Porcelain Thickness Research Articles

EFFECT OF REPEATED FIRINGS ON METAL CERAMIC BOND STRENGTH OF CO-CR ALLOY FABRICATED BY DIRECT METAL LASER SINTERING AN IN-VITRO STUDY

Purpose: The bond strength of metal ceramic restorations places a key role for the longevity of the prosthesis which could be affected by the fabrication technique and the number of firings. The current research evaluates the effect of repeated firings on bond strength of metal ceramic systems with copings fabricated from two processing techniques, lost wax technique through induction casting and direct metal laser sintering. Materials and Methods: 21 metal ceramic bars will be fabricated using Direct Metal Laser Sintering (Group DMLS) and 21 using conventional lost wax technique (Group Cast). Each sample will have a dimension of 25x3x0.5mm respectively. In the center of each bar, a 1.1mm thickness of porcelain will be fused onto an 8x3mm rectangular area. Each group is further subdivided into 3 subgroups which are subjected to repeated firings (3, 5, 7) and the bond strength is measured with positioning of the samples on a Universal Testing Machine. Results: Group ANOVA and Post Hoc Tukeys test showed comparison of overall bond strength of ceramic samples fabricated using DMLS & Casting subjected to different Firing was done and the difference in mean was statistically significant (p<0.05). Conclusion: The DMLS group showed slight superior bond strength properties when compared with Cast group.

Influence of Thickness of Opaque Porcelain and Alloy Color on the Final Color of Porcelain-Fused-to-Metal Restorations.

Despite the advent of metal-free solutions, porcelain-fused-to-metal restorations (PFM) are still widely used. Particularly for the latest ceramic systems, scarce information is present in the scientific literature about the ideal opaque layer thickness and the alloy color impact to achieve the desired final color of PFM restorations. This study aimed to evaluate the influence of opaque thickness variation layered on different metal alloys on the final color of PFM restorations. Opaque porcelain of one metal−ceramic system (VITA VM13) was layered in four different thicknesses (0.10 mm, 0.15 mm, 0.20 mm, and 0.25 mm) on three differently colored dental alloys: a gold−platinum alloy (yellowish), a gold−palladium alloy (light grayish), and a nickel−chromium alloy (dark grayish). The veneering porcelain layered over the opaque was kept constant (Base Dentine 0.45 mm, Transpa Dentine 0.50 mm, and Enamel 0.20 mm). Sixty specimens were fabricated, five samples for each combination of alloy/opaque thickness. The color difference (ΔE) between specimen and reference was measured using a clinical spectrophotometer. The two-way ANOVA revealed that the thickness of both the opaque (p < 0.001) and the metal alloy (p < 0.001) significantly influenced the ΔE values. Gray-colored alloys covered by a 0.10 mm thick opaque layer enabled the closest color match, whereas this occurred for yellow-color alloys covered by a 0.15 mm thick opaque layer. In contrast, the samples covered by a 0.25 mm thick opaque layer obtained the worst ΔE.

Effect of core and veneer porcelain thickness and resin cement on opalescence property of glass-ceramic veneers.

