High Translucency Research Articles

Optical Properties of Novel Resin Matrix Ceramic Systems at Different Thicknesses

Objectives: The purpose of this study was to investigate the effect of material and thickness on the translucency parameters (TP) and opalescence parameters (OP) for resin matrix ceramic blocks. Materials and Methods: 90 disc-shaped specimens (8 mm diameter and A2 shade, High Translucency) were fabricated from Vita Enamic, Lava Ultimate and GC Cerasmart resin-matrix ceramic blocks and prepared to thicknesses of 0.5 mm, 1 mm and 1.5 mm (n=10). A dental spectrophotometer (VITA Easyshade Advance) was used to calculate the TP and OP. All specimens were placed on white and black backgrounds. The color measurements were repeated three times for each of the specimens and the mean values of L, a and b were calculated. Data were analyzed by a two-way analysis of variance (ANOVA) and Tukey’s test. Results: For the 0.5 mm thickness groups, GC Cerasmart had the highest and Vita Enamic had the lowest TP values. For the 1 mm thickness groups, GC Cerasmart had the highest TP, whereas Vita Enamic had the lowest TP. For the 1.5 mm thickness groups, Lava Ultimate had the highest TP, whereas Vita Enamic had the lowest TP. For the 0.5 mm thickness groups, Vita Enamic, and GC Cerasmart had the highest and lowest OP, respectively. The OP values in the 1 mm thickness group of Vita Enamic groups were higher than the GC Cerasmart and Lava Ultimate groups. The OP values in the 1.5 mm thickness group Lava Ultimate group were higher than the GC Cerasmart and Vita Enamic groups. In all groups, the OP values showed an increase in parallel with the increase in thicknesses, in contrast, the TP values showed a decrease. Conclusions: Type and thickness of the resin matrix ceramics affect the optical properties of the materials.

Effects of substrate, ceramic thickness, translucency, and cement shade on the color of CAD/CAM lithium-disilicate crowns.

The aim of this in vitro study was to evaluate the effects of substrate colors, different levels of ceramic thickness and translucency, and cement shades on the color difference from a reference color of lithium-disilicate crowns. A premolar tooth preparation was made on a study model for 1.0 and 1.5 mm thick full-ceramic crowns. Digital impressions were taken (3Shape TRIOS) and crowns designed in a CAD program (DentalDesigner). Shade A1 crowns were milled (Everest, Kavo) from high-translucency (HT) and low-translucency IPS e.max (Ivoclar Vivadent) blocks. Twelve substrates were made of different colors and materials (Natural Die Material, Co-Cr, zirconia, and gold-colored alloy). Three different shades of try-in pastes were used to simulate the effect of cements (Variolink Esthetic try-in paste; Ivoclar). Shade measurement was done three times for each crown by a spectrophotometer (VITA Easyshade Advance); averages were compared to a reference crown (A1, HT, 1.5 mm, ND2 abutment, neutral try-in paste) with ΔE00 (CIEDE2000, according to the CIE latest standard) calculated. All the examined parameters influenced the ΔE00 of the crowns. The weakest effect was exerted by the try-in paste. All examined parameters influenced the final color of e.max CAD lithium-disilicate ceramic crowns. Matching the shade of ceramic crowns to the natural tooth color is a great challenge in dentistry. To meet patients' increasing esthetical expectations, CAD/CAM methods are very popular for full-ceramic crowns. However, several factors such as the shade of the abutment, luting cement color, ceramic thickness, and translucency may influence the final color. Our objective was to measure the optical effect of these factors on the final shade of CAD/CAM lithium-disilicate ceramic crowns.

Recent Advances in Dental Composites: An Overview

Composite resins are widely used aesthetic materials in restorative dentistry. These materials were introduced to overcome the inherent shortcomings of amalgam restorative materials. Dental amalgams are unesthetic and toxic. Earlier composites lack in mechanical properties to withstand the masticatory forces. Various filler particles have been added to composite resins to improve their physical and mechanical properties. Filled composite resins exhibit high compressive strength, abrasion resistance, ease of application and high translucency. Depending on the filler size and shapes, various composites have been developed until now. This article is a review of numerous types of composites that are technologically advanced to modify their properties.

