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.

Effect of sintering time on microstructure and optical properties of yttria-partially stabilized monolithic zirconia.

OBJECTIVES: To evaluate the impact of speed sintering on the microstructure and optical properties of 3 and 5 mol% yttria-partially stabilized monolithic zirconias. METHODS: 120 plate-shaped zirconia specimens (10x10x 0.4 mm) were prepared from three commercial 5 mol% yttria-partially stabilized zirconia blocks (5Y-PSZs); Katana UTML (Kuraray Noritake), Cercon xtML (Dentsply Sirona), and Zolid FX white (Amann Girrbach), and two commercial 3 mol% yttria-partially stabilized zirconia blocks (3Y-PSZs); Lava Plus (3 M ESPE) and InCoris (Sirona, GmbH). Specimens were either conventional sintered (CS) using a 7-hour program or speed sintered (SS) using a quick 90-minute program. The microstructure was inspected with a scanning electron microscope (SEM), and phase fractions were detected using x-ray diffraction analysis (XRD). Translucency (TP00), and contrast ratio (CR) were obtained using a spectrophotometer (VITA Easyshade V). Color difference (ΔE00) between both sintering processes was calculated with the CIEDE2000 formula. ΔE00 up to 1.8 was set as the acceptability threshold. Data were analyzed using two-way ANOVA, Krusakll-Wallis, and Mann-Whitney U tests. (n = 12, α = .05). RESULTS: Grain size was significantly decreased after SS for all tested materials (P < .0001). The average grain sizes of 5Y-PSZs were significantly larger than those of 3Y-PSZs. The atomic structure, microstructure, and transparency of CS and SS were all affected by the amount of yttria, the size of the crystals, and tetragonality. SS significantly reduced TP00 (F = 7135.95, P < 0.0001) and increased CR (F = 453.21, P < 0.0001). The CS Katana presented the highest TP00 and lowest CR value. ΔE00 between the CS and SS groups were clinically acceptable except for Lava, which had values above the set threshold (1.89). SIGNIFICANCE: SS altered the grain size and internal structure of the tested materials, which was reflected in translucency.

A novel intra-tumoral drug delivery carrier for treatment of oral squamous cell carcinoma.

The treatment of oral squamous cell carcinoma (OSCC) includes systemic chemotherapy and is associated with aggressive side effects on patients. This study evaluated a new intra-tumor-targeted drug delivery method for the treatment of OSCC induced on the dorsum of the tongue in white mice. The induced tumors were examined by needle biopsy. A targeted anticancer drug (Cetuximab) and [Cisplatin and 5 Fluorouracil (5-FU)] chemotherapeutic agents were loaded on polyethylene glycol-polylactide-polyethylene glycol (PEG-PLA-PEG) nanoparticles (NPs) designed for intralesional injection while systemic administration was used as control. Fourier transform infrared spectroscopy (FTIR) was performed to study NP chemical structure, a drug release profile was conducted to study release kinetics, and histopathological evaluation was performed before and after treatment to evaluate tissue reactions (n-28, ά = 0.05). The drug release profile was characteristic of the chemotherapeutic agent showing early quick ascend followed by sustained slow release. FTIR peaks identified the polymeric structure of the drug nano-carrier. Histopathologic examination of chemically induced OSCC revealed different grades ranging from non-invasive to invasive stages of OSCC. Intra-tumoral test group revealed significant remission of observed cancer grade compared to the systemically administered group (X2 = 12.63, P < 0.001). Finally, using synthesized PEG-PLA-PEG NPs for intralesional injection is a promising route for the treatment of OSCC.

Histomorphometric evaluation of 3D printed graphene oxide-enriched poly(ε-caprolactone) scaffolds for bone regeneration.

