Effect of Thermocycling, Surface Treatments and Microstructure on the Optical Properties and Roughness of CAD-CAM and Heat-Pressed Glass Ceramics

Effect of Coffee Thermocycling on Color Stability and Translucency of CAD-CAM Polychromatic High Translucent Zirconia Compared With Lithium Disilicate Glass Ceramic

AIMS AND OBJECTIVES

To evaluate the effect of coffee thermocycling on color stability and translucency of CAD-CAM polychromatic high translucent zirconia compared with lithium disilicate glass ceramic.

METHODS

Sixteen rectangular plates (14 × 16 × 1.0 mm) of two ceramic materials (IPS E.max CAD (IEC), IPS E.max ZirCAD Prime [IZP]) were prepared. Each specimen was measured for color coordinates using a spectrophotometer following 30,000 cycles of coffee thermocycling. CIELAB formula was used to determine color and translucency differences (ΔE and ΔTP). The means of ΔE and ΔTP were compared using independent samples t-test and were evaluated using their respective 50%:50% perceptibility and acceptability thresholds (PT and AT). One-way analysis of variance was performed to evaluate the translucency parameter (TP) and surface roughness (Ra) of each material.

RESULTS

Mean ΔE values of IEC (4.69) and IZP (4.64) were higher than the AT (ΔE ≤ 2.7) with no significant difference found between the two groups (p = 0.202). Considering the TP, only IEC showed a statistically significant increase in TP value (p < 0.001). However, the mean ΔTP of IEC (3.25) remained within the range of acceptability (1.3 < ΔTP ≤ 4.4).

CONCLUSIONS

Within the limitations of this current study, the color stability of all materials was clinically affected by coffee thermocycling. In terms of translucency, only lithium disilicate glass ceramic was influenced by coffee thermocycling. High translucent zirconia had superior translucency stability compared to lithium disilicate glass ceramic.

Impact of common social habits on optical properties of lithium disilicate glass ceramic crowns: An in vitro study

Statement of the problem

Patient stratifications considered the stability of color and treatment longevity are key success of restoration. Daily consumption of colored beverages, such as coffee, tea, and soft drinks, as well as the use of globally consumed materials, such as smokeless tobacco (ST), snuff, Khat, and Yerba mate, can change the color of restorative materials, such as lithium disilicate glass ceramics (LDGC). These changes can ultimately lead to treatment failure.

Purpose

This in vitro study aimed to evaluate color changes, translucency, and opalescence of full anatomical LDGC crowns exposed to commonly used and potentially colorant solutions.

Materials and methods

Ninety LDGC specimens/crowns were prepared and divided into nine groups according to immersion solution (control, Saudi Coffee, Cola, Khat, Yerba mate, Nescafe, ST Snuff, and Mixed Fruit Juice). The specimens were immersed in colorant solutions for 15 days with alternating twice daily at 37 °C. Color parameters were measured with a spectrophotometer and calculated using two backgrounds (black and white). Data were subjected to ANOVA followed by the Student t-test and Bonferroni test at a significant difference level (α = 0.05).

Results

The greatest color change (ΔE*) among groups after immersion was observed in Yerba mate (7.6 ± 1.6). The mean difference of before and after staining within Yerba mate group was 3.14 ± 1.6 (p = 0.001). Translucency mean values of groups after immersion into staining media were ranging between 7.6 ± 1.2 and 9.1 ± 2, showing a slight decrease compared with pre-staining values but was not significantly different. Immersion in Mixed Fruit Juice significantly reduced opalescence (7.4 ± 1.9) compared to (8.8 ± 1.7) before staining.

Conclusion

The findings confirm that appropriate user guidance helps to preserve both translucency and opalescence as well as prevent color changes. This can improve patient compliance and promote treatment longevity.

Effect of glazing and thermocycling on the fracture toughness and hardness of a New fully crystallized aluminosilicate CAD/CAM ceramic material

BACKGROUND

The mechanical properties of fully crystallized lithium aluminosilicate ceramics may be influenced by intraoral temperature variations and postmilling surface treatment. The purpose of this study is to explore the interplay among glazing, thermocycling, and the mechanical characteristics (namely, fracture toughness and hardness) of fully crystallized lithium aluminosilicate ceramics.

METHODS

Bending bars (n = 40) cut from LisiCAD blocks (GC, Japan) were randomly assigned to glazed or unglazed groups (n = 20) and subjected to the single edge v-notch beam method to create notches. A glazing firing cycle was applied to the glazed group, while the unglazed group was not subjected to glazing. Half of the specimens (n = 10) from both groups underwent thermocycling before fracture toughness testing. The fracture toughness (KIC) was evaluated at 23 ± 1 °C using a universal testing machine configured for three-point bending, and the crack length was measured via light microscopy. Seven specimens per group were selected for the hardness test. Hardness was assessed using a Vickers microhardness tester with a 1 kg load for 20 s, and each specimen underwent five indentations following ISO 14705:2016. The Shapiro-Wilk and Kolmogorov-Smirnov tests were used to evaluate the normality of the data and a two-way ANOVA was utilized for statistical analysis. The significance level was set at (α = 0.05).

RESULTS

Regardless of the thermocycling conditions, the glazed specimens exhibited significantly greater fracture toughness than did their unglazed counterparts (P < 0.001). Thermocycling had no significant impact on the fracture toughness of either the glazed or unglazed specimens. Furthermore, statistical analysis revealed no significant effects on hardness with thermocycling in either group, and glazing alone did not substantially affect hardness.

CONCLUSIONS

The impact of glazing on the fracture toughness of LiSiCAD restorations is noteworthy, but it has no significant influence on their hardness. Furthermore, within the parameters of this study, thermocycling was found to exert negligible effects on both fracture toughness and hardness.

Optical properties of zirconia-reinforced lithium silicate veneers obtained with CAD/CAM milling and hot-pressing techniques: a comparative in vitro study

Background and aims

Dental veneers have become increasingly required among patients, but little is known about the optical properties of veneers obtained from the same ceramic material through different processing techniques.

Methods

In this study we compared the translucency and the opalescence parameters of zirconia-reinforced lithium silicate (ZLS) veneers restorations fabricated through CAD/CAM milling and hot-pressing techniques on the upper central incisor. Eighty specimens divided into 8 groups (n=10) were sectioned (Celtra Duo) and heat pressed (Celtra Press) to obtain 0.8 mm thickness. The optical parameters were calculated from the color difference against different backgrounds. Analysis of variance, one way ANOVA and post-hoc multiple comparison tests were used to evaluate and compare the optical properties of the same material, with a significance level of p < 0.05.

Results

The processing method had significant effect on optical parameters. Celtra Duo HT proved to be the material with the highest transparency degree. The hot-pressing technique led to higher opacity than CAD/CAM milling technique.

Conclusions

For a bio-mimetic aesthetic prosthetic restoration, the ceramic materials must have the same translucency and opacity as the real tooth. The results of this study revealed that high translucency ZLS obtained through hot pressing technique was the material of choice, as it fulfilled these requirements.

Staining and bleaching susceptibility of zirconia-reinforced lithium silicate glass-ceramics with different thicknesses, translucencies, and fabrication methods

STATEMENT OF PROBLEM

The influence of different thicknesses, translucencies, and fabrication methods on the spectrophotometric and topographical properties of zirconia-reinforced lithium silicate glass-ceramics (ZLSs) for dental restorations remains unclear.

PURPOSE

The purpose of this in vitro study was to investigate the effect of thicknesses, translucencies, and fabrication methods on the color stability, translucency parameter, opalescence parameter, whiteness stability, transmitted irradiance, light transmittance, opacity, gloss, and roughness of ZLSs exposed to coffee staining and bleaching treatments.

