OcclusalSplintTherapyofTemporomandibularDisorders SunmeeBae, D.D.S.,M.S.D. Jeong-YunLee D.D.S.,Ph.D. 29

INTRODUCTION

1)

Temporomandibular joint disorder (TMD) is a term covering acute or chronic inflammation of the temporomandibular joint, which connects the mandible to the skull. It refers to a collective term embracing a number of clinical problems that involve the masticatory musculature, the TMJ and associated structures, or both.

Orthopedic stability in the masticatory system exists

Corresponding author : Dr. Jeong-Yun Lee Associate Professor

Dept. of Oral Medicine and Oral Diagnosis School of Dentistry& Dental Research Institute Seoul National University Daehakro 101, Jongnogu Seoul 110-744 Korea (ROK)

Tel: +82-2-2072-0212 Fax: +82-2-744-9135 E-mail: [email protected]

when the stable intercuspal position of the teeth is in harmony with the musculoskeletally stable position of the condyles. When this condition does not exist, micro trauma to the joint structures can result. The temporomandibular joint is susceptible to many of the conditions that affect other joints in the body, including ankylosis, arthritis, trauma, dislocations, developmental anomalies, and neoplasia. When these conditions on TMJ exceed structural tolerance, the weakest structure is destroyed. It brings TMJ dysfunction and pain.

Pain from the TMJs can emanate from the associated soft tissue structures of the joint or the osseous tissues themselves. Masticatory pain that emanates from the TMJs is called masticatory arthralgia. Arthralgic pains can arise only from pain-sensitive structures of the joint ad its ligaments. Masticatory pain emanates from masticatory muscles from pain-sensitive structures of the TMJs, or from both. It is therefore of considerable importance that the clinician should not only distinguish myalgia from arthralgia, but the type of myalgia or

Occlusal Splint Therapy of Temporomandibular Disorders

Sunmee Bae, D.D.S.,M.S.D.

^, Jeong-Yun Lee D.D.S.,Ph.D.

1)

Department of Oral Medicine, Department of Dentistry/Predentistry, Gangeung-Wonju National University, Gangwon, Korea (South)

2)

Department of Oral Medicine and Oral Diagnosis, Seoul National University School of Dentistry, Seoul, Korea (South)

Temporomandibular joint disorder (TMD) is a term covering various adverse conditions of the temporomandibular joint (TMJ).

Since tissue adaptation seems to play a major role in the natural course of TMD, treatment should be oriented toward promoting a joint condition that is most likely to repair or adapt. The occlusal stabilization splint fabricated and adjusted individually is one of the most commonly advocated devices for treatment of signs and symptoms of TMDs. By the review of previous studies, the efficacy of occlusal splint therapy in TMD patients is evaluated. Occlusal splint therapy was compared to: acupuncture, bite plates, biofeedback/stress management, visual feedback, relaxation, jaw exercises, non-occluding appliance and minimal/no treatment.

However, their mechanism of action or the precise conditions underlying the final therapeutic effect are mostly unknown. There is insufficient evidence either for or against the use of occlusal splint therapy for the treatment of TMDs. Establishing mechanism of occlusal splints helps to support using occlusal splint as therapeutic tools. The aim of this review is to put together and evaluate the mechanism of occlusal stabilization splint therapy in TMD patient.

Key words: Occlusal splint; Temporomandibular disorders, Efficacy, Mechanism

arthralgia must be correctly identified.

Signs and symptoms of temporomandibular joint disorder vary in their presentation and can be very complex. On average the symptoms will involve more than one of the numerous TMJ components: muscles, nerves, tendons, ligaments, bones, connective tissue, and the teeth. Ear pain associated with the swelling of proximal tissue is a symptom of temporomandibular joint disorder. In addition, many TMD patients produce joint sounds and have a restricted range of mandibular movements. TMD is stated to have a multifactorial etiology and may, in general, be caused by interplay of neuromuscular, temporomandibular joint (TMJ), occlusal, and psychological factors. Hence, TMD may find clinical expression in various intensities and combinations of signs and symptoms.

Since tissue adaptation seems to play a major role in the natural course of TMD, treatment should be oriented toward promoting a joint condition that is most likely to repair or adapt. There is no sufficient evidence that irreversible therapy is superior to reversible, conservative therapy. So conservative therapy is preferred and comes first. Four types of therapies should be initially considered for TMD patients. These therapies are patient education, physical therapy, pharmacologic therapy, and occlusal splint therapy. The individually fabricated and adjusted occlusal stabilization splint is one of the most commonly advocated devices for treatment of signs and symptoms of TMD. The vertical bite-rise will cause changes in the neuromuscular, arthrogenous, and occlusal relationships. However, their mechanism of action or the precise conditions underlying the final therapeutic effect are largely unknown.

The effectiveness of stabilization splint therapy in reducing symptoms in patients with TMD is controversial. Some studies reported different therapeutic results compared to control group while others didn't.

There was no evidence of a statistically significant difference in the effectiveness of splint therapy in reducing symptoms in patients with pain dysfunction syndrome compared with other active treatments. Some said that occulsal splint therapy is superior to other therapeutic modalities, while others didn't. There is weak evidence to suggest that the use of splint for the

treatment of TMD may be beneficial for reducing pain severity, at rest and on palpation, when compared to no treatment. There is insufficient evidence either for or against the use of splint therapy for the treatment of temporomandibular pain dysfunction syndrome. The aim of this review is to put together and evaluate the mechanism of occlusal stabilization splint therapy in reducing symptoms in patients with TMD. Searching of relevant key journals, and screening of reference lists of included studies were undertaken.

MAIN DISCOURSE

Pain dysfunction syndrome (PDS) is the most common temporomandibular disorder (TMD). Al-ani established the effectiveness of stabilization splint therapy in reducing symptoms in patients with pain dysfunction syndrome. 12 RCTs was analyzed. Occlusal splint therapy was compared to: acupuncture, bite plates, biofeedback/stress management, visual feedback, relaxation, jaw exercises, non-occluding appliance and minimal/no treatment. There was no evidence of a statistically significant difference in the effectiveness of occlusal splint therapy in reducing symptoms in patients with pain dysfunction syndrome compared with other active treatments. There is weak evidence to suggest that the use of occlusal splint for the treatment of PDS may be beneficial for reducing pain severity, at rest and on palpation, when compared to no treatment.

The published literature concerning splint therapy for PDS is considerable. However, a review of the literature shows no standardization of outcomes of the treatment.

There was little evidence of a difference in the effecti - veness of stabilization splint therapy in reducing symptoms in patients with pain dysfunction syndrome compared with other conventional treatments. However, the use of splint for the treatment of PDS may be beneficial for reducing pain severity, at rest and on palpation, when compared to no treatment.

Although many authors agreed with the effectiveness

of occlusal splint, the mechanism of action or the precise

conditions underlying the final therapeutic effect is

largely unknown. So, this review covers literatures

concerning action mechanism of occlusal splints and

evaluates them. It should be specially considered that each study shows different level of evidence.

1. Relaxing the muscles: muscle EMG activity, symmetry and postural control It has been well documented that tooth interferences to the CR arc of closure hyperactivate the lateral pterygoid muscle; posterior tooth interferences during excursive mandibular movements cause hyperactivity of the closing muscles; and the elimination of posterior excursive contacts by anterior guidance significantly reduces elevator muscle hyperactivity.

