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Functional disturbances of the masticatory system in school children.

The centralization of treatment for functional masticatory disturbances by the Copenhagen Municipality Children's Dental Service has made possible the present survey of symptoms and results of treatment in a child population. Over a period of four years, a total of 366 children, aged six to sixteen (two thirds girls), were referred for treatment. Their symptoms differed from those reported by adult patients by a marked attrition of the mandibular incisors and concomitant sensitivity to thermal and mechanical stimulation. Other symptoms of functional disturbance, such as reduced mandibular mobility and muscle tenderness, were similar to those reported for adult subjects. Treatment conformed to conventional principles with widespread use of soft bite-splints (Figure 5). Both symptoms and signs were eliminated in about 60 percent of the patients, while 34 percent were essentially symptom-free at the conclusion of treatment. The survey showed that functional disturbances in the mandibular apparatus occur in children, and that many can be treated with good results. The symptomatology, however, resembles that of a wide range of other ailments, especially with respect to headache and facial pain, necessitating a careful differential diagnosis before functional corrective treatment is started.

Adolescent↗

Biomechanical features of the periodontium: an experimental pilot study in vivo.

INTRODUCTION: The orthodontic application of a force or moment leads to a strain distribution in the periodontal ligament. The corresponding local deformation at the interface periodontal ligament-alveolar bone causes a distribution of normal and shearing tension that is thought to be the local stimulus for bone remodeling leading to orthodontic tooth movement. Although researchers have examined initial tooth movement and the biomechanical properties of the periodontal ligament, few have reported human, in-vivo studies. For such examinations, very small tooth displacements must be measured with extremely high resolution and accuracy. METHODS: By a highly sensitive goniometer (resolution <0.001 degrees ), rotations of premolars in 22 subjects with natural spacing and 14 subjects with pronounced anterior crowding were measured in vivo. The rotations followed sets of pure moment-time functions starting at zero and reaching specified final values within +/- 1.43 Ncm. RESULTS: Usually, thresholds were seen that had to be overcome by moment to produce measurable rotations of the tooth in the mesial or distal direction. The subjects with pronounced anterior crowding showed distinct asymmetry: Thresholds for rotations to the distal direction were significantly higher than for those to the mesial direction. CONCLUSIONS: The cases of symmetric thresholds indicated a shear thinning viscosity in the periodontium under increasing moment. In the case of asymmetric thresholds, the findings suggested a mesially directed pretension of the gingival fiber apparatus that might be connected with the mesial drift.

Adolescent↗

The effect of endodontic materials on periodontal ligament cell proliferation, alkaline phosphatase activity, and extracellular matrix protein synthesis in vitro.

Recent studies have demonstrated that periodontal ligament-derived (PDL) cells have the potential to regenerate a complete periodontal connective tissue attachment apparatus on both root and artificial substrates. To study the characteristics of endodontic materials conducive to periodontal regeneration, we have established an experimental model using PDL cell cultures that express a 42 kDa protein (CP42) associated with cementum extracellular matrix. In this report, the effect of gutta percha, dental amalgam, composite and calcium hydroxide on PDL cell proliferation, collagen and noncollagen protein synthesis, alkaline phosphatase activity, and CP42 expression are presented. While all substrates supported PDL cell attachment and proliferation, highest levels of alkaline phosphatase activity, collagen and noncollagen protein synthesis were observed in control cultures. Lowest levels of the above parameters were observed with gutta percha while amalgam, composite and calcium hydroxide had intermediate levels. Only control PDL cultures demonstrated CP42 expression. These data suggest that culture substrate can markedly influence periodontal extracellular matrix gene expression in vitro and provide an experimental model to select and develop endodontic materials compatible with periodontal regeneration in vivo.

Alkaline Phosphatase↗

Atlas-axis facet asymmetry. Implications in manual palpation.

