Design and Finite Element Analysis of Patient-Specific Total Temporomandibular Joint Implants

In this manuscript, we discuss our approach to developing novel patient-specific total TMJ prostheses. Our unique patient-fitted designs based on medical images of the patient’s TMJ offer accurate anatomical fit, and better fixation to host bone. Special features of the prostheses have potential to offer improved osseo-integration and durability of the devices. The design process is based on surgeon’s requirements, feedback, and pre-surgical planning to ensure anatomically accurate and clinically viable device design. We use the validated methodology of FE modeling and analysis to evaluate the device design by investigating stress and strain profiles under functional/normal and para-functional/worst-case TMJ loading scenarios

The Development of a Temporomandibular Force Simulator to Study Craniofacial Strain In-Vitro

An in-vitro musculoskeletal loading simulator was developed to replicate the internal forces of mastication, and then employed in a comparison of clinically relevant facial fracture repairs. Muscle forces are simulated by pneumatic pistons via 3D printed mounts that are reverse-engineered from CT scan to match muscle attachment sites, which are adhered to bone in order to simulate native stress distributions. Bite force and bone strain pattern of the craniofacial structure under load were measured using a force sensor and strain gauges respectively. In a series of five fresh-frozen cadaveric heads, it was found that strain patterns of the craniofacial structure were different between internal and external loading. In a zygomatic complex fracture with an intact zygomatic arch, an infraorbital rim plate made no difference in strain pattern. However, with a fractured arch, a repair done without an infraorbital rim plate better restored the strain pattern of an intact craniofacial structure

3D Innovations in Personalized Surgery

Current practice involves the use of 3D surgical planning and patient-specific solutions in multiple surgical areas of expertise. Patient-specific solutions have been endorsed for several years in numerous publications due to their associated benefits around accuracy, safety, and predictability of surgical outcome. The basis of 3D surgical planning is the use of high-quality medical images (e.g., CT, MRI, or PET-scans). The translation from 3D digital planning toward surgical applications was developed hand in hand with a rise in 3D printing applications of multiple biocompatible materials. These technical aspects of medical care require engineers’ or technical physicians’ expertise for optimal safe and effective implementation in daily clinical routines.The aim and scope of this Special Issue is high-tech solutions in personalized surgery, based on 3D technology and, more specifically, bone-related surgery. Full-papers or highly innovative technical notes or (systematic) reviews that relate to innovative personalized surgery are invited. This can include optimization of imaging for 3D VSP, optimization of 3D VSP workflow and its translation toward the surgical procedure, or optimization of personalized implants or devices in relation to bone surgery

A COMPARATIVE HISTOMORPHOLOGICAL AND MICRO CT STUDY OF THE PRIMARY STABILITY AND THE OSSEOINTEGRATION OF THE SYDNEY MINI-SCREW: AN ANIMAL STUDY USING NEW ZEALAND RABBITS

Introduction: Failure rate of orthodontic miniscrews (MSs) is 7-50%. To address this problem and to promote primary stability of the miniscrew (MS), we recently designed and developed The Sydney Mini Screw (SMS, Patent number: PCT2009014) which can be used with injectable bone graft substitutes (iBGS). The aim of this study was to assess in vivo dispersion of bone graft substitutes (BGS) and the integration of the SMS to the cortical and trabecular bone using New Zealand femur and tibia rabbit model. Method: Twenty-four MSs were randomly placed in each proximal tibia and femur of 6 New Zealand rabbits with an open surgery process. Aarhus MS was used as a control and the effect of injection of BGS was studied by implanting SMS with and without BGS injection. The dispersion and integration of the MS were studied by using micro CT (μCT) and histochemical analysis at two time points, 0 day and 8 weeks post-implantation. Results: BGS were successfully injected to the SMS and thereafter hardened in situ to fill the bone void. After 8 weeks, μCT results revealed that the iBGS were resorbed and bone tissue was formed around the MS and within its lateral exit holes. The osteointegration of the SMS samples showed similar histologic characteristics to that of Arhus controls, and initial drilling for injection of bone cements into SMS did not seem to affect adjacent bone quality. Conclusion: Results of this pilot animal study showed the high potential of SMS and the developed technique to promote the primary stability of MS. Keywords: Primary stability; orthodontic miniscrew; injectable bone graft substitute

