Biomechanical comparison of titanium miniplates versus a variety of CAD/CAM plates in mandibular reconstruction

Comparison of reconstruction plates and miniplates in mandibular defect reconstruction with free iliac flap

OBJECTIVE

Given the increasing demand for precise and reliable reconstructive techniques in maxillofacial surgery, we try to offer valuable insights for clinicians in selecting optimal fixation methods.

MATERIALS AND METHODS

Patients were categorized into miniplate and reconstruction plate groups for accuracy and bone healing comparison. We measured gonial angle, intercondylar, intergonial and anterior-posterior distance for general accuracy and distance of segmental endpoint to the sagittal plane for partial accuracy. The bone healing rate of the two groups was compared with CT images at 3, 6 and 12 months after operation.

RESULT

Considering directional indicators, the miniplate group exhibited a wider intercondylar distance than the reconstruction plate group (p = 0.029). At 6 months postoperatively, the miniplate group demonstrated a higher bone healing rate compared to the reconstruction plate group, with no significant differences at other time points.

CONCLUSION

Over a nearly 5-year review, mandibular reconstruction with vascularized iliac bone flaps showed that reconstruction plates better maintained condylar position accuracy, while miniplates had superior bone healing rates at 6 months. No significant differences were found in other accuracy indices between the two plates.

CLINICAL RELEVANCE

Clinicians' selection of fixation plates frequently depends on personal preference rather than evidence-based criteria. This study compares the precision and postoperative osseous healing outcomes of miniplates and reconstruction plates to provide a more scientifically grounded basis for clinical decision-making.

A preliminary study of the mechanical properties of 3D-printed personalized mesh titanium alloy prostheses and repair of hemi-mandibular defect in dogs

This study is a preliminary investigation exploring the mechanical properties of three-dimensional (3D)-printed personalized mesh titanium alloy prostheses and the feasibility of repairing hemi-mandibular defects. The ANSYS 14.0 software and selective laser melting (SLM) were used to produce personalized mesh titanium alloy scaffolds. Scaffolds printed using different parameters underwent fatigue property tests and scanning electron microscopy (SEM) of the fracture points. Models of hemi-mandibular defects (encompassing the temporomandibular joint) were created using beagle dogs. Freeze-dried allogeneic mandibles or 3D-printed personalized mesh titanium alloy prostheses were used for repair. Gross observation, computed tomography (CT), SEM, and histological examinations were used to compare the two repair methods. The prostheses with filament diameters of 0.5 and 0.7 mm could withstand 14,000 times and >600,000 cycles of alternating stresses, respectively. The truss-structure scaffold with a large aperture and large aperture ratio could withstand roughly 250,000 cycles of alternating forces. The allogeneic mandible graft required intraoperative shaping, while the 3D-printed mesh titanium alloy prostheses were personalized and did not require intraoperative shaping. The articular disc on the non-operated sides experienced degenerative changes. No liver and kidney toxicity was observed in the two groups of animals. The 3D-printed mesh titanium alloy prostheses could effectively restore the shape of the mandibular defect region and reconstruct the temporomandibular joint.

Biomechanical evaluation of CAD/CAM magnesium miniplates as a fixation strategy for the treatment of segmental mandibular reconstruction with a fibula free flap

Titanium patient-specific (CAD/CAM) plates are frequently used in mandibular reconstruction. However, titanium is a very stiff, non-degradable material which also induces artifacts in the imaging. Although magnesium has been proposed as a potential material alternative, the biomechanical conditions in the reconstructed mandible under magnesium CAD/CAM plate fixation are unknown. This study aimed to evaluate the primary fixation stability and potential of magnesium CAD/CAM miniplates. The biomechanical environment in a one segmental mandibular reconstruction with fibula free flap induced by a combination of a short posterior titanium CAD/CAM reconstruction plate and two anterior CAD/CAM miniplates of titanium and/or magnesium was evaluated, using computer modeling approaches. Output parameters were the strains in the healing regions and the stresses in the plates. Mechanical strains increased locally under magnesium fixation. Two plate-protective constellations for magnesium plates were identified: (1) pairing one magnesium miniplate with a parallel titanium miniplate and (2) pairing anterior magnesium miniplates with a posterior titanium reconstruction plate. Due to their degradability and reduced stiffness in comparison to titanium, magnesium plates could be beneficial for bone healing. Magnesium miniplates can be paired with titanium plates to ensure a non-occurrence of plate failure.