STUDY DESIGN: A basic study of six human cervical spines, documenting displacement with applied forces mimicking palpation. OBJECTIVES: To assess the issues of motion palpation of joint restrictions and the inferred link to disease. SUMMARY OF BACKGROUND DATA: Although several investigators have suggested that the issue of asymmetry and normal-abnormal function should be assessed, data are unavailable. METHODS: Atlas-axis specimens were harvested from six cadavers, cleaned of ligamentous and muscle tissue, and potted and secured with dental plaster. Forces (5-25 N) were applied along the mediolateral axis, and the corresponding displacement along three orthogonal axes were documented with infrared diodes and the Optotrak camera system (Northern Digital, Waterloo, Ontario, Canada). Specimen geometry and asymmetry were documented with plain radiographic film and a gimbal apparatus. RESULTS: Each of the six specimens displayed different behavior and differing degrees of asymmetry (e.g., facet inclination 17-35 degrees) so that each was analyzed as a case study. Asymmetrical and discontinuous force-displacement correlations were linked to anatomic asymmetry that appeared to be of natural occurrence. CONCLUSIONS: Asymmetrical joint geometry is common and causes asymmetrical joint dynamics. Thus, a clinician attempting to palpate vertebral motion would be misled by assuming that perceived restricted joint motion universally represented a finding potentially amenable to manipulation. For spine palpation to be a valid indicator for manipulation, the clinician applying it must first be able to differentiate between asymmetrical motion caused by vertebral fixation and that caused by asymmetrical joint anatomy.

Aged↗

[Correction of a dental and basal Class II with accentuated overjet using traction].

Correction of a dental and basal 2nd class with accentuated overjet using extraoral traction and programmed extractions of 17-27, 38-48 according to Armstrong's technique. The paper reports a case of dental and basal 2nd class with accentuated overjet treated using the extraction of 17-27, 38-48 and extraoral traction only, according to Armstrong's technique. Results obtained after 117 days of combined extraoral traction are reported in order to illustrate the reasons behind the choice of this apparatus and to demonstrate its evident efficacy in this case of 2nd class, 1st subdivision.

Cephalometry↗

Interspecific perspective on mechanical and nonmechanical models of primate circumorbital morphology.

Linear dimensions and angular orientations of the browridge, postorbital bar, and postorbital septum were obtained from a representative series of primates and compared with variables associated with several nonmechanical and biomechanical/mechanical models put forward to explain the form and function of the circumorbital region. Analyses of the results indicate that face size is the primary determinant of variation in primate circumorbital morphology. Anteroposterior browridge thickness is correlated with neural-orbital disjunction among anthropoid primates, but not among prosimians. This difference appears related to differences in the construction of the upper face and anterior cranial fossa between prosimians and anthropoids. Little support is demonstrated for the anterior dental loading model of browridge development. Mediolateral postorbital bar width and (to a lesser degree) browridge height are correlated with neurofacial torsion during mastication and variation in masticatory muscle size. These analyses further suggest that since circumorbital structures (especially the browridges) are located the farthest away from the chewing apparatus, they are least affected by masticatory stresses.

Animals↗

Vibrating-traction method for mechanical joint distraction.

Mechanical static traction has been adopted as one of the treatment procedures for joint diseases and fractures. The effect of mechanical vibration on the mechanical traction of the temporomandibular joint was studied in six human subjects. A mechanical traction force of 2000 gf was applied as a dynamic traction force with mechanical vibration or as a static traction force. The dynamic traction force with vibration was applied for 5 min to the right temporomandibular joint using a vibrating-traction apparatus which generated mechanical vibrations of 1000, 3000 or 4000 Hz. Application of a static traction force for 5 min was used as a control condition. Vertical condylar displacement was mathematically evaluated from the deviation of the mandible using Eddy current displacement sensors which were attached to the maxillary dental arch. Among the three vibration frequencies, 3000 Hz resulted in the maximum vertical condylar displacement for all six subjects, showing the mean condylar displacement of 668+/-242 microm. In contrast, vibrations of 1000 and 4000 Hz showed a smaller traction effect. Application of the static traction force for 5 min resulted in a mean vertical condylar displacement of 5.7+/-4.9 microm, showing almost no traction effect to the joint. From the results of this study, it was revealed that vibrating traction could distract a joint more effectively than could static traction and that the traction force necessary for effective vibrating traction was less than that for static traction.

Adult↗

Influence of humidity on dimensional stability of a range of ion-leachable cements.

The dimensional changes of a variety of dental restorative materials, occurring during and after setting, were investigated. The materials were tested under four different environmental conditions: 25 degrees C at laboratory humidity, 25 degrees C at 100% humidity, 37 degrees C at laboratory humidity and 37 degrees C at 100% humidity. Two materials setting by an acid-base reaction were also examined when protected with both a conventional varnish and a low-viscosity light-curable resin. The dimensional changes were recorded continuously using linear variable displacement transducers (LVDTs) over periods of up to 2 h. The materials investigated showed varying magnitudes of dimensional change. The shrinkage of conventional glass-ionomer cements (Fuji II and Opusfil) were the highest at 37 degrees C in air. This was attributed to the highest rate of water loss in the most desiccating environment. The shrinkage observed for the materials which set, even only in part, by a polymerization reaction will probably be due to the water loss and/or polymerization shrinkage. Exposure of these materials to a high-humidity environment reduced the shrinkage because of the swelling associated with water absorption. Application of the varnish and the protective resin over the cement surfaces also reduced shrinkage in Fuji II due to prevention of water exchange. The apparatus used in this study provided a simple and reliable method for measuring linear dimensional change. Data obtained in this study were comparable, where appropriate, to the values found in the literature.