A splint with equal- intensity contacts on all of the teeth, with immediate disclusion of all posterior teeth by the anterior teeth and condylar guidance in all movements, will relax the elevator and positioning muscles. The neuromuscular harmony provides optimal function and predictability to the system. The splint may be thought of as an exquisitely balanced arch of teeth that must function in a similar manner. Dylina reveals that very small (50m) occlusal interferences can cause changes in coordinated muscle activity.

The more balanced and frictionless splint, the better the opportunity for reducing muscle hyperactivity. A muscle that is fatigued through ongoing muscle hyperactivity can present with pain. If the hyperactivity is stopped, the pain caused by this activity usually disappears. Occlusal splints are a means of reversibly altering the occlusion to reduce masticatory muscle activity. Bodere reported the advantages of splint therapy in the reduction of nocturnal EMG masseter activity in patients with temporomandibular disorder (TMD).

There are literatures concerning EMG activity of facial and neck muscles upon different situations:

maximal clencing, postural position, during sleep. Even though most of those studies focused on masseter muscle activity, it also investigated temporal, neck and trunk muscle. The effect of splint on muscle is 1) muscle activity change 2) changing of postural activity of mandible and body (trunk and cervical muscle included) 3) establishing balance by reduction muscle asymmetry.

Many papers reported occlusal splint reduces muscle activity, but some reported opposite results. Most of papers based on non-controlled study, so it should be

considered. Well controlled studies are needed to establish reliable mechanism.

1) EMG activity change

Many papers reported splints reduce masseter EMG activity. In this review, those are covered from high evidence level, randomized controlled trial, controlled study to non-controlled study, case report study. The up-to date papers reviewed first.

The aim of this study was to compare the effectiveness of different occlusal splints associated with counseling and self-care in the management of signs and symptoms of myofascial pain. They assume different occlusal splints show different effectiveness on masseter muscle, in turns it helps to reveal occlusal splint mechanism. In a double-blind controlled clinical trial, 42 myofascial pain patients with chief complaint of pain in the masseter muscle area were randomly assigned to 1 of the 3 experimental groups: hard (HS), soft (SS) or non-occluding (NS) occlusal splints. The Modified Symptom Severity Index (Mod-SSI) and tenderness to palpation were used as outcome measures during a 90-day follow-up. All patients improved over time and all splints offered the benefit. The results showed that all the three different appliances (HS, SS, and NS) associated with counseling were able to equally reduce the Mod-SSI (symptoms-Tukey test) and digital palpation (signed Kruskal-Wallis) test between baseline and 90 days.

This paper proved occlusal splint effectiveness on masseter muscle. It is double-blind controlled clinical trial. There is no difference among different kinds of splints (HS,SS,NS). It is assumed occlusal splint material and occlusal contact pattern do a least function on splint mechanism.

The nociceptive trigeminal inhibitory (NTI) splint has been claimed to decrease the electromyographic (EMG) activity of jaw-closing muscles and relieve symptoms of various types of temporomandibular disorders (TMD) and bruxism. The present study was designed to address the question about EMG-changes during sleep. The pattern of reduction is different between splints. The patients received two 2-week splint treatments in a randomized cross-over fashion was investigated by Baad-Hansen.

There are two different groups treated with an NTI splint

and a standard flat occlusal splint (OS). This short-term study indicated a strong inhibitory effect on EMG-activity in jaw closing muscles during sleep of the NTI, but not the OS. However, the EMG-activity was not directly related to clinical outcome.

Shi and Wang reported the myoelectrical activity of the mandibular elevators in the postural position and during maximum clenching was smaller in patients with the occlusal splint than in those without.

Electromyograms (EMGs) of the temporal and masseter muscles in sixty patients with temporomandibular joint disturbance syndrome (TMJDS) and thirty controls were recorded and integrated on-line in the postural position and during maximum clenching, before and after occlusal splint therapy. The patients received two 2-week splint treatments in a randomized cross-over fashion;

Contrasting with the controls, the myoelectrical activity of the patients was higher in the postural position and lower during maximum clenching, whilst the former in percentage terms increased when compared to the latter.

After treatment, the EMG indexes in some patients returned partially, and in others completely, to a normal level. Tenderness in the mandibular elevators, deviated opening and organic change in the TMJ increased the postural myoelectrical activity, in percentage terms, against that of maximum clenching. The results show that the mandibular elevators in the patients with TMJDS were hyperactive and tense, and that the occlusal splint was useful for treating such dysfunction.

It is randomized controlled trial(RCT); Insertion of occlusal splint results in reducing EMG of mandibular elevators in the postural position and during maximum clenching.

It shows high level evidence for the action on muscle EMG activity of occlusal splint.

The next is controlled study: 60 person-experimental group and 30 person-control group. Two groups are compared before and after occlusal splint treatment. Shi and Wang measured Electromyographic activity of the masticatory muscles (masseter and anterior temporalis) before and 90, 120, and 150 days after treatment with interocclusal splints. In order to examine the effect of an occlusal splint on the integrated electromyography (EMG) of the masticatory muscles, EMG of bilateral masseter muscles of 23 patients with temporomandibular

joint disturbance syndrome (TMJDS), with and without an occlusal splint, was measured and integrated on line during maximum clenching. There was no statistically significant difference (p > 0.05) among the 3 periods.

Bilateral equilibrium of electromyographic activity was observed for the masseter and anterior temporalis muscles during the treatment. Occlusal splint can decrease masseter muscle activity and thus exert a therapeutic effect.

Bodere and Woda reported that EMG activity in postural position was higher in pain groups than in pain-free groups. The occlusal splint is commonly used in clinical practice. It has been recommended as a simple means to routinely record or provide centric relation closure and, more recently, to reduce migraines and tension-type headaches. However, the reason for the splint effect has yet to be explained. This study tested the hypothesis that it works through a decrease in masticatory muscle activity. The effect of a splint placed on the maxillary anterior teeth was investigated by recording the electromyographic (EMG) activity of the superficial masseter and anterior temporal muscles at postural position and when swallowing on the splint.

EMG recordings were obtained from 2 groups of pain patients (myofascial and neuropathic) and from 2 groups of pain-free patients (disc derangement and controls) unaware of the role of dental occlusion treatments. The occlusal splint strongly but temporarily decreased the postural EMG activity for masseter muscles in all groups except for the neuropathic group and for temporal muscles in the myofascial group. The EMG activity when swallowing with the occlusal splint was reduced in control, disc derangement, and myofascial groups;

however, EMG “hyperactivity” in the neuropathic pain

group seemed to be locked. The decrease of postural,

especially in the myofascial group, was and cannot be

considered as evidence to support the hypothesis of a

long-term muscle relaxation splint effect. However, the

results may uphold certain short-term clinical

approaches.

They investigated EMG in pain and

pain-free groups. Pain groups are divided myofascial and

neuropathic pain. Only myofascial groups reported the

decreased postural EMG activity. 23 patients are

researched and it is controlled study.

To clarify the effect of occlusal splint depending on sign and symptoms of patients and pre-treatment duration, short-term and long-term splint therapy were performed. Holmgren set up a study to compare the effect of occlusal splint before and after treatment.

Before treatment, that the occlusal splint changed significantly (in 71% of patients) the level of EMG activity during maximal clenching. However, these changes were not consistent and differed between patients and even, in some patients, between muscles.