Impact of the adjacent bone on pseudarthrosis in mandibular reconstruction with fibula free flaps

BACKGROUND

Mechanical and morphological factors have both been described to influence the rate of pseudarthrosis in mandibular reconstruction. By minimizing mechanical confounders, the present study aims to evaluate the impact of bone origin at the intersegmental gap on osseous union.

METHODS

Patients were screened retrospectively for undergoing multi-segment fibula free flap reconstruction of the mandible including the anterior part of the mandible and osteosynthesis using patient-specific 3D-printed titanium reconstruction plates. Percentage changes in bone volume and width at the bone interface between the fibula/fibula and fibula/mandible at the anterior intersegmental gaps within the same patient were determined using cone-beam computed tomography (CBCT). Additionally, representative samples of the intersegmental zones were assessed histologically and using micro-computed tomography (µCT).

RESULTS

The bone interface (p = 0.223) did not significantly impact the change in bone volume at the intersegmental gap. Radiotherapy (p < 0.001), time between CBCT scans (p = 0.006) and wound healing disorders (p = 0.005) were independent risk factors for osseous non-union. Preliminary analysis of the microstructure of the intersegmental bone did not indicate morphological differences between fibula-fibula and fibula-mandible intersegmental bones.

CONCLUSIONS

The bone interface at the intersegmental gap in mandibular reconstruction did not influence long-term bone healing significantly. Mechanical and clinical properties seem to be more relevant for surgical success.

Patient-specific 3D-printed mini-versus reconstruction plates for free flap fixation at the mandible: Retrospective study of clinical outcomes and complication rates

This study aimed to compare the clinical outcomes and complication rates of patient-specific 3D-printed mini- and reconstruction plates for free flap fixation in mandibular reconstruction. A retrospective monocentric study was carried out between April 2017 and December 2021 to analyze patients undergoing immediate mandibular reconstruction using fibula free flaps and osteosynthesis using patient-specific 3D-printed implants. Eighty-three patients with a mean age of 63.6 years were included. The mean follow-up period was 18.5 months. Patient-specific 3D-printed plates were designed as reconstruction plates (38 patients), miniplates (21 patients) or a combination of reconstruction- and miniplates (24 patients). With miniplates, plate removal was performed significantly more often via an intraoral approach (p < 0.001) and in an outpatient setting (p = 0.002). Univariate analysis showed a higher fistula rate with reconstruction plates (p = 0.037). Multivariate analysis showed no significant differences in complications. Case-control matching demonstrated significantly lower rates of fistula (p = 0.017) and non-union (p = 0.029) in the combined group. This retrospective study shows a tendency towards reduced complication rates with patient-specific 3D-printed miniplates in comparison to patient-specific 3D-printed reconstruction plates for immediate mandibular reconstruction with fibula free flaps.

Research progress of 3D printed poly (ether ether ketone) in the reconstruction of craniomaxillofacial bone defects