MATERIAL AND METHODS

Two pressable ZLSs (VITA AMBRIA, VA and Celtra Press, CP) and 2 machinable ZLSs (VITA Suprinity, VS and Celtra Duo, CD) were examined at high translucency (HT) and low translucency (LT) levels in 2 thicknesses (n=160). The specimens were evaluated at baseline, after coffee staining, and after bleaching. The color stability (ΔE2000), translucency parameter (TP), opalescence parameter (OP), whiteness index (WID), and whiteness stability (ΔWID) were measured with a spectrophotometer. Transmitted irradiance (It), light transmission (T), and opacity (O) were obtained from a light-polymerizing unit and a polymerization light collection device. Roughness stability (ΔSa%) was determined with an optical profilometer, and gloss stability (ΔGU%) was recorded with a gloss meter. Data of ΔCIE2000, ΔWID, ΔSa%, and ΔGU% were analyzed by 4-way ANOVA, and data of the TP, OP, WID, It, T, and O were analyzed by repeated 4-way ANOVA (α=.05).

RESULTS

VS-HT exceeded the ΔCIE2000 acceptability threshold after coffee staining and bleaching protocols. Pressable ZLSs exhibited greater color stability than machinable ZLSs. The 1-mm-thick VA, CP, and CD materials exceeded the ΔWID perceptibility threshold after bleaching. The highest TP and OP was displayed by the 1-mm-thick CP after bleaching. ΔGU increased after water storage and decreased after coffee staining and bleaching. ΔSa% significantly increased after bleaching (P<.05).

CONCLUSIONS

The color stability and other spectrophotometric properties of ZLSs depended on material thickness. The effects of ZLS fabrication methods and translucency levels on their measured properties were inconsistent. Subjecting 1-mm-thick ZLS materials to acidic media adversely impacted their stainability and surface texture.

Biosafety and chemical solubility studies of multiscale crystal-reinforced lithium disilicate glass-ceramics

Lithium disilicate (Li2 Si2 O5 ) glass-ceramics are currently a more widely used all-ceramic restorative material due to their good mechanical properties and excellent aesthetic properties. However, they have a series of problems such as high brittleness and low fracture toughness, which has become the main bottleneck restricting its development. Therefore, in order to compensate for these shortcomings, we propose to prepare a reinforced glass-ceramics with better mechanical properties and to test the biosafety and chemical solubility of the material. Li2 Si2 O5 whiskers were synthesized by a one-step hydrothermal method, and multi-scale crystal-enhanced Li2 Si2 O5 glass-ceramics were prepared by reaction sintering. The biosafety of multi-scale crystal-reinforced Li2 Si2 O5 glass-ceramics was investigated by in vitro cytotoxicity test, rabbit pyrogen test, mice bone marrow micronucleus test, skin sensitization test, sub-chronic systemic toxicity test, and chronic systemic toxicity test. Additionally, the chemical solubility of multi-scale crystal-reinforced Li2 Si2 O5 glass-ceramics was investigated. The test results showed that the material was non-cytotoxic, non-thermogenic, non-mutagenic, non-sensitizing, and non-systemic. The chemical solubility, determined to be 377 ± 245 μg/cm2 , complied with the ISO 6872 standard for the maximum solubility of ceramic materials. Multi-scale crystal-reinforced Li2 Si2 O5 glass-ceramics' biosafety and chemical solubility met current normative criteria, and they can move on to mechanical property measurements (such as flexural strength test, fatigue life test, friction and wear property study, etc.) and bonding property optimization, which shows promise for future clinical applications.

Effect of Thermo-mechanical Cycling on Fracture Resistance of Different CAD/CAM Crowns: An In Vitro Study

AIM

To evaluate the effect of thermo-mechanical cycling (TMC) on fracture resistance of different computer-aided design/computer-aided manufacture (CAD/CAM) crowns.

MATERIALS AND METHODS

A total of 42 CAD/CAM crowns were fabricated on epoxy resin maxillary first premolar teeth and divided into three groups (n = 14) according to the material used: IPS e.max CAD (Ivoclar Vivadent) lithium disilicate (LD), Vita ENAMIC (VE) (VITA Zahnfabrik), Tetric CAD (Ivoclar Vivadent). Also, each group was subdivided into two equal subgroups according to TMC (n = 7). Subgroups (O) without TMC and subgroup (W) with TMC (5-55°C, 30 second, 75,000 cycles). All samples in each group were cemented with a universal bond (Tetric N bond universal) and adhesive resin cement (Variolink Esthetic DC) (Ivoclar Vivadent). Subsequently, the samples were loaded to failure in a universal testing machine at a crosshead speed of 1 mm/min, and the fracture pattern and the fracture resistance in each group were recorded.

RESULTS

Fracture resistance was analyzed by one-way analysis of variance (ANOVA) test, followed by Tukey's post hoc test for pairwise comparison. Fracture resistance showed a significant difference between the tested groups before and after TMC; IPS e.max CAD has the highest value (1233.35 ± 97.72, 1165.73 ± 199.54 N) followed by Tetric CAD (927.62 ± 42.5, 992.04 ± 53.46 N) and Vita ENAMIC has lowest value (506.49 ± 74.24, 354.69 ± 90.36 N).

CONCLUSION

Thermo-mechanical cycling affected the fracture resistance of both polymer-based CAD/CAM crowns.

CLINICAL SIGNIFICANCE

For dental practitioners, both IPS e.max CAD and Tetric CAD can be used clinically for posterior teeth, providing satisfactory results and resistance to fracture. How to cite this article: Elmokadem MI, Haggag KM, Mohamed HR. Effect of Thermo-mechanical Cycling on Fracture Resistance of Different CAD/CAM Crowns: An In Vitro Study. J Contemp Dent Pract 2024;25(1):29-34.

Zirconia-Reinforced Lithium Silicate Ceramic in Digital Dentistry: A Comprehensive Literature Review of Our Current Understanding

Zirconia-reinforced lithium silicate (ZLS) ceramic is a new innovative dental material with unique a chemical composition that is designed to combine harmoniously with the appropriate optical properties of lithium disilicate and the enhanced mechanical strength of zirconia. A thorough understanding of ZLS materials is essential for both clinicians and dental technicians. At present, the mechanical behavior and optical properties of the ZLS ceramic system have not been extensively researched, and there is still a lack of consensus regarding the fabrication process and clinical behavior of ZLS all-ceramic restorations. The aim of the present study was to present a selection of comprehensive information concerning zirconia-reinforced lithium silicate ceramics and their optical and mechanical properties, as well as to assess data regarding cementation procedures and clinical outcomes for ZLS all-ceramic restorations. Three electronic databases (PubMed, Web of Science, and the Cochrane Library) were used for the research by two independent reviewers. The search was limited to articles published in the English language, as well as clinical and in vitro studies of color and studies on mechanical behavior and the cementation procedures of ZLS restorations. The exclusion criteria comprised abstracts, questionnaire-based studies, case reports, literature reviews, and studies that were not available in English. Zirconia-reinforced lithium-silicate-based ceramic presents a unique and complex microstructure that increases mechanical resistance but decreases aesthetic appearance, especially its translucency, due to tetragonal zirconia content. A material's thickness, the color of the underlying tooth structure, and the resin cement shade are important factors that influence the final shade and aesthetic appearance of ZLS restorations. Mechanical properties, which are defined by the fracture toughness, flexural strength, elastic modulus, and hardness of ZLS ceramic are higher compared to feldspathic, lithium disilicate, and hybrid ceramics, as well as resin nanoceramics; however, they are lower than translucent or high-translucency zirconia. Acid etching, sandblasting, and laser etching represent the most used methods to prepare the ZLS restoration surfaces for proper bonding procedures.

Effect of mouth rinses on the stainability of monolithic lithium disilicate glass-ceramics with different surface treatments: An in vitro study

STATEMENT OF PROBLEM

Mouth rinses have been reported to cause tooth surface discoloration. However, information regarding their effect on the stainability of monolithic glass-ceramics with different surface treatments is lacking.