After long-term occlusal splint therapy and improvement of the signs and symptoms of craniomandibular disorders, the number of patients who had an identical level of EMG activity during maximal clenching in the intercuspal position and on the occlusal splint tended to increase. Moreover, in these patients the level of symmetry of action in pairs of muscles during maximal clenching was strong, and the splint did not change this level of symmetry.

It suggested that occlusal splint has its effect on muscle activity and symmetry only for short-term after treatment and be short-lasting. We can assume that the other actions, for example, condyle relationship and occlusal factor, are dominated for latter period of therapy. This study contained 31 patients and compared before and after occlusion splint therapy. EMG activity and the effect on muscle is compared with control group on occlusal splint therapy period. It established the effect of splint on muscle and its background mechanism.

The elevator muscles are more efficient at a functioning length greater than the vertical dimension of occlusion.

The postural position of minimal muscle activity is at a larger vertical than clinical rest position interocclusal splints that increase the occlusal vertical dimension beyond the freeway space cause an immediate adaptation to a new freeway space at an increase vertical dimension.

Boero suggested the EMG activity of the postural muscles (anterior temporalis) is reduced with an increased vertical dimension of occlusion. Therefore, the increase in vertical with a splint allows a muscle to function more efficiently durning contact and be less active during postural functions, furthermore, if TMD symptom relies is related to muscle activity reduction, then a thicker splint should have greater therapeutic

effect.

This is review paper.

Non-controlled studies reporting masster activity reduction effect of occlusal splint are reviewed next.

Solberg and Clark set up a study that the masseteric EMG was recorded for 12-plus nights before, 12-16 consecutive nights during, and 6-10 nights after splint wear. Eight confirmed bruxist subjects were investigated using portable electromyographic equipment. Nocturnal masseteric muscle activity, as measured by electromyo - graphy, was reduced immediately following the insertion of a full arch maxillary stabilization splint. The mean nightly reduction ranged from 14-60 percent of pretreatment levels. It remained low until the splints were removed, at which time all but one subject's EMG values returned to pretreatment levels. Activity returned to pretreatment levels for most subjects immediately after the splints were discontinued. Although the short-term splint therapy did not show a permanent reduction in EMG levels, a dramatic reduction has been demonstrated during treatment.

It suggested that splints cannot prevent or heal bruxism but reduce severity and frequency by reducing masster muscle activity. After occlusal spint therapy, it is returned to original muscle activity level. It means the occlusal splint effect lasts only for a short-term. This is non- controlled study.

Clark and Beemsterboer monitored the level of nocturnal activity of the masseter muscle and symptoms before, during, and after occlusal splint therapy.

Twenty-five patients with symptoms of myofascial pain and abnormal jaw function were treated with use of a full arch maxillary occlusal splint. The level of nocturnal activity of the masseter muscle was monitored as were symptoms before, during, and after occlusal splint therapy. A decreased nocturnal EMG level during treatment was noted for 52% of the patients. A return to pretreatment EMG levels after removal of the splint was noticed in 92% of the patients; in 28% no change was shown and in 20%, an increase was shown in nocturnal EMG levels. The splint was most likely to reduce nocturnal EMG levels in patients with least severe symptoms.

Half of pateinets(52%) reported reduction of masseter muscle activity after occlusal splint therapy.

However 92% of patients went back to original activity

level. It is assumed the effect of occlusal splint is

temporary. 25 patients are researched and it is non-controlled prospective study.

Sheikholeslam reported that 3-6 months long-term occlusal splint therapy made effects on muscle activity and symmetry. The postural activity of the temporal and masseter muscles in thirty-one patients with signs and symptoms of functional disorders were studied: before, during and after 3-6 months of occlusal splint therapy.

The fluctuating signs and symptoms, as well as the postural activity of the temporal and masseter muscles were significantly reduced after treatment. Further, the coefficients of correlation within pairs of postural activity of the right and left muscles increased significantly.

occlusal splint can eliminate or diminish signs and symptoms of functional disorders and re-establish symmetric and reduced postural activity in the temporal and masseter muscles, which can facilitate procedures, such as functional analysis and occlusal adjustment.

31 patients are researched and it is non-controlled study.

Carr and Christensen reported the activities induced by the splint tended to stabilize within 1 week, with decreased postural activities in the masseter and anterior temporalis muscles, and increased postural activities in the suprahyoid muscles. As induced by an occlusal splint over a period of 1 week, this study monitored surface electromyographic changes in the postural contractile activities of jaw elevator and depressor muscles in six healthy adults. The immediate effect of the occlusal splint was to increase the postural contractile activities of the suprahyoid muscles. All postural muscle activities showed wide-ranging biological variation, but the activities induced by the splint tended to stabilize within 1 week, with decreased postural activities in the masseter and anterior temporalis muscles, and increased postural activities in the suprahyoid muscles.

It analyzed postural activities in the suprahyoid muscles, masseter and anterior temporalis muscle. 6 patients are researched and it is non-controlled study.

The effect of canine guidance of a full-arch maxillary flat occlusal splint on the level of activation of the anterior and posterior, temporal, masseter and suprahyoid muscles during maximal clenching, were studied in 14 subjects without craniomandibular disorders The design of splints has relevance to EMG activity. The effect of

canine guidance of a full-arch maxillary flat occlusal splint on the level of activation of the anterior and posterior, temporal, masseter and suprahyoid muscles during maximal clenching, were studied in 14 subjects without craniomandibular disorders. The results revealed that, the level of electromyographic activity of anterior and posterior temporal and suprahyoid muscles during maximal clenching on the occlusal splint in habitual closure was unchanged, as compared to biting in the intercuspal position (ICP), while the activity in the masseter muscle, on average, was increased slightly (13 percent). In contrast, the level of activation of the jaw elevator muscles decreased significantly during maximal clenching on the cuspid ramp of the splint, as compared to the biting in ICP or clenching on the splint. However, the degree of reduction of activity was not symmetrical, and was most pronounced in the masseter muscle of the biting side and in the anterior and posterior temporal muscles of the non-biting side. No significant difference was observed in the activity of the suprahyoid muscles.

The activity of jaw elevator muscle reduced when clenching at cuspid ramp. Its reduction pattern was not symmetric and showed pronounced reduction on masseter muscles of working side. It is non-controlled study and 14 patients participated.

These journals reviewed so far focused on EMG activity of masticatory muscle based on hypothesis that action mechanism of occlusal splint is related to muscle activity.

2) Evaluate muscle activity: VAS, bite force, EEG There are other modalities for analyzing the activity of muscles except EMG: Visual Analogue Scale (VAS) presenting awareness of tiredness, bite force, EEG. The next paper used these modalities to analyzed muscle activity.

This is case report including 6 patients. Treatment with

an occlusal splint is used for temporomandibular

disorders, bruxism, and occlusal disturbance to relieve

orofacial symptoms such as myofascial pain and jaw

movement restriction. However, the effects of various

types of occlusal splints have not been elucidated. Narita

evaluated effects of jaw clenching with soft and hard

occlusal splints on the awareness of tiredness, bite force,

and EEG activity. With these methods, it is possible to evaluate the effects of splints on muscle and motor cortex and eventually elucidate neurophysiological effects. Six healthy adults were used as subjects, with a visual analogue scale utilized to evaluate the awareness of each patient's tiredness both preceding the session and following the clenching trials. In addition, a Dental Prescale was used to measure bite force and an EEG recording was conducted while performing jaw clenching. Total bite forces (mean and standard deviation) were plotted for values obtained preceding and following each clenching trial with natural dentition (N.D.), a hard occlusal splint (Hard), and a soft occlusal splint (Soft). EEG power values (median, 25%, and 57%

values) obtained while clenching with the soft occlusal splint were plotted from the 1st to 6th EEG recordings.

