Clinical approach and diagnostic methods.
Introduction :
Occlusal malpositions or disturbances are very often responsible for mandibular positions considered pathogenic. Obstacles on the path of closure or avoidance reflexes, responsible for these defects, are generally difficult to observe and analyze in the oral cavity.
I)-Definitions:
Occlusal analysis on an articulator is a method of examining casts mounted on the articulator, allowing the observation of occlusal contacts (or their absence). It also allows the stages of equilibration to be predicted and/or the simulation on the plaster of occlusal modifications to be made as part of restorative treatment.
1-1)-Definition of occlusal functions:
Centering: concerns the situation of the mandibular position in OIM.
Wedging: concerns the stabilization of the mandibular position in OIM.
Guidance: concerns the trajectories for accessing the mandibular position in OIM.
1-1-1)-Centering function (where is the mandible located in OIM in space?)
At the IOM : The most important constraints.
To reduce musculoskeletal constraints, this spatial position must be centered,
In the transverse direction: a symmetrical mandibular situation with condylo-disco-temporal coaptation corresponds to a strict centering in the frontal plane. An asymmetry would be characterized by a mandibular deviation.
In the sagittal direction: there is a physiological anteposition of the OIM in relation to the occlusion in centric relation (ORC); this very slight strictly sagittal offset is less than 1 mm in relation to the ORC.
In the vertical direction: the mandibular position in OIM defines the height of the lower level of the face; it is in harmony with the osteo-muscular elements (vertical centering or vertical dimension of occlusion – DVO).
1-1-2)-Wedging function (is the mandible stable in OIM?)
Results in intra-arch and inter-arch stability.
a/- Dental stability or stability of occlusion: The stability of the tooth on its bony base, in its arch, means the absence of dental migration. For each tooth, the distribution of punctiform contacts on opposite cusp slopes is a guarantee of stability. Compliance with these requirements is obtained by the distribution of multiple occlusal contacts distributed harmoniously over the entire arch. The distribution of constraints reduces the effort undergone by each dental organ.
b /- Mandibular stability: The stability of the mandibular posture in OIM only makes sense if there is perfect stability of the arches over time (apart from the phenomena of wear and physiological dental migration). The resulting mandibular stabilization facilitates, through the precision and reproducibility of the position, muscular work. The maintenance of this mandibular posture is then achieved with low muscle recruitment, which further reduces the constraints applied. Similarly, the maintenance of the resting posture and the movements of mandibular elevation towards the OIM (in particular during swallowing) are facilitated.
1-1-3)-Guidance function (how does the mandible access the OIM?)
IOM Access Funnel:
Chewing and phonation are performed by complex cyclic movements that determine a functional envelope that falls within the limit envelope, through the possibilities of occlusal contacts in the different mandibular movements (return contacts towards the OIM or intercuspation trajectory). These inter-arch contact surfaces constitute the guidance zones that impose the functional mandibular trajectories by means of an architectural component: the occlusal anatomy.
These surfaces constitute real three-dimensional guide ramps creating a cone with an ellipsoidal base whose summit represents the OIM: the access funnel to the OIM.
These guiding surfaces direct mandibular movements under the protection of an essential neurophysiological component.
II)-Preliminary steps and necessary material : Mounting on articulator and control
Occlusal analysis, in addition to the articulator, requires various materials. First, the patient’s casts, made of synthetic plaster, if necessary cleaned to eliminate plaster bubbles replicating salivary beads. The mandibular cast is generally prepared with removable cuspid sectors, mounted on repositioning rods. The maxillary cast must have a double meshed base that allows to control the reproducibility of the centered relationship recordings.
For the occlusal analysis of the wedging and centering functions, the articulator is programmed with average values: 30° condylar slope and Bennett wings set to 0°, for Sam articulators.
Finally, additional equipment is required, consisting of: a scalpel or a cutter to rectify the casts; inked paper (generally 40 µm) of different colours, Miller forceps, a graphite pencil to note the rectifications on the plaster, and a wax spatula and sculpting wax to rectify the occlusal morphology by addition.
