Kurtosis, a new variable with possible diagnostic value in analysis of jaw muscle surface EMG.

BACKGROUND: There is a need for methods to compare differences of voltage levels and distribution anomalies in the study of skeletal muscle function. Calculating the kurtosis values has been found to be of value. AIM: The aim was to record and analyse voltage and kurtosis levels of SEMG recorded bilaterally in the masseter and anterior temporalis areas during rest and clenching and to compare the kurtosis levels between controls and patients with TMJ disc dysfunction. MATERIAL AND METHODS: Twenty-three healthy subjects and 21 patients with TMJ disc dysfunction were taken part in this study. Recordings were made with the BioPAK EMG System. Gain was adjusted to record the data within the range of ±2000 µV. SEMG was recorded in four facial areas, the right masseter, left masseter, right anterior temporalis, and left anterior temporalis areas. Kurtosis levels of SEMG, at clenching with maximal force, and mandibular rest, were compared between the control and patient groups. RESULTS: The kurtosis levels of clenches were significantly higher in patients in all four areas with sensitivity, 38.1% to 61.9%, and specificity, 82.6% to 100.0%. No differences were found in kurtosis levels during mandibular rest. CONCLUSION: The results support that kurtosis values of SEMG recorded during clenching have a potential diagnostic interest.

Is SEMG recorded "hyperactivity" during mandibular rest a sign of dysfunctional jaw muscle activity and temporomandibular disorders (TMD)?

BACKGROUND: Some authors state that above-normal surface electromyography (SEMG) levels during mandibular rest (MR) are a general sign of temporomandibular disorders (TMD). OBJECTIVE: The aim was to compare SEMG levels in the masseter and anterior temporalis areas during MR between patients with disc displacement (DD) and subjects identified as healthy. The hypothesis was that average SEMG levels would be higher in the patients during MR before and after repeated clenches with maximal effort. METHODS: Thirty-six healthy subjects, and 42 patients with DD, were included. SEMG levels were recorded bilaterally in the temporalis and masseter areas during MR before clenching and after repeated clenches with maximal effort. Multivariate analysis of variance (MANOVA) was used to compare the means of the log-transformed SEMG-values for the subject groups. RESULTS: The mean MR levels in the four areas before clenching ranged from -0.19 log (µV) to 1.20 log(µV) in healthy subjects and from -0.22 log(µV) to 0.96 log(µV) in patients. The mean MR levels in the four areas after repeated clenches ranged from -0.19 log (µV) to 1.04 log(µV) in healthy subjects and from -0.27 log(µV) to 0.93 log(µV) in patients. The MANOVA test showed no significant differences in the means for MR for the four areas between the groups at the 5% significance level. CONCLUSION: The hypothesis that jaw muscle SEMG levels during MR are on average generally higher in TMD patients is not supported. A possible explanation for the previous findings is that activity in other muscles was mislabelled as jaw muscle activity.

Gender differences in low and high pain palpation thresholds in the TMJ and neck areas.

The null hypothesis was that pain pressure thresholds are the same for young healthy males and females and do not differ between the temporomandibular joint (TMJ) and muscle sites. The aim of the current study was to compare pain pressure threshold levels using an algometer with a convex-formed contact piece and pressure increase rates similar to those in conventional finger palpation, making the conditions more like clinical examination of painful spots with commonly used physiotherapeutic methods. Healthy subjects, 12 male, mean age 22.5 +/- 1.62 (SD), and 12 female, 22.4 +/- 2.19 (SD), were enrolled. A transducer with a calibrated load range, 0 to 25 pounds, was used to measure pressure threshold levels for low (T1), VAS to approximately 2, and high (T2), VAS to approximately 8, pain levels bilaterally in the occipital (OC), sternocleidomastoid (SCM), upper trapezius (TU), transverse process of first vertebra (C1), and lateral temporomandibular joint (TMJ) areas. The null hypothesis was rejected. Levels T1 and T2 were significantly lower in the females in all tested areas. The range of the mean for T1 levels was 4.9-8.0 pounds for males and 3.2-5.1 pounds for females. For T2 levels, the range was 8.9-15.6 pounds for males and 6.2-10.3 pounds for females. Significant differences were found between muscle sites. These results support the use of different threshold levels: a) for males and females; and b) for different muscle areas.

A preliminary anatomical study on the association of condylar and occlusal asymmetry.

The aim of this study was to test the hypothesis that condylar and occlusion asymmetry are not associated. For each of 22 skulls, the asymmetry of condyles was graded by one examiner and the asymmetry of occlusion by another examiner, both blinded to each other's evaluation, as 0 = symmetrical, 1 = mild asymmetrical and 2 = severe asymmetrical. There were 18 condyles graded the same as to their occlusion, but in four, the grades differed by one degree. Nine were graded symmetrical, seven were mild, and six were graded severely asymmetrical condyles. The corresponding figures for occlusion were: 10 were graded symmetrical, seven were graded mildly asymmetrical, and five were graded severely asymmetrical occlusion. The relation between occlusion and condylar asymmetry was tested using Goodman-Kruskal's gamma and was found to be 0.970 (p < 0.001). The null hypothesis was not supported. The results indicate that asymmetry of occlusion and condyles are associated, which indicates the need for further studies on larger samples, and in vivo studies.