The jaw clenching task comprised 1min of maximal voluntary clenching under 3 kinds of clenching conditions: with natural dentition, and with soft and hard occlusal splints, which were each repeated 5 times.

Narita evaluated VAS scores (median, 25%, and 57%

values) for the awareness of tiredness. VAS scores plotted for clenching trials with natural dentition (N.D.), a hard occlusal splint (Hard), and a soft occlusal splint (Soft). Jaw clenching with natural dentition and a hard occlusal splint did not cause a significant awareness of tiredness following repetitive jaw clenching, and there was not a significant alteration of EEG spectrum values with those conditions. In contrast, jaw clenching with a soft occlusal splint caused a significant increase in awareness of tiredness, as well as significant decreases in bite force and EEG alpha 2 power spectrum values. In conclusion, Jaw clenching with a soft resilient occlusal splint causes an awareness of tiredness, which might be accompanied by declines in bite force and EEG spectrum values. This study revealed that different kinds of occlusal splints (HS,SS) lead to different results. This conclusion is conflicted with the study

mentioned before. Because the study by Alencar is randomized controlled trial while the study by Narita is case report, the conclusion by Alencar seems to be more reliable

With results and conclusion reviewed so far, we can conclude that occlusal splints reduce muscle activity and it is examined by measuring EMG activity of muscle and

other modalities (awareness of tiredness, bite force, EEG). It is reliable that occlusal splint shows therapeutic effect by relaxing muscle. There are many journals concerning muscle activity and some have high evidence level.

3) Postural activity changes Mandible and whole body muscles (including trunk and cervical muscles) Insertion of occlusal splint changes muscle activity, symmetry, VD and occlusion. All of these changes are co-related and have an impact on postural balance.

Occusal splint changes not only masticatory muscle including masseter muscle, but also whole body postural muscles, in turns it influence on postural activity.

Decreased muscular activity is suggested as possible explanations of the improved postural control.

Tecco investigate the surface electromyographic (sEMG) activity of neck, trunk, and masticatory muscles in subjects with temporomandibular joint (TMJ) internal derangement treated with anterior mandibular reposi tioning splints.

sEMG activities of the muscles in 34 adult subjects (22 females and 12 males; mean age 30.4 years) with TMJ internal derangement were compared with a control group of 34 untreated adults (20 females and 14 males; mean age 31.8 years). sEMG activities of seven muscles (anterior and posterior temporalis, masseter, posterior cervical, sternocleidomastoid, and upper and lower trapezius) were studied bilaterally, with the mandible in the rest position and during maximal voluntary clenching (MVC), at the beginning of therapy (T0) and after 10 weeks of treatment (T1). Paired and Student's t-tests were undertaken to determine differences between the T0 and T1 data and in sEMG activity between the study and control groups. At T0, paired masseter, sternocleidomastoid, and cervical muscles, in addition to the left anterior temporal and right lower trapezius, showed significantly greater sEMG activity (P

= 0.0001; P = 0.0001; for left cervical, P = 0.03; for right cervical, P = 0.0001; P = 0.006 and P = 0.007 muscles, respectively) compared with the control group.

This decreased over the remaining study period, such that

after treatment, sEMG activity revealed no statistically

significant difference when compared with the control

group. During MVC at T0, paired masseter and anterior

and posterior temporalis muscles showed significantly lower sEMG activity (P = 0.03; P = 0.005 and P = 0.04, respectively) compared with the control group. In contrast, at T1 sEMG activity significantly increased (P

= 0.02; P = 0.004 and P = 0.04, respectively), but no difference was observed in relation to the control group.

Previously on muscle EMG activity part, we focus on masticatory muscle, but this journal extends it to other muscles. Splint therapy in subjects with internal disk derangement seems to affect sEMG activity of the masticatory, neck, and trunk muscles.

Previous research has shown a relationship between head posture and rest position of the mandible. Should this relationship really be an interrelationship? Does a change in mandibular posture alone also alter head and neck posture? Urbanowicz demonstrated how a change in mandibular posture, specifically an increase in vertical dimension, contributes to craniovertical extension leading to suboccipital compression and upsetting the postural balance between the head and neck.

A model of physiologic equilibrium is presented for the craniomandi - bular articulation. In this study, VD change is suspected as a possible factor. A change in mandibular posture, specifically an increase in vertical dimension, contributes to craniovertical extension leading to suboccipital compression and upsetting the postural balance between the head and neck.

With the mandible at rest, the clinical postural position was measured and electromyographic recordings (in seated and supine position, eyes open and eyes closed, before as well as 15 min after insertion of an occlusal splint) were from the anterior temporal and masseter muscles in thirty-one patients with signs and symptoms of mandibular dysfunction and nocturnal bruxism.

The results indicated that when the patients were seated upright, there was a distinct postural activity in the anterior temporal and in some patients also in the masseter muscles. This postural activity decreased significantly with closure of the eyes and in supine position. Fifteen minutes after insertion of an occlusal splint, the postural activity in the temporal muscles decreased in 52%, increased in 22% and remained unchanged in 26% of the patients. Moreover, the postural activity reached its lowest level in supine position. The

results indicate that the supine position is the body position to be preferred for centric relation recording as well as for occlusal and splint adjustment. The occlusal splint puts the mandible in a more open position, which stretches and reduces postural activity (static load) in the jaw elevator muscles The stretching and relaxation can contribute directly to treatment of musclar disorders. This is non-controlled study including 31 symptomatic patients Carr and Christensen reported the activities induced by the splint are tended to stabilize within 1 week, with decreased postural activities in the masseter and anterior temporalis muscles, and increased postural activities in the suprahyoid muscles. The immediate effect of the occlusal splint was to increase the postural contractile activities of the suprahyoid muscles. This result showed that all postural muscle activities showed wide-ranging biological variation. Postural activities in the suprahyoid muscles are analyzed with masseter and anterior temporalis muscle. This is non-controlled study including 6 patients

After splint therapy, improved muscle symmetry influenced on whole body. The modifications induced by microgravity on the coordinated patterns of movement of the head, trunk, and limbs are reported on extensively.

However, apparently there is little data on the masticatory muscles. In normal gravitational conditions, information from the neck and stomatognathic apparatus play a role in maintaining the body's balance and equilibrium. The current pilot study used normal gravity conditions to investigate the hypothesis of a functional coupling between occlusion and neck muscles and body postural oscillations. The immediate effect of modified occlusal surfaces on the contraction pattern of the sternocleidomastoid muscles during maximum voluntary clenching and on the oscillation of the center of foot pressure was analyzed in 11 male astronauts (aged 31-54 yrs). All subjects were healthy and free from pathologies of the neck and stomatognathic apparatus. Occlusal splints were prepared using impressions of their dental arches. The splints were modeled on the mandibular arch, had only posterior contacts, and were modified to obtain a more symmetric, standardized contraction of the masseter and temporalis muscles during teeth clenching.

