Randomized clinical trial of zirconia laminate veneers sintered by using conventional versus speed process: 1-year follow-up.

STATEMENT OF PROBLEM: The application of highly translucent multilayered zirconia ceramic in minimally invasive esthetic dentistry allows the achievement of both esthetics and strength with minimal thickness. Clinical studies that have assessed the performance of zirconia ultrathin veneers sintered with the conventional and speed procedure are lacking. PURPOSE: The purpose of this clinical study was to evaluate the effect of speed sintering processes on the translucency and clinical performance of zirconia laminate veneers. MATERIAL AND METHODS: Four participants had their teeth restored with 32 ultratranslucent zirconia laminate veneers. Based on the zirconia sintering procedure, the participants were randomly allocated into 2 groups. The teeth were prepared by selective reduction over trial restorations. Zirconia veneers were milled from multilayer zirconia blanks and sintered either by speed sintering or conventional sintering as specified by the manufacturer's recommendations. The intaglio surface of the veneers were airborne-particle abraded with 50-µm aluminum-oxide, and the veneers were then adhesively bonded to the teeth with translucent light-polymerizing resin cement. The modified California Dental Association (CDA)/Ryge criteria were used to assess participants at baseline and every 3 months for 12 months. The translucency and the color difference of the tooth before and after veneer restoration were evaluated. For statistical analysis, the Pearson chi squared test, independent t test, and paired t test were used (α=.05). RESULTS: Translucency and color differences were significantly higher in the conventionally sintered group (P<.05). No restorations were lost. No significant differences were found between the 2 groups in the CDA/Ryge criteria or color parameter after follow-up intervals (P>.05). The primary qualitative changes observed at the final recall were marginal integrity and marginal discoloration. The color match and zirconia surface were rated Alfa. CONCLUSIONS: After 1 year of follow-up, both conventional and speed sintered ultrathin zirconia laminates showed satisfactory functional, esthetic, and color stability outcomes.

Preparation of ultrathin translucent zirconia laminate veneers using 3D printing reduction guides.

Minimizing and controlling the amount of tooth reduction during the preparation of ultrathin laminate veneers is a challenge for minimally invasive dentistry. The use of reduction guides is advised to reach the optimal space required for the definitive restoration without excessive reduction. The digital production of a reduction guide used to control tooth preparation for ultrathin laminate veneers is described.

Translucency of recent zirconia materials and material-related variables affecting their translucency: a systematic review and meta-analysis.

BACKGROUND: Recent forms of translucent zirconia material have been developed, offering a wide range of options and varieties for enhancing aesthetics, making it a preferred choice in the field of prosthetic dentistry. However, there is insufficient understanding regarding the recent types of zirconia materials and their optical behavior. Understanding the variables that influence the translucency of zirconia and identifying strategies to enhance its esthetics are crucial. PURPOSE: The current systemic review highlights a comprehensive understanding of different zirconia generations in relation to their optical characteristics and evaluates material-related variables affecting their translucency. METHODS: The present review studied in-vitro studies that evaluated the optical characteristics of different yttria content of yttria stabilized materials. The topics explored were: (1) the different zirconia material generations and their optical behavior; (2) material-related factors that affect their translucency. The research was restricted to online publication in the English language from July 1, 2010, to July 31, 2023, using PubMed, Scopus, and Science Direct resources. The search key terms and their combinations were "zirconia," "translucent zirconia," "cubic zirconia," "highly translucent zirconia," "yttria partially stabilized zirconia," "monolithic zirconia," "translucency," "optical properties," and "light transmission." RESULTS: The data obtained from fifty-three studies addressed the optical characteristics of various zirconia generations. They reported that changing yttria content had a significant impact on translucency. Different kinds of zirconia ceramics of the same generation have varying translucencies. Achieving optimum aesthetics with monolithic zirconia is challenging due to factors related to material aspects such as the presence of additives, point defects, microstructure, thickness, phase distribution, and sintering conditions. CONCLUSIONS: Newly developed monolithic dental zirconia ceramics have improved aesthetics and translucency. However, additional research is necessary to evaluate their performance and long-term durability. TRIAL REGISTRATION: This systematic review was registered in PROSPERO, under number CRD42023474482.