Effect of Thermocycle Aging on Color Stability of Monolithic Zirconia

Background: The color stability of dental restorative materials is important for long-term clinical success. Objectives: The objective of this study was to examine the effect of thermocycling on the color and translucency stability of monolithic zirconia. Materials and methods: A total of 80 disc-shaped specimens (1 cm diameter) were produced from monolithic zirconia material, Katana High Translucent (Kuraray Noritake Dental, Kurashiki, Japan). The specimens were prepared in four different thicknesses: 0.5 mm, 1 mm, 1.5 mm and 2 mm. Before thermocycling, color measurements of the specimens were made by a spectrophotometer (Spectro Shade TM MICRO; MHT Optic Research AG, Milan, Italy). After the thermal aging procedure, the color measurement was repeated. Data obtained from the study were analyzed with descriptive statistics, correlation analysis, one-way ANOVA and Tukey’s tests. Results: After thermocycling, the L*, a*, b* values decreased at all thicknesses. The maximum change in the L*, a* and b* values was observed in 0.5-mm-thick specimens, while the least change was observed in 2-mm-thick specimens. The amount of color change in the specimens after thermocycling was found to be the highest in 0.5-mm-thick specimens (ΔE = 0.91 ± 0.02), and the lowest in 2-mm-thick specimens (ΔE = 0.85 ± 0.01). While a statistically significant color change (ΔE) was observed in 0.5-mm-thick specimens (p E) was observed (p > 0.05) in 1-mm, 1.5-mm, and 2-mm-thick specimens. After thermocycling, the translucency parameter (TP) values decreased at all thicknesses. The highest change in the TP values was observed in 0.5-mm-thickspecimens (1.09 ± 0.03), while the lowest change was observed in 2-mm-thickspecimens (0.40 ± 0.04). While a statistically significant change in the TP values was observed in 0.5-mm-thick specimens (p 0.05). Conclusion: Although the color and translucency values after thermocycling exhibited statistically significant changes in the 0.5 mm thickness group, a statistically significant difference was not observed in the other thickness groups.

Fracture resistance of cingulum rest seats in CAD-CAM tooth-colored crowns for removable partial denture abutments

Statement of problemThe prevalent use of computer-aided design and computer-aided manufacturing (CAD-CAM) for tooth-colored ceramic materials has led to several case reports and retrospective clinical studies of surveyed crowns used to support removable partial dentures. How the specific contour of a cingulum rest seat affects the fracture resistance of these CAD-CAM tooth-colored materials is unknown. PurposeThe purpose of this in vitro study was to compare the fracture resistance of monolithic CAD-CAM tooth-colored mandibular canine–surveyed ceramic crowns with cingulum rest seats of different designs. Material and methodsFive groups (n=24/group) of CAD-CAM tooth-colored crowns were milled from the same standard tessellation language (STL) file: group EM, lithium disilicate–based material (IPS e.max CAD CEREC blocks); group SM, zirconia-based material (NexxZr T); group LP, zirconia-based material (Lava Plus High Translucency); group ZC, zirconia-based material (ZirCAD LT); and group MZ, composite resin (MZ100 CEREC blocks), used as a control. Crowns from each group were divided into 2 subgroups representing 2 shapes of cingulum rest seat design: round design subgroup (n=12) with 0.5-mm radius of curvature and sharp design subgroup (n=12) with 0.25-mm radius of curvature for the rest seat preparation. The crowns were cemented with resin cement to a composite resin die on a steel nut. After 24 hours of storage in water at 37°C, the specimens were statically loaded to fracture with a custom metal retainer on top of the cingulum rest seat by using a universal testing machine at a crosshead speed of 1.5 mm/min. Two-way ANOVA and the Tukey honestly significant difference tests were used to control the familywise error rate (α=.05). Representative specimens were examined using an optical stereomicroscope at ×10 magnification and a scanning electron microscope to determine the failure patterns and fracture mechanism. ResultsThe results of the ANOVA test indicated statistically significant differences by materials and rest seat designs (P<.001). The mean ±standard deviation maximal load capacity was 773.5 ±255.0 N for group MZ, 1124.9 ±283.9 N for group EM, 2784.1 ±400.5 N for group SM, 2526.9 ±547.1 N for group LP, and 3200.8 ±416.8 N for group ZC. The round design subgroups had an approximately 30% higher mean failure load than the sharp design subgroups for all surveyed crowns. ConclusionsThe present in vitro study demonstrated that zirconia-based groups fractured at twice the load as the lithium disilicate group. Of the 3 zirconia-based groups, group ZirCAD had a statistically greater fracture resistance than the other groups. Designing the cingulum rest seat to have a broad round shape provides a statistically significant higher fracture resistance than a sharp-shape design (P<.05).