The clinical challenge of bone defects in the craniomaxillofacial region, which can lead to significant physiological dysfunction and psychological distress, persists due to the complex and unique anatomy of craniomaxillofacial bones. These critical-sized defects require the use of bone grafts or substitutes for effective reconstruction. However, current biomaterials and methods have specific limitations in meeting the clinical demands for structural reinforcement, mechanical support, exceptional biological performance, and aesthetically pleasing reconstruction of the facial structure. These drawbacks have led to a growing need for novel materials and technologies. The growing development of 3D printing can offer significant advantages to address these issues, as demonstrated by the fabrication of patient-specific bioactive constructs with controlled structural design for complex bone defects in medical applications using this technology. Poly (ether ether ketone) (PEEK), among a number of materials used, is gaining recognition as a feasible substitute for a customized structure that closely resembles natural bone. It has proven to be an excellent, conformable, and 3D-printable material with the potential to replace traditional autografts and titanium implants. However, its biological inertness poses certain limitations. Therefore, this review summarizes the distinctive features of craniomaxillofacial bones and current methods for bone reconstruction, and then focuses on the increasingly applied 3D printed PEEK constructs in this field and an update on the advanced modifications for improved mechanical properties, biological performance, and antibacterial capacity. Exploring the potential of 3D printed PEEK is expected to lead to more cost-effective, biocompatible, and personalized treatment of craniomaxillofacial bone defects in clinical applications.

Patient-specific miniplates versus patient-specific reconstruction plate: A biomechanical comparison with 3D-printed plates in mandibular reconstruction

BACKGROUND

Patient-specific 3D-printed miniplates for free flap fixation in mandibular reconstruction were recently associated with enhanced osseous union. Higher mechanical strains resulting from these plates are discussed as reasons, but biomechanical studies are missing. This study aims to examine, whether patient-specific 3D-printed miniplates provide an increased interosteotomy movement (IOM) and lower stiffness compared with reconstruction plates.

METHODS

Polyurethane (PU) mandible and fibula models (Synbone AG, Malans, Schweiz) were used to simulate mandibular reconstruction with a one segment fibula flap equivalent. Osteosynthesis was performed using either four patient-specific 3D-printed miniplates (3D-Mini) or one patient-specific 3D-printed reconstruction plate (3D-Recon). Mastication was simulated using cyclic dynamic loading with increasing loads until material failure or a maximum load of 1000 N. Continuous IOM recording was carried out using a 3D optical tracking system (ARAMIS, Carl Zeiss GOM Metrology, Braunschweig, Germany).

FINDINGS

The averaged stiffness at a load of 100-300 N load did not differ between the groups (p = 0.296). There was a faster 1.0 mm vertical displacement in the 3D-Mini group (26 376 ± 14 190 cycles versus 44 817 ± 30 430 cycles, p = 0.018). The IOM were higher with miniplate fixation in the distal gap (p = 0.040). In the mesial gap, there was no significant difference between the groups (p = 0.160).

INTERPRETATION

Fixation with patient-specific 3D-printed miniplates results in higher mechanical strains. Lower rates of pseudarthrosis, as seen in clinical studies, might be caused by this phenomenon. Surgeons should evaluate the primary use of 3D-printed miniplates in mandibular reconstruction due to advantages of intraoral plate removal alongside safe osteosynthesis.

Clinical and Technical Validation of Novel Bite Force Measuring Device for Functional Analysis after Mandibular Reconstruction

Bite force measuring devices that are generally suitable for edentulous patients or patients undergoing mandibular reconstruction are missing. This study assesses the validity of a new bite force measuring device (prototype of loadpad^®, novel GmbH) and evaluates its feasibility in patients after segmental mandibular resection. Accuracy and reproducibility were analyzed with two different protocols using a universal testing machine (Z010 AllroundLine, Zwick/Roell, Ulm, Germany). Four groups were tested to evaluate the impact of silicone layers around the sensor: no silicone ("pure"), 2.0 mm soft silicone ("2-soft"), 7.0 mm soft silicone ("7-soft") and 2.0 mm hard silicone ("2-hard"). Thereafter, the device was tested in 10 patients prospectively who underwent mandibular reconstruction using a fibula free flap. Average relative deviations of the measured force in relation to the applied load reached 0.77% ("7-soft") to 5.28% ("2-hard"). Repeated measurements in "2-soft" revealed a mean relative deviation of 2.5% until an applied load of 600 N. Maximum bite force decreased postoperatively by 51.8% to a maximum mean bite force of 131.5 N. The novel device guarantees a high accuracy and degree of reproducibility. Furthermore, it offers new opportunities to quantify perioperative oral function after reconstructive surgery of the mandible also in edentulous patients.

