Introduction

Temporomandibular joint biomechanics is a complex system, since these articulations are connected to the lower jaw, and each works separately.^1,2 Functional changes can appear at one or both sides of the articulation, even more, there could be alterations without the patient noticing them.

TMJ disorders have been identified through the years with different nomenclature,³ they were first described by otolaryngologist James Costen in 1934, for this reason it was called «Costen’s syndrome». After 67 years from its first description, this group of symptoms have received different names such as: temporomandibular dysfunction pain syndrome, described by Schwartz (1955), temporomandibular joint dysfunction syndrome, (Shore 1959), temporomandibular joint functional alterations (Ramjford and As), myofacial dysfunction syndrome (Laskin 1969), chronic lesion of the meniscus, myofacial dysfunction pain, temporomandibular arthralgia, and presently, craniomandibular disorders, among others; nevertheless standardization of definition, diagnosis and treatment have not yet been achieved. Due to the amount of terms used in literature to describe it, it is difficult to determine it and know it as a single entity, therefore, the American Dental Association has adopted the term temporomandibular joint disorders (TMJD), considering this includes TMJ as well as all disorders associated to masticatory system functions.⁴

Masticatory function can result affected by some type of alteration, in cases when it is important and overcomes the physiological tolerance of the subject, creating a response within the system. This response can manifest itself with the presence of different clinical symptoms related to TMJD : articular noise caused by alterations of condyle movement on the disk, pain caused by TMJ alterations, pain caused by muscle spasm of the masticatory muscles, decrease in amount of mouth opening, limitation of mandibular movements and mandibular deviation.

Contemporary studies recommend use of four factors to establish diagnosis and follow TMJD’s evolution.^5-7

Study of TMJD shows complex and multifactorial etiology which could be grouped with respect to its origins.

Previously, occlusal disharmony was considered the sole responsible factor for TMJD, where TMJ exerts a totally passive activity,⁸ Campos,⁹ reinforces this theory, calling it «occlusal disease». Vartan Behsmila¹⁰ is also a part of this trend of thought, he explained that occlusal disharmony is always the cause for clicks in the TMJ. This author reports that occlusal rehabilitation as single intervention improves articular function. Dawson,¹¹ in the same trend, suggested that harmonization of occlusion almost invariably resulted in correction of the alteration, the noise disappears as soon as occlusion is corrected.

Presently, there is no direct cause-effect relationship between occlusal disharmony and articular alteration, nowadays it is accepted that TMJD’s origin is multi-factorial.^12-15 Okeson proposed that there are five factors associated to these conditions: occlusal conditions, trauma, emotional stress, deep pain and parafunctional activity. Echeverry Guzman reported that, in order for an alteration to exist at articular level, there must be a conjunction of psychological and physiological factors, since, if only one factor were to act, the body could tolerate it.

Four occlusal characteristics are frequently found In TMJD patients: presence of a skeletal anterior open bite, sliding from retruded contact position to maximum upper intercuspation position at 2 mm, extrusion greater to 2 mm and absence of four or more posterior teeth lost and never substituted.

Material and methods

The sample was composed of 50 patients suffering partial bi-maxillary tooth loss. Patients attended facilities of Prostheis 1 Clinic Chair, belonging to the School of Dentistry, National Northeastern University during school year 2015. During interview, patients were instructed on the reason for the study, their authorization was then requested by means of an informed consent form.

In a brief clinical history, patient’ s personal data and history of bruxism, trauma, and TMJ or close areas’ surgery were recorded since they could have triggered TMJD.

A visual examination was then conducted where present status of remaining teeth and prosthetic area was established determining type of existing edentulousness according to Kennedy´s classification.

Maximum oral opening was measured with a milimeter ruler, recording distance between incisal edges of upper and lower central incisors. Openings ranging 53 to 58 mm were considered normal. In lower values ranges, end-feed test was conducted on top; this test is conducted when placing the thumb over upper incisors and index finger over lower incisors applying soft but constant pressure in order to try to passively increase inter-incisal distance. A soft end-feel is the case when the aforementioned increase could be achieved, it is generally assumed that in this case the etiology of restriction is muscular, a hard end-feel is when this target was not reached, in which case the origins belong to intra-capsular causes.

In order to observe oral opening symmetry, patients were observed from the front, they were requested to open and close without further commentaries, this is due to the fact that when patients were requested to open slowly or to a certain degree, they tried to control movements, interfering thus with their natural movements and altering results. Symmetry is preserved when the lower jaw descends following the sagittal line of the face during the whole movement. Mandibular deflection was considered when the jaw described a trajectory away from the midline as it progressed towards the opening, conversely closing, a deviation is considered when during oral opening the lower jaw moves away from the sagittal line up to a certain point, only to return to it with its progress; the inverse procedure would take place during closure.

In order to relate mandibular movements with pain, the patient was requested to report symptomatology in his own words, then, targeted questions were used to complete information on pain location, intensity, duration and origin.

After this, masticatory muscles’ palpation was undertaken (masseter, temporal, lateral pterygoid and medial pterygoid) sternocleidomastoid, posterior cervical muscles, as well as retro-distal region. Masseter muscles were bilaterally palpated at their upper and lower insertions by placing fingers on the cygomatic arches and moving them to the lower insertions located in the lower ridge of the mandible. Temporal muscles were palpated bimanually, respectively, above cygomatic arch, temporomandibular joint and external aspect of the skull. Tendon insertions at the coronoid apophyses were palpated by placing the finger of one hand within the mouth, at the anterior ridge of the ascending ramus, and the finger of the other hand in the same area outside of the mouth.