Using zebrafish larval models to study brain injury, locomotor and neuroinflammatory outcomes following intracerebral haemorrhage

Intracerebral haemorrhage (ICH) is a devastating condition with limited treatment options, and current understanding of pathophysiology is incomplete.Spontaneous cerebral bleeding is a characteristic of the human condition that has proven difficult to recapitulate in existing pre-clinical rodent models. Zebrafish larvae are frequently used as vertebrate disease models and are associated with several advantages, including high fecundity, optical translucency and non-protected status prior to 5 days post-fertilisation. Furthermore, other groups have shown that zebrafish larvae can exhibit spontaneous ICH. The aim of this study was to investigate whether such models can be utilised to study the pathological consequences of bleeding in the brain, in the context of pre-clinical ICH research. Here, we compared existing genetic (bubblehead) and chemically inducible (atorvastatin) zebrafish larval models of spontaneous ICH and studied the subsequent disease processes. Through live, non-invasive imaging of transgenic fluorescent reporter lines and behavioural assessment we quantified brain injury, locomotor function and neuroinflammation following ICH. We show that ICH in both zebrafish larval models is comparable in timing, frequency and location. ICH results in increased brain cell death and a persistent locomotor deficit. Additionally, in haemorrhaged larvae we observed a significant increase in macrophage recruitment to the site of injury. Live in vivo imaging allowed us to track active macrophage-based phagocytosis of dying brain cells 24 hours after haemorrhage. Morphological analyses and quantification indicated that an increase in overall macrophage activation occurs in the haemorrhaged brain. Our study shows that in zebrafish larvae, bleeding in the brain induces quantifiable phenotypic outcomes that mimic key features of human ICH. We hope that this methodology will enable the pre-clinical ICH community to adopt the zebrafish larval model as an alternative to rodents, supporting future high throughput drug screening and as a complementary approach to elucidating crucial mechanisms associated with ICH pathophysiology.

EVALUATION OF BIAXIAL FLEXURAL STRENGTH AND TRANSLUCENCY OF MULTICHROMATIC TRANSLUCENT ZIRCONIA AND LITHIUM DISILICATE CERAMICS

INTRODUCTION: Full-contour (monolithic) zirconia restorations are gaining in popularity. High translucent zirconia materials and multilayered zirconia blocks might help to overcome the aesthetic drawbacks of traditional zirconia for fabrication of monolithic restorations OBJECTIVES: Were to evaluate the biaxial flexural strength and translucency of CAD/CAM: multichromatic ultra-translucent zirconia and comparing it with multichromatic high translucency Lithium Disilicate glass-ceramic. MATERIALS AND METHODS40 ceramic specimens were divided into two main groups; Group I: CAD/CAM multichromatic ultratranslucent Zirconia( UTML KATANA Zirconia) & Group II: Pressable multichromatic high translucent Lithium Disilicate glass-ceramic (e.max press multi). Each group was subdivided into two sub groups; sub group A: disc specimens (12mm diameter×1.5mm thickness) were fabricated (n=10) & thermocycled (500 cycles, 5°/55°C, 15 sec dwell time).Then, biaxial flexural strength was measured in MPa. Sub group B: rectangular specimens (12mm length × 10mm width × 1.5mm thickness) were fabricated (n=10). Spectrophotometric analysis was conducted to evaluate and compare the degree of translucency by translucency parameter (TP). Data were analyzed using student t-test & ANOVA with repeated measures test. RESULTS Statistical analysis of Biaxial flexural strength using student t-test revealed that group I (607.24 ± 71.79) showed higher statistically significant biaxial flexural strength values than group II (290.69 ± 41.19) ( p <0.001*). Results of translucency revealed that there were significant statistical differences between the two subgroups where IPS e.max Press Multi provided better translucency than UTML KATANA zirconia. CONCLUSIONS: Multi layered zirconia showed higher mechanical, but lower optical properties than lithium disilicate. The multi layered zirconia showed four layers with different light transmittance capabilities. It might therefore be useful for enhancing the aesthetic appearance of full-contour zirconia restorations made from this material in stress bearing areas.

