Modifica di Asse Trasversale Cerniera (sezione)

==Discussion==

In the context of this chapter, one of the deepest tensions characterizing modern gnathology has emerged: the importance of the '6 degrees of freedom' in ensuring optimal masticatory efficiency and the growing tendency of the 'RDC' to exclude mandibular kinematic tools from clinical practice. While the stated goal of the RDC is to improve diagnostic effectiveness by eliminating methodologies with low clinical validity, the assertion of removing kinematic replicators from dental practice appears controversial. This is because mandibular kinematics is a fundamental element in understanding not only mandibular movements but also the masticatory forces that influence the duration and effectiveness of mastication.

Masticatory efficiency, for example, does not depend solely on the strength applied by the muscles or the robustness of the dental structure but also on the mandible's ability to move through its '6 degrees of freedom', allowing the proper functioning of the teeth in cutting and grinding food. Each degree of freedom—three translations (along the <math>x, y, z</math> axes) and three rotations (around the same axes)—contributes to the complex interaction between dental surfaces and muscular forces, which is in turn influenced by the normal and tangential forces generated by occlusal contact. In the case of molar teeth, the natural inclination of the cusps helps reduce the dispersion of metabolic energy during the cutting process, maximizing masticatory efficiency. Without this natural inclination, mastication would become less efficient, leading to higher energy expenditure and increased muscular and joint load. As shown in previous simulations, an incorrect localization of the transverse hinge axis (<math>_tHA</math>) can significantly affect the precision of the cusps and, therefore, the proper alignment of the teeth during occlusal contact.

The RDC's argument is based on the assumption that mandibular kinematic tools, such as gnathological replicators and pantographs, do not make a significant contribution to improving prosthetic rehabilitations. However, this statement seems debatable in light of biomechanical and clinical evidence. In particular, diagnostic tools that allow the analysis of mandibular movements in three dimensions, such as the SICAT JMT and Zebris JMA systems, have shown that mandibular movement is not purely rotational but involves a component of 'rototranslation'. This combination of movement is crucial for faithfully replicating mandibular function, especially in patients with complex occlusal issues. Mandibular kinematics provides a deeper understanding not only of the occlusal contact angle but also of how muscular forces and dental resistances balance during the masticatory cycle. The RDC tends to argue that three-dimensional analysis tools are too costly, complex, and not useful in daily practice. However, the data presented in this chapter indicate the opposite: the use of such tools can prevent significant errors in prosthetic rehabilitation and improve therapeutic effectiveness.

In the simulations presented, we demonstrated that even a small error in the localization of <math>_tHA</math> can lead to significant discrepancies in the position of dental cusps. Specifically, with a mandibular opening of just 3 mm and cusps inclined at <math>5^\circ</math>, an error in the localization of the axis of 10 mm can cause a vertical cuspal error of nearly 1 mm. While this may seem minimal, it is a discrepancy sufficient to compromise the prosthetic's effectiveness and cause discomfort for the patient.

On the other hand, with a mandibular opening of 0 mm (mouth closed), the cuspal error is theoretically zero only in the case of flat cusps (<math>0^\circ</math>), whereas with cusps inclined by even a few degrees, an error margin is still introduced due to the projection of the localization error onto the inclination itself. This shows that without accurate kinematic analysis, it is impossible to guarantee proper alignment of the cusps and occlusal surfaces, with significant repercussions on the patient's masticatory function.

In light of these observations, it is clear that the exclusion of kinematic tools from clinical practice, as suggested by the RDC, is not a scientifically founded choice. Kinematic tools offer a unique understanding of mandibular movements, allowing clinicians to accurately replicate mandibular motions and ensure superior prosthetic treatment. Removing such tools from clinical practice could reduce diagnostic and treatment precision, leading to an increased risk of malocclusion, temporomandibular disorders, and patient discomfort.

The data presented clearly show that determining the transverse hinge axis (<math>_tHA</math>) and controlling rototranslational movements are crucial for minimizing energy dispersion and optimizing masticatory efficiency. The inclination of the cusps, the proper alignment of occlusal surfaces, and the precision in localizing the axis of rotation must be treated with the utmost care to avoid errors that could compromise clinical outcomes.

In conclusion, while the RDC argues that kinematic tools are not essential for daily clinical practice, the scientific evidence presented indicates that these tools are crucial for accurate evaluation and rehabilitation of masticatory function. Eliminating these tools from clinical practice would not only reduce diagnostic accuracy but also compromise the quality of care provided to patients. It is therefore essential that professionals continue to integrate the use of advanced kinematic tools into their practice to ensure optimal prosthetic treatment and a high quality of life for patients. {{q2|But then, is it enough to only know the dynamics of <math>_tHA</math>?|.....certainly not. The mandibular kinematic phenomenon, being a 6 degrees of freedom dynamic, requires mandatory knowledge of the vertical axis <math>_aHA</math> on the axial plane and the sagittal axis <math>_cHA</math> on the coronal plane. Topics we will address in the next chapters|The answer does not lie in the RDC's assertions but in science. Science speaks of 'Masticatory Efficiency,' a phenomenon that concerns neither TMD diagnosis nor RDC claims.}}


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