Effect of surface treatments on biaxial flexural strength, fatigue resistance, and fracture toughness of high versus low translucency zirconia.

BACKGROUND: Mechanical surface treatments can deteriorate the mechanical properties of zirconia. This study evaluated and compared the biaxial flexural strength, fracture toughness, and fatigue resistance of high translucency (HT) to low translucency (LT) zirconia after various mechanical surface treatments. METHODS: Four hundred eighty zirconia discs were prepared by milling and sintering two HT (Katana and BruxZir) and LT (Cercon and Lava) zirconia blocks at targeted dimensions of 12 mm diameter × 1.2 mm thickness. Sintered zirconia discs received one of the following surface treatments: low-pressure airborne particle abrasion (APA) using 50 µm alumina particles, grinding using 400 grit silicon carbide paper, while as-sintered specimens served as control. Internal structure and surface roughness were evaluated by scanning electron microscope (SEM) and a non-contact laser profilometer, respectively. Half of the discs were tested for initial biaxial flexural strength, while the rest was subjected to 106 cyclic fatigue loadings, followed by measuring the residual biaxial flexural strength. Fractured surfaces were examined for critical size defects (c) using SEM to calculate the fracture toughness (KIC). The effect of surface treatments, zirconia type, and cyclic fatigue on the biaxial flexural strength was statistically analyzed using three-way analysis of variance (ANOVA) and Tukey HSD post hoc tests (α = 0.05). Weibull analysis was done to evaluate the reliability of the flexural strength for different materials. RESULTS: The initial biaxial flexural strength of LT zirconia was significantly higher (p < 0.001) than that of HT zirconia in all groups. While low APA significantly increased the biaxial flexural strength of LT zirconia, no significant change was observed for HT zirconia except for Katana. Surface grinding and cyclic fatigue significantly reduced the flexural strength of all groups. High translucency zirconia reported higher fracture toughness, yet with lower Weibull moduli, compared to LT zirconia. CONCLUSION: LT zirconia has higher biaxial flexural strength, yet with lower fracture toughness and fatigue resistance, compared to HT zirconia. Low-pressure APA has significantly increased the biaxial flexural strength in all zirconia groups except BruxZir. Grinding was deteriorating to biaxial flexural strength and fracture toughness in all zirconia types. Cyclic fatigue has significantly decreased the biaxial flexural strength and reliability of HT and LT zirconia.

Effect of chemical aging on color stability and surface properties of stained all-ceramic restorations.

OBJECTIVES: To study the effect of artificial aging on color stability, translucency, and surface roughness of stained all-ceramic restorations. MATERIALS AND METHODS: Disc-shaped specimens were fabricated from six different all-ceramic materials: two glass ceramics (Vita Mark II and Empress CAD), two lithium disilicate based ceramics (e.max and Suprinity), and two zirconia-based materials (ZirCAD LT and ZirCAD MT Multi). The discs were stained using two universal stains; IPS Ivocolor stain or Vita Akzent stain. Color change (ΔE) and the translucency parameter (TP) were measured before and after artificial aging. The surface roughness (Ra) was evaluated using atomic force microscopy, while the surface microstructure was evaluated using scanning electron microscopy (SEM). Quantitative elemental analysis was performed using the energy dispersive X-ray (EDX). Leached ions were analyzed by inductively coupled plasma (ICP) (n = 12, α = 0.05). RESULTS: Artificial aging had significantly changed the color (ΔE) and decreased the translucency (TP) of all stained ceramics. The mean surface roughness (Ra) was significantly increased in all specimens, which was also confirmed in the SEM scans. EDX analysis revealed a decrease in the elemental composition of the stained surface as a result of ceramic degradation, except for Ca and Zn in IPS Ivocolor stain. Furthermore, the ICP analysis revealed that most compositional elements of stain and glaze were detected in the aging solution. CONCLUSIONS: Chemical aging had significantly affected the optical parameters and surface texture of stained monolithic ceramics. CLINICAL SIGNIFICANCE: Stained ceramics are liable to color degradation. Each type of stain should be used with its corresponding type of ceramic. Stained all-ceramic restorations are liable to color change and surface degradation during function.

Osteogenesis ability of CAD-CAM biodegradable polylactic acid scaffolds for reconstruction of jaw defects.

