STATEMENT OF PROBLEM
When sintering zirconia, conventional processing may not provide uniform heating and consumes more energy than an alternative method using microwave energy.


PURPOSE
The purpose of this study was to compare the surface quality, mechanical and physical properties, and dimensional stability obtained by sintering yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) in a conventional furnace versus a microwave furnace.


MATERIAL AND METHODS
Twenty bars of Y-TZP were prepared from Zircad blocks. Ten specimens were used for sintering in a conventional furnace. The remaining 10 specimens were sintered in a microwave furnace. The sintering temperature used for both techniques was 1500°C. The flexural strength of all specimens was measured with the 3-point bend test with a universal testing machine with a cross head speed of 1.0 mm/min. Density was measured by applying the Archimedes method, and specimen length, width, and thickness were measured with a digital micrometer. The phase composition and average grain size of these ceramics were examined by using X-ray diffraction, and microstructure characteristics were studied with scanning electron microscopy. Data obtained were analyzed by using independent t tests (α=.05).


RESULTS
No significant difference between conventional and microwave sintering for either flexural strength, t18=0.49 (P=.63) or density, t18=0.07 (P=.95) was found. Specimens in both groups exhibited a uniform firing shrinkage of approximately 24.6% in all dimensions. The surface of selected specimens examined with a scanning electron microscope showed no visible difference in grain shape or porosity size between the 2 sintering methods.


CONCLUSIONS
Under the conditions of this study, it appears that either microwave or conventional zirconia sintering may be used for processing zirconia for dental use. However, microwave energy provides uniformity of heating, allowing the use of higher heating rates, which can increase productivity and save energy.

Applying microwave technology in sintering of dental zirconia

In full-arch rehabilitation with implant-supported fixed prostheses, using monolithic zirconia seems to have several advantages regarding function and esthetics. However, the current scientific evidence is still limited. Thus, the aim of this investigation was to systematically review the literature on monolithic zirconia restorations for full-arch rehabilitation, particularly pursuing the survival rate and mechanical and biological complications. This study’s protocol was registered in PROSPERO (CRD42022301799). The primary literature search was performed in PubMed/MedLine and Web of Science, and a manual search was performed (checking cross-references). The focused question was, “In an adult population with one or both edentulous arches (P), the oral rehabilitation with implant-supported fixed-monolithic zirconia (full arch) (I), compared with oral rehabilitation using fixed-metal-ceramic prosthesis on implants (C), did show superior clinical results (O) in a minimum follow-up of 1 year (T)?” Inclusion and exclusion criteria were defined. Joana Briggs Institute tools were used to evaluate the quality of the studies. Meta-analysis was performed for the variable survival rate (%), applying the specific continuous moderator (follow-up). Data heterogeneity (I2) was assessed. From the initial search, 327 references were obtained. After eliminating duplicates and applying the inclusion/exclusion criteria by reading the titles, abstracts, and full text, seven articles were included. All included articles were observational longitudinal retrospective studies, with a number of prostheses between 7 and 2039. The mean age was 60 years, and the mean follow-up was 49.7 months. They had mandibular, maxillary, or bimaxillary rehabilitations, always with screw-retained retention, with an average survival rate of 97.23%. The number of implants ranged between four and eight. The quality of the articles was over 70%, and the heterogeneity was considered low (I2 = 28.64%). Within a mean follow-up of around four years, full-arch implant-supported monolithic zirconia rehabilitations had a high survival rate and minimal complications.

https://www.mdpi.com/2673-1592/5/2/29/pdf?version=1681905091

The Success and Complications of Complete-Arch Implant-Supported Fixed Monolithic Zirconia Restorations: A Systematic Review

Purpose To evaluate the relationship between different dimensional parameters in implant-supported monolithic zirconia fixed complete dental prostheses (IFCDPs) and the incidence of framework fracture in a large sample of cases in-vivo. Materials and methods This retrospective observational study evaluated all patients rehabilitated with screw-retained zirconia IFCDPs between January 2013 and April 2019 at a private practice. The minimum follow-up period was 1 year after occlusal loading. Fractures were classified as: type I - fractures that happened between but not involving the two most posterior screw-access openings (SAOs) and type II - fractures of the distal cantilever. Cantilever length, distal connector cross-sectional area, and screw access opening length were measured using data obtained from digital scans. Logistic regression was performed to evaluate the relationship between type I and II fractures and the independent variables (dimensional parameters). Using the receiver operating characteristic curves, two parameters were identified to be useful for establishing a cut-off and predicting type II fractures. Results A total of 180 prostheses delivered to 140 patients were analyzed. Five implants failed in three patients: three before delivery of the definitive prostheses and two after. Ten prostheses failed (5.6% prosthetic failure rate): 2 because of implant failures, and 8 because of framework fractures. Five fractures were classified as type I and three as type II. Significant associations were found between cantilever length and type I fractures (Wald = 5.772, df = 1, p = 0.016), distal connector cross-sectional area and type II fractures (Wald = 3.806, df = 1, p = 0.051), and cantilever length and the total number of fractures (Wald = 6.117, df = 1, p = 0.013). Conclusion Zirconia IFCDPs may be reliable medium-term solutions if some dimensional parameters are followed. The ratios between the cantilever length and cross-sectional connector area should be less than 0.51, while the ratio between the cantilever length and screw access opening length should be less than1.48. This article is protected by copyright. All rights reserved.

