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1.  Marginal fit of anterior 3-unit fixed partial zirconia restorations using different CAD/CAM systems 
PURPOSE
Few studies have investigated the marginal accuracy of 3-unit zirconia fixed partial dentures (FPDs) fabricated by computer-aided design/computer-aided manufacturing (CAD/CAM) system. The purpose of this study was to compare the marginal fit of zirconia FPDs made using two CAD/CAM systems with that of metal-ceramic FPDs.
MATERIALS AND METHODS
Artificial resin maxillary central and lateral incisors were prepared for 3-unit FPDs and fixed in yellow stone. This model was duplicated to epoxy resin die. On the resin die, 15 three-unit FPDs were fabricated per group (45 in total): Group A, zirconia 3-unit FPDs made with the Everest system; Group B, zirconia 3-unit FPDs made with the Lava system; and Group C, metal-ceramic 3-unit FPDs. They were cemented to resin dies with resin cement. After removal of pontic, each retainer was separated and observed under a microscope (Presize 440C). Marginal gaps of experimental groups were analyzed using one-way ANOVA and Duncan test.
RESULTS
Mean marginal gaps of 3-unit FPDs were 60.46 µm for the Everest group, 78.71 µm for the Lava group, and 81.32 µm for the metal-ceramic group. The Everest group demonstrated significantly smaller marginal gap than the Lava and the metal-ceramic groups (P<.05). The marginal gap did not significantly differ between the Lava and the metal-ceramic groups (P>.05).
CONCLUSION
The marginal gaps of anterior 3-unit zirconia FPD differed according to CAD/CAM systems, but still fell within clinically acceptable ranges compared with conventional metal-ceramic restoration.
doi:10.4047/jap.2013.5.3.219
PMCID: PMC3774934  PMID: 24049561
Marginal fit; CAD/CAM; Zirconia FPD
2.  Comparative fracture strength analysis of Lava and Digident CAD/CAM zirconia ceramic crowns 
PURPOSE
All-ceramic crowns are subject to fracture during function. To minimize this common clinical complication, zirconium oxide has been used as the framework for all-ceramic crowns. The aim of this study was to compare the fracture strengths of two computer-aided design/computer-aided manufacturing (CAD/CAM) zirconia crown systems: Lava and Digident.
MATERIALS AND METHODS
Twenty Lava CAD/CAM zirconia crowns and twenty Digident CAD/CAM zirconia crowns were fabricated. A metal die was also duplicated from the original prepared tooth for fracture testing. A universal testing machine was used to determine the fracture strength of the crowns.
RESULTS
The mean fracture strengths were as follows: 54.9 ± 15.6 N for the Lava CAD/CAM zirconia crowns and 87.0 ± 16.0 N for the Digident CAD/CAM zirconia crowns. The difference between the mean fracture strengths of the Lava and Digident crowns was statistically significant (P<.001). Lava CAD/CAM zirconia crowns showed a complete fracture of both the veneering porcelain and the core whereas the Digident CAD/CAM zirconia crowns showed fracture only of the veneering porcelain.
CONCLUSION
The fracture strengths of CAD/CAM zirconia crowns differ depending on the compatibility of the core material and the veneering porcelain.
doi:10.4047/jap.2013.5.2.92
PMCID: PMC3675299  PMID: 23755332
All-ceramic crown; Fracture strength; Lava CAD/CAM; Digident CAD/CAM; Zirconia
3.  Chlorination of ortho-position on Polychlorinated Biphenyls Increases Protein Kinase C Activity in Neuronal Cells 
Toxicological Research  2012;28(2):107-112.
