Porcelain Firing Research Articles

Influence of firing conditions and production methods on fracture strength of titanium-based metal ceramic crowns

Objectives: This study evaluated the effect of argon atmosphere compared with vacuum during porcelain firing on the fracture strength of crowns made of porcelain and electron beam melted (EBM) Ti-6Al-4 V, cast commercially pure titanium or milled commercially pure titanium. Methods: Sixty crown copings of c. p. titanium, Ti-6Al-4 V alloy and porcelain were fabricated using three production techniques. The copings were fired either under vacuum or in an argon gas atmosphere. Specimens were subdivided into groups of cast c. p. titanium, milled c. p. titanium and EBM Ti-6Al-4 V which were further subdivided according to firing modes employing either vacuum or argon gas. The 60 specimens were subjected to cyclic preloading and thermocycling, and were then individually loaded until interface fractured. Differences between the group mean values were calculated using the one-way ANOVA and Tukey’s range test. Two fractured samples from each group were cut with a diamond blade and examined using SEM and EDS for visualization and chemical composition analysis of the fractured interface. Results: The highest mean fracture strength values, though not significant, were recorded for the groups fired in argon atmosphere, and the lowest mean fracture strength values were recorded for the groups fired in vacuum, with one exception. Comparing the two main groups of firing atmosphere, no significant difference could be documented. SEM and EDS analysis indicated clear differences in composition and structure between the groups included in the study. Conclusions: Firing in argon atmosphere does not significantly improve the fracture strength of porcelain bonded to titanium.

Achieving the Desired Esthetic with Current CAD-CAM Ceramics

The demand for tooth-colored restorations has grown considerably during the last decades. Restoration of anterior teeth is a difficult task, even for an experienced operator. Color is the most important determinant of esthetics. The esthetic appearance of a restoration should match the surrounding dental tissue. This requires that the optical properties of the restorative material be similar to that of the natural teeth. Thus, for an acceptable esthetic result, favorable shade matching of the all-ceramic restoration should be achieved by controlling light absorption, reflection and transmission of the ceramic material. There are many different ceramic systems that can be used to achieve highly esthetic results. These ceramic systems include In-Ceram, Hi-Ceram, IPS-Empress, Optec, and CAD-CAM ceramics. All ceramic systems have different composition, microstructure, crystalline content and phases. Direct transmission, translucency, opacity and opalescence, all influence the optical properties of the ceramic restoration. Other factors include the thickness of porcelain, number of porcelain firing, glazing, porcelain powder/liquid ratio, surface texture and even the resin shade. This article focuses on controlling these variables to achieve the best possible esthetic result with an all ceramic system with the emphasis on CAD-CAM systems.

Effect of Temperature And Number of Opaque Porcelain Firing on Bond Strength of Metal-Ceramic Fixed Partial Denture

Effect of Temperature And Number of Opaque Porcelain Firing on Bond Strength of Metal-Ceramic Fixed Partial Denture

Evaluation of effects of porcelain firing on the marginal fit changes of porcelain–fused-to -metal crown fabricated utilizing two different margin designs and two commercially available base metal alloys

Aim: To find the marginal fit of the porcelain fused to metal crowns by two different margin designs (shoulder and chamfer) and two commercially available base metal alloys.Material and Methods: Tooth preparation of first central incisor for porcelain-fused-to-metal crown with shoulder margin and second incisor for porcelain-fused-to-metal crown with chamfer margin was done. Wax pattern of the same was prepared. Impression of both prepared ivorine incisors was made by light body impression material and poured with pattern resin. Both the patterns were invested and casted with cobalt chromium alloy for making master dies. Two wax patterns of unprepared central incisors were fabricated, one with shoulder margin and another with chamfer margin. These patterns were then cut back to the size of the coping. Four rings were invested. In each ring ten patterns, five with shoulder margin and five with deep chamfer margin were sprued together to ensure that each group would pass through the same investing and casting procedure, followed by ceramic firing and measurement.Results: Marginal fit change or marginal discrepancy (before and after firing) between the groups was highly significant.Conclusions: Veneered crowns exhibited highly significant marginal distortion than non- veneered copings after porcelain firing. Shoulder margin is better in minimizing marginal discrepancy compared to deep chamfer margin. Marginal discrepancy is less when cerabond base metal alloy is used with shoulder margin as compared to commend base metal alloy used for shoulder margin.