PURPOSE

The purpose of this in vitro study was to assess the effect of mouth rinses on the color change of milled and pressed monolithic lithium disilicate glass-ceramics with different surface treatments.

MATERIAL AND METHODS

Fifty-six Ø12×1.5-mm disk specimens were fabricated using 2 different processing techniques: milling and pressing. Each group was subdivided into 2 subgroups according to surface treatments: glazed and polished. Specimens were then immersed in 2 different types of mouth rinse (n=7): chlorhexidine (CHX) and Listerine (LST). Color parameters were assessed using a digital spectrophotometer. Color difference (ΔE00) was calculated and compared with perceptibility (ΔE00=0.8) and acceptability (ΔE00=1.8) thresholds. The data were analyzed using ANOVA and Tukey post hoc tests (α=.05).

RESULTS

The color difference (ΔE00) was significantly affected by the type of processing technique, surface treatment, and mouth rinse (P<.001) and their interaction (P=.008). All ΔE00 values were below the selected clinical acceptability threshold (ΔE00=1.8). Milled groups (ΔE00=1.13) showed greater discoloration than pressed groups (ΔE00=0.86). Glazed specimens (ΔE00=0.70) were more resistant to discoloration than polished specimens (ΔE00=1.28) and immersion in CHX (ΔE00=1.09) led to more discoloration than immersion in LST (ΔE00=0.89).

CONCLUSIONS

The color of milled and pressed monolithic lithium disilicate glass-ceramics with different surface treatments was affected by using CHX and LST mouth rinses. Glazed lithium disilicate glass-ceramics showed less staining compared with those that were polished. Specimens immersed in CHX showed more discoloration than those immersed in LST.

Thickness, Annealing, and Surface Roughness Effect on Magnetic and Significant Properties of Co40Fe40B10Dy10 Thin Films

In this study, Co40Fe40B10Dy10 thin films were deposited using a direct current (DC) magnetron sputtering technique. The films were deposited on glass substrates with thicknesses of 10, 20, 30, 40, and 50 nm, and heat-treated in a vacuum annealing furnace at 100, 200, and 300 °C. Various instruments were used to examine and analyze the effects of roughness on the magnetic, adhesive, and mechanical properties. From the low frequency alternating current magnetic susceptibility (χac) results, the optimum resonance frequency is 50 Hz, and the maximum χac value tends to increase with the increase in the thicknesses and annealing temperatures. The maximum χac value is 0.18 at a film thickness of 50 nm and an annealing temperature of 300 °C. From the four-point probe, it is found that the resistivity and sheet resistance values decrease with the increase in film deposition thicknesses and higher annealing temperatures. From the magnetic force microscopy (MFM), the stripe-like magnetic domain distribution is more obvious with the increase in annealing temperature. According to the contact angle data, at the same annealing temperature, the contact angle decreases as the thickness increases due to changes in surface morphology. The maximal surface energy value at 300 °C is 34.71 mJ/mm2. The transmittance decreases with increasing film thickness, while the absorption intensity is inversely proportional to the transmittance, implying that the thickness effect suppresses the photon signal. Smoother roughness has less domain pinning, more carrier conductivity, and less light scattering, resulting in superior magnetic, electrical, adhesive, and optical performance.

Resistance of PETG Materials on Thermocycling and Brushing

The aim was to assess the impact of thermocycling and brushing on the surface roughness and mass of PETG material-the most commonly used for orthodontic retainers. A total of 96 specimens were exposed to thermocycling and brushing with three different kinds of toothbrushes depending on the number and thickness of the bristles. Surface roughness and mass were evaluated three times: initially, after thermocycling, and after brushing. In all four brands, both thermocycling and brushing increased surface roughness significantly (p < 0.001), with Biolon having the lowest and Track A having the highest. In terms of brushing, only Biolon samples showed statistically significant increased roughness after brushing with all three types of brushes, in comparison to Erkodur A1, where differences were not statistically significant. Thermocycling increased the mass of all samples, but a statistically significant difference was found only in Biolon (p = 0.0203), while after brushing, decreased mass was found in all specimens, statistically significant only in Essix C+ (CS 1560: p = 0.016). PETG material showed instability when exposed to external influences- thermocycling produced an increase in roughness and mass, and brushing mostly caused an increase in roughness and decrease in mass. Erkodur A1 demonstrated the greatest stability, whereas Biolon demonstrated the lowest.

An engineering perspective of ceramics applied in dental reconstructions

The demands for dental materials continue to grow, driven by the desire to reach a better performance than currently achieved by the available materials. In the dental restorative ceramic field, the structures evolved from the metal-ceramic systems to highly translucent multilayered zirconia, aiming not only for tailored mechanical properties but also for the aesthetics to mimic natural teeth. Ceramics are widely used in prosthetic dentistry due to their attractive clinical properties, including high strength, biocompatibility, chemical stability, and a good combination of optical properties. Metal-ceramics type has always been the golden standard of dental reconstruction. However, this system lacks aesthetic aspects. For this reason, efforts are made to develop materials that met both the mechanical features necessary for the safe performance of the restoration as well as the aesthetic aspects, aiming for a beautiful smile. In this field, glass and high-strength core ceramics have been highly investigated for applications in dental restoration due to their excellent combination of mechanical properties and translucency. However, since these are recent materials when compared with the metal-ceramic system, many studies are still required to guarantee the quality and longevity of these systems. Therefore, a background on available dental materials properties is a starting point to provoke a discussion on the development of potential alternatives to rehabilitate lost hard and soft tissue structures with ceramic-based tooth and implant-supported reconstructions. This review aims to bring the most recent materials research of the two major categories of ceramic restorations: ceramic-metal system and all-ceramic restorations. The practical aspects are herein presented regarding the evolution and development of materials, technologies applications, strength, color, and aesthetics. A trend was observed to use high-strength core ceramics type due to their ability to be manufactured by CAD/CAM technology. In addition, the impacts of COVID-19 on the market of dental restorative ceramics are presented.

Effect of ceramic and resin cement type on color stability and translucency of ceramic laminate veneers for diastema closure: an in vitro study

To investigate the effect of resin cements on the color stability and translucency of ceramic laminate veneers used for diastema closure. Sixty resin abutments were prepared for ceramic laminate veneers and divided into six groups according to the ceramic type (lithium disilicate, zirconia-reinforced lithium silicate, and translucent zirconia) and the cement type (Variolink Esthetic LC and RelyX Veneer). Color coordinates and translucency were analyzed after cementation and after soaking in the coffee solution. Differences in color and translucency were estimated, and results were statistically assessed (α = 0.05). Ceramic materials showed a significant impact on color changes after soaking in coffee within Variolink Esthetic groups. Translucent zirconia showed the highest color change, followed by zirconia reinforced lithium silicate and lithium disilicate. Ceramic materials showed a significant impact among the RelyX Veneer groups. A significant interaction in color changes was found between ceramic types and cement types after cementation, and after soaking in coffee was found. All groups showed a clinically acceptable difference in translucency parameters after soaking in coffee. The resin cement affects the color and translucency of ceramic laminate veneers used for diastema closure, and ceramic laminate veneers bonded with Variolink Esthetic LC resin cement are more translucent, while ceramic laminate veneers bonded with RelyX Veneer resin are more resistant to coffee staining. The lithium disilicate laminate veneer is more resistant to coffee staining than zirconia reinforced lithium silicate and translucent zirconia laminate veneers used for diastema closure.

Surface roughness and characteristics of CAD/CAM zirconia and glass ceramics after combined treatment procedures

BACKGROUND

The roughening of the inner surface of a fixed ceramic restoration is an important factor for the bonding process. The aim of this study is to investigate the effect of combined surface treatments (acid etching, air-abrasion and Er: YAG Laser) on surface roughness of CAD/CAM fabricated zirconia (ZrO₂) and lithium-disilicate glass ceramics (LDS).

