Reconstruction of canine mandibular bone defects using a bone transport reconstruction plate

3D printed plates based on generative design biomechanically outperform manual digital fitting and conventional systems printed in photopolymers in bridging mandibular bone defects of critical size in dogs

Conventional plate osteosynthesis of critical-sized bone defects in canine mandibles can fail to restore former functionality and stability due to adaption limits. Three-dimensional (3D) printed patient-specific implants are becoming increasingly popular as these can be customized to avoid critical structures, achieve perfect alignment to individual bone contours, and may provide better stability. Using a 3D surface model for the mandible, four plate designs were created and evaluated for their properties to stabilize a defined 30 mm critical-size bone defect. Design-1 was manually designed, and further shape optimized using Autodesk ^® Fusion 360 (ADF360) and finite element analysis (FE) to generate Design-2. Design-4 was created with the generative design (GD) function from ADF360 using preplaced screw terminals and loading conditions as boundaries. A 12-hole reconstruction titanium locking plate (LP) (2.4/3.0 mm) was also tested, which was scanned, converted to a STL file and 3D printed (Design-3). Each design was 3D printed from a photopolymer resin (VPW) and a photopolymer resin in combination with a thermoplastic elastomer (VPWT) and loaded in cantilever bending using a customized servo-hydraulic mechanical testing system; n = 5 repetitions each. No material defects pre- or post-failure testing were found in the printed mandibles and screws. Plate fractures were most often observed in similar locations, depending on the design. Design-4 has 2.8-3.6 times ultimate strength compared to other plates, even though only 40% more volume was used. Maximum load capacities did not differ significantly from those of the other three designs. All plate types, except D3, were 35% stronger when made of VPW, compared to VPWT. VPWT D3 plates were only 6% stronger. Generative design is faster and easier to handle than optimizing manually designed plates using FE to create customized implants with maximum load-bearing capacity and minimum material requirements. Although guidelines for selecting appropriate outcomes and subsequent refinements to the optimized design are still needed, this may represent a straightforward approach to implementing additive manufacturing in individualized surgical care. The aim of this work is to analyze different design techniques, which can later be used for the development of implants made of biocompatible materials.

Nonvascularized Bone Graft Reconstruction of the Irradiated Murine Mandible: An Analogue of Clinical Head and Neck Cancer Treatment

Nonvascularized bone grafts (NBGs) represent a practical method of mandibular reconstruction that is precluded in head and neck cancer patients by the destructive effects of radiotherapy. Advances in tissue-engineering may restore NBGs as a viable surgical technique, but expeditious translation demands a small-animal model that approximates clinical practice. This study establishes a murine model of irradiated mandibular reconstruction using a segmental iliac crest NBG for the investigation of imperative bone healing strategies. Twenty-seven male isogenic Lewis rats were divided into 2 groups; control bone graft and irradiated bone graft (XBG). Additional Lewis rats served as graft donors. The XBG group was administered a fractionated dose of 35Gy. All rats underwent reconstruction of a segmental, critical-sized defect of the left hemi-mandible with a 5 mm NBG from the iliac crest, secured by a custom radiolucent plate. Following a 60-day recovery period, hemi-mandibles were evaluated for bony union, bone mineralization, and biomechanical strength (P < 0.05). Bony union rates were significantly reduced in the XBG group (42%) compared with controls (80%). Mandibles in the XBG group further demonstrated substantial radiation injury through significant reductions in all metrics of bone mineralization and biomechanical strength. These observations are consistent with the clinical sequelae of radiotherapy that limit NBGs to nonirradiated patients. This investigation provides a clinically relevant, quantitative model in which innovations in tissue engineering may be evaluated in the setting of radiotherapy to ultimately provide the advantages of NBGs to head and neck cancer patients and reconstructive surgeons.

Critical Size Defects for Bone Regeneration Experiments in the Dog Mandible: A Systematic Review

OBJECTIVES

To perform a systematic literature review of studies involving critical size defects (CSDs) in the dog mandible and calvarium to find out the common characteristics of CSDs.

MATERIALS AND METHODS

Internet search of the literature was performed on June 2016 based on specific keywords. The search process included 5 databases. The Animal Research Reporting In Vivo Experiment (ARRIVE) guidelines was used to assess the quality of the included studies.

RESULTS

Nine studies have met the inclusion criteria and subjected to quality evaluation. All the defects (N = 156) were located in the mandible. Only 2 articles showed randomized controlled studies, whereas the remaining 7 were nonrandomized controlled studies. The geometry of the defects was either rectangular, box, cylindrical (circular), arch, or saddle shaped.