Effect of ice-quenching on the change in hardness of a Pd-Au-Zn alloy during porcelain firing simulation.

This study examined the effect of ice-quenching after degassing on the change in hardness of a Pd-Au-Zn alloy during porcelain firing simulations. By ice-quenching after degassing, the specimens were softened due to homogenization without the need for an additional softening heat treatment. The lowered hardness by ice-quenching after degassing was recovered greatly from the first stage of porcelain firing process by controlling the cooling rate. The increase in hardness during cooling after porcelain firing was attributed to the precipitation of the f.c.t. PdZn phase containing Au, which caused severe lattice strain in the interphase boundary between the precipitates and matrix of the f.c.c. structure. The final hardness was slightly higher in the ice-quenched specimen than in the specimen cooled at stage 0 (the most effective cooling rate for alloy hardening) after degassing. This was attributed to the more active grain interior precipitation during cooling in the ice-quenched specimen after degassing.

Pd-Au-Ag계 금속-도재용 합금의 탈가스 처리 후 급냉 처리가 모의소성과정에서 경도변화에 미치는 영향

본 연구에서는 Pd-Au-Ag계 금속-도재용 합금의 탈가스 처리(degassing) 후 급냉 처리가 모의소성과정에서 경도변화에 미치는 영향을 관찰하여 다음과 같은 결과를 얻었다.BR 1. 탈가스 후 급냉에 의해 경도는 하강하였고, 이는 급냉에 따른 합금의 균질화에 의해 유도되었다.BR 2. 탈가스 후 급냉하여 낮아진 경도는 나머지 모의소성 과정의 첫 단계인 1st opaque 단계에서 완전히 회복되었으며, 이는 석출에 의해 유도되었다.BR 3. 탈가스 후 급냉 처리는 이후 모의소성과정 동안 시편의 경도변화에 아무런 영향을 미치지 않았다.BRBR 이상의 결과로부터 금속-도재용 합금을 탈가스 후 급냉 처리한다면 최종 보철물의 내구성에 영향을 미치지 않고 금속하부구조물에 대한 도재 소성 전처리 작업을 효과적으로 할 수 있을 것으로 생각되었다.

금속-세라믹용 Pd-Au-Ag-Sn계 합금의 모의소성 후 계류에 따른 석출경화

This experiment was carried out to examine whether the post-firing heat treatment is effective in increasing the hardness of metal-ceramic alloy of the Pd-Au-Ag-Sn system. Precipitation hardening by holding at 600°C after simulated complete porcelain firing in a metal-ceramic alloy of the Pd-Au-Ag-Sn system was examined by observing the change in hardness, crystal structure, and microstructure using a hardness test, X-ray diffraction (XRD), and field emission scanning electron microscopy (FE-SEM). The hardness of the alloy increased apparently by holding the specimen at 600°C for 30 min after simulated complete porcelain firing. The formation of fine grain interior precipitates during holding at 600°C caused the formation of lattice strain in the grain interior, resulting in apparent hardening. The faster cooling rate (stage 0) during simulated complete porcelain firing resulted in more effective precipitation hardening during holding at 600°C. From the above results, an appropriate post-firing heat treatment, such as holding at 600°C for 30 min after complete porcelain firing may increase the durability of metal-ceramic prostheses composed of Pd-Au-Ag-Sn alloy.

A Landmark in the History of Chinese Ceramics: The Invention of Blue-and-white Porcelain in the Tang Dynasty (618–907 A.D.)

