Urbano Santana-Penín

Changes in EMG activity during clenching in chronic pain patients with unilateral temporomandibular disorders

The study assessed the differences in electromyographic (EMG) activity recorded during clenching in women with chronic unilateral temporomandibular disorders (TMDs) as compared to control subjects. Seventy-five full dentate, normo-occlusion, right-handed, similarly aged female subjects were recruited. Twenty five subjects presented with right side TMD, 25 presented with left side TMD and 25 pain-free control subjects participated. Using integrated surface EMG over a 1 s contraction, the anterior temporalis and masseter muscles were evaluated bilaterally while subjects performed maximum voluntary clenching. Lower EMG activation was observed in patients with TMD as compared to control subjects (temporalis: 195.74+/-18.57 vs. 275.74+/-22.11, P=0.011; masseters: 151.09+/-17.37 vs. 283.29+/-31.87, P<0.001). An asymmetry index (SAI) was calculated to determine ratios of right to left sided activation. Patients with right-sided TMD demonstrated preferential use of their left-sided muscles (SAI -5.35+/-4.02) whereas patients with left-sided TMD demonstrated preferential use of their right-sided muscles (SAI 6.95+/-2.82), (P=0.016). This unilateral reduction in temporalis and masseter activity could be considered as a specific protective functional adaptation of the neuromuscular system due to nociceptive input. The asymmetry index (SAI) may be a useful measure in discriminating patients with right vs. left-sided TMD.

Temporomandibular disorders: the habitual chewing side syndrome.

Background Temporomandibular disorders are the most common cause of chronic orofacial pain, but, except where they occur subsequent to trauma, their cause remains unknown. This cross-sectional study assessed chewing function (habitual chewing side) and the differences of the chewing side and condylar path and lateral anterior guidance angles in participants with chronic unilateral temporomandibular disorder. This is the preliminary report of a randomized trial that aimed to test the effect of a new occlusal adjustment therapy. Methods The masticatory function of 21 randomly selected completely dentate participants with chronic temporomandibular disorders (all but one with unilateral symptoms) was assessed by observing them eat almonds, inspecting the lateral horizontal movement of the jaw, with kinesiography, and by means of interview. The condylar path in the sagittal plane and the lateral anterior guidance angles with respect to the Frankfort horizontal plane in the frontal plane were measured on both sides in each individual. Results Sixteen of 20 participants with unilateral symptoms chewed on the affected side; the concordance (Fisher’s exact test, P = .003) and the concordance-symmetry level (Kappa coefficient κ = 0.689; 95% confidence interval [CI], 0.38 to 0.99; P = .002) were significant. The mean condylar path angle was steeper (53.47(10.88) degrees versus 46.16(7.25) degrees; P = .001), and the mean lateral anterior guidance angle was flatter (41.63(13.35) degrees versus 48.32(9.53) degrees P = .036) on the symptomatic side. Discussion The results of this study support the use of a new term based on etiology, “habitual chewing side syndrome”, instead of the nonspecific symptom-based “temporomandibular joint disorders”; this denomination is characterized in adults by a steeper condylar path, flatter lateral anterior guidance, and habitual chewing on the symptomatic side.

Clenching TMJs-Loads Increases in Partial Edentates: A 3D Finite Element Study

Goal This study tests the hypothesis of loading-dependence on the temporomandibular joint during clenching on the particular of experimentally partial edentate conditions. Methodology A complete and detailed finite element model of the temporomandibular joint (TMJ) was used. The closing movement of the mouth was reproduced by contracting the closing muscles of the masticatory system. Electromyography (EMG) data were taken from 10 healthy, dentulate volunteers, both with and without intraoral appliances. The intraoral appliances served to mimic nine partially edentulate (PE) conditions for each volunteer. The EMG data were fed into the finite element model (FEM) for each condition and the loading of the joint was analyzed. Results The results obtained show that muscular activity decreases when the contact between teeth disappears. In particular, the numerical results showed that when there is no contact between the posterior teeth an overload of the joints appeared. Moreover, the existence of a unilateral unique molar induced asymmetric overloading in the TMJ disc without posterior contact. Conclusions During clenching, a uniform distribution of the dental contact along the maxillar arches prevents the TMJ from overloading. In contrast, severe partial edentation seems to induce overloading of the TMJ with severity depending on the type of contact.

Surface raw electromyography has a moderate discriminatory capacity for differentiating between healthy individuals and those with TMD: A diagnostic study