PEEK for Oral Applications: Recent Advances in Mechanical and Adhesive Properties

Polyetheretherketone (PEEK) is a thermoplastic material widely used in engineering applications due to its good biomechanical properties and high temperature stability. Compared to traditional metal and ceramic dental materials, PEEK dental implants exhibit less stress shielding, thus better matching the mechanical properties of bone. As a promising medical material, PEEK can be used as implant abutments, removable and fixed prostheses, and maxillofacial prostheses. It can be blended with materials such as fibers and ceramics to improve its mechanical strength for better clinical dental applications. Compared to conventional pressed and CAD/CAM milling fabrication, 3D-printed PEEK exhibits excellent flexural and tensile strength and parameters such as printing temperature and speed can affect its mechanical properties. However, the bioinert nature of PEEK can make adhesive bonding difficult. The bond strength can be improved by roughening or introducing functional groups on the PEEK surface by sandblasting, acid etching, plasma treatment, laser treatment, and adhesive systems. This paper provides a comprehensive overview of the research progress on the mechanical properties of PEEK for dental applications in the context of specific applications, composites, and their preparation processes. In addition, the research on the adhesive properties of PEEK over the past few years is highlighted. Thus, this review aims to build a conceptual and practical toolkit for the study of the mechanical and adhesive properties of PEEK materials. More importantly, it provides a rationale and a general new basis for the application of PEEK in the dental field.

The Precision of Different Types of Plates Fabricated With a Computer-Aided Design and Manufacturing System in Mandibular Reconstruction With Fibular-Free Flaps

Computer-assisted surgery (CAS) has been introduced to mandible reconstruction with fibular-free flap in cutting guide placement. When CAS cooperates with different plate fixations, the results show various degrees of errors by which this study aimed to evaluate. Mock surgeries were conducted in 3D-printed mandibles with 2 types of defects, limited or extensive, reconstructed from 2 ameloblastoma patients. Three types of fixations, miniplate, manually bending reconstruction plate, and patient-specific plate, are tested, each of which was performed 3 times in each type of defect, adding up to 18 surgeries. One with the least errors was selected and applied to patients whose 3D-printed mandibles were derived. Finally, in vivo errors were compared with the mock. In limited defect, average errors show no statistical significance among all types. In extensive defect, patient-specific plate had a significantly lower average condylar error than manually bending reconstruction plate and miniplate (8.09±2.52 mm vs. 25.49±2.72 and 23.13±13.54 mm, respectively). When patient-specific plate was applied in vivo , the errors were not significantly different from the mock. Patient-specific plates that cooperated with CAS showed the least errors. Nevertheless, manually bent reconstruction plates and miniplates could be applied in limited defects with caution.

Towards mechanobiologically optimized mandible reconstruction: CAD/CAM miniplates vs. reconstruction plates for fibula free flap fixation: A finite element study

Due to their advantages in applicability, patient-specific (CAD/CAM) reconstruction plates are increasingly used in fibula free flap mandible reconstruction. In addition, recently, CAD/CAM miniplates, with further advantages in postoperative management, have been introduced. However, biomechanical conditions induced by CAD/CAM systems remain partially unknown. This study aimed to evaluate the primary fixation stability of CAD/CAM fixators. For a patient-specific scenario, the biomechanical conditions induced in a one segmental fibula free flap stabilized using either a CAD/CAM reconstruction plate or CAD/CAM miniplates were determined using finite element analysis. The main output parameters were the strains between intersegmental bone surfaces and stresses in the fixation systems due to different biting scenarios. CAD/CAM miniplates resulted in higher mechanical strains in the mesial interosseous gap, whereas CAD/CAM reconstruction plate fixation resulted in higher strains in the distal interosseous gap. For all investigated fixation systems, stresses in the fixation systems were below the material yield stress and thus material failure would not be expected. While the use of CAD/CAM miniplates resulted in strain values considered adequate to promote bone healing in the mesial interosseous gap, in the distal interosseous gap CAD/CAM reconstruction plate fixation might result in more beneficial tissue straining. A mechanical failure of the fixation systems would not be expected.