Novel finite element-based plate design for bridging mandibular defects:Reducing mechanical failure

Introduction: When the application of a free vascularised flap is not possible, a segmental mandibular defect is often reconstructed using a conventional reconstruction plate. Mechanical failure of such reconstructions is mostly caused by plate fracture and screw pull-out. This study aims to develop a reliable, mechanically superior, yet slender patient-specific reconstruction plate that reduces failure due to these causes. Patients and Methods: Eight patients were included in the study. Indications were as follows: fractured reconstruction plate (2), loosened screws (1) and primary reconstruction of a mandibular continuity defect (5). Failed conventional reconstructions were studied using finite element analysis (FEA). A 3D virtual surgical plan (3D-VSP) with a novel patient-specific (PS) titanium plate was developed for each patient. Postoperative CBCT scanning was performed to validate reconstruction accuracy. Results: All PS plates were placed accurately according to the 3D-VSP. Mean 3D screw entry point deviation was 1.54 mm (SD: 0.85, R: 0.10–3.19), and mean screw angular deviation was 5.76° (SD: 3.27, R: 1.26–16.62). FEA indicated decreased stress and screw pull-out inducing forces. No mechanical failures appeared (mean follow-up: 16 months, R: 7–29). Conclusion: Reconstructing mandibular continuity defects with bookshelf-reconstruction plates with FEA underpinning the design seems to reduce the risk of screw pull-out and plate fractures

Evaluation of deflection characteristics of mini implants following placement: An Ex-vivo study

AIM OF THE STUDY: To radiographically evaluate and compare the deflection characteristics of self-drilling titanium alloy mini implants when inserted into bone similar to the human mandible. METHOD: 80 self drilling titanium alloy implants of the following sizes were used: 1.3mm, 1.4mm, 1.5mm and 1.6mm diameters and 10mm, 8mm, 7mm and 6mm lengths. 5 mini implants of each of the possible combinations of lengths and diameters were tested for study. The implants were inserted perpendicularly into bovine rib bone held in a custom made stand. The rib bone was made into segments 1.5cm wide using an osteotome and embedded in autopolymerising acrylic resin blocks with four bone segments in each block. Thus a total of twenty resin blocks were made. Insertion torque was set at 1Kgf in the long handle implant driver with attached torque gauge. Each resin block contained one implant per bone segment and individual blocks contained implants of identical lengths but varying diameter. The resin blocks were then radiographically exposed and the deviation of the long axis of the implant from a true vertical line drawn through the centre of entry of the implant into cortical bone was measured. RESULTS: There was an increase in deflection of the mini implant with increase in length. On the other hand, increase in diameter resulted in decrease in the amount of deflection observed. CONCLUSION: Selecting an implant depends on anatomical limitations like cortical bone thickness, proximity to adjacent roots, or any other vital structures and implant design. For insertion into thicker bone such as the mandible, it is preferable to use a thicker and shorter mini implants as they exhibit lesser deflection. In areas of lesser cortical bone, a thinner and longer mini implant can be considered as the resistance offered by the bone will be lesser

A Comparison of Photoelastic and Finite Elements Analysis in Internal Connection and Bone Level Dental Implants

This study is a contribution to our understanding of the mechanical behaviour of dental implants through the use of the finite element and the photoelastic methods. Two internal connection and bone level dental implants with different design have been analysed (M-12 by Oxtein S.L., Zaragoza, Spain, and ASTRA, from Dentsply Sirona, Charlotte, NC, USA), evaluating the stress distribution produced by axial stresses and a comparison has been established between them, as well as between the two methods used, in order to validate the adopted hypotheses and correlate the numerical modelling performed with experimental tests. To load the implant in laboratory testing, a column was placed, such that the loading point was about 9.3 mm from the upper free surface of the resin plate. This column connects the implant with the weights used to define the test load. In turn, support for both plates was achieved by two 6 mm bolts 130 mm apart and located on a parallel line with the resin (flush with the maximum level of the implant), at a depth of 90 mm. The results obtained with both methods used were similar enough. The comparison of results is fundamentally visual, but ensures that, at least in the range of forces used, both methods are similar. Therefore, the photoelastic method can be used to confirm in a real way the virtual conditions of the finite element models, with the implications in the investigation of dental implants that this entails