1,720,976 research outputs found
Vibroacoustic analysis of dental air turbine noise
No full textObjective The objective of this study is to analyze the noise mechanism of dental air turbine handpiece with vibroacoustic simulation. Materials and methods The operational part of the Gentle Silence Lux 8000B (KaVo Dental GmbH) was disassembled and scanned. The scanned data were rendered to smooth irregularities and then virtually reassembled. The rendering was 3D mesh modeled for the analysis. And, the interior void space and exterior space was mesh modeled as air layer. As per simulation input informations, the material property of steel was provided for the handpiece components. Supplied air pressure of 0.22 MPa at the inlet and static temperature of 25 degrees C was provided as operating conditions. Twenty virtual microphones were arrayed to measure the noise. Vibroacoustic noise simulation was performed with ACTRAN 2021 (MSC software corporation). Results The mean value of noise ranged from 49.88 to 66.38 dB while the peak value ranged from 69.53 to 81.64 dB depending on the microphone position. All microphones showed the similar noise pattern which had peak amplitude at around 4500 Hz. The calculated natural frequency of interior air layer was 4478.92 Hz and 7573.77 Hz. Discussion The simulated result showed similar tonal noise of dental handpiece suggesting air resonance phenomenon as a possible cause of dental handpiece noise. Conclusion Vibroacoustic analysis of the air layer contained within the dental air turbine handpiece showed the resonance peak noise at 4478.92 Hz under the simulated conditions.N
Reliability of digital repeated-scan superimposition and single-scan techniques for wear volume loss assessment on flat surfaces
No full textObjectives: Evidence on the reliability of digital techniques for wear volume assessment using three-dimensional (3D) scan datasets is scarce. This study evaluated the reliability of a repeated-scan superimposition technique and two single-scan techniques in assessing wear volume loss on flat surfaces of 3D-printed resin specimens. Methods: Cuboid-shaped (15×10×10 mm) resin specimens were 3D-printed (n = 14) and scanned before and after 200,000 cycles of masticatory simulation. For the repeated-scan superimposition technique, digital 3D models of specimens before and after masticatory simulation were superimposed, and the volume loss was determined. The first single-scan technique utilized a computer-aided design freeware program, while the second one employed a 3D-metrology software program. In the freeware program, the worn area of 3D objects was edited directly to obtain a flat surface. In the 3D-metrology software program, the worn area was deleted first and then filled to the flat surface. The volume differences before and after editing were calculated in each software program. Agreement between the three measurement techniques was determined through intraclass correlation coefficients (ICCs). One-way analysis of variance was performed to compare the wear volume loss assessed by the three techniques (α = 0.05). Results: High inter-technique reliability was observed between the three assessment techniques (ICC = 0.998, p < .001). On pair-wise comparisons of two of the three techniques, all pairs showed high consistency (ICC ≥ 0.999, p < .001). No significant difference was found in the wear volume loss assessed using the three techniques (p = .996). Conclusions: Digital repeated-scan superimposition and two single-scan techniques demonstrated high reliability in assessing wear volume loss on flat surfaces. Clinical significance: The repeated-scan superimposition technique can be effectively utilized to assess wear volume loss of anatomically shaped specimens and flat surfaces. This study indicates that the single-scan techniques may serve as a suitable alternative to the repeated-scan superimposition technique when evaluating wear volume loss of flat surfaces.N
Panoramic radiographic evaluation of the mandibular morphological changes in elderly dentate and edentulous subjects
No full textObjective. The aim of the present study was to analyze the changes in the gonial angle, ramus height, condyle height and cortical bone thickness in relation to gender and dental status in elderly patients. Materials and methods. The study population comprised 240 patients (age ranged from 60-69 years) who had digital panoramic radiographs taken for various purposes. One group consisted of 120 patients, 60 men and 60 women, who had all natural teeth present except for third molars. The second group consisted of the remaining 120 patients (60 men and 60 women) who were in a completely edentulous state (maxilla and mandible). The gonial angle, ramus height, condylar height and cortical bone thickness of the mandible were measured by computer software on their panoramic radiographs. Results. Women showed larger gonial angles than men, while men had greater cortical bone thickness and ramus height (p < 0.05). However, no significant difference in condylar height was found between both genders (p > 0.05). Edentulous subjects had a larger gonial angle than dentate subjects, while dentate subjects had greater cortical bone thickness on both sides and left side of condylar height (p < 0.05). The gonial angle had statistically negative correlations with cortical bone thickness and ramus height, regardless of gender. Conclusions. The outcomes of the present study indicate that the edentulous women undergo morphological changes of the mandible influenced by the dental status more than men.N
Improving wear resistance of acrylic resin denture teeth by using zirconia complete crowns fabricated with a CAD-CAM double-scanning method: A clinical report
No full text© 2022 Editorial Council for The Journal of Prosthetic DentistryAcrylic resin denture teeth can wear and chip when opposed by zirconia prostheses. This clinical report describes the use of zirconia complete crowns to prevent these problems. The predictability of treatment was improved by using the computer-aided design and computer-aided manufacturing (CAD-CAM) double-scanning method.N
