Stress distribution in mandible and temporomandibular joint by mandibular distraction: a 3-dimensional finite-element analysis

Biomechanical Effects of Different Load Cases with an Implant-Supported Full Bridge on Four Implants in an Edentulous Mandible: A Three-Dimensional Finite Element Analysis (3D-FEA)

The long-term success and predictability of implant-supported restorations largely depends on the biomechanical forces (stresses) acting on implants and the surrounding alveolar bone in the mandible. The aim of our study was to investigate the biomechanical behavior of an edentulous mandible with an implant-supported full bridge on four implants under simulated masticatory forces, in the context of different loading schemes, using a three-dimensional finite element analysis (3D-FEA). A patient-specific 3D finite element model was constructed using pre- and post-implantation computer tomography (CT) images of a patient undergoing implant treatment. Simplified masticatory forces set at 300 N were exerted vertically on the denture in four different simulated load cases (LC1-LC4). Two sets of simulations for different implants and denture materials (S1: titanium and titanium; S2: titanium and cobalt-chromium, respectively) were made. Stress outputs were taken as maximum (Pmax) and minimum principal stress (Pmin) and equivalent stress (Peqv) values. The highest peak Pmax values were observed for LC2 (where the modelled masticatory force excluded the cantilevers of the denture extending behind the terminal implants), both regarding the cortical bone (S1 Pmax: 89.57 MPa, S2 Pmax: 102.98 MPa) and trabecular bone (S1 Pmax: 3.03 MPa, S2 Pmax: 2.62 MPa). Overall, LC1-where masticatory forces covered the entire mesio-distal surface of the denture, including the cantilever-was the most advantageous. Peak Pmax values in the cortical bone and the trabecular bone were 14.97-15.87% and 87.96-94.54% higher in the case of S2, respectively. To ensure the long-term maintenance and longevity of treatment for implant-supported restorations in the mandible, efforts to establish the stresses of the surrounding bone in the physiological range, with the most even stress distribution possible, have paramount importance.

Does the flatting of the curve of spee affect the chewing force distribution in the mandible? (3D finite element study)

OBJECTIVE:

To search the effects of Curve of Spee (COS) flatting on the stresses and displacement on the different mandible landmarks and lower teeth during posterior teeth loading using three-dimensional (3D) finite element analysis.

MATERIALS AND METHODS:

Three-dimensional hemi mandibular model was created from real selected mandible. The lower teeth was aligned originally in a curved form with 2.4 mm depth at the cusp tip of the second premolar. Another replica with flat aligned teeth was formed to confirm the analysis by up righting premolars and molars. A load was applied at mesio-buccal cusp of the lower first molar on both models, and the resultant stresses and displacements on the mandibular landmarks and the lower teeth were tested.

RESULTS:

Von mises over the mandible was higher in flat than in curve model. The highest stress levels were detected at the Mesio-buccal cusp tip of first molar for flat and curved simulation (5053, 3304) Mpa respectively. Mesio-distally, the teeth displacement was higher in curve model than in flat one. The maximum distal displacement, in flat model, was seen in central and lateral incisors. While, in curve model, the maximum distal displacement was grasped within first and second premolars.

CONCLUSIONS:

Flatting the COS magnify the stresses over whole mandible and reduce lower teeth displacement mesio-distally. We speculated that the readjustment of the COS after orthodontic treatment could reduce the stress and displacements on the lower anterior teeth and decrease the lower anterior teeth crowding relapse.

Correction of rabbit model with mandibular ramus shortening by distraction osteogenesis at condylar neck

PURPOSE

The rabbit model has been established to mimic the effect of temporomandibular joint (TMJ) arthroplasty of ankylosis, and distraction at the level of the condylar neck is used to elongate the ascending ramus. The histomorphologic changes of TMJ and distraction gap were investigated.

MATERIALS AND METHODS

The unilateral condyles and articular discs were extirpated, and the experimental mandibular rami were shortened by 5 mm. An embedded distracter was used to restore the height of the mandibular ramus by unilateral condylar neck distraction (0.8 mm daily for 7 days). A total of 12 adult white rabbits were used, 8 in the experimental group and 4 in the control group. Of the 8 rabbits in the experimental group, 4 each were killed at 4 and 8 weeks after completion of distraction. The TMJ and distracted calluses were harvested and processed for radiographic and histologic examination.

RESULTS

An open bite was seen in all rabbits postoperatively that had diminished at the end of distraction. The newly formed condyles radiologically showed remodeling, flattening, and sclerosis. The bony transport disc had gradually remodeled to a new condyle that was similar to the original condyle in appearance and structure. The surface of the transport disc was covered with a fibrous tissue. Moreover, the bony regeneration was perfect in the distraction gap.

CONCLUSION

These results suggest that distraction osteogenesis at the condylar neck using the traditional preauricular approach of TMJ surgery, without the additional incision, can be performed concurrently with arthroplasty of TMJ ankylosis at the same region.