The use of surface electromyography (sEMG) to identify subjects with chronic temporomandibular disorders (TMD) is controversial. The main objective of this study is to determine the diagnostic accuracy of EMG to differentiate between healthy subjects and those with TMD. This study evaluated 53 individuals with TMD who were referred to the university service and who fulfilled the eligibility criteria during the period of the study. Thirty-eight dental students were also recruited satisfying same eligibility criteria but without TMD. The inclusion criteria were to be fully dentate, have normal occlusion, and be righthanded. The exclusion criteria were periodontal pathology, caries or damaged dental tissues, orthodontic therapy, maxillofacial disease, botulinum A toxin therapy, and psychological disorders. The means of the masseter muscles, right (RM) and left (LM), and temporalis muscles, right (RT) and left (LT), and intraindividual indexes during resting and during clenching were calculated. Raw sEMG activity was used to determine the cutoff points and calculate the diagnostic accuracy of sEMG. The diagnostic accuracy of these variables for a diagnosis of TMD was evaluated by using the Receiver Operating Characteristic (ROC) curve and the area under it (AUC). A new transformed diagnostic variable was obtained by using the Generalized Additive Models (GAM). Optimal cutoff points were obtained where the sensitivity and specificity were similar and by the Youden index. The highest estimated AUC was 0.660 (95% CI 0.605-0.871) corresponding to the rLT variable during rest. When rLT and rACTIVITY (differences divided by sums of temporalis versus masseter muscles) were considered as a linear combination, the AUC increased to 0.742 (95% CI; 0.783-0.934). In conclusion, the raw sEMG evaluation of rest provided moderate sensitivity and specificity to discriminate between healthy individuals and those with TMD. The use of the indexes (mainly assessing the dominance of temporalis over masseter muscles during rest) is strongly recommended to increase the discriminatory capacity of raw sEMG evaluation.

Muscular activity during isometric incisal biting.

This study attempted to estimate TMJ loading during incisal loading using a custom load-cell device and surface electromyographic (sEMG) recordings of the main jaw closers to assess the outcome correlation. Study participants were 23 healthy volunteers. The incisal loads having submaximal and mean intensity were recorded using a calibrated electronic load cell; simultaneously, surface electromyography (sEMG) of the right and left masseter and temporalis muscles was recorded. Readings of the resting, clenching in maximal and submaximal intercuspal positions and mean (50%) incisal loads were recorded. Clenching sEMG activity was used as a reference for normalization. The mean (SD) submaximal incisal load recorded was 498 (305.78)N, and the mean at 50% of the submaximal load was 268.93 (147.37)N. Mean (SD) sEMG activity during submaximal clenching was 141.23 (87.76)μV, with no significant differences between the four muscles. During submaximal voluntary incisal loading, the normalized mean sEMG activity was 49.99 (34.54)µV %, and 27.17(15.29)µV % during mean (50%) effort. The incisal load was generated mainly by the masseter muscles, as these showed a positive correlation during mean but not during submaximal effort. In the edge-to-edge jaw position, the mean incisal load effort seems to be physiological, but excessive TMJ loads can be expected from chronic or excessive incisal loading. In conclusion, incisal loads require the activity of the masseter muscles, which show a positive correlation between sEMG activity and effective incisal loads during mean, but not during submaximal, effort, and the masseter muscles are dominant over the temporalis muscles during submaximal incisal biting.

An accurate method for occlusal registration and altered-cast impression for removable partial dentures during the same visit as the framework try-in

Preparation of mandibular distal-extension removable partial dentures usually requires a secondary impression (the altered-cast impression) to improve the stability of the prosthesis. A potential problem with conventional altered-cast impression procedures is incorrect or incomplete seating of the framework in the mouth or on the cast. This article describes a procedure for obtaining the interjaw relationship and an accurate altered-cast impression in a single appointment (that of the framework try-in).

The occlusal plane indicator: A new device for determining the inclination of the occlusal plane

Accurate determination of the inclination of the occlusal plane is important in a number of situations, and includes confirming the correct development of the dentition in children, providing a basis for nonanatomic tooth design in the preparation of fixed prostheses, and assisting in decisions as to whether to perform intrusions or extrusions. This article describes a simple device for determination of the inclination of the occlusal plane.

Simple method for articulator mounting of mandibular diagnostic casts

The method described in this article is inexpensive, simple, and rapid and can be performed by a single operator. There is no risk of the rubber bands slipping, because they are included within the stone itself.

An esthetically attractive twin-flex clasp for removable partial dentures

The cosmetic appearance of a removable partial denture is of great importance to both the patient and the dentist. Traditional facial clasp arms are usually unsightly. Other options are expensive and/or technically difficult, and may require time-consuming maintenance. Furthermore, when these clasps are broken, replacement of the entire removable partial denture may be required. This article describes a procedure for making a simple but effective twin-flex clasp. The clasp has excellent esthetics and can be readily adjusted or replaced.

Approach towards the porous fibrous structure of the periodontal ligament using micro-computerized tomography and finite element analysis

The periodontal ligament (PDL) is a porous and fibrous soft tissue situated around the tooth, which plays a key role in the transmission of loads from the tooth to the alveolar bone of the mandible. Although several studies have tried to characterize its mechanical properties, the behaviour of this tissue is not clear yet. In this study, a new simulation methodology based on a material model which considers the contribution of porous and fibrous structure with different material model formulations depending on the effort direction is proposed. The defined material model was characterized by a non-linear approximation of the porous fibrous matrix to experimental results obtained from samples of similar species and was validated by rigorous test simulations under tensile and compressive loads. The global PDL response was also validated using the parameters of the characterization in a finite element model of full human canine tooth obtained by micro-tomography. The results suggest that the porous contribution has high influence during compression because the bulk modulus of the material depends on the ability of interstitial fluid to drain. On the other hand, the collagen fibres running along the load direction are the main responsible of the ligament stiffness during tensile efforts. Thus, a material model with distinct responses depending of the load direction is proposed. Furthermore, the results suggest the importance of considering 3D finite element models based of the real morphology of human PDL for representing the irregular stress distribution caused by the coupling of complex material models and irregular morphologies.