Polychlorinated biphenyls (PCBs) are persistent and bioaccumulative environmental pollutants. Recently, it is suggested that neurotoxic effects such as motor dysfunction and impairment in memory and learning have been associated with PCB exposure. However, structure relationship of PCB congeners with neurotoxic effects remains unknown. Since PKC signaling pathway is implicated in the modulation of motor behavior as well as learning and memory and the role of PKC are subspecies-specific, we attempted to study the effects of structurally distinct PCBs on the total PKC activity as well as subspecies of PKC in cerebellar granule cell culture model. Cells were exposed to 0, 25 and 50 μM of PCB-126, PCB-169, PCB-114, PCB-157, PCB-52 and PCB-4 for 15 min. Cells were subsequently analyzed by [3H] phorbol ester binding assay or immunoblotted against PKC-α and -ε monoclonal antibodies. While non-dioxin-like-PCB (PCB-52 and PCB-4) induced a translocation of PKC-α and -ε from cytosol to membrane fraction, dioxin-like PCBs (PCB-126, -169, -114, -157) had no effects. [3H] Phorbol ester binding assay also revealed structure-dependent increase similar to translocation of PKC isozymes. While PCB-4 induced translocation of PKC-α and -ε was inhibited by ROS inhibitor, the pattern of translocation was not affected in presence of AhR inhibitor. It is suggested that PCB-4-induced PKC activity may not be mediated via AhR-dependent pathway. Taken together, our findings suggest that chlorination of ortho-position in PCB may be a critical structural moiety associated with neurotoxic effects, which may be preferentially mediated via non-AhR-dependent pathway. Therefore, the present study may contribute to understanding the neurotoxic mechanism of PCBs as well as providing a basis for establishing a better neurotoxic assessment.
doi:10.5487/TR.2012.28.2.107
PMCID: PMC3834409  PMID: 24278597
Polychlorinated biphenyls; Protein kinase C; Cerebellar granule cell; ROS; AhR; Structureactivity relationship
4.  A study on the fracture strength of collarless metal-ceramic fixed partial dentures 
PURPOSE
The objective of this study was to evaluate fracture strength of collarless metal-ceramic FPDs according to their metal coping designs.
MATERIALS AND METHODS
Four different facial margin design groups were investigated. Group A was a coping with a thin facial metal collar, group B was a collarless coping with its facial metal to the shoulder, group C was a collarless coping with its facial metal 1 mm short of the shoulder, and group D was a collarless coping with its facial metal 2 mm short of the shoulder. Fifteen 3-unit collarless metal-ceramic FPDs were fabricated in each group. Finished FPDs were cemented to PBT (Polybutylene terephthalate) dies with resin cement. The fracture strength test was carried out using universal testing machine (Instron 4465, Instron Co., Norwood MA, USA) at a cross head speed of 0.5 mm/min. Aluminum foil folded to about 1 mm of thickness was inserted between the plunger tip and the incisal edge of the pontic. Vertical load was applied until catastrophic porcelain fracture occurred.
RESULTS
The greater the bulk of unsupported facial shoulder porcelain was, the lower the fracture strength became. However, there were no significant differences between experimental groups (P > .05).
CONCLUSION
All groups of collarless metal-ceramic FPDs had higher fracture strength than maximum incisive biting force. Modified collarless metal-ceramic FPD can be an alternative to all-ceramic FPDs in clinical situations.
doi:10.4047/jap.2010.2.4.134
PMCID: PMC3024503  PMID: 21264192
Fracture strength; Collarless metal-ceramic fixed partial denture; Modified collarless coping; Porcelain margin
5.  A histomorphometric study of dental implants with different surface characteristics 
PURPOSE
One of the major keys to achieve successful osseointegration of the implant is its surface properties. The aim of this study was to investigate the bone response to dental implants with different surface characteristics using the rabbit tibia model. Tricalcium phosphate (TCP) coated, anodic oxidized and turned (control) surfaces were compared.
MATERIALS AND METHODS
Seventy two implants were placed in the tibia of eighteen rabbits. Nine rabbits were sacrificed at 3 weeks of healing and the remaining nine were sacrificed at 6 weeks of healing. The bone-to-implant contact (BIC) and the bone volume density (BVD) were assessed by light microscope after 3 and 6 weeks of healing.
RESULTS
Statistical analysis showed that no significant differences in the BIC and BVD were observed between the different implant surfaces and the control group at 3 weeks and 6 weeks of healing. Data also suggested that the BVD of all the surfaces showed significant difference at 3 and 6 weeks.
