Orthodontics and masticatory dysfunction

Orthodontics and masticatory dysfunction:

1. Introduction :

In 1934, COSTEN was the first to describe a link between certain malocclusions, the loss of posterior dental alignment and vertical dimension, with temporomandibular disorders (TMD). These temporomandibular disorders are the main cause of non-dental pain in the orofacial region. Their definition in the occlusodontics lexicon is as follows: “Symptomatic expression of a myoarthropathy of the masticatory system”. Their etiology and pathophysiology remain poorly understood. Nowadays, the etiology seems multifactorial involving a large number of direct and indirect factors; occlusion is often cited as one of the main factors causing these TMDs. In various epidemiological studies, the signs and symptoms of TMD are frequently found in children and adolescents and show an increased prevalence in subjects between 15 and 45 years of age.

2. Role of occlusion and condyle position in the occurrence of TMD:

Occlusion and condylar position have long been seen as the main etiological agents of TMD.

TMJ disorders were considered a separate disease, caused by occlusion, or an overly eccentric position of the condyle.

1. Role given to occlusion in the appearance of TMD:
2. Responsibility for occlusion:

• People with certain untreated malocclusions (class II div 2, overbites, etc.)
• Patients with an anterior guide that is too large, or people who completely lack an incisal guide (case of open bites).
• People with severe maxillomandibular dysharmonies are more likely to develop TMD.
• Radiographs taken before treatment of both TMJs should be performed. The position of each condyle in its socket should be assessed, and orthodontic treatment should allow a good position at the end, that is, a concentric position of the condyle in the glenoid fossa.
• Orthodontic treatment, when properly performed, reduces the subsequent risk of developing TMD.
• Compliance with gnathological principles (gnathology = study of the bony bases, more particularly the mandible) during treatment finishing reduces the risk of TMD
• The use of certain traditional orthodontic procedures and/or appliances may increase the risk of TMD.
• Adult patients who present with occlusal disturbances with the presence of TMD symptoms will likely require occlusal correction (may have spontaneous correction of TMD).
• A retrusive position of the mandible, whether constitutional or after a treatment procedure (e.g. class III treatment), is a major factor in the etiology of TMD.
• When the mandible is in this retrusive position, the articular disc can slide in front of the condyle.

Orthodontics and masticatory dysfunction

2. Questioning the main role of occlusion in the appearance of TMD:

The opinions of authors, or case series from the 1970s and 1980s, incriminating occlusion as the main etiological factor of TMD, have been questioned due to the low scientific level they presented. The groups studied, the criteria used, and the methods of analysis employed did not allow definitive conclusions to be drawn. The role of occlusion is now considered secondary in the multifactorial etiology of TMD.

2.  Role given to the mandibular position in the appearance of TMD:

The Centered Relationship is a very controversial topic in orthodontics. Its definition has changed several times over the past century, its role in the development of TMD has long been highlighted. There is no meta-analysis (epidemiological study that resembles all the articles discussing the same subject) on the subject, however, RINCHUSE and KANDASAMY, using in-depth scientific research in a systematic review, try to refute some received dogmas, of non-scientific origin.

1. Responsibility for condylar position:

• The position of the mandibular condyle in the glenoid fossa seems to play a preponderant role in the appearance of TMD for some authors.
• Studies carried out in the 1970s and 1969 by PAMEIJER and GLICKMAN show that even if complete mouth rehabilitations have been carried out in the ORC position, patients continue to have an occlusion functioning in OIM.
• Thus, there is not a single position of the condyle in the fossa, but a certain number of acceptable positions (convenience occlusion), as concluded by RINCHUSE, JOHNSTON, MOHL and MAC NAMARA SELIGMAN and OKESON in their articles.
• MAC NAMARA, SELIGMAN and OKESON in 1995 only found signs of TTM from a slip greater than 4mm, and even added that this slip is a result of TTM rather than a cause. 

