共查询到20条相似文献，搜索用时 5 毫秒
1.
Statement of problem
Limited information is available regarding the influence of object translucency on the scanning accuracy of a powder-free intraoral scanner.Purpose
The purpose of this in vitro study was to evaluate the scanning accuracy of a confocal microscopy principle powder-free intraoral scanner on ceramic copings and to analyze the relationship between scanning accuracy and object translucency.Methods
Six slice specimens (12×10 mm) and 6 offset copings (1.00-mm thickness) were made from different translucent homogeneous ceramic blocks (CEREC Blocs, S0-M to S5-M, highest to lowest translucency). The primary sintered zirconia offset coping was produced in the same way as the control. Optical parameters related to the translucency of each slice were measured with a spectrophotometer. Three-dimensional (3D) datasets of the surface morphology of offset copings were obtained by using the intraoral scanner. The same white wax resin bases were used for registration. Quantitative parameters of scanning trueness and precision were measured. One-way ANOVA was used to analyze the values of each parameter among the 6 ceramic blocks. Bivariate correlation was used to analyze the relationships between each parameter of scanning accuracy and translucency (α=.05).Results
Translucent copings showed a positive 3D bias (S0-M to S5-M: 0.149 ±0.038 mm to 0.068 ±0.020 mm), a narrower collar diameter (Dd=?0.067 mm), larger convergence angle (ΔΦ=2.79 degrees), and larger curvature radius of the internal gingivoaxial corner (Δρ=0.236 mm). The smaller the percentage sum of scattering and absorption, the greater was the occurrence of scanning bias (r=?0.918) and curvature (r=?0.935) decrease.Conclusions
Use of the tested powder-free intraoral scanner, higher translucency objects (greater translucency than S1-M/A1C) resulted in lower scanning accuracy and morphological changes. Therefore, more suitable methods of measurement are still required. 相似文献2.
Xiaoqiang Liu Yao Tan Jianzhang Liu Jianguo Tan 《The Journal of prosthetic dentistry》2018,119(4):540-544
A digital technique for fabricating an implant-supported interim restoration is presented. The labial cervical architecture of the natural tooth is captured before extraction and registered to form the emergence profile of the interim restoration. A well-contoured interim restoration is fabricated before surgery and connected to the immediately placed implant with a customized interim abutment. 相似文献
3.
Xiaoqiang Liu Jingting Yu Jianfeng Zhou Jianguo Tan 《The Journal of prosthetic dentistry》2018,119(3):345-349
This paper presents a digitally guided dual technique that provides references for gingival and bone resection during crown lengthening surgery. The architecture of the teeth, gingiva, and alveolar bone is scanned and registered to design dual guides consisting of a gingivectomy guide and an alveolectomy guide that are used in periodontal surgery for esthetic rehabilitation. 相似文献
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Hanqi Gao Jianzhang Liu Xiaoqiang Liu Jianguo Tan 《The Journal of prosthetic dentistry》2019,121(4):561-565
This article presents an impression technique involving transfer of the position of implants and the emergence profile of splinted interim prostheses fabricated on nonindexed interim abutments to definitive single crowns fabricated on indexed abutments. 相似文献
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Xiaoqiang Liu Man Li Jianzhang Liu Jianguo Tan 《The Journal of prosthetic dentistry》2019,121(5):733-736
This article presents a technique for fabricating a passively fitting implant-supported screw-retained complete-arch interim restoration with resistance to early fracture. Two gypsum casts were obtained from an implant impression using the splinting technique. The complete-arch interim restoration with abutment access holes, which was reinforced with a glass fiber splint, was fabricated on one cast and connected to restorative abutments on the other cast extraorally to eliminate stresses from the polymerization shrinkage of resin. 相似文献
6.