METHODS

Sixty ZrO₂ (Ceramill Zi) and LDS (IPS e.max CAD) specimens, (5 mm in width, 5 mm in length and 1.5 mm in height) were fabricated using CAD/CAM and sintered according to the manufacturer's instructions. All specimens subjected to three surface treatment combinations; etching with 4% hydrofluoric acide (HF), airborne-particle abrasion with 110-μm alumina (Al₂O₃) (AP) and Er:YAG laser (Er:YAG) (Group A-HF + AP; Group B-Er:YAG + AP, and Group C-Er:YAG + HF). Perthometer was used to measure the surface roughness of the specimens before and after the tretments.

RESULTS

Group A presented the highest Ra (LDS 0.81 ± 0.27 and ZrO₂ 0.67 ± 0.21 after treatment) and Group C the lowest (LDS 0.45 ± 0.13 and ZrO₂ 0.26 ± 0.07, after treatment). Compared with before treatment, the Ra were significantly different only in Group A both ZrO₂ and LDS after treatment (p < 0.05). Qualitative SEM images suggested the surface topography of the ZrO₂ was smoother than the LDS. Less surface changes were observed in the Er:YAG combined procedures than HF + AP.

CONCLUSIONS

HF + AP was significantly succesful in modifying the ceramic surface. Er:YAG did not sufficiently promote the surface topography, even if combined with any other treatments. Overall, surface tretments on ZrO₂ not easier than LDS.

Physical, Optical, and Mechanical Properties of Ceramic Materials after Coffee Immersion and Evaluation of Cleaning Impact with Different Oral Hygiene Tools

This study aimed to evaluate the effect of three oral hygiene tools, a regular toothbrush, an electronic toothbrush, and mouthwash, on the color stability of three different computer-aided design (CAD) and computer-aided manufactured (CAM) ceramic blocks. Feldspathic ceramic (Vita Triluxe Forte), hybrid resin ceramic (Vita Enamic), and lithium disilicate glass-ceramic (IPS e.max CAD) were used in this study. A CAD/CAM system and 81 (27 of each material) samples of ceramic blocks were used. All samples were immersed in black coffee for 15 days, and the coffee was changed twice per day. Using a spectrophotometer probe, samples on a grey background were scanned, and physical properties like surface hardness and depth were measured using interferometry and a 3D non-contact surface metrology. After 30 days of application of oral hygiene tools, instruments were used to measure various physical, mechanical, and optical properties. Vita Triluxe had the highest average color variation values (ΔE₀₀) after 15 and 30 days of immersion in coffee in both regular and electronic toothbrushes. Moreover, IPS e.max CAD had the least ΔE₀₀ values with no significant differences among the groups. The surface roughness (Ra) of the Vita Enamic ceramic increased when using a regular toothbrush, and the surface height (Rz) for the Vita Enamic ceramic increased when an electronic toothbrush was used. IPS e.max CAD had the greatest modules of elasticity forces, and Vita Triluxe Forte had the lowest when used with a regular toothbrush. The ΔE₀₀ values of the tested materials were minimally increased or decreased after 30 days of cleaning, and all were clinically acceptable. Ra and Rz were the highest for Vita Enamic in comparison to the other groups. The highest percentage in IPS e.max CAD was associated with a type 1 fracture, whereas type 3 was predominantly observed with Vita Enamic, and type 2 in the Vita Triluxe group without significant differences.

Influence of Surface Type with Coffee Immersion on Surface Topography and Optical and Mechanical Properties of Selected Ceramic Materials

BACKGROUND The aim of this study was to assess and compare the effect of surface type (glazed or polished) with coffee immersion and aging on surface topography (Ra), optical properties (TP, OP), and mechanical properties (fracture forces and modes) of zirconia-reinforced lithium silicate (Vita Suprinity), hybrid polymer-infiltrated-feldspathic ceramic network material (Vita Enamic), and leucite-containing feldspathic glass (Vitablocs® Mark II) made by computer-aided design and computer-aided manufactured (CAD/CAM) ceramic materials. MATERIAL AND METHODS Fifty-four specimens were assembled out of the above 3 CAD/CAMs ceramic materials. Each group was divided into glazed or polished surfaces, having 9 specimens of every type and stained in coffee for 15 days. Ra and color of specimens in the form of TP and OP were recorded before and after immersion in staining material. Fracture forces and modes were analyzed after the 90-day aging. Data were analyzed using ANOVA, then post hoc analysis and Bonferroni tests. RESULTS Our study found significant differences in Ra, TP, and Op before and after coffee immersion between glazed and polished specimens, with higher values in the polished surfaces among the 3 ceramic materials. The highest values of fracture resistance were noted in Vita Suprinity, and Vita Enamic had the lowest values, without significant differences among groups. CONCLUSIONS Most of the TP and OP values were in acceptable clinical range, and Vita Suprinity had superior TP than the other groups. Reparable fracture types were observed in Vita Suprinity, whereas semi-reparable and non-reparable were predominant in other groups.

In vitro study of surface properties and microbial adhesion of various dental polymers fabricated by different manufacturing techniques after thermocycling

OBJECTIVES

The study aims to investigate surface properties and microbial adhesion of various dental polymers fabricated by different manufacturing techniques before and after thermocycling.

MATERIALS AND METHODS

The following six materials were used to fabricate disk-shaped specimens: conventional denture polymer (Vertex Acrylic Resin, VAR), CAD/CAM denture polymer (Organic PMMA eco Pink, OP), conventional temporary polymer (Protemp™ 4, PT), CAD/CAM temporary polymer (Die Material, DM), conventional denture framework polymer (BioHPP, PB), and CAD/CAM denture framework polymer (breCAM.BioHPP, CB). The specimens were tested before and after thermocycling (5000 and 10,000 cycles, 5 °C/55 °C). Surface roughness (SR), hydrophobicity, and surface topography were determined by profilometry, water contact angle, and scanning electron microscopy (SEM). Then specimens were incubated with Staphylococcus aureus, Streptococcus mutans, and Candida albicans for 24 h, respectively. Microbial adhesion was assessed using colony-forming unit counts, XTT assay, and SEM.

RESULTS

SR and hydrophobicity of VAR group were higher than that of OP group. S. aureus and C. albicans adhesion on VAR and PT groups were higher than that on OP and DM groups, respectively. There was no difference in surface properties and microbial adhesion between PB and CB groups. After thermocycling, SR (expect OP group) of all materials increased and hydrophobicity decreased, and the amount and activity of S. aureus and C. albicans adhesion also increased. The adhesion of S. aureus and C. albicans showed a moderate positive correlation with SR, independent of hydrophobicity.

CONCLUSIONS

CAD/CAM denture polymers and temporary polymers showed less S. aureus and C. albicans adhesion when compared to conventional ones, which were mainly affected by surface roughness, independent of hydrophobicity. Thermocycling could increase surface roughness, decrease hydrophobicity, and affect microbial adhesion of the materials.

CLINICAL SIGNIFICANCE

CAD/CAM dental polymers may be a better choice for the manufacture of temporary restorations and dentures to reduce microbial adhesion.

Fractographic and Microhardness Evaluation of All-Ceramic Hot-Pressed and CAD/CAM Restorations after Hydrothermal Aging

All-ceramic dental restorations have great advantages, such as highly esthetical properties, a less complex fabrication, and a similar abrasion resistance to enamel. Despite these advantages, ceramic materials are more prone to fracture due to their brittle microstructure. The main aim of this in vitro study was to determine the difference in hot-pressed and milled glass-ceramic mechanical properties such as fracture resistance and microhardness (VHN). Four types of ceramics, two hot-pressed and two milled, feldspathic glass-ceramics and zirconia-reinforced glass-ceramics were selected in this study and tested using the static loading test and Vicker’s testing. Hydrothermal aging, consisting of different baths with temperatures between 5 degrees Celsius and 55 degrees Celsius, was chosen as the in vitro aging method. Statistical analyses are performed using SPSS Statistics software at a significance level of p < 0.05. Micro-hardness values decrease after hydrothermal aging. The static loading test reveals a significant difference between the feldspathic hot-pressed glass-ceramic, which fractures at lower forces, and milled zirconia-reinforced lithium silicate glass-ceramic, which fractures at greater forces (N). Fractographic analysis of the fractured fragments resulted in the static loading test revealing different surface features about the crack origins and propagations under a stereomicroscope.

