Difference between revisions of "Transverse Hinge Axis"

==Scientific Philosophy and Clinical Implications==

In the previous chapter, "[[Jaw_movements_analysis._Part_1:_Electrognathographic_Replicator]]", the disconnection between clinicians and the bioengineering foundations of diagnostic tools such as kinematic replicators was highlighted. This disconnect is particularly evident with outdated instruments like the Sirognathograph and the Kinesiograph K7,<ref>C. Martín et al. "Kinesiographic study of the mandible in young patients with unilateral posterior crossbite." Am J Orthod Dentofacial Orthop. 2000 Nov.</ref> common clinical tools that, despite widespread use, fail to faithfully reproduce the three-dimensional movements of the mandible. These instruments have a significant limitation: they lose three angular degrees of freedom, two of which could theoretically be recovered, while one, related to the <math>Y</math> axis, remains undefinable. This poses a broader problem, namely the risk that technological innovation, driven by industrial cycles, creates tools that do not fully reflect the complexity of biophysical reality. It would therefore be desirable for professionals to collaborate with research centers to critically evaluate these devices before their use. Adopting technology solely based on the manufacturer's reputation has led to the phenomenon of the Research Diagnostic Criteria "RDC," which was created to eliminate methods and tools with low clinical validity. This chapter will explore the concept of the "Hinge Axis" <math>HA</math>, an extensively studied and debated topic that continues to raise questions regarding its actual clinical and diagnostic usefulness. The determination of the hinge axis was traditionally performed using methods initially described by McCollum,<ref name="McCollum19602">B.B. McCollum. "The mandibular hinge axis and a method of locating it." J Prosthet Dent. 1960;10:428–435.</ref><ref name="McCollum19392">B.B. McCollum. "Fundamentals Involved in Prescribing Restorative Dental Remedies." Dent Items Interest. 1939;61:522–535, 641–648, 724–736, 852, 863, 942–950.</ref> and subsequently perfected over the years.<ref name="Lauritzen19612">A.G. Lauritzen, L.W. Wolford. "Hinge axis location on an experimental basis." J Prosthet Dent. 1961;11:1059–1067.</ref><ref name="Lauritzen19702">A.G. Lauritzen. Arbeitsanleitung für die Lauritzen Technik. Manual 6, Post Graduate Course 1970. (According to Bosman).</ref><ref name="Lauritzen19742">A.G. Lauritzen. Atlas of occlusal analysis. Colorado Springs: HAH Publications, 1974:95–105.</ref> This method, known as the "kinematic pantographic method,"<ref name="Bosman19742">A.E. Bosman. Hinge axis determination of the mandible. Leiden: Stafleu & Tholen, 1974.</ref> uses the length of the mandibular opening segment as a key parameter, providing generally acceptable accuracy, though not free from errors.