CONCLUSION

There is a lack of homogeneity in reporting data on CSDs in the dog mandible. Future animal studies should include a negative control group for an objective comparison and evaluation of any new biomedical materials. More awareness is needed for the Animal Research Reporting In Vivo Experiment (ARRIVE) guidelines to improve data reporting, which can facilitate comparison and reproducibility of future studies.

A composite critical-size rabbit mandibular defect for evaluation of craniofacial tissue regeneration

Translational biomaterials targeted toward the regeneration of large bone defects in the mandible require a preclinical model that accurately recapitulates the regenerative challenges present in humans. Computational modeling and in vitro assays do not fully replicate the in vivo environment. Consequently, in vivo models can have specific applications such as those of the mandibular angle defect, which is used to investigate bone regeneration in a nonload-bearing area, and the inferior border mandibular defect, which is a model for composite bone and nerve regeneration, with both models avoiding involvement of soft tissue or teeth. In this protocol, we describe a reproducible load-bearing critical-size composite tissue defect comprising loss of soft tissue, bone and tooth in the mandible of a rabbit. We have previously used this procedure to investigate bone regeneration, vascularization and infection prevention in response to new biomaterial formulations for craniofacial tissue engineering applications. This surgical approach can be adapted to investigate models such as that of regeneration in the context of osteoporosis or irradiation. The procedure can be performed by researchers with basic surgical skills such as dissection and suturing. The procedure takes 1.5-2 h, with ∼2 h of immediate postoperative care, and animals should be monitored daily for the remainder of the study. For bone tissue engineering applications, tissue collection typically occurs 12 weeks after surgery. In this protocol, we will present the necessary steps to ensure reproducibility; tips to minimize complications during and after surgery; and analytical techniques for assessing soft tissue, bone and vessel regeneration by gross evaluation, microcomputed tomography (microCT) and histology.

A New Way to Accelerate the Distraction of the Transpalatal Suture in Growing Dogs Using Recombinant Human Bone Morphogenetic Protein-2

OBJECTIVE

The purpose of this study was to evaluate the administration of recombinant human bone morphogenetic protein-2 (rhBMP-2) on trans-sutural distraction osteogenesis (TSDO) of the transverse palatal suture in growing dogs.

STUDY DESIGN

A total of 36 growing dogs were used in this study. The experimental animals were treated with different elastic force and rhBMP-2. The bone regeneration was determined with X-ray, histology, and clinical evaluation. The computed values underwent statistical analyses using analysis of variance.

RESULTS

The maxillary complex was most noticeably advanced with an applied elastic force of 600 g (22.4 ± 5.0 mm) and 800 g + rhBMP-2 (24 ± 5.1 mm). Immunohistochemical staining showed that the expression of bone morphogenetic protein-2 and bone morphogenetic protein-4 varied with different elastic force. These changes were statistically significant when 600 g and 800 g + rhBMP-2 were applied within 2 weeks of distraction when compared with controls (P < .05).

CONCLUSIONS

The results of this study suggest that TSDO in the growing dog should be safe and well tolerated when inducing bony lengthening of the maxilla. rhBMP-2 plays an important role in bone regeneration using TSDO.

Dynamic Analysis of New Bone Obtained by Nonvascular Transport Distraction Osteogenesis in Canines

PURPOSE

The aim of the present study was to construct a nonvascular transport disc to repair the canine mandibular defects model and to perform a dynamic analysis of the new bone obtained by nonvascular transport distraction osteogenesis (NTDO) in canines.

MATERIALS AND METHODS

Thirty adult dogs were randomly divided into 3 groups, with 10 dogs in each group. Canine mandibular defect models of NTDO were constructed. All the dogs were marked by tetracycline hydrochloride at a different distraction stage. The dogs were euthanized at 2, 4, and 12 weeks after distraction, and the quality ratio of calcium and phosphate for the new bone was measured using electron dispersive spectroscopy.

RESULTS

The canine mandibular defects were successfully repaired. Using tetracycline hydrochloride, we successfully observed the quality and speed of new bone formation. The quality ratio of calcium and phosphate was similar between the new bone formation and the original bone. The time spent using a nonvascular transport disc to repair mandibular defects was consistent with using a vascularized transport disc, and the quality of the new bone and the original bone was exactly the same.