Objective: Restoring large boney defects using bone grafts alone is an unpredictable procedure. Biodegradable polymeric scaffolds suffer rapid biodegradation and lack sufficient osteo-conductivity. The aim of this study was to histomorphometrically evaluate three-dimensional printed graphene oxide-enriched poly(ε-caprolactone) (PCL) scaffolds for bone regeneration in a rabbit defect model using two different concentrations of graphene oxide. Basic characteristic properties and mount of new bone regeneration formation were evaluated. Methods: two concentrations of graphene oxide (1 and 3 wt%) were added to PCL scaffolds using hot blind technique while pure PCL scaffolds served as a control. Laboratory characterization included scanning electron microscopy (SEM), x-ray diffraction analysis (XRD), contact angle, internal porosity, in addition to density measurements. All scaffolds were subjected to biodegradation evaluation and cell cytotoxicity test. In vivo bone regeneration was evaluated in the tibia defect of a rabbit model by measuring the amount of new bone formation (n = 15, ά = 0.05). Results: SEM images showed slight reduction in pore size and increase in filament width of scaffolds with increasing GO contents. However, the printed scaffolds matched well with the dimensions of the original design. XRD patterns revealed characteristic peaks identifying microstructure of scaffolds. Addition of GO increased crystallinity of the scaffolds. The contact angle and porosity readings indicated reduction in measurements with increased content of GO indicating improved wetting properties while the density followed an opposing pattern. Higher biodegradability values were associated with higher GO content resulting in acceleration of observed biodegradation. The results of cytotoxicity test showed reduction in cell viability with higher GO content. Bone regeneration was significantly enhanced for 1 wt% GO scaffolds compared to other groups as was evident by higher bone density observed in x-ray images and higher amount of new bone formation observed at different time intervals. Significance: Graphene oxide improved the physical and biological properties of PCL scaffolds and significantly enhanced new bone regeneration.

Fractographic analysis of fractured fixation screws in implant-supported restorations.

OBJECTIVES: The aim of this study was to fractographically examine clinically fractured fixation screws used to fix implant supported restorations and to estimate stress at failure. METHODS: 20 clinically fractured titanium implant fixation screws were collected and analyzed under scanning electron microscope in order to locate critical crack origin and calculate stress at fracture. Principles of fractographic analysis were applied using relative equations and cause and conditions of screw fracture were calculated. X-rays and patients' records were collected after approval of necessary consent forms. RESULTS: Fractographic analysis revealed location and dimensions of critical crack size for every fractured screw examined. Two patterns of screw fracture were identified; the first was related to improper seating of fixation screw leading to damage at screw threads and eventual fracture of screw body. The second was related to slow crack growth propagation causing final fracture of screw body. The calculated stress at failure ranged from 755 to 804 MPa. Patients' records revealed that 75% of fractured screws were related to single unit screw retained restorations. SIGNIFICANCE: Single unit screw retained restorations and improperly seated implant abutments impose high stress concentration on fixation screw which may result in fixation screw fracture.

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.

The polymerization efficiency of a bulk-fill composite based on matrix-modification technology.

OBJECTIVES: To evaluate the polymerization efficiency of a matrix-modified bulk-fill composite, and compare it to a conventional composite which has a similar filler system. The degree of conversion (DC%) and monomer elution were measured over different storage periods. Additionally, fillers' content was examined. MATERIALS AND METHODS: Cylindrical specimens were prepared, in bulk and incrementally, from Filtek Bulk Fill (B) and Filtek Supreme XTE (S) composites using a Teflon mold, for each test (n = 6). Using attenuated total reflection method of Fourier transformation infrared spectroscopy, DC% was measured after 24 hours, 7 days, and 30 days. Using high-performance liquid chromatography, elution of hydroxyethyl methacrylate, triethylene glycol dimethacrylate, urethane dimethacrylate, and bisphenol-A glycidyl dimethacrylate was measured after 24 hours, 7 days and 30 days. Filler content was examined by scanning electron microscopy (SEM). Data were analyzed using 2-way mixed-model analysis of variance (α = 0.05). RESULTS: There was no significant difference in DC% over different storage periods between B-bulk and S-incremental. Higher monomer elution was detected significantly from S than B. The elution quantity and rate varied significantly over storage periods and between different monomers. SEM images showed differences in fillers' sizes and agglomeration between both materials. CONCLUSIONS: Matrix-modified bulk-fill composites could be packed and cured in bulk with polymerization efficiency similar to conventional composites.

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.

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.

Osteogenesis ability of CAD/CAM porous zirconia scaffolds enriched with nano-hydroxyapatite particles.

BACKGROUND: The aim of this study was to evaluate osteogenesis ability of CAD/CAM porous zirconia scaffolds enriched with hydroxy apatite used to augment large boney defects in a dog model. METHODS: Surgical defects were made bilaterally on the lower jaw of 12 Beagle dogs. Cone beam CT images were used to create three dimensional images of the healed defects. Porous zirconia scaffolds were fabricated by milling custom made CAD/CAM blocks into the desired shape. After sintering, the pores of half of the scaffolds were filled with a nano-hydroxy apatite (HA) powder while the other half served as control. The scaffolds were inserted bilaterally in the healed mandibular jaw defects and were secured in position by resorbable fixation screws. After a healing time of 6 weeks, bone-scaffold interface was subjected to histomorphometric analysis to detect the amount of new bone formation. Stained histological sections were analyzed using a computer software (n=12, α=0.05). Mercury porosimetery was used to measure pore sizes, chemical composition was analyzed using energy dispersive x-ray analysis (EDX), and the crystal structure was identified using x-ray diffraction micro-analysis (XRD). RESULTS: HA enriched zirconia scaffolds revealed significantly higher volume of new bone formation (33% ± 14) compared to the controls (21% ± 11). New bone deposition started by coating the pore cavity walls and proceeded by filling the entire pore volume. Bone in-growth started from the surface of the scaffold and propagated towards the scaffold core. Islands of entrapped hydroxy apatite particles were observed in mineralized bone matrix. CONCLUSIONS: Within the limitations of this study, hydroxy apatite enhanced osteogenesis ability of porous zirconia scaffolds.

