Surface roughness and optical characteristics evaluations after chairside adjustment of different zirconia types.

STATEMENT OF PROBLEM: Limited evidence is available for the effect of chairside adjustment using rotary cutting instruments on the surface roughness and optical properties of different zirconia types. PURPOSE: To evaluate the effect of simulated adjustments on surface roughness and optical properties of different zirconia types. MATERIALS AND METHODS: Three Partially Stabilized Zirconia (PSZ) types based on mole percent yttria (Y) concentration from the same manufacturer (Katana; Kuraray) were used: 3Y-PSZ, 4Y-PSZ, and 5Y-PSZ. Thirty disk-shaped specimens (Ø14 × 1.2 mm) from different zirconia types (N = 90) were prepared. Specimens were either left without adjustment (NA), adjusted with Dialite ZR finishing and polishing system (Brasseler) (APol), or adjusted with course diamond instruments only (ADia). The specimens were distributed into 9 groups (n = 10): Group 3Y-PSZ/NA, Group 3Y-PSZ/APol, Group 3Y-PSZ/ADia, Group 4Y-PSZ/NA, Group 4Y-PSZ/APol, Group 4Y-PSZ/ADia, Group 5Y-PSZ/NA, Group 5Y-PSZ/APol, and Group 5Y-PSZ/ADia. The surface roughness of specimen was analyzed using an Atomic Force Microscope (AFM) (Bruker's Dimension Icon, Bruker) and Root Means Square (RMS) were recorded (nm). Surface Gloss (SG), Translucency Parameter (TP), and Contrast Ratio (CR) values of all groups were recorded using an integrating sphere spectrophotometer. Statistical analysis was performed using analysis of variance (ANOVA) and Tukey's multiple comparison tests for pairwise comparisons at p < 0.05 and 95% confidence interval. RESULTS: APol had no effect on the surface roughness (p = 0.88) while ADia had a significant negative effect (p < 0.05) despite the type of zirconia. Out of the three testes optical properties, only SG was negatively affected by ADia for all types of zirconia (p < 0.05). The two adjustment types did not affect the TP of all the tested zirconia (p = 0.91). The CR was not affected by the tested adjustments for all zirconia types (p = 0.726). CONCLUSION: Proper zirconia adjustment following a sequence of burs and polishers can maintain acceptable roughness and optical properties. Adjustment of zirconia with rough diamond can lead to deleterious effects and should be avoided. CLINICAL SIGNIFICANCE: Chairside adjustment of zirconia could lead to rougher surface and unpredictable changes of surface gloss. Therefore, zirconia adjustment should be minimized to the greatest extent possible and a proper protocol should be followed if had to be done.

Zirconia restoration types, properties, tooth preparation design, and bonding. A narrative review.

OBJECTIVE: The purpose of this review was to provide dental professionals with information regarding the various types of zirconia restorations, their mechanical and optical properties, tooth preparation design, and bonding protocol in an effort to enhance the longevity and durability of zirconia restorations. OVERVIEW: The yttria content of zirconia ceramics determines their classification. The mechanical and optical properties of each type are discussed, with an emphasis on the effect of yttria concentration on the properties of zirconia. The processing and sintering methods are also discussed as they have a direct impact on the properties of zirconia. The design of tooth preparation, specifically occlusal reduction, varies depending on the type of zirconia used in each case. Finally, a protocol for zirconia restoration bonding is described to ensure optimal bonding to the tooth structure. CONCLUSION: Not all zirconia restorations are the same. The selection of zirconia type based on yttria concentration, processing and sintering methods, tooth preparation design, and adherence to the bonding protocol are all critical to the success and longevity of zirconia restorations. CLINICAL SIGNIFICANCE: Zirconia restorations are the most commonly used indirect restorative material. The selection of the most appropriate zirconia type based on its yttria content, which determines its strength and translucency, is critical to the success and the longevity of the restoration. Tooth preparation design also influences the strength and translucency of the zirconia. Air-borne particle abrasion, followed by a ceramic primer and resin cement, can ensure a durable bond to the tooth structure.

Strength and phase transformation of different zirconia types after chairside adjustment.

