Rapid prototyped patient specific guiding implants in critical mandibular reconstruction

Reconstruction of Composite Mandible Defects Using a Cellular Bone Allograft and Soft Tissue Free Flap Coverage

Study Design

Retrospective case series.

Objective

Cellular bone allografts (CBAs) contain the components of a successful bone graft with no autologous component and have been used extensively outside the head and neck. Descriptions of their utilization for mandible reconstruction are limited. We review our experience utilizing a CBA, with no autologous component, for the reconstruction of mandible defects.

Methods

Patients undergoing reconstruction of a composite mandible defect with a CBA, no added autologous component, within a patient-specific graft cage and soft tissue free flap coverage were retrospectively identified. Graft survival and defect management are assessed and results of post-operative imaging reported.

Results

Five subjects, aged 23-56 years, underwent reconstruction of mandible defects with the described technique. Defects resulted from gunshot wounds in 4 patients and the composite resection of a low-grade malignancy in one. The defect was definitively managed in 4 subjects, 3 of which had post-operative imaging demonstrating bone formation. The fifth experienced graft failure after developing an orocutaneous fistula and was successful salvaged with an osteocutaneous fibula free flap.

Conclusions

Our early experience is promising that a CBA, with no autologous component, and soft tissue free flap coverage can be used for the reconstruction of composite mandible defects in select patients.

Mandibular reconstruction in head and neck cancer: which is the gold standard?

INTRODUCTION

The aim of this study is to perform a systematic review to compare the outcomes of the different surgical options for mandibular reconstruction in head and neck cancer.

MATERIAL AND METHODS

93 articles were selected. Four groups were identified: titanium plate without flaps, titanium plate covered by soft tissue flap, bone tissue flaps and double flaps. We compared patients' characteristics, site of mandibulectomy, type of reconstruction and complications.

RESULTS

4697 patients were reported. The groups were not homogeneous regarding the type of defect and the treatment history. A significant difference in terms of post-operative complications was found between group 1 and group 2 (p < 0.00001), and between group 2 and group 3 (p < 0.00001). Total complications rate for group 4 was significantly higher when compared to group 3 (p < 0.00001), but no significant difference was found with group 2.

CONCLUSION

These results suggest that mandibular reconstruction using a microvascular bone flap is the best surgical option in patients without significant comorbidities.

Primary Reconstruction in Segmental Resection of Mandible-An Outcome Analysis of Different Reconstructive Techniques

Functional and cosmetic defects in the maxillofacial region may result from trauma, inflammatory disease, benign or malignant tumors. There are several well established reconstructive options for restoring mandibular continuity and function. Traditionally, surgeons have used their past experience to determine the best way to perform the osteotomy, graft harvesting, and graft shaping procedures for mandibular reconstruction. Focus has now shifted to optimize functional and aesthetic outcomes in mandible reconstruction. Refinements in surgical techniques continue to improve patient's quality of life. The purpose of this study was to evaluate the outcome of a range of reconstructive techniques in 20 patients who underwent segmental resection of mandible during the period 2004-2017.

Effect of Surface Tooling Techniques of Medical Titanium Implants on Bacterial Biofilm Formation In Vitro

The aim of this study was to assess the biofilm formation of Streptococcus mutans, Staphylococcus aureus, Enterococcus faecalis, and Escherichia coli on titanium implants with CAD-CAM tooling techniques. Twenty specimens of titanium were studied: Titanium grade 2 tooled with a Planmeca CAD-CAM milling device (TiGrade 2), Ti6Al4V grade 5 as it comes from CAD-DMLS device (computer aided design-direct metal laser sintering device) (TiGrade 5), Ti6Al4V grade 23 as it comes from a CAD-CAM milling device (TiGrade 23), and CAD-DMLS TiGrade 5 polished with an abrasive disc (TiGrade 5 polished). Bacterial adhesion on the implants was completed with and without saliva treatment to mimic both extraoral and intraoral surgical methods of implant placement. Five specimens/implant types were used in the bacterial adhesion experiments. Autoclaved implant specimens were placed in petri plates and immersed in saliva solution for 30 min at room temperature and then washed 3×with 1 ×PBS. Bacterial suspensions of each strain were made and added to the specimens after saliva treatment. Biofilm was allowed to form for 24 h at 37 °C and the adhered bacteria was calculated. Tooling techniques had an insignificant effect on the bacterial adhesion by all the bacterial strains studied. However, there was a significant difference in biofilm formation between the saliva-treated and non-saliva-treated implants. Saliva contamination enhanced S. mutans, S. aureus, and E. faecalis adhesion in all material types studied. S. aureus was found to be the most adherent strain in the saliva-treated group, whereas E. coli was the most adherent strain in the non-saliva-treated group. In conclusion, CAD-CAM tooling techniques have little effect on bacterial adhesion. Saliva coating enhances the biofilm formation; therefore, saliva contamination of the implant must be minimized during implant placement. Further extensive studies are needed to evaluate the effects of surface treatments of the titanium implant on soft tissue response and to prevent the factors causing implant infection and failure.