Influence of polymerization time on properties of dual-curing cements in combination with high translucency monolithic zirconia

PurposeThe aim of this in vitro study was to assess conversion degree (DC), micro-hardness (MH) and bond strength of two dual-curing resin cements employed under translucent monolithic zirconia irradiated with different time protocols. Methods84 square shaped samples of 1mm thickness were prepared from high translucency zirconia blocks and divided into two groups (n=24) according to the cement employed: (1) Rely-X Ultimate; (2) Panavia SA. Each group was further divided into 3 subgroups (n=8) according to the irradiation time: (a) no light; (b) 20s; (c) 120s. Light curing was performed 60s after the sample was placed on the diamond support of a FT-IR spectrophotometer with a high power multiLED lamp. Final DC% were calculated after 10min. After 24h, Vickers Test on the cement layer was performed. The same protocol was used to lute composite cylinders in order to evaluate microshear bond-strength test. ANOVA and Bonferroni tests were performed to find differences between MH and bond-strength to zirconia, while for DC% the Scheirer–Ray–Hare two-way test was used. ResultsThe two cements reached higher DC% in subgroup (b) and (c). As concern MH, statistics showed an increase in curing time was able to improve MH significantly. Bond-strength was not affected by irradiation time only for Panavia SA. ConclusionsThe first null hypothesis has to be rejected since DC% and MH of the dual-cements tested were influenced by the curing time. The second null hypothesis is partially rejected since the bond strength was influenced by the curing time only for Rely-X Ultimate.

COMPARISON BETWEEN CHAIR-SIDE AND LABORATORY AIR PARTICLE ABRASION ON SHEAR BOND STRENGTH OF 3 DIFFERENT TYPES OF ZIRCONIA TO COMPOSITE RESIN

Purpose: To compare between the effect of chair-side and laboratory air particle abrasion (APA) on shear bond strength of different types of zirconia to composite resin.Materials and Methods: Study was divided into 2 groups (n=36): laboratory (L) and chair- side (C) according to APA application methods. Each group was further divided into 3 subgroups according to type of zirconia used (High-Translucency (HT), Super-Translucency (ST), and Top- Translucency (TT)). Using CADCAM 8x8x3 zirconia cuboids were constructed, cleaned and sintered. Composite cuboids having dimensions of 6x6x3 were also constructed using custom made plexi-plates. Composite cuboids were cemented centrally to the zirconia cuboids with light cure under 5kg for 6 mins. After thermocycling for 1000 cycles, all specimens were dried and collected for testing. The shear bond strength of the specimens was measured utilizing universal testing machine at a crosshead speed of 0.5 mm/min. Failure load was recorded in Newton and SBS was calculated as follows: SBS (MPa) = load (N)/area(mm2).Results: CHT scored the highest mean SBS (12.69±5.59) followed by CST (11.38 ±3.42) and then CTT (8.13±3.4). All chair-side mean SBS values were more than lab SBS values. LHT (7.87±5.17), LTT (7.4±5.75) and the least was LST (6.00±2.48). T-student test revealed significant difference between tested groups (P=0.001).Conclusions: Chair- side APA showed higher mean values of SBS and may present a logical and practical alternative to lab APA in treating zirconia surfaces before cementation.

Optical properties of contemporary monolithic CAD-CAM restorative materials at different thicknesses.

This study evaluated the optical properties of contemporary monolithic CAD-CAM materials with different chemical compositions. Totally, 210 rectangular-shaped, A2 shade specimens (12 × 14 mm) were fabricated from VITA Suprinity T, VITA Enamic T, VITA Mark II, GC Cerasmart LT, Lava Ultimate LT, IPS e.max CAD LT and Prettau Anterior blocks and polished to thicknesses of 0.5 ± 0.01 and 1.0 ± 0.01 mm (n = 15 each material). A dental spectrophotometer (VITA Easyshade Compact) was used to calculate the translucency parameter (TP) and opalescence parameter (OP) values of all tested materials. Statistical analysis was performed using one-way analysis of variance, multiple comparison Tukey's test and independent samples t-test (P = .05). In the 0.5-mm thickness group, GC Cerasmart and Prettau Anterior had the highest and lowest translucency values, respectively. VITA Suprinity had the highest OP value, whereas VITA Mark II and Prettau Anterior had the lowest OP values. In the 1.0-mm thickness group, GC Cerasmart and Lava Ultimate had the highest translucency, whereas Prettau Anterior had the lowest translucency. VITA Suprinity and Prettau Anterior had the highest and lowest OP values, respectively. The optical properties of monolithic restorative materials were influenced by the type and thickness of the material used. According to the results of this study, monolithic materials with different chemical compositions have revealed different optical properties. To obtain esthetic restorations and provide shade matching with natural dentition especially for anterior teeth, monolithic materials should be carefully chosen.