A digital method for wear volume loss analysis using a single-scan three-dimensional dataset
No full textA straightforward digital method of evaluating wear volume loss is described. This method allows the measurement of the wear by analyzing only the three-dimensional scan dataset of the worn specimen without needing a separate baseline scan. Compared to the conventional method, involving superimposition of the two datasets scanned before and after the wear test, this method can reduce labor and accuracy errors caused by repeated scans and superimposition procedures. Further, this analysis can be conducted using free computer-aided design software, which makes it more efficient for the analysis of wear volume loss of restorative materials. (c) 2021 Association for Dental Sciences of the Republic of China. Publishing services by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/ licenses/by/4.0/).Y
3D finite element analysis of stress distribution on the shape of resected root-end or with/without bone graft of a maxillary premolar during endodontic microsurgery
No full textBackground/purpose: Apical root resection pattern affects the stress distribution behavior in the apical region of the resected tooth. The purpose of the study was to compare the biomechanical responses of resected teeth between endodontic microsurgery (horizontal resection) and targeted endodontic microsurgery (round resection). Materials and methods: Five different models were developed. The basic model without resection (NR) was regarded as the control model, and the others involved: horizontal resection without bone grafting (HN), horizontal resection with bone grafting (HG), round resection without bone grafting (RN), and round resection with bone grafting (RG) models. A static load of 100 N was applied to the buccal and palatal cusps of all the teeth in a 30° oblique direction. The maximum von-Mises stress and tooth displacement values were analyzed and compared. Results: Both the HN and RN models exhibited lower stress distribution values on bone compared with the NR (control) model. Regarding maximum stress distribution at the root apex, the stress value of the RN model was slightly higher compared to the HN model, whereas the RG model displayed a slightly lower stress value in comparison with the HG model. For maximum tooth displacement value, there were no significant differences between the HN and RN models, as well as the HG and RG models. Conclusion: The round resection pattern had comparable stress distribution behaviors at the root apex and tooth displacement values with the horizontal resection pattern. Targeted endodontic microsurgery might provide better biomechanical response of the resected tooth after root-end resection.Y
Effect of layer thickness and printing orientation on the color stability and stainability of a 3D-printed resin material
No full text© 2022 Editorial Council for The Journal of Prosthetic DentistryStatement of problem: Although 3-dimensional (3D)–printed resin prostheses are widely used, studies on the effects of the manufacturing parameters of 3D printing on the color stability and stainability of these prostheses are lacking. Purpose: The purpose of this in vitro study was to investigate the effects of layer thickness and printing orientation on the color stability and stainability of a 3D-printed resin. In addition, the influence of roughness and water contact angle was evaluated. Material and methods: Color changes (ΔE00) in tooth-colored resin specimens produced by 3D printing with 2 different layer thicknesses and 3 different printing orientations and immersed in 3 types of aging media (distilled water, coffee solution, and wine) were evaluated (n=10). The CIELab color values were measured with a spectrophotometer at baseline and different time points (1, 3, 7, 15, and 30 days). The surface roughness (Ra) of resin specimens was measured at various time points (baseline, 7, 15, and 30 days) by confocal laser scanning microscopy after immersion in coffee solution (n=15). The water contact angle was determined by using the sessile drop method (n=10). The ΔE00 values were analyzed by using the 3-way repeated measures ANOVA followed by the Bonferroni test and Dunnett T3 test (α=.05). Ra values were analyzed by 3-way repeated measures ANOVA (α=.05). The water contact angle data were analyzed by 2-way ANOVA (α=.05). Results: The 3-way repeated measures ANOVA showed that layer thickness, printing orientation, and storage time significantly influenced the ΔE00 values of the 3D-printed resin specimens in each aging medium (P<.001). The ΔE00 values in the 0-degree subgroups were significantly lower than those in the 45- and 90-degree subgroups (P<.05). The ΔE00 values in the 25-μm thick groups were significantly higher than those in the 100-μm thick groups (P<.05). The ΔE00 values demonstrated an increase up to 15 days in all aging media. In distilled water, the ΔE00 values of the specimens increased or decreased depending on the groups, whereas in the coffee solution, the values decreased after 15 days (P<.001); in red wine, the values demonstrated a continuous increase up to 30 days in all groups (P<.001). The 3-way repeated measures ANOVA showed that the Ra values did not change significantly with immersion time (P=.444). The 2-way ANOVA showed that the water contact angle was not significantly affected by layer thickness (P=.921) or printing orientation (P=.062). Conclusions: Layer thickness and printing orientation affected the color stability and stainability of the 3D-printed resin. The discoloration of the 3D-printed resin differed with time, depending on the type of aging media used.N
심한 골흡수가 있는 하악에서 임플란트지지-보철치료에 대한 삼차원 유한요소 분석을 이용한 생체역학적 분석
Get PDF학위논문(석사)--서울대학교 대학원 :치의학대학원 치의과학과,2019. 8. Kwon, Ho-Beom.1. 목 적
이 연구의 목적은 협측 골흡수가 동반된 하악 부분 무치악 모형에서 협측 캔틸레버가 있는 보철물의 생체역학적 움직임을 평가하고, 여러 보철물 설계 디자인을 비교하는 것이었다.
