Dental application of novel finite element analysis software for three-dimensional finite element modeling of a dentulous mandible from its computed tomography images.

This study focused on the application of novel finite-element analysis software for constructing a finite-element model from the computed tomography data of a human dentulous mandible. The finite-element model is necessary for evaluating the mechanical response of the alveolar part of the mandible, resulting from occlusal force applied to the teeth during biting. Commercially available patient-specific general computed tomography-based finite-element analysis software was solely applied to the finite-element analysis for the extraction of computed tomography data. The mandibular bone with teeth was extracted from the original images. Both the enamel and the dentin were extracted after image processing, and the periodontal ligament was created from the segmented dentin. The constructed finite-element model was reasonably accurate using a total of 234,644 nodes and 1,268,784 tetrahedral and 40,665 shell elements. The elastic moduli of the heterogeneous mandibular bone were determined from the bone density data of the computed tomography images. The results suggested that the software applied in this study is both useful and powerful for creating a more accurate three-dimensional finite-element model of a dentulous mandible from the computed tomography data without the need for any other software.

New method for determining surface roughness of tongue.

OBJECTIVE: The degree of atrophy of the lingual papillae in elderly individuals was evaluated using a quantitative method. SUBJECTS AND METHODS: One hundred and eighty-two subjects living in nursing homes and 20 healthy adults as controls were studied. To express the degree of atrophy of the lingual papillae quantitatively, lingual surface roughness was determined by taking an impression with silicone dental material. Based on the impressions obtained from the elderly subjects, they were classified by three expert dentists into three groups: Normal, Smooth and Rough. The same determinations were also performed in the 20 healthy controls and compared with 38 of the elderly subjects who had agreement from all of the experts and without the presence of fissures (Normal, n = 6; Smooth, n = 12; Rough, n = 20). RESULTS: The roughness average value for the controls was 65.0 µm, while that for the elderly subjects in the Normal, Smooth and Rough groups was 73.9 µm, 42.2 µm and 94.1 µm, respectively, which were significantly different. CONCLUSION: The present results indicate that the present technique of obtaining an impression of the tongue surface is simple and reliable for routine evaluation and quantification of the degree of atrophy as well as morphology of the lingual papillae.

Effects of sandblasting media and steam cleaning on bond strength of titanium-porcelain.

The effects of sandblasting media and steam cleaning treatment after sandblast were examined on tensile bond strength of porcelain to titanium. The use of the commercially available silica-coated alumina particles for sandblast was significantly effective for increasing bond strength than the conventional alumina. It might be due to the increased surface roughness and existence of remaining silica on titanium surface. Additional application of the steam cleaning on titanium surface after sandblasting could make the surface configuration clear in SEM by removing some sandblasted particles loosely embedded in titanium as well as the debris and oily contaminants. The resultant bond strength was significantly improved to reach almost the maximum strength of this porcelain-titanium system regardless of the kind of sandblasting media used, which was confirmed by the observation of the failure mode showing that most of the fracture surface was occupied by cohesive failure in porcelain.

Three-dimensional finite element modeling from CT images of tooth and its validation.

The aim of this study was to develop a three-dimensional (3D) finite element (FE) model of a sound extracted human second premolar from micro-CT data using commercially available software tools. A detailed 3D FE model of the tooth could be constructed and was experimentally validated by comparing strains calculated in the FE model with strain gauge measurement of the tooth under loading. The regression coefficient and its standard error in the regression analysis between strains calculated by the FE model and measured with strain gauge measurement were 0.82 and 0.06, respectively, and the correlation coefficient was found to be highly significant. These results suggested that an FE model reconstructed from micro-CT data could be used as a valid model to estimate the actual strains with acceptable accuracy.

Electropolishing of CP titanium and its alloys in an alcoholic solution-based electrolyte.

A newly developed electropolishing system, equipped with an original agitation function for an electrolyte and using a safe electrolyte composed of an alcoholic solution, was applied for wrought and cast CP titanium and its alloys. Surface roughness and morphology of the polished surfaces were then examined. Under an electrolytic condition of 70-75 V, 2.0 kA/m2, and 30 degrees C, wrought CP Ti and Ti-6Al-4V alloy achieved an apparent mirror-like finishing with an average surface roughness (Ra) of 0.03 and 0.12 microm respectively. Under the same condition, on the other hand, cast CP Ti and Ti-6Al-7Nb alloy produced rougher polished surfaces with average Ra values of 0.67-0.80 microm, and the finishing was apparently shiny, but not mirror-like. SEM observation of the polished surfaces showed that wrought CP Ti was even and completely featureless, while wrought Ti-6Al-4V alloy was pitted. For cast CP Ti, a needle-like phase containing traces of iron was observed on the polished surface.

Cementum crack formation by repeated loading in vitro.

BACKGROUND: In this study, the hypothesis was adopted that fatigue destruction may develop on the cementum of the root surface because of the repeated occlusal stresses loaded on the tooth as in the case of prolonged occlusal trauma. The purpose of this study is to clarify whether cemental fatigue destruction occurs when repeated stresses are loaded on the occlusal surface of a tooth. METHODS: The teeth used were five human mandible premolars from individuals 14 to 22 years of age. The teeth were freshly extracted in orthodontic treatment. They were free of decay and fillings, and their roots were straight. One half of the root was embedded in cold curing acrylic resin, and a compressive load of 5.0 kgf was repeatedly applied along the tooth axis in water 1 million times with a speed of one time per second. Changes in the tooth surface were observed by taking photographs with a stereoscopic microscope and a digital camera after every 100,000 loadings. Cracks were dyed with 2% methylene blue solution, and crack areas were measured using gray-scaled and binary-processed photographs. Data were analyzed using image analysis software. RESULTS: It was confirmed that cracks significantly developed on the buccal, mesial, and distal surfaces but not on the lingual surface; crack areas showed a tendency to significantly increase after 500,000 loadings; extension of the crack from the cemento-enamel junction to the root apex increased with time, and the average extension was 0.67 +/- 0.12 mm after 1 million loadings. CONCLUSION: This study revealed that cementum cracks developed in the cervix by repeated loadings and extended toward the root apex with time, suggesting that repeated stresses by occlusion or strong stresses such as by bruxism may trigger the development of site-specific attachment loss, which is one of the potential factors inducing periodontal diseases.