CONCLUSION
The present study has showed that osseointegration occurred in all investigated types of surface-treated implants. In the current study all of the threads of the implants were observed to calculate BIC and BVD values (instead of choosing some of the threads from the bone cortex for example), which didn't make BIC or BVD percentage values better than in the control group, therefore the clinical relevance of these results remains to be shown.
doi:10.4047/jap.2010.2.4.142
PMCID: PMC3024504  PMID: 21264193
Surface modification; Bone-to-implant contact; Bone volume density; Tricalcium phosphate coating; Anodic oxidation
6.  Implants and all-ceramic restorations in a patient treated for aggressive periodontitis: a case report 
A 23-year-old female with aggressive periodontitis was treated using dental implants and LAVA system. The severely compromised teeth were extracted irrespective of initial conservative periodontal treatment. An implant-supported overdenture with 4 implants was fabricated for the maxilla and all-ceramic restorations for the mandible. Esthetic and functional goals were achieved with team approach involving periodontists and prosthodontists. This case report describes a treatment procedure for a generalized aggressive periodontitis patient with severe bone resorption.
doi:10.4047/jap.2010.2.3.97
PMCID: PMC2994702  PMID: 21165277
Aggressive periodontitis; Rehabilitation; Implant-supported overdenture; 3M LAVA™ system
7.  Use of separate single-tooth implant restorations to replace two or more consecutive posterior teeth: a prospective cohort study for up to 1 year 
PURPOSE
The aim of this study was to evaluate the periodontal and prosthodontic complications of multiple freestanding implants in the posterior jaws for up to 1 year of function.
MATERIALS AND METHODS
Eight patients received 20 implants posterior to canines. Two or more implants were consecutively inserted to each patient. Single crowns were delivered onto the implants. Marginal bone loss, implant mobility, probing depth, and screw loosening were examined to evaluate the clinical success of such restorations for maximum 1 year of functional loading.
RESULTS
All the implants performed well during the observation period. Neither periodontal nor prosthodontic complications were found except a slight porcelain chipping. While the marginal bone level was on average 0.09 mm lower around the implant after 6 months of loading, it was 0.15 mm higher after 1 year.
CONCLUSION
Within the limits of this investigation, separate single-tooth implant restorations to replace consecutive missing teeth may clinically function well in the posterior jaw.
doi:10.4047/jap.2010.2.2.54
PMCID: PMC2984517  PMID: 21165189
Separate restoration; Freestanding implant; Consecutive teeth; Marginal bone loss; Single-tooth implant
8.  Influence of porcelain veneering on the marginal fit of Digident and Lava CAD/CAM zirconia ceramic crowns 
PURPOSE
Marginal fit is a very important factor considering the restoration's long-term success. However, adding porcelain to copings can cause distortion and lead to an inadequate fit which exposes more luting material to the oral environment and causes secondary caries. The purpose of this study was to compare the marginal fit of 2 different all-ceramic crown systems before and after porcelain veneering. This study was also intended to verify the marginal fit of crowns originated from green machining of partially sintered blocks of zirconia (Lava CAD/CAM system) and that of crowns obtained through machining of fully sintered blocks of zirconia (Digident CAD/CAM system).
MATERIALS AND METHODS
20 crowns were made per each system and the marginal fit was evaluated through a light microscope with image processing (Accura 2000) at 50 points that were randomly selected. Each crown was measured twice: the first measurement was done after obtaining a 0.5 mm coping and the second measurement was done after porcelain veneering. The means and standard deviations were calculated and statistical inferences among the 2 groups were made using independent t-test and within the same group through paired t-test.