Absorption↗

An ultrastructural study of the differentiation of mesenchymal cells in implants of allogeneic dentine matrix on the amputated dental pulp of the dog.

The sequential transition of the cells adjacent to autolysed antigen-extracted allogeneic dentine matrix was observed in a cavity on the amputated pulp in vivo. One week post-operatively, cells having poorly developed organelles and many free ribosomes, reminiscent of dedifferentiated or embryonic cells, were seen in migration and forming attachments to the allogeneic dentine matrix. Two weeks post-operatively, the cells close to that matrix had polarized nuclei and a clear distal area with minute processes, suggestive of preodontoblasts. Matrix vesicles were observed in the newly formed predentine-like matrix close to the allogeneic matrix. Some of the matrix vesicles contained needle-like crystals. Four weeks post-operatively, long, polarized cells with a well-developed endoplasmic reticulum and Golgi apparatus were seen. They contacted via a terminal web with desmosomes and tight junctions, and each had a long process extending into the predentine-like matrix, suggesting that they were identical to odontoblasts. These findings suggest that in the repair of the amputated pulp implanted with allogeneic dentine matrix the differentiation of odontogenic cells and initial mineralization may be analogous to those in normal dentinogenesis.

Animals↗

New attachment formation in the human periodontium by guided tissue regeneration. Case reports.

The aim of the present study was to evaluate whether a regenerative surgical procedure, based on guided tissue regeneration, could predictably result in the formation of a new attachment in human teeth. The material included 12 teeth in 10 patients with advanced periodontal disease. Following flap elevation, scaling, root planing and removal of granulation tissue, a teflon membrane was placed over the denuded root surface in such a way that the epithelium and the gingival connective tissue were prevented from reaching contact with the root during healing. The flap was replaced on the outer surface of the membrane and secured with interdental sutures. This design of wound preparation gives preference to the cells originating from the periodontal ligament (PDL-cells) to repopulate the wound area adjacent to the root. Histologic analysis of the result of treatment was made in 5 of the 12 teeth scheduled for extraction. In the remaining 7 teeth, the result was evaluated using clinical measurements. The result of healing disclosed that in all teeth treated, substantial amounts of new attachment had formed. This suggests that predictable restitution of the attachment apparatus can be accomplished by using a method of treatment which is based on the principle of guided tissue regeneration.

Adult↗

A device for investigating neuromuscular control in the human masticatory system.

A new apparatus has been developed to study the control of mastication in humans. The subject places his/her teeth on fixed upper and mobile lower bite plates; the device then enables opening and closing movements of the lower jaw against a controlled resistance. It is also possible to vary the number of teeth in contact with the device during an experiment from the entire dental arcade to a single tooth. The specially designed lower bite plate is dynamic and allows for both rotation and translation of the lower jaw during movement, thus, permitting the natural curvilinear trajectory of the jaw. The lower bite plate can follow chewing initiated by the subject without resisting the movement ('no force' mode) via a dedicated microprocessor controlled compensation mechanism. Another function of the device is to inject a constant predetermined load onto the lower bite plate so that the subject 'chews' against a fixed resistance simulating rapidly yielding food bolus ('fixed force' mode). The device can be programmed to increase or decrease the force during the closing or opening phase of chewing by feeding the position information into the force compensation system so both position and force change in parallel, hence, simulating a bite onto a non-yielding, or sticky, food bolus ('normal chewing' mode). By use of a jaw position compensation mechanism, the device can actively move the lower jaw, following any imposed position pattern ('position controlled' mode). The chewing simulator also has a mode that holds the position at a fixed level and allows the force to change ('position hold' mode). Furthermore, the device can inject additional rapid or slow forces or displacements onto the lower bite plate in order to elicit reflexes so that the response of jaw muscles to such stimuli can be examined at various jaw positions, force levels, phases of motion and velocities. The different modes of the apparatus can be used to study the operation and feedback control of human mastication; in particular whether modulations in jaw muscle activity and reflexes are due to changes in force, velocity, position, chewing cycle phase or a combination of these factors.