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.

Design Criteria for Patient-specific Mandibular Continuity Defect Reconstructed Implant with Lightweight Structure using Weighted Topology Optimization and Validated with Biomechanical Fatigue Testing

This study developed design criterion for patient-specific reconstructed implants with appearance consideration and structural optimization of various mandibular continuity defects. The different mandible continuity defects include C (from left to right canines), B (from 1^st premolar to 3^rd molar), and A (from 3^rd molar to ramus) segments defined based on the mandible image. The finite element (FE) analysis and weighted topology optimization methods were combined to design internal support beam structures within different reconstructed implants with corresponding occlusal conditions. Five continuity mandibular defects (single B/C/A+B and combination of B+C and B+C+B segments) were restored using additive manufacturing (AM) reconstructed implant and bone plate to confirm reasonable design criterion through biomechanical fatigue testing. The worst mandible strength was filtered based on the material mechanics and results from segmental bone length, thickness, and height statistics from the established database containing mandible images of 105 patients. The weighted optimization analysis results indicated that the sizes and positions of internal supporting beams within the reconstructed C, B, and A+B implants can be defined parametrically through corresponding segmental bone length, width, and height. The FE analysis found that the weight variation percentage between the parametric designed implants and original core solid implants in the C, B, and A+B was reduced by 54.3%, 63.7%, and 69.7%, respectively. The maximum stress values of the reconstructed implant and the remaining bone were not obviously reduced but the stress values were far lower than the material ultimate strength. The biomechanical fatigue testing indicated that all cases using the AM reconstructed implant could pass the 250,000 dynamic load. However, condyle head, bone plate fracture, and bone screw loosening could be found in cases using bone plates. This study developed a design criterion for patient-specific reconstructed implants for various mandibular continuity defects applicable for AM to further clinical use.

Investigation of Patient-Specific Maxillofacial Implant Prototype Development by Metal Fused Filament Fabrication (MF3) of Ti-6Al-4V

Additive manufacturing (AM) and related digital technologies have enabled several advanced solutions in medicine and dentistry, in particular, the design and fabrication of patient-specific implants. In this study, the feasibility of metal fused filament fabrication (MF³) to manufacture patient-specific maxillofacial implants is investigated. Here, the design and fabrication of a maxillofacial implant prototype in Ti-6Al-4V using MF³ is reported for the first time. The cone-beam computed tomography (CBCT) image data of the patient’s oral anatomy was digitally processed to design a 3D CAD model of the hard tissue and fabricate a physical model by stereolithography (SLA). Using the digital and physical models, bone loss condition was analyzed, and a maxillofacial implant initial design was identified. Three-dimensional (3D) CAD models of the implant prototypes were designed that match the patient’s anatomy and dental implant requirement. In this preliminary stage, the CAD models of the prototypes were designed in a simplified form. MF³ printing of the prototypes was simulated to investigate potential deformation and residual stresses. The patient-specific implant prototypes were fabricated by MF³ printing followed by debinding and sintering using a support structure for the first time. MF³ printed green part dimensions fairly matched with simulation prediction. Sintered parts were characterized for surface integrity after cutting the support structures off. An overall 18 ± 2% shrinkage was observed in the sintered parts relative to the green parts. A relative density of 81 ± 4% indicated 19% total porosity including 11% open interconnected porosity in the sintered parts, which would favor bone healing and high osteointegration in the metallic implants. The surface roughness of Ra: 18 ± 5 µm and a Rockwell hardness of 6.5 ± 0.8 HRC were observed. The outcome of the work can be leveraged to further investigate the potential of MF³ to manufacture patient-specific custom implants out of Ti-6Al-4V.

