The impact of various substrates, ceramic shades, and brands on the ultimate color and masking capacity of highly translucent monolithic zirconia: an in vitro study.

This study aimed to examine the impact of substrates, ceramic shades, and brands on the color and masking ability of highly translucent monolithic zirconia (HTMZ) using CIELab and CIEΔE2000 metrics. A total of 156 1-mm thick HTMZ disks in shades A1, A2, and A3 were produced using Dental Direkt and Kerox zirconia brands. Four 3-mm thick substrates (nickel-chromium alloy, non-precious gold alloy (NPG), zirconia shade A2, and resin composite shade A2) were prepared. HTMZ disks were overlaid on these substrates, and color measurements were taken with a spectrophotometer. Color differences (ΔE) were analyzed using CIELab and CIEΔE2000 formulas. The influence of brand, shade, substrate, and their interactions on ΔE values was assessed with a General Linear Model (GLM) and LSD pairwise comparison test. Spearman's correlation test examined the relationship between CIELab and CIEΔE2000 values. Results indicated that ΔEab was significantly influenced by substrate type and shade, while ΔE2000 was also affected by the ceramic brand. Mean color differences across ceramic-substrate groups were within clinically acceptable and perceptible ranges (clinically perceptible: ∆Eab ≥ 1.3 and ∆E2000 ≥ 0.8; clinically acceptable: 0.8 < ∆E2000 ≤ 1.8 and 1.3 < ∆Eab ≤ 2.7), except for NPG, which had ΔE values exceeding the perceptible range (ΔE2000: 1.1 ± 0.11 to 1.8 ± 0.31; ΔEab: 1.61 ± 0.15 to 2.16 ± 0.36). A significant correlation (r = 0.974, P < 0.001) was found between ΔEab and ΔE2000. Various ceramic brands and shades led to notable ΔE variations, yet average color differences within all ceramic-substrate groups remained clinically acceptable. Both ΔEab and ΔE2000 were reliable methods with a strong correlation for measuring color differences.

Could various angulated implant depths affect the positional accuracy of digital impressions? An in vitro study.

PURPOSE: The purpose of this in vitro investigation was to assess how implant depth could affect the three-dimensional positional accuracy of digital impressions made from angulated implants. MATERIALS AND METHODS: Four modified maxillary models were printed and divided into four study groups. In each model, two angulated implant analogs were placed at the sites of the first premolar and first molar at four different depths of 1 (G1), 2 (G2), 3 (G3), and 4 (G4) mm from the models' edentate area. Scan bodies were connected to the analogs, and one operator made 10 full-arch scans for each master model using an intraoral scanner. Afterward, the marginal gingival part of all models was removed, and digital scans were performed for each model using a laboratory scanner to achieve a reference STL file as the control group. One-way ANOVA and Leven's tests were used to measure and compare the 3D distance deviations across research groups after the superimposing test and control scans. RESULTS: A significant difference between research groups was revealed by trueness and precision analysis (p < 0.001). The trueness and precision results obtained for G1 and G4 were significantly better than those for G2 and G3 (p < 0.05). CONCLUSION: This study demonstrated that implant depth could affect the digital implant impressions' 3D positional accuracy.

Effect of denture cleansers on color stability and surface properties of denture base material containing titanium dioxide nanoparticles.