RESULTS
The means and standard deviations of the marginal fit were 61.52 ± 2.88 µm for the Digident CAD/CAM zirconia ceramic crowns before porcelain veneering and 83.15 ± 3.51 µm after porcelain veneering. Lava CAD/CAM zirconia ceramic crowns showed means and standard deviations of 62.22 ± 1.78 µm before porcelain veneering and 82.03 ± 1.85 µm after porcelain veneering. Both groups showed significant differences when analyzing the marginal gaps before and after porcelain veneering within each group. However, no significant differences were found when comparing the marginal gaps of each group before porcelain veneering and after porcelain veneering as well.
CONCLUSION
The 2 all-ceramic crown systems showed marginal gaps that were within a reported clinically acceptable range of marginal discrepancy.
doi:10.4047/jap.2010.2.2.33
PMCID: PMC2984519  PMID: 21165185
Marginal fit; Digident CAD/CAM Zirconia Ceramic Crown; Lava CAD/CAM Ceramic Crown; Porcelain veneering
9.  Biomechanical evaluation of dental implants with different surfaces: Removal torque and resonance frequency analysis in rabbits 
STATEMENT OF PROBLEM
Macroscopic and especially microscopic properties of implant surfaces play a major role in the osseous healing of dental implants. Dental implants with modified surfaces have shown stronger osseointegration than implants which are only turned (machined). Advanced surface modification techniques such as anodic oxidation and Ca-P application have been developed to achieve faster and stronger bonding between the host bone and the implant.
PURPOSE
The purpose of this study was to investigate the effect of surface treatment of titanium dental implant on implant stability after insertion using the rabbit tibia model.
MATERIAL AND METHODS
Three test groups were prepared: sandblasted, large-grit and acid-etched (SLA) implants, anodic oxidized implants, and anodized implants with Ca-P immersion. The turned implants served as control. Twenty rabbits received 80 implants in the tibia. Resonance frequencies were measured at the time of implant insertion, 2 weeks and 4 weeks of healing. Removal torque values (RTV) were measured 2 and 4 weeks after insertion.
RESULTS
The implant stability quotient (ISQ) values of implants for resonance frequency analysis (RFA) increased significantly (P < .05) during 2 weeks of healing period although there were no significant differences among the test and control groups (P > .05). The test and control implants also showed significantly higher ISQ values during 4 weeks of healing period (P < .05). No significant differences, however, were found among all the groups. All the groups showed no significant differences in ISQ values between 2 and 4 weeks after implant insertion (P > .05). The SLA, anodized and Ca-P immersed implants showed higher RTVs at 2 and 4 weeks of healing than the machined one (P < .05). However, there was no significant difference among the experimental groups.
CONCLUSION
The surface-modified implants appear to provide superior implant stability to the turned one. Under the limitation of this study, however, we suggest that neither anodic oxidation nor Ca-P immersion techniques have any advantage over the conventional SLA technique with respect to implant stability.
doi:10.4047/jap.2009.1.2.107
PMCID: PMC2994679  PMID: 21165264
surface treatment; bone to implant contact; removal torque; dental implant
10.  Isoniazid Could Be Used for Antibiotic-loaded Bone Cement for Musculoskeletal Tuberculosis: An In Vitro Study 
Background
Antibiotic-loaded bone cement (ALBC) has been used in serious cases of musculoskeletal tuberculosis, but the type and amount of antibiotic that should be used in ALBC have not been determined.
Questions/purposes
We therefore determined the (1) elution characteristics and (2) antimycobacterial activity of isoniazid- and rifampicin-loaded bone cement.
Methods
A total of 240 elution samples of each of three discs from 40 g bone cement mixed with one of eight dosages: 1 g, 2 g, and 4 g isoniazid, 1 g, 2 g, and 4 g rifampicin, and a combination of 1 + 1 g or 2 + 2 g of isoniazid and rifampicin. The polymerization of rifampicin-loaded bone cement was delayed to mean 122.5 ± 31.1 minutes. We measured the quantity of isoniazid and rifampicin and the antimycobacterial activity on Days 1, 3, 7, 14, and 30.
