Effect of occlusal contact on TMJ loading during occlusion: An in silico study

Alterations in occlusal features may have significant consequences, ranging from dental aesthetics to health issues. Temporomandibular joint disorders (TMDs) are often associated with joint overload, and the correlation between occlusal features and TMDs has been thoroughly discussed. In current work, we introduced a novel stomatognathic model that aligns well with in vivo experimental measurements, specifically designed to decouple the impact of occlusal contact and periodontal ligament (PDL) negative feedback on temporomandibular joint (TMJ) loading. Utilizing an in-silico approach, the simulation analysis included six symmetric occlusal contact scenarios. Furthermore, a biomechanical lever model was employed to clarify the mechanical mechanism and investigate the multi-factorial effects of TMJ overload. These findings indicate that anterior shifts in the occlusal centre lead to increased TMJ loading, particularly in occlusal contact cases with anteroposterior changes. Considering the symmetrical distribution of occlusal contact, mediolateral alterations had a more modest effect on TMJ loading. Additionally, potential negative feedback activated by principal strain of periodontal could not only alleviate joint load but also diminish occlusal force. These investigations enhance our understanding of the intricate interactions between masticatory muscles, occlusal forces, and joint contact forces, thereby providing motivation for future comprehensive studies on TMJ biomechanical overload.

A theoretical analysis of longitudinal temporomandibular joint compressive stresses and mandibular growth

OBJECTIVES

To determine if temporomandibular joint (TMJ) compressive stresses during incisor biting (1) differed between growing children over time, and (2) were correlated with Frankfort Horizontal-mandibular plane angle (FHMPA, °) and ramus length (Condylion-Gonion (Co-Go), mm).

MATERIALS AND METHODS

Three-dimensional anatomical geometries, FHMPA and Co-Go, were measured longitudinally from lateral and posteroanterior cephalographs1 of children aged 6 (T1), 12 (T2), and 18 (T3) years. Geometries were used in numerical models to estimate subject-specific TMJ eminence shape and forces for incisor bite-forces of 3, 5, and 8 Newtons at T1, T2, and T3, respectively. TMJ compressive stresses were estimated via two steps: First, TMJ force divided by age-dependent mandibular condylar dimensions, and second, modified by loading surfaces' congruency. Analysis of variance and Tukey honest significant difference post-hoc tests, plus repeated measures and mixed effects model analyses were used to evaluate differences in variables between facial groups. Regression analyses tested for correlation between age-dependent compressive stresses, FHMPA, and Co-Go.

RESULTS

Sixty-five of 842 potential subjects had T1-T3 cephalographs and were grouped by FHMPA at T3. Dolichofacial (FHMPA ≥ 27°, n = 36) compared to meso-brachyfacial (FHMPA< 27°, n = 29) subjects had significantly larger FHMPA at T1-T3, shorter Co-Go at T2 and T3 (all P < .01), and larger increases in TMJ compressive stresses with age (P < .0001). Higher compressive stresses were correlated with larger FHMPA (all R2 ≥ 0.41) and shorter Co-Go (all R2 ≥ 0.49).

CONCLUSIONS

Estimated TMJ compressive stress increases from ages 6 to 18 years were significantly larger in dolichofacial compared to meso-brachyfacial subjects and correlated to FHMPA and Co-Go.

Frankfort Mandibular Plane Angle: Critically Appraised Topic (CAT)

PURPOSE

The objective of this Critically Appraised Topic was to determine the level of evidence relative to the usefulness of the Frankfort mandibular plane angle in prosthodontic treatment.

MATERIALS AND METHODS

The Patient Intervention Comparison Outcome (PICO) mesh heading received zero PubMed references, as did Frankfort Mandibular Plane Angle (FMA) as a determinant for dental occlusion and Frankfort Mandibular Plane Angle as a determinant of the occlusal scheme. Frankfort Mandibular Plane Angle alone received 168 PubMed citations that highlighted 2 DiPietro articles and a third from the orthodontics literature which was a Randomized Controlled Trial not relevant to the PICO. Four others, three prosthodontic and one orthodontic publication, were related to the PICO. A Google search revealed one additional article, which was a narrative review.

RESULTS

Nine articles were related to the search, 2 of which were clinical trials that revealed no evidence to support the use of FMA as a diagnostic test.

CONCLUSION

Based on the limited data presented above, there is a lack of evidence to support the use of FMA as a diagnostic procedure to predict outcomes, or dictate prosthodontic treatment.

The relation of cephalometric features to internal derangements of the temporomandibular joint: A systematic review and meta-analysis of observational studies

PURPOSE

To review and summarize the data on the relationship between craniofacial morphology features and internal derangement (ID) of the temporomandibular joint (TMJ).

METHOD

A systematic review was designed and registered at PROSPERO, CRD42019132731. The PubMed, Embase and Scopus databases were searched for cephalometric studies comparing craniofacial morphology between female patients with TMJ ID and controls. The Newcastle-Ottawa Scale (NOS) was used for quality assessment. Weighted mean differences for cephalometric measurements were pooled for subsequent meta-analysis.

RESULT

From the establishment date to August 2020, 14 of 1038 collected records were selected, which consisted of 772 patients with TMJ ID and 423 controls. These records were eventually pooled for the designed statistical analysis after the NOS quality assessment. Compared with the controls, TMJ ID patients had obviously smaller, retruded and clockwise-rotated mandible, showing significantly decreased S-Na, S-Go, Go-Me, Ar-Pog, Ar-Go, SNB, Na perp Pog, and increased FH-MP, SN-MP, PP-MP, SN to Ar-Go, S-Ar-Go and ANB.

CONCLUSION

Certain craniofacial morphology features were found strongly associated with the presence of TMJ ID, especially the size and position of the mandible.

Mechanobehavior and Ontogenesis of the Temporomandibular Joint

Craniofacial secondary cartilages of the mandibular condyle and temporomandibular joint (TMJ) eminence grow in response to the local mechanical environment. The intervening TMJ disc distributes normal loads over the cartilage surfaces and provides lubrication. A better understanding of the mechanical environment and its effects on growth, development, and degeneration of the TMJ may improve treatments aimed at modifying jaw growth and preventing or reversing degenerative joint disease (DJD). This review highlights data recorded in human subjects and from computer modeling that elucidate the role of mechanics in TMJ ontogeny. Presented data provide an approximation of the age-related changes in jaw-loading behaviors and TMJ contact mechanics. The cells of the mandibular condyle, eminence, and disc respond to the mechanical environment associated with behaviors and ultimately determine the TMJ components' mature morphologies and susceptibility to precocious development of DJD compared to postcranial joints. The TMJ disc may be especially prone to degenerative change due to its avascularity and steep oxygen and glucose gradients consequent to high cell density and rate of nutrient consumption, as well as low solute diffusivities. The combined effects of strain-related hypoxia and limited glucose concentrations dramatically affect synthesis of the extracellular matrix (ECM), which limit repair capabilities. Magnitude and frequency of jaw loading influence this localized in situ environment, including stem and fibrocartilage cell chemistry, as well as the rate of ECM mechanical fatigue. Key in vivo measurements to characterize the mechanical environment include the concentration of work input to articulating tissues, known as energy density, and the percentage of time that muscles are used to load the jaws out of a total recording time, known as duty factor. Combining these measurements into a mechanobehavioral score and linking these to results of computer models of strain-regulated biochemical events may elucidate the mechanisms responsible for growth, maintenance, and deterioration of TMJ tissues.