The effect of experimental occlusal interferences on nerve growth factor levels in periodontal tissues.

OBJECTIVE: To test the hypothesis that experimental occlusal interferences increase the nerve growth factor (NGF) levels in periodontal tissues and cause an up-regulation of preprotachykinin-A (PPTA) mRNA. BACKGROUND: NGF is related to hyperalgesia and inflammation. PPTA mRNA, a primer of substance P, is a possible factor in the aetiology of pain. METHODS: Experimental interferences were created by placing inlays in the right maxillary molars of 15 dogs. The right side molars formed the experimental group. The left side molars served as controls. Three dogs with cavities prepared without changing the occlusion formed a sham group. The dogs in the first group were sacrificed, 3 at each time, after 3, 7, 14, 30, and 60 days. The sham group was sacrificed after 14 days. The levels of NGF in periodontal tissues and PPTA mRNA in the trigeminal ganglions were detected by ELISA and TR-PCR. Comparisons were made with paired t-tests and a multivariate MANOVA test. RESULTS: On all measurement days, there were higher levels of NGF mRNA, PPTA mRNA, and NGF on the experimental than on the control side in 14 of 15 comparisons and in the sham group. NGF production in periodontium was time-dependent. No differences in NGF protein levels were observed between the control and the sham groups. CONCLUSION: The results which need confirmation in further tests are of clinical interest. They indicate that occlusal experimental interferences may be an etiologic factor in oral facial pain by increasing mRNA and NGF protein levels in the periodontal tissues.

Magnetic resonance imaging on TMJ disc thickness in TMD patients: a pilot study.

STATEMENT OF PROBLEM: Studies of temporomandibular joint (TMJ) discs removed from autopsy specimens and in surgery indicate that they are often thicker in patients with temporomandibular disorders (TMDs). Disc thickness may also change when the condyle moves in and out of the joint fossa during opening and closing. PURPOSE: The purpose of this pilot study was to test the hypothesis that the TMJ disc thickness is greater in TMD patients than in healthy subjects and is affected by the degree of jaw opening. MATERIAL AND METHODS: Magnetic resonance images (MRI) were made of the TMJs in young volunteers, 9 asymptomatic subjects and 9 TMD subjects, at closed and at 10-, 20-, and 30-mm open positions. The thickness of the anterior and posterior bands of the discs and the intermediate zones was measured and compared between TMD and control groups, and between closed and opened positions, using the repeated-measures method in general linear model (alpha=.05). RESULTS: The hypothesis that the disc was thicker in the TMD than in the control group was supported with respect to the anterior band and intermediate zone (P<.046), but not with respect to the posterior band. The hypothesis that the thickness is affected by the degree of jaw opening was only supported for the posterior band, where it increased during opening in both groups (P<.005). CONCLUSIONS: The results indicate that the anterior band and the intermediate zone of the TMJ discs are thicker in TMD patients than in healthy subjects. The posterior band thickness increases with mouth opening in both asymptomatic and TMD subjects.

Experimentally created nonbalanced occlusion effects on the thickness of the temporomandibular joint disc in rats.

OBJECTIVES: To test the hypothesis that experimentally created physiologically nonbalanced occlusion will not affect the thickness of the temporomandibular joint (TMJ) discs in rats. MATERIAL AND METHODS: Twenty-four 8-week-old Sprague-Dawley rats were equally divided into a control group that was left untreated and an experimental group where a nonbalanced occlusion was created. Elastic rubber bands, 1 mm in diameter, were inserted and 1 week later were replaced by plastic material between the first and the second molars of the left maxillary and the right mandibular dentitions to move the first molars about 0.8 mm mesially. This created and maintained a physiologically nonbalanced occlusion. The animals were euthanized 8 weeks later, and the TMJ disc thickness was measured on histologically prepared slices using an electronic meter. Two-way univariate analysis of variance was used to compare the groups (alpha level = .05). RESULTS: The intermediate zone was thicker in the experimental group than in the control group (P = .003), but no differences were found between groups regarding the anterior and posterior bands. There were no significant sex-related effects on this observation. CONCLUSION: The hypothesis is rejected. The results indicate that the intermediate zone of rat TMJ disc has the ability to adapt to the alteration of the space between condyle and fossa caused by occlusion changes. Further studies on larger groups that are followed for longer times are needed.

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

STATEMENT OF PROBLEM: The temporomandibular joint (TMJ) disc is often observed to be thicker in temporomandibular disorder (TMD) patients. This clinical observation requires verification. PURPOSE: The purpose of this pilot study was to investigate whether the TMJ disc responds to dysfunctional occlusal changes by an increase in thickness. MATERIAL AND METHODS: Twelve 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). RESULTS: All 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. CONCLUSIONS: The 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.

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 alpha-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.