STATEMENT OF PROBLEM: Reconstruction of alveolar bony defects is difficult using grafting materials in a powder form. A biodegradable scaffold material might simplify the procedure. PURPOSE: The purpose of this in vivo study was to evaluate osteogenesis ability of a biodegradable CAD-CAM-fabricated polylactic acid (PLA) scaffold enriched with calcium phosphate salts including hydroxyapatite (HA) and beta tricalcium phosphate (ß-TCP) used to reconstruct mandibular defects in a dog model. MATERIAL AND METHODS: Surgical defects were made bilaterally in the mandible of male beagle dogs. Computerized tomography images were obtained for determination of the 3-dimensional shape of the defects after 3 months of healing. Porous PLA scaffolds were fabricated by milling custom-made CAD-CAM blocks into the desired shape. After milling, half of the scaffolds were prepared by filling the pores of the scaffolds by a mixture of HA and ß-TCP. Scaffolds were inserted in the mandibular defects bilaterally. After a healing time of 8 weeks, the bone-scaffold interface was analyzed histomorphometrically to detect the amount of new bone formation. Stained histological sections were examined using a computer software and depth of new bone formation was assessed (n=14, α=.05). RESULTS: Histomorphometric analysis revealed that enriched scaffolds with calcium phosphates had significantly (t=4.4, P<.001) higher amounts of new bone formation (1.3 ±0.33 mm) compared with the controls (0.7 ±0.39 mm). Average new bone growth in enriched scaffolds was 1.3 mm while almost half this value was observed in uncoated scaffolds, 0.7 mm. CONCLUSIONS: Within the limitations of this animal study, HA and ß-TCP enhanced osteogenesis ability of CAD-CAM-fabricated PLA scaffolds.

Clinical Management Protocol for Dental Implants Inserted in Patients with Active Lichen Planus. Part II 4-Year Follow-Up.

PURPOSE: To evaluate marginal bone loss (MBL) of dental implants inserted in active lichen planus patients. MATERIALS AND METHODS: The study included 59 subjects divided into 3 groups depending on their lichen planus diagnosis and administration of a low dose of corticosteroids: 17 healthy individuals, 20 controlled lichen planus patients controlled using low doses of systemic corticosteroids, and 22 noncontrolled lichen planus patients. During 4-year follow-up sessions MBL was evaluated, and biopsies were collected from lichen planus patients and examined. Two-way ANOVA was used to analyze the data (α = 0.05). RESULTS: There was no statistically significant difference in MBL between healthy and controlled patients; however, noncontrolled patients exhibited increased MBL (F = 1309, p < 0.001) which reached 2.53 mm after 4 years. There were significant interactions between state of the disease (F = 1309, p < 0.001), evaluation time (F = 317, p < 0.001), and interaction between state of the disease and observation time (F = 159, p < 0.001). Histopathologic examination of collected biopsies revealed healthy tissue architecture of the controlled patients, while inflammatory cellular infiltration and signs of classical destructive tissue were observed for noncontrolled patients. CONCLUSIONS: Lichen planus patients receiving dental implants should be controlled on a low-dose of corticosteroids to prevent accelerated MBL and to reduce remission of clinical manifestations.

Ultrastructural Analysis and Long-term Evaluation of Composite-Zirconia Bond Strength.

PURPOSE: To evaluate the influence of different aging techniques on zirconia-composite microtensile bond strength using different surface treatments over a 5-year follow-up period. MATERIALS AND METHODS: Zirconia disks received three surface treatments: airborne-particle abrasion with 50-µm aluminum oxide particles, selective infiltration etching (SIE), or fusion sputtering (FS). The specimens were bonded to pre-aged composite disks using a composite cement containing phosphate monomers (Panavia F2.0). Bonded specimens were sectioned into microbars (1 x 1 x 6 mm) using a precision cutting machine, and all microbars received thermocycling (15,000 cycles between 5°C and 55°C). Initial microtensile bond strength was evaluated, and the test was repeated after storage in the following media for five years (artificial saliva, 20% ethanol, 5% NaOH, 4% acetic acid, and 5% phosphoric acid). The test was repeated every 12 months for 5 years. Scanning electron microscopic images were used to analyze the zirconia-composite interface. A repeated measures ANOVA and Bonferroni post-hoc tests were used to analyze the data (n = 20, α = 0.05). RESULTS: Significantly higher microtensile bond strength was observed for SIE compared to fusion sputtering and airborne particle abrasion. Five years of artificial aging resulted in significant reduction of zirconia-composite bond strength for all tested specimens. Zirconia-composite bond strength was more sensitive to storage in sodium hydroxide and phosphoric acid, while it was least affected when stored under saliva. These changes were related to the mechanism of ultra-structural interaction between surface treatment and adhesive, as deterioration of the hybrid layer (composite-infiltrated ceramic) was responsible for bond degeneration. CONCLUSION: Zirconia-composite bond strength was influenced by 5 years of artificial aging.