STATEMENT OF PROBLEM: Limited evidence is available for the effect of chairside adjustment using diamond instruments on different types of zirconia. PURPOSE: The purpose of this in vitro study was to evaluate the effect of simulated adjustments on the biaxial flexural strength and phase transformation of 3 different zirconia types. MATERIAL AND METHODS: Three zirconia types from the same manufacturer (Katana; Kuraray) were used: High Translucency (3Y-PSZ), Super Translucent Multi Layered (4Y-PSZ), and Ultra Translucent Multi Layered (5Y-PSZ). Thirty disk-shaped specimens (Ø14×1.2 mm) were fabricated according to the International Organization for Standardization (ISO) Standard 6872 from different zirconia types (N=90). Specimens were either left without adjustment (NA), adjusted with Dialite ZR finishing and polishing system (Brasseler) (APol), or adjusted with course diamond instruments only (ADia). The specimens were distributed into 9 groups (n=10): group 3Y-PSZ/NA, group 3Y-PSZ/APol, group 3Y-PSZ/ADia, group 4Y-PSZ/NA, group 4Y-PSZ/APol, group 4Y-PSZ/ADia, group 5Y-PSZ/NA, group 5Y-PSZ/APol, and group 5Y-PSZ/ADia. The biaxial flexural strength of each specimen was measured by using a universal testing machine (Model 4411; Instron) and according to ISO 6872. X-ray diffraction analysis was conducted to quantify the monoclinic phase transformation. Scanning electron microscopy images were obtained to evaluate the fracture pattern. Statistical analysis was performed by using analysis of variance (ANOVA) and Tukey multiple comparison tests for pairwise comparisons (α=.05). RESULTS: The mean biaxial flexural strengths ranked from the highest to the lowest were for 3Y-PSZ, 4Y-PSZ, and 5Y-PSZ under any test condition (P=.007). Chairside adjustment with a diamond instrument significantly decreased the flexural strength of all zirconia types (P<.05). No statistically significant difference was found between the effect of APol and ADia on the strength of zirconia 3Y-PSZ (P=.603), 4Y-PSZ (P=.993), and 5Y-PSZ (P=.660). Phase transformation did not occur in the 5Y-PSZ groups. ADia groups had significantly higher phase transformation values regardless of zirconia type (P<.05). CONCLUSIONS: The biaxial flexural strength of zirconia decreased significantly after chairside adjustment with diamond instruments regardless of the yttria percentage. Adjustment with the Dialite ZR finishing and polishing system caused less tetragonal to monoclinic phase transformation than adjustment with a course-grit diamond instrument.

Effects of two Postprocessing Methods onto Surface Dimension of in-Office Fabricated Stereolithographic Implant Surgical Guides.

PURPOSE: To evaluate the effects of two postprocessing methods in terms of the overall, intaglio, and cameo surface dimensions of in-office stereolithographic fabricated implant surgical guides. MATERIALS AND METHODS: Twenty identical implant surgical guides were fabricated using a stereolithographic printer. Ten guides were postprocessed using an automated method. The other ten guides were postprocessed using a series of hand washing in combination with ultrasonics. Each guide was then scanned using cone-beam computed tomography to produce a set of digital imaging and communications in medicine (DICOM) files which were converted into standard tessellation language (STL) files. The STL file was then superimposed onto the original STL design file using the best fit alignment. The average positive and negative surface discrepancy differences in terms of means and variances were analyzed using t-test (α = 0.05). RESULTS: For the alternative group, the average positive and negative overall, intaglio, and cameo surface discrepancies were 77.38 ± 10.68 µm and -67.74 ± 6.55 µm; 78.83 ± 8.65 µm and -68.16 ± 5.26 µm; and 70.5 ± 8.48 µm -64.84 ± 5.55 µm, respectively. For the automated group, the average positive and negative overall, intaglio, and cameo surface discrepancies were 51.88 ± 4.38 µm and -170.7 ± 11.49 µm; 64.3 ± 4.44 µm and -89.45 ± 6.25 µm; and 83.59 ± 4.81 µm and -144.26 ± 13.19 µm, respectively. There was a statistical difference between the means of the two methods for the overall, intaglio, and cameo positive and negative discrepancies (p < 0.001). CONCLUSIONS: For a single implant tooth-supported implant guide, using hand washing with ultrasonics appeared to be consistently better than the automated method. The manual method presented with more positive discrepancies, while the automated method presented with more negative discrepancies.

Exploring the use of pulsed erbium lasers to retrieve a zirconia crown from a zirconia implant abutment.