Framework Fracture of Zirconia Supported Full Arch Implant Rehabilitation: A Retrospective Evaluation of Cantilever Length and Distal Cross-Sectional Connection Area in 140 Patients Over an Up-To-7 Year Follow-Up Period.

Comparison of wear and fracture resistance of additively and subtractively manufactured screw-retained, implant-supported crowns.

Crystal structure and morphology of CeO2 doped stabilized zirconia ceramics under high-frequency microwave field sintering

Purpose This study aimed to biomechanically evaluate the effects of cantilever length and implant inclination on the stress distribution of mandibular prosthetic restorations constructed from monolithic zirconia ceramic. Materials and methods Mandibular full-arch prostheses supported by four implants constructed from monolithic zirconia were designed using either a 5-mm or 9-mm cantilever length and a 15-degree or 30-degree distal tilt for the posterior implants. A simulated static load of 600 N was applied from the right side at a 45-degree angle. Von Mises and principal stress values in superstructures were analyzed using the Mesh VR Studio program. Results When the effects of cantilever length were examined, in the models with the 15-degree implant tilt, stress values for posterior implants, porcelain, and cortical bone were lower when the cantilever length was shorter (5 mm). In the models with the 30-degree implant tilt, stress values in all implants (except for the anterior implant on the right) and in the porcelain superstructure were lower when the cantilever length was shorter; however, stress values for cortical and spongious bone were lower with the longer (9 mm) cantilever. When the effects of implant inclination were examined, in the models with a 5-mm cantilever, stress values for posterior implants and cortical bone were lower when the implant tilt was more severe (30 degrees). In the models with a 9-mm cantilever length, stress values for the right anterior implant, posterior implants, and cortical bone were lower when the implant tilt was less severe (15 degrees). Conclusion Cantilever length and posterior implant inclination affected the distribution of force. Increasing the cantilever length led to a reduction in stress values in distally tilted posterior implants. Moreover, increasing the distal inclination led to a reduction in stress values in both the distally tilted posterior implants and cortical bone tissue in the model with a short cantilever. The monolithic zirconia full-arch porcelain superstructure was not affected by implant angulation, but was affected by cantilever length, with lower stress values observed with a longer cantilever.

/pdf/effects-of-cantilever-length-and-implant-inclination-on-the-r4yiaa7oyk.pdf

Effects of Cantilever Length and Implant Inclination on the Stress Distribution of Mandibular Prosthetic Restorations Constructed from Monolithic Zirconia Ceramic.

Statement of problem The wear of monolithic zirconia against enamel has been widely studied, but how zirconia affects different opposing restorative materials is not clear. Purpose The purpose of this in vitro study was to investigate the depth of wear and volumetric loss of different restorative materials opposed by monolithic zirconia. Material and methods Sixty-six O10×3-mm specimens (n=11) were fabricated from monolithic zirconia, zirconia reinforced ceramic, lithium disilicate ceramic, feldspathic ceramic, ORMOCER, and ceramic optimized polymer. A 2-body pin-on-disk wear test was performed by using monolithic zirconia pins. The specimens were scanned with a noncontact profilometer after the tests. The scan parameters were a frame size area of 1.5×1.5 mm, frequency of 400 Hz, and scan sensitivity of 2 μm. After the evaluation of depth and volume loss, the specimens were analyzed with a scanning electron microscope. The Kruskal-Wallis test was used to analyze the differences in wear values across the specimen groups, and pairwise comparison tests were performed with a post hoc test (α=.05). Results Maximum depth of wear was 257.55 ±18.88 μm for lithium disilicate ceramic, 295.36 ±14.46 μm for zirconia reinforced ceramic, 421.82 ±214.49 μm for ORMOCER, 333.73 ±79.09 μm for ceramic optimized polymer, 146.27 ±22.86 μm for feldspathic ceramic, and 41.55 ±5.04 μm for monolithic zirconia. The depth of wear was not significantly different among lithium disilicate, zirconia-reinforced ceramic, ORMOCER, and ceramic optimized polymer (P .05). Conclusions The tested ceramic-based materials had favorable wear resistance compared with the tested composite resin–based ones. However, the ceramics tended to crack formation than the composite resins.

Wear of monolithic zirconia against different CAD-CAM and indirect restorative materials.