Effect of veneering techniques and subsequent aging on translucency of bilayered zirconia

Purposethis study compared the translucency of zirconia specimens veneered with different veneering techniques, and compared the change in translucency after aging. Materials and methodsFifty slice specimens (0.50 ± 0.01 mm thick) were fabricated of IPS e.maxZirCAD core material, and ZL1 IPS e.maxZirLiner (0.10-mm thick) was layered. The specimens were randomly divided into five groups (n = 10/group). Group Ι (traditional layering technique) was veneered (0.60 mm) by condensing and sintering IPS e.max Ceram low-fusing nano-fluorapatite veneering porcelain; Group ΙΙ (High translucency press on technique) was veneered (0.60 mm) by heat-pressing HT IPS e.maxZirPressfluorapatite glass-ceramic ingots; Group ΙΙΙ (Low translucency press on technique) was veneered (0.60 mm) by heat-pressing LT IPS e.maxZirPressfluorapatite glass-ceramic ingots; Group ΙѴ (High translucency CAD-ON technique) was veneered (0.60 mm) by HT IPS e.max CAD lithium disilicate glass ceramic blocks and GroupѴ (Low translucency CAD-ON technique) was veneered (0.60 mm) by LT IPS e.max CAD lithium disilicate glass ceramic blocks. CIE (L∗, a∗, b∗) parameters were measured and translucency was calculated for each veneering technique before and after aging according to the following equation: TP = [(L∗B-L∗W)2 + (a∗B-a∗W)2 + (b∗B-b∗W)2]1/2. One-way analysis of variance (ANOVA) combined with Bonferroni's post-hoc test and Paired t-test were used to analyze the data (α = 0.05). ResultsStatistical analysis utilizing One-way ANOVA showed that, pressing technique had higher translucency than build-up and CAD on techniques. There was a significant difference between the three techniques except for the low translucency Pressing and CAD on techniques when compared with the build up after aging. Using Paired-t test to determine the effect of aging, a significant decrease of translucency was found in all techniques after aging except for the low translucency Pressing and CAD on techniques. ConclusionVeneering zirconia with both layering and pressing techniques produced more translucent samples than with CAD-ON veneering technique. Aging caused a decrease in translucency of all samples.

Graded Ultra-Translucent Zirconia (5Y-PSZ) for Strength and Functionalities

Ultra-translucent zirconias are drawing immense attention due to their fascinating esthetic appearance. However, the high translucency came at the expense of diminishing strength along with the reduced ability of transformation toughening due to the increased cubic zirconia content. We aim to address these issues by infiltrating glass on the surface of an ultra-translucent zirconia (5Y-PSZ). Glasses of different shades can be used and the resulting graded glass/zirconia layer is expected to improve the material’s flexural strength without compromising its esthetics. We also aim to elucidate how clinically relevant surface treatments—namely, air abrasion, glazing, or polishing—affect the fracture resistance of these zirconias with a high cubic content. All surface treatments were performed on bar-shaped (2 × 3 × 25 mm3) and plate-shaped (12 × 12 × 1 mm3) specimens, which were then subjected to a 4-point bending test and translucency measurements, respectively. 5Y-PSZ proved to be significantly more translucent than 3Y-TZP but also much weaker. Our hypothesis was accepted, as the strength of the glass-infiltrated ultra-translucent 5Y-PSZ (582 ± 20 MPa) is over 70% higher than its uninfiltrated counterpart (324 ± 57 MPa). Its strength is also over 25% higher than the highly polished 5Y-PSZ (467 ± 38 MPa). In addition, the translucency of 5Y-PSZ (translucency parameter [TP] = 34, contrast ratio [CR] = 0.31) is not affected by glass infiltration (TP = 34, CR = 0.32) when the residual surface glass is removed by gentle polishing using 6- and then 3-µm diamond grits. Finally, both air abrasion and the presence of a glaze layer on the tensile surface decreased flexural strength significantly, being 274 ± 55 and 211 ± 21 MPa, respectively. With a combined high strength and translucency, the newly developed glass-infiltrated 5Y-PSZ may be considered a suitable material for next-generation, damage-resistant, and esthetic dental restorations.

Monolithic Ceramics: Effect of Finishing Techniques on Surface Properties, Bacterial Adhesion and Cell Viability.