BACKGROUND: Removal of cement-retained implant fixed restorations when needed, can be challenging. Conventional methods of crown removal are time consuming and costly for patients and practitioners. This research explored the use of two different types of pulsed erbium lasers as a non-invasive tool to retrieve cemented zirconia crowns from zirconia implant abutments. MATERIALS AND METHODS: Twenty identical zirconia crowns were cemented onto 20 identical zirconia prefabricated abutments using self-adhesive resin cement. The specimens were divided into two groups for laser assisted crown removal; G1 for erbium-doped yttrium aluminum garnet laser (Er:YAG), and G2 for erbium, chromium-doped yttrium, scandium, gallium and garnet (Er,Cr:YSGG). For the G1, after the first crown removal, the specimens were re-cemented and removed again using the Er:YAG laser. Times needed to remove the crowns were recorded and analyzed using ANOVA (α = 0.05). The surfaces of the crown and the abutment were further examined using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) analyses. RESULTS: The average times of zirconia crown removal from zirconia abutments were 5 min 20 sec and 5 min 15 sec for the Er:YAG laser of first and second experiments (G1), and 5 min 55 sec for the Er,Cr:YSGG laser experiment (G2). No statistical differences were observed among the groups. SEM and EDS examinations of the materials showed no visual surface damaging or material alteration from the two pulsed erbium lasers. CONCLUSIONS: Both types of pulsed erbium lasers can be viable alternatives for retrieving a zirconia crown from a zirconia implant abutment. Despite operating at different wavelengths, the Er:YAG and Er,Cr:YSGG lasers, perform similarly in removing a zirconia crown from a zirconia implant abutment with similar parameters. There are no visual and elemental composition damages as a result of irradiation with pulsed erbium lasers.

Intaglio Surface Dimension and Guide Tube Deviations of Implant Surgical Guides Influenced by Printing Layer Thickness and Angulation Setting.

PURPOSE: To measure overall intaglio dimensional and tube deviations of implant guides printed at 50 and 100 µm layer thickness at 0°, 45°, and 90° angulation using a stereolithographic (SLA) printer. MATERIALS AND METHODS: A surgical implant guide design from a subject missing a maxillary right central incisor, used as the original standard tessellation language (STL) were stereolithographically fabricated at each thickness and angulation, 50 and 100 µm layer thickness at 0°, 45°, and 90° angulation (n = 10 each group). The guide was then scanned using cone beam computed tomography. The digital imaging and communications in medicine (DICOM) scanned files were then converted to an STL format. The overall dimensional deviations of the intaglio surface and the positioning of the implant guide tube were then superimposed onto the original designed STL file using best-fitting alignment. A t-test and an F-test as well as ANOVA followed by a post hoc t-test were used to determine statistical significant differences (α = 0.05) for the intaglio surface and guide tube deviation, respectively. RESULTS: The overall intaglio surface discrepancies (µm) printed at 0°, 45°, and 90° were 55.07 ± 1.36, 52.39 ± 2.09, and 61.02 ± 15.96 for 50 µm layer; and 98.38 ± 10.55, 84.47 ± 10.61, and 90.26 ± 5 for 100 µm layer with statistically significant differences for both t-test and F-test, p < 0.001. The maximal guide tube linear deviations (µm) printed at 0°, 45°, and 90° were 10.78 ± 3.84, 8.16 ± 3.68, and 12.57 ± 5.39 for 50 µm layer (ANOVA, p = 0.096); and 10.95 ± 5.23, 16.79 ± 4.97, and 22.63 ± 2.81 for 100 µm layer (ANOVA, p < 0.001). The maximal guide tube angular deviations (°) printed at 0°, 45°, and 90° were 1.29 ± 0.30, 0.64 ± 0.13, and 0.56 ± 0.21 for 50 µm layer (ANOVA, p < 0.001); and 1.57 ± 0.29, 0.86 ± 0.14, and 1.02 ± 0.31 for 100 µm layer (ANOVA, p = 0.034). There was a statistical difference in the deviations between 50 and 100 µm layer printing in all printed angulations except at 0° (t-test, p = 0.05, p = 0.03, and p = 0.001 for 0°, 45°, and 90°) and linear deviations (t-test, p < 0.001, p = 0.009, and p = 0.001 for 0°, 45°, and 90°). CONCLUSION: Printing at 50 µm layer reduces dimensional intaglio deviations in general and reduces tube angular deviations with different angulations of printing. However, the deviations were only ∼60 to 100 µm for the intaglio dimension deviations; and ∼0.04 to 0.26 mm and ∼0.25° to ∼2° for tube deviations.