Fracture resistance of three-unit zirconia fixed partial denture with modified framework.

Obtaining ideal prosthetic framework design is at times hindered by anatomical limitations in the posterior region that might increase the risk for zirconia restoration fracture. Modification such as increasing the bulk thickness especially in the connector region could result in strengthening the zirconia framework. Three-unit zirconia fixed partial dentures replacing mandibular molars were fabricated using the following two techniques: CAD/CAM technology and manual copy milling. Modified framework with unveneered full thickness connectors were designed and fabricated with the aforementioned methods. Conventional frameworks (0.5 mm thick with rounded 3 mm connectors) served as control (N = 20). After cementation on epoxy dies, the frameworks were loaded to fracture in a universal testing machine. Fractured surfaces were prepared for examination using scanning electron microscopy. Statistical analysis revealed significant differences in fracture resistance between conventional and modified framework design for both fabrication techniques tested. SEM examination indicated that critical crack originated at the tensile surface of the connectors for conventional frameworks. The critical crack for modified frameworks occurred on the axial wall of the abutments. The modification of the zirconia framework design presented significant improvement of the fracture resistance compared to the conventional design.

Two-stage implant placement technique for the management of irradiated jaws: An animal study.

STATEMENT OF PROBLEM: Radiotherapy results in diminished bone remodeling capacity and an elevated risk of osteoradionecrosis, which can negatively influence the survival rate of dental implants. Patients receiving radiotherapy are advised not to receive dental implants during or soon after completing their radiotherapy. PURPOSE: The purpose of this animal study was to investigate a 2-stage implant placement technique designed to diminish applied trauma on irradiated bone. MATERIAL AND METHODS: Two groups of white New Zealand rabbits received radiotherapy in ascending doses (2, 4, 8 Gy), while a nonirradiated group served as control. Three weeks after completion of the last radiotherapy session, one of the irradiated groups and the control group received titanium dental implants bilaterally in the femur head. For the second irradiated group, an osteotomy was performed, and the surgical wound was left to heal for 2 weeks before implant placement. All animals were sacrificed 4 weeks after implant placement, and histomorphometric analysis was used to study bone-implant contact (n=14, α=.05). RESULTS: Statistical analysis revealed significantly higher (F=159, P<.001) bone-implant contact in the 2-stage (40.2 ±1.9) implant placement technique than in the immediately placed implants (21.2 ±2.3) in irradiated bone. Both of the groups had a significantly lower bone-to-implant contact ratio than the non-irradiated control (64.2 ±3.8). CONCLUSIONS: Within the limitations of this animal study, the 2-stage implant placement technique could be used to reduce trauma in irradiated bone and to improve wound healing around dental implants.

Clinical Management Protocol for Dental Implants Inserted in Patients with Active Lichen Planus.

