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.

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.

Electromyographic activity in patients with temporomandibular disorders.

Evaluation of masticatory muscle activity by surface electromyography (EMG) is a valuable tool for diagnosing dysfunction of the masticatory apparatus. However, controversy exists with regard to the usefulness of the EMG for patients with temporomandibular disorders (TMD). Forty patients with TMD were subjected to surface EMG of the masticatory muscles. These patients had consulted because of temporomandibular pain and clicks. In most cases (75%), the symptoms affected the patient's left side. Overall mean resting activity was 2.52 microV+/-1.25 microV (s.d.), which is slightly higher than in comparable healthy subjects (1.92+/-1.20 microV). Mean resting activity was highest in the anterior digastric muscle (3.49 microV) on the left side. Overall mean activity during clenching was 66.77+/-35.22 microV, which is about half that observed in healthy subjects (110.30+/-82.97 microV). During leftward movement of the jaw, activity was on average highest in the left digastric, while during rightward movement, activity was on average highest in the right anterior temporal (AT). Our results thus indicate that patients with temporomandibular joint (TMJ) disorder show: (1) a slight increase in basal tone; (2) a significantly reduced capacity for clenching; and (3) an apparently paradoxical inhibition of the dysfunctional-side AT during movement of the mandible towards that side.

Differences in bonding to acid-etched or Er:YAG-laser-treated enamel and dentin surfaces.

STATEMENT OF PROBLEM: Er:YAG (erbium-doped yttrium aluminium garnet) lasers have been effective in the removal of dental tissues. It has been suggested that they are also useful for preparing dental surfaces for adhesion, but results to date have been controversial. PURPOSE: This study compared the tensile strength of bracket-tooth bonds obtained after preparation of the surface for adhesion (dentin or enamel) by conventional acid-etching or by Er:YAG laser etching and investigated microstructure of resin-tooth interfaces using the 2 procedures. MATERIAL AND METHODS: Eighty healthy human premolars were used. Brackets were cemented to acid-etched enamel, laser-etched enamel, acid-etched dentin, or laser-etched dentin (20 teeth per group). Dentin was previously exposed using a high-speed handpiece. Acid-etching was with 37% orthophosphoric acid (15 seconds for enamel, 5 seconds for dentin). Laser etching was with Er:YAG laser (four 200 mJ pulses per second for enamel; four 160 mJ pulses per second for dentin). Brackets were bonded with autocuring resin paste, having first applied a primer (dentin only) and then light-cured bonding resin. Tensile strength was determined with a universal testing machine. Data were analyzed with 2-way ANOVA and subsequent t test with Bonferroni correction. Fracture patterns were compared by the Wilcoxon test with Bonferroni correction. For SEM studies of the resin-tooth interface, a total of 12 premolars were used (3 for each tissue per treatment combination). RESULTS: Mean tensile bond strength for acid-etched enamel (14.05 +/- 5.03 MPa) was significantly higher (P<.05) than for laser-etched enamel (8.45 +/- 3.07 MPa), and significantly higher (P<.05) for acid-etched dentin (4.70 +/- 2.50 MPa) than laser-etched dentin (2.48 +/- 1.94 MPa). Bond failure after laser etching was due to microcohesive fracture of tooth tissue. SEM studies of both resin-enamel and resin-dentin interfaces indicated extensive subsurface fissuring after laser etching. CONCLUSION: Adhesion to dental hard tissues after Er:YAG laser etching is inferior to that obtained after conventional acid etching. Enamel and dentin surfaces prepared by Er:YAG laser etching show extensive subsurface fissuring that is unfavorable to adhesion.

A secure method for making removable dies.

Removable dies greatly facilitate fixed prosthesis fabrication and accurate marginal fit. The major difficulty when using removable dies is the correct positioning of the dowel pin in the stone base. This article describes a method for preparing removable dies that ensures accurate positioning of the dowel pin and provides external landmarks for precise location of the cuts to be made with the die saw. The method described is accurate, simple, inexpensive and can be performed in the dental laboratory.

Masseteric silent period in healthy young adults.

The length of the silent period (SP) has been subject of extensive researches and its use has been established for the diagnosis of dysfunctional individuals. Because of its great variability we should be cautious about its assessment. This study is aimed to find the normal values taken in symptomless subjects using a commercial/medical recording system, designed for clinical use. Thirty-six readings of the SP have been taken causing a chin tap. The assessment of the motor dysfunction and the subsequent depressed activity gave the result of 32.37 ms (SD = 19.47, ranged from 15 to 110). This is slightly more extended than the results described by the majority of the Authors.

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).

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.

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.

[Anomalies of the inclination of the occlusal plane: early treatment using indirect guide-planes--electromyographic response]. / Anomalies d'inclinaison du plan occlusal: traitement précoce par les pistes indirectes--réponse électromyographique.

We discuss five cases of ANGLE's malocclusion Classes I, II or III that were rehabilitated basically by: restoration of masticatory function (previously pathological); the use of removable orthopaedic plates with indirect guideplanes. The patients (aged 6-15 years when treatment began) now have symmetrical balanced occlusion. Surface electromyography was used to study the function of the anterior temporal, surface masseter, deep masseter and anterior digastric muscles of 12 patients during rehabilitation of severe malocclusion. Electromyograms were obtained both with and without orthopaedic guideplanes installed. There were no significant differences as regards mean resting myoelectric activity. During maximum voluntary clenching in centric occlusion, the anterior temporal muscles were the most active, followed by the surface masseters. The activity of the anterior temporal muscles during clenching was significantly less (P < 0.01) with guideplanes than without. During lateral displacements, the non-working side anterior temporal muscle exhibited a significantly higher potential than the other muscles monitored, especially with guideplanes installed. The activity was lees with guideplanes during swallowing.

[Median inter-incisor line. Clinical symptomatology]. / Ligne médiane interincisive. Sémiologie clinique.

Since unilateral mastication causes asymmetry of mouth and face, a child's interincisal midline can reveal the first signs of alteration of masticatory function. Early detection of the functional pathology, preferably before it has established itself as such, allows the clinician to correct it by means that are relatively unburdensome for the patient, thereby forestalling severe organic alteration and favouring proper, balanced occlusal development. Centering the mandible in stable centric occlusion, together with simple treatment promoting alternating bilateral mastication, allows the correct development of the growing patient's stomatognathic system.