Ting Lu Ling Peng Fu Xiong Xiao-Yu Lin Ping Zhang Zhi-Ting Lin Bu-Ling Wu 《The Journal of prosthetic dentistry》2018,119(3):363-368
Statement of problem
The introduction of polymer-infiltrated ceramic network (PICN) materials may provide more options for dentists in restoring short clinical crowns and extensively damaged posterior teeth, but clinical data for their performance are lacking.Purpose
The purpose of this clinical study was to compare the 3-year performance and survival rates of PICN material with those of conservative ceramic onlay restorations for endodontically treated posterior teeth using the CEREC AC chair-side system.Material and methods
A total of 101 onlay restorations of endodontically treated posterior teeth using the CEREC AC chair-side system were provided in 93 participants. The 101 teeth were divided into 2 groups: Vita Enamic group and Vitablocs Mark II group. Using the modified US Public Health Service quality evaluation system, 2 calibrated evaluators examined the performance of the onlay restorations over 3 years. The Kaplan-Meier method was adopted to analyze the survival rate of restorations (α=.05). The log rank test was used to compare the survival rates of the 2 groups. The Fisher exact test was performed to detect differences in the success rates for extensively damaged teeth and short clinical crown restorations between the 2 groups. The Silness and Löe gingival index was also recorded.Results
The restoration survival rates in the 2 groups were 97.0% (Vita Enamic) and 90.7% (Vitablocs Mark II) (P>.05). Five failures were recorded (4.95%). These failures were caused by restoration debonding (60%), ceramic fractures (20%), and tooth fractures (20%). There were no significant differences between the success rates of restoring extensively damaged teeth and short clinical crowns between the 2 groups (P>.05). The periodontal condition of 25% of participants was improved 3 years after the onlay restorations.Conclusions
Onlay restorations of endodontically treated posterior teeth with Vita Enamic using the CEREC AC chair-side system are clinically promising prosthodontic alternatives, with a survival rate of 97.0% after 3 years. More research is needed to verify the results of this study. 相似文献7.
Domingo Santos Pantaleón Brian R. Morrow David R. Cagna Cornelis H. Pameijer Franklin Garcia-Godoy 《The Journal of prosthetic dentistry》2018,119(3):390-396
Statement of problem
Limited information is available on the effect of an incomplete ferrule because of the varying residual axial wall heights and the volume of residual tooth structure on the fracture resistance of endodontically treated and restored maxillary incisors.Purpose
The purpose of this in vitro investigation was to examine the effect of varying residual axial wall heights, residual coronal tooth structure, and the absence of 1 proximal axial wall on the fracture resistance and failure mode of endodontically treated teeth restored with metal posts.Material and methods
Sixty intact human maxillary central incisors were divided into 6 groups (n=10): no ferrule (NF), 2-mm complete ferrule (CF2), 2-mm (IF2), 3-mm (IF3), and 4-mm (IF4) incomplete ferrules missing a single interproximal wall, and a control group that had a 6-mm incomplete ferrule (IF6). Cast metal post-and-cores were placed in all experimental specimens except for controls. Control specimens received 1 interproximal cavity preparation extending to the root canal access and a composite resin restoration. Complete metal crowns were then cemented on all specimens. Completed specimens were subjected to thermocycling (6000 cycles, 5°C/55°C) followed by the immediate testing of fracture resistance. Failed specimens were sectioned buccolingually and evaluated to identify the failure mode. The data were analyzed with an analysis of variance (ANOVA) and the Student-Newman-Keuls multiple comparison test (α=.05).Results
An incomplete ferrule (IF2) with 1 interproximal wall missing had significantly reduced fracture resistance (697 N) compared with a complete ferrule (932 N). An increase of 3 to 4 mm of remaining wall height improved fracture resistance, from 844 N (IF3) to 853 N (IF4). Partial decementation was noticed in 8 NF and 5 IF2 specimens. IF3 and IF4 had no decementations. Radicular fractures and cracks (catastrophic failure) were observed in all IF2, IF3, and IF4, 9 CF2, and 6 NF specimens. In 7 specimens without posts (IF6, control), composite resin foundation and/or coronal dentin fracture were observed and the failure was considered repairable.Conclusions
The results of this in vitro study indicated that specimens with a 2-mm ferrule of uniform height were more resistant to fracture than specimens with a 2-mm ferrule and 1 missing interproximal wall. An increased wall height of 3 or 4 mm was associated with a significant increase in fracture resistance and can compensate for the missing interproximal wall. 相似文献8.
