Which region of the TMJ disc we find the highest concentration of stresses when a orthopedic chin cup is installed?

Por Flávio Siqueira Calçada, MSc in Temporomandibular Disorder and Orofacial Pain, São Leopoldo Mandic School of Dentistry, Campinas, SP, Brazil

By means of computer simulation, researchers from São Leopoldo Mandic School of Dentistry, Campinas, São Paulo, Brazil, assessed stress generation on TMJ disc during orthopedic chin cup therapy. They found greater stress at the lower surface of the three-dimensional TMJ disc model where the mandibular condyle touches the structure. Results are disclosed by the article “Distribution of stress on TMJ disc induced by use of chin cup therapy: assessment by the finite element method” published on Dental Press Journal of Orthodontics (DPJO), volume 22, number 5.

A three-dimensional TMJ disc model was manufactured with a view to having stress distribution on TMJ disc induced by use of orthopedic chin cup assessed. Computed tomographic scans of a young dry scull provided data necessary for mandible and mandibular fossa manufacturing. The TMJ disc was graphically designed at the space between condyle and articular fossa with the aid of CAD-like software (Rhinoceros 3D). The model was immediately transferred to ANSYS software. The latter carried out simulations and estimated stress generated on TMJ disc by means of the finite element method (FEM).

A 4.9-N (500g) load was applied on Pogonion at inclinations of 30.4 and 50 degrees relative to Gonion-Mental mandibular plane. Loads going in three different directions were decomposed at both y and z axes of ANSYS software, thus producing vectors necessary for different simulations. The vectors were directly applied to the lower surface of the TMJ disc model, particularly to the area touching the upper surface of the condyle. Stress deriving from compression and stress present at the disc model were assessed by means of FEM.

Similarly to normal function, the TMJ disc absorbs load (TANAKA, et al., 2001) and distributes stress generated by orthopedic therapy, thus transferring less intense stress to the mandibular fossa and cranial base. Another rather fruitful finding was that the more orthopedic appliance loads were simulated vertically, the more stress decreased at the three-dimensional model.

Based on results obtained, clinicians are provided a better understanding of effects produced by this kind of therapy over morphologic changes and mandibular growth inhibition in their patients.

References

TANAKA, E., et al. Stress analysis in the TMJ during jaw openning by use of a three-dimensional finite element model based on magnetic resonance images. Int J Oral Maxillofac Surg. [online]. 2001, vol. 30, no. 5, pp. 421-430, ISSN: 0901-5027 [viewed 26 February 2018]. DOI: 10.1054/ijom.2001.0132. Avaliable from: https://www.ncbi.nlm.nih.gov/pubmed/11720045

To read the article, access it:

CALÇADA, F.S., et al. Distribution of stress on TMJ disc induced by use of chincup therapy: assessment by the finite element method. Dental Press J. Orthod. [online]. 2017, vol. 22, no. 5, pp. 83-89, ISSN: 2176-9451 [viewed 26 February 2018]. DOI: 10.1590/2177-6709.22.5.083-089.oar. Disponível em: http://ref.scielo.org/nqw7g5