Sven E. Widmalm

Oral parafunctions as temporomandibular disorder risk factors in children.

Oral parafunctions are generally considered to be important factors in the etiology of temporomandibular disorders (TMDs) and many reports have been published about their prevalence in adults and schoolchildren. However, few have included significant numbers of children below the age of 7. The aim of this study was to examine the association between parafunctions and oral/facial TMD-related pain in preschool children. Bruxism, nail biting, and thumb sucking were found to be significantly associated with important oral/facial pain symptoms of clinical interest in the diagnoses of TMD indicating that those parafunctions are risk factors. The study included 525 4- to 6-year-old African-American and Caucasian children, mean age 5.1 +/- 0.65 (SD). An alpha level of 5% was chosen for comparison with a Pearson Chi-Square test. Bonferroni correction was made and a p-value of < 0.005 was accepted as significance level. Only 28% of the children had no history of any parafunction. More girls (82%) than boys (63%) in the Caucasian subgroup had at least one parafunction (p approximately 0.00017). No such difference was found in the African-American subgroup where the corresponding figures were 71% for girls and 73% for boys. Thumb sucking was reported by 57% of the children, more often by Caucasian girls (69%) than by Caucasian boys (43%) (p < 0.00001). Thirty percent still had the habit. Forty-one percent had a history of nail biting. Bruxism was noted in 20% of the children, but occurred mostly in combination with other parafunctions and was seldom (in 3.4%) the only parafunction. Of the 10 pain variables, bruxism was significantly associated with eight, thumb sucking with three, and nail biting with two. Analysis with logistic regression confirmed the results. Association does not, however, tell if a parafunction is the cause or the consequence of pain, or if a third factor is causing both pain and increased prevalence of oral parafunctions. Further prospective longitudinal studies including higher age groups are needed to clarify those relations and to determine if there are long-term effects of childhood parafunctions.

A clinical study of temporomandibular joint (TMJ) vibrations in TMJ dysfunction patients.

Using electrovibratography (EVG), the vibrations of 309 temporomandibular joints (TMJs) from 213 patients with clinical symptoms of temporomandibular joint dysfunction (TMD) were compared to TMJ arthrography. Of 309 imaged joints, 221 had an internal derangement (ID) and 88 were arthrographically normal (NID). Among the parameters derived from the power spectrum function of joint vibration, the total power density from 0 to 600 Hz (I(T)), the peak power density I(max)), and the power density at each 50 Hz frequency range (I(f)), each of these was significantly greater in ID than in NID patients. The frequency range that included (I(max) and the frequency range containing 50%, 75%, and 90% of I(T) was significantly lower in ID than in NID patients. The diagnostic sensitivity and specificity of a patients perception of TMJ sounds were 43% and 80%, respectively, while those for a doctors perception were 54% and 72%. When using I(T) as a parameter, the sensitivity and specificity of the EVG were 75% and 77%, respectively. By using these parameters of TMJ vibration energy analysis, a separation may be made between patients with normal joint anatomy and internal derangement.

Clinical Use of Qualitative Electromyography in the Evaluation of Jaw Muscle Function: A Practitioner's Guide

THE JOURNAL OF CRANIOMANDIBULAR PRACTICE 63 • the lateral pterygoid during protrusion and the deep masseter during retrusion; • the suprahyoid, infrahyoid, and lateral pterygoid muscles during jaw opening; and • the neck/cervical muscles during head movements. The diagnostic value of the EMG recordings increases if considered in conjunction with simultaneous data acquisition of both the TMJ sound/ vibrations and translatory movements of the mandible.9,10 EMG recordings may also be augmented by an analysis of relative occlusal forces and additional recordings of a patients response to electrical stimulation. While more encompassing with regard to muscle function, the EMG evaluation cannot replace traditional examination methods.3 Some authors have cautioned against the use of electronic instrumentation, except for biofeedback, emphasizing the potential diagnostic weaknesses while concurrently advocating that the methods are not cost effective.11-12 However, the expenses associated with the application and the purchase of equipment are modest when compared with most other procedures and equipment in the dental office. Nonetheless, critics have focused on errors that properly trained clinicians do not make. Practitioners who have received EMG evaluation training avoid the mistakes that occur as the result of applying unfamiliar techniques. The appropriate use of the instrumentation and a pragmatic interpretation of the advantages and limitations of clinical information generated through calibrated measurement tools are the products of an educational program that provides the clinician with adequate preparation in the assessment of EMG recordings. Therefore, it is unfortunate when misplaced criticisms lead to ignoring the unique advantages of EMG instrumentation, in cases where the monitoring of muscle activity is critical to the development of a meaningful diagnosis. It is not possible to calculate, in monetary terms, the value of increased diagnostic accuracy. Financial assessments will always differ among practitioners, patients, health care administrators and politicians. Therefore, cost effectiveness will not be discussed further. This article is not a review of EMG research. The purpose is to give examples of clinical applications wherein relatively simple EMG recordings of muscle activity provide valuable additional qualitative information with regard to diagnosis and treatment planning that cannot be obtained through other examination techniques. Diagnosis has often been based on qualitative data/recordings. Under such parameters, it is appropriate to study cause-and-effect relationships of phenomena as indicated by changes in EMG activity level, deviations from normal in jaw movement patterns and variable observations of TM joint sounds. Even if often cited, the statement “diagnosis is more art than science” is worth remembering. Nonetheless, the value of qualitative electro-diagnostic data is