Use of a tongue-pressure measurement system to assist fabrication of palatal augmentation prostheses.

PURPOSE: The purpose of this study was to determine a baseline value of tongue pressure on the palatal region in normal subjects that could then be used to assist in fabrication of a palatal augmentation prosthesis (PAP). MATERIALS AND METHODS: A tongue-pressure measurement system with 36 rubber pressure sensors was constructed for this study. This system was applied to 16 normal subjects, and the tongue pressure on the palatal region was measured when they were swallowing. RESULTS: The maximum tongue pressures seen during swallowing were 85.0 g/cm2 in the early stage, 95.0 g/cm2 in the middle stage, and 93.0 g/cm2 in the late stage. The average maximum tongue pressure throughout swallowing was 91.0 g/cm2. The tongue pressure in the early stage ranged from 3.37 g/cm2 to 8.74 g/cm2. A significant difference was found between the anterior and the posterior regions and between the central and the posterior regions. The value in the middle stage ranged from 5.32 g/cm2 to 10.22 g/cm2. Significant differences were found between the anterior and the posterior regions and between the central and the posterior regions. Values in the late stage ranged from 6.80 g/cm2 to 7.91 g/cm2. CONCLUSION: The average maximum tongue pressure against the palate of approximately 90 g/cm2 suggests that a PAP sufficient for swallowing should be strong enough to withstand this amount of pressure. The device is also useful to check for variations in the tongue contact area during trial of the prosthesis.

Application of alumina coping to porcelain laminate veneered crown: part 1 masking ability for discolored teeth.

A densely sintered high-purity alumina has been successfully utilized as a coping for all-ceramic crown. In order to apply the alumina coping to the porcelain laminate veneer restoration for the discolored teeth, the present study evaluated its masking ability when it was thinner than the proposed thickness for the crown. Colorimetric examination was performed on white and black backgrounds for the 0.7 mm thick porcelain laminate veneer with 0.40 or 0.25 mm thick alumina coping and 0.7 mm thick porcelain without coping. With the presence of the coping, the porcelain appeared significantly lighter. Judging from the calculated color differences delta E and the literature, it was suggested that the masking ability of the alumina coping would be sufficient with a 0.25 mm thickness for the porcelain laminate veneer for heavily discolored teeth.

Temperature- and deflection- dependences of orthodontic force with Ni-Ti wires.

Orthodontic forces of Ni-Ti wires examined under the retrained condition on the dental arch model were evaluated with the changes in temperature and deflection. The tested specimens were a commercially available superelastic (W1) wire and two shape memory wires with their nominal A(f) points were 35 degrees C (W2) and 40 degrees C (W3), respectively. They showed typical superelastic hysteresis loops under the restraint condition at 40 degrees C. The force levels were significantly larger than those generally obtained by simple three-bending test. The recovery forces in the plateau region at 1.0 mm deflection were much larger than desired in the clinical guidelines around oral temperatures. In the shape memory wire W3, the recovery force rapidly decreased to zero by a small reduction of the deflection from its maximum. However, the wire again exerted the force with the remaining permanent deflection by temperature rising. It was small compared to the guidelines of desirable orthodontic force and seemed to be useful especially for the hypersensitive patients.

Corrosion behavior of dental alloys in various types of electrolyzed water.

The corrosion behavior of dental alloys was examined in electrolyzed strong acid water, weak acid water and neutral water using a 7-day immersion test. The precious metal alloys, gold alloy. Au-Ag-Pd alloy and silver alloy showed the greatest surface color change and dissolution of constituents in the strong acid water and the smallest in the neutral water. The release of Au from gold alloy was especially marked in the strong acid water. Co-Cr alloy showed greater corrosion and tarnish resistance in the strong acid water rather than in the weak acid water and the neutral water. X-ray microanalysis revealed that the corrosion products on the precious metal alloys were silver chloride crystals and the thin brown products on Co-Cr alloy were cobalt and chromium oxides. Ti was sound in all three types of electrolyzed water. The neutral water appeared the least corrosive to metals among the three types showing equivalent bactericidal activity.

Durability of bactericidal activity in electrolyzed neutral water by storage.

Electrolyzed strong and weak acid waters have been widely used for sterilization in clinical dentistry because of their excellent bactericidal activities. Electrolyzed neutral water was recently developed with a new concept of long-term good durability in addition to the excellent bactericidal activity similar to acid waters. The present study, evaluated the storage life of this water compared with the acid waters in terms of the changes in pH, oxidation-reduction potential (ORP), residual chlorine and bactericidal activity under several conditions using Staphylococcus aureus 209P. The strong acid water showed a rapid deterioration of its bactericidal activity. The weak acid and neutral waters exhibited excellent durability. Although all the bacteria were annihilated by the contact with the waters even stored for 40 days in the uncapped bottle, the neutral water was superior in further long-term duration.