2. 방 법
환자의 CT 영상을 기반으로 총 3개의 유한요소 모형을 제작하였다. 유한요소 모형은 제2소구치와 제1대구치가 결손된 하악 구치부에 임플란트가 식립되고 제1소구치와 제2대구치가 포함된 모형이었다. 첫 번째 모형(CP2)은 골 양에 기반하여 2개의 임플란트가 식립된 모형이었고 보철물에 협측 캔틸레버가 존재하였다. 두 번째 모형(BP2)은 보철물을 기준으로 식립된 2개의 임플란트가 포함되었다. 세 번째 모형(BP3)은 보철물을 기준으로 식립된 3개의 임플란트가 포함된 모형이었다. 모든 모형에서 466.4N의 전하중이 지대주나사에 가해졌다. 저작력을 가정한 하중이 교합면에 75도로 가해졌다. 피질골, 해면골 및 임플란트 구성요소에서 최대등가응력이 관찰되었다.
3. 결 과
캔틸레버 모형이 다른 디자인 만큼 우수한 응력 분포를 나타내었다. 최대등가응력은 모형 CP2와 모형 BP3에서는 제1소구치 지대주에, 모형 BP2 에서는 대구치지대주에 집중되었다. 피질골에서 최대 등가 응력은 주로 임플란트 경부 주위에 집중되었으며 CP2에서 293 MPa, BP2 에서 348 MPa, 그리고 BP3 에서 791 MPa 이었다. 해면골에서는 CP2를 제외하고 모두 소구치 부위 임플란트의 첨부에 최대등가응력이 집중되었고, CP2에서는 응력이 임플란트 경부 주변에 집중되었다. 해면골에서의 최대등가응력은 CP2 에서 26 MPa, BP2 에서 348 MPa, BP3에서 791 MPa 이었다. 최대등가응력의 최대값은 CP2 와 BP2에서 유의미한 차이가 없었다.
4. 결 론
골흡수가 심한 부분 무치악 하악에서 골의 양을 기반으로 임플란트를 식립했을 때 보철물을 기준으로 식립하는 방법 만큼 좋은 결과를 보여주었다. 캔틸레버 보철물이 있는 모형에서는 보철물에서 가장 큰 최대등가응력이 관찰되었다. 골에서는 캔틸레버 보철물이 있는 모형에서 가장 작은 최대응가응력이 관찰되었다.1. Purpose
The purpose of this study was to evaluate the biomechanical behavior of a buccal cantilever and to compare it with other prosthetic designs to determine the best design in terms of stress distribution within the bone of a buccally resorbed partially edentulous mandible.
2. Material and methods
Based on patient computed tomography (CT) scan data, three finite element models were created. Each model composed of the severely resorbed mandible, the first premolar, the second molar and the implants that replaced the second premolar and the first molar. The first model had two implants placed based on bone quantity creating a buccal cantilever (CP2). The second model had two prosthetic-driven implants (BP2). The third model had three prosthetic-driven implants (BP3). In all models preload of 466.4 N on the abutment screw was applied. A load simulating chewing cycle was applied at seventy-five degrees to the occlusal surfaces of the prostheses. The maximum load magnitude was 262 N. The maximum von Mises stresses were demonstrated and compared in cortical and cancellous bone as well as the implant components.
3. Results
The results showed that the cantilever model exhibited better stress distribution compared to the other models. The overall maximum von Mises stress in each model was concentrated on the premolar abutment for CP2 (1036 MPa), on the molar screw for BP2 (982 MPa) and on the premolar abutment for BP3 (922 MPa). In the cortical bone, the maximum von Mises stress was around the neck of the implants with values as follows: 293 MPa in CP2, 348 MPa in BP2 and 791 MPa in BP3. For the cancellous bone von Mises stress was concentrated at the apex of the premolar implants for BP2 and BP3. For CP2 the maximum von Mises stress was around the implant neck. The recorded values were 26 MPa in CP2, 348 MPa in BP2 and 791 MPa in BP3. Von Mises stress peaks in the implants components did not exhibit significant difference.