Statement of problem Prosthetic complications have been frequently reported in implant-supported complete-arch prosthesis. Prosthetic restorations designed with an all-on-four treatment concept and fabricated from zirconia ceramic may be used to overcome these problems. Purpose The purpose of this biomechanical study was to evaluate the effects of cantilever length and inclination of implant on the stress distribution in bone tissue, implant, and a monolithic zirconia ceramic-lithium disilicate glass-ceramic superstructure for all-on-four prosthesis. Material and methods All-on-four mandibular prosthesis fabricated from a zirconia and lithium disilicate glass-ceramic (LDGC) superstructure was designed with cantilever lengths of either 5 mm or 9 mm and posterior implants with a distal tilt of either 15 or 30 degrees. Stresses were evaluated with a simulated application of a static load of 600 N. Results Increasing implant inclination from 15 to 30 degrees led to a decrease in maximum principal stress (MaxPS) values of approximately 4 to 7 MPa in cortical bone around all implants except the right anterior implant in the designs with short cantilevers and an increase in MaxPS values (approximately 3 to 19 MPa) in the same places in the designs with the long cantilevers. Increasing cantilever length from 5 to 9 mm resulted in an increase in minimum principal stress (MinPS) values of approximately 3 to 13 MPa in the cortical bone surrounding all posterior implants. In the designs with the long cantilever, MaxPS values increased approximately 3 to 4 MPa in spongy bone adjacent to the right posterior implant. An increase in cantilever length also led to higher vMS values at the first and second implant grooves in the right posterior implant in the design with the 15-degree implant tilt. An increase in implant inclination in the design with the short cantilever resulted in lower vMS values at the apex and all grooves of the left posterior implant, whereas in the design with the long cantilever, an increase in implant inclination resulted in lower stress values in the first and second grooves of the same implant. An increase in implant inclination led to in an increase in vMS values in the core structure. Conclusions In zirconia ceramic restorations by using an all-on-four design with an LDGC superstructure, short cantilevers may be preferable because they result in a more favorable distribution of stress than long cantilevers. An increase in implant angulation from 15 to 30 degrees decreased MaxPS values in cortical bone.

The effect of the design of a mandibular implant-supported zirconia prosthesis on stress distribution.

Introduction: High fracture resistance of prostheses are well accepted by both patients and dentists to have a proper restoration of the dentition. The research  designated  assess polymerization  time  effect distinct   and complete temperatures on mechanical properties (denture base resin) of a high strength. The research  purpose is to assess  and compare the procedure  used in  polymerization distinct effect autoclave on the elastic modulus  and transverse strength of a high strength acrylic resin  to the conventional heat polymerizing. Methods: Rectangular sample of ninety-one  polymarised high heat  strength denture base resin  were created.  Polymerized  sample done by hot water regarded as  control group  and the other groups were polymerized in autoclave at different temperatures and time lenghts. After deflasking of sample before procedure it was kept  forty eight hours in water. Three parameters were used  when conducting  transverse strength test bending using calibrated  universal testing machine  with a  load of 500 kg cell and a crosshead speed of 5 mm/min. One-way ANOVA was used in assessing transverse strength and elastic modulus data.  And for  comparison   of the groups application of Tukey HSD trial  has been seen appropriate (p <0.05). Results: Specimens that polymerized by autoclave at 130oC for 20 and 30 minutes showed significantly better characteristics compared to the other groups. Conclusion:  Upgrading of  base resins  transverse strength is required  because the  research  indicated autoclave polymerization at 130°C for 20 and 30 minutes may be an alternative polymerization method.

https://jdmt.mums.ac.ir/article_16372_1eb9810b3f1d66a284369e070f82d502.pdf

Evaluation of the Transverse Strength and Elastic Modulus of High Impact Denture Base Material

Objectives: The objective of this study is to compare the characteristics of the concept of platform-switched implants (PSW) that have recently emerged in implant dentistry and its effects on the marginal bone loss (MBL) around the implant with platform-matched implants (PMI). Data: In the study, PSW implant-abutment connection system, MBL, and peri-implant hard and soft tissue changes were examined. The research terms used in the study are dental implant, platform switching concept, switched platform, platform mismatch, platform-matched implants, and dental implant-abutment design. Sources: In the electronic research, the language was selected as English and studies conducted until March 2018 were investigated without year limitation. The electronic studies include the National Library of Medicine, PubMed/Medline, Web of Science, Cochrane Oral Health Group Trials, and Cochrane Central Register of Controlled Trials. Study selection: Studies, retrospective or prospective clinical human studies, either randomized systematic review and meta-analyses, and finite element analyses (FEA) were examined. Case reports and studies of animal experiments were excluded from the review. Conclusions: It was observed that clinical trials consisted of short and medium-term follow-ups and biomechanical studies were limited. It was observed that PSW implant systems obtain positive results in reducing the MBL and are more aesthetic in terms of soft tissue formation compared to PMI systems, and interest has been gradually increasing in the PSW system in recent years. It was revealed that long-term clinical trials for the PSW system are required.

/pdf/the-impact-of-platform-switched-implants-on-the-marginal-rau0civzom.pdf

The Impact of Platform-Switched Implants on the Marginal Bone Level and Soft Tissue Dimensions

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