PURPOSE: To investigate the effect of different denture cleansers on color stability, surface roughness, and hardness of polymethylmethacrylate (PMMA) infused with titanium dioxide nanoparticles (TiO2 NPs) at concentrations of 1% and 2% by weight on each. MATERIALS AND METHODS: In this in vitro study, 90 disc-shaped specimens (10×10×2 mm) were divided into 3 main groups: the non-containing nanoparticle group (0wt% concentration), 1wt% concentration, and 2wt% concentration TiO2 NPs groups. Each group was further assorted into 3 subgroups (n = 10): immersed in distilled water, oxygenating tablet (Corega), and 0.5% sodium hypochlorite. Color change, surface roughness, and hardness values were assessed after 90 and 180 days of storage. Color changes (∆E) were measured with a spectrophotometer (VITA, Easy Shade V, Germany) and assessed using the CIE L*a*b* colorimetric system and the American National Bureau of Standards (NBS = 0.92×∆E). The surface roughness and surface hardness values were measured using a profilometer device and Vickers hardness tester, respectively. First, ANOVA-repeated measurements were performed, followed by the Tukey test. The significance level in this study was considered 0.05. RESULTS: At all concentrations, there were significant differences in the mean color changes of samples immersed in cleansers compared to distilled water (p < 0.01). Moreover, hypochlorite caused a significant increase compared to Corega at 0wt% concentration after 90 days and at 1wt% concentration after 90 and 180 days. Evaluations also showed that the mean NBS values in all cleanser groups were in the range of appreciable change, except the water group. In addition, only hypochlorite changed the color higher than the clinically acceptable range (∆E >3.7). The mean roughness of samples immersed in hypochlorite at 0wt% concentration was significantly higher than the samples containing TiO2 NPs (p = 0.006). No significant difference was observed in surface roughness of samples containing different concentrations of TiO2 NPs immersed in different cleansers; however, hypochlorite increased the surface roughness of samples without TiO2 NPs compared to samples containing TiO2 NPs after 180 days. The immersion time in cleansers had a significant influence on the surface roughness and hardness while having no effect on the color. CONCLUSION: In general, the cleansers had a significant effect on color change in all groups compared to distilled water. The adverse effect of hypochlorite was more than Corega. The cleansers in the samples containing TiO2 NPs did not make a significant difference in surface roughness in comparison with the distilled water groups. Surface hardness of the samples was not affected in a steady pattern by the cleansers.

Comparison of the accuracy of impressions made of 2 implants with interfering axial convergence with CAD-CAM impression copings and the altered cast technique: An in vitro study.

STATEMENT OF PROBLEM: Studies that evaluated the accuracy of different methods for making an impression of 2 implants in close proximity or with adverse axial convergence are lacking. PURPOSE: The purpose of this in vitro study was to compare the accuracy of impressions made with metal and resin computer-aided design and computer-aided manufacturing (CAD-CAM) impression copings and an altered cast technique. MATERIAL AND METHODS: Two implant analogs with an interimplant angulation of 50 degrees were placed in an acrylic resin master model. Thirty impressions were made with 3 techniques (n=10). Two angled abutments were scanned to print 40 impression copings from a castable resin, half of which were cast with nickel-chromium alloy (M-CAD) and half of these were used in the R-CAD group. Impressions were made and poured. For the altered cast technique (Alt-cast), casts with only the mesial analogs were made and hollowed at the site of the distal analogs. The position of the distal analogs was transferred by resin indices (n=10) fabricated with light-polymerized resin on the master model. The linear displacements of mesial (ΔR1) and distal (ΔR2) analogs and the interanalog distance (ΔRt) were measured with a coordinate measuring machine. The data were analyzed by using the Kruskal-Wallis and Dunn post hoc tests (α=.05). RESULTS: No significant difference was found between the M-CAD and R-CAD groups regarding ΔR1 (P=.722), ΔR2 (P=.576), or ΔRt (P=.939). However, the Alt-cast group differed from the M-CAD group in ΔR1 (P<.001), ΔR2 (P<.001), and ΔRt (P=.002) and also from the R-CAD group in ΔR1 (P=.001), ΔR2 (P=.002), and ΔRt (P=.003). CONCLUSIONS: The impressions made with metal and resin CAD-CAM impression copings were more accurate than those made with the Alt-cast technique although all techniques had acceptable accuracy.

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.

Estimating the Severity of Oral Lesions Via Analysis of Cone Beam Computed Tomography Reports: A Proposed Deep Learning Model.

OBJECTIVES: Several factors such as unavailability of specialists, dental phobia, and financial difficulties may lead to a delay between receiving an oral radiology report and consulting a dentist. The primary aim of this study was to distinguish between high-risk and low-risk oral lesions according to the radiologist's reports of cone beam computed tomography (CBCT) images. Such a facility may be employed by dentist or his/her assistant to make the patient aware of the severity and the grade of the oral lesion and referral for immediate treatment or other follow-up care. METHODS: A total number of 1134 CBCT radiography reports owned by Shiraz University of Medical Sciences were collected. The severity level of each sample was specified by three experts, and an annotation was carried out accordingly. After preprocessing the data, a deep learning model, referred to as CNN-LSTM, was developed, which aims to detect the degree of severity of the problem based on analysis of the radiologist's report. Unlike traditional models which usually use a simple collection of words, the proposed deep model uses words embedded in dense vector representations, which empowers it to effectively capture semantic similarities. RESULTS: The results indicated that the proposed model outperformed its counterparts in terms of precision, recall, and F1 criteria. This suggests its potential as a reliable tool for early estimation of the severity of oral lesions. CONCLUSIONS: This study shows the effectiveness of deep learning in the analysis of textual reports and accurately distinguishing between high-risk and low-risk lesions. Employing the proposed model which can Provide timely warnings about the need for follow-up and prompt treatment can shield the patient from the risks associated with delays. CLINICAL SIGNIFICANCE: Our collaboratively collected and expert-annotated dataset serves as a valuable resource for exploratory research. The results demonstrate the pivotal role of our deep learning model could play in assessing the severity of oral lesions in dental reports.