This study aimed to analyze the effect of core and veneer porcelain thickness and resin cement on the opalescence property (OP) of glass-ceramic veneers, which were used to restore discolored teeth. IPS e.max CAD LT A3 ceramic specimens were fabricated by computer aided design and computer aided manufacturing (CAD/CAM). The thickness values of core porcelain groups were 0.25 and 0.50 mm, and those of the core/veneer porcelain groups were 0.25 mm core/0.25 mm dentin, 0.50 mm core/0.25 mm dentin, 0.50 mm core/0.50 mm dentin, and 0.50 mm core/0.25 mm dentin/0.25 mm incisal. To simulate the clinical bonding procedure of porcelain veneer, resin cement Variolink N Bleach XL was coated at the bottom of CAD/CAM porcelain veneer specimens to make composite specimens of CAD/CAM porcelain veneer and resin cement. The L*a*b* values of specimens in the reflection and transmission pattern were measured by a spectrophotometer. Then, the OP was calculated. The OP values of 0.25 and 0.50 mm core porcelain groups, and 0.25 mm core/0.25 mm dentin, 0.50 mm core/0.25 mm dentin, 0.50 mm core/0.50 mm dentin, and 0.50 mm core/0.25 mm dentin/0.25 mm incisal core/veneer porcelain groups were 6.10±0.50, 7.00±0.24, 6.40±0.24, 7.08±0.28, 7.16±0.21, and 7.86±0.11 respectively. With increasing thickness of core porcelain, the OP values increased significantly (P<0.05). When 0.25 mm-thick dentin porcelain was added, no significant difference was found in the OP values of specimens with the same core porcelain thickness (P>0.05). For the 0.50 mm core porcelain group, no significant difference was found between 0.25 and 0.50 mm-thick dentin porcelain groups (P>0.05), but the OP values increased significantly after increasing the 0.25 mm incisal porcelain (P<0.05). The OP values of 0.25 mm core/0.25 mm dentin, 0.50 mm core/0.25 mm dentin, 0.50 mm core/0.50 mm dentin, and 0.50 mm core/0.25 mm dentin/0.25 mm incisal CAD/CAM porcelain veneer-resin cement composite specimens were 6.29±0.31, 7.56±0.36, 7.67±0.30, and 8.65±0.53. The OP values increased with increasing thickness of the porcelain layer (P<0.05), but no statistically signi-ficant difference was found between the groups of 0.50 mm core/0.25 mm dentin and 0.50 mm core/0.50 mm dentin (P=0.733). The influence of porcelain layer thickness and resin cement on the OP value was statistically different (P<0.05), and no interaction was found between the total thickness and the presence of resin cement (P>0.05). When using glass-ceramic veneers for discolored teeth, the following are recommended to improve the OP and obtain a natural and realistic effect: adopt the design of direct sintering incisal porcelain with core porcelain; appropriately increase the thickness of core porcelain; and select resin cement with opaque effect.

Effect of firing procedures and layering thickness of porcelain on internal adaptation of zirconia cantilever resin-bonded fixed dental prostheses.

This study evaluated the influence of firing procedures and layering thickness of porcelain on internal adaptation of maxillary anterior cantilever zirconia resin-bonded fixed dental prostheses (RBFDPs). The maxillary right central incisor on a model was prepared for a single-retainer zirconia RBFDP. A total of 36 frameworks of cantilever zirconia RBFDPs were classified into three groups (CB0.5, CB1.0, and CB2.0 groups) based on the thickness of the cut-back on the facial surface (0.5 mm, 1.0 mm, and 2.0 mm, respectively). Feldspathic porcelain was layered onto the facial surface of the zirconia RBFDP frameworks. Internal space widths between the abutment tooth and the framework were measured before and after porcelain firing by a replica technique. The internal space values before and after porcelain firings were compared using the paired t-test within the same group (α = 0.05). Differences in internal space values (distortion) between before and after porcelain firing were compared using one-way analysis of variance and Tukey multiple comparison tests. For all framework designs, internal space values after porcelain firing were significantly higher than those before firing. Among all groups, the CB0.5 group showed the lowest internal distortion values for the whole measured area. The CB2.0 group showed higher distortion values than the CB1.0 group. Porcelain firing procedures negatively impacted the internal space in cantilever zirconia RBFDPs. In addition, the increased volume of layering porcelain had a negative effect on the internal distortion of maxillary anterior cantilever zirconia RBFDPs.

Evaluation of Knowledge and Practice of Dentists in Yazd about Tooth Preparation Principles of Abutment Teeth for a Metal-Ceramic Crown in 2019

Introduction: Improper tooth preparation in a fixed metal-ceramic prosthesis leads to a prosthesis construction with an insufficient thickness of porcelain or too thick porcelain on the base metal structure. The present designed study aimed to evaluate the knowledge and practice of dentists in Yazd about the basic principles of tooth preparation for the metal-ceramic veneer. Materials &amp; Methods: This was a descriptive cross-sectional study. A valid and reliable questionnaire containing personal information, seven knowledge questions, and six practice questions was designed. After confirmation, it was distributed and collected among general dentists in Yazd in 2019. Data were analyzed by t-test and ANOVA. Results: 177 dentists answered Questionnaires. Average knowledge scores were 4.50 ± 1.51 out of 7 and mean performance scores were 4.59 ± 0.81 out of 6. The knowledge of the group under 30 years old was higher than the group of 30 to 39 (p value = 0.017). Differences in participants’ performance scores based on age groups weren’t significant (p value = 0.827). Women had higher knowledge than men (p value = 0.029). But no difference was observed in the performance scores of the two genders (p value = 0.092). According to work experience, there were no significant differences in Comparison of knowledge, practice scores and participation in additional courses (p value &gt; 0.05). Conclusion: The knowledge of Yazd dentists and their level of practice have been moderate and favorable. In some areas, lack of knowledge and practice were significant. It also seems that the current postgraduate courses don’t have much impact on the knowledge and practice of dentists. Therefore it’s necessary to correct and update these courses.

