Definitions and Descriptions

Gnathology is the branch of Odontology dealing with the so called "cranio - mandibular" disorders, that's to indicate those disfunctions and pathologies of the masticatory system from a non strictly dental point of view.
Gnathology, in fact, concerns about joints and muscles, and in particular, the joint between mandibula and skull (Temporo Mandibular Joint or TMJ) and about the lowering and elevating muscles of the mandibula.

The disorders and the real disfunctions of these anatomical structures, are very common, although they generally go unnoticed because they're not always symptomatic. Unfortunately it must be said that the great majority of the dentists only has a vague powdering about Gnathology, in the best cases on quite uncorrect, not updated and not rational knowledge.
For this reason, diagnosis is often vague, therapeutical approach is confusing and results quite mediocre.

The Dentalsynergy group moves in this field basing on post-graduate updates having solid weight, modern and rational guidelines.

The anatomical structures of gnathological concern are (in a nutshell) the mandibula, the articular disk, the cranic base (fossa and tubercule), muscles and ligaments (see pictures).
The mandibula has two articulating heads called "condyles" that move into two grossly bowl shaped spaces under the cranic base. In between these two bone structures there is a cartylage disk having functions of surface adaptation and shock absorber of the mastication weight. The disk is situated inside an articuar capsule and held into position and driven while in movement by ligaments connecting it to the neighboring structures.

The muscular structures are made of muscles elevating and lowering the mandibula. Without too much details, the main elevating muscles are the masseter and the temporal, while the lowering muscles are those of the mouth pavement and the digastric.

When opening the mouth, the condyles slide forward and downward following the glenoid fossa and, at maximum aperture, they practically reach the top of the articular tubercle (sometimes even passing it). The disk follows the condyle in this movement, staying constantly interposed thanks to its ligaments. Just in asimilar way, the mandibula performs its lateral movements always with the articular disks accompanying the condyles.

The disorders of the Temporo Mandibular Joint can be classified under a few cathegories.

Disk displacement WITH reduction (click)

This ailment occurs when (with closed mouth) the disk is not in its proper position on top of the condyle confronting the fossa, but in a more anterior position. As a consequence, as soon as the mandibula starts opening, the condyle finds an obstacle to its movement and slows down. If the opposite articulation is normal, the mouth appears to be opening with a deviation towards the affected side.
At a certain point, the opening push wins over the elastic resistence of the disk and the condyle performs a forward jump, repositioning itself under the disk with a typical sound known as "click". Looking at the patient, we can observe that the mandibula which had a trajectory deviation, straighten the course instantly.
From this point on, the mandibula follows a perfectly straight opening path.
As the patient closes his mouth, he follows a path which is inverted in a way that, almost at the same point in which the disk had been "recaptured", it goes "lost" again with a click and a jump symmetrically opposite of those in aperture. In this case the click is called "reciprocal" (= both in aperture and closure).
If the affected condyles are both, the mandibula will show two reciprocal clicks at the condyle and the trajectory will mark an "S" shape.

Disk displacement WITHOUT reduction (locking)
Just like in the previous case, in this situation, the disk is in front of the condyle when this is in rest position with closed mouth. The difference is that, as soon as the mandibula begins its opening path, the condyle is not able to recapture the disk, so there is no "reduction" (= there is no "click").
It happens that the disk elastically curls itself in front of the condyle and prevents it from advancing: the result is that the patient has a movement limit on the affected part, the mandibula performs a deviated aperture towards the locked side, and the aperture's wideness as a whole is lower than normal.
This condition is very often subsequent to a period in which the affected TMJ had a click and is determined by a further forward slide of the disk. Two subdivisions are possible:
- Acute: the patient having a click, all of a sudden can't perceive it anymore and he instantly falls into blocked condition.
- Chronic: The patient has a movement reduction since a long time and he may have developed some adaptation.

Ligament compression
In all those situations in which the disk is displaced, the condyle rests upon a structure which is not normally involved: the posterior ligament of the disk. This anatomical structure is rich in blood vessels and nerves so it may occur to the mandibular movements to be painful due to continuous friction on sensitive parts and the formation of liquid bubbles inside the articular capsule. Sometimes a sound may be heard, similar to sand rubbing or newspaper rolling, due to the bone parts contact.
This specific kind of disease usually chronicizes, with alternating phases of acute symptoms or remissions, according to weight on the articulation. One possible negative result is the deformation of the condyle with formation of arthrosis.