Effects of Substrate and Cement Shade on the Translucency and Color of CAD/CAM Lithium-Disilicate and Zirconia Ceramic Materials

The aim of this in vitro study was to evaluate the effects of substrate and cement shades on the translucency and color of lithium-disilicate and zirconia CAD/CAM materials. Two light-cured resin cements (RelyX Veneer Cement; 3M; Choice 2 Veneer Cement; Bisco Dental) with a standardized thickness (0.1 mm) were tested in combination with two different monolithic CAD/CAM materials (E-Max CAD (LI2SI2O5); Ivoclar Vivadent; Katana (ZrO2); Kuraray-Noritake Dental) on two different colored composite substrates used as a dentin (Filtek Supreme XTE; 3M); for a total of 12 combinations (n = 10). The specimens’ color was measured with a spectrophotometer (Spectroshade; MHT). Measurements were taken using the CIELAB color coordinate system (L*a*b*) against black and white backgrounds. L*a*b* values were statistically analyzed for the variables Substrate, Ceramic, and Cement by applying a Three-Way ANOVA followed by the Tukey Test for post-hoc comparison (p < 0.05). Translucency Parameter (TP) and Constant Ratio (CR) were assessed to evaluate translucency; acceptability and perceptibility thresholds (ΔE00 1.8 and 0.8) were used. Statistically significant influence was found for factors ceramic material, cement shade, and substrate color (p < 0.05). Unacceptable color differences were reported for Li2Si2O5. Opacity was significantly higher when white opaque cement shade was employed. Ceramic type and cement shade significantly influenced L*a*b* color coordinates. The final translucency and color of ceramic restorations can, therefore, be influenced by ceramic material, cement shade, and substrate color.

Enamel wear against monolithic zirconia restorations: A meta-analysis and systematic review of in vitro studies

OBJECTIVE

An assessment was performed to identify and evaluate dental enamel wear caused by monolithic zirconia restoration. Literature searches were conducted in PubMed, Science Direct, Cochrane Evidence, and the Cochrane Library up to May 2020.

MATERIAL AND METHODS

Studies were selected for systematic review according to the inclusion (articles conducted on the wear of enamel samples opposing monolithic zirconia) and exclusion (case reports, non-English articles, and monolithic zirconia samples facing other materials rather than human enamel) criteria. Of those, articles on polished and glazed monolithic zirconia subjected to a 50 N vertical load with a range of 240,000-250,000 cycles, equivalent to 1 year of in vivo mastication, were included in the meta-analysis.

RESULTS

In total, 3968 articles were pooled. Twenty-five articles met the inclusion criteria for the systematic review. Three studies were included in the meta-analysis. The results showed that the enamel wear against monolithic zirconia was within the statistically accepted level. Moreover, the polished monolithic zirconia surface caused less enamel wear than the glazed surface.

CONCLUSION

This review indicates that monolithic zirconia restorations cause acceptable antagonist enamel wear. Moreover, the meta-analysis results agreed that the final restoration's surface texture plays an essential role in the wear process.

CLINICAL SIGNIFICANCE

Monolithic zirconia restorations have been widely used in dental practice because they eliminate the chipping problems resulting from using veneered restorations. With recent technology development, monolithic zirconia has obtained more esthetic features and a more natural look. However, due to the high strength and surface roughness of monolithic zirconia, wear on the antagonist's teeth was detected. The results showed that this wear amount was statistically acceptable and lower than other ceramics such as feldspathic porcelain and enamel. Furthermore, surface treatment methods must be applied to minimize tooth wear, as polished or glazed surfaces interfere with enamel loss.

Masking Abilities of Dental Cad/Cam Resin Composite Materials Related to Substrate and Luting Material

An outstanding treatment challenge related to aesthetic monolithic materials is to mask discolored substrates in aesthetic areas. The purpose of the study is to evaluate the substrate masking ability of different resin composite materials and the influence of their association with luting agents and substrates. Five types of 2M2 HT (high translucency) resin composite materials were selected: Vita Enamic [E] and four types of nanoparticle-filled composites Lava Ultimate [L], Cerasmart [C], Shofu HC [S], and Hyramic [H]. Resin composite Vita VM LC with different shades was used for the substrates: 2M2, 3M2, and CP2. Variolink Esthetic Try-inpastes neutral, light+, and warm+ colors were chosen to simulate the luting agent color. Optical parameters (TP (translucency), CR (contrast ratio), and OP (opalesce)) and color differences ΔE (chromatic difference) were calculated. Statistical analyses were performed to evaluate the comparisons between the groups and establish correlations. TP average values for all materials were in the range of 21.49–24.53. OP average values were in the rage of 6.31–7.85. OP is moderate positive correlated to TP and CR is negative and strong correlated to TP. Related to materials, average color changes decrease as following: E > H > C > L > S. Referring to the tryin material, warm colors induce marked color changes of the restoration. The differences of the color changes determined by all studied substrates are significant. For the final aesthetic aspect of the restoration, it is essential to consider the underlying dental structure, luting agent, and restoration material as a whole unit. The masking ability of the investigated resin matrix ceramic materials materials shows differences, the best behavior demonstrated Shofu HC and Lava Ultimate. Marked color changes are related to high chroma substrates. For substrates with a darker color, the association with warm try-in pastes lead to marked color changes, but with neutral and light try-in pastes at most perceivable.

Microstructural considerations for novel lithium disilicate glass ceramics: A review

OBJECTIVE

To review the ultrastructural characteristics of novel lithium disilicate based glass ceramics (LDC), how their manufacturing process influences their structure and their clinical use.

OVERVIEW

Lithium disilicate based glass ceramic has been successfully used for indirect restorations ranging from partial tooth coverage up to tooth replacement for over 20 years. It combines esthetic and mechanical properties, unlike any other indirect material which makes it an indispensable part of esthetic and restorative dentistry. Recently, novel LDCs have been introduced to the market. Parameters for their use and their microstructure are still not been widely known. This article will review these materials and highlight with high-resolution scanning electron microscopic images their structural aspects and their resulting clinical relevance.

CONCLUSION

Restorations made from LDCs are reliable and can be predictably used only when proper guidelines and protocols during manufacturing and clinical use are followed. For novel LDCs manufacturing and long-term bonding protocols still must be established. Moreover, novel LDCs machinable blocks should be crystallized or heat-treated after milling for superior performance.

CLINICAL SIGNIFICANCE

With more and newer etchable LDC materials entering the market, clinicians and technicians need to be aware of the differences in manufacturing and the resulting microstructure to ensure a successful treatment outcome that will last.

