Key Engineering Materials Vols. 493-494

Abstract: The purpose of this study was to evaluate the effect of different surface treatments and adhesive systems on bond strength of composite resin to porcelain when there is need to repair the restoration.Materials and methods: Rectangular discs (10mm x 12mm) with a height of 2mm were prepared from leucite-reinforced feldspathic ceramic CAD/CAM blocks (Vitablocs), embedded in acrylic resin, and bur cut porcelain surfaces were created. The specimens were divided into three groups (n=20) according to the surface treatments: Er:YAG laser at 2W for 20 seconds, air abrasion with 50µm Al₂O₃ at 2.5 bar for 15 seconds, and the last group left untreated as control. After silane (Monobond S) application on ten specimens from each group, composite rods (Aelite Flo LV) with 4.25mm diameter and 4mm height were bonded to ceramic surfaces with a self-etch adhesive system (All-Bond SE). The remaining ten specimens from each group were etched with 36% orthophosphoric acid (Blue Etch Dental Etching Gel), and after silane and bonding agent (One-Step Plus) application composite rods with the mentioned dimensions were bonded. All groups were stored in distilled water at 37°C for one day before mechanical testing. Shear testing of all groups were performed on a universal testing machine with a load cell of 50kg and at a crosshead speed of 1.5mm/min. Results were statistically analyzed using Mann Whitney U and Kruskall Wallis tests.Results: The bond strength values of the self-etch adhesive system in the lased and control groups were statistically higher in comparison to the other adhesive system (p<0.01, p<0.05, respectively). The highest bond strength values were obtained in the Er:YAG lased and self-etch adhesive applied group.Conclusions: When there is need to repair of a porcelain restoration, a self-etch adhesive application after Er:YAG laser treatment could be the method of choice.

Abstract: The aim of this study was to evaluate the stiffness, elastic limit and strength of CAD/CAM manufactured metal and zirconia posts in comparison to prefabricated zirconia and glass-fiber posts. Materials and methods: Four types of posts were investigated in this study (n=40). Prefabricated posts made of zirconia (Cosmopost) and glass-fiber reinforced composite (FRC Postec Plus), and Cr-Co (Magnum Lucens) and zirconia (Zirkonzahn) posts manufactured with a CAD/CAM system were used. Artificial root canals with similar diameters to those of the posts were drilled on a stainless steel metal block and the posts were cemented with a self-etch/self-adhesive dual cure resin cement (Totalcem). The posts were loaded in a universal testing device at an inclination of 135 degrees at a crosshead speed of 1mm/min. The force-deflection curves were recorded, and stiffness, elastic limit and strength of the posts were determined. Data were analyzed statistically using Mann Whitney U and Kruskall Wallis tests.Results: The difference between the strength, elastic limit and also stiffness values of the groups was statistically highly significant (p<0.01). CAD/CAM Cr-Co posts showed the highest values of strength, elastic limit and stiffness amongst all the posts investigated. CAD/CAM zirconia posts had the lowest values of strength, and FRC had the lowest values of elastic limit and stiffness. Cosmopost had higher values of elastic limit and stiffness compared to CAD/CAM zirconia posts.Conclusions: If an endodontic post restoration is required, functional load and aesthetics should be considered in addition to mechanical properties of the material selected.

Abstract: Calcium hydroxide cement used in dentistry has advantages of proper alkaline pH, releasing calcium ions and promoting tissue regeneration. However, it also has some drawbacks such as high solubility and low strength. In this study, the properties of nano-hydroxyapatite (nHA) added calcium hydroxide cement was investigated for overcoming these drawbacks. Stoichiometric nHA powder was synthesized using orthophosphoric acid and calcium hydroxide. 5, 10 and 15 percent (in w/w) of synthesized nHA powder was added to commercial calcium hydroxide cement and the obtained nanocomposite was characterized by setting time, compressive strength, pH, Ca dissolution, antibacterial tests and SEM. Nanometric size and purity of synthesized apatite was confirmed by XRD and TEM. Setting time increased by increasing the content of nHA. SEM micrographs showed less microporosity for sample with 5% nHA. Adding 5% nHA to calcium hydroxide cement increased compressive strength to 60%, while further additions had an adverse effect. Adding nHA slightly decreased pH and increased Ca dissolution. The antibacterial test revealed that inhibition zone was about 2-2.5 mm for calcium hydroxide cement and sample with 5% nHA and less than 1 mm for other samples. Finally, nanocomposite with 5% nHA exhibited adequate properties to overcome the drawbacks of calcium hydroxide cements.