The gnathological muscular ailments are less defined from an anatomical POV, but are very often quite painful. The muscles moving the mandibula in all directions are quite many and, apart from the main (and most affected) ones, listed in the anatomical section, it's not worth knowing them all at this divulgative level.
To be underlined is that the muscles ache or hurt whenever they work TOO MUCH and/or IN THE WRONG WAY. In a nutshell, muscles working to eccess, face phoenomena of contraction, fatigue and spasm.
But why should the masticatory muscles work too much or in the wrong way, to begin with? The causes are many and very complex, sometimes hard to detect, but can be listed as follows:

Clenching - It's the patient's habit of keeping the teeth in a very tight contact and pulsating the closure muscles (masseter and temporal, mainly).
Bruxism - It's the habit of rubbing the teeth tightly between them, having them slide in all directions (grinding) sometimes also producing noise.
Most of the times, both these phoenomena have a NON dental origin: for example the patient relieves daily life's stress. The results are a series of consequences like teeth abrasion, fractures or muscular pain.

Bad Habits - A classic example is the use of chewing gum: it obliges the muscles to work for hours uselessly, with all the already described consequences.

Occlusal Issues - In a small number of cases, the closed position of the two dental arches ("occlusion" or "mastication") may cause a postural problem to the mandibula, being compensated by asymmetrical muscular tensions: to keep the dental position, the muscles are forced to work the wrong way. The most frequent problems are pre-contacts, interferences, occlusal instability and loss of vertical dimension.

The main approach to understand cranio mandibular (gnathological) disorders is clinical. First of all it is based on a series of tests and observations that help to distinguish if the problem is articular or muscolar. A correct sequence of analysis, allows in most of the cases to correctly cathegorize the patient's complaint.

It must though be said that in the last years, diagnostic protocols got much more precise, swiping away the general approximation by which these ailments were got rid of in the past. Knowing and applying those new diagnostic protocols though, is not a completely immediate matter and requires an operator owning a pluriennal, updtaed and consolidated training.

More than that, we have to point out what is now considered to be the most important instrumental diagnosis in gnathology: the Magnetic Resonance Imaging (MRI). As it happens for all joints, this exam is the only one consenting to visualize a very important element of the TMJ: the articular disk.
The latter, as a matter of facts, is not visible in any X-Ray images, a fact from which we can derive the substantial uselessness of these, from panoramics to transcranial views. Further, the MRI has the advantage of allowing unlimited repetitions beacuse it does not use radiations and therfore leaves no consequences.

By combining both the clinical examination and the MRI, the gnathologist will be able to formulate a correct diagnosis and to suggest a proper treatment.

Cranio mandibular disorders (obviously) have different approaches according to the diagnosis. The principles are assimilable to orthopaedic and physiotherapic criteria, so we speak of movemnts aimed at joint reconditioning, muscular relaxation therapies and devices with orthopaedic functions (bite).
Bites deserve a special mention because facing a cranio mandibular disorder, it is extremely common to be suggested to build and use one of these devices. The problem is that in almost every case the proposed bite is the classic "bite plane", but the function that such a device can perform may fit some kinds of problems and less others; also it may be contraindicated in some cases.
As already stated, if the diagnosis is not pecise, the generic application of "a bite" does not solve much so, within a modern approach, it's the combination of more techniques that leads to the most appropriate solution.

Mandibular exercise - It is a set of exercises and movements executed in the attept to recover from the classic joint issues (click), and also to obtain muscular stretching and relaxation.

Neuromuscular Bite - It is a transparent resin plate applied over a dental arch (generally the upper one) bringing teeth to rest on a different surface, specifically created. It has some aspects in common with the old concept of bite "plane" although differently from this, it is conceived with a reduced lingual size and more precise lateral guides. A good neuromuscular bite requires a technique to record  a patient's "rest" or "neuromuscular" position being the most precise possible and implies some rather rigorous construction and adjusting phases. The aim is to achieve the comfort position for the patient by which a good muscular relaxation should be reached. It can also be used as a protection of the teeth in parafunctional cases (bruxism and clunching).

Repositioning Bite - It's a special bite used specifically in the treatment of disk displacement with reduction. It's mounted on the upper arch and it has an internal chute that obliges the mandibula to close in an advanced posture and in particular in that position in which, having pulled the condyle forward and having recaptured the disk, the click disappears during movement.

Distraction Bite - This bite is built on the lower dental arch and is basically a neuromuscular bite on which a pre-contact (= spot being hit first when closing) has been created on one side only, in a way that the patient, closing his teeth, won't be able to do so having one single contact on that side. It's used in case of compression of the posterior ligament and is then adjusted until a symptomatic improvement is reached, after which it is reconverted into neuromuscular.