Results
Isoniazid eluted in almost all the samples while rifampicin was detected only on Day 1 with 2 g (0.7 ± 0.4 ug/mL/day), and until Day 14 with 4 g (0.1 ± 0.0u g/mL/day). Most of the samples containing isoniazid showed antimycobacterial activity while the samples containing rifampicin showed antimycobacterial activity only on Day 1 with 1 g (0.52 ± 0.18 ug/mL), until Day 14 with 2 g (0.03 ± 0.00 ug/mL), and until Day 30 with 4 g (1.84 ± 1.90 ug/mL).
Conclusion
Rifampicin was unsuitable for ALBC because of its delayed polymerization. Isoniazid eluted and showed antimycobacterial activity for 30 days.
Clinical Relevance
The data suggest isoniazid could be considered for use in ALBC for musculoskeletal tuberculosis if used with systemic treatment. For preventing resistance and systemic toxicity, a combination with a second-line drug and an in vivo study would be needed.
doi:10.1007/s11999-013-2899-5
PMCID: PMC3676586  PMID: 23504536
11.  Neurologic Recovery According to the Spinal Fracture Patterns by Denis Classification 
Yonsei Medical Journal  2013;54(3):715-719.
Purpose
Although Denis classification is considered as one of most clinically useful schemes for the evaluation of spinal fracture, there is little documentation on the relationship between fracture pattern and the neurologic recovery. The purpose is to evaluate the correlation between the fracture patterns according to Denis classification and neurologic recovery.
Materials and Methods
The 38 patients (26 men and 12 women) in this series had an average follow-up of 47.1 months, and they were all managed surgically. Denis classification had been used prospectively to determine the fracture morphology. Frankel Scale and American Spinal Injury Association Spinal Cord Injury Assessment Form [American Spinal Injury Association (ASIA) score] were obtained before surgery, after surgery and at the final follow-up.
Results
The common injuries making neurologic deterioration were burst fracture and fracture-dislocation. The degree of neurologic deficits seen first and at the final follow-up was more severe in fracture-dislocation than burst fracture. The neurologic recovery was not different between burst fracture and fracture-dislocation, assessed by Frankel grading and ASIA scoring system. The neurologic recovery evaluated by ASIA score was not different between the lumbar and thoracic spinal fracture. The neurologic recovery assessed by Frankel grade was greater in the lumbar spinal fractures in than the thoracic spinal fractures.
Conclusion
The severity of initial and the final follow-up neurologic deficits were correlated with the fracture patterns according to Denis classification, but the neurologic recovery was not correlated.
doi:10.3349/ymj.2013.54.3.715
PMCID: PMC3635638  PMID: 23549820
Spine; fracture; Denis classification; neurologic recovery
12.  Esthetic improvement in the patient with one missing maxillary central incisor restored with porcelain laminate veneers 
This article describes esthetic improvement in a patient with a missing maxillary left central incisor. Space analysis of the anterior dentition showed that minor tooth rearrangement was needed. Optimal space distribution for restorations was attained by orthodontic treatment. Through transforming tooth shape with porcelain laminate veneers, the maxillary left lateral incisor was transformed into central incisor and the maxillary left canine into a lateral incisor. The maxillary right central incisor was also restored for esthetic improvement. In a case of changing a tooth shape with porcelain laminate veneers, pre-treatment evaluation, space analysis and diagnostic wax-up are important factors.
doi:10.4047/jap.2010.2.3.77
PMCID: PMC2994698  PMID: 21165273
Porcelain laminate veneers; Missing central incisor; Orthodontic treatment
13.  Esthetic restorations of maxillary anterior teeth with orthodontic treatment and porcelain laminate veneers: a case report 
If orthodontists and restorative dentists establish the interdisciplinary approach to esthetic dentistry, the esthetic and functional outcome of their combined efforts will be greatly enhanced. This article describes satisfying esthetic results obtained by the distribution of space for restoration by orthodontic treatment and porcelain laminate veneers in uneven space between maxillary anterior teeth. It is proposed that the use of orthodontic treatment for re-distribution of the space and the use of porcelain laminate veneers to alter crown anatomy provide maximum esthetic and functional correction for patients with irregular interdental spacing.
doi:10.4047/jap.2010.2.2.61
PMCID: PMC2984523  PMID: 21165191
Interdental spacing; Orthodontic treatment; Porcelain laminate veneers; Interdisciplinary approach
14.  Comparison of polymer-based temporary crown and fixed partial denture materials by diametral tensile strength 
PURPOSE
The purpose of this study was to investigate the diametral tensile strength of polymer-based temporary crown and fixed partial denture (FPD) materials, and the change of the diametral tensile strength with time.