Effect of cut-out rescanning protocol on the accuracy of digital impressions in convergent implants positioned at varying depths: An in vitro study.

BACKGROUND: This study aimed to assess the effect of the "cut-out rescan" strategy on the accuracy of intraoral digital scans from 25° convergent implants positioned at two distinct depths. MATERIAL AND METHODS: Two customized models were fabricated, each designated to receive two posterior converged implant fixtures: one at a depth of 1 mm and the other at a depth of 4 mm. Initially, the models were scanned as reference casts using a lab scanner. The test group was involved in scanning the 1-mm and 4-mm implant models using an intraoral scanner in the following order: (1) scanning the 1-mm (T1; n = 10) and (2) 4-mm (T4; n = 10) implant groups with scan bodies connected to both fixtures in each model; (3) cut-out rescan (COR) in the 1-mm (COR1; n = 10) and (4) 4-mm (COR4; n = 10) models, leading to 40 digital files in standard tessellation language format. The mean absolute deviation (MAD), in terms of trueness and precision, between the experimental and control scans was assessed through the alignment of their respective datasets using three-dimensional analysis software. Two-way analysis of variance (ANOVA) and Levene's tests were used to analyze the data. RESULTS: The COR4 group exhibited the highest MAD, indicative of both trueness and precision (Mean ±SD: 55.659 ±34.802). In contrast, the T1 group demonstrated the lowest MAD (Mean ±SD: 43.225 ±19.237). However, the ANOVA analysis showed no significant influence of depth (P = 0.506) or type of scan (P = 0.442) on the MAD. Precision also did not differ significantly across groups (P = 0.071). CONCLUSIONS: The cut-out rescan approach demonstrated an accuracy comparable to that of the one-time scan method. CLINICAL SIGNIFICANCE: Digital intraoral scanning provides clinicians with a range of tools to navigate challenging conditions in which conventional methods may prove difficult, such as cases involving angled adjacent implants. In these scenarios, the cut-out rescan tool serves as a valuable resource, aiding clinicians in overcoming the challenges associated with impression-making owing to the convergence of placed implants.

Effects of oxalate desensitizer with different resin cement-retained indirect composite inlays on fracture resistance of teeth.

PURPOSE: This study investigated whether the tubular occluding effect of oxalate desensitizer (OX) during adhesive cementation (three resin cements) influenced fracture resistance of teeth restored with adhesive inlays. MATERIALS AND METHODS: Ninety intact maxillary premolars were randomly divided into 9 groups of 10 each. The two control groups were Gr 1, intact teeth and Gr 2, mesio-occlusodistal preparation only. In six experimental groups, the composite inlays were cemented with ED Primer II/Panavia F 2.0, Excite DSC/Variolink II, and One-Step Plus/Duolink according to manufacturers' instructions (Groups 3, 5, and 7, respectively) or with OX during cementation (Groups 4, 6, and 8, respectively). In Group 9, inlays were cemented with a resin cement without adhesive system. After thermocycling, fracture strength was tested. The data were analyzed using two-way and one-way ANOVA and LSD post hoc tests (α = 0.05). RESULTS: Fracture resistance of the six groups were significantly affected by OX (p = 0.002) but not by the resin cement type (p > 0.05). The interaction of the two factors was statistically significant (p = 0.052). A statistically significant difference between all groups was found (p < 0.001). The mean fracture resistances (N) were: Gr1 = 1168 ± 157,(a) Gr2 = 360 ± 110,(d) Gr3 = 1026 ± 188,(b) Gr4 = 887 ± 143,(c) Gr5 = 1007 ± 132,(b) Gr6 = 810 ± 164,(c) Gr7 = 1033 ± 218,(a) Gr8 = 955 ± 147,(ab) Gr9 = 780 ± 86(c) (groups with the same superscript letter indicate statistical similarity). CONCLUSIONS: Combining an OX with three resin cements had a significant negative effect on the fracture resistance of premolars restored with composite inlay cemented with Panavia F2.0 and Variolink II, but it had no significant effect when cemented with Duolink.

