Structure and movement, let’s not kill Chronos

2.1. Measure the structure

We have developed the ability to analyse the structure in a systematic and detailed way, isolating it from time, and therefore depriving it of the movement that animates it, fixing the moment with static photographic and radiographic images. With direct cephalometric techniques or indirect on radiography we have defined points and reference systems, measured dimensions and distances, compared, made proportions, and described the layout [7]. The morphological bio-typology is represented by specific Indices expressed in (%), obtained from the proportion of direct linear measurements (mm), these consider the maximum horizontality and verticality on the frontal plane, verticality and depth on the sagittal plane. In addition, indirect angular measurements (degree) of the anterior and posterior profile, the goniac angle of the mandible, the inclination of the bi-spinal plane, the anterior and posterior cranial fossae with respect to Frankfurt Plane (PFH) are used [8-10].

The real challenge is to know how to correlate the structure with the type and quality of the functions that shaped it.

3.1. Measure the movement

To make a correct diagnosis of the chewing organ, in addition to a static evaluation, it is necessary to add the evaluation of the mandibular dynamics. And it is in this context that the exploration of Planas Chewing Functional Angles (AFMP) takes on significance, so called because they were born from his clinical intuition. Planas was the first to clinically evaluate mandibular movements quickly and easily. We recall that a physiological mandibular dynamic is characterized by the alternation of unilateral chewing, to obtain an ideally symmetrical function, with a prevalence of the translational components over the rotating ones, i.e. horizontality over verticality.

3.2. AFMP and its characteristics

AFMPs are the expression of mandibular lateral movements in the frontal plane. They are explored by asking the patient to bring the mandible into a canine head-to-head relationship alternately from either side. They are performed with open lips and their direction is centrifugal, that is, from the inside to the outside. For these reasons they are considered analysis movements, to distinguish them from true functional movements that are performed with closed lips, in a centripetal direction with the presence of food and ending the cycle in the position of maximum intercuspation. The left and right AFMPs are evaluated against a horizontal line passing through the incisal edge of the maxillary central incisors. Symmetry and amplitude are analysed: equal and flattened angles imply lateral mandibular excursions with horizontal prevalence and therefore facilitated lateral movements (Fig. 1) [12], while steep equal angles are indicative of the prevalence of the vertical component which clinically translates into a vitiated chewing with straight movements in opening and closing. When the angles are asymmetrical, the vertical dimension in dynamics on one side and on the other are different, that is an expression of an underlying functional asymmetry. In this case, chewing will be facilitated on the minor AFMP side [11].

3.3. Three-dimensional evaluation

A three-dimensional conception of the system implies analysing the movements in the 3 planes of space: on the frontal plane the transverse and vertical dimension, it is the plane on which we value the AFMP; on the sagittal plane the vertical and anteroposterior dimensions; and on the horizontal one, the most difficult to appreciate in our daily clinic, we value the lateral extension of the movement and its anteroposterior component. To illustrate the usefulness of considering this plane in daily clinical practice, we show the use of Planas Indirect Tracks with Gothic Arch which were devised by Planas to rehabilitate the latero-protrusive component in mandibular laterality movements [12]. Changing the opening of the angle, rendering it wider, we allow the contact and rubbing between the incisors during the movement of laterality and therefore the recruitment of more propioceptive information for a better control.

Fig. 1PIPS with gothic arch

4.1. Maturation of the occlusal plane

This concept, also developed by Planas, is a real paradigm shift. It adds to the meaning of system that of “evolutionary process”. It proposes to us a system open to the influences of the environment and in constant change, like the subject to which it belongs. How far we are from the standard image of dental arches that present us a mouth in a static way, fixed over time, immutable, to which we are usually used. In the human species there are two dentitions, both with the purpose of leading the system to its functional fullness. This process is expressed thanks to a powerful masticatory function that transforms initially punctiform dental contacts into ever larger contact surfaces. The abrasion process, which under healthy conditions is physiological, favours the activation of a greater number of periodontal receptors afferent to the CNS, thus a greater amount of information processed and a recruitment of more muscle fibers that improve movement control and system protection. It is the movement through function that coordinates all the elements of the system, and this is only possible thanks to time [13]. The Process of Maturation of the occlusal plane is equivalent in both dentitions: in the deciduous one it foresees that the occlusal plane becomes plane, horizontal and parallel to Camper’s plane; in the permanent dentition, a progressive reduction of the cusps is clinically evidenced until reaching a helical plane which is associated with an AMFP almost equal to 0° and a freer and wider mandibular movement, which recruits the greatest number of periodontal receptors. In both situations, this plane has a meaning of greater stability and transfers information that comes directly from the anatomy of the TMJ. Practically in this last stage of maturation, the occlusal plane is a direct expression of the joint function. This degree of maturation is exceptionally reached in our environment as we are not exposed to intense functional requirements.

The bio-typological consideration is interesting in this aspect, mesodermal individuals have an advantage over ectodermal and endodermal ones due to the increased muscle strength they are capable of developing [14]. This allows them progressively wider (horizontal) and short (vertical) chewing cycles, more and more efficient.

4.2. Importance of environmental factors

Since the ontogenetic process of the upper jaw and especially of the mandible has a reasonable duration over time and is influenced for a longer period by environmental factors, Planas highlights the role of correct chewing as a powerful function, as a stimulus for robust and healthy growth, and with a protective action in higher risk biotypes. A biotype that is not well predisposed but functionally solicited in a balanced way can still have a harmonious development. This can be of great help in choosing the objectives of a Therapeutic Rehabilitation that is expressed through Function. Nowadays, most of the problems of the SS are related to a weak function that does not allow true physiological chewing and harmonious growth, clinically evidenced by underdeveloped structure, collapsed arches, dental crowding, and with a pathological dynamics, vertical or unilateral prevalent chewing, sometimes associated to TMJ disorders [15]. Mandibular movements must be alternate and free. The clinician's task is to free movement by removing obstacles and giving to the system the possibility to manifest its potential for a self-correction in order to achieve an Intrinsic Order of the elements of the system through a healthy function.

Movement, function, are present in all our patients, as they are endowed with vital energy, how much time do we spend analysing it? How do we concretize our evaluation of movement in the treatment we propose?