Effect of occlusal hypofunction on centre of resistance in maxillary central incisor using the finite element method.

OBJECTIVES: To determine differences in the location of centre of resistance (Cres) between functional and hypofunctional teeth and to evaluate the relationship between the pulp cavity volume and locations of the Cres, using the finite element (FE) method. DESIGN: Retrospective cohort study. PARTICIPANTS: FE models of right maxillary central incisor, derived from cone-beam computed tomography (CBCT) images of 46 participants, were divided into normal function (n = 23) and hypofunction (n = 23) groups using anterior overbite and cephalometric measurements. METHODS: Measurements of the tooth and pulp cavity volume were made from the CBCT. Cres levels were presented as percentages of the root length from the root's apex. All data were analysed and compared using the independent t-test (P < 0.05). The relationship between the location of Cres and volume ratios were evaluated statistically. RESULTS: The means of the pulp cavity/tooth volume and root canal/ root volume ratio of the maxillary central incisor in the anterior open bite group were significantly greater than those in the normal group. The average location of Cres in the anterior open bite group was 0.6 mm (3.7%) apically from the normal group, measured from root apex. The difference was statistically significant (P < 0.01). There was a significant correlation between root canal/root volume ratio and locations of Cres (r = -0.780, P < 0.001). CONCLUSIONS: The Cres in the hypofunctional group was located more apical than the functional group. As the pulp cavity volume increased, the level of Cres shifted apically.

Wear of various restorative materials against 5Y-ZP zirconia.

STATEMENT OF PROBLEM: The ceramic 5-mol% yttria-stabilized zirconia (5Y-ZP) has been developed for dental use in the esthetic zone with greater translucency than 3-mol% yttria-stabilized zirconia (3Y-ZP). However, studies on the wear behavior of 5Y-ZP zirconia against clinically relevant antagonist materials are lacking. PURPOSE: The purpose of this in vitro study was to investigate the wear behavior of 5Y-ZP zirconia against the antagonists 5Y-ZP zirconia, lithium disilicate, palladium alloy, and human enamel. MATERIALS AND METHODS: Flat specimens (n=8) were fabricated from 5Y-ZP zirconia, lithium disilicate, palladium alloy, and human central incisor enamel. A custom wear-simulating device with a sliding pin-on-plate configuration was used for a total of 120 000 wear cycles at 1.6-Hz frequency under a 49-N vertical load while submerged in distilled water at room temperature. The wear volume and maximum wear depth of flat specimens were evaluated with a 3D profilometer. Scanning electron microscopy was used to analyze the characteristics of the worn surfaces. RESULTS: After wear simulation, the 5Y-ZP zirconia and palladium-silver alloy specimens exhibited the least amount of material loss, both in terms of maximum wear depth and wear volume (0.079 ±0.042 µm, 0.001 ±0.001 mm3 and 0.637 ±0.307 µm, 0.001 ±0.000 mm3, respectively). This was followed by human enamel (6.034 ±1.086 µm, 0.009 ±0.001 mm3) and by lithium disilicate, which showed excessive material loss (38.342 ±2.569 µm, 0.213 ±0.024 mm3). Scanning electron microscopy revealed variations in wear mechanisms among the materials. CONCLUSIONS: The 5Y-ZP zirconia and palladium-silver alloy exhibited the lowest wear, followed by human enamel and lithium disilicate. Slight grain dislodgement was displayed on worn 5Y-ZP surfaces, while more apparent grain dislodgement and wear grooves were found on lithium disilicate. Plastic deformation of worn palladium-silver alloy accumulated at the end of wear track. Cracks were detected in the human enamel specimens.

Does pulp cavity affect the center of resistance in three-dimensional tooth model? A finite element method study.