PURPOSE: To propose a treatment protocol for management of implant candidates suffering from active lichen planus. MATERIALS AND METHODS: Twenty-three patients who were diagnosed with active lichen planus were referred to a dental practice seeking dental implants. Patients received dental implants using open flap technique and sequential osteotomy. After a healing time of 6 weeks, implants were put into occlusal contact using interim prostheses. Of the 55 inserted implants, 42 failed after a short clinical service time (7 to 11 weeks). Failed implants were surgically removed, and osteotomy sites were carefully cleaned using manual curettes and scrubbing of osteotomy walls. CD4/CD8 cell count and gingival biopsies were collected from the surgical sites. Patients were put on an ascending dose (5 mg/10 days) of oral corticosteroids until a daily dose of 20 mg/day was achieved and maintained for 2 weeks. All patients received ten sessions of low-energy soft tissue laser irradiation at the implant insertion sites to assess soft tissue healing through improving blood circulation, reduction of inflammation, and sterilization of the osteotomy region. After approximately 8 weeks, a new set of 42 implants was placed, and definitive restorations were cemented using early loading technique. Marginal bone levels around inserted implants were periodically evaluated every 3 months using digital periapical radiographs (α = 0.05). RESULTS: Primary blood tests revealed a high CD8 cell count, while soft tissue biopsies revealed infiltration of inflammatory cells at the epithelium soft tissue interface of the examined tissue. Repetition of immunological investigations after administration of the oral corticosteroids and soft tissue laser irradiation revealed reduction of CD8 cell counts and disappearance of inflammatory cell infiltration of the examined soft tissue biopsy. Patients reported marked improvement of the oral mucosa after treatment. All implants (n = 42) were functional after 3 years of clinical observation. There was an initial reduction in marginal bone level after 3 months from insertion time, after which it remained constant during the following observation periods. CONCLUSION: Active lichen planus should be managed with oral corticosteroids and soft tissue laser irradiation before insertion of dental implants.

Microtensile Bond Strength of Resin-bonded Hightranslucency Zirconia Using Different Surface Treatments.

PURPOSE: To evaluate the effect of a novel surface treatment intended to improve bond strength to high-translucency zirconia. MATERIALS AND METHODS: Fully sintered high-translucency zirconia disks (Incoris TZI) were divided into four groups according to the surface treatment received: modified fusion sputtering technique, selective infiltration etching, low pressure particle abrasion using 30-µm alumina particles, while 50-µm particle abrasion served as control. Surface roughness was evaluated quantitatively using a contact profilometer. The disks were bonded to pre-aged composite resin disks using a light-polymerized adhesive resin (RelyX ultimate). The bilayered disks were sectioned into microbars and zirconia-resin bond strength was evaluated using the microtensile bond strength test (MTBS). The test was repeated after 3 months of water storage (37°C). Scanning electron microscopic examination of the zirconia resin interface was performed at different magnifications. A repeated measures ANOVA and Bonferroni post-hoc test were used to analyze the data (n = 20, α = 0.05). RESULTS: One-way ANOVA revealed significant differences in average surface roughness (Ra) between the tested groups (p < 0.001). The highest Ra value was recorded for fusion sputtering (12.23 ± 0.11 µm), followed by 50-µm particle abrasion (6.400 ± 0.887), then low pressure 30-µm particle abrasion (2.4 ± 0.15 µm), while the lowest surface roughness was recorded for the selective infiltration group (0.368 ± 0.04 µm). Modified fusion sputtering and selective infiltration etching produced significantly higher MTBS values at each of the tested intervals (p < 0.001) compared to particle abrasion using different particle sizes. Water storage resulted in reduction in the bond strength of 30-µm abraded specimens, which was attributed to structural defects observed at the zirconia/ resin interface. Scanning electron microscopic examination revealed a nanoporous surface characteristic of selective etching surface treatment, and modified fusion sputtering resulted in the creation of surface-fused microbeads. CONCLUSION: Within the limitations of this study, selective infiltration etching and modified fusion sputtering techniques established a strong, stable, durable bond to high-translucency zirconia.

Low Energy Surface Activation of Zirconia Based Restorations.

PURPOSE: To evaluate the influence of low energy surface activation technique on the biaxial flexure strength of zirconia frameworks. MATERIALS AND METHODS: Zirconia discs were prepared by cutting CAD/CAM zirconia blocks. Sintered discs were airborne particle abraded using one of the following particles: 30 µm alumina particles, 50 µm alumina particles, or modified round edges 30 µm alumina particles at low pressure. Scanning electron microscopy, x-ray diffraction analysis, surface roughness, and biaxial flexure strength tests were performed (n = 20). Fractured specimens were fractographically analyzed (α = 0.05). RESULTS: Low energy surface activation resulted in 7% monoclinic crystallographic transformation, increasing surface roughness from 0.05 to 0.3 µm and in significant increase in biaxial flexure strength (1718 MPa) compared 30 µm (1064 MPa), 50 µm (1210 MPa), and as-sintered specimens (1150 MPa). CONCLUSIONS: Low energy surface activation of zirconia specimens improved the biaxial flexure strength of zirconia frameworks without creation of surface damage. Clinical implications: by controlling particle size and shape of alumina, the flexure strength of zirconia restorations could be increased usinglow pressure particle abrasion.