Cumulative Inaccuracies in Implementation of Additive Manufacturing Through Medical Imaging, 3D Thresholding, and 3D Modeling: A Case Study for an End-Use Implant

In craniomaxillofacial surgical procedures, an emerging practice adopts the preoperative virtual planning that uses medical imaging (computed tomography), 3D thresholding (segmentation), 3D modeling (digital design), and additive manufacturing (3D printing) for the procurement of an end-use implant. The objective of this case study was to evaluate the cumulative spatial inaccuracies arising from each step of the process chain when various computed tomography protocols and thresholding values were independently changed. A custom-made quality assurance instrument (Phantom) was used to evaluate the medical imaging error. A sus domesticus (domestic pig) head was analyzed to determine the 3D thresholding error. The 3D modeling error was estimated from the computer-aided design software. Finally, the end-use implant was used to evaluate the additive manufacturing error. The results were verified using accurate measurement instruments and techniques. A worst-case cumulative error of 1.7 mm (3.0%) was estimated for one boundary condition and 2.3 mm (4.1%) for two boundary conditions considering the maximum length (56.9 mm) of the end-use implant. Uncertainty from the clinical imaging to the end-use implant was 0.8 mm (1.4%). This study helps practitioners establish and corroborate surgical practices that are within the bounds of an appropriate accuracy for clinical treatment and restoration.

Segmental Mandibular Reconstruction Using Tissue Engineering Strategies: A Systematic Review of Individual Patient Data

Objective

The aim of the systematic review was to analyze the current clinical evidence concerning the use of tissue engineering as a treatment strategy for reconstruction of segmental defects of the mandible and their clinical outcomes using individual patient data.

Methods

A systematic review of the literature was conducted using PubMed and Cochrane Library on May 21, 2019. The eligibility criteria included patients in whom segmental mandibular reconstruction was carried out using tissue engineering as the primary treatment strategy. After screening and checking for eligibility, individual patient data were extracted to the extent it was available. Data extraction included the type of tissue engineering strategy, demographics, and indication for treatment, and outcomes included clinical and radiographic outcome measures, vitality of engineered bone, dental rehabilitation, and patient-reported outcome measures and complications.

Results

Out of a total of 408 articles identified, 44 articles reporting on 285 patients were included, of which 179 patients fulfilled the inclusion criteria. The different tissue engineering treatment strategies could be broadly classified into 5 groups: "prefabrication," "cell culture," "bone morphogenetic protein (BMP) without autografts," "BMP with autografts," and "scaffolds containing autografts." Most included studies were case reports or case series. A wide variety of components were used as scaffolds, cells, and biological substances. There was not a single outcome measure that was both objective and consistently reported, although most studies reported successful outcome.

Discussion

A wide variety of tissue engineering strategies were used for segmental mandibular reconstruction that could be classified into 5 groups. Due to the low number of treated patients, lack of standardized and consistent reporting outcomes, lack of comparative studies, and low evidence of reported literature, there is insufficient evidence to recommend any particular tissue engineering strategy.

Reconstruction of a Large Posttraumatic Mandibular Defect Using Bone Tissue Engineering With Fresh-Frozen Humeral Allograft Seeded With Autologous Bone Marrow Aspirate and Vascularized With a Radial Forearm Flap

INTRODUCTION

Currently, vascularized autologous bone transplantation is considered the gold standard for large mandibular continuity defect reconstruction. Donor site morbidity is a major concern. Therefore, bone tissue engineering (BTE) seems to be the ideal solution. Fresh-frozen bone allograft is the closest material to autologous bone. The purpose of this clinical report is to show a new technique of large mandibular continuity defect reconstruction using a fresh-frozen humeral allograft seeded with autologous iliac bone marrow aspirate and vascularized with a radial forearm flap.

