Evaluation of bite force recovery in patients with maxillofacial fracture

Mechanical evaluation of mandibular fractures stabilized with absorbable implants or intraoral splints in cats

Introduction

The goal of this cadaver study in cats was to compare the mechanical properties of intact mandibles (C) with mandibles whose simulated fracture was located between the third and fourth premolar teeth and repaired with four possible treatments: (1) Stout multiple loop interdental wiring plus bis-acryl composite intraoral splint (S); (2) modified Risdon interdental wiring plus bis-acryl composite intraoral splint (R); (3) ultrasound-aided absorbable fixation plate (P); and (4) ultrasound-aided absorbable fixation mesh (M).

Materials and methods

Thirty feline mandibles were randomly assigned to the control and treatment groups. Mandibles were loaded by cantilever bending on the canine tooth, first in non-destructive cyclic loading followed by destructive ramp-to-failure loading.

Results

Cyclic loading showed no differences between the treatment groups in angular deflection (a measure of sample flexion under non-destructive loads); however, the R group had significantly higher angular deflection than the C group. In destructive testing, no differences in mechanical properties were found between the treatment groups; however, all treatment groups demonstrated significantly lower maximum bending moment, bending stiffness, energy to failure, and maximum force when compared to the control group. The main mode of failure of the intraoral splint groups (S and R) was fracture of the bis-acryl composite (50%), and the main mode of failure of the absorbable fixation groups (P and M) was fracture of the pins (91.7%).

Discussion

Intraoral splint and absorbable fixation methods have low strength and stiffness. The four treatments tested provided similar stabilization of mandibular fractures located between the third and fourth premolar teeth.

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.

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.