Necati Kaleli Duygu Sarac Safak Külünk Özgür Öztürk 《The Journal of prosthetic dentistry》2018,119(3):437-445
Statement of problem
In recent years, the use of resin-matrix ceramics and polyetheretherketone (PEEK) abutments has been suggested to absorb excessive stresses on dental implants. However, only a few studies have evaluated the effect of these materials on stress distribution in implants and peripheral bone structure.Purpose
The purpose of this finite element analysis was to evaluate the biomechanical behaviors of resin-matrix ceramics and PEEK customized abutments in terms of stress distribution in implants and peripheral bone.Material and methods
Three-dimensional (3D) models of a bone-level implant system and a titanium base abutment were created by using the standard tessellation language (STL) data of original implant components. An anatomic customized abutment and a maxillary right second premolar crown were then modeled over the titanium base abutment. A bone block representing the maxillary right premolar area was created, and the implant was placed in the bone block with 100% osseointegration. Six different models were created according to combinations of restoration materials (translucent zirconia [TZI], lithium disilicate glass ceramic [IPS], polymer-infiltrated hybrid ceramic [VTE]), and customized abutment materials (PEEK and zirconia). In each model, the implants were loaded vertically (200 N) and obliquely (100 N). The stress distribution in the crown, implant, and abutments was evaluated through the von Mises stress analysis, and the stress distribution in the peripheral bone was examined through the maximum and minimum principal stress analyses.Results
The oblique load resulted in high stress values in the implant components, restorative crown, and cortical bone. Low stress values were observed in the VTE crowns. Zirconia customized abutments exhibited higher stress values than PEEK customized abutments. The stress distributions in the implant and peripheral bone were similar in all models.Conclusions
Changes in restoration and customized abutment material did not affect stress distribution in the implant and peripheral bone. 相似文献9.
10.
Haddad Arabi Bulaqi Ali Barzegar Mojgan Paknejad Hamed Safari 《The Journal of prosthetic dentistry》2019,121(3):548.e1-548.e7
Statement of problem
Contamination with salivary fluids or blood during the treatment process changes the preload, remaining torque, and removal torque of retained screws, which ultimately affects the resistance to screw loosening. In previous studies, no consensus has been reached as to whether contamination can be used as a lubricant.Purpose
The purpose of this 3-dimensional (3D) finite element analysis study was to compare the preload, remaining torque, and removal torque under different frictional conditions in the processes of tightening, waiting period, and removal of abutment screws using a numeric method and finite element analysis.Material and methods
Three-dimensional finite element models of a single implant restoration including a crown, dental implant, abutment, and abutment screw, along with the surrounding bone, were constructed. The geometry of all threaded interfaces was designed as a threaded helix. The Abaqus software was used to perform the dynamic simulation of 3 steps such as tightening, waiting period, and removal. Three static and kinetic friction conditions were considered to determine the effect of different frictional conditions. The values of preload at the tightening step, remaining torque at the waiting period, and removal torque at the removal step were evaluated and compared with theoretically predicted values.Results
The amount of removal torque required to loosen the abutment screw was smaller than the insertion torque for all frictional conditions. By decreasing the coefficient of friction, the remaining torque and the preload increased, and the torsional relaxation and removal torque decreased.Conclusions
Although the value of the removal torque decreased by decreasing the coefficient of friction, the resistance to screw loosening increased with the increase of the preload and the increase of the remaining torque in the implant complex assembly. Considering the biological complications of fluid lubricants, clinicians may contaminate the abutment screw with lubricants. Gold-coated screws should also be preferred to noncoated screws. 相似文献11.
Yanning Chen Chenmin Yao Cui Huang Yake Wang 《The Journal of prosthetic dentistry》2019,121(3):549.e1-549.e7
Statement of problem
Although newly developed photoinitiators can make up for the limitations of camphorquinone, their absorption spectra are different. However, little attention has been paid to the compatibility of available wavelength spectra of light-polymerization units (LPUs) and photoinitiators within resin cements.Purpose
The purpose of this in vitro study was to evaluate the effect of monowave and polywave light-emitting diode (LED) units on the adhesion of dual-polymerizing self-adhesive resin cements to monolithic zirconia.Material and methods
Monowave LPUs and polywave LPUs were chosen to polymerize 2 dual-polymerizing self-adhesive resin cements. Ninety-six zirconia disks were randomly divided into 4 groups as different combinations of LPUs and resin cements, namely ES-U200, BS-U200, ES-SC, and BS-SC. Resin cements were adhered to zirconia disks, and the microshear bond strength (μSBS) test was conducted after 24 hours of H2O storage (24 h) and 10?000 thermocycles (10k/TC). Failure modes were examined by stereomicroscopy and scanning electron microscopy (SEM). The degree of conversion (DC) was tested both immediately and 24 hours later. In statistical analyses, 2-way ANOVA and the Tukey honestly significant difference post hoc test were performed for μSBS and DC results, and chi-square test was performed for failure mode analysis (α=.05 for all tests).Results
The 2-way ANOVA demonstrated that different combinations of LPUs and resin cements, as well as different artificial aging levels, significantly influenced microshear bond strength values (P<.001). The interactions between 2 factors were also significant (P<.001). The BS-SC group possessed relatively high bond strength in both 24-hour and 10k/TC aging levels. For the same resin cement, no significant difference was found in the immediate DC (P=.405 for U200 and P=.708 for SC). At 24 hours, DC and BS-U200 values were significantly higher than ES-U200 values (P=.002), whereas BS-SC values were not significantly different from ES-SC values (P=.284).Conclusions
Within the limitation of this in vitro study, the emission spectra of LED units significantly influenced the bond strengths, DC, and failure mode of dual-polymerizing self-adhesive resin cements to zirconia at both immediate and artificial aging levels. The LPU should provide light energy to match the absorption wavelengths of photoinitiators in the resin cements. 相似文献12.