This study investigates the origin and development of Tang blue-and-white porcelain. Test samples consist of excavated shards of blue-and-white porcelain, white porcelain, Tang tricolor pottery, and blue-on-white pottery from the Tang strata of the Baihe and the Huangye kiln sites. The chemical compositions, firing temperatures, and physical properties were studied scientifically, and multivariate statistical analysis was applied to analyze the compositional data. The results show that Tang blue-and-white porcelain developed from a mature manufacturing technology of white porcelain in the late Tang. Moreover, the type of cobalt pigment used is similar to that used for blue-on-white pottery. This study contributes to our understanding of the invention of Tang blue-and-white porcelain.Statement of significance In recent years, several shards of blue-and-white porcelain have been found in the late Tang strata of the Huangye and the Baihe kiln sites in Gongyi district of Henan Province (Henan Provincial Institute of Cultural Relics and Archaeology 2005,17; 2007; 2009,22). Notably, these are the only pieces of blue-and-white wares of the Tang dynasty that have been excavated at a kiln site. For the very first time, with data analysis of the chemical compositions and comparisons among pottery and porcelain throughout distinct time periods of the Tang Dynasty, this study explicates the invention of Tang blue-and-white porcelain from a scientific standpoint. Derived from Tang tricolor pottery, blue-on-white pottery and, especially, white porcelain production, raw materials and firing techniques lay the groundwork for the emergence of blue-and-white wares. The invention of Tang blue-and-white porcelain marks a crucial milestone in the developmental history of ancient Chinese ceramics.

Influence of porcelain firing and cementation on the marginal adaptation of metal-ceramic restorations prepared by different methods

Statement of problemMarginal adaptation plays an important role in the survival of metal-ceramic restorations. Porcelain firings and cementation may affect the adaptation of restorations. Moreover, conventional casting procedures and casting imperfections may cause deteriorations in the marginal adaptation of metal-ceramic restorations. PurposeThe purpose of this in vitro study was to compare the marginal adaptation after fabrication of the framework, porcelain application, and cementation of metal-ceramic restorations prepared by using the conventional lost-wax technique, milling, direct metal laser sintering (DMLS), and LaserCUSING, a direct process powder-bed system. Alterations in the marginal adaptation of the metal frameworks during the fabrication stages and the precision of fabrication methods were evaluated. Material and methodsForty-eight metal dies simulating prepared premolar and molar abutment teeth were fabricated to investigate marginal adaptation. They were divided into 4 groups (n=12) according to the fabrication method used (group C serving as the control group: lost-wax method; group M: milling method; group LS: DMLS method; group DP: direct process powder-bed method). Sixty marginal discrepancy measurements were recorded separately on each abutment tooth after fabrication of the framework, porcelain application, and cementation by using a stereomicroscope. Thereafter, each group was divided into 3 subgroups according to the measurements recorded in each fabrication stage: subgroup F (framework), subgroup P (porcelain application), and subgroup C (cementation). Data were statistically analyzed with univariate analysis of variance (followed by 1-way ANOVA and Tamhane T2 test (α=.05). ResultsThe lowest marginal discrepancy values were observed in restorations prepared by using the direct process powder-bed method, and this was significantly different (P<.001) from the other methods. The highest marginal discrepancy values were recorded after the cementation procedure in all groups. ConclusionsThe results showed that the direct process powder-bed method is quite successful in terms of marginal adaptation. The marginal discrepancy increased after porcelain application and cementation.

금속-세라믹용 Pd-Au-Ag-Sn계 합금의 모의 소성에 따른 경도변화에 미치는 냉각 속도의 영향

금속-세라믹용 Pd-Au-Ag-Sn계 합금의 모의 소성에 따른 경도변화에 미치는 냉각 속도의 영향

Porcelain bonding to novel Co–Cr alloys: Influence of interfacial reactions on phase stability, plasticity and adhesion

ObjectiveThe objective of the present study was to determine the hardness and adhesion strength at the porcelain to alloy interface. Methods15 bi-layer porcelain veneered Co–Cr specimens of each alloy group [cast, powder metallurgy (PM), CAD/CAM(CC)] were manufactured. 12 bi-layered specimens were tested using four-point bend strain energy release rate adhesion test. One before and after porcelain firing specimen of each alloy group were nano-indented at the bulk and metal-porcelain interface to determine the mechanical properties. Electron backscatter diffraction was used to determine the microstructure and phase of the indented areas. ResultsThe results obtained from the four-point bend strain energy release rate test indicated highest adhesion energy of 92.15J/m2 observed in the CC produced Co–Cr alloy. This was followed by the PM alloy with an adhesion energy of 62.24J/m2 and cast alloy with an adhesion energy of 42.83J/m2. All comparisons of adhesion energy between the three alloys were found to be statistically significant (p<.05). Nano-indentation test indicated higher hardness values of 4.6–6.1GPa at the metal-porcelain interface compared to the bulk, which had hardness values of 3.1–3.9GPa. SignificanceThe adhesion of the alloy to porcelain was found to be inversely related to the hardness of the interfacial layer at the alloy surface. Lower interfacial hardness was found to be accompanied with higher adhesion energy due to the additional plastic energy consumed during crack propagation along the more ductile interface region of the alloy.

