GNATOLOGY
DEFINITION OF GNATOLOGY
Gnathology is that branch of dentistry that deals with the so-called "cranio-mandibular" disorders, that is, the dysfunctions and pathologies of the chewing system from a not strictly dental point of view.
Gnathology therefore deals with joints and muscles and in particular the joint between the mandible and the skull (temporomandibular joint or TMJ) and the system of elevators and lowering muscles of the mandible.
Disorders and actual dysfunctions of these anatomical structures are extremely common, even if they generally go unnoticed because they are not always symptomatic. It must also be said that, unfortunately, the great majority of dentists have a vague smattering of Gnathology which in the best of cases is based on knowledge that is not entirely correct, sometimes not very rational and often not updated.
For this reason, the diagnosis ends up being vague, the therapeutic approach confused and the results quite mediocre.
Our firm moves in this field on the basis of post-graduate updates of sure weight and following modern and rational guidelines.
ANATOMY AND PHYSIOLOGY OF CHEWING
The anatomical structures involved in the gnathological field are (in a nutshell) the mandible, the articular disc, the base of the skull (fossa and tubercle), muscles and ligaments (see figures)
The mandible has two articular heads called "condyles", which move within two roughly bowl-shaped spaces under the skull base. Interposed between these two bone structures, there is a cartilage disc with the function of adaptation between the surfaces and shock absorber of the chewing load. The disc is contained within a joint capsule and guided into position and movement by ligaments that connect it to surrounding structures.
Then there are the muscular structures, roughly distinguishable in the levator and lowering muscles of the mandible. Without going into excessive detail, the main levator muscles of the mandible are the masseter and the temporal, while the main lowering muscles are those of the floor of the mouth and the digastric.
During the opening of the mouth, the mandibular condyles slide forward and down along the glenoid fossa and, at maximum opening, practically reach the apex of the articular tubercle (sometimes exceeding it). The disc follows the condyles in sliding, constantly remaining in the interposition position thanks to the ligaments. Similarly, the mandible performs lateral movements, always with the articular discs accompanying the condyles
DISORDERS OF THE JOINT
Disorders of the temporomandibular joint can be classified into a few broad categories.
DISC DISPLACEMENT WITH REDUCTION (CLICK)
This disturbance occurs when the disc (with the mouth closed) is not in the correct position above the condyle, interposed with the fossa, but moved forward. As a consequence, as soon as the mandible opens, the condyle finds an obstacle to movement and slows down the stroke. If the opposite joint is normal, the mouth opens with a deviation to the affected side.
At a certain point, the opening thrust overcomes the elastic resistance of the disc and the condyle jumps forward, repositioning itself under the disc with a characteristic sound called "click". Looking at the patient, it is observed that the jaw which had deviated, instantly straightens.
From this point on, the mandible follows a straight path of opening.
When the patient closes his mouth, he makes a reverse path so that, more or less in the same point in which the disc was "recaptured", it is again "lost" with a click and a click that are the reverse of those of opening. In this case the click is called "reciprocal" (= both in opening and closing).
If both condyles are affected, the mandible will have two reciprocal clicks at the condyles and a trajectory of movement that follows an "S".
DISC DISPLACEMENT WITHOUT REDUCTION (LOCKING)
As in the previous disorder, in this situation, the disc is in front of the condyle when it is in the initial position with the mouth closed. The difference is that as soon as the mandible begins the opening movement, the condyle cannot recapture the disc and therefore there is no "reduction" (= no "click").
In essence, the disc shrinks elastically in front of the condyle and prevents it from advancing: the result is that the patient has a limitation of movement on the affected side, the mandible makes an opening deviated towards the blocked side, and the opening itself is of a less than normal overall width.
This condition is very often subsequent to a period in which the affected TMJ had a click, and is determined by the further sliding forward of the disc. It is divided into two types:
- Acute: the patient who had a click suddenly no longer hears it and the jaw freezes in a lightning-fast way.
- Chronic: the patient has had a reduction in movement for a long time and has sometimes developed adaptations.
COMPRESSION OF THE LIGAMENT
In all situations in which the disc is not in the correct position, the condyle of the mandible rests on a part not normally involved: the posterior ligament of the disc. This anatomical structure is rich in blood vessels and nerves, so it can happen that the movements of the jaw are also very painful due to the continuous stress of sensitive parts and the formation of liquid effusions in the joint capsule. Sometimes there is a joint noise similar to a rubbing of sand, or crumpled paper, due to the rubbing of bony parts between them.
This type of pathology usually becomes chronic, alternating acute and symptom remission phases, depending on the load on the joint. A possible negative evolution is the deformation of the condyle, with the formation of arthrosis.
MUSCULATURE DISORDERS
Gnathological disorders of muscular origin are less defined from an anatomical point of view, but often very painful as symptoms. The muscles that are found to act to move the jaw in all directions are many and, apart from the main (and most affected) listed in the anatomy, it is not worth knowing them all at a popular level.