Investigating the biocompatibility, flexural strength, and surface roughness of denture base resin containing copper oxide nanoparticles: An in vitro study.

Aim: This study aimed to evaluate the biocompatibility, flexural strength, and surface roughness of polymethyl methacrylate (PMMA) containing Copper Oxide Nanoparticles (CuO NPs) at different concentrations. Methods: 25 heat-polymerized PMMA wax patterns fabricated in 5 groups containing 0.5, 5, 50, and 500 µg/ml CuO NPs and nanoparticle (NP)-free PMMA discs were prepared. 5 growth mediums (DMEM with 10% FBS and 1% penicillin-streptomycin) without disks were also incubated similarly to serve as the control groups. The cytotoxicity of the discs was measured by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay on cultured Human Gingival Fibroblasts. The number of 1.3 × 104 cells were seeded in each well of 96-well plates (5 wells for the extract of each specimen). Days 1, 3, 5, and 7 were the intervals that the culture media were in direct contact with the PMMA discs for either 24 or 72 h. After that, a total of 40 specimens with 65 × 10 × 2.5 mm dimensions were prepared in five groups (n = 8). The specimens were subjected to a rugosimeter for the evaluation of surface roughness. The flexural strength test was performed using a universal testing machine. Microscopic evaluation was performed for the dispersion of the NPs. Non-parametric Kruskal-Wallis test and parametric one-way ANOVA test were used for data analysis. Results: The samples containing 500 µg/ml NPs showed the lowest percentage of cell viability at all incubation periods, while the highest cell viability was observed in NP-free PMMA 24 h after the seventh day of incubation. NPs at 50 and 500 µg/ml concentrations showed strongly significant differences in cytotoxicity compared to the 0 concentration and the control group (p < 0.001). Although all the samples demonstrated an increasing pattern of cell viability on the third, fifth, and seventh days, the percentage of cell viability was significantly lower after 72 h than after 24 h in all incubation periods (p < 0.001). NPs significantly increased flexural strength (p = 0.005) but did not affect the surface roughness of the PMMA discs (p = 0.396). Significance: The CuO NPs were cytotoxic only when applied in high concentrations, but presented a descending trend over time. No cytotoxic effect was observed in the experimental groups after seven days of incubation. Furthermore, CuO NPs increased flexural strength, but the surface roughness of the PMMA discs was not affected.

Influence of different concentrations of titanium dioxide and copper oxide nanoparticles on water sorption and solubility of heat-cured PMMA denture base resin.

OBJECTIVES: This study aimed to evaluate the effect of different concentrations of titanium dioxide (TiO2 ) and copper oxide (CuO) nanoparticles on the water sorption and solubility of heat-cured polymethyl methacrylate (PMMA). MATERIALS AND METHODS: Fifty disc-shaped specimens (10 × 2 mm) of heat-cured PMMA were prepared and divided into five groups (n = 10) to be modified with 2.5 wt.% or 7.5 wt.% of either TiO2 or CuO nanoparticles. One group was left unmodified, serving as the control group. Water sorption and solubility were measured by weighing the specimens before and after immersion in distilled water and desiccation. The data were analyzed by using one-way ANOVA and Tukey's post hoc test (α = .05). RESULTS: The 2.5 wt.% CuO nanoparticles significantly decreased the water sorption (p = .016), but did not change the water solubility (p = .222) compared with the control group. The 7.5 wt.% CuO and both concentration of TiO2 nanoparticles did not change the water sorption, but significantly increased the solubility of heat-cured PMMA (p ≤ .05). CONCLUSION: Adding 2.5 wt.% CuO nanoparticles to heat-cured PMMA decreases the water sorption; although, it has no significant effect on the solubility. Likewise, 2.5 and 7.5 wt.% TiO2 and 7.5 wt.% CuO do not affect the water sorption, but increase the water solubility of heat-cured PMMA. CLINICAL SIGNIFICANCE: Reinforcing the heat-cured PMMA denture base resin materials with the right concentration and type of nanoparticles can decrease the water sorption of resin base materials, and consequently can influence the durability of dentures.

Comparing Castability of Nickel-Chromium, Cobalt-Chromium, and Non-Precious Gold Color Alloys, Using two Different Casting Techniques.