Fracture rate of 188695 lithium disilicate and zirconia ceramic restorations after up to 7.5 years of clinical service: A dental laboratory survey.

STATEMENT OF PROBLEM: The use of ceramic materials has increased significantly because of high esthetic demands, low costs, and ease of fabrication. Long-term, clinically based evidence is scarce, and laboratory studies have limited relevance in determining clinical durability. PURPOSE: The purpose of this dental laboratory survey was to evaluate the fracture rate of layered and monolithic lithium disilicate and zirconia single crowns and fixed partial dentures after up to 7.5 years of clinical service. MATERIAL AND METHODS: Two commercial dental laboratories with a database system that was able to track the number of remakes because of fracture only were identified. Lithium disilicate restorations (monolithic and layered) were categorized according to restoration type (single crown, fixed partial denture, veneer, and onlay). Zirconia restorations (monolithic and layered) were categorized according to type (single crown, fixed partial denture) and then into anterior or posterior restoration. Restoration remakes due to poor fit, shade, or marginal integrity were excluded from the evaluation. Data were analyzed, and statistical significance was evaluated with chi-square tests (α=.05). RESULTS: A total of 188 695 (51 751 lithium disilicate and 136 944 zirconia) restorations were included in the analysis, with an overall fracture rate of 1.35%. Lithium disilicate monolithic single crowns had a fracture rate of 0.96%, which was significantly lower than that of layered single crowns at 1.26% (P<.05). When the different types of lithium disilicate restorations were compared, fixed partial denture (monolithic and layered) fracture rates were significantly higher than those of single crowns (P<.001). Monolithic zirconia single crowns (0.54%) fractured at a lower rate than layered zirconia single crowns (2.83%) and monolithic fixed partial dentures (1.83%) (P<.001), while layered single crowns (2.83%) had a higher fracture rate than that of layered fixed partial dentures (1.93%) (P<.001). Monolithic anterior and posterior zirconia restorations fractured at a lower rate than layered anterior and posterior zirconia restorations (P<.05). Posterior monolithic zirconia restorations fractured at a lower rate than anterior restorations, while posterior layered zirconia restorations fractured at a higher rate than anterior zirconia restorations (P<.05). CONCLUSIONS: Within the 7.5-year period, restorations fabricated with lithium disilicate and zirconia restorations had relatively low fracture rates. Monolithic restorations fractured at a lower rate than layered restorations.

Effect of different treatments on the flexural strength of fully versus partially stabilized monolithic zirconia.

STATEMENT OF PROBLEM: Recent monolithic zirconia materials used for indirect restorations are predominantly fully stabilized zirconia with claims of enhanced optical properties. These restorations may behave differently from the conventional partially stabilized zirconia restorations, which may negatively affect some of the core properties required for restoration success. PURPOSE: The purpose of this in vitro study was to evaluate and compare the effects of staining, airborne-particle abrasion, and artificial aging on the flexural strength of fully and partially stabilized zirconia material. MATERIAL AND METHODS: Each partially stabilized monolithic zirconia (PSZ) and fully stabilized zirconia (FSZ) material and a zirconia core material (control) were prepared as bar-shaped specimens (2×2×25 mm) and divided into 6 groups (n=8/subgroup): regular sintering, vacuum sintering, stained, airborne-particle abrasion, artificially aged regular sintering, and artificially aged vacuum sintering. Critical load to fracture was determined for all groups by using monotonic uniaxial loading in accordance with International Organization for Standardization standard 6872. Data were analyzed using univariate analysis of variance, followed by the Tukey honest significant difference post hoc test (α=.05). RESULTS: The control and PSZ (1034 and 1008 MPa) displayed a significantly higher (P<.05) flexural strength than FSZ (582 MPa). Airborne-particle abrasion significantly (P<.05) enhanced the strength of the control and PSZ (1413 and 1227 MPa) but significantly (P<.05) reduced the flexural strength of the FSZ (442 MPa). Staining, artificial aging, and vacuum sintering had no significant effects on any of the groups. CONCLUSIONS: Fully stabilized zirconia may behave differently from conventional PSZ, especially with regard to airborne-particle abrasion, which may weaken the FSZ. The strength of PSZ is approximately double the strength of FSZ. Both of the zirconia materials showed resistance to artificial aging.