CONCLUSION

When the bone mass is insufficient or the conditions are not suitable for a vascularized transport disc, the nonvascular transport disc can be used as an alternative.

Dentate transport discs can be used to reconstruct large segmental mandibular defects

PURPOSE

This study tested the use of a dentate transport segment for the reconstruction of a large U-shaped defect in the anterior segment of the canine mandible using a novel curved reconstruction plate. The quality and quantity of bone regenerate formed by dentate versus edentulous transport segments were compared.

MATERIALS AND METHODS

In 5 adult foxhound dogs, a defect of 70 to 75 mm was created in the canine mandible by excising the mandible anterior to the right and left fourth premolars. Reconstruction was performed by trifocal distraction osteogenesis using a bone transport reconstruction plate (BTRP-02), with 2 transport units being activated simultaneously, one on either side of the defect, 1 dentate and 1 edentulous. Bilateral distraction proceeded at a rate of 1 mm/day until the segments docked against each other in the midline. After 39 to 44 days of consolidation, the animals were euthanized. The quantity and quality of bone regeneration on the 2 sides were compared using micro-computed tomography.

RESULTS

The defect reconstruction was successful. The amount and quality of bone formed by the transport segments were similar on the 2 sides. There were no major differences in the bone volume fraction and density of the regenerate bone formed by the 2 transport segments. The bone volume fraction and density of the regenerate bone were considerably lower than those of the host bone in the distal segments, likely owing to the short consolidation period.

CONCLUSIONS

Bone transport remains a viable option in reconstructing anterior segmental defects in the mandible. The use of dentate or edentulous transport segments for reconstruction provides options for the surgeon in often highly compromised patients requiring these surgeries.

Biomimetic scaffolds facilitate healing of critical-sized segmental mandibular defects

OBJECTIVE

To investigate the efficacy of biomimetic PLGA scaffolds, alone and in combination with bone morphogenic protein (BMP-2) and adipose-derived stem cells (ASCs), to heal a critical-sized segmental mandibular defect in a rat model.

STUDY DESIGN

Prospective animal study.

METHODS

ASCs were isolated and cultured from the inguinal fat of Lewis rat pups. Using three-dimensional printing, PLGA scaffolds were fabricated and impregnated with BMP-2 and/or ASCs. Critical-sized 5-mm segmental mandibular defects were created in adult Lewis rats and implanted with (1) blank PLGA scaffolds, (2) PLGA scaffolds with ASCs, (3) PLGA scaffolds with BMP, or (4) PLGA scaffolds with BMP and ASCs. Animals were sacrificed at 12weeks. Bone regeneration was assessed using microCT, and graded on a semi-quantitative bone formation and bone union scale.

RESULTS

Twenty-eight rats underwent creation of segmental mandibular defects with implantation of scaffolds. Nine rats suffered complications and were excluded from analysis, leaving 19 animals for inclusion in the study. MicroCT analysis demonstrated no bridging of the segmental bony defect in rats implanted with blank scaffolds (median bone union score=0). Rats implanted with scaffolds containing BMP-2 (median bone union=2.0), ASCs (median bone union=1.5), and combination of BMP and ASCs (median bone union=1.0) demonstrated healing of critical-sized segmental mandibular defects. Bone regeneration was most robust in the BMP-2 treated scaffolds.

CONCLUSIONS

The current study utilizes a novel animal model to study the efficacy of biomimetic scaffolds carrying osteogenic factors to induce healing of a critical-sized segmental mandibular defect.

LEVEL OF EVIDENCE

N/A, Basic Science Animal Research.

Defining the critical-sized defect in a rat segmental mandibulectomy model

IMPORTANCE

Advances in tissue engineering offer potential alternatives to current mandibular reconstructive techniques; however, before clinical translation of this technology, a relevant animal model must be used to validate possible interventions.

OBJECTIVE

To establish the critical-sized segmental mandibular defect that does not heal spontaneously in the rat mandible.

DESIGN AND SETTING

Prospective study of mandibular defect healing in 29 Sprague-Dawley rats in an animal laboratory.

INTERVENTIONS

The rats underwent creation of 1 of 4 segmental mandibular defects measuring 0, 1, 3, and 5 mm. All mandibular wounds were internally fixated with 1-mm microplates and screws and allowed to heal for 12 weeks, after which the animals were killed humanely.

MAIN OUTCOMES AND MEASURES

Analysis with micro-computed tomography of bony union and formation graded on semiquantitative scales.