MATERIAL AND METHODS
One monomethacrylate-based temporary crown and FPD material (Trim) and three dimethacrylate-based ones (Protemp 3 Garant, Temphase, Luxtemp) were investigated. 20 specimens (ø 4 mm × 6 mm) were fabricated and randomly divided into two groups (Group I: Immediately, Group II: 1 hour) according to the measurement time after completion of mixing. Universal Testing Machine was used to load the specimens at a cross-head speed of 0.5 mm/min. The data were analyzed using one-way ANOVA, the multiple comparison Scheffe test and independent sample t test (α = 0.05).
RESULTS
Trim showed severe permanent deformation without an obvious fracture during loading at both times. There were statistically significant differences among the dimethacrylate-based materials. The dimethacrylate-based materials presented an increase in strength from 5 minutes to 1 hour and were as follows: Protemp 3 Garant (23.16 - 37.6 MPa), Temphase (22.27 - 28.08 MPa), Luxatemp (14.46 - 20.59 MPa). Protemp 3 Garant showed the highest value.
CONCLUSION
The dimethacrylate-based temporary materials tested were stronger in diametral tensile strength than the monomethacrylate-based one. The diametral tensile strength of the materials investigated increased with time.
doi:10.4047/jap.2010.2.1.14
PMCID: PMC2984512  PMID: 21165182
Polymer-based temporary crown and fixed partial denture materials; Diametral tensile strength
15.  Trend analysis of prosthodontic treatment modality between 2005 and 2008 in Seoul National University Dental Hospital 
PURPOSE
The aim of this article is to analyze the preference for treatment modality of dentists.
MATERIAL AND METHODS
Data of 20,038 patients was involved. Data analysis were done by distribution according to the various kinds of prosthesis, including complete denture, removable partial denture, fixed partial denture, implant-supported dental prosthesis as well as distribution according to the professional titles of the dentists finishing the treatment, including resident and professors.
RESULTS
The number of cases of dental prosthesis increased year by year. 61.06% of the patients accepted fixed partial denture restoration. The number of patients who accepted implant supported restoration is also increasing year by year. The number of complete denture, implant-supported dental prosthesis finished by professors was larger than that done by residents, while it was contrary for removable partial denture, fixed partial denture, and the difference was statistically significant (P<.05).
CONCLUSION
Professors and residents have some difference in the categorization of prosthesis finished. Fixed partial denture and implant-supported dental prosthesis are preferred.
doi:10.4047/jap.2010.2.1.4
PMCID: PMC2984513  PMID: 21165180
Treatment modality; Fixed partial denture; Implant-supported dental prosthesis
16.  The effect of low temperature aging on the mechanical property & phase stability of Y-TZP ceramics 
STATEMENT OF PROBLEM
Recently Yttrium-stabilized tetragonal zirconia polycrystal (Y-TZP) has been introduced due to superior flexural strength and fracture toughness compared to other dental ceramic systems. Although zirconia has outstanding mechanical properties, the phenomenon of decrease in the life-time of zirconia resulted from degradation in flexural strength after low temperature aging has been reported.
PURPOSE
The objective of this study was to investigate degradation of flexural strength of Y-TZP ceramics after various low temperature aging treatments and to evaluate the phase stability and micro-structural change after aging by using X-ray diffraction analysis and a scanning electron microscope (SEM).