Surface EMG activity of the sternocleidomastoid muscles

was recorded during a maximal voluntary clench with and without the splint. Sternocleidomastoid potentials were standardized as percent of the mean potentials recorded during a maximum contralateral rotation of the head, and the symmetry of the EMG waves of left- and right-side muscles was measured. Body sway was assessed with and without the splint, either with eyes open or closed. The variations of the center of foot pressure were analyzed through bivariate analysis, and the area of the 90% standard ellipse was computed.

Within each visual condition (eyes open or closed), the difference between the areas of oscillation measured with and without the splint was computed. Muscular activity was more symmetric with the splint. The area of oscillation of the center of foot pressure was larger without the splint than with the splint, both with eyes open and eyes closed. The modifications, induced by the occlusal splint in the sternocleidomastoid muscles' symmetry, and center of foot pressure differential area with closed eyes, were significantly related (p < 0.05):

the larger the increment in muscular symmetry, the smaller the area of oscillation with the splint as compared to without the splint. A functionally more symmetric maxillo-mandibular position resulted in a more symmetric sternocleidomastoid muscle contraction pattern and less body sway. Modifications in the contraction of the masticatory muscles may therefore affect the whole body.

This is a pilot study in male astronauts. It is assumed occlusal splints influence the whole body.

Balancing the occlusion has a beneficial on postural muscles. Bergamini investigated balancing rate of paired muscle. The influence between dental occlusion and body posture has been discussed in the past ten years by several authors with controversial conclusions. The objective of this study was to access, using surface electromyography (EMG), the rest activity of paired sternocleidomastoids, erectors spinae at L4 level, and soleus muscles in a group of 24 volunteer subjects (12 males, 12 females, aged 23-25 yrs) affected by sub-clinical dental malocclusions in different situations of dental occlusion. The subjects' occlusion was neuromuscularly balanced (registered on an acrylic wafer). Rest activity was assessed using the sEMG. The

measurements were achieved on subjects while standing barefooted, before (Test 1), and 15 minutes after they wore the acrylic wafer (Test 2). The result was a significant reduction of the mean voltage for each muscle. Paired muscles were registered and the balancing rate between right and left muscles showed improvement for all the paired muscles (Wilcoxon test p < 0.05). No significant difference was noted in the relaxation and balancing rates between the muscles tested. The data confirmed a beneficial effect of balancing the occlusion with an acrylic wafer on the following paired postural muscles: sternocleidomostoid, erector spinae, and soleus.

The balance of occlusion contributes to postural balance of muscles. It is non-controlled study.

Alterations in the temporomandibular complex can reflect in adaptations of the individual's entire muscular system, intervening with the head position and scapular waist, developing postural alterations and modifying all corporal biomechanics. The aim of this study was to evaluate the head position (HP) and head postural alterations before and after installation of occlusal splints.

There were statistically differences for HP, between the initial values and after 1 week of use of the occlusal device (p= 0.048) and also between 1 week and 1 month of evaluation (p= 0.001). The individual's postural position can suffer biomechanical alterations due to stomatognathic alterations, causing clinically visible changes in dysfunctional individuals and affecting the performance of the involved structures.

It is non-controlled study including 21 patients. Occlusal splints modify head position and finally change postural position.

The articles that have no control group and low grade evidence level like case report are insufficient to show clear relevance between occlusal splint and postural activity change. Many studies concerning postural activity change by occlusal splint can be unreliable and outdated.

4) Muscle symmetry and balance

There are papers reporting occlusal splints improved

the symmetry of muscle pair. Some are controlled

studies, however most of them are non-controlled study

comparing before and after occlusal splint treatment.

The aim of present study was to evaluate the symmetry of masticatory muscles' activity at various clenching levels in the intercuspal position in patients with functional disorders and in healthy subjects. The purpose was also to determine the effect of full-arch maxillary stabilization splint on the asymmetry of masticatory muscle activity in patients with temporomandibular dysfunction. TMD patients showed higher asymmetry than control group. In this study 6 TMD patients and 12 healthy subjects were investigated.

Surface EMG recordings were obtained from left and right anterior temporal, left and right masseter and from the sub-mandibular group in the region of the anterior belly of the digastric muscle on the left and right side during clenching with the maximum 100% voluntary contraction (MVC) as well as during clenching at 50%

and 25% of the maximum activity in the position of maximal intercuspation of teeth. In order to quantify asymmetrical masticatory muscle activity, the asymmetry index (AI) was calculated for each subject and for each muscle from the average anterior temporal, masseter and digastric potentials recorded during each test (100%

MVC, 50% MVC and 25% MVC). In the group of patients EMG recordings were repeated during and after the splint therapy. The asymmetries of masticatory muscle activity was present in both groups, but in the group of TMD patients the asymmetry indices for anterior temporal muscle at 100% MVC (p = 0.049) and 50% MVC (p = 0.031) were significantly higher. Results have shown that the use of splint suppressed the asymmetry of all muscles, as during the splint therapy the asymmetry indices were lowered. After the therapy, the level of temporal muscle symmetry during submaximal clenching in the intercuspal position increased significantly (p = 0.046).

TMD patients had more muscle asymmetry compared to healthy people.

After occlusal splint therapy, their asymmetry is reduced in every muscle. It is controlled study including 6 TMD patients and 12 healthy control group.

Botelho set up a study to analyze the immediate effect of resilient splints through surface electromyography testing and to compare the findings with the electromyo - graphic profiles of asymptomatic subjects. The partici - pants were 30 subjects, 15 patients with TMD (TMD

Group) and 15 healthy subjects (Control Group), classified according to Research Diagnostic Criteria (RDC/TMD) Axis I. A resilient occlusal splint was made for each patient in the TMD Group from two mm thick silicon to cover all teeth. The EMG examination was performed before and immediately after installing the splint. Three tests were performed as follows: 1) Maximum Voluntary Contraction (MVC) using cotton rolls (standards test); 2) MVC in maximal intercuspation position; and 3 MVC with the splint in position. The EMG signal was recorded for five seconds. EMG indices were calculated to assess muscle symmetry, jaw torque, and impact. There was a statistically significant difference when comparing the results among the study groups. The symmetry index values in the Control Group were higher than the TMD Initial Group and similar to the TMD Group after the installation of the splint. The index values of torque were higher in TMD Initial Group when compared with the Controls. Impact values were lower than normal values in the TMD Initial Group and restored upon installation of the splint. The resilient occlusal splints may be used as complementary or adjunctive treatment of temporomandibular disorders.

This article covered muscle symmetry, jaw torque, and impact. It is controlled study

From here, non-controlled studies covering muscle symmetry improvement are reviewed. The up-to date paper comes first. Sheikholeslam reported contrasting result. It showed that 3-6 months long-term occlusal splint therapy also made an effect on muscle activity and symmetry. The postural activity of the temporal and masseter muscles in thirty-one patients with signs and symptoms of functional disorders were studied: before, during and after 3-6 months of occlusal splint therapy.

The fluctuating signs and symptoms, as well as the postural activity of the temporal and masseter muscles were significantly reduced after treatment. Further, the coefficients of correlation within pairs of postural activity of the right and left muscles increased significantly.

occlusal splint can eliminate or diminish signs and

symptoms of functional disorders and re-establish

symmetric and reduced postural activity in the temporal

and masseter muscles, which can facilitate procedures,

such as functional analysis and occlusal adjustment.