Asymmetric muscle function in patients with developmental mandibular asymmetry

The aim was to test the hypothesis that developmental mandibular asymmetry is associated with increased asymmetry in muscle activity. Patients with mandibular condylar and/or ramus hyperplasia having unilateral cross-bite were compared with healthy subjects with normal occlusion. Muscle activity was recorded with surface electrodes in the masseter, suprahyoid, sternocleidomastoid muscle (SCM) and upper trapezius areas during jaw opening-closing-clenching, head-neck flexion-extension, and elevation-lowering of shoulders. Root mean square (RMS) and mean power frequency (MPF) values were calculated and analysed using anova and t-tests with P < 0.05 chosen as significance level. The SCM and masseter muscles showed co-activation during jaw and head movements, significantly more asymmetric in the patients than in the healthy subjects. The RMS and MPF values were higher in the patients than in the controls in the SCM and suprahyoid areas on both sides during jaw opening-closing movement. The results indicate that the ability to perform symmetric jaw and neck muscle activities is disturbed in patients with developmental mandibular asymmetry. This is of clinical interest because asymmetric activity may be an etiologic factor in temporomandibular joint and cervical pain. The results support that co-activation occurs between jaw and neck muscles during voluntary jaw opening and indicate that postural antigravity reflex activity occurs in the masseter area during head extension. Further studies, where EMG recordings are made from the DMA patients at early stages are motivated to verify activity sources and test if the asymmetric activity is associated with muscle and joint pain in the jaw and cervical areas.

Race and Gender as TMD Risk Factors in Children

The aim of this study was to record the prevalence in preschool children of oral/facial pain symptoms of clinical interest in the diagnoses of temporomandibular disorders (TMD) and to analyze the association with the race and gender factors. Children, 525 4-6 year olds, mean age 5.1 +/- 0.65 (SD), 326 Caucasian and 199 African American, from a preschool and kindergarten program in a low income industrial area, who participated in a voluntary oral health examination, were examined. Comparisons were made using Chi-Square test. An alpha-level of 5% was chosen, and the effect of making multiple comparisons was compensated for by Bonferroni correction. No gender differences were found, but racial differences were observed regarding six of the 10 variables. Twenty-five percent of the children had recurrent (at least one to two times per week) headache. Thirteen percent had recurrent earache, African-American children more often than Caucasian children (p approximately 0.0038). Thirteen percent had recurrent temporomandibular joint (TMJ) pain, and 11% had recurrent neck pain. Pain or tiredness in the jaws during chewing was reported by 29% of the children, more often by African-American than by Caucasian (p < 0.00001). Pain at jaw opening occurred in 13% of the children, more often in the African-American than in the Caucasian children (p approximately 0.00004). Palpation pain was found in the posterior TMJ area in 28%, in the lateral TMJ area in 22%, in the masseter area in 19%, in the anterior temporalis area in 15% and was found more often in all of those regions in the African-American than in the Caucasian children (p approximately 0.00001), except for the temporalis area. In conclusion, this study showed that mild, but distinct, TMD-related oral/facial pain symptoms occur already by ages 4-6 with significant differences in distribution observed between the African-American and the Caucasian races. While gender seems to play a negligible role in this age group, this does not necessarily mean that race is a causative factor. The pain symptoms may be caused by other factors with different distribution in the two racial subgroups.

SEMG activity of jaw-closing muscles during biting with different unilateral occlusal supports

The aim of this study was to test the hypothesis that experimental and reversible changes of occlusion affect the levels of surface electromyographic (SEMG) activity in the anterior temporalis and masseter areas during unilateral maximal voluntary biting (MVB) in centric and eccentric position. Changes were achieved by letting 21 healthy subjects bite with and without a cotton roll between the teeth. The placement alternated between sides and between premolar and molar areas. The SEMG activity level was lower when biting in eccentric position without than with a cotton roll between teeth (P < 0.043). It was always lower with premolar than with molar support when biting with a cotton roll (P < 0.013). In the anterior temporalis areas, the SEMG activity was always lower on the balancing than on the working side (P < 0.001). Such a difference was also found in the masseter areas but only during molar-supported centric biting (P = 0.024). No differences were found when comparing the SEMG levels in masseter areas between centric and eccentric biting (P > 0.05). In the anterior temporalis area, the balancing side SEMG activity was lower in eccentric than in centric but only in molar-supported biting (P = 0.026). These results support that the masseter and anterior temporalis muscles have different roles in keeping the mandible in balance during unilateral supported MVB. Changes in occlusal stability achieved by biting with versus without a cotton roll were found to affect the SEMG activity levels.