The thing that should be emphasized instead is that muscles hurt when they work TOO MUCH and / or BAD. Basically, the muscles forced to work in excess, undergo phenomena of contracture, fatigue, spasm.
But why should the chewing and facial muscles work too much and badly? The causes are multiple and complex, and sometimes difficult to recognize, but they can be summarily distinguished as follows:
Serramento - This is the patient's habit of keeping the teeth in very close contact and making the closing muscles pulsate (masseter and temporal predominantly)
Bruxism - It is the habit of tightly rubbing the teeth together making them slide in all directions (grinding) sometimes also producing noise.
Both of these phenomena are in most cases due to NON-dental causes: the patient relieves in this way, for example, the stresses of everyday life. The result is a series of consequences including abrasion or fracture of the teeth and muscle problems.
Bad habits - A classic example is the constant use of chewing gum: it forces the muscles to work unnecessarily for hours, with the consequences already described.
Occlusal problems - In a small number of cases, actually the closed position of the two dental arches (occlusion or "chewing") can cause a jaw posture problem that is compensated by asymmetrical muscular tensions: to maintain the position of the teeth, the musculature is forced to work poorly. The most frequent problems are pre-contacts, interference, occlusal instability, loss of vertical dimension
DIAGNOSIS OF SKULL - MANDIBULAR DISORDERS
To understand craniomandibular (or gnathological) disorders the main approach is clinical. It consists of a series of tests and observations that help first of all to distinguish whether the problem is articular or muscular. A correct analysis sequence allows in most cases to identify with some certainty which category the disorder that the patient reports belongs to.
It must be said, however, that the diagnostic protocols have become very defined in recent years, sweeping away the general approximation with which these disorders were hastily liquidated previously. Knowing and applying these new diagnostic protocols, however, is not entirely immediate and requires an operator with an updated and consolidated multi-year training.
In addition to this, we must mention what is now the most important instrumental examination in the gnathological field: Magnetic Resonance (MRI). As with all other joints, this exam is the only one that allows you to visualize a very important element of the TMJ, that is, the articular disc.
The latter in fact, is not visible with any type of radiography, which is the reason for the substantial uselessness of these examinations, from the panoramic to the old transcranials. The Resonance also has the advantage that it can be repeated an infinite number of times because it does not use radiation and therefore leaves no consequence.
By combining the clinical examination with MRI, the gnathologist will be able to make a correct diagnosis and suggest an appropriate treatment plan.
GNATHOLOGICAL THERAPY
Cranio-mandibular disorders have (evidently) different approaches depending on the diagnosis. The operating principles are however similar to orthopedic / physiotherapeutic criteria, therefore we are talking about movements to recondition the joints, muscle relaxation therapies and devices with orthopedic function (bite).
Bites deserve a separate mention because it is extremely common, in the face of a cranial mandibular problem, to be asked to construct one of these devices. The problem is that in almost all the times, the bite that is proposed is a classic "bite plane", but the function that a device like this can perform is good for certain types of problems, less so for others, being in certain cases contraindicated.
As already mentioned, if the diagnosis is inaccurate, the generic application of "one bite" does not solve much, therefore, in a modern approach, it is the combination of various techniques that leads to the most appropriate solution.
Exercises for the jaw - This is a set of exercises and movements that are performed both to try to recover classic joint disorders (click), and to obtain elongation (stretching) and relaxation of the muscles.
Neuromuscular Bite - It is a transparent resin plate that is applied over an arch (generally the upper one) and which causes the teeth to close on a different surface, created ad hoc. Classically it has some aspects in common with the old concept of bite "plane", even if unlike the latter, the neuromuscular is conceived with reduced lingual dimensions and more precise lateral guides. A good neuromuscular bite also requires a technique for recording the patient's "rest" or "neuromuscular" position, which is as precise as possible, and involves subsequent construction and adjustment phases, which are rather rigorous. The goal is to obtain a comfortable position for the patient, in which you can have a good relaxation of the muscles. It can also be used to protect the teeth in cases of parafunction (bruxism and clenching).
Repositioning Bite - It is a special bite that is used exclusively for the therapy of dislocation with reduction. It is mounted on the upper arch and has a slide inside the mouth that forces the jaw to close in an advanced position, and in particular in the position in which, when the condyles are moved forward and the disc is recaptured, the click disappears in the movement.
Subsequent adjustments will serve to bring the patient into the therapeutically most advantageous position.
Distraction Bite - This bite is built on the lower arch and is essentially a neuromuscular bite to which a pre-contact has been created (= point that touches first) on one side only, so that the patient, closing his teeth, does not he will be able to close them all, but he will have a single contact only on that side. It is used in cases of compression of the posterior ligament and is then adjusted until the symptoms are improved, after which it is transformed back into neuromuscular.