METHODS

A 33-year-old man presented with severe cranio-facial trauma resulting in several fractures of the facial skeleton including a comminuted mandibular fracture from left parasymphysis to left angle, which caused a large continuity defect.

RESULTS

Result at 6 months was aesthetically and functionally satisfactory with osseointegration of the bone graft.

DISCUSSION

The authors chose to use iliac bone marrow aspirate to seed the allograft scaffold since hematopoietic stem cells and mesenchymal stem cell are able to differentiate into osteoblasts, ease of harvest of the iliac crest and its low rate of morbidity. Contemporary biomaterials used for BTE are bioceramic but bone is still the better scaffold to engineer bone and only allografting avoids donor site morbidity. Vascularization is one of the main challenges of BTE; insertion of autologous vascular bundles from pedicle or free flaps is 1 solution. The authors chose the radial forearm flap since the pedicle is long and the authors did not need a great amount of soft tissue.

No differences in infections between patient-specific implants and conventional mini-plates in mandibular bilateral sagittal split osteotomy - Up to 3-year follow-up

The use of individually designed osteotomies, combined with individually manufactured osteosynthesis material, is rapidly becoming a standard for more challenging maxillofacial surgery. The benefits of patient-specific implants (PSI) in orthognathic surgery are clear in complex cases. PSIs can enhance precision and ease up the surgical protocol. We previously reported on the benefits of PSIs as reposition and fixation systems during Le Fort I osteotomy. The aim of this study was to evaluate a cohort of 28 patients, treated with bilateral sagittal split osteotomy (BSSO) and PSIs for fixation, with regard to healing for up to 3 years. A retrospective cohort of 48 patients with conventional mini-plate repositioned mandibles was also collected for statistical analysis. No statistically significant differences were found with regard to infection, soft tissue problems, or reoperations between these two groups.

Craniomaxillofacial patient-specific CAD/CAM implants based on cone-beam tomography data - A feasibility study

Customized implants have simplified surgical procedures and have improved patient outcome in craniomaxillofacial surgery. Traditionally, patient-specific data is gathered by conventional computed tomography (CT). However, cone-beam CT (CBCT) can generate a 3D reconstruction of the area of interest with a lower dose of radiation at reduced cost. In this study, we investigated the feasibility of using CBCT data to design and generate customized implants for patients requiring craniomaxillofacial reconstruction. We used CBCT to generate 62 implants for 51 consecutive patients admitted to our department between January 2015 and December 2017. The indications for reconstruction and types of reconstruction were very variable. In all cases, the implants were well fitted and no implant-related complications were detected. Pre-surgical planning was faster and more efficient as we did not have to consult a radiologist. Although CBCT data is more difficult to process than conventional CT data for the implant provider, the clinical advantages are pronounced and we now use CBCT as standard in our department. In conclusion, we have shown that using CBCT to design and manufacture customized implants for reconstruction of the craniomaxillofacial area is feasible and recommend this approach to other departments.

The use of patient-specific implants in orthognathic surgery: A series of 30 mandible sagittal split osteotomy patients

PURPOSE

Virtual surgery combined with patient-specific saw and drill guides and osteosynthesis materials are rapidly spreading from reconstructive surgery to orthognathic surgery. Most commercial partners are already providing computer-aided design and computer-aided manufacture (CAD/CAM) wafers and patient-specific saw guides. Clear benefits have been demonstrated for custom-made drill guides combined with individually designed three-dimensional (3D) printed patient-specific implants (PSI) as a reposition and fixation system in Le Fort I osteotomy.

MATERIALS AND METHODS

We treated 30 patients who underwent bilateral sagittal split osteotomy (BSSO) due to class II dento-skeletal deformities with the additional use of drill guides combined with PSI as a fixation and positioning system.

RESULTS

The PSIs fitted bilaterally with total precision in 11 of the 30 patients. In 17 patients, the PSIs were used with some modifications. In 2 of 30 patients, the PSIs could not be used as a fixation due to misfit.

CONCLUSION

Due to unpredictable fitting, the use of PSIs with drill guides alone in BSSO without wafers cannot be recommended. Further studies are needed to evaluate the interfering parts, which seem to be related to condylar positioning and bony interferences at the osteotomy sites.