Fracture of layered zirconia restorations at 5 years: A dental laboratory survey.

STATEMENT OF PROBLEM: The use of ceramic restorations has significantly increased in recent years because of their esthetic properties and the high cost of noble metals. However, given the lack of long-term clinical trials and the limitations of in vitro studies, the durability of ceramic restorations is still questionable. PURPOSE: The purpose of this retrospective study was to determine the fracture rate of layered zirconia restorations at up to 5 years of clinical performance by using a dental laboratory survey model. MATERIAL AND METHODS: Data up to 5 years were collected from 2 commercial dental laboratories. Layered zirconia restorations returned to the laboratory for remaking because of failure (fracture) were identified and included. Restorations were categorized as anterior or posterior. Each category was further divided into complete coverage single crowns (SCs) and multiple unit fixed dental prostheses (FDPs). Fracture rates were compared and analyzed using the chi-square test (α=.05). RESULTS: A total of 31594 restoration records were reviewed and included 13419 anterior restorations (10134 SCs and 3285 FDPs) and 18175 posterior restorations (12810 SCs and 5365 FDPs). The overall fracture rate up to 5 years for all restorations (anterior and posterior) was 3.31%. The fracture rates for anterior restorations were less than for posterior restorations. The fracture rates for anterior SCs were approximately half those of the posterior SC fracture rate, and the combined fracture rate (anterior and posterior) was 3.25%. For FDPs, anterior FDPs fractured at a rate similar to that of posterior FDPs. The combined fracture rate (anterior and posterior FDPs) was 3.47%. CONCLUSIONS: Layered zirconia restorations displayed relatively low fracture rates in the relatively short term of 5 years.

Influence of increment thickness on dentin bond strength and light transmission of composite base materials.

OBJECTIVES: Bulk-fill resin composites (BFCs) are gaining popularity in restorative dentistry due to the reduced chair time and ease of application. This study aimed to evaluate the influence of increment thickness on dentin bond strength and light transmission of different BFCs and a new discontinuous fiber-reinforced composite. MATERIALS AND METHODS: One hundred eighty extracted sound human molars were prepared for a shear bond strength (SBS) test. The teeth were divided into four groups (n = 45) according to the resin composite used: regular particulate filler resin composite: (1) G-ænial Anterior [GA] (control); bulk-fill resin composites: (2) Tetric EvoCeram Bulk Fill [TEBF] and (3) SDR; and discontinuous fiber-reinforced composite: (4) everX Posterior [EXP]. Each group was subdivided according to increment thickness (2, 4, and 6 mm). The irradiance power through the material of all groups/subgroups was quantified (MARC® Resin Calibrator; BlueLight Analytics Inc.). Data were analyzed using two-way ANOVA followed by Tukey's post hoc test. RESULTS: SBS and light irradiance decreased as the increment's height increased (p < 0.05), regardless of the type of resin composite used. EXP presented the highest SBS in 2- and 4-mm-thick increments when compared to other composites, although the differences were not statistically significant (p > 0.05). Light irradiance mean values arranged in descending order were (p < 0.05) EXP, SDR, TEBF, and GA. CONCLUSIONS: As increment thickness increased, the light transmission decreased for all tested resin composites. Discontinuous fiber-reinforced composite showed the highest value of curing light transmission, which was also seen in improved bonding strength to the underlying dentin surface. CLINICAL RELEVANCE: Discontinuous fiber-reinforced composite can be applied safely in bulks of 4-mm increments same as other bulk-fill composites, although, in 2-mm thickness, the investigated composites showed better performance.

Fracture rate of monolithic zirconia restorations up to 5 years: A dental laboratory survey.