Statement of the Problem: The castability of nonprecious gold color alloy using torch/ centrifugal and induction/vacuum-pressure casting techniques has not been studied yet. Purpose: This study was conducted to compare the castability of nickel chromium, cobalt-chromium and nonprecious gold color alloy using torch/centrifugal and induction/ vacuum-pressure casting techniques. Materials and Method: In this in vitro study, a total number of 54 identical acrylic wax meshes were prepared and divided into 6 different groups of 9 each. Group 1: nickel-chromium alloy, which was casted with induction technique. Group 2: nickel-chromium alloy was casted with centrifugal technique. Group 3: cobalt-chromium alloy was casted with induction technique. Group 4: cobalt-chromium alloy was casted with centrifugal technique. Group 5: nonprecious gold color alloy was casted with induction technique. Group 6: nonprecious gold color alloy was casted with centrifugal technique. Then castability of specimens was measured using modified Whitlock's method. The results were analyzed using two way ANOVA and post hoc tests. Results: ANOVA test revealed no statistically significant difference between different alloys with a p Value of 0.313. Moreover, it represented no significant differences within the groups regarding alloy types and casting techniques with a p Value of 0.511 and 0.682, respectively. Conclusion: No significant difference was found in the castability value of nickel-chromium, cobalt-chromium, and nonprecious gold color alloys. In addition, the castability value of three alloys tested in this study was not different by using torch/centrifugal or induction/vacuum-pressure casting machines.

Evaluation of microhardness and water sorption/solubility of dual-cure resin cement through monolithic zirconia in different shades.

Aim: The objective is to evaluate the effect of shades of monolithic zirconia on the microhardness and sorption/solubility of the underlying two dual-cured resin types of cement. Materials and Methods: Eighty samples of two dual-cured resin cement discs were polymerized under 60 monolithic zirconia discs in three shades and directly activated resin discs of cement were used as the control group (n = 10). After 24 h storage at 37°C in an incubator, Vickers microhardness and the sorption and solubility were measured. Statistical Analysis Used: Two-way ANOVA , one-way ANOVA, Independent t-test, Tukey's honestly significant difference, and Tamhane's T2 tests. Results: The mean microhardness of the Variolink N resin cements were significantly higher than Panavia SA ones (P < 0.001). Furthermore, Variolink N cements exhibited lower sorption/solubility than Panavia SA resin cements (both P < 0.05). The ceramic shade had a significant influence on the microhardness of both cements (P < 0.001) but had no significant effect on the sorption/solubility of resin cements (P > 0.05). Conclusion: Interposition of monolithic zirconia decreases the microhardness of resin cement especially Panavia SA. In Variolink N, by increasing the chroma saturation of ceramics, the microhardness decreased, however in Panavia SA, it was altered by the shades, but not in a specific pattern. For both cements, there were no statistical differences between the sorption/solubility of samples photo-cured under different shades. There was a reverse correlation between microhardness and water sorption/solubility of both cements.

Evaluation of Antimicrobial and Antibiofilm Activities of Copper Oxide Nanoparticles within Soft Denture Liners against Oral Pathogens.

OBJECTIVES: Soft denture liners provide a favorable environment for adhesion and colonization of microorganisms. This in vitro study aimed to examine the efficacy of different concentrations of copper oxide nanoparticles (CuO NPs) incorporation into soft denture liner on the biofilm formation of the microbial species. METHODS: Field Emission Scanning Electron Microscopy (FESEM) images from NPs were recorded. Antifungal susceptibility testing of CuO NPs against five standard strains of Candida albicans (CBS 10261, 1905, 1912, 1949, 2730), Streptococcus mutans (ATCC35668), Streptococcus sobrinus (ATCC27607), and Streptococcus salivarius (ATCC9222) was performed by the broth microdilution method with the Clinical and Laboratory Standards Institute reference method. The biofilm inhibition percentages of CuO NPs on the soft denture liners were determined by XTT assay. RESULTS: The characterization of CuO NPs by scanning electron microscope (SEM) analyses confirmed the synthesis of NPs with appropriate structure and size with a mean diameter of 18.3 ± 9.1 nm. The CuO NPs successfully inhibited the growth of the tested standard strains of C. albicans and Streptococcus spp. at concentrations ranging from 64 to 128 µg mL-1. Indeed, incorporation of CuO NPs at a concentration of 500 µg mL-1 into the soft denture liners exhibited a significant activity (75%) in inhibition of C. albicans. biofilm formation in a dose-dependent manner. The biofilm formation of C. albicans in the presence of CuO NPs was lower than Streptococcus spp. in comparison with the control group (p < 0.05). CONCLUSION: Incorporation of CuO NPs significantly decreased the colonization and plaque formation of the oral pathogens, especially C. albicans accumulation. These NPs may be useful as a promising agent for the antimicrobial management of soft denture liner materials.