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.

Fatigue behavior of zirconia under different loading conditions.

PURPOSE: To investigate the influence of surface damage on the fatigue behavior of zirconia under two different loading conditions. MATERIALS AND METHODS: One hundred twenty zirconia bar-shaped received either airborne particle abrasion using 50µm or 120µm alumina particles while polished specimens served as control. The specimens were subjected to two fatigue regimes: dynamic fatigue (1,000,000 cycles, 1hz and 0.5s contact time) or static fatigue (a constant load applied for 5000s) under water using the staircase application of the load. The flexure strength after fatigue (dynamic fatigue strength) was compared to the initial flexure strength of the tested specimens (α=0.05). The critical crack shape and size of fractured specimens was examined using scanning electron microscopy. RESULTS: Compared to the initial flexure strength of the tested specimens, dynamic fatigue strength was 86.3% for the polished specimens, 73.4% for 50µm particle abrasion, and 42.3% for 120µm particle abrasion while the static fatigue strength was 85.9%, 78.5%, and 51.5% respectively. Significant statistical differences (F=223.679, P<0.001) were found between different surface treatments but not between dynamic and static fatigue strengths for the same type of surface treatment. CONCLUSIONS: The dynamic and static fatigue strengths of zirconia are significantly influenced by type of surface damage. CLINICAL IMPLICATIONS: Within the limitations of this study, surface damage have great influence on fatigue behavior of 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.

Survival of resin infiltrated ceramics under influence of fatigue.

PURPOSE: to evaluate influence of cyclic fatigue on two resin infiltrated ceramics and three all-ceramic crowns manufactured using CAD/CAM technology. MATERIALS AND METHODS: CAD/CAM anatomically shaped crowns were manufactured using two resin infiltrated ceramics (Lava Ultimate and Vita Enamic), two reinforced glass ceramic milling blocks ((IPS)Empress CAD and (IPS)e.max CAD) and a veneered zirconia core ((IPS)Zir CAD). (IPS)e.max CAD and (IPS)Zir CAD were milled into 0.5mm thick anatomically shaped core structure which received standardized press-on veneer ceramic. The manufactured crowns were cemented on standardized resin dies using a resin adhesive (Panavia F2.0). Initial fracture strength of half of the specimens was calculated using one cycle load to failure in a universal testing machine. The remaining crowns were subjected to 3.7 million chewing cycles (load range 50-200N at 3s interval) in a custom made pneumatic fatigue tester. Survival statistics were calculated and Weibull modulus was measured from fitted load-cycle-failure diagrams. Scanning electron microscopy was performed to fractographically analyze fractured surfaces. Data were analyzed using two way analysis of variance and Bonferroni post hoc tests (α=0.05). RESULTS: Dynamic fatigue resulted in significant reduction (F=7.54, P<0.005) of the initial fracture strength of the tested specimens. Zirconia showed the highest deterioration percent (34% reduction in strength) followed by (IPS)Empress (32.2%), (IPS)e.max (27.1%) while Lava Ultimate and Vita Enamic showed the lowest percent of reduction in strength. The two types of resin infiltrated ceramics and (IPS)Empress demonstrated the highest percent of fracture incidences under the influence of fatigue (35-45% splitting). None of the tested veneered zirconia restorations were fractured during testing, however, chipping of the veneer ceramics was observed in 6 crowns. The lowest percent of failure was observed for (IPS)e.max crowns manifested as 3 cases of minor chipping in addition to two complete fracture incidences. SEM images demonstrated the internal structure of the tested materials and detected location and size of the critical crack. CONCLUSION: The internal structure of the tested materials significantly influenced their fatigue behavior. Resin infiltrated ceramics were least influenced by fatigue while the characteristic strength of zirconia prevented core fracture but failure still occurred from the weaker veneer ceramic.

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.

Novel zirconia surface treatments for enhanced osseointegration: laboratory characterization.