Electrochemical Characteristics of a Cobalt Alloy with a Protective Passive Layer

AbstractThe aim of this study was to assess the quality of the passive layer formed on the surface of a CoCr alloy used on dentures to see the effect on resistance to pitting corrosion and electrochemical parameters. Studies were performed using on potentiodynamic tests and electrochemical impedance spectroscopy. The passive layer was formed spontaneously and by electrochemical method on samples after casting and after simulation porcelain firing on metal. Samples of the passivation electrochemical characterized by the improvement in corrosion resistance. Prolonging the passivation time from one to 24 hours and increasing the potential value from 0 to 200 mV improved the quality of the passive layer and all characteristics of electrochemical parameters.

Pd-Ag-In-Au계 금속-세라믹 합금의 모의소성에 따른 경도 및 미세구조의 변화

Change in hardness and microstructure during porcelain firing simulation in a Pd-Ag-In-Au metal-ceramic alloy was examined by observing the change in hardness, crystal structure and microstructure. In the as-cast specimen, the matrix was composed of the Pd3Ga phase(f.c.t.), and the particle-like structures were composed of the Pd-Ag-based phase(f.c.c.). The precipitates which covered the particle-like structures were composed of the Pd3In phase(f.c.t.). Specimen which was cooled by ice quenching after oxidation was softened due to homogenization of the microstructure, and then it was hardened due to precipitation during the simulated firing stages. The decrease in hardness by subsequent firing schedule was resulted from reduction of precipitates in the particle-like structures.

The effect of simulating porcelain firing on the elemental composition, microstructure, and mechanical properties of electroformed gold restorations

Background/purposeThe mechanical properties of pure gold (Au) are modified by thermal treatments. Thus, the aim of this study was to evaluate the effect of porcelain firing on the elemental composition, microstructure, and mechanical properties of electroformed Au crowns. Materials and methodsTwenty electroformed Au specimens were prepared and divided into two groups. The first group did not receive any treatment (ELEC), and the other group was subjected to porcelain firing (PFIR). After metallographic grinding and polishing, all were investigated by scanning electron microscopy, and elemental composition was determined using energy-dispersive X-ray spectroscopy (EDX). Internal porosity was identified by quantitative image processing. Mechanical properties including Martens hardness (HM), indentation modulus (EIT), elastic index (ηΙΤ), and Vickers hardness (HV) were determined by instrumented indentation testing. The results were statistically analyzed using unpaired t test (α=0.05). ResultsA random distribution of tiny pores was identified in cross section, but no significant difference was found between groups [ELEC (%), 0.24±0.13; PFIR (%), 0.31±0.7]. Backscattered electron images revealed no mean atomic number contrast for both groups, indicating that the material was a single-phase alloy, whereas no differences between groups were identified in the composition of C, N, O, and Au after EDX analysis. By contrast, all mechanical properties tested showed statistically significant differences, with the PFIR group showing significantly lower HM, ηΙΤ, and HV but increased EIT compared with those of the ELEC group. ConclusionAlthough microstructure and elemental composition of electroformed Au crowns remain unchanged, the mechanical properties are significantly affected by the thermal treatment of porcelain firing.

Hardening by cooling rate control and post-firing heat treatment in Pd-Ag-Sn alloy for bonding porcelain.