Comparison of interim restorations fabricated by CAD/CAM with those fabricated manually.

STATEMENT OF PROBLEM: Interim restorations represent an essential treatment step; however, the optimal resin material for long-term interim restorations requires investigation. PURPOSE: The purpose of this in vitro study was to compare the color stability, water sorption, wear resistance, surface hardness, fracture resistance, and microleakage of computer-aided design/computer-aided manufacturing-(CAD/CAM) fabricated interim restorations with those of manually fabricated interim restorations. MATERIAL AND METHODS: Epoxy replicas were made from a prepared maxillary first premolar. On the replicas, interim crowns were fabricated and divided into the following groups: CAD/CAM poly(methyl methacrylate) (PMMA) blocks (CC), autopolymerizing temporary resin (AP), automix temporary resin (AM), and thermoplastic resin (TP). After cementation, all specimens were subjected to thermocycling and dynamic fatigue. The CIE Laboratory color coordinates were then recorded before and after immersion in coffee, tea, carbonated cola, and red wine. Water sorption was evaluated by using an immersion technique. Wear resistance was measured in a surface abrasion device. Vickers microhardness was measured on polished specimens. Fracture resistance was evaluated by axial loading with a universal testing machine. Marginal dye penetration was evaluated by sectioning the interim restorations after immersion in methylene blue (α=.05). RESULTS: Colorimetric analysis revealed a large degree of color alteration (ΔE) in the manually fabricated interim restorations: AP = ΔE of 6.7 ±2); AM = ΔE of 7.1 ±1.5), and TP = ΔE of =5.4 ±3.1. The CC group demonstrated color stability (ΔE=2.1 ±0.2). CAD/CAM interim restorations demonstrated significantly lower water sorption, higher wear resistance, higher surface hardness, and significantly higher fracture resistance (1289±56N) compared with manually fabricated interim restorations (AP=996 ±45, AM=899 ±37, and TP=1179 ±41). The stereomicroscopic examination of sectioned specimens demonstrated the absence of dye penetration in all tested specimens. CONCLUSIONS: CAD/CAM interim crowns presented stable physical and mechanical properties and may be used for long-term interim restorations.

Fracture and Fatigue Resistance of Cemented versus Fused CAD-on Veneers over Customized Zirconia Implant Abutments.

PURPOSE: To evaluate the fracture mechanics of cemented versus fused CAD-on veneers on customized zirconia implant abutments. MATERIALS AND METHODS: Forty-five identical customized CAD/CAM zirconia implant abutments (0.5 mm thick) were prepared and seated on short titanium implant abutments (Ti base). A second scan was made to fabricate 45 CAD-on veneers (IPS Empress CAD, A2). Fifteen CAD-on veneers were cemented on the zirconia abutments (Panavia F2.0). Another 15 were fused to the zirconia abutments using low-fusing glass, while manually layered veneers served as control (n = 15). The restorations were subjected to artificial aging (3.2 million cycles between 5 and 10 kg in a water bath at 37°C) before being axially loaded to failure. Fractured specimens were examined using scanning electron microscopy to detect fracture origin, location, and size of critical crack. Stress at failure was calculated using fractography principles (alpha = 0.05). RESULTS: Cemented CAD-on restorations demonstrated significantly higher (F = 72, p < 0.001) fracture load compared to fused CAD-on and manually layered restorations. Fractographic analysis of fractured specimens indicated that cemented CAD-on veneers failed due to radial cracks originating from the veneer/resin interface. Branching of the critical crack was observed in the bulk of the veneer. Fused CAD-on veneers demonstrated cohesive fracture originating at the thickest part of the veneer ceramic, while manually layered veneers failed due to interfacial fracture at the zirconia/veneer interface. CONCLUSIONS: Within the limitations of this study, cemented CAD-on veneers on customized zirconia implant abutments demonstrated higher fracture than fused and manually layered veneers.

Microtensile bond strength of lithium disilicate ceramics to resin adhesives.