Assessment of internal fit and micro leakage of conventionally fabricated ceramometallic restoration versus CAD wax and press veneering (in-vitro study)

Statement of problemAccuracy of internal fit and microleakage for CAD-CAM systems used in metal coping fabrication and veneered with layering or pressing porcelain in ceramometallic restoration is unclear.Material and methodsA master metal die was milled to resemble the right mandibular first molar preparation for coverage with ceramometallic restoration. Master die was duplicated to twenty-four resin specimen dies.They were divided into two groups according to metal coping construction technique using either conventional (C) or CAD (D) wax. Each group was subdivided into two subgroups (n = 6) according to the technique of porcelain veneering (layered or pressed) to fabricate ceramometallic restorations, where subgroup (CL, DL) were conventionally layered by porcelain and (CP, DP) were press veneered. A standardized thickness of metal and porcelain was performed in all specimens as per manufacturer’s instructions for techniques ceramometallic restoration construction.Evaluation of internal fit was done with silicone replica technique using stereomicroscope at ×24 magnification where the thickness of silicon layer was measured at 20 reference points on each specimen. Then specimens were subjected to thermocycling. Sectioned specimens were assessed for microleakage using a stereomicroscope at ×12 magnification along die-cement interface with a five scale score.ResultsMean internal gap values of veneering showed a statistically nonsignificant difference between specimens made with layering(L) and pressing(P). Different techniques of wax construction showed a non-significant difference in internal gap values between specimens made with conventional(C) and CAD(D) waxing. However, a significant difference was found in the internal gap at different sites. The highest internal gap was found at the occlusal surface, while the lowest gap was found at the finish line. The highest mean microleakage score was found with CAD wax and press veneering, while the lowest mean microleakage score was found with conventional wax and press veneering.ConclusionBoth construction techniques of ceramometallic restoration were considered reliable in restoration production within a clinically acceptable range regarding internal fit and microleakage. There is a strong positive correlation between internal fit and microleakage of ceramometallic restoration constructed.

Effect of light intensity, light-curing unit exposure time, and porcelain thickness of ips e.max press and vintage LD press on the hardness of resin cement

Background: Porcelain veneer restoration is the primary choice for indirect restoration, especially for anterior teeth, given its high esthetic properties and lower failure rate than resin composites. Glass-based ceramics such as IPS e.max Press and Vintage LD Press are a choice for veneer due to its superior physical properties. Resin cement is used to attach the veneer restoration to the teeth. The polymerization of resin cement used in veneer restoration affects the stability, mechanical properties, and resistance of the restoration. The composition and thickness of the porcelain material affect the light-curing unit to cured resin cement. Objectives: The aim of this study was to evaluate the influence of porcelain thickness, light intensity, and exposure time in the hardness of resin cement. Methods: Porcelain samples measuring 5 mm in diameter with three types of thicknesses of IPS e.max Press and Vintage LD Press were used in the study. Resin cement in a metal mold was placed under a porcelain sample before curing with a light-emitting diode (LED) intensity of 1300 or 1700 mW/cm2. The hardness test was then carried out on the bottom of the resin cement. Result: The highest hardness value was obtained from a Vintage LD Press with a thickness of 0.7 mm (cured at 1300 mW/cm2 for 20 s). A four-way ANOVA test showed significant differences for brands, thicknesses, and times of exposure (P

Effect of Incisal Porcelain Veneering Thickness on the Fracture Resistance of CAD/CAM Zirconia All-Ceramic Anterior Crowns.