It

is non-controlled study including 31 patients

Besides muscle activity change, occlusal splints can also cause an improvement in muscle symmetry. Muscle symmetry is related to static neuromuscular equilibrium of occlusion. Humsi did a prospective study about masseter muscle symmetry after splint therapy. In 36 myogenous craniomandibular disorder patients, the immediate effects of a stabilization splint on the symmetry in the activities of the masseter and anterior temporal muscles during submaximal clenching at five clenching levels were investigated electromyographically. After the adjustment of the splint necessary at the time of delivery, 20 splints remained free from occlusal interferences throughout the treatment period and thus needed no further adjustment. These splints caused an immediate improvement in masseter muscle symmetry at the time of delivery (p less than 0.01). No such response was found for temporal muscle activity. The immediate changes in masseter muscle activity suggest that muscular symmetry is an objective basis in the evaluation of the treatment provided.

It is non-controlled study including 36 patients

To clarity the effect of occlusal splint depending on sign and symptoms of patients and pre-treatment duration, short-term and long-term splint therapy were performed. Holmgren set up a study to compare the effect of occlusal splint before and after treatment.

Before treatment, that the occlusal splint changed significantly (in 71% of patients) the level of EMG activity during maximal clenching. However, these changes were not consistent and differed between patients and even, in some patients, between muscles.

After long-term occlusal splint therapy and improvement of the signs and symptoms of craniomandibular disorders, the number of patients who had an identical level of EMG activity during maximal clenching in the intercuspal position and on the occlusal splint tended to increase. Moreover, in these patients the level of symmetry of action in pairs of muscles during maximal clenching was strong, and the splint did not change this level of symmetry.

It suggested that occlusal splint has its effect on muscle activity and symmetry only for short-term after treatment and be short-lasting. We can assume that the other actions ,for example, condyle

relationship and occlusal factor, is dominated for latter period of therapy. It is non-controlled study including 31 patients.

Lobbezoo set a study to gain an insight into the influence of a vertical bite-rise (clenching in intercuspal occlusion vs. clenching on an occlusal stabilization splint), the mode of visual feedback (VF; obtained from the compound masseter signal, from the compound anterior temporalis signal, or from the compound signal of both masseter and anterior temporalis muscles) and the EMG clenching level (10% MVC and 50% MVC) on the muscle balance between the masseter and the anterior temporalis muscles. In a study of 118 patients with temporomandibular dysfunction treated with occlusal splint therapy, symptoms of pain and limited mobility of the mandible had decreased more distinct than clicking sounds of the temporomandibular joints. Interestingly, an untreated control group showed similar results after two years follow-up. The muscle balance was quantified as the logarithmic value of the ratio between the summated mean rectified EMG activity of the masseter muscles and this activity of the anterior temporalis muscles. The muscle balance was influenced significantly by the mode of VF (p < 0.01), the muscle balance shifting toward the group of muscles from which VF was obtained. When VF was obtained from the masseter muscles, decrease in the anterior temporalis EMG activity was observed when the vertical dimension was increased (p < 0.05-0.01).

When VF was obtained from the anterior temporalis muscles, the activity of the masseter muscles was raised with respect to that of the anterior temporalis muscles during clenching with a vertical bite-rise (p < 0.05-0.01).

When VF was obtained from both groups of muscles, the masseteric EMG activity increased, whereas the anterior temporalis EMG activity decreased. Hence, regardless of the mode of VF, a relatively lower activity level of the anterior temporalis muscles was achieved after insertion of an occlusal stabilization splint.

It is non-controlled study including 21 patients.

Ferrario researched the relevance between occlusal

splint therapy and muscle relevance and suggested its

possible mechanism. Surface electromyography (EMG)

allows the quantification of the occlusal equilibrium in

dysfunctional patients, for instance in those with

temporomandibular disorders (TMD). Fourteen patients (ten women, four men) with internal derangement type I were selected among the TMD patients referred to a private practice in Milan. A stabilization splint with posterior contacts was made for each patient. To verify the static neuromuscular equilibrium of occlusion, EMG activity of left and right temporal and masseter muscles was recorded in all patients and the activity (ratio between the activities of the temporal and masseter muscles) index was computed over a maximum voluntary clench test of 3 s. Muscular waveforms were also analyzed by computing a percentage overlapping coefficient (POC, an index of the symmetric distribution of the muscular activity determined by the occlusion).

The total electrical activity was measured by calculating the area under the entire muscular waveforms. In all patients EMG was performed just before and immediately after the insertion of the splint and data were compared by paired Student's t-tests. Overall, the splint reduced the electrical activity of the analyzed muscles (P < 0.005) and made it more equilibrated both between the left and right side (larger symmetry in the masseter muscle POC, P < 0.05) and between the temporal and masseter muscles (activity index, P <

0.01).

It is non-controlled study including 14 patients.

This result suggests splint can make a balance not only between left and right side, but also each muscles. The following study investigated muscle balance between the masseter and the anterior temporalis muscles.

Then, how occlusal splint exert an influence on muscle activity? The action mechanism can be explained as

“disclusion time”. Seven women patients at Tufts University School of Dental Medicine were evaluated for the subjective symptoms of a myofascial pain dysfunction. Each patient was evaluated by an occlusal analysis of the T-Scan computer to determine posterior disclusion time during excursive movements, and EMG analysis of the masseter and temporalis muscles. Each patient was then treated occlusally by developing immediate complete anterior guidance. This adjustment process involved the removal of all lateral and protrusive interferences prior to habitual closure adjustments. No attempt was made to retrude the mandible in centric relation, and splints were not used to deprogram the

musculature before adjustment. In this study, protrusive movements and interferences were not examined, and there was no control group. Kerstein and Wright analyzed post-treatment EMG and T-Scan computer in seven patients in approximately 1 months' time. It revealed that by shortening disclusion times to less than 0.5 second in any lateral excursions, muscle function returned to normal in all 7 patients. A direct correlation seemed to exist between contractile and disclusion time.

Lengthy disclusion time leads to excessive muscle activity that introduces spasm and fatigue of the masseter and temporal muscles. These results indicated that a partial explanation of the etiology of MPDS may be the time the molars and nonworking premolars remain in contact during excursive movements--a phenomenon termed.

It is non-controlled study including 7 patients Temperature was changed after muscular disorder treatment. It can be influenced by either the hyperactivity or hyperemia.

Barao evaluated the effect of occlusal splint treatment on the temperature of masseter (inferior, intermediate and superior), anterior temporal, digastric and trapezius muscles in patients with temporomandibular disorder (TMD). Mean temperature of the masseter muscle is higher in asymptomatic patients compared to patients with arthritis. Use of occlusal splint promoted a significant increase on the muscles temperature. There was symmetry in the temperature of muscles on the right and left sides both before and after the treatment.

Thirty patients (6 male and 24 female) aged from 16 to 57 years (mean 37.8±11.4 years) were selected. The patients were diagnosed with muscular TMD by clinical examination (application of Research Diagnostic Criteria questionnaire and physical examination). Occlusal splints in acrylic resin were inserted in all patients with a weekly follow-up. The superficial thermography (degrees C) on the both sides of the muscles was performed using a digital thermometer in a controlled temperature room.

This procedure was performed before occlusal splint insertion (patient with pain) and after the completion of the treatment (patient without pain). After occlusal splint treatment a significant increase in temperature was observed in each muscle, both in the right and left sides.

