The Effect of Bioactive Glass and Sintering Conditions on the Properties of Titanium-Hydroxyapatite Composites

Titanium-hydroxyapatite (Ti-HA) based composites have been widely investigated as viable materials to be used in dentistry. However, sintering of these composites is very challenging due to decomposition of HA and oxidation of Ti. The objective of this study was to investigate the effect of incorporating a bioactive glass in Ti-HA composites sintered in different atmospheric conditions. The bioactive glass was prepared and added to different percentages of Ti-HA mixtures and divided into two groups. Samples in Group 1 were sintered with air atmosphere, while samples in Group 2 were sintered with vacuum furnace. All samples were later subjected to XRD, SEM, density, micro-hardness, and compression strength tests. XRD results showed that in Group 1, the major phases were assigned to Ti and HA while the minor phases were assigned to oxidised Ti. Whereas, Group 2 showed that the major phases were assigned to HA and the minor phases showed decomposition of HA to Ca3(PO4)2(TCP) and Ca4(PO4)2O (TTCP). Oxidized Ti was also present in this group. In terms of density, micro-hardness and compression strength, statistical analyses showed that samples in Group 1 have a significant difference (p = 0.000) as compared to those in Group 2. Sintering Ti-HA composites incorporated with BGby using air atmosphere furnace could reduce the decomposition of HA and oxidation of Ti, thus improve the density, micro-hardness and compression strength of the composites.

Fracture resistance of three different all-ceramic crowns: In vitro study

PURPOSE

To evaluate the fracture resistance and failure mode of three different all-ceramic crowns; CEREC Bloc, IPS e.Max Press and Cercon in a simulated clinical situation.

METHODS

30 extracted maxillary premolars were prepared and randomly assigned to three groups equally according to the type of crown used. The first was the CEREC group: monolithic feldspathic crowns (CEREC Blocs). The second was the E.Max group: monolithic lithium disilicate crowns (IPS e.Max Press). The third group was the Cercon group: bilayered partially stabilized zirconia crowns (Cercon). All crowns were cemented using dual-cured resin cement (ParaCore). The specimens were then subjected to thermocycling (5-55°C/500 cycles) and loaded to failure at an angle of 45° to the occlusal surface of the crown. Failure data was statistically analyzed using one-way ANOVA and Tukey's HSD post hoc test at α= 0.05. Fractographic analysis was performed to determine the fracture modes of the failed specimens.

RESULTS

The mean fracture values for CEREC, E.Max and Cercon groups were 387± 60 N, 452 ± 86 N, and 540 ± 171 N, respectively. Significant differences were found between CEREC and Cercon groups (P< 0.05). Catastrophic fracture within the ceramic crown was the major failure mode of the CEREC group. For E.Max and Cercon groups, the major failure mode was exhibiting severe tooth fracture while the ceramic crown remained intact.

CLINICAL SIGNIFICANCE

CEREC, IPS e.Max Press and Cercon crowns are clinically applicable as they exceeded the normal masticatory forces. However, the CEREC crown is preferred as it maintains the integrity of the natural abutment.

The effect of moisture conditions on the constitution of two bioceramic-based root canal sealers

Background/purpose

Intraradicular moisture is not standardized and alters the sealing properties and adhesion of root sealers. The aim of this work was to evaluate the effect of different moisture on the constitution of bioceramic sealers.

Materials and methods

The sealers were evaluated before mixing, and after setting using X-ray diffraction (XRD), Energy Dispersive Analysis (EDX) and Scanning Electron Microscope (SEM) techniques. Twenty four extracted teeth were prepared and assigned to four groups according to the moisture conditions: (1) dry: using ethanol as final irrigation, (2) normal: using paper points until the last one appeared dry, (3) moist: using a Luer adapter for 5 s followed by 1 paper point, and (4) wet: the canals remained totally flooded. The roots were filled with MTA Fillapex^® and Endosequence^® BC and kept in phosphate buffer solution at 37 °C for 10 days. Each root was sectioned transversally and longitudinally. The sealers harvested from longitudinal sections were analysed using XRD. Whilst the transverse sections were analysed using SEM/EDX.

Results

The XRD analysis showed MTA Fillapex composed of Bismuth trioxide, calcium silicate and tricalcium aluminate. The intensity of peaks in the wet condition was reduced. Endosequence BC contained mainly calcium silicate, calcium silicate hydrate, zirconia and calcium hydroxide. The wet condition showed a small increase in hydrated calcium silicate. The EDX analysis showed changes in the elemental concentrations with different moisture conditions. The surface morphology differed with different moisture conditions.

Conclusion

Tested sealers have different constitution that not affected by the degree of moisture. However, it changed their relative quantity.

Microwave-assisted fabrication of titanium implants with controlled surface topography for rapid bone healing

Morphological surface modifications have been reported to enhance the performance of biomedical implants. However, current methods of introducing graded porosity involves postprocessing techniques that lead to formation of microcracks, delamination, loss of fatigue strength, and, overall, poor mechanical properties. To address these issues, we developed a microwave sintering procedure whereby pure titanium powder can be readily densified into implants with graded porosity in a single step. Using this approach, surface topography of implants can be closely controlled to have a distinctive combination of surface area, pore size, and surface roughness. In this study, the effect of various surface topographies on in vitro response of neonatal rat calvarial osteoblast in terms of attachment and proliferation is studied. Certain graded surfaces nearly double the chance of cell viability in early stages (∼one month) and are therefore expected to improve the rate of healing. On the other hand, while the osteoblast morphology significantly differs in each sample at different periods, there is no straightforward correlation between early proliferation and quantitative surface parameters such as average roughness or surface area. This indicates that the nature of cell-surface interactions likely depends on other factors, including spatial parameters.

Gradient surface porosity in titanium dental implants: relation between processing parameters and microstructure

To be successful, an implant should be biocompatible, strong and contain surface pores to promote osseointegration. A one-step microwave sintering procedure of titanium powders was attempted in this work. The idea was to take advantage of the peculiar way microwave couple with metallic powders, i.e. generating heat in the interior of the sample and dissipating it away through the surface. This non-conventional heating of titanium powder produced a dense core with surface porosity. The dense core provides the strength while the surface pores promote bone growth. The experiments were carried out in a semi-industrial grade microwave cavity using a alpha-SiC susceptor. Power levels of 1-1.5 kW, and soaking periods of approximately 30 min were used. Microstructural characterization was carried out by a scanning electron microscope. The sintered titanium had gradient porosity on the surface with a thickness of about 100-200 microm depending on the microwave power. The pores were interconnected with size ranging from 30 to 100 microm. This kind of microstructure is favorable for cell growth. Tensile strength values as high as 400 MPa were obtained for these samples.