Surface Characterisation of Dental Resin Composites Related to Conditioning and Finishing

Due to the little information related to surface processing and conditioning of resin matrix ceramic materials previous glazing, the main purpose of this in vitro study was to investigate the effect of different surface treatments on the surface morphology of different resin composite materials. Five types of resin composite CAD-CAM materials: a resin composite ceramic Vita Enamic (E) and four types of nanoparticle-filled resins, like Lava Ultimate (L), Cerasmart (C), Shofu HC (S), Hyramic (H) were taken into consideration. Specimens received the following surface treatment protocols: conventional polishing [p], polishing and glazing [pg], conditioning with CoJet [c], conditioning with CoJet and glazing [cg], sandblasting [s], sandblasting and glazing [sg], etching [e], etching and glazing [eg]. Surface roughness was analyzed for all samples and nanosurface topographic characterization was made by Atomic Force Microscopy. The highest roughness was registered for sandblasted surfaces [s], followed by tribochemical silica airborne particle abrasion [c], and etching [e]. A very strong correlated conditioning behavior of resin nanoceramic materials, like L, C and S samples was found. The microroughness decreased thus [s] > [c] > [e]. These are moderate correlated with H, and are moderate negative correlated to E, where e is more efficient. Three-dimensional images indicated visible grain boundaries after conditioning, for all materials. After polishing and glazing, surfaces became smoother. For all tested conditioning and finishing methods, surface roughness values were within clinically acceptable limits. Finishing by polishing was proved to be a good choice for all materials taken into consideration, polishing and glazing likewise, excepting Hyramic. For Enamic and Shofu HC sandblasting or tribochemical conditioning and glazing and for Hyramic polishing and glazing are not the best options, related to nanoroughness values. Referring to the nanosurface topography, for Enamic, Cerasmart and Hyramic, glazing would be the method of choice, associated with the adequate conditioning method for each material.

Optical Properties and Color Stability of Dental PEEK Related to Artificial Ageing and Staining

Considering that the processes of PEEK discoloration caused by either intrinsic or extrinsic factors require elucidation, the aim of this study was to investigate the long-term effect of the combined action of ageing and immersing solutions on the optical properties and color stability of PEEK material, related to surface processing (polishing or glazing). (2) Methods: This study aims to determine the influence of different ageing and staining protocols on optical properties, color changes, and surface roughness of a reinforced PEEK material (bioHPP, Bredent, Senden, Germany). For ageing, specimens were submitted to 5000 cycles in a 55 °C bath and a 5 °C bath filled with distilled water. For staining, thermal cycling was performed in a hot coffee bath (55 °C) and a bath filled with distilled water (37 °C) and in a cold juice bath (5 °C) and a bath filled with distilled water (37 °C). Translucency (TP) and opalescence (OP) parameters were determined, the total color change value (ΔΕ*) was calculated, specimens’ surface roughness was analyzed, and statistical analyses were performed. (3) Results: The mean TP values of the studied samples were in the interval of 1.25–3.60, which is lower than those reported for natural teeth or other aesthetic restoration materials. The OP values of PEEK were registered in the range of 0.27–0.75, being also lower than those of natural teeth or other aesthetic restoration materials. OP has a very strong positive relationship with TP. The mean registered Ra values for all subgroups were below 0.13 µm. Artificial ageing and staining in hot coffee proved to increase the roughness values. (4) Conclusions: The glazing of PEEK has a favorable effect on surface roughness and opalescence, irrespective of the artificial ageing or staining protocols. Artificial ageing damages the color stability and roughness of PEEK, regardless of surface processing, and decreases the translucency and opalescence of glazed surfaces. Immersion in hot coffee leads to perceivable discolorations.

A REVIEW OF MECHANICAL BEHAVIOR OF DENTAL CERAMIC RESTORATIONS

Dental ceramics are well known for restoring the function and aesthetic of lost or damaged teeth. Understanding these materials’ mechanical and aesthetic properties can make a suitable choice for those materials. The longevity of dental ceramics depends on several factors, including manufacturing method, clinical process, and the oral cavity’s aqueous environment. Failure mechanisms in restorative ceramics are complex and a combination of several factors. Different microstructures in the crystalline phase will involve the propagation of cracks and eventually the fatigue of ceramic materials. Large grains reduce mechanical performance compared to small grain sizes. Aesthetic materials used for veneering are weaker than the core materials and fail when even subjected to small loads. The soft bonding in the core–veneer interface and possible residual stresses created during the veneering method are drawbacks of these systems. Studies on the mechanical behavior of these materials have grown significantly in recent years and provide helpful information about static and fatigue experimentation and the failure behavior of various materials used in dental crowns.

Effect of external staining on the optical properties and surface roughness of monolithic zirconia of different thicknesses

STATEMENT OF PROBLEM

The effect of the number of external staining applications on the color, translucency, and surface roughness of monolithic zirconia is not known.

PURPOSE

The purpose of this in vitro study was to investigate the effect of glazing and repeated external staining on the color, translucency, and surface roughness of 2 types of monolithic zirconia with 2 different thicknesses.

MATERIAL AND METHODS

Thirty-two 10×10-mm monolithic zirconia blocks, of which 16 were super high translucent and 16 were high translucent, were milled. The thickness of half the blocks was 0.7 mm, and the others were 1.2-mm thick. Four specimens in each subgroup were colored with value stain, and the other half with yellow stain. Staining was repeated twice for each specimen. The color and translucency of each specimen were measured before overglazing as the baseline, after overglazing, and after each staining process by using a spectrophotometer. The surface roughness (Ra) was measured after overglazing, the first staining, and the second staining. Data were analyzed by using repeated measures ANOVA and the independent t test (α=.05).

RESULTS

The number of coloring, type of coloring, and thickness changed the optical properties of monolithic zirconia. a∗, b∗, L∗ Value and ΔE were affected by the stage of firing (glazing, first staining, and second staining) (P<.001). ΔE Increased after the first and second staining in each type and thickness of monolithic zirconia and each type of stain. The amount of ΔE change was more for the first staining stage. The color difference (ΔE) after overglazing ranged from 3.08 to 3.75. The highest changes in color were related to the first staining with yellow colorant of super-high-translucent monolithic zirconia (cubeX²) with 0.7-mm thickness (ΔE=17.62). The surface roughness of the specimens was affected by the number of colorings (P<.001). In all groups, the first staining increased the surface roughness, and the second staining decreased the surface roughness. The type of monolithic zirconia (P=.756), thickness (P=.735), and type of stain (P=.239) had no significant effect on the surface roughness.

CONCLUSIONS

The first stage of staining with both stains caused more color change in all types and thicknesses of monolithic zirconia. Translucency increased after glazing and decreased after the first and second staining. The first staining increased the surface roughness, and the second decreased the surface roughness.

Surface roughness and color measurements of glazed or polished hybrid, feldspathic, and Zirconia CAD/CAM restorative materials after hot and cold coffee immersion

Background

The purpose of this study evaluates and compares the effect of surface roughness (Ra) and color stability on computer-aided design/computer-aided manufacturing (CAD/CAM) hybrid resin (Vita Enamic), feldspathic (Vitablocs® Mark II), and lithium disilicate Zirconia (Vita Suprinity) glazed or polished ceramics immersed in hot Arabic Qahwa and cold coffee.

Methods

A total of 96 standardized samples were prepared from CAD/CAM restorative materials. Half of the samples were polished as per the manufacturer’s instructions using a porcelain polishing kit, and the other half were glazed. Samples were distributed and immersed in hot Arabian Qahwa and cold coffee followed by thermocycling. Ra measurements and color changes were conducted before and after immersion. SEM images were captured from each type of glazed or polished ceramic. One-way ANOVA paired Student’s t-test, and Bonferroni test were conducted to detect significant difference between the groups. P > 0.05 was a significant level.

Results

Of all the tested samples, Ra increased without any significant difference; however, mean color changes (ΔE*) showed significant differences. An increase in Ra was noted for all the glazed and polished samples after immersion and thermocycling. However, differences were significant only in VM II. In addition, ΔE* was significant only in Vita Suprinity (VS) samples. For immersion groups, significant Ra changes were noticed in glazed samples, only in Vita Enamic (VE) with no ΔE*. In polished samples, mean Ra changes were observed in VM II and VS samples. Significant differences were also noticed in polished VE and VS subgroups of ΔE*.

Conclusions

Ra affects all the tested samples, providing higher values on the polished specimens. The ΔE* caused by hot Arabic Qahwa and cold coffee on glazed or polished CAD/CAM restorative materials were clinically acceptable.