PURPOSE: To evaluate the influence of the internal structure of lithium disilicate glass ceramics (LDC) on the microtensile bond strength to a resin adhesive using two surface treatments. MATERIALS AND METHODS: Milling blocks of three types of LDC were sectioned (4 mm thick) using a precision cutting machine: IPS Empress 2 (conventional LDC), IPSe.max CAD (a refined crystal high strength LDC), and Celtra (zirconia reinforced LDC). Cut specimens received crystallization heat treatment as suggested by the manufacturers. Two surface treatments were performed on each group: hydrofluoric acid etching (HF) and airborne particle abrasion using 50-µm glass beads, while the as-cut surface served as control. Treated surfaces were examined using scanning electron microscopy (SEM). The disks were coated with a silane primer and bonded to pre-aged resin composite disks (Tetric EvoCeram) using a resin adhesive (Variolink II) and then stored in water for 3 months. Bonded specimens were sectioned into micro-bars (1x1x6 mm) and microtensile bond strength test (MTBS) was performed. Data were analyzed using two-way ANOVA and Tukey's post-hoc test (α=0.05). RESULTS: Statistical analysis revealed significant differences in microtensile bond strength values between different LDCs (F=67, p<0.001), different surface treatments (F=232, p<0.001), and interaction between LDC and surface treatments (F=10.6, p<0.001). Microtensile bond strength of Celtra ceramic (30.4±4.6 MPa) was significantly higher than both IPS Empress 2 (21.5±5.9 MPa) and IPSe.max ceramics (25.8±4.8 MPa), which had almost comparable MTBS values. SEM images demonstrated homogenous glassy matrix and reinforcing zirconia fillers characteristic of Celtra ceramic. Heat treatment resulted in growth and maturation of lithium disilicate crystals. Particle abrasion resulted in abrasion of the glass matrix and exposure of lithium disilicate crystals, while HF etching produced a microrough surface, which resulted in higher MTBS values and reduction in the percentage of adhesive failure for all groups. CONCLUSIONS: Within the limitations of this study, bond strength to lithium disilicate ceramics depends on proper surface treatment and on the chemical composition of the glass ceramic.

Comparative analysis of dimensional changes in autoclavable polyvinyl siloxane (PVS) impressions under various Sterilization/Disinfection Protocols: A randomized controlled trial.

Background: Impressions that maintain their dimensional stability after autoclaving effectively control cross-infection and contamination resulting from a patient's oral secretions. Purpose: The study aimed to assess the dimensional stability of autoclavable polyvinyl siloxanes after disinfection and sterilization. Methods: A stainless steel metal model containing three full veneer crown preparations was fabricated according to ANSI/ADA specification No. 19. Reference grooves were established on the occlusal and axial surfaces of the abutments for accurate measurements. Forty impressions were created from the master model using single-step impression technique monophase polyvinyl siloxane material (AFFINIS, Coltene/Whaledent, Altstatten, Switzerland). The impressions were categorized into four groups: Group A (control, ten untreated impressions), Group B (ten disinfected impressions with 5.25 % sodium hypochlorite [NaOCl]), Group C (ten disinfected impressions with 2 % glutaraldehyde), and Group D (ten autoclaved impressions at 134 °C for 18 min). Subsequently, stone casts were produced using type IV gypsum products (Gelstone R, BK Giulini Chemie, Ludwigshafen/Rh., Germany). The dimensional accuracy of the obtained casts was assessed by measuring the inter-abutment measurements (between the abutments) and the intra-abutment measurements (diameter and height of the abutments). These measurements were performed using a universal measuring microscope (Olympus stereomicroscope B061 Imaging Corp. Tokyo, Japan) with a precision of 0.001 mm. The dimensions of the stone casts from the study groups were then compared to those of the control group. Data analysis was performed using a one-way ANOVA with a significance level of α = 0.05. Results: AFFINIS impressions subjected to chemical disinfection in 5.25 % NaOCl and 2 % glutaraldehyde with different immersion times showed slight expansion in the intra- and inter-abutment measurements. The impressions autoclaved at 134 °C for 18 min showed slight shrinkage in the intra- and inter-abutment measurements. The dimensional change was statistically non-significant, and the percent of dimensional changes within the experimental groups was within the clinically accepted limit (α < 0.5). Conclusion: AFFINIS polyvinyl siloxanes retain dimensional stability suitable for clinical use when subjected to chemical disinfection and steam autoclaving.