STATEMENT OF PROBLEM: The demand for ceramic restorations has increased over the past years because of their esthetic properties and the high cost of noble metals. However, the lack of long-term clinical studies and the difficulty of interpreting in vitro studies have placed the durability of ceramic restorations in doubt. PURPOSE: The purpose of this study was to determine the failure rate of monolithic zirconia restorations due to fracture up to 5 years of clinical performance. MATERIAL AND METHODS: Data were collected over 5 years from 2 commercial dental laboratories. Restorations that were returned to the laboratory for remake because of catastrophic failure (fracture) were identified and included. Restorations were categorized as anterior or posterior. Each category was further divided into complete-coverage single crowns (SCs) and multiple-unit fixed dental prostheses (FDPs). Fracture rates were compared and analyzed using a chi-square test (α=.05). RESULTS: A total of 39827 restoration records were reviewed and included 3731 anterior restorations (1952 SC; 1799 FDP) and 36096 posterior restorations (29808 SC; 6288 FDP). The overall fracture rate of up to 5 years for all restorations (anterior and posterior) was 1.09%. Fracture rates were 2.06% for all anterior restorations and 0.99% for all posterior restorations. Fracture rates were 0.97% for anterior SCs and 0.69% for posterior SCs, and the combined fracture rate (anterior and posterior) was 0.71%. For FDPs, 3.26% restorations fractured anteriorly and 2.42% fractured posteriorly, and the combined fracture rate (anterior and posterior) was 2.60%. CONCLUSION: Within the relative short-term evaluation of 5 years, restorations fabricated from monolithic zirconia material displayed relatively low fracture rates. Anterior restorations fractured at a slightly higher rate than posterior restorations, and FDPs fractured at a rate double that of SCs.

Complete-arch implant-supported monolithic zirconia fixed dental prostheses: A systematic review.

STATEMENT OF PROBLEM: Monolithic zirconia prostheses are emerging as a promising option in the implant-based rehabilitations of edentulous patients, yet their clinical performance is not fully documented. PURPOSE: The purpose of this systematic review was to assess the clinical performance of complete-arch implant-supported monolithic zirconia fixed dental prostheses. MATERIAL AND METHODS: The electronic databases PubMed, Science Direct, and Cochrane Library were searched for clinical studies on complete-arch implant-supported monolithic zirconia fixed dental prostheses. Human studies with a mean follow-up of at least 1 year and published in an English-language peer-reviewed journal up to June 2015 were included. Two independent examiners conducted the search and the review process. RESULTS: The search generated 903 titles. Eighteen qualifying studies were retrieved for full-text evaluation. Nine studies were included on the basis of preestablished criteria. Eight studies reported satisfactory clinical and esthetic outcomes. One study demonstrated prosthesis failure. Clinical studies are lacking on the long-term outcome of complete-arch implant-supported monolithic zirconia prostheses. CONCLUSIONS: Complete-arch dental implant restoration with monolithic zirconia is associated with high short-term success. Despite the many advantages and short-term favorable reports, studies of longer duration are necessary to validate the broad application of this therapy.

Impact of gastric acidic challenge on surface topography and optical properties of monolithic zirconia.

OBJECTIVE: To evaluate the surface topography and optical properties of monolithic zirconia after immersion in simulated gastric acid. MATERIALS AND METHODS: Four partially stabilized (PSZ) and one fully stabilized (FSZ) zirconia materials were selected for the study: Prettau (PRT, Zirkonzahn), Zenostar (ZEN, Ivoclar), Bruxzir (BRX, Glidewell), Katana (KAT, Noritake) and FSZ Prettau Anterior (PRTA, Zirkonzahn). IPS e.max (Ivoclar) was used as a control. The specimens (10×10×1.2mm, n=5 per material) were cut, sintered, polished and cleaned before immersed in 5ml of simulated gastric acid solution (Hydrochloric acid (HCl) 0.06M, 0.113% solution in deionized distal water, pH 1.2) for 96h in a 37°C incubator. Specimens were weighed and examined for morphological changes under scanning electron microscope (SEM) coupled with energy dispersive X-ray spectroscopy (EDX). Surface roughness was evaluated by a confocal microscope. Surface gloss and translucency parameter (TP) values were determined by a reflection spectrophotometer before and after acid immersion. The data was analyzed by one-way ANOVA followed by Tukey's HSD post hoc test (p<0.05). RESULTS: PRTA displayed the most weight loss (1.40%) among the zirconia specimens. IPS e.max showed about three times more weight loss (3.05%) than zirconia specimens as an average. SEM examination indicated areas of degradation, bead-like shapes and smoothening of the polishing scratches after acid immersion. EDX displayed ion interactions and possible ion leaching from all specimens. Sa and Sq values for PRTA, ZEN and IPS e.max were significantly lower (p<0.05) after acid immersion. TP values increased significantly for PRT, ZEN and IPS e.max (p<0.05), while the surface gloss of ZEN, PRTA and IPS e.max increased (p<0.05). SIGNIFICANCE: Monolithic zirconia materials show some surface alterations in an acidic environment with minimum effect on their optical properties. Whether a smoother surface is in fact a sign of true corrosion resistance or is purely the result of an evenly progressive corrosive process is yet to be confirmed by further research.