Wenhao Li Jingming Liu Su Chen Yao Wang Zhenting Zhang 《The Journal of prosthetic dentistry》2017,117(1):48-54
Statement of problem
Gastroesophageal reflux disease (GERD) is typically diagnosed based on symptoms of regurgitation and heartburn, although it may also manifest as asthma-like symptoms, laryngitis, or dental erosion.Purpose
The purpose of this prospective, cross-sectional study was to assess the prevalence of dental erosion in people with GERD and to evaluate the association between GERD and dental erosion.Material and methods
The presence, severity, and pattern of dental erosion was assessed in 51 participants with GERD and 50 participants without GERD using the Smith and Knight tooth wear index. Medical, dietary, and dental histories were collected by questionnaire. Factors potentially related to dental erosion, including GERD, were evaluated by logistic regression.Results
Dental erosion was observed in 31 (60.8%) participants with GERD and 14 (28%) participants without GERD. Bivariate analysis revealed that participants with GERD were more likely to experience dental erosion (crude odds ratio [cOR]: 2.74; 95% CI: 1.19, 6.32) than participants without GERD. Multivariate analysis also revealed that participants with GERD had a higher risk of dental erosion (adjusted odds ratio [aOR]: 3.97; 95% CI: 1.45, 10.89). Consumption of grains and legumes, the most frequently consumed foods in China, did not correlate with dental erosion. However, carbonated beverage consumption was significantly associated with GERD and dental erosion (aOR: 3.34; 95% CI: 1.01, 11.04; P=.04).Conclusions
GERD was positively correlated with dental erosion. Carbonated beverage consumption can increase the risk of both GERD and dental erosion. 相似文献13.
Statement of problem
Heat treatment has been used to reduce the residual stress of alloys fabricated by selective laser melting (SLM) to avoid deformation. Co-Cr metal-ceramic alloys are used to fabricate metal-ceramic restorations and removable partial dentures (RPDs) on the same substrate by SLM. A heat treatment that enables the fabrication of metal-ceramic restorations and RPDs with excellent mechanical properties should be evaluated.Purpose
The purpose of this in vitro study was to determine the effects of 2 heat treatments on the mechanical properties of SLM Co-Cr metal-ceramic alloys intended for the fabrication of thin RPDs.Material and methods
Tensile bars were manufactured using cast metal-ceramics (C-MC group), RPD alloys (C-RPD group), and SLM Co-Cr metal-ceramic alloys. The SLM specimens were subjected to 2 different heat treatments, L1 at 880°C and L2 at 1100°C, and were further divided into subgroups (L1-MC, L1-RPD, L2-MC, and L2-RPD). Thirty-six tensile specimens were prepared in C-RPD, L1-RPD, and L2-RPD (simulated partial denture alloys for clinical use) and in C-MC, L1-MC, and L2-MC (simulated metal-ceramic alloys); 18 metal-ceramic bond strength specimens were prepared in C-MC, L1-MC, and L2-MC groups (n=6). The tensile test and 3-point bend test were conducted using a universal testing machine. The fracture surfaces of the L2-RPD tensile bar were examined using a scanning electron microscope. The Student t test (α=.05) was used for statistical analysis.Results
No significant differences were observed between the bond strengths of L1-MC and C-MC (P=.74) or between those of L2-MC and C-MC (P=.124). The 0.2% yield strength (σ0.2) and elongation of all SLM specimens exceeded the minimum requirements required for the fabrication of thin RPDs as prescribed in ISO 22674:2016. The σ0.2 value of L1-MC and L2-MC was significantly higher than that of C-MC. Significant differences in σ0.2 values were found among the 3 RPD groups, L1-RPD>L2-RPD>C-RPD. For the elongation, significant differences were found among the 3 groups, L2-RPD>C-RPD>L1-RPD. The fracture surface of L2-RPD showed clear submicroscale dimples with fusion defects.Conclusions
When Co-Cr metal copings and RPD frameworks were fabricated on the same substrate simultaneously using SLM, heat treatment at 1100°C was found more suitable than at 880°C to release residual stress, considering the toughness required for dental prostheses. 相似文献14.
