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ePaper created 2017-03-17, 11:08:54 | version 1.38.0
K i n e s i o g r a p h i c a n a l y s i s Introduction The phylogenetic evolution has produced a num- ber of postural changes related to the attainment of the upright position, and the TMJ, in its rela- tionship to the tympanic cavity, has undergone a transformation. In fact, while both in anthropo- morphic and in nonanthropomorphic monkeys, the rear portion of the TMJ is bounded posteri- orly by the postglenoid process1—a bony protu- berance of marked thickness that delimits and separates the mandibular fossa from the tym- panic cavity2—in Homo sapiens, this process has had a progressive thinning, ending in a factual disappearance. Therefore, in modern man, the rear wall of the mandibular fossa forms the front wall of the tympanic cavity. It is a thin layer, crossed by a canal (named Huguier’s or Civinini’s canal, after the researcher who first described it) that connects the two structures.3, 4 The soft- tissue that makes up the retrodiscal portion of the TMJ is histologically unfit to withstand com- pressive forces, as the retrodiscal portion of the TMJ, richly vascularized and innervated,5 essen- tially acts as a hydrodynamic support. It is worth considering that some of the connective fibers of the retrodiscal tissue penetrate the Huguier’s canal,6 forming the discomallear ligament and reaching the tympanic cavity, attaching to the malleus head and neck. In summary, these char- acteristics make the posterior region of the TMJ unsuitable for bearing the functional loads of mastication and swallowing, since, under opti- mum conditions, the condyle should never cause excessive compression of retrodiscal tissue. In fact, prolonged and constant compressive stress, linked for instance to dysfunctional situations, determines stresses that tend over time to result in reparative fibrotic processes,7, 8 leading to structural changes9, 10 responsible for a diferent biomechanical response of the tissue. The study of mandibular movement on the horizontal plane is associated with the interin- cisal point movement. Gysi in his records11 was the first to describe the Gothic arch: In classic gnathology the lateral tracings on the horizontal plane are described as an anterolateral shift. Symmetrical on both sides, the lateral tracings on the frontal plane are usually described as an anterolateral development. In patients with dys- function, kinesiographs show as a norm a defor- mation of the Gothic arch: One of the two later- al tracings tends to lose the anterolateral direction to acquire a tendency to posterioriza- tion (Fig. 1). Guichet has described a 60° conic volume in which the working condyle can shift during the lateral excursion.12 The interincisal point used in the recording of the Gothic arch can be placed geometrically in relation to the condyles.13, 14 Mongini has described in the posi- tion of maximum intercuspation the relation- ships between the interincisal point and the position of the condyles.15 Through the aid of a kinesiograph during lat- eral excursion, the tracing of the interincisal point on the horizontal plane can be placed in relation to the movement of the working con- dyle: during lateral excursion, the balancing condyle always shifts in the anteromedial direc- tion, while the working condyle can move both in the anterolateral direction and in the postero- lateral one. The interincisal point will have the same tendency of the working condyle move- ment (Fig. 2). The Gothic arch, which highlights the excursive interincisal movements of the point on the horizontal plane, can be considered a horizontal section of a volume defined by Posselt with the trajectories of maximum move- ments of opening, laterality and protrusion.16 The volume of Posselt can be defined as a 3-D perimeter within which the jaw can achieve its functional movements. In patients with dysfunction, an asymmet- rical Gothic arch, altered and reduced in its de- velopments, is practically the norm and must be interpreted as a planar representation of the deformation of the entire Posselt volume (Fig. 3). Alternating unilateral mastication allows better control of the food bolus and of the forces that develop during mastication; from a biomechan- ical point of view, it tends to symmetrically allo- cate the distribution of load on the dental, perio- dontal, bone, joint and muscle structures. This alternation of the masticatory cycles is permit- ted by the symmetry of the functional mastica- tory angles of Planas (AFMP, angles fonctionnels masticatoires de Planas). The AFMPs are the angles that are created on the frontal plane between the lateral distances and the horizontal plane, while the functional horizontal mastica- tory angles (AFMO) are those that are created on the horizontal plane between the lateral dis- tances and the frontal plane (Fig. 4). In the pres- ence of a retrusive AFMO, there will be a defor- mation of the Gothic arch structure (Fig. 1). The purpose of this work was to analyze the angles of lateral tracings, seeking to observe the relation of coherence between the frontal plane and the horizontal plane (AFMP/AFMO). This consistency respects the correspondence Journal of Oral Science & Rehabilitation Volume 3 | Issue 1/2017 61