When the muscles were compared in the same period

(before or after therapy) there was no significant difference among them. It is non-controlled trial and 30 patients participated.

Contrasting result is reported by Nemcovsky. The skin surface temperature (SST) over the masseter muscles was measured in 19 patients suffering from myofascial pain (MP) and 20 controls who had no history of any temporomandibular disorder. Seven measurements with intervals of 2 weeks were carried out. MP patients received an occlusal stabilization appliance during their second visit as their only treatment. Clinical symptoms, including muscle sensitivity to palpation, jaw movement and general feeling were evaluated at each visit and compared to baseline. The results indicated that SST in the control group remained almost unchanged throughout the study. In the MP group, the mean temperature decreased during the study after initial treatment.

Accordingly, there was a probability of 88.5% that the occlusal appliance treatment in the MP group would cause a decrease of SST over the masseter muscle. A significant relationship between clinical improvement and a decrease of SST was found in the MP group.

This paper covers the effect of occlusal splint: skin surface temperature (SST) over the masseter muscles. It is controlled study; 19 patients suffering from myofascial pain (MP) and 20 controls are researched.

The effect of splint on muscle temperature is controversial. The journal

suggested increased muscle temperature after occlusal splint therapy, otherwise the study by Nemcovsky

insisted decrease of skin surface temperature. Both Journal concluded that occlusal splint brings changes of muscles .We cannot clearly demonstrated the causual relationship between temperature changes and occlusal splint therapy.

However, there must be some relevance between muscles and temperature.

5) Against the effect on muscle for splint therapy Until now, this review focused on one side that occlusal splints reduce muscle activity. However, a consensus has not been reached regarding the effects of an occlusal splint. Some studies reported occlusal splint increased muscle activity, however the others insisted occlusal splint has no effect on muscle. At another point,

occlusal splint material (hard/soft splint) has an impact on the effectiveness. They showed different effect on muscle. Most of studies are non-controlled study, so the evidence is not fully reliable. Nevertheless because occlusal splint mechanisms on muscle are not established, it is worth to review those papers.

Although several articles reviewed so far reported that occlusal splint reduces jaw muscle activity, contrasting findings have been reported. The short-term effect (3-6 weeks) of the use of a stabilization splint was investigated in a group of 35 myogenous temporomandi - bular disorder patients. The patients were clinically examined and surface EMG recordings of the temporal and masseter muscles were made during clenching in the intercuspal position (ICP), immediately after the insertion of the occlusal splint, and after at least 3 weeks of splint treatment. With the use of the error variance of the activity index changes in EMG activity were investigated. Three groups of patients were then recognized. One group showed a decrease in temporal muscle activity during splint treatment. Another group did not show any significant change during splint treatment. The third group showed an increase of temporal muscle activity. short-term usage of an occlusal splint noted that electromyographic activity was decreased in 15 of 35 subjects, while it was increased in 4 others and remained unchanged in 16. This conflicting result among groups suggests weak relevance between muscle activity and occlusal splint therapy.

It is non-controlled study containing 35 patients

With the mandible at rest, the clinical postural position

was measured and electromyographic recordings (in

seated and supine position, eyes open and eyes closed,

before as well as 15 min after insertion of an occlusal

splint) were from the anterior temporal and masseter

muscles in thirty-one patients with signs and symptoms

of mandibular dysfunction and nocturnal bruxism. The

results indicated that when the patients were seated

upright, there was a distinct postural activity in the

anterior temporal and in some patients also in the

masseter muscles. This postural activity decreased

significantly with closure of the eyes and in supine

position.

Fifteen minutes after insertion of an occlusal

splint, the postural activity in the temporal muscles

decreased in 52%, increased in 22% and remained unchanged in 26% of the patients. This inconsistent result suggests weak relevance between EMG activity and occlusal splint therapy.

The other study of Holmgren reported unchanged postural activity when patients were treated with a flat occlusal splint. The effects of occlusal adjustments on the myoelectric activity of the anterior temporal and masseter muscles, with the mandible at rest and during maximal clenching in the intercuspal position (ICP), were studied in 24 nocturnal bruxism patients. Before the occlusal adjustment, the patients were treated with a flat occlusal splint for chronic craniomandibular disorders. The results revealed that within the short term the occlusal adjustment, in terms of increased number of occlusal contacts and teeth in contact in ICP, did not change the postural activity, whereas, on average, the level of activation of the jaw elevators, in terms of normalized electromyogram, increased during maximal clenching in ICP. The increase of activity was more pronounced in the masseter muscle than in the anterior temporal muscle.

Increased number of occlusal contacts and teeth in contact in ICP, did not change the postural activity, It is non-controlled study containing 24 patients In addition, considerations must be made regarding the different types of occlusal splints available. For example, soft resilient occlusal splints are commonly used to manage patients with masticatory muscle pain, while that study also suggested that a soft occlusal splint is an effective short-term solution for reducing the signs and symptoms of masticatory muscle. Soft splint made an increase on muscleactivity. It is non-controlled trial.

Harkins et al. found an increase in the occurrence of clenching and bruxism with hard occlusal splints.

It is non-controlled study.

Okeson reported those decreased the electromyo - graphic activities of jaw closing muscles, while soft occlusal splints increased those activities. This study investigated the effects of on nighttime muscle activity.

The nocturnal muscle activity of ten participants was recorded while wearing a hard and then a soft occlusal splint. The hard occlusal splint significantly reduced muscle activity in eight of the ten participants. The soft occlusal splint significantly reduced muscle activity in

only one participant while causing a statistically significant increase in muscle activity in five of the ten participants.

This conflicting result between hard and soft occlusal splints suggests that constant VD and contact do a major role in occlusal splint action.

We can accept the hypothesis that occlusal splint relax muscles. Some reliable studies with high evidence level support this hypothesis. However the opinion that occlusal splint changes postural activity is still controversial. More controlled study is needed to get a scientific background. To Obtain overall consensus about mechanism of splint therapy, more randomized controlled trail with enough size is essential.

2. Regulating condylar position and improving the stress distribution

1) Condyle

Temporomandibular joints are load bearing and susceptible to overload. The susceptibility of TMJ to bear overload is reported by following study. When splints were placed in monkeys in one study, a lateral deviation from the CR arc of closure resulted, as did bone density changes in the condyles. This has led to cartilage breakdown and arthritis in the condylar heads.

This study support that occlusal splint should adopt CR as a treatment position because it allows the condyle to seat in centric relation.

Hu et.el investigate the biomechanical mechanism of occlusal splint therapy of temporomandibular joint disorders (TMD). The changes of stress distribution on the mandible with TMD before and after occlusal splint therapy were simulated and analyzed by three- dimensional finite element method. Occlusal splint influenced the character of stress distribution on the mandible. It might distinctly decrease maximum and minimum principal stresses on each region of the mandible with TMD, among which the stress on condylar surface of ill side was reduced more significantly, and the stress distribution of bilateral condyles was close to equality and balance. Meanwhile, the stress symmetry on every position of the mandible was improved slightly.

Occlusal splint can alleviate even eliminate the injury to

the temporomandibular joint, and make unbalance of

joint inner environment adjusted and restored by regulating condylar position and improving the stress distribution.

This is primarily thought to be one of the main biomechanical mechanism of occlusal splint treatment.