2. RC recording: the gnathological approach:

There appears to be little benefit in analyzing patients’ articulator casts to compare differences between OIM and ORC, and it should be remembered that a large proportion of the population has this discrepancy without having TMD.

In the past the RC was considered a retrusive position but now it is considered an anterosuperior position. Recent data suggest that the concept of a terminal hinge axis is no longer valid since there is an instantaneous center of rotation of the condyle.

3. Role of articulators:

• Mounting casts on an articulator has been a subject of debate among practitioners for about thirty years. 
• RINCHUSE in 1995 considers that articulators are very useful during major fixed or removable prosthetic restorations, or during surgical procedures, in order to maintain a certain DV. However, their usefulness in ODF remains equivocal. A review of the “journal of clinical orthodontics” published in 2001 estimates that 21% of the practitioners questioned mount their cases on articulators regularly, 44% occasionally, and finally 35% never mount.
• Orthodontists are just as (or even more) involved in occlusion modifications (static and functional) as other dental professionals, particularly dental technicians, who also use an articulator.

The point of view against the assembly (limitations of the articulator) :

• An articulator cannot exactly simulate human mandibular movements, being based on the now false theory of the terminal hinge axis.
• There is no evidence that orthodontic treatment with model mounting improves the quality of outcomes in terms of TMJ health or TMD improvement.
• There is no scientific evidence that the use of an articulator influences the diagnosis in any way. 
• RC recordings are only reliable under experimental conditions. 
• Errors when recording the RC or editing reduce the interest of the editing. 
• The bite recordings used for articulator placement are static recordings and do not capture actual mandibular movements.

Orthodontics and masticatory dysfunction

3. The role of orthodontic treatments in the onset of TMD:

Gnathologists suggest that orthodontic treatments can lead to TMD in two ways:

• Directly by the orthodontic appliances used (uni or bi maxillary, fixed or functional) or by certain therapies (with or without extractions). Ex. intermaxillary elastics
• Indirectly by poor occlusal finishing leading to interferences and prematurity, or by an eccentric condylar position.

1. The role of extractions in orthodontic treatments:

   The use of dental extractions involves the responsibility of the dental surgeon and the orthodontist. Extracting generally healthy teeth in order to achieve the desired therapeutic objectives could have significant consequences on the temporomandibular joints.

Many authors have responded to this topic. We will first see the authors who think that extractions play a role in the development of TTM, due to the appearance of harmful effects that are found in the various articles:

• A change in occlusion with a retraction of the maxillary incisors, themselves responsible for a distal positioning of the mandible and condyles in the glenoid fossa in a posterior position
• Joint noises
• Muscle pain
• A decrease in mouth opening
• A deviation of the inter-incisive line

2. The role of different types of orthodontic appliances in temporomandibular disorders:

Many studies have attempted to show the link between the various types of orthodontic mechanics (functional therapy, orthopedic, orthodontic) and the appearance of TMD, on the subject the opinions of the authors diverge.

1. The influence of certain processing aids:

The triggers for TMD are related to distal pressure on the condyles, resulting in compression of the disc. The disc will be brought forward, and the condyles will exert pressure against the highly vascularized and innervated part of the retrodiscal tissues, thus causing pain. 

The use of Class II elastics and extraoral force devices will pull the maxilla backwards, the masticatory muscles will then tend to move the mandible back to compensate for the maxillary movement when the teeth close together, and thus exert distal pressure on the condyles.

2. The influence of single or double jaw treatments:

LARSSON and RONNËRMAN conducted a study in 1981 on 23 patients who had been treated 10 years previously. 18 were treated with fixed therapy and 5 received activator treatment.

Symptoms of moderate dysfunction were found in 8 patients, while only 1 patient presented severe signs of dysfunction.

The authors therefore conclude that orthodontic treatments do not create joint problems, however they note a slightly higher prevalence of symptoms in patients treated with fixed orthodontics in both arches, than only in the maxilla.