4. Conclusion
Considering the severely resorbed partially edentulous posterior mandible, placing implants based on the available bone quantity is more desirable than prosthetic-driven implant placement in terms of biomechanical behavior. The cantilever model created the highest maximum von Mises stress among the three models with regard to the prosthesis. However, when considering the bone, the cantilever model recorded the lowest maximum von Mises stress.Ⅰ. INTRODUCTION, page 1
Ⅱ. MATERIAL AND METHODS, page 7
Ⅲ. RESULT, page 11
Ⅳ. DISCUSSION, page 12
V. CONCLUSION, page 18
REFERENCES, page 19
TABLES, page 27
FIGURES, page 30
국문초록, page 40Maste
Stress Distribution on Trephine-Resected Root-end in Targeted Endodontic Microsurgery: A Finite Element Analysis
No full textCopyright © 2022 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.INTRODUCTION: This study aimed to determine if stress distribution from occlusal loads after targeted endodontic microsurgery (TEMS) differed for trephine-resected flat and curved root-ends, with and without bone graft. METHODS: Finite element analysis models were constructed from cone-beam computed tomography data of a TEMS-treated maxillary central incisor. Models included flat and curved resected root-ends, with and without apical bone graft, and normal or root canal filled controls. In centric occlusion, axial force was directed on mesial and distal lingual marginal ridges at 120° angle. For lateral excursion, additional mesiodistal forces were applied from centric occlusion. For edge biting, axial force was directed on the incisal edge. Under occlusal loads, stress distribution patterns on tooth and root-end circumference were analyzed. RESULTS: In normal and root filled controls, occlusal stress was distributed on labial and palatal root surfaces, concentrated in the labial cervical area, and maximized at the apex. For resected root-ends, occlusal loads concentrated stress on the labial cervical area. With bone graft, maximum stress concentration shifted to the apex, which implied stress relief and dispersion from the cervical root area. Stress patterns on the root-end were more widely spread in models with apical bone graft, whereas curved root-end showed stress concentrating arc especially when without apical bone support. The mean stress values on root-end circumference were significantly higher in curved than flat root-end (P < .05), especially with apical bone support (P < .05). CONCLUSIONS: Occlusal stress patterns on a maxillary central incisor were markedly affected by root-end resection configuration and apical bone support. Trephine-resected curved root-end had stress pattern concentrated on its circumference. Curved and flat root-ends had labial cervical stress that was relieved by bone graft. TEMS resected root-ends should be flattened and bone grafted to disperse stress from occlusal loads.N
Comparison of the clinical outcomes of resin-modified glass ionomer and self-adhesive resin cementations for full-coverage zirconia restorations
No full textObjectives: Both resin-modified glass ionomer cement (RMGIC) and self-adhesive resin cement (SAC) may be suitable for cementation of full-coverage zirconia restorations. This retrospective study aimed to investigate the clinical outcomes of zirconia-based restorations cemented with RMGIC and compare them with those cemented with SAC.Methods: Cases of full-coverage zirconia-based restorations cemented with either RMGIC or SAC between March 2016 and February 2019 were evaluated in this study. The clinical outcomes of the restorations were analyzed according to the type of cement used. In addition, cumulative success and survival rates were evaluated according to the cement and abutment types. Non-inferiority, Kaplan-Meier, and Cox hazard tests were conducted (& alpha;=.05).Results: A total of 288 full-coverage zirconia-based restorations (natural teeth, 157; implant restorations, 131) were analyzed. Loss of retention occurred in only one case; a single-unit implant crown cemented with RMGIC, which decemented 4.25 years post-restoration. RMGIC was non-inferior to SAC in terms of loss of retention (<5%). For single-unit natural tooth restorations, the four-year success rates in the RMGIC and SAC groups were 100% and 95.65%, respectively (p=.122). For single-unit implant restorations, the four-year success rates in the RMGIC and SAC groups were 95.66% and 100%, respectively (p=.365). The hazard ratios of all the predictor variables, including cement type, were not significant (p>.05).Conclusions: Cementation of full-coverage zirconia restorations of both natural teeth and implants using RMGIC and SAC yields satisfactory clinical outcomes. Furthermore, RMGIC is non-inferior to SAC in terms of cementation success.Clinical Significance: Cementation with RMGIC or SAC for full-coverage zirconia restorations has favorable clinical outcomes in both natural teeth and implants. Both RMGIC and SAC have advantages in the cementation of full-coverage zirconia restorations to abutments with favorable geometries.N
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