Temporomandibular joints are susceptible to overload.

Splints reduce stress on condyle by 1) TMJ distraction 2) free movement on new postural position without interference. Most of studies compared condyle/fossa changes before and after occlusal splint therapy. It is researched with X-ray radiography, MRI image, axis indicator, intra articular pressure measurement. The latter part covered disc recapture. The mechanism to improve symptom is assumed that splints had an impact on condyle/disc complex. However, that is not valid conclusion but still hypothesis. Those papers are reviewed from high evidence level, controlled study to non-controlled study, case report.

Pain and joint noises associated with temporomandi - bular joint (TMJ) internal derangement are often treated by using an intra-oral splint. This study evaluated whether an anterior repositioning splint (AR splint) could be more effective in the treatment of these symptoms than a full-arch maxillary stabilization splint (FAMS splint), because of its capability to re-establish immediately the normal condyle/disk relationship. The authors treated 40 patients (average age 16.8; range 8.0-24.0) with confirmed internal derangement, joint pain, and joint noises in at least one TMJ for at least two months, with AR splint (20 subjects) or FAMS splint (20 subjects); 10 untreated patients comprised the control group. Joint noise, joint pain, and the intensity of pain were assessed using a visual analogic scale (VAS), and the pain was characterized (i.e., constant or chewing/biting pain) and evaluated monthly for eight months. Significantly fewer AR splint patients experienced pain after four months of treatment. A significantly lower intensity of pain was experienced by the AR splint patients after two months of treatment.

Significantly fewer AR splint patients experienced chewing/biting pain after eight months of treatment. The frequency of joint noises decreased over time, with no significant differences between the groups. In conclusion, the AR splint seems to be more effective in decreasing

pain, but it seems to make no difference in the treatment of joint noises. It is controlled study. This study done by Tecco, proved the effect of occlusal splint by evaluating symptom improvement and noise reduction. It is assumed the mechanisms of occlusal splints are based on re-establishment of condyle/disk relationship. However, there is no definite evidence. The papers reviewed next are controlled study. They measured condyle/fossa relationship and condyle displacement after occlusal splint treatment with variable methods and tried to support this assumption.

The computed tomography of elderly TMJDS patients treated with and without splint was studied in three dimensions. The results showed that the condyle was in a retruded position in the glenoid fossa in sagittal dimension and the horizontal condylar angle appeared asymmetry in axial dimension. Under the splint treatment, the retruded condyle can be adjusted to the center of the glenoid fossa and the horizontal condylar angle can be balanced, since the splint may correct the vertical dimension and eliminate the occlusal interferences.

Condyle/fossa relationship is evaluated with CT image. This study was designed as controlled study.

Temporomandibular joint (TMJ) patients with disc

displacement without reduction have a misaligned

disc-condyle structural relation. As the condition

becomes chronic, painful osteoarthritic changes may

occur. Stress distribution induces osseous reaction. For

these patients, splint therapy may help to position the

condyle to a more structurally compatible and functional

position and to decrease the loading force of articular

surfaces. Hersek set up a study (1) to evaluate osseous

reactions and pain relief in patients with disc

displacement without reduction after splint therapy and

(2) to use single photon emission tomography (SPECT)

bone imaging to compare the results with the opposite

joint of the patient. Before splint therapy, the ratios of

affected TMJ to nonaffected TMJ and of affected TMJ

to occipital bone were found to be significantly higher

than the ratios after splint therapy (P < 0.005). Six-month

splint therapy has a positive effect on the osseous

reaction and pain related to internal derangements of

TMJs.

This study reported positive result after occlusal

splint therapy. They evaluated osseous reaction ad pain.

It is controlled study and 12 patients participated.

Fantini and Paiva reported that deprogramming occlusal splint for an average period of 7.8 ± 2.1 months results in greater mean condylar displacement values, especially vertically, between CR and MHI positions The sample consisted of 22 subjects, 11 male and 11 female, with an average age of 14.2 ± 1.4 years, with Class II malocclusion and with no apparent signs or symptoms of temporomandibular dysfunction (TMD). Condylar displacement was measured using a Panadent axis position indicator in decimal fractions of a millimeter.

The original mean vertical displacements and the corresponding standard deviations were 4.24 ± 2.53 mm and 3.86 ± 2.72 mm, respectively, for the right and left sides. Because a significant negative correlation was observed between original condylar displacements and age factors, the displacement values were statistically adjusted to 2.74 ± 2.00 mm and 2.44 ± 1.93 mm. On the horizontal plane, the mean displacements measured were -0.72 ± 1.53 mm on the right side and -0.51 ± 1.98 mm on the left. The mean displacement on the transversal plane was 0.03 ± 0.87 mm. A comparison between these values and those observed in non-deprogrammed groups, as well as those published in the related literature, indicates that use of occlusal splints results in greater mean condylar displacement values, especially vertically, between CR and MHI positions, which contributed to a more accurate orthodontic diagnosis.

They analyzed condyle change with axis position indicator. The displacement showed statistical difference between groups. It is controlled study and 22 patients participated.

To measure the positional changes of temporomandibular joint (TMJ) disk and condyle with insertion of anterior repositioning splint (ARS) using magnetic resonance imaging (MRI) for further understanding of the splint therapy mechanisms, a controlled study by Chen et al is designed.

Twenty-two patients with temporomandibular joint clicks were included; 31 TMJs were diagnosed as anterior disk displacement with reduction (disk-displaced group), and the other 13 TMJs were normal (normal group). All joints were scanned oblique-sagittally by MRI before

splint treatment in three positions including closed-mouth position of centric occlusion (the position before insertion of ARS), incisors' edge to edge position, and mandibular least forward protrusion position (the position after insertion of ARS). RESULTS: 1) Disk-condyle angle: In closed-mouth position, the average angle was 54.23 degrees in the disk-displaced group, while it was 9.80 degrees in the normal group; in incisors' edge to edge position and mandibular least forward protrusion position, the angle was reduced to normal in most of the disk-displaced cases. 2) Disk position: From closed-mouth position to incisors' edge to edge position or mandibular least forward protrusion position, the forward displaced disk moved backward significantly, while the disk with normal position did not change significantly in the three positions. 3) Condyle position:

From closed-mouth position to incisors' edge to edge position or mandibular least forward protrusion position, the condyle moved forward and downward significantly both in the disk-displaced group and in the normal group.

With insertion of the splint, the condyle moved anteriorly and inferiorly and the disk moved posteriorly, most of the anterior displaced disks could be reduced to normal positions in the joint fossa. The result indicated that the splint protruded condyle forward and prevented the backward reduced disk from displacing forward again during mouth closing.

They analyzed Disk-condyle angle with MRI image. It is controlled study.

The following article opposes the hypothesis that splint therapy changes condyle/disc relationship. Stabilization appliances and mandibular anterior repositioning appliances have been used to treat patients with internal derangement of the temporomandibular joint (TMJ) based on the assumption that these appliances work by decompressing the TMJ. The purpose of this study was to indirectly test this assumption. Bilateral TMJ tomograms of 7 subjects with unilateral anterior disc displacement without reduction (ADDwor) were taken during comfortable closure and during maximum clenching in maximum intercuspation; tomograms were also taken with the 2 types of occlusal appliances in use.

Outlines of the condyle and the temporal fossa were

automatically determined by an edge-detection protocol,

and the minimum joint space dimension of the joints