Statement of Problem In some clinical situations, the vertical length of either a prepared tooth or an implant abutment is short, while the occlusal clearance to be restored by a porcelain crown is large. Incisal thickness of the veneering porcelain should be considered to prevent mechanical failure of the crown. Purpose The aim of this study is to evaluate the effect of two different incisal veneering porcelain thickness on the fracture resistance of the anterior all-ceramic CAD/CAM zirconia crown system as compared with the conventionally used metal ceramic crown system. Method CAD/CAM zirconia all-ceramic and metal ceramic crowns were fabricated on the prepared dies with standardized dimensions and designs using standardized methods according to the manufacturer's instructions. All crowns were then adhesively luted with resin-based cement (Multilink cement system), subjected to thermal cycling and cyclic loading, and were loaded until fracture using the universal testing machine to indicate the fracture resistance for each crown material in each veneering thickness. Results Statistical analysis was carried out, and the results showed that the fracture resistance of the nickel-chromium metal ceramic group was significantly higher than that of the CAD/CAM zirconia all-ceramic group. Also, the fracture resistance of crowns with 1.5 mm incisal veneering thickness was significantly higher than those with 3 mm incisal veneering thickness in both groups. Furthermore, there was no significant difference in the fracture mode of the two groups where 50% of the total specimens demonstrated Mode II (veneer chipping), while 35% demonstrated Mode I (visible crack) and only 15% demonstrated Mode III (bulk fracture). Conclusion High failure load values were demonstrated by the specimens in this study, which suggest sufficient strength of both incisal veneering thickness in both crown systems to withstand clinical applications; however, the fracture patterns still underline the requirement of a core design that support a consistent thickness of the veneering ceramic, and it is recommended to conduct long-term prospective clinical studies to confirm findings reported in the present study.

Degree of conversion of resin cements polymerized under different thicknesses of feldspathic porcelain

Aim The aim of this study is to evaluate the degree of conversion (DC) of resin cements polymerized under different thicknesses of feldspathic dental ceramic. Methods: Forty samples of RelyX ARC and RelyX Veneer resin cements were polymerized under Starlight feldspathic ceramic discs (DeguDent Gmbh) with 0.5 mm, 1.2 mm, 1.8 mm, and 2.4 mm in thickness. The control group was cured without the interposition of ceramic. The DC measurements were performed 10 minutes, 1 hour, and 24 hours after the light-activation in a Nexus 670 FTIR spectrophotometer. Data were analyzed by two-way repeated measure ANOVA and Fisher PLSD test. Results: The RelyX ARC showed higher DC for all ceramic thicknesses. There was significant decrease in DC related to an increase in ceramic thickness. For RelyX ARC, the values of DC obtained after 1 hour and 24 hours did not differ statistically between them, but they were higher than those analyzed after 10 minutes. For RelyX Veneer cement, there was gradual increase in the DC up to 24 hours. Conclusion: The higher the thicknesses of ceramic, the lower DC of the resin cement.

An In-Vitro Study on the Influence of Ceramic Thickness in the Color of Titanium Ceramic Restoration

Background: Various factors such as metal alloy, thickness of the opaque porcelain, different methods of condensation of ceramic, thickness of the dentine ceramic, different ceramic firing condition affect the color of final ceramic restoration. It is not considered significant while taking single variable into account but several subtle changes in these factors lead to discernible color change.&#x0D; Purpose: The aim of this study was to evaluate the influence of ceramic thickness over color of ceramic layered on the titanium casting.&#x0D; Methods: Ultra low fusing ceramics of different thickness (0.5mm, 1mm, 1.5mm and 2mm) was veneered over a metal substrate of pure titanium and spectrophotometric analysis of 20 such discs was done to determine parameters (CIELAB system). One-way ANOVA and multiple comparison results of ANOVA were performed for statistical analysis.&#x0D; Results: The different thickness of ceramic significantly influences the ΔE value. There was significant change in the L* value (P&lt;0.05) with different thickness of titanium metal ceramic tabs. There was also significant difference in C*ab values with different thickness of ceramic.&#x0D; Conclusions: The thickness of the ceramic has significant effect in the L* value of the titanium ceramic restoration. The thicker restoration appeared darker than the thinner one. There was also significant effect in the color saturation or chroma with different thickness of ceramic. Chroma decreased with increased thickness. Color difference between groups were significant. Overall thickness had effect on the final color of the titanium ceramic restoration.&#x0D;

Effects of veneering porcelain thickness and background shade on the shade match of zirconia-based restorations.