Afferent Pathways↗

The use of sedatives in dental care: legal aspects in Sweden.

The patient's rights and the dentist's obligations within Swedish dental care are governed by the Dental Care Act. The general dentist Instruction enjoins on every dentist, in accordance with science and tested experience, to advise and, as far as possible, to inform the patient about the treatment the patient's condition requires. Dentists have the right to prescribe sedative drugs. Intravenous injection of sedative agents may not at present be used by dentists. Dentists have the right to use nitrous oxide analgesia after undergoing training approved by the National Board of Health and Welfare. With regard to the nitrous oxide apparatus, it is stipulated that the concentration of oxygen must never fall below 40% volume. There are special directions for ventilation in the treatment room, portable exsuction, and other measures when nitrous oxide analgesia is used. It is specially directed how dentists shall keep case records in general. Stipulations also exist for the keeping of case records on nitrous oxide analgesia. Dentists are bound to report secondary effects of drugs to the National Board of Health and Welfare.

Dental Care↗

[Influence of types and surface treatment of dental alloy and film thickness of cements on bond strength of dental luting cements].

The goal of this study was to test the influence of the type and oxidation treatment of dental casting alloys on the tensile bond strength of luting cements. Also, the influence of film thickness of luting cements on the tensile bond strength of different dental casting alloys was examined. Four different luting cements (zinc phosphate, polycarboxylate, glass ionomer and adhesive resin cements) and four different dental casting alloys (Au-Ag-Cu, Ag-Pd, hardened Ag-Pd and Ni-Cr alloys) were used. Cylindrical alloy rods for the tensile bond strength test were casted, and then, top surfaces of the rods were cemented with each luting cement to the bottom surfaces of other rods, using the film thickness adjustment apparatus. The film thickness of luting cement was adjusted to 20, 30, 50, 75 or 100 microns. The tensile bond strengths of each cement to different casting alloys at each film thickness were measured one day after the rods had been cemented. The tensile bond strength of the zinc phosphate cement could not be determined in this study due to the separation of the alloy rods cemented with the zinc phosphate cement in water before the tensile test. The tensile bond strength to the adhesive resin cement to any alloy showed the greatest strength; however, that of the glass ionomer cement to any alloy was the lowest strength among the cements examined. The Ni-Cr alloy had the highest bond strength of any luting cement, compared to other alloys. The tensile bond strengths of luting cements significantly decreased with the increase in film thickness of cement layer. The adhesive resin cement had the greatest bond strength, and the glass ionomer cement was the lowest bond strength at any film thickness. The oxidation treatment significantly increased the bond strength of the adhesive resin cement to both Au-Ag-Cu and Ag-Pd alloys. The tensile bond strength of the adhesive resin cement was most dependent upon the film thickness of cement layer, and that of the polycarboxylate cement was least dependent upon the film thickness of cement layer among the cements examined. In addition, the oxidation treatment for precious alloys could be a factor contributing to the increase in the bond strength of the adhesive resin cement.

Adhesiveness↗

[A fundamental study on measurement of study cast].

The dental study cast has a complicated shape. Therefore, many dead angles are recognized during three-dimensional (3-D) measurement using a light source. To overcome this problem, several divisional measurement methods have been developed. However, in these methods, inadequate accuracy and the discontinuity of data were observed on the reconstructed image. In this study, a new divisional measurement method was developed and the overall accuracy was evaluated. The standardized stone model, which has three spheres, was kept by the specifically designed high precision jig. The distances between the reference points of each sphere were measured by using a 3-D curved shape measurement apparatus with a laser source. Then the values were compared with those obtained by using a contact type 3-D measurement apparatus. There were slight differences between the two methods, but they were not statistically significant. In addition, when the individual data were combined, the distances between the reference points of each sphere were not significantly different. These results suggested that the shape of the study cast can be accurately measured by the divisional measurement method.

Image Processing, Computer-Assisted↗

Elastic outward bending of loaded buccal and lingual premolar walls in relation to cavity size and form.