Clinical approach and diagnostic methods.
III)-Stages of occlusal analysis on articulator:
1)-OIM/RC:
Casts can also be observed in maximum intercuspation occlusion (MIO).
It is then necessary to free the condylar movements by unscrewing the screws of the condylar slopes, the housings can then turn freely.
In many cases it is preferable to completely remove the articulator housings to be able to place the models in OIM without constraint.
Occlusal analysis on an articulator consists of comparing and balancing, for the RC and OIM positions, on the one hand, the dental contacts on the casts and, on the other hand, the situations of the condylar balls in the articulator housings. The use of the articulator also makes it possible to precisely evaluate the difference in vertical dimension between these two positions.
2)- Wedging function:
With the casts mounted in RC, the articulator is closed up to the first occlusal contact, with no stress being exerted on the articulator. In most cases, one or two dental contacts and more or less significant inocclusion zones are observed. More engagement guarantees stability
3)-Centering function:
On the maxillary cast, a median line is drawn between the central incisors and extended vertically on the vestibular surface of the mandibular incisors in centric relation.
The casts are then placed in OIM. The observation of a shift between the lines drawn on the casts indicates a centering defect.
Clinical approach and diagnostic methods.
4)-Guidance function:
Propulsion and diduction movements (working lateralizations) can be simulated on a programmed articulator. However, traditional articulators do not allow the functional contacts observed during retropulsion to be simulated. Occlusal analysis of the guidance function on an articulator is therefore limited to the observation of dental guidance during centrifugal lateral movements (group function or canine function) and during propulsion.
5)-DV analysis
5-1- Evaluation of the DVRC:
Since the casts are in RC, the vertical dimension of centric relation (DVRC) is evaluated by direct reading on the incisal rod of the graduation marked in relation to the 0 line (generally thicker). The incisal rod must be supported on the incisal table during the first occlusal contact appearing on the path of closure of the articulator in RC.
5- 2-Evaluation of DVIM:
The casts are placed in OIM and the corresponding vertical dimension (DVIM) is located by direct reading on the incisal rod put back in contact with the incisal table. It is noted and compared to the DVRC.
In general, DVRC is superior to DVIM because it corresponds to the establishment of premature contact on the closing path to the OIM.
5-3- DVA evaluation:
The assessment of the anterior vertical dimension (AVD) is done by removing the cuspid sectors from the mandibular cast, with the articulator set to RC. In general, the AVD read on the incisal rod is lower than the DVRC.
Different relative situations of DVRC, DVIM and DVA can appear and they lead to different balancing proposals. It is also possible to evaluate the consequences of an increase in the vertical dimension.
Clinical approach and diagnostic methods.
IV)-Balancing of plaster casts:
The balancing of the casts on the articulator should be considered as a simulation of the possible balancing to be carried out later in the mouth. It is the final result of the first which indicates or contraindicates the second, the latter being able to use subtractive or additive techniques.
A)-General principles:
– From the outset, major disturbances of the functional curves are corrected by subtraction on the extruded teeth or fixed prostheses whose morphology is in contradiction with the usually accepted rules.
– Rectifications by subtraction of plaster seek to restore the teeth to a natural morphology, limiting the contact surfaces in favor of occlusal contact points. This leads to rejuvenating the teeth by reproducing the natural morphology of the teeth (cusps, pits, grooves, embrasures), we ensure that when closing, the forces are exerted along the major axis of the teeth concerned: wedging role.
– For some authors, the remodeling of the maxillary arch would aim more to improve the morphology of the teeth while the remodeling of the mandibular arch would have a vocation of functional adaptation. In fact, the choice of rectification between two antagonistic teeth is made towards the one that benefits the most from remodeling by excluding as much as possible the teeth presenting a correct morphology.
– Gaps are filled by adding inlay wax, which can be used to improve occlusal morphology, compensate for inocclusions or replace missing teeth.
-The intervention timeline varies according to the authors: It seems preferable to begin the equilibration by establishing the occlusal setting, during closure in the RC position.
