Bioceramics Development and Applications

Calcium phosphate ceramics have been used as synthetic grafts for bone repair. This family of alloplastic grafts is an alternative to allografts (from other individuals from the same specie), autografts (from the same individual) or xenografts (from individuals from other species). Sintered bovine bone is basically composed mainly by hydroxyapatite (HA), Ca10(PO4)6(OH)2 but chemical analyses indicate the presence of Mg. Chemical and heat treatments are generally required to eliminate biological hazard. However, the more crystalline hydroxyapatite, the less resorbable the product is. An approach to have a highly crystalline and still resorbable material is to use additions of alpha or beta tricalcium phosphate, Ca3(PO4)2 , (TCP). The addition of fractions of some bioactive glasses to hydroxyapatite has shown to be effective in promoting its decomposition to tricalcium phosphate. In addition, glass reinforced hydroxyapatite composite are materials with higher compressive strength due to liquid phase sintering. In this study, novel scaffolds based on hydroxyapatite and tricalcium phosphate are presented.

In order to perform new dental implant, we carried out investigations on α-alumina and calcium phosphate based composites. α-Alumina nano-powder were synthesized using reverse micelle method while calcium phosphate nano-powders with different molar ratio starting from 1.8 to 1.1 were synthesized by precipitation method, using calcium nitrate (Ca(NO3)2.4H2O) and ammonium hydrogen orthophosphate (NH4H2PO4) as precursor materials as source for calcium (Ca²+) and phosphate ((PO4)3-) ions respectively. Samples of respectively 5, 10 and 20% weight of Calcium phosphate powder were mixed with alumina, consolidated and sintered at 1400°C for 4 hours. The synthesized composites, in form of pellets were characterized for bulk density, apparent porosity, hardness and flexural strength properties.

Egg shells have been used as a calcium source for synthesis of tetra calcium phosphate (ETTCP) by solid state reaction method. The cell parameters and cell volume of ETTCP measured by X-ray powder diffraction method were lower than the tetra calcium phosphate prepared using synthetic Ca(CO)3 (pure TTCP) for comparison. The vibration bands of ETTCP were also slightly different from the vibration bands of pure TTCP characterized by Fourier transformed infrared spectroscopy. ETTCP has been tried as a main component in a self setting bone cement to evaluate the advantages of the presence of the biologically relevant ions such as Mg2+, Sr2+, SiO2- 4, F-, K+ and Na+ ions in the cement properties. The setting time of the ETTCP derived cement was ~ 11 min compared to ~ 16 min of the pure TTCP derived cement. The amount of hydroxyapatite formed as the end product was about 12% higher for ETTCP derived cement than pure TTCP derived cement after 28 days of immersion in phosphate buffer solution as confirmed by phase analysis. Elemental analysis also indicates the presence of trace elements in minor concentration in ETTCP derived cement. Although both the cements showed similar compressive strength after 28 days, the initial strength of the ETTCP derived cement was remarkably higher during initial stages of the hardening reaction (24 h–7 days) compared to TTCP derived cement. Cell viability of L6 cells was higher and cell spreading was more for the ETTCP derived cement than pure TTCP derived cement. The present study has demonstrated the advantages of eggshell derived TTCP in bone cement formulations due to the presence of biologically relevant ions. This may help the clinician with brief surgical procedure by using faster setting cement as well as the patient to have quick recovery with a higher initial strength of cement.

Frictional resistance is crucial between arch wires and brackets, sometimes benefic and in other clinical situations undesirable, making difficult to apply orthodontic forces efficiently. There are many variables that influence frictional resistance and the method of ligation is one of the most important. The objective of this study was to compare static and kinetic frictional resistance during the sliding of 0.016” and 0.016” × 0.022” SS arch wires (upper and lower) through orthodontic brackets, using different methods of ligation (elastomeric ties, low friction elastomeric ties, stainless steel ligature, active and passive self-ligating brackets). It was developed an original methodology to evaluate frictional resistance to sliding with different methods of ligation. The results showed that the method of ligation that generated the highest static and kinetic frictional resistance values was elastomeric ties, followed by low friction elastomeric ties>metallic ligature> and at last self-ligating brackets for all arch wires.

Purpose: To assess how sandblasting influences shear bond strength (SBS) between nano-ceramic-resin and two resin cements. Methods: 40 nano-ceramic-resin blocks were divided into two groups (n=20): a control (C) and a test group (S_50) where air abrasion (50 µm, 0.28 MPa,10 s) was applied. Each group was divided into two subgroups (n=10) according to the applied luting material: a self-etch dual-cure resin cement (LP) and a dual-cure resin cement (LR). SBSs were determined with a universal testing machine at a crosshead speed of 0.5 mm/min. Fracture patterns were evaluated by a stereomicroscope (25x) and classified into adhesive, cohesive and mixed. One-way ANOVA test (α=.01) was used to establish differences between groups, considering SBS as dependent and the type of surface treatment as independent variable. Results: Mean SBS (MPa) obtained for P were 8.68 ± 1.16 for C and 13.91 ± 2.58 for S_50. Sandblasting positively affected (p<0.01) the self-adhesive cement adhesion to nano-ceramic resin. Group C_LP showed 100% of adhesive fractures, while S_50_LP had some cohesive (20%) and mixed fractures (10%). The fracture pattern of group C_LR was 60% cohesive, 20% adhesive and 20% mixed, while group S_50-LR showed 100% of cohesive failure. Conclusion: Sandblasting is suggested when luting nano-ceramic resin with LP.