The aim was to study effects of the size and form of the occlusal part of Class II cavities on elastic outward bending during loading of buccal and lingual walls, separated by the preparation. Twenty newly extracted caries-free premolars were used. A special arrangement for standardized cavity preparation was set up. In order to obtain accurate measurements of the outward bending of loaded cavity walls, an electronic tensile test device was constructed. Methodologic studies showed an insignificant departure from linearity between between outward bending and load. All deformation was elastic. Correction factors were determined for strain of the apparatus as well as for indentation in the tooth substance. Measurement accuracy was calculated to +/- 0.12 N for force and +/- 0.2 micron for movement. In accordance with statistical principles, a few outlying measurements were discarded. The outward bending of buccal and lingual walls of cavities suitable for conservative restoration with dental amalgam was about 0.15 micron per Newton. Outward bending increased dramatically with exaggerated cavity depth and width. In the light of present knowledge of average chewing forces and tooth contacts in the habitual intercuspal position in young dentate adults, there seems to be little risk of leakage between conservative restorations and cavity walls as a result of elastic outward bending, though the risk certainly does increase with the depth and width of the cavity.

Bicuspid↗

Temporomandibular disorders among school children.

A large volume of literature is available on the Temporomandibular Disorders (TMD) in adults. However, relatively little information is available on this condition in children. The present study is aimed at providing a comprehensive survey on Temporomandibular Joint Status in Saudi Arabian Children in the Western Region of the Kingdom. This is a report on the prevalence of TMDs in children. Five hundred and two children aged 3-7 years old were examined for signs and symptoms of TMDs in a classroom setting. Eighty-three (16.53%) presented with TMDs, with 34 (14.46%) males 49 (18.35%) female (This difference between sexes is significant P < 0.001); 39 (7.8%) of the children had TMJ sounds; 34 (6.77%) had associated muscle tenderness; 13 (2.59%) had pain during TMJ movement; 17 (3.39%) had deviation of the mandible during movement; and 9 (1.7%) had a restricted mouth opening. There is a general tendency for these signs and symptoms to be more significantly prevalent in females. None of the children had sought dental treatment for these conditions. The importance of TMJ examinations in the overall clinical assessment of the pediatric patient should not be overlooked. Identifying this subject early in life would allow us to follow up the patient and intervene in the appropriate time to avoid future problem in the TMJ apparatus.

Age Distribution↗

Effect of acid type on kinetics and mechanism of dental enamel demineralization.

The influence of acid type (pKa effects) of weak organic acid buffers on dissolution kinetics of dental enamel was critically examined for rigorous testing of the behavioral validity of the physical model of Patel et al. (1987). Quantitative evaluation of this model indicated that monitoring initial dissolution rates was a viable approach to critical testing of the model. Initial dissolution rates were determined in 0.1 mol/L acetate (pKa = 4.77), benzoate (pKa = 4.20), and salicylate (pKa = 2.98) buffers (pH = 4.50, mu = 0.50), with ground bovine enamel blocks of known surface area mounted in a rotating disk apparatus. The Levich theory was used to study dependence of dissolution rates on stirring rates in these buffers. The experimental data were analyzed by the physical model which includes pKa effects, complexation of the buffer anion with the other ions, surface kinetics, simultaneous diffusion and equilibrium of all species in enamel pores, diffusion layer thickness, and bulk solution composition. The KIAP (formula: see text) governing the dissolution reaction and the surface resistance factor were deduced from the model. Dissolution kinetics was also followed in these buffers in the presence of calcium or phosphate common ions. In effect, by conducting both the stirring rate studies and common ion experiments, we derived the driving force function independently by these two techniques. The results obtained in this study were consistent with the model, indicating that pKa effects on the dissolution of dental enamel can be accounted for quantitatively by the model, and it was found that weak acids do not influence either the apparent solubility or the surface reaction process of bovine dental enamel.

Acetates↗

Magnetron sputtered tin coatings on unbiased ceramic substrates.

OBJECTIVES: The aim of this work was to study the application of tin oxide coatings on alumina, with a view to developing improved bonding for high-alumina dental ceramics. METHODS: By use of a magnetron sputtering technique, alumina was coated with tin which was subsequently oxidized, and the bond strength of coated surfaces to a resin-based dental cement was measured in tension. Tensile bond strength data were assessed for their degree of skewness and the homogeneity of the residual variances with a view to applying appropriate transformations prior to performing ANOVA with subsequent Tukey's analysis as necessary. The color of coatings, as a function of the amount of oxidation of the surface, was noted. Coatings were characterized by SEM and EDAX. It has been found possible to produce esthetic tin oxide coatings on alumina using a simplified magnetron sputtering apparatus in conjunction with post-deposition oxidation. RESULTS: Although mean tensile bond strength (TBS) values in excess of 15 MPa were recorded for a number of groups, no causal relationship was found between coating time and mean TBS. SIGNIFICANCE: The need exists for improved bonding of alumina-based ceramics; further development of a magnetron sputtering technique may provide the means for achieving this.

Aluminum Oxide↗