This study evaluated the morphology, biofilm formation, and viability of human gingival fibroblasts in contact with two monolithic ceramics after two different finishing techniques: polishing or glazing. For this, 92 blocks (4.5 × 4.5 × 1.5 mm) of each ceramic were made using high translucency zirconia partially stabilized by yttrium (YZHT) and lithium silicate reinforced by zirconium (ZLS). Blocks were sintered and then divided into glazing (g) or polishing (p) surface finish. Surface roughness (Ra and RSm) was evaluated through a contact rugosimeter and profilometry. Specimens were contaminated for heterotypic biofilm formation with Streptococcus mutans, Streptococcus sanguinis and Candida albicans for 16 hours. Biofilm was quantified by counting the colony forming units (CFU/mL) and analyzed by scanning electron microscopy (SEM). Fibroblast viability was evaluated by MTT assay. Surface free energy (SFE) was also determined. Roughness data were evaluated using nonparametric tests, while SFE, MTT and CFU results were evaluated by analysis of variance and Tukey test, and MTT data were also submitted to t-test (all, α=0.05). Results showed that polished samples presented a lower high profile mean ( p<0.001); however, YZHTg presented less space between defects ( p=0.0002). SFE showed that YZHT presented higher SFE than ZLS. Profilometry evidenced more homogeneity on polished surfaces. The interaction of finishing technique and microorganisms influenced the CFU ( p=0.00). MTT assay demonstrated initial severe cytotoxic behavior for polished surfaces. SEM images showed homogeneous surfaces, except for glazed YZHT. Glazed surfaces have a greater roughness and tend to accumulate more biofilm. Polished surfaces have higher SFE; however, they are temporarily cytotoxic.

Evaluation of shear bond strength and shear stress on zirconia reinforced lithium silicate and high translucency zirconia.

This study evaluated the shear stress distribution on the adhesive interface and the bond strength between resin cement and two ceramics. For finite element analysis (FEA), a tridimensional model was made using computer-aided design software. This model consisted of a ceramic slice (10x10x2mm) partially embedded on acrylic resin with a resin cement cylinder (Ø=3.4 mm and h=3mm) cemented on the external surface. Results of maximum principal stress and maximum principal shear were obtained to evaluate the stress generated on the ceramic and the cylinder surfaces. In order to reproduce the in vitro test, similar samples to the computational model were manufactured according to ceramic material (Zirconia reinforced lithium silicate - ZLS and high translucency Zirconia - YZHT), (N=48, n=12). Half of the specimens were submitted to shear bond test after 24h using a universal testing machine (0.5 mm/min, 50kgf) until fracture. The other half was stored (a) (180 days, water, 37ºC) prior to the test. Bond strength was calculated in MPa and submitted to analysis of variance. The results showed that ceramic material influenced bond strength mean values (p=0.002), while aging did not: YZHT (19.80±6.44)a, YZHTa (17.95±7.21)a, ZLS (11.88±5.40)b, ZLSa (11.76±3.32)b. FEA results showed tensile and shear stress on ceramic and cylinder surfaces with more intensity on their periphery. Although the stress distribution was similar for both conditions, YZHT showed higher bond strength values; however, both materials seemed to promote durable bond strength.

Effect of ceramic material and resin cement systems on the color stability of laminate veneers after accelerated aging

Statement of problemLaminate veneers are susceptible to color change during clinical service. Studies that compare the effects of different ceramic and resin cement systems on color stability are lacking. PurposeThe purpose of this in vitro study was to evaluate the color stability of laminate veneers after accelerated aging using different ceramic and resin cement systems. Material and methodsCeramic specimens (N=168; shade A1; thickness, 0.50 ±0.05 mm; diameter, 10.00 ±0.10 mm) were prepared using nanofluorapatite and lithium disilicate (high translucency [HT] to low translucency [LT]) ceramics. Light-polymerizing (LP) cements were classified by brightness (high or low). Dual-polymerizing cements were classified by composition (base-only [DB] or base-catalyst [DC]) for comparison of color stability on the basis of polymerization type. DB cement was light-polymerizing, whereas DC cement was dual-polymerizing. They were further classified by shade (transparent, white, or yellow [n=7, each]). Color difference (ΔE) values were obtained by spectrophotometric quantification of L* (lightness), a* (green-red), and b* (blue-yellow) values before and after aging. The Kruskal-Wallis, Mann-Whitney U, Wilcoxon signed rank, and Bonferroni post hoc tests were used for statistical analysis. ResultsAfter specimens were subjected to accelerated aging, HT ceramic specimens luted with yellow-shade DC cement exhibited the greatest color change (ΔE=2.11), whereas HT and LT ceramic specimens luted with low-brightness LP cement exhibited the least color change (ΔE=1.37). In HT ceramic specimens, which exhibited the greatest color change of the 3 ceramic types, transparent shade cement exhibited significantly lower ΔE values than the other shades with DB (P<.001) and DC cements (P=.010). High-brightness cement exhibited significantly higher ΔE values than low-brightness cement when used with NF (P=.017), HT (P<.001), and LT (P<.001) ceramics. The ΔE values of DB cement were not always lower than those of DC cement. For all specimens, the aging of laminate veneers decreased the L* values and increased the a* and b* values. ConclusionsCeramic and resin-cement systems affected the color stability of laminate veneers. Relative to other ceramics, HT lithium disilicate ceramics exhibited greater color changes upon aging. For HT ceramics, the use of transparent shade resin cement is recommended. The lower the brightness of resin cement, the higher the color stability of veneers. For luting of 0.5-mm-thick laminate veneers with dual-polymerizing cement, light polymerization did not yield better color stability than dual polymerization over time.