The effect of staining and vacuum sintering on optical and mechanical properties of partially and fully stabilized monolithic zirconia.

The effect of staining and vacuum sintering on optical properties and the bi-axial flexural strength of partially and fully stabilized monolithic zirconia (PSZ, FSZ) were evaluated. Disc-shaped specimens divided into three subgroups (n=15): non-stained, stained and non-stained with vacuum sintering. After staining and sintering, optical properties were evaluated using a reflection spectrophotometer and bi-axial flexural strength was tested using the piston-on-three balls technique. Statistical analysis was performed using multivariate analysis of variance (MANOVA) followed by post-hoc Tukey's tests (p<0.05). Staining decreased translucency parameter (TP) values of FSZ (p<0.05). Sintering under vacuum enhanced TP values for PSZ (p<0.05). Staining enhanced surface gloss for both types of zirconia (p<0.05). Staining increased bi-axial flexural strength of FSZ (p<0.05), while it decreased the strength of PSZ (p<0.05). Sintering under vacuum provided minimal benefits with either type of zirconia.

Load-Bearing Capacity of Fiber-Reinforced Composite Abutments and One-Piece Implants.

Fiber-reinforced composites (FRC) can potentially help in a physiologic stress transmission due to its excellent biomechanical matching with living tissues. Novel one-piece FRC implants and abutments with two different fiber orientations were loaded until failure to assess the load-bearing capacity, fracture patterns, and precision of fit. The one-piece FRC implants showed significantly higher load-bearing capacity compared to FRC abutments regardless of the fiber orientation (p < 0.001). For FRC abutments, bidirectional abutments showed significantly higher loads compared to unidirectional abutments (p < 0.001). The type of structure and fiber orientation are strong determinant factors of the load-bearing capacity of FRC implants and abutments.

Optical properties and light irradiance of monolithic zirconia at variable thicknesses.

OBJECTIVES: The aims of this study were to: (1) estimate the effect of polishing on the surface gloss of monolithic zirconia, (2) measure and compare the translucency of monolithic zirconia at variable thicknesses, and (3) determine the effect of zirconia thickness on irradiance and total irradiant energy. METHODS: Four monolithic partially stabilized zirconia (PSZ) brands; Prettau® (PRT, Zirkonzahn), Bruxzir® (BRX, Glidewell), Zenostar® (ZEN, Wieland), Katana® (KAT, Noritake), and one fully stabilized zirconia (FSZ); Prettau Anterior® (PRTA, Zirkonzahn) were used to fabricate specimens (n=5/subgroup) with different thicknesses (0.5, 0.7, 1.0, 1.2, 1.5, and 2.0mm). Zirconia core material ICE® Zircon (ICE, Zirkonzahn) was used as a control. Surface gloss and translucency were evaluated using a reflection spectrophotometer. Irradiance and total irradiant energy transmitted through each specimen was quantified using MARC® Resin Calibrator. All specimens were then subjected to a standardized polishing method and the surface gloss, translucency, irradiance, and total irradiant energy measurements were repeated. Statistical analysis was performed using two-way ANOVA and post-hoc Tukey's tests (p<0.05). RESULTS: Surface gloss was significantly affected by polishing (p<0.05), regardless of brand and thickness. Translucency values ranged from 5.65 to 20.40 before polishing and 5.10 to 19.95 after polishing. The ranking from least to highest translucent (after polish) was: BRX=ICE=PRT

Degree of conversion of dual-polymerizing cements light polymerized through monolithic zirconia of different thicknesses and types.

