Difference between revisions of "4° Clinical case: Temporomandibular disorders"

===== Silent period of the masticator muscles =====

Figure 4 shows the neuromuscular responses of the silent period to chin percussion through a triggered neurological hammer when the patient was asked to clench her teeth maximally. If from a neurological point of view it is not possible to highlight elements referable to organic alterations of the _tCNS, some electrophysiological characteristics, however, are to be referred to a functional disorder of the system. In the upper trace, a decrease in the motor neuron reactivation phase can be seen immediately following the silent period. The possible neurophysiological mechanism capable of determining a similar decrease in facilitatory activities on the mandibular silent period can be ascribed to a change in the spindle motor drive induced by the input of muscle proprioceptors and nociceptors. The neuronal network of this process would take place through a loop formed by: muscle nociceptive afferents, the subnucleus caudalis of the V, inhibitory interneurons on static motor neurons and, as a last link, the modulation of the sensitivity of the neuromuscular spindles..<ref>Ro J.Y.,Capra  N.F.: Physiological evidence for caudal brainstem projections of jaw muscle spindle afferents.Exp.Brain Res 1999;128: 425-434</ref> <ref>Capra N.F.,Ro J.Y.: Experimental muscle pain produces central modulation of proprioceptive signals arising from jaw muscle spindles. Pain 2000; 86: 151-162.</ref><ref>Appelberg B.,Hulliger M.,Johansson H.Sojka P.: Actions on g-motoneurones elicited by electrical stimulation of group III muscle afferent fibers in the hind limb of the cat.J Physiol. 1983;335: 275-292.</ref><ref>Macefield  G.,Hagbarth E,Gorman R, Gandevia SC,, Burke D.: Decline in spindle support to a-motoneurones during sustained voluntary contractions.J.Physiol 1991;440:497-512.</ref><ref>Mense S.,Skeppar P.: Discharge behavior of feline gamma-motoneurones following induction of an  artificial myositis.Pain 1991; 46: 201-210.</ref><ref>Pedersen J, Ljubisavljevic M, Bergenheim M.,Johansson H.: Alterations in information trasmission  in ensembles  of primary muscle spindle afferents after muscle fatigue in heteronymous muscle.Neuroscience 1998;84: 953-959.</ref>  Also in this context the inhibitory component most likely prevails over the excitatory one and this could be ascribed to a malocclusion as we will see later. In particular, it can be noted the overlapping of the jaw jerk behavior, previously tested, in a path rectification condition. The arrow indicates the jaw jerk on all traces and the decrease in amplitude can be observed for the right masseter while it is relatively symmetrical on the temporal muscles.<br />

The finalization of the definitively diagnosed clinical case of DTMs resulted in a restoration of the masticatory function, disappearance of the symptoms as well as an aesthetic improvement. The various phases of the rehabilitation can be followed in the gallery of images in figure 9. In particular, the Functional Neuro-Evoked Centric position is not only centered having moved slightly to the right but also retruded. It is interesting to make a comparison with figure 5a to understand the spatial differences. Element 22, in fact, is no longer in crossbite but in a head-to-head position while element 23 has a much more incisal centric contact with respect to the previous clinical situation, so as to note the occlusal space in the medial area of element 24 which it was generated with the current mandibular spatial position determined with the Functional Neuro Evoked Centric. This new occlusal arrangement was only possible because the stable and mainly frozen centric position in the molar sector. The molars through the previously exposed neuromotor balance on the centric cusp stabilize the occlusion and generate a bilateral balance in the mandibular movements as will be shortly described.

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File:Clicker end1.jpg|'''Figure 9a:''' Frontal view of functional neuro-evoked rehabilitation and incisal normocclusal restoration with two crowns in Empress (work performed in 1992)

File:Clicker end2 .jpg|'''Figure 9b:''' Occlusal view of functional neuro-evoked rehabilitation and incisal normocclusal restoration with two crowns in Empress (work performed in 1992)

File:Clicker end3.jpg|'''Figure 9c:''' Peculiarities of neurognathological parameters. Occlusal view of the left mediotrusive detail. (work done in 1992)

</gallery></center>

In figure 9c and 9d, we can see not only the well balanced centric contacts but above all the mediotrusive excursions. A few more words should be spent on this subject. Benedikt Sagl et al.<ref>Sagl B, Schmid-Schwap M, Piehslinger E, Rausch-Fan X, Stavness I. The effect of tooth cusp morphology and grinding direction on TMJ loading during bruxism. Front Physiol. 2022 Sep 15;13:964930. doi: 10.3389/fphys.2022.964930. eCollection 2022.PMID: 36187792 </ref> state, in their study in which the contribution of tooth inclination, medio-otrusive and laterotrusive excursion and von Mises stresses on the articular disc was analysed, that mediotrusive bruxing generates higher loads than laterotrusive simulations. In this sense it is not clear whether the mediotrusive contacts are a protective or a pejorative element in the generation of temporomandibular joint disorders. So much so that an article by Walton TR and Layton DM<ref>Walton TR, Layton DM. Mediotrusive Occlusal Contacts: Best Evidence Consensus Statement. J Prosthodont. 2021 Apr;30(S1):43-51. doi: 10.1111/jopr.13328.PMID: 33783093</ref> increases the confusion as they first state that the presence of TM interference in patient populations is large and varies from 0% to 77% and then conclude that TM interference should be avoided in any occlusal treatment regimen to minimize pulpal, periodontal, structural and mechanical complications or exacerbation of temporomandibular disorders (TMD). The confusion increases when he concludes that natural molar MT interferences should only be eliminated if signs and symptoms of TMD are present. The question that arises is the following