure-reducing device (PRD) to investigate its clinical applicability. First, we used the finite element analysis (FEA). We designed four models of CMP (P1 to P4), and the result showed that CMP with posterior PRD deployment (P4 group) had the maximum total deformation in the protrusion and right excursion positions, and in clenching and left excursion positions, posterior screws had the minimum von Mises stress. Second, the P4 CMP-PRD was produced using LaserCUSING from titanium alloy (Ti-6Al-4V). The fracture test result revealed that the maximum static pressure that could be withstood was 189 N, and a fatigue test was conducted for 5,000,000 cycles. Third, animal study was conducted on five male 4-month-old Lanyu pigs. Four animals completed the experiment. Two animals had CMP exposure in the oral cavity, but there was no significant inflammation, and one animal had a rear wing fracture. According to a CT scan, the lingual cortex of the mandible crawled along the CMP surface, and a bony front-to-back connection was noted in one animal. A histological examination indicated that CMP was significantly less reactive than control materials (p = 0.0170). Adequate PRD deployment in CMP may solve a challenge associated with CMP, thus promoting its use in clinical practice.

Cystathionine γ-lyase-H2S facilitates mandibular defect healing via inducing osteogenic differentiation of bone marrow mesenchymal stem cells

OBJECTIVE

To investigate the effects of endogenous hydrogen sulfide (H₂S) synthase, cystathionine-γ-lyase (CSE), on the healing of mandibular defect and the osteogenic differentiation of human mandibular bone marrow mesenchymal stem cells (HM-BMMSCs).

METHODS

Sixty 8-week male C57BL/6 wild-type (WT) mice and CSE knockout (CSE^-/-) mice were divided into WT group, CSE^-/- group and CSE^-/- + GYY4137 (a slow-releasing H₂S donor) group. Mandibular defect healing in each group was identified by micro-CT. The histological staining and immunohistochemical staining were adopted to evaluate bone regeneration and reconstruction of mandibular defect. HM-BMMSCs were extracted and cultured for osteogenic induction, which were divided into control group, PAG (a CSE inhibitor) group, GYY4137 group and PAG + GYY4137 group. The mineralization of HM-BMMSCs in each group was determined by alkaline phosphatase (ALP) staining and alizarin red staining. Moreover, mRNA expressions of ALP and Runt-related transcription factor 2 (RUNX2) were detected by RT-PCR.

RESULTS

Mandibular defect healing in CSE^-/- mice was undesirable. When exogenous H₂S were supplemented to CSE^-/- mice, the new bone mass increased with higher degrees of bone mineralization and bone maturity. Bone mineral density (BMD), bone volume fraction (BV/TV) and bone trabecular thickness (Tb.Th) also significantly increased. in vitro experiments showed that PAG attenuated ALP activity and mineralized nodule formation ability in HM-BMMSCs, and repressed mRNA expressions of ALP and RUNX2. All these osteogenic indexes of HM-BMMSCs were reversed after exogenous H₂S was supplemented.

CONCLUSION

It is demonstrated that CSE deficiency thwarts the healing of mandibular defect. Blocking the synthesis of H₂S inhibits the osteogenic differentiation of HM-BMMSCs, thereby affects bone healing.