STATEMENT OF PROBLEM: Monolithic zirconia restorations are increasingly common. Dual-polymerizing cements have been advocated for cementation. The opacious nature of zirconia restoration can attenuate light, compromising optimal resin polymerization and eventually restoration debonding. PURPOSE: The purpose of this in vitro study was to evaluate the influence of material thickness on light irradiance, radiant exposure, and the degree of monomer conversion (DC) of 2 dual-polymerizing resin cements light-polymerized through different brands of monolithic zirconia. MATERIAL AND METHODS: Dual-polymerizing resin cements (RelyX Ultimate; 3M-ESPE, and Variolink II; Ivoclar, Vivadent) were mixed according to the manufacturers' instructions with a film thickness of 40 µm, placed under a 10 × 10 mm specimen of monolithic zirconia (Prettau Anterior by Zirkonzahn, Katana by Noritake, BruxZir by Glidewell, and Zenostar by Wieland) and a zirconia core control (ICE zirkon by Zirkonzahn) at various thicknesses (0.50, 1.00, 1.50, and 2.00 mm, n = 5 of each thickness). Each specimen was irradiated for 20 seconds (RelyX Ultimate) and 40 seconds (Variolink II) with Elipar S10 (3M-ESPE, 1200 mW/cm(2)). The amount of irradiance and radiant exposure was quantified for each specimen. Fourier transform infrared spectroscopy was used to measure the DC from the bottom surface of the resin. Statistical analysis was performed with 2-way ANOVA and post hoc Tukey honest significant difference (HSD) tests (α = .05). RESULTS: Light irradiance and radiant exposure decreased as the thickness of the specimen increased (P < .05) regardless of the brand. The ranking from least to highest was BruxZir < ICE zircon = Wieland < Katana = Prettau Anterior. The zirconia brand, thickness, and cement type had a significant effect on the DC (P < .001). The DC decreased significantly as the thickness of the zirconia increased (P < .001). Katana and Prettau Anterior showed the highest DC and BruxZir showed the lowest. CONCLUSION: The thickness of zirconia affects the DC of resin-based cements. The DC of the resin cements differed significantly between cements and among zirconia brands. More polymerizing time may be needed to deliver sufficient energy through some brands of zirconia.

In vitro assessment of the soft tissue/implant interface using porcine gingival explants.

The biologic seal of peri-implant soft tissue is crucial for long-term prognosis of oral implants. This in vitro study describes a novel tissue culture model using porcine gingival explants to evaluate the soft tissue/implant interface. Two different types of substrates were investigated: (a) plain polymer: BisGMA-TEGDMA (50-50 %) and (b) unidirectional fiber-reinforced composite (FRC). Porcine gingival explants were obtained from a local slaughterhouse. The experimental implants (n = 4) were inserted into the middle of freshly excised porcine gingival explants and cultured at the air/liquid interface up to 14 days. Porcine gingival explants with no implants served as baseline controls. The specimens were fixed and processed for the preparation of undecalcified samples. Histological analysis of the soft tissue/implant interface was carried out using a light-microscope. Microscopic evaluation suggests that the gingival explants established epithelial and connective tissue attachment to both implant types over the incubation period. FRC surfaces seemed to have a favorable tissue response with a sign of an outward epithelial migration. However, tissue degeneration was observed at the end of the experiment. In conclusion, this in vitro model maintains mucosal viability and ability to histologically evaluate soft tissue attachment to biomaterials rendering it a time efficient and cost effective model that may reduce the need for animal experiments.

Blood and fibroblast responses to thermoset BisGMA-TEGDMA/glass fiber-reinforced composite implants in vitro.

OBJECTIVES: This in vitro study was designed to evaluate both blood and human gingival fibroblast responses on fiber-reinforced composite (FRC) aimed to be used as oral implant abutment material. MATERIAL AND METHODS: Two different types of substrates were investigated: (a) Plain polymer (BisGMA 50%-TEGDMA 50%) and (b) FRC. The average surface roughness (Ra) was measured using spinning-disk confocal microscope. The phase composition was identified using X-ray diffraction analyzer. The degree of monomer conversion (DC%) was determined using FTIR spectrometry. The blood response, including the blood-clotting ability and platelet adhesion morphology, was evaluated. Fibroblast cell responses were studied in cell culture environment using routine test conditions. RESULTS: The Ra of the substrates investigated was less than 0.1 µm with no signs of surface crystallization. The DC% was 89.1 ± 0.5%. The FRC substrates had a shorter clotting time and higher platelets activation state than plain polymer substrates. The FRC substrates showed higher (P < 0.01-0.001) amount of adhered cells than plain polymer substrates at all time points investigated. The strength of attachment was evaluated using serial trypsinization, the number of cells detached from FRC substrates was 59 ± 5%, whereas those detached from the plane polymer substrates was 70 ± 5%, indicating a stronger (P < 0.01) cell attachment on the FRC surfaces. Fibroblasts grew more efficiently on FRC than on plain polymer substrates, showing significantly higher (P < 0.01) cell metabolic activities throughout the experiment. CONCLUSIONS: The presence of E-glass fibers enhances blood and fibroblast responses on composite surfaces in vitro.