Increased rate of pseudarthrosis in the anterior intersegmental gap after mandibular reconstruction with fibula free flaps: a volumetric analysis

OBJECTIVES

Pseudarthrosis after mandibular reconstruction leads to chronic overload of the osteosynthesis and impedes dental rehabilitation. This study evaluates the impact of gap site on osseous union in mandible reconstruction using a new volumetric analysis method with repeated cone-beam computed tomography (CBCT).

METHODS

The degree of bone regeneration was evaluated in 16 patients after mandible reconstruction with a fibula free flap and patient-specific reconstruction plates. Percentual bone volume and width changes in intersegmental gaps were retrospectively analyzed using a baseline CBCT in comparison to a follow-up CBCT. Patients' characteristics, plate-related complications, and gap sites (anterior/posterior) were analyzed. Detailed assessments of both gap sites (buccal/lingual/superior/inferior) were additionally performed.

RESULTS

Intersegmental gap width (p = 0.002) and site (p < 0.001) significantly influence bone volume change over two consecutive CBCTs. An initial larger gap width resulted in a lower bone volume change. In addition, anterior gaps showed significantly less bone volume changes. Initial gap width was larger at posterior segmental gaps (2.97 vs 1.65 mm, p = 0.017).

CONCLUSIONS

A methodology framework has been developed that allows to quantify pseuarthrosis in reconstructed mandibles using CBCT imaging. The study identifies the anterior segmental gap as a further risk factor for pseudarthrosis in reconstructions with CAD/CAM reconstruction plates. Future research should evaluate whether this outcome is related to the biomechanics induced at this site.

3D Printing and Virtual Surgical Planning in Oral and Maxillofacial Surgery

Compared to traditional manufacturing methods, additive manufacturing and 3D printing stand out in their ability to rapidly fabricate complex structures and precise geometries. The growing need for products with different designs, purposes and materials led to the development of 3D printing, serving as a driving force for the 4th industrial revolution and digitization of manufacturing. 3D printing has had a global impact on healthcare, with patient-customized implants now replacing generic implantable medical devices. This revolution has had a particularly significant impact on oral and maxillofacial surgery, where surgeons rely on precision medicine in everyday practice. Trauma, orthognathic surgery and total joint replacement therapy represent several examples of treatments improved by 3D technologies. The widespread and rapid implementation of 3D technologies in clinical settings has led to the development of point-of-care treatment facilities with in-house infrastructure, enabling surgical teams to participate in the 3D design and manufacturing of devices. 3D technologies have had a tremendous impact on clinical outcomes and on the way clinicians approach treatment planning. The current review offers our perspective on the implementation of 3D-based technologies in the field of oral and maxillofacial surgery, while indicating major clinical applications. Moreover, the current report outlines the 3D printing point-of-care concept in the field of oral and maxillofacial surgery.

Optimal placement of fixation system for scaffold-based mandibular reconstruction