RESULTS

Seven animals were included in each experimental group. No 5-mm segmental defects successfully developed bony union, whereas all 0- and 1-mm defects had continuous bony growth across the original defect on micro-computed tomography. Three of the 3-mm defects had bony continuity, and 3 had no healing of the bony wound. Bone union scores were significantly lower for the 5-mm defects compared with the 0-, 1-, and 3-mm defects (P < .01).

CONCLUSIONS AND RELEVANCE

The rat segmental mandible model cannot heal a 5-mm segmental mandibular defect. Successful healing of 0-, 1-, and 3-mm defects confirms adequate stabilization of bony wounds with internal fixation with 1-mm microplates. The rat segmental mandibular critical-sized defect provides a clinically relevant testing ground for translatable mandibular tissue engineering efforts.

Transsutural distraction and tissue regeneration of the midfacial skeleton: experimental studies in growing dogs

Objective : The purpose of this study was to evaluate the effect of different mechanical forces on the expansion of the palatine suture using transsutural distraction osteogenesis. Methods : A total of 48 dogs were used in this study. The experimental groups were treated with a custom-designed internal distractor. Bone regeneration was determined with x-rays and histology. The computed values underwent statistical analyses using analysis of variance. Results : The maxillary complex was most noticeably advanced with an applied mechanical force of 600 g (20.15 ± 1.36 mm), compared with forces of 400 g (19.88 ± 1.41 mm) and 800 g (2.24 ± 0.93 mm). Immunohistochemical staining showed that the expression of bone morphogenetic protein-2 and bone morphogenetic protein-4 fluctuated with different mechanical forces. These changes were statistically significant when 600 g of force was applied within 30 days of distraction (P < .05). Conclusions : Transsutural distraction osteogenesis in the growing dog should be safe and well tolerated in inducing bony lengthening of the maxilla, and the optimal force is 600 × g. Bone morphogenetic protein-2 and bone morphogenetic protein-4 may play an important roles in the signaling pathways that link mechanical forces and biological responses.

Composite mandibulectomy: a novel animal model

OBJECTIVES

Segmental mandibular defects can result after the treatment of various pathologic processes, including osteoradionecrosis, tumor resection, or fracture nonunion with sequestration. The variety of etiologies and the frequency of occurrence make the reconstruction of segmental mandibular defects a topic of significant interest. Despite these incentives, a well-established small-animal model of the segmental mandibulectomy, including composite resection, does not exist. The objective of this study is the creation of a reliable animal model that can be used to study the reconstruction of en bloc mandibular defects. Surgical techniques and an array of reconstructive options are described.

STUDY DESIGN

Description of an animal model.

SETTING

Animal laboratory at a quaternary care university medical center.

METHODS

We present an Animal Research Oversight Committee-approved prospective analysis of survival operations in the rat model. A detailed, stepwise description of surgical technique and relevant intraoperative anatomy is presented. Postoperative management, early pitfalls, surgical complications, and future applications are discussed.

RESULTS

A total of 72 operations were performed by a single individual between July and October 2010. Two intraoperative and 9 postoperative complications were recognized. There were 6 orocutaneous fistulas, 2 abscesses, and 1 seroma. There were 4 fatalities, which were attributed to anesthetic complications (2, intraoperative), hematoma formation (1, postoperative), and foreign-body aspiration (1, postoperative).

CONCLUSION

This novel animal model reliably replicates the en bloc segmental mandibular defects seen in our patient population and can be manipulated to achieve a wide variety of research objectives.

Transport distraction osteogenesis for maxillomandibular reconstruction: current concepts and applications

Reconstruction of the facial skeleton remains a herculean task for a reconstructive surgeon, even with the availability of ample reconstructive options. Transport distraction osteogenesis is a novel reconstructive modality in the armamentarium of a maxillofacial reconstructive surgeon with obvious advantages of osteogenesis and histogenesis from the residual host tissues after tumor ablative surgeries or trauma and also, precludes donor site morbidity. This paper reviews the current concepts, principles involved and applications of transport distraction osteogenesis in maxillomandibular reconstruction.