Crepitation and Clicking As Signs of TMD in Preschool Children

Children [N = 540, age 5.1 +/- 0.72 (SD)], were tested for association between temporomandibular (TM) joint sounds and symptoms of TM disorder (TMD). The prevalence of TMJ sounds as found by auscultation and confirmed by self-report was 16.7%. There was significant association after Bonferroni correction between the presence of TM joint sounds, as reported by the children, and all but one of the eleven pain/dysfunction variables. There was significant association also between crepitation as heard at auscultation and palpation tenderness in the TMJ and masseter areas (p < 0.001), but not between clicking and any of the TMD variables. Agreement between subjects and examiners regarding the presence of TMJ sounds was poor (kappa = 0.097). The results indicate that joint sounds and TMD symptoms are common already in small children and thus demonstrate a possible early onset of TMD. Patients own reports of TMJ sounds may have more clinical relevance than auscultation findings.

Computerized classification of temporomandibular joint sounds

Sounds, such as eliciting and/or crepitation, evoked in the temporomandibular (jaw) joint during function may indicate pathology. Analysis of the reduced interference time-frequency distribution of these sounds is of diagnostic value. However, visual evaluation is expensive and error prone, and there is, thus, a need for automated analysis. The aim of this study was to find the optimal signal representation and pattern recognition method for computerized classification of temporomandibular joint sounds. Concepts of time-shift invariance with and without scale invariance were employed and mutually compared. The automated analysis methods provided classification results that were similar to previous visual classification of the sounds. It was found that the classifier performance was significantly improved when scale invariance was omitted. This behavior occurred because scale invariance interfered with the frequency content of the signal. Therefore, scale invariance should not be pursued in the classification scheme employed in this study.

The effect of physiological nonbalanced occlusion on the thickness of the temporomandibular joint disc: A pilot autopsy study

STATEMENT OF PROBLEMnThe temporomandibular joint (TMJ) disc is often observed to be thicker in temporomandibular disorder (TMD) patients. This clinical observation requires verification.nnnPURPOSEnThe purpose of this pilot study was to investigate whether the TMJ disc responds to dysfunctional occlusal changes by an increase in thickness.nnnMATERIAL AND METHODSnTwelve cadaver heads were divided into 2 groups, 1 with physiologically balanced occlusion (BO), 7 cadaver heads and 14 joints, and the other with physiologically nonbalanced occlusion (NO), 5 cadaver heads and 9 joints. The NO group had defining traits, such as reverse articulation or tightly locked occlusion. The latter is an occlusal relationship with drifted, tilted, and/or supraerupted teeth, often seen in patients who have lost posterior teeth. Histological sections from the lateral, center, and medial parts of the joints stained with haematoxylin and eosin were used for measuring the disc thickness. Student t tests and Bonferroni correction were used to compare groups (alpha=.05).nnnRESULTSnAll 9 mean thickness values were higher in the NO than in the BO group. According to the t tests, the posterior band was thicker in the lateral (P=.007) and center (P=.015) sections, and the intermediate zone was thicker in the lateral section (P=.008) in the NO than in the BO group. These differences were not significant after Bonferroni corrections.nnnCONCLUSIONSnThe results suggest that the TMJ disc has the ability to adapt to alteration of the space between condyle and fossa caused by occlusal changes. Further studies from larger groups should be undertaken.

Inaudible Temporomandibular Joint Vibrations

Abstract The aim was to test the hypothesis that inaudible vibrations with significant amounts of energy increasing during jaw movements can be recorded in the temporomandibular joint (TMJ) area. Twenty one subjects, who could perform wide opening movements without feeling discomfort, 12 with and 9 without TMJ sounds audible at conventional auscultation with a stethoscope, were included. Recordings were made during opening-closing, 2/s without tooth contact, and during mandibular rest, using accelerometers with a flat frequency response between the filter cutoff frequencies 0.1 Hz and 1000 Hz. The signals were digitized using a 24 bits card and sampled with the rate 96000 Hz. Power spectral analyses, and independent and paired samples t-tests were used in the analysis of the vibration power observed in frequency bands corresponding to audible and inaudible frequencies. An α-level of 5% was chosen for accepting a difference as being significant. In the group with audible sounds, about 47% of the total vibration energy was in the inaudible area below 20 Hz during opening-closing and about 76% during mandibular rest. In the group without audible sounds, the corresponding proportions were significantly different, 85% vs. 69%. The energy content of the vibrations, both those below and those above 20 Hz, increased significantly during jaw movement in both groups. Furthermore, percentage of signal energy above 20 Hz showed a noticeable increase in the group of subjects with audible sounds. This can physically be explained by decreased damping properties of damaged tissues surrounding the TMJ. Vibrations in the TMJ area can be observed with significant portions in the inaudible area below 20 Hz both during mandibular rest and during jaw movements whether or not the subjects have audible joint sounds. Further studies are needed to identify sources and evaluate possible diagnostic value.