He Cai Shuying Yang Xibo Pei Hai Qing Jian Wang 《The Journal of prosthetic dentistry》2017,117(3):405-409
Statement of problem
Gingival displacement is recognized as a substantive and difficult procedure in fixed prosthodontics. However, a realistic simulation of gingival displacement is unavailable for preclinical dental students.Purpose
The purpose of this study was to evaluate whether practice-based preclinical instruction of gingival displacement with animal models could improve students’ skill in patient care.Material and methods
Isolated bovine mandibles (calves were younger than 6 months of age) and isolated porcine hemimandibles were prepared for this study. Twenty-two general dental practitioners with at least 5 years of experience were randomly selected and assigned to perform gingival displacement on both bovine and porcine jaws. Those practitioners were then asked to assess the clinical similarity of gingival displacement between human teeth and animal teeth. The data were analyzed with the paired t test (α=.05). Upon confirmation that the animal jaw provided a similar gingival displacement environment to that of human teeth, 80 predoctoral dental students were enrolled and randomized into 2 groups. Half of them underwent the new practice-based instruction, while the others underwent traditional preclinical teaching only (lectures, online video, or live demonstration). After preclinical learning, clinical performance in gingival displacement was evaluated for all students in terms of the effect of gingival displacement and quality of impression. The data were analyzed with the chi-square test (α=.05).Results
The dentogingival environments of porcine and bovine jaws were similar to those of human jaws, and no significant difference was detected between these 2 animal models (P=.178). A significant increase occurred in the acceptable rate of the effect of gingival displacement (P<.001) and the quality of impression (P<.001) among students who received the practice-based instruction compared with those who received traditional teaching.Conclusions
These findings suggest that this practice-based instruction of gingival displacement with animal models is an effective method of promoting dental students’ learning of gingival displacement. 相似文献15.
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Soares PV Santos-Filho PC Gomide HA Araujo CA Martins LR Soares CJ 《The Journal of prosthetic dentistry》2008,99(2):114-122
STATEMENT OF PROBLEM: Unresolved controversy exists concerning the preferred cavity design and restorative technique used to restore endodontically treated maxillary premolars to minimize strain and improve stress distribution under occlusal load. PURPOSE: The purpose of this study was to analyze the influence of cavity design and restorative material on strain measurement and stress distribution in maxillary premolars under occlusal loading conditions, and correlate these influences with the failure modes analyzed in Part I. MATERIAL AND METHODS: For the strain gauge test, 21 additional specimens were prepared as described in Part 1 of this study (n=3). Two strain gauges were fixed on the buccal (B) and palatal (P) cusps of each specimen with cyanoacrylate adhesive. The specimens were submitted to continuous axial compression loading at a speed of 0.5 mm/min, using a 6-mm sphere, to a maximum limit of 150 N in a universal testing machine. Total strain values were obtained by combining the B and P cusp strain values. These values were submitted to 2-way ANOVA and the Dunnet test (alpha=.05). For finite element analyses, 7 numerical 2-D models were generated: MODd, direct mesio-occlusal-distal preparation; MODi, indirect mesio-occlusal-distal preparation; AM, MODd restored with amalgam; CR, MODd restored with composite resin; LPR, MODi restored with laboratory-processed composite resin; and LGC, MODi restored with leucite-reinforced glass ceramic; each corresponding to 1 of the experimental groups tested in Part I of this study. The models were analyzed with finite element software, using the von Mises criteria for stress distribution analysis. RESULTS: With the strain gauge test, MODd, MODi, and AM groups showed significantly higher strain values than the CR, LPR, and LGC. Finite element analyses revealed that tooth structure removal and the type of restorative material altered the stress distribution pattern. The MODd, MODi, AM, and LPR models showed higher stress concentration within the tooth structure. CONCLUSIONS: The specimens with adhesive restorations were shown to behave in a manner similar to the biomechanical behavior of healthy teeth, while the behavior of those restored with amalgam restorations was more like that observed for teeth with nonrestored cavity preparations. These results directly correlate with the fracture mode results obtained in Part I of this study. 相似文献
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Liang Chen Cornelis Johannes Kleverlaan Kunneng Liang Deqin Yang 《The Journal of prosthetic dentistry》2017,117(4):552-558