Architecture and microstructure of cortical bone in reconstructed canine mandibles after bone transport distraction osteogenesis

Reconstruction of the canine mandible using bone transport distraction osteogenesis has been shown to be a suitable method for correcting segmental bone defects produced by cancer, gunshots, and trauma. Although the mechanical quality of the new regenerate cortical bone seems to be related to the mineralization process, several questions regarding the microstructural patterns of the new bony tissue remain unanswered. The purpose of this study was to quantify any microstructural differences that may exist between the regenerate and control cortical bone. Five adult American foxhound dogs underwent unilateral bone transport distraction of the mandible to repair bone defects of 30-35 mm. Animals were killed 12 weeks after the beginning of the consolidation period. Fourteen cylindrical cortical samples were extracted from the superior, medial, and inferior aspects of the lingual and buccal plates of the reconstructed aspect of the mandible, and 21 specimens were collected similarly from the contralateral aspect of the mandible. Specimens were evaluated using histomorphometric and micro-computed tomographic techniques to compare their microstructure. Except for differences in haversian canal area, histomorphometric analyses suggested no statistical differences in microstructure between regenerate and control cortical bone. Morphological evaluation suggested a consistent level of anisotropy, possibly related to the distraction vector. After 12 weeks' consolidation, bone created during bone transport distraction osteogenesis was comparable to native bone in microstructure, architecture, and mechanical properties. It is proposed that, after enough time, the properties of the regenerate bone will be identical to that of native bone.

Three-dimensional evaluation of mandibular bone regenerated by bone transport distraction osteogenesis

The purpose of this study was to evaluate the structure and material properties of native mandibular bone and those of early regenerate bone, produced by bone transport distraction osteogenesis. Ten adult foxhounds were divided into two groups of five animals each. In all animals, a 3- to 4-cm defect was created on one side of the mandible. A bone transport reconstruction plate, consisting of a reconstruction plate with an attached intraoral transport unit, was utilized to stabilize the mandible and regenerate bone at a rate of 1 mm/day. After the distraction period was finished, the animals were killed at 6 and 12 weeks of consolidation. Micro-computed tomography was used to assess the morphometric and structural indices of regenerate bone and matching bone from the unoperated contralateral side. Significant new bone was formed within the defect in the 6- and 12-week groups. Significant differences (P ≤ 0.05) between mandibular regenerated and native bone were found in regard to bone volume fraction, mineral density, bone surface ratio, trabecular thickness, trabecular separation, and connectivity density, which increased from 12 to 18 weeks of consolidation. We showed that regenerated bone is still mineralizing and that native bone appears denser because of a thick outer layer of cortical bone that is not yet formed in the regenerate. However, the regenerate showed a significantly higher number of thicker trabeculae.

Bone regeneration and docking site healing after bone transport distraction osteogenesis in the canine mandible

PURPOSE

Bone transport distraction osteogenesis provides a promising alternative to traditional grafting techniques. However, existing bone transport distraction osteogenesis devices have many limitations. The purpose of this research was to test a new device, the mandibular bone transport reconstruction plate, in an animal model with comparable mandible size to humans and to histologically and mechanically examine the regenerate bone.

MATERIALS AND METHODS

Eleven adult foxhounds were divided into an unreconstructed control group of 5 animals and an experimental group of 6 animals. In each animal, a 34-mm segmental defect was created in the mandible. The defect was reconstructed with a bone transport reconstruction plate. Histologic and biomechanical characteristics of the regenerate and unrepaired defect were analyzed and compared with bone on the contralateral side of the mandible after 4 weeks of consolidation.

RESULTS

The reconstructed defect was bridged with new bone, with little bone in the control defect. Regenerate density and microhardness were 22.3% and 42.6%, respectively, lower than the contralateral normal bone. Likewise, the anisotropy of the experimental group was statistically lower than in the contralateral bone. Half the experimental animals showed nonunion at the docking site.

CONCLUSION

The device was very stable and easy to install and activate. After 1 month of consolidation, the defect was bridged with new bone, with evidence of active bone formation. Regenerate bone was less mature than the control bone. Studies are underway to identify when the regenerate properties compare with normal bone and to identify methods to augment bone union at the docking site.

Biomechanical configurations of mandibular transport distraction osteogenesis devices

Mandibular bone transport (MBT) distraction osteogenesis devices are used for achieving reconstruction of mandibular defects in a predictable way, with few complications, less complexity than other alternative surgical procedures, and minimal tissue morbidity. However, selection of appropriate MBT device characteristics is critical for ensuring both their mechanical soundness and their optimal distraction function for each patient's condition. This article assesses six characteristics of currently available MBT devices to characterize their design and function and to classify them in a way that assists the selection of the best device option for each clinical case. In addition, the present work provides a framework for both the biomechanical conception of new devices and the modification of existing ones.