Dental pre-contacts and craniomandibular disorders

By Dr. Andrea Gizdulich

Pathological occlusion can be defined as that capable of generating proprioceptive inputs that disturb normal muscle function and bring the mandible into malposition with the maxillary skull complex1-3. Real dental interferences caused by marked coronal malpositions, as well as simple pre-contacts, generate a sensory response, mostly coming from periodontal receptors, but also from all other stomatognathic proprioceptors, which inform the CNS of the disturbing element3. On the basis of this continuous information the CNS sets up a function model aimed at avoiding harmful contact, which causes a displacement of the mandibular bone and a consequent condylar displacement, of variable entity and absolutely individual: the masticatory muscles as well as the cervical and hyoid ones, they are therefore called upon to do additional work, having to work in order to originate and terminate every masticatory, phonatory and swallowing movement by integrating this new information. In other words, a new postural attitude of the jaw is achieved which must be maintained for all 24 hours and which will determine muscular hypertonus4, 5 of all the competent territories. The perpetuation of this functional request over time initiates an overload capable of generating real structural damage6-8 with formation of myofascial trigger points9, that is hypercontracted sarcomeres, shortened until they constitute small nodules contained within muscle bands, incapable to release for exhaustion of energy resources.

The mandibular dislocation, however, generates new areas of dental interference - secondary deflation contacts - which will in turn act by creating new proprioceptive information to be integrated and processed until the CNS stabilizes the mandible in the so-called maximum intercuspidation position (PMI), ie that Intermaxillary relationship determined by the largest possible number of dental contacts 2, 3. This cranio-mandibular relationship is regulated by the continuous dynamic equilibrium of sensory organs and neuromuscular actions, linked in a perpetual mechanism3.

Dental pre-contacts, commonly studied under static conditions, are widely understood in common practice as those areas of premature contact which is achieved by maintaining the mandible in a position of habitual occlusion or in centric relation10, following a "preconditioned" model of jaw positioning: the identification of these areas of first contact and their pathogenetic role cannot be of great significance if the surveys are performed keeping the mandible in a position induced and subjectively conditioned by the operator or even simply in the position of habitual occlusion of the patient, not necessarily physiological as conditioned by the patient's adaptive, proprioceptive memory. These analyzes, therefore, should be coordinated with other functional investigations able to demonstrate the physiological position of the jaw and its movement towards the position of maximum intercuspidation2, 3: this allows to identify the consequentiality of the dental contacts when the jaw moves along the individual neuromuscular trajectory, in maximum muscle balance.

The introduction of an occlusal check through TENS stimulation and application of adhesive waxes is ideally suited to this purpose, allowing the individual's neuromuscular trajectory to be found and the first deflationary contacts to be identified through involuntary muscle contractions2, 3.

On the contrary, investigating prematurity with simple articulation papers will not be a truly therapeutic act, nor will vision of the contact areas really inform about the work balance of the masticatory apparatus.

Every human being can easily cohabit with his / her functional structure, even if altered or pathological, and this arrangement can be elaborated over the years in a perception of health more or less assimilable to the ideal physiological conditions, but it can also suddenly and inexplicably exhaust the individual capacities of adaptation, starting to show algic-dysfunctional symptoms typical of cranio-mandibular disorders (DCM) 1-3, 11-13. The onset of painful and dysfunctional symptoms occurs in completely unpredictable ways and times, making any correlation between the degree of dysfunction and the extent of the symptomatology impossible.

The importance of an objective verification of the degree of muscular balance, even for the most common dental rehabilitations, therefore appears increasingly clear2, 12.

For this purpose kinesiographic techniques of analysis of mandibular and electromyographic kinetics (EMG) have been in use for some time, with the aid of TENS2, 32, which represent the most reliable non-invasive means of functional investigation to measure the pathophysiological state of the apparatus masticatory18, 19.

However, a complete analysis should also include the assessment of areas and pressure loads made in the dental contact, which represents the final verification of the correct stomatognathic balance. It is evident that the mere demonstration of the good morphological matching of the arches or the vision of the contact surfaces between antagonist teeth cannot be sufficient in itself to demonstrate the physiopathologic state of the masticatory apparatus, but it represents an indispensable final verification of every dental therapy . whose orthopedic success can obviously not be achieved without ensuring adequate distribution of dental contacts 20. The analysis of the occlusal contacts was performed with the T-scan II system (Tekscan Occlusal Diagnostic System, Tekscan Inc ®) (Fig. 2 ), consisting of a printed circuit sensor 100 µm thick, housed on a support fork and connected to a computer that displays the contact areas and the degree of pressure reached.

It is clear that the presence of an altered position of the jaw cannot be demonstrated with routine clinical investigations alone and it is equally clear that the complete occlusal correction must originate from the correct knowledge of the orthopedic position of the jaw (ie of the correct intermaxillary relationship), and be secondarily completed with the correct adaptation of the dental and cuspid morphology, necessary for maintaining the physiological position of maximum intercuspidation.

It is also confirmed that the muscular and articular balance, expressed by the improvement of the oral opening both in the degree and in the fluidity of movement, can be achieved and maintained by minimizing the propioceptive input deriving from contacts on the cuspid slopes (interference according to Jankelson) 3 . These contacts in fact generate forces with tangential components to the teeth capable of damaging the tissues3, 12 and require a neuromotor regulation which, by causing an alteration of the spatial position of the jaw compared to that of neuromuscular equilibrium, triggers the framework of cranio-mandibular disorder.

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