Purpose. The aim of this study was to evaluate three novel surface treatments intended to improve osseointegration of zirconia implants: selective infiltration etching treatment (SIE), fusion sputtering (FS), and low pressure particle abrasion (LPPA). The effects of surface treatments on roughness, topography, hardness, and porosity of implants were also assessed. Materials and Methods. 45 zirconia discs (19 mm in diameter × 3 mm in thickness) received 3 different surface treatments: selective infiltration etching, low pressure particle abrasion with 30 µm alumina, and fusion sputtering while nontreated surface served as control. Surface roughness was evaluated quantitatively using profilometery, porosity was evaluated using mercury prosimetry, and Vickers microhardness was used to assess surface hardness. Surface topography was analyzed using scanning and atomic force microscopy (α = 0.05). Results. There were significant differences between all groups regarding surface roughness (F = 1678, P < 0.001), porosity (F = 3278, P < 0.001), and hardness (F = 1106.158, P < 0.001). Scanning and atomic force microscopy revealed a nanoporous surface characteristic of SIE, and FS resulted in the creation of surface microbeads, while LPPA resulted in limited abrasion of the surface. Conclusion. Within the limitations of the study, changes in surface characteristics and topography of zirconia implants have been observed after different surface treatment approaches. Thus possibilities for enhanced osseointegration could be additionally offered.

A 5-year comparison of marginal bone level following immediate loading of single-tooth implants placed in healed alveolar ridges and extraction sockets in the maxilla.

PURPOSE: The aim of present investigation was to evaluate marginal bone level after 5-year follow-up of implants placed in healed ridges and fresh extraction sockets in maxilla with immediate loading protocol. MATERIALS AND METHODS: Thirty-six patients in need of a single-tooth replacement in the anterior maxilla received 42 Astra Tech implants (Astra Tech Implant system™, Dentsply Implants, Mölndal, Sweden). Implants were placed either in healed ridges (group I) or immediately into fresh extraction sockets (group II). Implants were restored and placed into functional loading immediately by using a prefabricated abutment. Marginal bone level relative to the implant reference point was recorded at implant placement, crown cementation, 12, 36, and 60 months following loading using intra-oral radiographs. Measurements were made on the mesial and distal sides of each implant. RESULTS: Overall, two implants were lost from the group II, before final crown cementation: they were excluded from the study. The mean change in marginal bone loss (MBL) after implant placement was 0.26 ± 0.161 mm for 1 year, and 0.26 ± 0.171 mm for 3 years, and 0.21 ± 0.185 mm for 5 years in extraction sockets and was 0.26 ± 0.176 mm for 1 year and 0.21 ± 0.175 mm for 3 years, and 0.19 ± 0.172 mm for 5 years in healed ridges group. Significant reduction of marginal bone was more pronounced in implants inserted in healed ridges (P < 0.041) compared to fresh surgical extraction sockets (P < 0.540). Significant MBL was observed on the mesial side of the implant after cementation of the provisional (P < 0.007) and after 12 months (P < 0.034) compared to the distal side which remained stable for 3 and 5 years observation period. CONCLUSIONS: Within the limitations of this study, responses of local bone to immediately loaded implants placed either in extraction sockets or healed ridges were similar. Functional loading technique by using prefabricated abutment placed during the surgery time seems to maintain marginal bone around implant in both healed and fresh extraction sites.

Influence of crystal structure on debonding failure of zirconia veneered restorations.

OBJECTIVE: Delamination of porcelain from intact zirconia framework was recently reported as the most common failure mode of these restorations. The aim of this study was to investigate the influence of different laboratory surface treatments on crystals structure and fracture strength of zirconia veneered restorations. METHODS: Zirconia discs received airborne particle abrasion with either 50 or 120µm alumina particles then half of the specimens were annealed to remove surface pre-stresses, while assintered discs served as a control. Crystal structure of each group was evaluated using X-ray diffraction analysis (XRD). The discs were then veneered with porcelain and biaxially loaded to fracture with the veneer surface in tension (α=0.05). RESULTS: Regarding debonding failure, 50µm particle abrasion significantly increased biaxial flexure strength compared to as-sintered specimens. On the contrary 120µm particle abrasion resulted in significant reduction in flexure strength and was associated with higher percent of monoclinic phase (7%). However for both types of particle sizes, annealing reduced initial failure load as it led to complete reverse transformation of the monoclinic phase which was associated with zirconia grain pull-out at the critical crack location. SIGNIFICANCE: Paying attention to the surface treatment of zirconia before veneering could reduce chances of delamination and significantly improve the strength of the bilayered restorations.