Effect of Decontamination and Cleaning on the Shear Bond Strength of High Translucency Zirconia.

(1) Background: This study evaluated the bonding performance of high translucency zirconia after diverse surficial decontamination and cleaning procedures. (2) Methods: High translucency zirconia (LavaTM Esthetic) specimens (2.0 mm × 20 mm × 10 mm) were exposed to different surface treatments prior to bonding to CoCr cylinders (d = 5 mm, height = 3 mm). All surfaces were sandblasted (40 µm aluminum oxide, 2 bar) and treated with alcohol (al), saliva (s), saliva + water (sw), or saliva + NaOCl + water (sn) before bonding was performed with the following adhesive luting systems: RelyXTM Unicem 2 (RX), ScotchbondTM Universal (SBU) + RelyXTM Ultimate (RU) or Monobond Plus (MP) + Multilink® Automix (ML). After 24 h, thermocycling (TC:12,000 × 5 °C/55 °C) and 90 days of storage at 37 °C in distilled water, the shear bond strength (SBS) was evaluated according to ISO/TS 11,405:2015. Failure modes along bonding areas were characterized. Means and standard deviations (n = 10 per group) were determined and statistically analyzed with one-way ANOVA/Bonferroni (α = 0.05). (3) Results: The SBS after 24 h varied between 3.5 (sRX) and 69.4 MPa (snMP + ML). Values from 0 (sRX) to 70.3 MPa (swRX) were found after TC. Data after 90 days of storage showed the lowest values for sRX (0 MPa) and the highest values for alSBU + RU (75.5 MPa). Adhesive failure was noted at all aging conditions. (4) Conclusions: SBU + RU or RX and MP + ML including saliva decontamination of the ceramic surface with water or NaOCl + water allow efficient bonding to LavaTM Esthetic.

Novel Translucent and Strong Submicron Alumina Ceramics for Dental Restorations

An ideal ceramic restorative material should possess excellent aesthetic and mechanical properties. We hypothesize that the high translucency and strength of polycrystalline ceramics can be achieved through microstructural tailoring. The aim of this study is to demonstrate the superior optical and mechanical properties of a new class of submicron grain-sized alumina ceramics relative to the current state-of-the-art dental ceramic materials. The translucency, the in-line transmission (TIT) in particular, of these submicron alumina ceramics has been examined with the Rayleigh-Gans-Debye light-scattering model. The theoretical predictions related very well with the measured TIT values. The translucency parameter (TP) and contrast ratio (CR) of the newly developed aluminas were measured with a reflectance spectrophotometer on a black-and-white background. For comparison, the TIT, TP, and CR values for a variety of dental ceramics, mostly measured in-house but also cited from the literature, were included. The flexural strength of the aluminas was determined with the 4-point bending test. Our findings have shown that for polycrystalline alumina ceramics, an average grain size <1 µm coupled with a porosity level <0.7% could yield translucency values (TIT, TP, CR) similar to those of the commercial high-translucency porcelains. These values are far superior to the high-translucency lithium disilicate glass-ceramic and zirconias, including the most translucent cubic-containing zirconias. The strength of these submicron grain-sized aluminas was significantly higher than that of the cubic-containing zirconia (e.g., Zpex Smile) and lithia-based glass-ceramics (e.g., IPS e.max CAD HT). A coarse-grained alumina could also reach a translucency level comparable to that of dental porcelain. However, the relatively low strength of this material has limited its clinical indications to structurally less demanding applications, such as orthodontic brackets. With a combined high strength and translucency, the newly developed submicron grain-sized alumina may be considered a suitable material for dental restorations.