OBJECTIVES: To compare the center of resistance (Cres) of the maxillary central incisor in models with and without the pulp cavity and to evaluate the association of pulp cavity/tooth volume ratio and difference in Cres position between the two models. MATERIALS AND METHODS: CBCT images of the right maxillary central incisor were collected from 18 subjects. Pulp cavity/tooth volume ratio was measured, and finite element models of teeth and periodontal structures were generated. Cres location was presented as a percentage of root length measured from the root apex. Differences in Cres positions between models were compared using the paired t-test, while the correlation between pulp cavity/tooth volume ratio and a difference in Cres was evaluated by Pearson's correlation coefficient. RESULTS: For the pulp cavity model, the average location of the Cres measured from the apex of the root was 58.8% ± 3.0%, which resulted in a difference of 4.1% ± 1.1% (0.5 mm) apically, when compared with the model without pulp cavity. Differences in Cres between the models were statistically significant (P < 0.01), while the correlation between pulp cavity/tooth volume ratio and a difference in Cres between models was significantly positive (r = 0.709, P = 0.001). CONCLUSIONS: In the pulp cavity model, the Cres was located in a more apical position. The difference in Cres between models increased as the pulp cavity/tooth volume ratio increased. CLINICAL RELEVANCE: The line of force must be applied more apically in the pulp cavity model to achieve the desired orthodontic tooth movement.

Three-dimensional volumetric evaluation of dental pulp cavity/tooth ratio in anterior open bite malocclusion using cone beam computed tomography.

OBJECTIVES: To assess and compare pulp cavity/tooth volume ratio of maxillary permanent teeth between patients exhibiting anterior open bite malocclusion and those exhibiting anterior normal overbite using cone beam computed tomography (CBCT). MATERIALS AND METHODS: 3D dental images from 44 patients aged between 15 and 29 years were analyzed. The DICOM files of all dental images were imported into an image processing software for calculating pulp cavity volume and tooth volume. Differences of pulp cavity volume, tooth volume, and pulp cavity/tooth volume ratio of each tooth type from both types of occlusions were analyzed using the independent t test. The intra-class correlation coefficient was used to evaluate intra-examiner reliability. RESULTS: The means of pulp cavity/tooth volume ratio in anterior open bite group were significantly greater than those in anterior normal overbite group (central incisor p = 0.001; lateral incisor p = 0.00025 and canine p = 0.004). The means of root canal/root volume ratio in anterior open bite group were significantly greater than anterior normal overbite group (central incisor p = 0.00001; lateral incisor p = 0.00007; and canine p = 0.001), whereas there were no significant differences of the means of pulp chamber/crown volume was observed. CONCLUSION: Anterior open bite malocclusion might lead to an increase of the pulp cavity volume and decrease of the tooth volume due to occlusal hypofunction. CLINICAL RELEVANCE: Orthodontic force should be carefully determined in anterior open bite patient due to the greater root canal volume and lesser root volume.

Validity and Reliability of Intraoral Camera with Fluorescent Aids for Oral Potentially Malignant Disorders Screening in Teledentistry.

There is limited documentation of using fluorescence images in oral potentially malignant disorders (OPMDs) and oral cancer screening through the field of teledentistry. This study aims to develop and evaluate the validity and reliability of the intraoral camera with the combination method of autofluorescence and LED white light used for OPMDs and oral cancer screening in teledentistry. The intraoral camera with fluorescent aids, which uses a combined method of both autofluorescence and LED white light, was developed before the device was evaluated for validity and reliability as a OPMDs screening tool for teledentistry. All lesions of thirty-four OPMD patients underwent biopsy for definitive diagnosis and were examined by an oral medicine specialist. Both images under autofluorescent and LED white light mode captured from the device were sent online and interpreted for the initial diagnosis and dysplastic features in addition to being compared to the direct clinical examination and histopathological findings. The combination method was also compared with autofluorescence method alone. The device provided good image quality, which was enough for initial diagnosis. Using the combination method, sensitivity, specificity, PPV, and NPV of the device via teledentistry were 87.5%, 84.6%, 63.6%, and 95.7%, respectively, which were higher than autofluorescence method alone in every parameter. The concordance of dysplastic lesion was 85.29% and 79.41% for category of lesion. The validity and reliability results of the combination method for the screening of dysplasia in OPMDs were higher than autofluorescent method alone. The intraoral camera with fluorescent aids for the OPMDs screening can be utilized for screening via teledentistry.