The effect of bleaching on the optical and physical properties of externally stained monolithic zirconia.

OBJECTIVE: This study aimed to investigate the effects of bleaching on the color, translucency, surface roughness, and surface hardness of monolithic zirconia with external stainin . METHODS: In this experimental study, 32 specimens of monolithic zirconia (1 × 1 mm; shade A2) were divided into two groups based on random permuted blocks. Overglaze and staining procedures were performed with a yellow stain or a value stain (GC Stain). Baseline color, translucency, roughness, and surface hardness were measured. The specimens were then randomly bleached with hydrogen peroxide (HP) 40% (20 min, twice with a 1-week interval in between) as office bleaching or carbamide peroxide (CP) 20% (4 h per day for 14 days) as home bleaching. Finally, the color, translucency, surface roughness, and surface hardness were measured again. RESULTS: Bleaching with CP and HP caused a perceptible change in the color of the specimens (ΔE > 2), although this change was within the clinically acceptable range (ΔE < 3.3). HP significantly reduced the surface hardness of the specimens (p = 0.043). Changes in surface roughness of the specimens were neither statistically nor clinically significant (p = 0.19 and p = 0.25 for office and home bleaching, respectively). CONCLUSION: The effects of home and office bleaching on the surface characteristics of monolithic zirconia were almost the same. It is not necessary to exchange or even to polish the surfaces of zirconia restorations after exposure to bleaching agents. Further studies are recommended to confirm the color stability of externally stained monolithic zirconia.

The Effect of Different Foundation Materials on the Color of Monolithic Zirconia at Different Thicknesses.

STATEMENT OF THE PROBLEM: Monolithic zirconia restoration has been introduced to overcome the porcelain chipping. Different factors can affect the color of monolithic zirconia, so achieving the desired color in the restorations is considered as a challenge. PURPOSE: The purpose of this in vitro study was to determine the effect of different foundation materials on the color of monolithic zirconia at different thicknesses. MATERIALS AND METHOD: In this experimental study, thirty ceramic disks in three thicknesses (i.e. 0.6mm, 1.1mm and 1.5mm) were fabricated from high translucency shade A2 monolithic zirconia block. Disk shaped foundation materials were fabricated from nickel chromium alloy (Ni-Cr), non-precious gold alloy (NPG), zirconia, and shade A2 composite resin. The color was measured by a spectrophotometer. The color differences (∆E) in the control and the test groups were calculated. The data were analyzed using two way ANOVA and compared with the posthoc Tukey test (a=0.05). RESULTS: Ceramic thickness and foundation materials had a significant effect on the mean values of ∆E of monolithic zirconia ceramics (p= 0.001). The highest amount of ∆E value was observed in NPG, while Ni-Cr resulted in the lowest ∆E. Unacceptable results (∆E>2.25) were observed for monolithic zirconia ceramics on NPG foundation material with a thicknesses of 0.6 and 1.1mm. The mean L* values of all foundation materials were higher than those of the control group except for Ni-Cr. The highest a* was seen in NPG and the mean b* values of all tested foundation materials were higher than those of the control group except for Ni-Cr. CONCLUSION: Increasing the thickness of monolithic zirconia decreased the color mismatch. High translucent monolithic zirconia could mask the color of Ni-Cr and zirconia in all three thicknesses (∆E<2.25), while it could not mask the color of NPG under thickness of 1.5mm.

Marginal Fit of Full Contour Monolithic Zirconia in Different Thicknesses and Layered Zirconia Crowns.