In-vivo-wear in composite and ceramic full mouth rehabilitations over 3 years

The aim of this study was to quantify and to compare the wear rates of premolar (PM) and molar (M) restorations of lithium disilicate ceramic (LS2) and an experimental CAD/CAM polymer (COMP) in cases of complex rehabilitations with changes in vertical dimension of occlusion (VDO). Twelve patients with severe tooth wear underwent prosthetic rehabilitation, restoring the VDO with antagonistic occlusal coverage restorations either out of LS2 (n = 6 patients, n = 16 posterior restorations/patient; N = 96 restorations/year) or COMP (n = 6 patients; n = 16 posterior restorations/patient; N = 96 restorations/year). Data was obtained by digitalization of plaster casts with a laboratory scanner at annual recalls (350 ± 86 days; 755 ± 92 days; 1102 ± 97 days). Each annual recall dataset of premolar and molar restorations (N = 192) was overlaid individually with the corresponding baseline dataset using an iterative best-fit method. Mean vertical loss of the occlusal contact areas (OCAs) was calculated for each restoration and recall time. For LS2 restorations, the mean wear rate per month over 1 year was 7.5 ± 3.4 μm (PM), 7.8 ± 2.0 μm (M), over 2 years 3.8 ± 1.6 µm (PM), 4.4 ± 1.5 µm (M), over 3 years 2.8 ± 1.3 µm (PM), 3.4 ± 1.7 µm (M). For COMP restorations, the mean wear rate per month over 1 year was 15.5 ± 8.9 μm (PM), 28.5 ± 20.2 μm (M), over 2 years 9.2 ± 5.9 µm (PM), 16.7 ± 14.9 µm (M), over 3 years 8.6 ± 5.3 µm (PM), 9.5 ± 8.0 µm (M). Three COMP restorations fractured after two years and therefore were not considered in the 3-year results. The wear rates in the LS2 group showed significant differences between premolars and molars restorations (p = 0.041; p = 0.023; p = 0.045). The wear rates in COMP group differed significantly between premolars and molars only in the first two years (p < 0.0001; p = 0.007). COMP restorations show much higher wear rates compared to LS2. The presented results suggest that with increasing time in situ, the monthly wear rates for both materials decreased over time. On the basis of this limited dataset, both LS2 and COMP restorations show reasonable clinical wear rates after 3 years follow-up. Wear of COMP restorations was higher, however prosthodontic treatment was less invasive. LS2 showed less wear, yet tooth preparation was necessary. Clinicians should balance well between necessary preparation invasiveness and long-term occlusal stability in patients with worn dentitions.

Optical behaviors, surface treatment, adhesion, and clinical indications of zirconia-reinforced lithium silicate (ZLS): A narrative review

OBJECTIVES

The present narrative review was focused on the optical properties, surface treatment, adhesion, and clinical indications of zirconia-reinforced lithium silicate ceramics (ZLS) for Computer-aided design / Computer-aided manufacturing (CAD/CAM) technologies.

DATA/SOURCES

A literature search was performed by 3 calibrated independent researchers on PubMed, Scopus, Embase, Google Scholar, Dynamed, and Open Grey. The criteria for inclusion were: 1) papers addressing at least one of the following variables about ZLS: optical properties, surface treatment, adhesion, and clinical indications; 2) in vitro, in silico, or in vivo studies; 3) case reports; 4) systematic reviews. The exclusion criteria were: 1) animal studies; 2) non-dental studies; 3) studies only focusing on ZLS used in the heat-pressed process.

STUDY SELECTION

98 records among in vitro studies and case reports were included.

CONCLUSIONS

Despite the promising microstructure characteristics of ZLS, increased translucency compared to lithium disilicate ceramics (LS₂) was not proven, but acceptable color changes and stability were reported. Mechanical polishing was the most effective method to reduce surface roughness. Moreover, machinability and handling of ZLS resulted harder than LS₂. Conventional acid etching procedures seemed effective in conditioning ZLS surface, but no protocol has been established yet. Besides, silane-coupling and dual-curing resin cements were recommended.

CLINICAL SIGNIFICANCE

ZLSs can be used for anterior and posterior fixed single-unit CAD/CAM restorations onto both natural teeth and implants, but do not seem to represent a viable treatment option for endocrowns onto posterior teeth or fixed dental prostheses.

Zirconia-reinforced lithium silicate (ZLS) mechanical and biological properties: A literature review

OBJECTIVES

This paper aimed to provide a literature review of the mechanical and biological properties of zirconia-reinforced lithium silicate glass-ceramics (ZLS) in Computer-aided design / Computer-aided manufacturing (CAD/CAM) systems.

DATA/SOURCES

An extensive search of the literature for papers related to ZLS was made on the databases of PubMed/Medline, Scopus, Embase, Google Scholar, Dynamed, and Open Grey. The papers were selected by 3 independent calibrated reviewers.

STUDY SELECTION

The search strategy produced 937 records. After the removal of duplicates and the exclusion of papers that did not meet the inclusion criteria, 71 papers were included.

CONCLUSIONS

After reviewing the included records, it was found that two types of ZLS (Vita Suprinity PC; Vita Zahnfabrik and Celtra Duo; Dentsply Sirona) are nowadays available on the market for CAD/CAM systems, similar in their chemical composition, microstructure, and biological-mechanical properties. ZLS is reported to be a biocompatible material, whose fracture resistance can withstand physiological chewing loads. The firing process influences the improvements of strength and fatigue failure load, with a volumetric shrinkage. To date, ZLS can be considered a viable alternative to other glass-ceramics for fixed single restorations.

CLINICAL SIGNIFICANCE

. As to biocompatibility and mechanical properties of ZLS, data are still scarce, often controversial and limited to short-term observational periods. These promising ceramics require further in vitro/in vivo studies to accurately define mechanical and biological properties, mainly in the long-term performance of restorations produced with such materials.

Bending Behaviour of Polymeric Materials Used on Biomechanics Orthodontic Appliances

This paper discusses the issues of strength and creep of polymeric materials used in orthodontic appliances. Orthodontic biomechanics is focused on the movement of individual teeth or dental groups as a result of the force applied by orthodontic appliances. Stresses in the construction of functional and biomechanical appliances is generated when using the apparatus in the oral cavity. The orthodontic appliance must maintain its shape and not be damaged during treatment so strength and creep resistance are fundamental properties. It was assumed that the clinical success of orthodontic appliances can be determined by these performance properties. The aim of the work was the experimental assessment of comparative bending strength and creep resistance of selected popular polymer materials used in the production of biomechanical orthodontic appliances. Four commercial materials manufactured by the world class producers were tested: NextDent Ortho Rigid (Vertex-Dental B.V., Soesterberg, The Netherlands) marked as "1A"; Erkocryl (ERKODENT Erich Kopp GmbH, Pfalzgrafenweiler, Germany)-"2A"; Vertex Orthoplast (Vertex Dental B.V.), blue, marked as "3A" and material with the same name as "3A" but orange, marked in the article as "4A". All the tests were carried out after aging in artificial saliva for 48 h at a temperature of 37 °C. Flexular strength and flexular modulus were made using the three point bending method according to the ISO 178 technical standard. Creep tests were carried out according to the method contained in ISO 899-2. The creep test was carried out in an artificial saliva bath at 37 °C. The creep tests showed significant differences in the strength, modulus and deformability of the tested materials. The strength reliability of the tested materials also varied. The research shows that the 2A material can be used for orthodontic applications in which long-term stresses should be lower than 20 MPa.