Background. Effects of veneering porcelain thickness and background shade on the shade match of zirconia-based restorations are unclear. The aim of this study was to evaluate the impacts of veneering porcelain thickness and background shade on the shade match of zirconia-based restorations. Methods. Forty A2 shade veneered zirconia disk specimens (10 mm in diameter) were fabricated, with veneering porcelain thicknesses of 1.6, 1.8, 2.0 and 2.2 mm. Three backgrounds were made of A2 shade composite resin (A2), nickel-chromium alloy (NC) and amalgam (AM). The veneered zirconia specimens were placed on the backgrounds. CIELab values were measured with a spectrophotometer. ΔE values were measured to determine color differences between the specimens and the A2 VITA classical shade (target shade). ΔE values were compared with an acceptability threshold (ΔE=3.7). Repeated measures ANOVA, Bonferroni, and 1-sample t-test were used to analyze data (P<0.05). Results. Mean ΔE values ranged between 1.9 and 5.0. The veneering porcelain thickness, the background shade and their interaction affected the ΔE (P<0.0001). The minimum veneering porcelain thickness for the shade match was 2 mm for NC and 1.8 mm for AM. Conclusion. Veneering porcelain thickness and background shade affected the shade match of zirconia-based restorations. With dark-shaded backgrounds, the amount of veneering porcelain thickness needed for the shade match might be beyond acceptable clinical limits. Tooth-shaded backgrounds are esthetically advocated rather than dark-shaded backgrounds in zirconia-based restorations.

Effect of tooth substrate and porcelain thickness on porcelain veneer failure loads in vitro

Statement of problemBonded porcelain veneers are widely used esthetic restorations. High success and survival rates have been reported, but failures do occur. Fractures are the commonest failure mode. Minimally invasive or thin veneers have gained popularity. Increased enamel and porcelain thickness improve the strength of veneers bonded to enamel, but less is known about dentin or mixed substrates. PurposeThe purpose of this in vitro study was to measure the influences of tooth substrate type (all-enamel, all-dentin, or half-dentin-half-enamel) and veneer thickness on the loads needed to cause initial and catastrophic porcelain veneer failure. Material and methodsModel discoid porcelain veneer specimens of varying thicknesses were bonded to the flattened facial surfaces of incisors with different enamel and dentin tooth substrates, artificially aged, and loaded to failure with a small sphere. Initial and catastrophic fracture events were identified and analyzed statistically and fractographically. ResultsFracture events included initial Hertzian cracks, intermediate radial cracks, and catastrophic gross failure. All specimens retained some porcelain after catastrophic failure. Cement failure occurred at the cement–porcelain interface not at the cement–tooth interface. Porcelain veneers bonded to enamel were substantially stronger and more damage-tolerant than those bonded to dentin or mixed substrates. Increased porcelain thickness substantially raised the loads to catastrophic failure on enamel substrates but only moderately raised the loads to catastrophic failure on dentin or mixed substrates. The veneers bonded to half-dentin-half-enamel behaved remarkably like those bonded wholly to dentin. ConclusionsPorcelain veneers bonded to enamel were substantially stronger and more damage-tolerant than those bonded to dentin or half-enamel-half dentin.

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 number of firings on the color and translucency of ceramic core materials with veneer ceramic of different thicknesses

Statement of problemWhether masking or translucency should be the goal for achieving an esthetic restoration with ceramic materials is unknown. PurposeThe purpose of this in vitro study was to examine the effect of the number of firings on the color and translucency of ceramic core material with different thicknesses of veneer ceramic. Material and methodsThree different ceramic systems were used: IPS Empress (IE), IPS e.max Press (IEP), and Turkom Cera (TC). Ninety disk-shaped cores, 10 mm in diameter and 0.8 mm in thickness were prepared using each system (n=30). The specimens were divided into 3 subgroups (n=10) according to the thickness of the veneering ceramic: 0.5, 1.0, and 1.5 mm. The specimens were fired 1, 3, and 5 times, and the color parameters of the specimens were measured. The color measurements were repeated, and the data were statistically evaluated using 2-way and multifactorial analysis of variance, the Duncan test, and the Bonferroni post hoc test. ResultsThe number of firings affected the translucency parameter and CIELab values. Increased porcelain thickness led to decreased translucency parameter and L* values and increased a* and b* values (P<.05). The IE system was the most translucent (P<.001). The changes with increased firing periods were not statistically significant (P>.05). The number of firings affected the color change of the IE and IEP systems but not of the translucency parameter system. ConclusionsRepeated firings and porcelain thickness affected the final color and translucency of the ceramic systems tested. These 2 factors adversely affected the esthetic result and should be considered in both the preparation and the laboratory phase.