Prefabricated CAD-CAM scaffolds for management of oro-antral communication: A case report and histological analysis.

INTRODUCTION: Oro-control communication is one of the complications associated with dental extraction and oral surgeries. This case report presents a minimally invasive surgical approach for bone regeneration at the site of oro-antral communication utilizing a prefabricated computer-aided design and computer-aided manufacturing (CAD-CAM) allogenic bone block. METHODS: A 20-year-old healthy female, nonsmoker, with a badly destructed upper right first molar was referred for dental implant placement after extraction. Cone beam computerized tomography images revealed the presence of a large bone defect associated with oro-antral communication with the maxillary sinus and insufficient bone for dental implant placement. A prefabricated CAD-CAM allogenic bone scaffold was fabricated. After surgical exposure, the scaffold was secured in place and covered with a non-resorbable membrane. A dental implant was placed after 5 months, and a trephining biopsy was processed for histological evaluation. RESULTS: Closure of the oro-antral communication was clinically observed. The average width of the alveolar bone was 12 mm, and the average height was 11 mm. Histological analysis at 5-month intervals showed thin newly formed bone trabeculae encircling remnants of graft material surrounded by osteoid tissue. The newly formed bone percentages were 32 ± 18% and 28 ± 17% volume remained after the biodegradation of the scaffold. Specific immune-histochemical staining by anti-vascular epithelial growth factor expression index value was 32.06%. CONCLUSIONS: A prefabricated CAD-CAM scaffold was successfully used to seal a large oro-antral communication and regenerate sufficient bone to place a dental implant.

Influence of surface nano-roughness on osseointegration of zirconia implants in rabbit femur heads using selective infiltration etching technique.

This study evaluates osseous healing of selective infiltration-etched (SIE) zirconia implants compared to as-sintered zirconia and titanium implants. Twenty implants of each group were inserted in 40 adult New Zealand white male rabbits. After 4 and 6 weeks, bone blocks containing the implants were retrieved, sectioned, and processed to evaluate bone-implant contact (BIC) and peri-implant bone density. SIE zirconia implants had significantly higher BIC and marginally higher bone density. The results suggest that selective infiltration-etched zirconia implant surface may improve implant osseointegration.

Influence of a nanoporous zirconia implant surface of on cell viability of human osteoblasts.

PURPOSE: The dense nonretentive surface of zirconia implants was modified into a nanoporous surface using selective infiltration etching surface treatment. The aim of this study was to investigate the influence of such a nanoporous modified zirconia surface on the attachment of human osteoblasts. MATERIALS AND METHODS: Human osteoblasts were cultured for 21 days on (i) selective infiltration etched zirconia (nanoporous surface), (ii) polished zirconia, (iii) polished titanium, or (iv) airborne particle abraded acid etched (SLA) titanium disks. After the culture period the following parameters were assessed: number of cells, the morphology of the cells, the attachment of the cells, alkaline phosphatase activity, and the level of total protein (α= 0.05). RESULTS: Statistical analysis revealed a significantly higher cell count on the third (F = 17.4, p < 0.001) and eighth day (F = 163, p < 0.001) for nanoporous zirconia and SLA titanium surfaces compared to polished specimens. The number of cells (nanoporous zirconia 160 ± 20/mm(2) , SLA titanium 133 ± 15/mm(2) ) and cell size (nanoporous zirconia 50.7 ± 3 µm, SLA titanium 42.5 ± 4 µm) were significantly higher than polished specimens. Nanoporous zirconia specimens demonstrated comparable alkaline phosphatase activity (0.0036 ± 0.0035 ng/µl) and intracellular protein content (72.7 ± 0.9 ng/µl) compared to other tested groups. Scanning electron microscopy revealed that cells attached on the polished surface using finger-like processes, whereas on the nanoporous surface, finger-like processes were not observed, as the cell membrane appeared to be in close proximity to the underlying surface. CONCLUSION: The findings of this study suggest that a nanoporous zirconia surface favors cell growth and attachment compared to a polished surface. It was proposed that a nanoporous zirconia surface may improve clinical performance of zirconia implants.