Abstract: Rough surfaces of denture prosthesis promote adhesion of microorganisms and plaque formation. In dentistry ferric oxide, tin oxide, chrome oxide and pumice are the most commonly used materials for polishing of resins and other materials. Clinoptilolite that is in zeolitic structure resembles to pumice due to alumina silicate formations in its constitution. Surface roughness was evaluated by means of a surface roughness analyzing instrument, Perthometer There were 10 specimens for each acrylic resin and bis-acryl composite resin material and polishing method combination. Conventional lathe polishing with polishing paste served as surface roughness was determined with a profilometer and SEM microscope. ANOVA was applied to the all measurements and was statistically significant (p<0.001). The p-values were calculated using paired t-tests. The materials in order that are most successful at polishing PMMA surface are; clinoptilolite Ra 0,5 > Fe₂O₃ Ra 0,6 > Cr₂O₃ Ra 0,8> pumice Ra 1,2 > SnO₂ Ra 1,6. the surface roughness values for Bis-acryl Composite are as follows: clinoptilolite Ra 0,6 > Fe₂O₃ 0,8 Ra > Cr₂O₃ Ra 0,9 > pumice Ra 1,4 > SnO₂ Ra 1,9. The most successful material for PMMA and Composite resin were clinoptilolite followed by; clinoptilolite, Fe₂O₃, Cr₂O₃, pumice, and SnO₂ in order. The same results were confirmed with the scanning electron microscopic images. Within the light of the present study Clinoptilolite can be an alternative to pumice for polishing of PMMA.

Abstract: Hydroxyapatite (HA) has been widely used as bone grafts due to its chemical and structural similarities to the mineral phase of hard tissues. Applying the combination of osteogenic proteins with HA materials can accelerate bone regeneration in defective areas. The aim of the study was investigating the treatment of HA particles with different amino acids such as serine (Ser), asparagine (Asn), aspartic acid (Asp) and arginine (Arg) to enhance the adsorption ability of HA carrier for delivering therapeutic proteins in body. Results: The crystallinity of HA reduced when amino acids were added during HA preparation. Depending on the types of amino acid, the specific surface area of the amino acid-functionalized HA particles varied from 105 to 149 m²/g. Bovine serum albumin (BSA) and lysozyme were used as model proteins for adsorption study. The protein adsorption onto the surface of amino acid-functionalized HA depended on the polarities of HA particles, whereby positively charged Arg-HA had higher affinity towards BSA (0.269 mg/m²) compared to lysozyme (0.133 mg/m²). Alternatively, the binding affinity of lysozyme (0.2 mg/m²) onto the negatively charged Asp-HA was higher compared to BSA (0.129 mg/m²). The amino acids functionalized-HA particles that had higher proteins adsorption demonstrated a lower protein release rate.

Abstract: Synthetic clcium phosphate based materials, such as hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂; HAp) and tricalcium phosphate (Ca₃(PO₄)₂; TCP), are compounds with high potential for clinical applications to orthopedic and dental region. In previous study, we have reported that the hollow and porous apatite microsphere could be prepared by salt-assisted ultrasonic spray-pyrolysis (SAUSP) technique using sodium chloride (NaCl). In this case, these microspheres have some problems of (i) decrease of dissolubility of microspheres and (ii) cytotoxicity arising from chloride ions elution. To overcome these disadvantages, we prepared novel microspheres by SAUSP technique using potassium nitrate (KNO₃) instead of NaCl. The resulting microsphere was washed with pure water to remove the KNO₃ phase. The particle shapes of the powders were observed by scanning electron microscopy (SEM); the diameters of the microspheres were of 0.5 - 3.0 m, and the fine pores with the sizes of ~50 nm were present on the surface of the microspheres. The TNP-470 agent as a model of drug were loaded on these microspheres with nano-pores in the surface. In the KNO₃ concentration of 1.00 mol·dm^-3, 70 % of the total TNP-470 from the microspheres was rapidly released within 1 h. The remaining 30 % was slowly released up to 24 h following immersion, and total amount of TNP-470 released from the microspheres was 42 g·mg^-1.