AIM: Use of monolithic zirconia for fabrication of all-ceramic crowns eliminates several shortcomings of layered zirconia crowns. Long-term success of restorations highly depends on the marginal fit. The crown thickness is among the factors that affect the marginal integrity. Meanwhile, reduced thickness of crowns has several advantages such as preservation of tooth structure. The aim of this study was to evaluate the marginal fit of monolithic zirconia crowns in reduced thickness and to compare the marginal fit of full-contour monolithic zirconia in different thicknesses with layered zirconia crowns. MATERIALS AND METHODS: In this in vitro study, two standard brass dies (7 mm × 5 mm length diameter) were prepared with a heavy chamfer finish line with 0.5 and 1 mm depth. By using a CAD-CAM system, 30 crowns were made in three groups (n = 10) of 1-mm thick layered zirconia, 1-mm thick monolithic zirconia, and 0.5-mm thick monolithic zirconia. Crowns were placed on master dies and randomly numbered. The marginal gap was measured on 18 points by using a digital microscope (×230). The mean ± standard deviation (SD) values were calculated and analyzed by Statistical Package for the Social Sciences (SPSS) software program through Kruskal-Wallis and Mann-Whitney tests (α = 0.05). RESULTS: The marginal gap of 1-mm layered zirconia was significantly different from that of 1-mm monolithic zirconia (P = 0.001) and 0.5-mm monolithic zirconia (P = 0.004). Analysis of variance (ANOVA) revealed no significant difference between 0.5 and 1 mm thicknesses of monolithic zirconia (P = 0.141). CONCLUSION: Marginal gap in all the three groups was clinically acceptable. The two different thicknesses of monolithic zirconia crowns had no significant effect on the restoration marginal fit; however, layered zirconia crowns showed a significantly higher marginal gap than monolithic zirconia crowns.

Effect of different coloring techniques and surface treatment methods on the surface roughness of monolithic zirconia.

BACKGROUND: This study aimed to evaluate the effect of different coloring techniques and surface treatment methods on the surface roughness of monolithic zirconia ceramic. MATERIALS AND METHODS: In this in vitro study seventy-two disk-shaped monolithic zirconia (2 mm × 10 mm) were divided into three coloring techniques groups (white, internal staining, external staining) (n = 24). Each group was subdivided into four surface treatment subgroups (n = 6), as unpolished, polished with Shofu polishing kit, polished with dental direct polishing kit, and glazed. Profilometer was used to measure the Ra (roughness average) and Rz (roughness height) surface roughness values (µm) and scanning electron microscopy (SEM) for visual inspection of the surface morphology. The surface roughness parameters were calculated and analyzed with two-way ANOVA and Tukey's post hoc test (α = 0.05). RESULTS: The coloring technique, surface treatment method, and interaction of these two parameters significantly affected the Ra and Rz parameters (P < 0.05). Concerning the surface treatment, the Rz value was significantly higher in the unpolished subgroup, followed by the glazed and polished subgroups. However, the two polishing systems were not significantly different. The internal staining group had significantly higher Rz value than the other staining method, when the specimens were glazed or polished with Shofu kit. SEM showed multiple scratches in unpolished samples which were smoothened by glazing and specially by polishing. CONCLUSION: Among all the studied surface treatment methods, the lowest surface roughness was observed in highly polished monolithic zirconia, which was even less than the glazed one. The internal staining method can create a rougher surface for some of the surface treatment methods.

Accuracy of different impression materials in parallel and nonparallel implants.

BACKGROUND: A precise impression is mandatory to obtain passive fit in implant-supported prostheses. The aim of this study was to compare the accuracy of three impression materials in both parallel and nonparallel implant positions. MATERIALS AND METHODS: In this experimental study, two partial dentate maxillary acrylic models with four implant analogues in canines and lateral incisors areas were used. One model was simulating the parallel condition and the other nonparallel one, in which implants were tilted 30° bucally and 20° in either mesial or distal directions. Thirty stone casts were made from each model using polyether (Impregum), additional silicone (Monopren) and vinyl siloxanether (Identium), with open tray technique. The distortion values in three-dimensions (X, Y and Z-axis) were measured by coordinate measuring machine. Two-way analysis of variance (ANOVA), one-way ANOVA and Tukey tests were used for data analysis (α = 0.05). RESULTS: Under parallel condition, all the materials showed comparable, accurate casts (P = 0.74). In the presence of angulated implants, while Monopren showed more accurate results compared to Impregum (P = 0.01), Identium yielded almost similar results to those produced by Impregum (P = 0.27) and Monopren (P = 0.26). CONCLUSION: Within the limitations of this study, in parallel conditions, the type of impression material cannot affect the accuracy of the implant impressions; however, in nonparallel conditions, polyvinyl siloxane is shown to be a better choice, followed by vinyl siloxanether and polyether respectively.