MATERIAL AND METHODS
Y-TZP blocks of Vita In-Ceram YZ (Vita Zahnfabrik, Bad Säckingen, Germany) were prepared in 40 mm (length) × 4 mm (width) × 3 mm (height) samples. Specimens were artificially aged in distilled water by heat-treatment at a temperature of 75, 100, 125, 150, 175, 200, and 225℃ for 10 hours, in order to induce the phase transformation at the surface. To measure the mechanical property, the specimens were subjected to a four-point bending test using a universal testing machine (Instron model 3365; Instron, Canton, Mass, USA). In addition, X-ray diffraction analysis (DMAX 2500; Rigaku, Tokyo, Japan) and SEM (Hitachi s4700; Jeol Ltd, Tokyo, Japan) were performed to estimate the phase transformation. The statistical analysis was done using SAS 9.1.3 (SAS institute, USA). The flexural strength data of the experimental groups were analyzed by one-way analysis of variance and to detect statistically significant differences (α= .05).
RESULTS
The mean flexural strength of sintered Vita In-Ceram YZ without autoclaving was 798 MPa. When applied aging temperature at below 125℃ for 10 hours, the flexural strength of Vita In-Ceram YZ increased up to 1,161 MPa. However, at above 150℃, the flexural strength started to decrease. Although low temperature aging caused the tetragonal-to-monoclinic phase transformation related to temperature, the minimum flexural strength was above 700 MPa.
CONCLUSION
The monoclinic phase started to appear after aging treatment above 100℃. With the higher aging temperature, the fraction of monoclinic phase increased. The ratio of monoclinic/tetragonal + monoclinic phase reached a plateau value, circa 75% above 175℃. The point of monoclinic concentration at which the flexural strength begins to decrease was between 12% and 54%.
doi:10.4047/jap.2009.1.3.113
PMCID: PMC2994687  PMID: 21165265
Low temperature aging; Y-TZP ceramic; Phase transformation; Mechanical property
17.  Shear bond strength of veneering porcelain to zirconia and metal cores 
STATEMENT OF PROBLEM
Zirconia-based restorations have the common technical complication of delamination, or porcelain chipping, from the zirconia core. Thus the shear bond strength between the zirconia core and the veneering porcelain requires investigation in order to facilitate the material's clinical use.
PURPOSE
The purpose of this study was to evaluate the bonding strength of the porcelain veneer to the zirconia core and to other various metal alloys (high noble metal alloy and base metal alloy).
MATERIAL AND METHODS
15 rectangular (4×4×9mm) specimens each of zirconia (Cercon), base metal alloy (Tillite), high noble metal alloy (Degudent H) were fabricated for the shear bond strength test. The veneering porcelain recommended by the manufacturer for each type of material was fired to the core in thickness of 3mm. After firing, the specimens were embedded in the PTFE mold, placed on a mounting jig, and subjected to shear force in a universal testing machine. Load was applied at a crosshead speed of 0.5mm/min until fracture. The average shear strength (MPa) was analyzed with the one-way ANOVA and the Tukey's test (α= .05). The fractured specimens were examined using SEM and EDX to determine the failure pattern.
RESULTS
The mean shear strength (± SD) in MPa was 25.43 (± 3.12) in the zirconia group, 35.87 (± 4.23) in the base metal group, 38.00 (± 5.23) in the high noble metal group. The ANOVA showed a significant difference among groups, and the Tukey's test presented a significant difference between the zirconia group and the metal group. Microscopic examination showed that the failure primarily occurred near the interface with the residual veneering porcelain remaining on the core.
CONCLUSION
There was a significant difference between the metal ceramic and zirconia ceramic group in shear bond strength. There was no significant difference between the base metal alloy and the high noble metal alloy.
doi:10.4047/jap.2009.1.3.129
PMCID: PMC2994690  PMID: 21165268
Zirconia ceramic; Delamination; Core-veneer ceramic; Shear bond strength; Failure mode
18.  Complexities in Understanding the Nature of the Dose-Response for Dioxins and Related Compounds 
Dose-Response  2006;3(3):267-272.
doi:10.2203/dose-response.003.03.001
PMCID: PMC2475953  PMID: 18648623

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