A current challenge in bone tissue engineering is to create favourable biomechanical conditions conducive to tissue regeneration for a scaffold implanted in a segmental defect. This is particularly the case immediately following surgical implantation when a firm mechanical union between the scaffold and host bone is yet to be established via osseointegration. For mandibular reconstruction of a large segmental defect, the position of the fixation system is shown here to have a profound effect on the mechanical stimulus (for tissue regeneration within the scaffold), structural strength, and structural stiffness of the tissue scaffold-host bone construct under physiological load. This research combines computer tomography (CT)-based finite element (FE) modelling with multiobjective optimisation to determine the optimal height and angle to place a titanium fixation plate on a reconstructed mandible so as to enhance tissue ingrowth, structural strength and structural stiffness of the scaffold-host bone construct. To this end, the respective design criteria for fixation plate placement are to: (i) maximise the volume of the tissue scaffold experiencing levels of mechanical stimulus sufficient to initiate bone apposition, (ii) minimise peak stress in the scaffold so that it remains intact with a diminished risk of failure and, (iii) minimise scaffold ridge displacement so that the reconstructed jawbone resists deformation under physiological load. First, a CT-based FE model of a reconstructed human mandible implanted with a bioceramic tissue scaffold is developed to visualise and quantify changes in the biomechanical responses as the fixation plate's height and/or angle are varied. The volume of the scaffold experiencing appositional mechanical stimulus is observed to increase with the height of the fixation plate. Also, as the principal load-transfer mechanism to the scaffold is via the fixation system, there is a significant ingress of appositional stimulus from the buccal side towards the centre of the scaffold, notably in the region bounded by the screws. Next, surrogate modelling is implemented to generate bivariate cubic polynomial functions of the three biomechanical responses with respect to the two design variables (height and angle). Finally, as the three design objectives are found to be competing, bi- and tri-objective particle swarm optimisation algorithms are invoked to determine the most optimal Pareto solution, which represents the best possible trade-off between the competing design objectives. It is recommended that consideration be given to placing the fixation system along the upper boundary of the mandible with a small clockwise rotation about its posterior end. The methodology developed here forms a useful decision aid for optimal surgical planning.

Removal of patient-specific reconstruction plates after mandible reconstruction with a fibula free flap: is the plate the problem?

Computer-aided microvascular mandible reconstruction is an increasingly common procedure in oral and maxillofacial surgery. The aim of this retrospective single-centre study was to evaluate the rate and specifics of hardware removal after fibula free flap (FFF) fixation with a patient-specific reconstruction plate. The study included patients who underwent hardware removal between April 2017 and October 2019. Statistical analyses were performed regarding the different indications for plate removal (dental implantation versus complication) and the surgical approach (intraoral versus extraoral). Plate removal was performed in 29 of 98 patients (29.6%) after FFF fixation with a patient-specific reconstruction plate. Plate removal was done prior to dental implantation in 58.6% of cases and due to complications in 41.4%. Complications seen between reconstructive surgery and plate removal were less frequent in the dental rehabilitation group (8/17 vs 12/12; P=0.002). Within this group, 35.3% of plates were removed intraorally, and the majority of partial plate removals were performed in the patients with plate removal for dental rehabilitation (72.7% vs 27.3%). Hospitalization was shorter with an intraoral approach (1.7 days vs 4.0 days, P=0.052). The removal of patient-specific reconstruction plates prior to dental implantation is often partial and can be performed intraorally. The use of patient-specific miniplates for fixation of FFF might facilitate later dental rehabilitation.

3D-printed PEEK implant for mandibular defects repair - a new method

Functional reconstruction of large-size mandibular continuity defect is still a major challenge in the oral and maxillofacial surgery due to the unsatisfactory repair effects and various complications. This study aimed to develop a new functional repair method for mandibular defects combined with 3D-printed polyetheretherketone (PEEK) implant and the free vascularized fibula graft, and evaluated the service performance of the implant under whole masticatory motion. The design criteria and workflows of the mandibular reconstruction were established based on the requirements of safety, functionality, and shape consistency. Both the biomechanical behavior and the mechanobiological property of mandibular reconstruction under various masticatory motion were investigated by the finite element analysis. The maximum von Mises stress of each component was lower than the yield strength of the corresponding material and the safety factor was more than 2.3 times, which indicated the security of the repair method can be guaranteed. Moreover, the actual deformation of the reconstruction model was lower than that of the normal mandible under most clenching tasks, which assured the primary stability. More than 80% of the volume elements in the bone graft can obtain effective mechanical stimulation, which benefited to reduce the risks of bone resorption. Finally, the novel repair method was applied in clinic and good clinical performances have been achieved. Compared with the conventional fibular bone graft for surgical mandibular reconstruction, this study provides excellent safety and stability to accomplish the functional reconstruction and aesthetic restoration of the mandible defect.