GNATOLOGY
DEFINITION
Gnathology is the branch of dentistry that deals with the so-called "cranio-mandibular" disorders, or 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 elevating and lowering muscles of the mandible.
Disorders and actual dysfunctions of these anatomical structures are extremely common, even if they generally go unnoticed since not always symptomatic. It has to be said that, unfortunately, the great majority of dentists have a vague culture about Gnathology, in the best of cases based on not entirely correct knowledge, sometimes not very rational and often not updated information.
For this reason, the diagnosis ends up being vague, the therapeutic approach confused and the results quite mediocre.
Our studio manages this clinical area 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 elevating and lowering muscles of the mandible. Without going into excessive detail, the main elevating 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 mouth opening, the condyles slide forward and down along the glenoid fossa and, at maximum opening, practically reach the apex of the articular tubercle (sometimes passing it). The disc follows the condyles by sliding, constantly keeping the interposed 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 case occurs when the disc (with mouth closed) is not in the correct position above the condyle, interposed with the fossa, but slided forward. As a consequence, as soon as the mandible opens, the condyle finds an obstacle to movement and slows down. If the opposite joint is normal, the mouth opens with a deviation towards 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, the jaw which had deviated, instantly centers itself.
From this point on, the mandible follows a straight opening path.
When the patient closes his mouth, he moves along the reverse path so that, more or less in the same point in which the disc was "recaptured", it is again "lost" with a click. If the mandible clicks both while opening and closing, the click is called "reciprocal" (= both in opening and closing).
If both condyles are affected, the mandible will have two reciprocal clicks and a trajectory following an "S".
DISC DISPLACEMENT WITHOUT REDUCTION (LOCKING)
As in the previous disorder, in this situation, the disc is in front of the condyle in the initial position with closed mouth. 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 rebounds 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 opens with a deviation towards the blocked side, and the opening itself reaches a smaller 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 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 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 painful due to the compression of sensitive parts and the formation of liquid spills inside the joint capsule. Sometimes there is a joint noise similar to a sand rubbing, or crumpled paper, due to the rubbing of bony parts between them.
This type of pathology usually becomes chronic, alternating acute symptoms with partial remission phases, depending on the load on the joint. A possible negative evolution is the deformation of the condyle, building an arthrosis.
MUSCULAR DISORDERS
Gnathological disorders of muscular origin are less defined from an anatomical point of view, but often very painful as for their symptoms. The muscles involved can be many and, apart from the main (and most affected) ones, listed in the anatomy, it is not worth knowing them all at a divulgative level.
The thing that should be emphasized instead is that muscles hurt when they work TOO MUCH and / or BADLY. 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:
CLENCHING - This is defined as 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, for example, this way releaves stresses of everyday life. This has 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, the closed position of the dental arches (occlusion) occurs in a jaw posture that is compensated by asymmetrical muscular tensions: to keep the teeth position, the muscles are 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 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 belongs to.
It must be said, that the diagnostic protocols have become very defined in recent years, sweeping away the general approximation with which these disorders were hastily dismissed previously. Knowing and applying these new diagnostic protocols, however, is not easy and requires an operator with an updated and consolidated multiple-year training.
In addition to this, the most important instrumental examination in the gnathological field must be mentioned: Magnetic Resonance (MRI). As with all other joints, this exam is the only one that allows to visualize a very important element of the TMJ: the articular disc.
The latter in fact, is not visible with any kind of radiography, which is the reason for the substantial uselessness of these exams. The Resonance also has the advantage that it can be repeated an infinite number of times because it doesn't use radiation and therefore has no consequences.
By combining the clinical examination with MRI, the gnathologist will be able to do a correct diagnosis and suggest an appropriate treatment plan.
GNATHOLOGICAL THERAPY
Cranio-mandibular disorders have different approaches depending on the diagnosis. The procedure principles ar similar to orthopedic / physiotherapeutic criteria, therefore we are talking about movements to recondition the joints, muscle relaxation therapies and devices with orthopedic function (bites).
Bites deserve a separate mention because it is extremely common, in the face of a cranial mandibular problem, to be asked to build one of these devices. The fact is that usually, the proposed one is a classic "bite plane", but the function such a device can perform is only good for certain problems, less so for others, being sometimes even 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 a dental arch (generally the upper one) causing the teeth to close on a different ad hoc created surface. Classically it has some aspects in common with the old concept of "bite plane", even if unlike the latter, the neuromuscular one is conceived with reduced lingual dimensions and more precise lateral guides. A good neuromuscular bite also requires a complex registration technique recording the patient's "rest" or "neuromuscular" position, which even if precise as possible, will involve subsequent adjustment phases, which follow rather rigorous protocols. The goal is to obtain a comfortable position for the patient, in which he 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 one in which, when the condyles are moved forward and the disc is recaptured, the click disappears.
Subsequent adjustments will serve to bring the patient to the best therapeutical position.
Distraction Bite - This bite is built on the lower arch and is essentially a neuromuscular bite where an intended pre-contact (= point that touches first) has been created on one side only, so that the patient, closing his teeth, will not be able to touch them all, but he will have a single contacy on that side. It is used in cases of compression of the posterior ligament and is then adjusted until the symptoms fade, after which it is transformed into neuromuscular.