Abstract: We prepared silver-containing hydroxyapatite (Ag-HAp) powders by an ultrasonic spray-pyrolysis (USSP) technique and evaluated their antibacterial activity.　　Ag-HAp powders with Ag contents of 0, 1, 2, 5, and 20 mol% as nominal composition were prepared by the above USSP technique. The droplets of starting solutions were dried at 300 °C and then pyrolyzed at 850 °C to prepare the Ag-HAp powders. Ag-HAp powders showed a HAp single phase and were composed of spherical particles with a diameter of 0.5 - 3.0 μm. To evaluate the antibacterial activity of resulting powders, colony count method was performed using Staphylococcus aureus. Ag-HAp powders with the contents of Ag more than 5 mol% showed good antibacterial activity.

Abstract: A biodegradable drug delivery system was established using an apatite cement containing simvastatin. The in-vitro drug release from apatite with lower-crystallinity was investigated under simulated osteoblast and osteoclast conditions (SOB and SOC). Apatite cement containing 6% simvastatin had lower crystallinity as the same as natural bone. In-vitro drug release tests were performed under SOB in simulated body fluid (pH 7.8), and then under SOC in acetate buffer (pH4.5) at 37.0｡C, and the process repeated twice. The device had lower drug release rates under SOB, but significantly higher rates under SOC. The simvastatin release rate was 15 times higher under SOC than SOB. The device showed dissolution medium responsive drug release. After implantation of the APC containing simvastatin in osteoporosis rats, the bone mineral density was evaluated by the X-ray computed tomography. The result indicated that the bone mineral density of APC implanted rat was significantly higher than that of control diseased.

Abstract: Injectable hydroxyapatite/collagen nanocomposite (HAp/Col) artificial bone was prepared utilizing gelation of sodium alginate (Na-Alg). Mass ratio of the HAp/Col powder, with or without Ca adsorption treatment and Na-Alg (80-120, 300-400, 500-600 cP in viscosity at 10 g/dm³) was fixed at 90/10. Injectable HAp/Col was prepared by mixing the HAp/Col powder with Na-Alg solution at several powder (HAp/Col)/liquid (Na-Alg solution) ratios (P/L ratio, g/cm³). The result of consistency measurement suggested that the operability of injectable HAp/Col paste could be controlled by both the P/L ratio and the viscosity of Na-Alg solution. According to the consistency measurement and practical feelings during mixing, P/L=1/1.67 (80-120 cP) and 1/1.89 (300-400, 500-600 cP) were considered to be the highest P/L ratio allowed to mix the HAp/Col paste with a spatula. At the P/L=1/2.33 (80-120 cP), the paste prepared with the non-treated HAp/Col powder, placed in an incubator (37 °C,relative humidity 100%) for 24h, demonstrated gel-like property, while the paste prepared with Ca-treated HAp/Col powder did putty-like property. The difference in their property might be caused by the initial bonding behavior between Alg and Ca²⁺ after mixing. The setting time measurement with Gillmore needle was impossible because they were toosoft for this method. Even though, their operability and coalescence/settingproperty could be used as the injectable bone filler.

Abstract: Tests were performed to assess the parameters influencing the injectability of cement pastes loaded with large particles, such as porogens or drug-delivery agents. The use of non-setting model pastes permitted to demonstrate that two phase separation mechanisms occurred simultaneously, i.e. the separation between liquid and powder, known as filter-pressing phenomenon, and the separation between larger and smaller particles.