Palpation of lateral pterygoid muscles was conducted through functional manipulation, requesting the patient to perform a protrusion movement against resistance created by the operator, who exerted an anterior-posterior force at the level of the chin, for the medial pterygoid muscle, large cotton pads were placed in both arches, and the patient was instructed to bite onto them in order to assess presence of pain when performing these movements. Sternocleidomastoid muscles and posterior cervical muscles were simply palpated in order to ascertain presence of trigger points, describing these trigger points as foci of a deep painful stimulus which might cause central excitatory effects , that is to say, they will transmit pain to different regions, and in this case to the TMJ.

Finally, a bi-manual tactile exploration was conducted, (with index fingers simultaneously placed on the condyles) and TMJ auscultation by placing in the condylar zone the stethoscope´s great diaphragms (Rappaport, model BK3003, MELIPAL) (adult) on one side and then the other; the patient was then requested to perform lateral, protrusion, retrusion as well as opening and closing movements. Presence of noise was characterized according to sound, simple click was described as the sound perceived during jaw opening or closing, similar to the sound caused when replacing the lid of a highlighting pen. Nevertheless, when the same sound was found during opening and closing movements, it was called reciprocal click. Onset of a more intense and brusque freely heard noise was called pop, even to the point of bewildering auscultation operator. On the other hand, crepitation can be described as the crunchy noise created when rubbing two bricks. At a later point, coincidence of nose onset with pain was ascertained.

Frequency of articular noise onset in partially edentulous patients was determined with this examination, as well as characterization of different articular noises, most prevalent type of articular noise, presence or absence of painful symptomatology during noise onset, and relationship of articular noise presence with Kennedy´s classification.

Results

Figure 1 Characterization of noise types. 

Figure 2 Presence of pain in patients exhibiting articular noise. 

Thus, high incidence of simple clicks related to Kennedy´s class II were observed. In addition, in class III almost same amount of articular noises were recorded than in class II, but with a more balanced distribution.

Table II was drafted using the same method to relate TMJ without articular noises with Kennedy’ s classes.

Most notable alterations observed were:

Discussion

Okeson, after a long bibliographic recompilation of different epidemiologic studies, concluded that 50% of the world population exhibited at least one symptom of temporomandibular disorders, and that 20 to 30%^16-19 exhibited noise or vibrations in the joint and approximately 41% exhibited painful symptoms. Studies²⁰ conducted with 739 university students aged 18-25 years, revealed that 76% exhibited one or many signs associated to TMJD, nevertheless, only 26% of all students reported presence of one symptom related to these disorders. In other words, 50% of the group exhibited signs which had not been detected by the patient; it was also observed that only 10% exhibited symptoms that warranted a request for treatment.

Within local causes that can be responsible for TMJD, Ash, names occlusal interferences of support and ill-designed connectors of a removable dental prosthesis, which prevent centric occlusion and/or eccentric movements (laterality and protrusion). He achieved a bibliographic recompilation of influence of shortened dental arches, and he concluded that loss of all molars was compatible with aesthetics, but not with occlusal instability. There are studies where no increase of TMJD was found as long as all premolars were present:²¹ Nevertheless, other reports^22-25 suggest that loss of posterior teeth may play an important role in the demise of the temporomandibular joint.

Sadowsky²⁶ determined that extraction of premolars for orthodontic reasons increases onset of articular noises, but these do not necessarily cause problems that would warrant alterations in TMJ’s normal functioning.

An interesting datum is provided by a study where it was determined that 21.4% of subjects with ages ranking 15-54 years used prostheses; in the group 55-64 years old, they wore removable partial dentures. Among partially edentulous subjects who did not wear prostheses, the probability that missing teeth were on the lower jaw was six times higher than for the upper jaw. Conjunction of this study and those which highlighted relationship between absence of teeth and temporomandibular disorders fosters the increase of preventive and conservative measures of oral/dental health and hygiene. Therefore, loss of more than five teeth, especially in the posterior area, is a characteristic present in patients with some sort of TMJD. This last characteristic was present in most recorded patients, since Kennedy’s classes I, II and III represented 98% of all cases found in the studied population.

Teran and others conducted research on prevalence of functional disorders of the masticatory system in edentulous patients. Obtained results showed values somewhat higher to those found in the present study. According to this study, 67% of studied population presented signs of temporomandibular disorders, 56% exhibited articular sounds when opening and closing, mainly click sounds (21-26%)

On the other hand, Hittunen et al in the University of Helsinki studied occlusal unbalance and its relation to TTM in elderly patients suffering loss of tooth support. They classified cases according to area of the mouth and severity of tooth loss, and found no relationship between seriousness of TMJD and loss of dental support, they further observed lack of improvement with use of prostheses. Findings by Ortega showed significant tendency among greater number of lost teeth and TMJD frequency in healthy control patients. Loss of posterior dental support.

Loss of posterior dental support might favor greater TMJD incidence due to greater condyle mobility and posterior contraction of masticatory musculature. Nevertheless, although this association was significant among healthy control patients, no clear tendency was found to relate an increase of TMJD with greater number of lost teeth.

The complex biomechanics of the lower jaw forces both temporomandibular articulations to simultaneously and coordinately develop different activities with what Alonso calls «dental articulation». Many authors mention that this is the cause for TMJ alterations, nevertheless, not all patients suffer them.

Presently, it is believed that origins of temporomandibular disorders are of a multi-factorial nature. Okeson proposed that there are five factors associated to this type of condition: trauma, emotional stress, deep pain, parafunctional activities and occlusal circumstances (absence of teeth, premature contacts, poor tooth alignment, etcetera).

Conclusion