The first step is to balance the anterior groups on the closing path, the next steps consist of adapting, one after the other, the lateral sectors.
B)- Analysis and adaptation of previously closed sectors:
If the DVIM > DVA, there is no contact on the teeth anterior to the DVIM.
There are three therapeutic possibilities:
– either reduce the DVIM until it comes into contact with the anterior sectors
– either move the front teeth by orthodontics or surgery.
– either remove the occlusion with a prosthesis.
If the DVA > DVIM, it is because there is, in centric relation, one or more previous prematurities. The equilibration simulates the reduction of these prematurities which can be dental or mucous
From a morphological point of view, rectifications are made to try to establish contacts between the free mandibular edges and the proximal crests of the maxillary teeth, while respecting the usual and relative dimensions of the teeth between them. It is considered that rectifications by subtraction of the anterior teeth, to gain 1 mm at the level of the incisal rod, are acceptable in most clinical situations. If the mutilations are too important, or if we end up with a poor aesthetic situation. Balancing of the anterior teeth is contraindicated.
C)-Evaluation and adaptation of the lateral sectors in closure:
The method consists of treating both sides of the arch one after the other. The incisal rod is adjusted to the DVIM. The inked paper is placed between the arches and the articulator closed. The points obtained are rectified until the incisal rod is in contact with the incisal table for the DVIM. The rectifications are done in successive stages, by marking with a pencil the occlusal surfaces resculpted with a scalpel, until the greatest number of stabilizing contacts is obtained. The operation is then repeated on the second cuspidate sector. The pencil marks allow the memory of the rectifications carried out on the casts to be preserved.
D/ Evaluation and adaptation of lateral sectors in lateral movements:
The methodology remains the same and consists of removing the traces of inked paper which materialize the interferences without modifying the DVIM.
However, semi-adaptable articulators programmed on average values can only claim to simulate the lateral dental contacts corresponding to the working lateralizations.
These movements can be performed on the articulator in order to highlight possible posterior interferences that would prevent the classic canine function or group function guidance. The casts are then balanced in order to establish these guidances, provided that the occlusal rectifications do not disturb the wedging and centering functions found during the first phases of equilibration.
At the end of the occlusal analysis and equilibration, we obtain the reestablishment of dental meshing at the DVIM on casts mounted in RC on the articulator.
This meshing restores the occlusal functions of mandibular wedging and centering.
The situation obtained prefigures the balanced situation in the mouth and thus provides the means to decide whether or not to initiate a therapeutic approach by equilibration. In some cases, the corrections made on the plaster cannot be transposed into the mouth because they prove to be too significant or too mutilating. In other cases, the equilibration made on the plaster guides the occlusal arrangements to be made and the restorative dentistry work.
Occlusal analysis on an articulator is therefore an intellectual and practical exercise which allows us to understand and illustrate the roles of mandibular wedging and centering in maintaining the health of the masticatory system.
Clinical approach and diagnostic methods.
Iv)-Imaging:
X-ray examinations allow the joint structures to be partially or completely seen :
Panoramic radiography should be a systematic examination; it allows us to judge the shape and integrity of the condylar processes.
The scanner allows a much finer appreciation of the bone structures. The computed tomographic sections, mouth closed and open, allow to appreciate the relative position of the supracondylar processes in different orientations.
Magnetic resonance imaging allows to see the soft tissues : disc, capsule, muscle. The examination of choice of the articular structures. (detect the disc dislocation, its level, its degree of reversibility and its reducible nature.
V)-Electromyography:
Allows you to check and measure the state of contracture of the muscles accessible to the electrodes.
Clinical approach and diagnostic methods.
Cracked teeth can be healed with modern techniques.
Gum disease can be prevented with proper brushing.
Dental implants integrate with the bone for a long-lasting solution.
Yellowed teeth can be brightened with professional whitening.
Dental X-rays reveal problems that are invisible to the naked eye.
Sensitive teeth benefit from specific toothpastes.
A diet low in sugar protects against cavities.