The aim of this study was to determine the hardening effect by controlling the cooling rate during the porcelain firing process and performing an additional post-firing heat treatment in a Pd-Ag-Sn alloy. The most effective cooling rate for alloy hardening was determined by cooling the specimens at various cooling rates after oxidation treatment. A subsequent porcelain firing simulation followed by cooling at the selected cooling rate was performed. A post-firing heat treatment was then done at 600°C in a porcelain furnace. The hardening mechanism was characterized by a hardness test, X-ray diffraction, field emission scanning electron microscopy and energy dispersive X-ray spectroscopy. Alloy softening occurred during the porcelain firing process followed by cooling at a controlled cooling rate. A post-firing heat treatment allowed apparent precipitation hardening. It is advisable to perform a postfiring heat treatment at 600°C in a porcelain furnace by annealing metal substructure after porcelain fusing.

Effect of Repeated Firings on Microtensile Bond Strength of Bi-layered Lithium Disilicate Ceramics (e.max CAD and e.max Press)

To achieve acceptable contour, color, esthetics, and occlusal relations, the porcelain may be subjected to several firing cycles. This study sought to assess the effect of multiple firing cycles on the microtensile bond strength (MTBS) of lithium disilicate-based ceramics (e.max Press, e.max CAD). IPS e.max computer aided design (CAD) cores were fabricated using CAD/(Computer Aided Manufacturing (CAM)) technology, and IPS e.max Press cores were fabricated using the heat-pressing technique (12 × 12 × 4 mm(3)). Cores in each group were divided into three subgroups based on the number of firing cycles (three, five, and seven cycles). After porcelain application, the samples were sectioned into microbars and a total of 20 sound microbars in each group were subjected to tensile load in a microtensile tester at a crosshead speed of 1 mm/minute. Microtensile bond strength of the core to the veneering porcelain was analyzed using one-way analysis of variance (ANOVA). Pairwise comparisons were made using the Tukey's test (p < 0.05). In the e.max CAD, the mean MTBS values were 22.07 ± 6.63, 34.68 ± 7.07, and 26.05 ± 10.29 MPa following three, five, and seven firing cycles respectively. These values for the e.max Press were 34.46 ± 9.28, 23.09 ± 5.02, and 31.26 ± 12.25 MPa respectively. There was significant difference in bond strength of e.max CAD (p < 0.003) and e.max Press (p < 0.002) based on the number of firing cycles. Increasing the number of porcelain firing cycles decreased the bond strength of the core to the veneering porcelain in both ceramics. It is better to decrease the number of firing cycle as much as possible.

Effect of softening-heat treatment on hardness change of an Au-Pd-Zn-In-Sn metal-ceramic alloy during porcelain firing simulation

Effect of softening-heat treatment on hardness change of an Au-Pd-Zn-In-Sn metal-ceramic alloy during porcelain firing simulation

Effects of multiple firings on the low-temperature degradation of dental yttria-stabilized tetragonal zirconia

Statement of problemThe clinical failure of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) substrates may be attributed to their susceptibility to low-temperature degradation (LTD). The acceleration of LTD by multiple veneering firings of Y-TZP remains poorly understood. PurposeThe purpose of this in vitro study was to evaluate the effects of different numbers of veneering firing cycles on the LTD of Y-TZP. Material and methodsNinety bar-shaped specimens were cut from a machinable Y-TZP block and fully sintered. The Y-TZP bars were divided into 3 groups; each group received 1, 3, or 5 veneering porcelain firing cycles. Specimens from each firing cycle (n=10) were then subjected to hydrothermal aging in an autoclave sterilizer for 10 or 20 hours to accelerate the LTD of Y-TZP. Specimens without hydrothermal aging served as the control. XRD was used to characterize phase transformations. The flexural strength and surface Vickers hardness of the 9 subgroups were investigated, and scanning electron microscopy was used to characterize the fractured surface morphology. ResultsHydrothermal aging increased the monoclinic phase, although increased hydrothermal aging time provided no additional effects. Veneering firings did not enhance the influence of hydrothermal aging on phase transformation. No statistical significance was found among the 9 groups in terms of flexural strength or surface Vickers hardness (P>.05). ConclusionsAdditional veneering porcelain firing cycles do not accelerate the LTD of Y-TZP.