Orthodontics and masticatory dysfunction

3. The influence of the type of fixed or functional treatment:

BROADBENT, BOWBEER, WITZIG, SPAHL, MEHTA and STACK emphasize the preventive role of orthodontic treatment in TMD in cases of non-extraction therapies, the use of functional appliances only, or in less common therapies involving the extraction of the second molar and its replacement by the 3rd. These publications published between 1971 and 1988 are not based on any statistical study, they only present the authors’ point of view.

JANSON and HASUND conducted a retrospective study (using the files of patients already undergoing surgery) in 1981 on 90 subjects with a Class II, 1 malocclusion, the results showed a statistically lower dysfunctional index of clinical examination and anamnesis for the group of subjects who did not benefit from extractions compared to the group whose malocclusion was not treated or treated with extractions of four premolars. Orthodontic treatments do not represent a risk factor for ATM according to the authors, but treatments with activators lead to a significant improvement in function, and thus this type of therapy should be used as often as necessary. ( It is better to treat class II div 1 by advancement of the mandible with an activator then orthodontic treatment, than to treat by extraction and alveolar compensation).

3. Do orthodontic treatments create occlusal conditions leading to TMJ disorders?

The appearance of occlusal interferences occurring during orthodontic treatments can, during dental movements according to some authors, be the cause of temporomandibular joint dysfunction.

Unfavorable role of orthodontic therapies in the appearance of occlusal interferences .

Non-working occlusal contacts were found equally in treated and untreated patients. These types of occlusal contacts showed no relationship with the presence of signs and symptoms of temporomandibular dysfunction.

4. The role of orthodontic therapies in the position of the articular condyle:

According to some authors, the effect of certain orthodontic treatments would be to influence the position of the condyle distally in the fossa, thus causing joint disorders. 

There is no statistically significant correlation between changes in condyle position in the fossa and the use of FEO, certain types of elastics, or treatment with or without extractions.

The fact of the change of the joint space during treatment can be explained by the growth and remodeling of the condyle, the fossa, and the remodeling of one in relation to the other, in fact the joint adapts with the correction of the malocclusion.

Orthodontic treatments should not be considered responsible for the creation of TMD, regardless of the orthodontic technique used.

4. Canine protection:

• One of the most widely defended principles of the gnathological school is the mutual protection of occlusion by the canines, or OPC. Only the canines, or sometimes the first premolars, should come into contact during the diduction movements, thus protecting the rest of the dentition from occlusal shear stresses.
• This occlusion must be achieved in patients treated in orthodontics or during prosthetic/conservative restorations (125). Gnathologists accuse practitioners who do not achieve this functional occlusion of causing TMD and relapses.
• OPC (Canine Protection Occlusion) is considered more of an established fact rather than an optimal functional occlusion model, and not based on the level of evidence.
• Balanced occlusion without interference, or group function are valid occlusions.
• Each patient is different, their stomatognathic system is unique, other models may be equally acceptable, the most important point remains the absence of occlusal interference. 
• The patient’s chewing pattern, craniofacial morphology, dental mesh, oral health status, and parafunctions provide important information to guide the practitioner toward the best functional occlusion for the patient. 
• Improvement should be made in the recording of functional occlusion, taking into account the subject’s parafunctions.
• A recording that would be dynamic, rather than static.

Orthodontics and masticatory dysfunction

Dental crowns are used to restore the shape and function of a damaged tooth.
Bruxism, or teeth grinding, can cause premature wear and often requires wearing a retainer at night.
Dental abscesses are painful infections that require prompt treatment to avoid complications. Gum grafting is a surgical procedure that can treat gum recession. Dentists use composite materials for fillings because they match the natural color of the teeth.
A diet high in sugar increases the risk of developing tooth decay.
Pediatric dental care is essential to establish good hygiene habits from an early age.
 

Orthodontics and masticatory dysfunction