Fracture strength of veneered translucent zirconium dioxide crowns with different porcelain thicknesses

Objective: To evaluate fracture strength of veneered translucent zirconium dioxide crowns designed with different porcelain layer thicknesses.Materials and Methods: Sixty crowns, divided into six groups of 10, were used in this study. Groups were divided according to different thicknesses of porcelain veneer on translucent zirconium dioxide cores of equal thickness (0.5 mm). Porcelain thicknesses were 2.5, 2.0, 1.0, 0.8, 0.5 and 0.3 mm. Crowns were artificially aged before loaded to fracture. Determination of fracture mode was performed using light microscope.Results: Group 1.0 mm showed significantly (p ≤ .05) highest fracture loads (mean 1540 N) in comparison with groups 2.5, 2.0 and 0.3 mm (mean 851, 910 and 1202 N). There was no significant difference (p>.05) in fracture loads among groups 1.0, 0.8 and 0.5 mm (mean 1540, 1313 and 1286 N). There were significantly (p ≤ .05) more complete fractures in group 0.3 mm compared to all other groups which presented mainly cohesive fractures.Conclusions: Translucent zirconium dioxide crowns can be veneered with minimal thickness layer of 0.5 mm porcelain without showing significantly reduced fracture strength compared to traditionally veneered (1.0–2.0 mm) crowns. Fracture strength of micro-veneered crowns with a layer of porcelain (0.3 mm) is lower than that of traditionally veneered crowns but still within range of what may be considered clinically sufficient. Porcelain layers of 2.0 mm or thicker should be used where expected loads are low only.

Effect of Opaque Porcelain Thickness Bond Strength of Porcelain to Ni-Cr Alloys

Objectives: Metal-ceramic restorations are the standard by which all esthetic restorations are measured. Fracture of dental restorations is a multifactorial problem, which is serious and costly. Debonding of porcelain from the metal substructure and the bond strength depend on many factors. The purpose of this study was to determine whether the opaque porcelain thickness has a significant effect on metal ceramic bond strength utilizing the ISO 9663 standard crack initiation test. Methods: Thirty rectangular Ni-Cr metal bars (25×5×0.3mm) were fabricated according to ISO9663 standards. The metal bars were divided into three groups of 10. Opaque, body and enamel Noritake porcelain were applied on the middle of the bar according to ISO9663 standards up to 1mm porcelain thickness. The opaque porcelain thicknesses were 0.1, 0.2, and 0.3 mm, respectively in the three groups. The 3-point bending test was applied according to the ISO9663 standards and fracture strength (Ffail) was measured using a universal testing machine with a crosshead speed of 1.5mm/minute. Results: Analyses of the data by one-way ANOVA demonstrated no significant differences in bond strength among the three experimental groups (P=0.26). Conclusion: Within the limitations of this study, it is concluded that 0.1mm opaque porcelain provides sufficient bond strength between metal and ceramic in metal-ceramic restorations.

Considerations Regarding the Influence of Layering Thickness on the Esthetics of a Metal Ceramic Restoration

A fixed restoration has many important properties. Not only it has to resist in the harsh oral environment but it also has to resist bite forces and to remain intact for an extended period of time and porcelain has all these qualities and it also gives excellent esthetic results. The aim of the study was to evaluate the influence of each layer of porcelain fused to the metal coping on the final aspect of a metal ceramic restoration using the Ivoclar dSign system. Therefore we have chosen three methods to apply the porcelain by varying the thickness of the dentin and enamel layers fused on the metal substructure. The layer thickness of the opaque porcelain, the body porcelain (dentin), and the incisal porcelain greatly influence the final aspect of the metal ceramic restoration and this variation must be taken into consideration in order for the dental technician to obtain the desired shade

The bending stress distribution in bilayered and graded zirconia-based dental ceramics