Comparison of the microstructure and phase stability of as-cast, CAD/CAM and powder metallurgy manufactured Co–Cr dental alloys

ObjectiveThe objective of this study was to identify the different microstructures produced by CC, PM and as-cast techniques for Co–Cr alloys and their phase stability following porcelain firings. MethodsThree bi-layer porcelain veneered Co–Cr specimens and one monolithic Co–Cr specimen of each alloy group [cast, powder metallurgy (PM), CAD/CAM (CC)] were manufactured and analyzed using electron backscatter diffraction (EBSD), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD). Specimens were treated to incremental numbers of porcelain firings (control 0, 5, 15) with crystallographic data, grain size and chemical composition subsequently obtained and analyzed. ResultsEBSD datasets of the cast alloy indicated large grains >200μm whereas PM and CC alloy consisted of mean arithmetic grain sizes of 29.6μm and 19.2μm respectively. XRD and EBSD results both indicated the highest increase in hcp content (>13vol%) for cast Co–Cr alloy after treatment with porcelain firing while PM and CC indicated <2vol% hcp content. A fine grain interfacial layer developed on all surfaces of the alloy after porcelain firing. The depth of this layer increased with porcelain firings for as-cast and PM but no significant increase (p>.05) was observed in CC. EDS line scans indicated an increase in Cr content at the alloy surface after porcelain firing treatment for all three alloys. SignificancePM and CC produced alloy had superior fcc phase stability after porcelain firings compared to a traditional cast alloy. It is recommended that PM and CC alloys be used for porcelain-fused-to-metal restorations.

Effect of PFM Firing Cycles on the Mechanical Properties, Phase Composition, and Microstructure of Nickel‐Chromium Alloy

The purpose of this study was to compare the mechanical properties of beryllium-free nickel-chromium (Ni-Cr) dental casting alloy before and after each porcelain firing cycle (once fired, twice fired, and thrice fired) and to relate these properties to the microstructural changes and changes in X-ray diffraction patterns of Ni-Cr alloy that occur after each porcelain firing cycle. Forty tensile bar specimens and 20 disc-shaped specimens of Ni-Cr alloy were prepared. These specimens were divided into four groups. The first group was not heat treated and tested in the as-cast condition, thus serving as control group. The second, third, and fourth groups were fired once, twice, and thrice, respectively. Tensile bar specimens were loaded to failure in tension using a universal testing machine. Values of ultimate tensile strength, 0.1% yield strength, and percentage elongations were determined. Microstructural study and hardness testing were done using an optical microscope and digital Vickers hardness tester, respectively, on disc-shaped specimens. Disc-shaped specimens were again used to obtain the X-ray diffraction patterns by using diffractometer Bruker D8 focus. Statistical comparisons of the mechanical properties and hardness of the alloy were made with ANOVA. Intergroup comparisons of the data in the as-cast and fired specimens were analyzed by applying Tukey's HSD multiple comparison tests. Before porcelain firing, the alloy exhibited higher ultimate tensile strength (548 MPa), 0.1% yield strength (327 MPa), hardness (192 HV), and lower elongation values (18%). After each firing cycle, there was a significant (p < 0.001) decrease in ultimate strength (464 MPa for three times fired specimens), 0.1% yield strength (284 MPa for three times fired group), and hardness (164 HV for three times fired group) and significant (p < 0.001) increase in elongation value (28% for three times fired group) of Ni-Cr alloy. The microstructure of the control group specimen exhibited heterogeneous microstructure, and after each firing, microstructure of the alloy was gradually homogenized by formation of grain boundaries at the interdendritic interfaces. X-ray diffraction pattern shows that the alloy exhibited four strong diffraction peaks within the range of 2θ = 40° to 100°. After a third firing, intensity of these planes increased. Results of this study confirmed that nickel-based alloys become weaker after each firing process. After firing treatment, the microstructure of alloys showed decreased dendritic structure (i.e., homogenization, which was responsible for decrease in strength and an increase in ductility of the alloy); however, this decreased strength and hardness of Ni-Cr alloy after heat treatment was still superior to those of the most noble metal alloys used in dentistry. X-ray diffraction study showed that firing process led to relieving of stresses, which ultimately resulted in stability in the crystal structure of alloy.