In Vitro Study of Comparative Evaluation of Marginal and Internal Fit between Heat-Pressed and CAD-CAM Monolithic Glass-Ceramic Restorations after Thermal Aging

The accuracy of newly developed ceramic materials is still being studied. Marginal and internal adaptation are known factors that have an essential impact on the long term success of dental restorations. The aim of this in vitro study was to evaluate the marginal and internal fit of heat-pressed and milled monolithic glass-ceramic restorations based on their ceramic type, processing technique, and in vitro thermocycling. Thirty-two crowns were studied and divided into four groups (n = 8), according to the ceramic material (feldspathic glass-ceramic (F) and zirconia reinforced lithium silicate glass-ceramic (ZLS)) and to their technological obtaining processes (milling (M) and heat-pressing (P)). A typodont preparation was scanned with a D2000 3D scanner to obtain identical 32 resin 3D-printed abutment teeth. Marginal and internal gaps were measured using the silicone replica technique under 40× magnification. The crowns were further cemented and thermally aged for 10,000 cycles After cementation and thermocycling of the samples, marginal and internal gaps were assessed using micro-CT (micro-computed tomography)) analysis. Data were statistically analyzed using statistical tests. Significant differences were found before and after cementation and thermocycling among the tested materials (p < 0.05). Related to technological processing, significant differences were seen in the marginal area between FP and FM (p < 0.05) Significant differences were also found in the axial and occlusal areas between the ZLSP and ZLSM. Thermocycling and cementation did not have a significant effect on the tested materials (p < 0.05). The technological processes influenced the marginal and internal fit of the crowns in favor of the CAD/CAM (computer aided design/computer aided manufacturing)technologies. Thermal aging had little effect on marginal adaptability; it increased the values for all the tested samples in a small way, but the values remained in their clinically acceptable range for all of the crowns.

Surface Quality Evaluation of Removable Thermoplastic Dental Appliances Related to Staining Beverages and Cleaning Agents

(1) Background: Thermoplastic materials are not inert and subject to changes in the oral environment, which affect their surface quality. Color stability and topographic characteristics of clear thermoplastic appliances are critical considerations. The study aimed to evaluate the optical changes and surface topography of different thermoplastic materials related to staining beverages and cleaning agents. (2) Methods: Thermoplastic polyethylene terephthalate glycol (PET-G) material specimens were selected for the study: S (Duran, Scheu-Dental GmbH, Iserlohn, Germany), D (Biolon, Dreve Dentamid GmbH, Unna, Germany), and B (Crystal, Bio Art Dental Equipment, Sao Carlos, Brazil). Four different media were involved for immersion: coffee (C) and black tea (T) at 55 °C, Coca-Cola (K) at 5 °C, and distilled water (W) at 22 °C. As for cleaning, chemical options and mechanical brushing were selected (P-powder, T-tablets, and X-brushing). Color changes, and mean surface roughness were measured at 24 h, 48 h, and after 7 days. Statistical analysis was performed. After the testing period, atomic force microscopy (AFM) analyses and SEM images were registered in order to characterize the surface topography. (3) Results: Quantitative color change evaluations revealed a slight change in color after 24 h and an extremely marked change after 48 h, respective 7 days. Mean roughness values are kept below the clinically acceptable limit of 0.20 µm for all samples. Related to mean nanoroughness values Sa, and 3D evaluations of the surface quality, Biolon samples have demonstrated the most constant behavior, while Crystal samples are visibly influenced by water immersion. Related to the cleaning method, the topography of Duran samples was influenced by mechanical brushing. (4) Conclusions: Nanoscale investigations provided high accuracy and more realistic surface quality examinations of the examined samples compared to profilometry. Both SEM and AFM should be used for a more detailed description of the surface topography.

Surface Characterization and Optical Properties of Reinforced Dental Glass-Ceramics Related to Artificial Aging

The development of various dental glass-ceramic materials and the evolution of novel processing technologies lead to an essential change in the clinical and technical workflow. The long-term success of a dental restoration treatment is defined by its durability, which is directly influenced by the oral environment. This study's purpose was to evaluate the artificial aging behavior of nanostructured, respective microstructured ceramics related to surface topography, roughness, and optical properties. Six monolithic restoration materials were selected: milled lithium disilicate glass-ceramic (LDS-M) MT (medium translucency), hot-pressed lithium disilicate glass-ceramic (LDS-P) MT and HT (high translucency), milled zirconia-reinforced lithium silicate ceramic (ZLS-M) MT and hot-pressed zirconia-reinforced lithium silicate ceramic (ZLS-P) MT and HT, resulting n = 96 surfaces. All the samples were artificially aged by thermal cycling, and all investigations were made before and after thermal cycling. In terms of optical properties, differences recorded between ZLS and LDS ceramics are not significant. Thermal cycling increases the translucency of ZLS and LDS glass-ceramic materials significantly, with the most harmful effect on the pressed and polished samples. Micro- and nano roughness are significantly influenced by in vitro aging and a negative correlation was recorded. Glazed samples are characterized by significant rougher surfaces for all types of materials. On nanolevel, ZLS materials are significantly smoothed by thermal cycling.

Hardness and Wear Resistance of Dental Biomedical Nanomaterials in a Humid Environment with Non-Stationary Temperatures

This study discusses a quantitative fatigue evaluation of polymer-ceramic composites for dental restorations, i.e., commercial material (Filtek Z550) and experimental materials Ex-nano (G), Ex-flow (G). Their evaluation is based on the following descriptors: microhardness, scratch resistance, and sliding wear. In order to reflect factors of environmental degradation conditions, thermal fatigue was simulated with a special computer-controlled device performing algorithms of thermocycling. Specimens intended for the surface strength and wear tests underwent 10⁴ hydrothermal fatigue cycles. Thermocycling was preceded by aging, which meant immersing the specimens in artificial saliva at 37 °C for 30 days. Microhardness tests were performed with the Vickers hardness test method. The scratch test was done with a Rockwell diamond cone indenter. Sliding ball-on-disc friction tests were performed against an alumina ball in the presence of artificial saliva. A direct positive correlation was found between thermocycling fatigue and microhardness. The dominant mechanism of the wear of the experimental composites after thermocycling is the removal of fragments of the materials in the form of flakes from the friction surface (spalling). Hydrothermal fatigue is synergistic with mechanical fatigue.

The Effect of Thermocycling and Surface Treatments on the Surface Roughness and Microhardness of Three Heat-Pressed Ceramics Systems

Dental ceramic restorations are widely used in restorative dentistry. However, these restorations can be affected once cemented in the oral cavity by several factors. How can conventional surface treatments, such as glazing and mechanical polishing, diminish the effects of aging? The purpose of this in vitro study was to evaluate the effect of thermocycling and conventional surface treatments on the surface roughness and microhardness of three types of glass-ceramics by using a profilometer, scanning electron microscopy (SEM), atomic force microscopy (AFM), and a microhardness tester. Three types of ceramic systems (zirconia reinforced lithium silicate glass-ceramic, lithium disilicate glass-ceramic, and feldspathic glass-ceramic) (n = 48) were prepared. The samples were subjected to thermocycling for 10,000 cycles. Surface roughness was evaluated numerically using a profilometer and visually by using SEM and AFM. Microhardness was performed using a microhardness tester. The data were interpreted using the ANOVA test, and the results were correlated using Pearson’s correlation formula (r). Significant differences were found before and after thermocycling for the Ra (p < 0.01) and Rz (p < 0.05) parameters. As well, differences between glazed and polished surfaces were significant before and after thermocycling for surface roughness and microhardness (p < 0.05). A correlation was made between average surface roughness and microhardness (r = −460) and for the maximum surface roughness and microhardness (r = −606). Aging increases the roughness and decreases in time the microhardness. The tested ceramic systems behaved differently to the aging and surface treatments. Surface treatments had a significant impact on the microhardness and surface characteristics. The glazed groups were reported with higher surface roughness and lower microhardness when compared to the polished groups before and after thermocycling. The measuring roughness techniques determine the scale-dependent values for the Ra (Sa) and Rz (Sq) parameters. Thermocycling almost doubled the surface roughness for all the tested samples. Microhardness decreased only for the Celtra glazed samples. Nano-roughness increased the values for Vita and slightly for Emax. Thermocycling had little effect on Emax ceramic and a more significant impact on Celtra Press ceramic.