The purpose of this study was to evaluate the biaxial flexural stresses in classic bilayered and in graded zirconia-feldspathic porcelain composites. A finite element method and an analytical model were used to simulate the piston-on-ring test and to predict the biaxial stress distributions across the thickness of the bilayer and graded zirconia-feldspathic porcelain discs. An axisymmetric model and a flexure formula of Hsueh et al. were used in the FEM and analytical analysis, respectively. Four porcelain thicknesses were tested in the bilayered discs. In graded discs, continuous and stepwise transitions from the bottom zirconia layer to the top porcelain layer were studied. The resulting stresses across the thickness, measured along the central axis of the disc, for the bilayered and graded discs were compared. In bilayered discs, the maximum tensile stress decreased while the stress mismatch (at the interface) increased with the porcelain layer thickness. The optimised balance between both variables is achieved for a porcelain thickness ratio in the range of 0.30–0.35. In graded discs, the highest tensile stresses were registered for porcelain rich interlayers (p=0.25) whereas the zirconia rich ones (p=8) yield the lowest tensile stresses. In addition, the maximum stresses in a graded structure can be tailored by altering compositional gradients. A decrease in maximum stresses with increasing values of p (a scaling exponent in the power law function) was observed. Our findings showed a good agreement between the analytical and simulated models, particularly in the tensile region of the disc. Graded zirconia-feldspathic porcelain composites exhibited a more favourable stress distribution relative to conventional bilayered systems. This fact can significantly impact the clinical performance of zirconia-feldspathic porcelain prostheses, namely reducing the fracture incidence of zirconia and the chipping and delamination of porcelain.

Experimental and finite element study of residual thermal stresses in veneered Y-TZP structures

The main complications of zirconia-based laminated systems are chipping and delamination of veneering porcelain, which has been found to be directly associated with the development of residual thermal stresses in the porcelain layer. This study investigates the effects of cooling rate and specimen geometry on the residual stress states in porcelain-veneered zirconia structures. Bilayers of three different shapes (bars, semi-cylindrical shells, and arch-cubic structures) with 1.5mm and 0.7mm thickness of dentin porcelain and zirconia framework, respectively, were subjected to two cooling protocols: slow cooling (SC) at 32°C/min and extremely-slow cooling (XSC) at 2°C/min. The residual thermal stresses were determined using the Vickers indentation method and validated by finite element analysis. The residual stress profiles were similar among geometries in the same cooling protocol. XSC groups presented significantly higher tensile stresses (p=0.000), especially for curved interfaces. XSC is a time-consuming process that showed no beneficial effect regarding residual stresses compared to the manufacturer recommended slow cooling rate.

Effectiveness of Combination of Dentin and Enamel Layers on the Masking Ability of Porcelain.

This study evaluated the masking ability of different porcelain thicknesses and combination of enamel and/or dentin porcelain layers over simulated background dental substrates with higher (A2) and lower (C4) color values. Combination of the enamel (E) and dentin (D) monolayer porcelain disks with different thicknesses (0.5 mm, 0.8 mm, and 1 mm) resulted in the following bilayer groups (n=10): D1E1, D1E0.8; D1E0.5; D0.8E0.8; D0.8E0.5, and D0.5E0.5. CIELAB color coordinates were measured with a spectrophotometer. The translucency parameter of mono and bilayer specimens and the masking ability estimated by color variation (ΔE*ab) of bilayer specimens over simulated dental substrates were evaluated. Linear regression analysis was used to investigate the relationships translucency parameter × ΔE*, translucency parameter × porcelain thickness, and ΔE* × porcelain thickness. Data were analyzed statistically (α= 0.05). Thinner porcelain disks were associated with higher translucency. Porcelain monolayers were considerably more translucent than bilayers (enamel + dentin). Dentin porcelain was less translucent than enamel porcelain with same thickness. ΔE* was always lower when measured over A2 background. Higher ΔE* was observed for the C4 background, indicating poorer masking ability. Increased ΔE* was significantly associated with increased translucency for both backgrounds. Decreased translucency and ΔE* were associated with increased total porcelain thickness or increased dentin thickness for both backgrounds. In conclusion, increased porcelain thickness (particularly increased dentin layer) and increased porcelain opacity resulted in better masking ability of the dental backgrounds.