The combined effects of binder addition and different sintering methods on the mechanical properties of bovine hydroxyapatite

Hydroxyapatite (HA) from bovine bones has been used as a biomaterial in dentistry due to its biocompatibility and bioactivity. However, dense HA bioceramics still present inadequate properties for applications that require high mechanical performance, such as infrastructure. Microstructural reinforcements and control of ceramic processing steps are methods to improve these shortcomings. The present study assessed the effects of polyvinyl butyral (PVB) addition in combination with two sintering methodologies (2-step and conventional), on the mechanical properties of polycrystalline bovine HA bioceramics. The samples were divided into four groups (with 15 samples per group): conventional sintering with binder (HBC) and without binder (HWC) and 2-step sintering with (HB2) and without binder (HW2). HA was extracted from bovine bones, turned into nanoparticles in a ball mill, and subjected to uniaxial and isostatic pressing into discs, according to ISO 6872 standards. All groups were characterized by x-ray diffractometry (XRD), differential thermal analysis (DTA) and Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and relative density. Besides, mechanical analyses (biaxial flexural strength (BFS) and modulus of elasticity) were also performed. The characterization results demonstrated that adding agglutinants or the sintering method did not affect HA's chemical and structural characteristics. Even so, the HWC group showed the highest mechanical values for BFS and modulus of elasticity being 109.0 (98.0; 117.0) MPa and 105.17 ± 14.65 GPa, respectively. The HA ceramics submitted to conventional sintering and without the addition of binders achieved better mechanical properties than the other groups. The impacts of each variable were discussed and correlated to the final microstructures and mechanical properties.

Clinical Evaluation of Lithium Disilicate Veneers Manufactured by CAD/CAM Compared with Heat-pressed Methods: Randomized Controlled Clinical Trial

CLINICAL RELEVANCE

Lithium disilicate veneers for esthetic restorations show great accuracy and similarity, regardless of the type of fabrication technique.

SUMMARY

Clinical Evaluation of Ceramic Inlays and Onlays Fabricated With Two Systems: Five-Year Follow-Up

This study evaluated the five-year clinical performance of ceramic inlays and onlays made with two systems: sintered Duceram (Dentsply-Degussa) and pressable IPS Empress (Ivoclar Vivadent). Eighty-six restorations were placed by a single operator in 35 patients with a median age of 33 years. The restorations were cemented with dual-cured resin cement (Variolink II, Ivoclar Vivadent) and Syntac Classic adhesive under rubber dam. The evaluations were conducted by two independent investigators at baseline, and at one, two, three, and five years using the modified United States Public Health Service (USPHS) criteria. At the five-year recall, 26 patients were evaluated (74.28%), totalling 62 (72.09%) restorations. Four IPS restorations were fractured, two restorations presented secondary caries (one from IPS and one from Duceram), and two restorations showed unacceptable defects at the restoration margin and needed replacement (one restoration from each ceramic system). A general success rate of 87% was recorded. The Fisher exact test revealed no significant difference between Duceram and IPS Empress ceramic systems for all aspects evaluated at different recall appointments (p>0.05). The McNemar chi-square test showed significant differences in relation to marginal discoloration, marginal integrity, and surface texture between the baseline and five-year recall for both systems (p<0.001), with an increased percentage of Bravo scores. However, few Charlie or Delta scores were attributed to these restorations. In conclusion, these two types of ceramic materials demonstrated acceptable clinical performance after five years.

The effect of tin-electroplating on the bond of four dental alloys to resin cement: an in vitro study

STATEMENT OF THE PROBLEM

Nickel-chromium alloys are indicated for the construction of resin-bonded fixed partial dentures; however, the potential toxicity of nickel has been a source of concern. Composite cements do not develop an adequate bond to air abraded noble alloys, which cannot be electrolytically etched. Tin-electroplating of noble alloys appears to be an alternative treatment for resin bonding.

PURPOSE

This in vitro study investigated the effect of tin-electroplating on the bond of a composite cement to base and noble alloys.

MATERIAL AND METHODS

Tensile tests were made with disks of four alloys that were cemented to each other with an adhesive composite cement after (1) air abrasion with 50 microns aluminum oxide and (2) air abrasion plus tin-electroplating.

RESULTS

Tin-electroplating increased the bond strength of metal-ceramic gold alloy (Au,Pd,Pt) to a level comparable to the nickel-chromium alloy, but had a harmful effect on type IV gold alloy.

CONCLUSIONS

Despite the recommendation for tin-electroplating of type IV gold alloys, this procedure did not improve bond strength to composite in this study.

Tensile bond strength of a resinous cement to a nickel-chromium alloy modified with five surface treatments

A problem associated with resin-bonded fixed partial dentures is inadvertent dislodgment at the metal/cement interface. It has been suggested that Panavia Ex resinous cement requires only air abrasion of the alloy with 50 microns aluminum oxide particles to record reliable bond strength values. The purpose of this study was to discuss the consequences of changes in the type of air abrasion and surface oxidation of the alloy. Fifty pairs of disks of a Ni-Cr alloy were treated by five methods: (1) air abrasion with 50 microns aluminum oxide (control), (2) air abrasion with 50 microns glass beads, (3) air abrasion with a mixture of aluminum oxide and glass beads (ratio 1:1), (4) air abrasion with aluminum oxide and immersion in acid solution of potassium permanganate, and (5) air abrasion with aluminum oxide and immersion in aqueous solution of potassium permanganate. The disks were cemented to each other with Panavia Ex composite resinous cement and tensile tests were conducted at a crosshead speed of 0.5 mm/ minute. No statistically significant differences were recorded among the treatments for the alloys used in this study except air abrasion with glass beads, which exhibited the lowest bond strength values.

A comparison of tensile bond strengths of resin-retained prostheses made using five alloys

This in vitro study evaluated the bond strength of metal frameworks cast using Ni-Cr, Ni-Cr-Be, Cu-Al, type IV gold, and noble metal ceramic alloy with and without tin electroplating. The castings were luted to human teeth using Panavia Ex resin. It was found that tin electroplating had a negative effect for the Cu-Al and type IV gold alloys and a positive effect for gold for metal ceramic restorations. The best results were obtained using the Ni-Cr alloy.

Tensile bond strength of a composite resin cement for bonded prosthesis to various dental alloys

The development of composite resin cements that chemically bond to dental alloys has improved the construction of resin-bonded prostheses. Composite resins can be selected for various situations, but specific clinical situations may require different alloys. This study evaluated the ability of a composite resin cement to bond to various dental alloys of different compositions. Ten pairs of disks for each alloy (two NiCr, two NiCrBe, one CuAl, one gold type IV, and one gold for metal ceramic) were bonded to a composite resin cement after air abrasion was performed with aluminum oxide. The disks were then rinsed in tap water and were ultrasonically cleaned in distilled water for 2 minutes. The tensile tests exhibited greater values for alloys ultrasonically cleaned, and the best results were recorded by NiCr and NiCrBe alloys.

[Surface roughness of investment samples and their metal castings]

Three phosphate bonded investments and three calcium type were studied observing the influence of investment on the final cast surface roughness. Increased dilution also incremented roughness for the phosphate investments. Between the two types of investments there was only significant difference concerning two specific commercial brands, but there were differences in the same type of investment among these different brands.