FRACTURE RESISTANCE OF DIFFERENT ESTHETIC POST AND CORE MATERIALS AND ASSESSMENT THEIR MODE OF FAILURE

Purpose: This in vitro study measured fracture resistance of different esthetic post and core materials and compare their modes of failures. Statement of problem: Increase esthetic demand and patient awareness have encouraged development of esthetic post and core systems. Translucency of ceramic restorations is accompanied by marked decrease in alumina content that may affect mechanical properties. Methods:40 extracted human central incisors were used in this study. Teeth were randomly divided into 4 groups of 10 each: group 1:Translucent Zirconia(TZ);group 2:High Translucency IPS E.Max (T-IPS); group 3:Polymer Infiltrated Ceramic (Vita Enamic) (PIC) and group 4: Control group (C), teeth were endodontically treated with no posts and cores. Posts and cores were processed according to manufacturer instructions cemented to teeth with adhesive resin cement; then specimens were mounted to acrylic resin blocks, attached to Instron universal testing machine, and loaded with a crosshead speed of 0.5 mm/min, until fracture. Types of failures were also recorded in different groups. Data were statistically analyzed using 1-way analysis of variance (ANOVA), and Scheffe test made pairwise comparison (α = 0.05). Results: TZ group showed the highest fracture resistance (454 .4±41.6 N). T-IPS showed higher results(360.4±35.7N) than PIC(300.9±35.6 N) and control(276.7±32.5 N) and the two latter groups were not significantly different from each other P <0.001.As regard mode of failure TZ showed 80% non-restorable type, T-IPS 40%,PIC 50% and control group showed 20% non-restorable type respectively.Conclusions: Regarding fracture strength and mode of failure, High Translucent IPS-E Max post and core can be an alternative treatment method when compared with other techniques.

Evaluation of color change in CAD-On restorations using different core/veneer thickness ratios and different veneer translucencies

Statement of problemThe introduction of partially stabilized zirconium dioxide to the dental field created a path for development of new designs and applications, but still, a minimum framework thickness of 0.5 mm with the remaining thickness of the restoration used for building the ceramic veneer was always recommended. This might have possibly affected the final shade of the restorartion due to the whitish color of Y-TZP. PurposeThis in vitro study was designed to evaluate the color reproduction ability of CAD-veneered zirconia restorations through the effect of different core-veneer thickness ratios and different translucencies of the Cad-on veneering material. MethodsSixty CAD-On restorations were constructed and classified into 3 groups (n = 20) of different core/veneer thickness ratios (0.5:1 mm, 0.7:0.8 mm, 1:0.5 mm). Each group was subdivided into 2 sub-groups (n = 10) according to the CAD-On veneer translucency (High Translucency HT, Low Translucency LT). Cad-On restorations were constructed using the CEREC InLab CAD/CAM System. Color change (ΔE) between groups of the CAD-On restorations was measured using Vita EasyShade Compact. All data was statistically analyzed and presented as mean and standard deviation values. Repeated measurements of data were analyzed with analysis of variance (ANOVA) for significant differences. ResultsThere was significant difference (P < 0.05) for varrying the core/veneer thickness ratio over (ΔE) while both the veneer translucency and interaction between the core/veneer thickness ratio and veneer transluency had no significant effect. ConclusionThere was a visually perceptible color change for all core/veneer thickness ratios and all veneer translucencies, but they were all in the clinically acceptable range.

EFFECT OF SURFACE TREATMENT AND ARTIFICIAL AGING ON MICROTENSILE BOND STRENGTH OF ZIRCONIA TO RESIN CEMENT

Statement of problem: Reliable bond to zirconia based materials has proven to be difficult which is the major limitation against luting zirconia restorations.Purpose: This in vitro study compared effect of selective infiltration etching (SIE) and tribo-chemical silica sandblasting (TSS) on microtensile bond strength to zirconia based material before and after different artificial aging intervals. Materials and methods: Twenty Lava plus high translucency zirconia disks (3 M, ESPE) were randomly divided into two study groups according to their surface treatment: (a) selective infiltration etching (SIE) and (b) tribo-chemical silica sandblasting (TSS). Zirconia disks were bonded to composite resin specimens using Panavia F2.0 resin cement. Zirconia resin bond strength was evaluated using the microtensile bond strength test (MTBS) and the test was repeated before and after the following intervals of accelerated artificial aging; 1 week, 2 weeks, 3 weeks and 4 weeks of water storage (37°C). A repeated measures ANOVA and Bonferroni post-hoc tests were used to analyze the data.Results: The interaction between surface treatments and storage times were statistically significant. Data analysis revealed significant differences between the two surface treatments (P<0.05).Selective infiltration etched specimens demonstrated relatively higher MTBS values than TSS (48.5 and 24.8 MPa).SEM examination of broken microbars revealed more interfacial failure type for TSS than SIE specimens that showed a predominantly cohesive failure type. Conclusions: Selective infiltration etching provided superior micro-tensile bond strength results compared to tribo-chemical silica sandblasting. Established bond strength by selective infiltration etching was not affected by artificial aging as tribo-chemical silica sandblasting.