Osteoblastic early attachment onto the surface of bioadhesive peptide modified pure titanium / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the long-term integrity and the biological function of interface between the bioadhesive peptide modified implant surface and peri-implant tissue.</p><p><b>METHODS</b>A short bioadhesive peptide containing Glycine-Tyrosine-Arginine-Glycine-Asparticacid-Serine (GYRGDS) sequence was immobilized onto the titanium implant surface by means of sol-gel coating technique and self-assembled monolayers (SAM). The chemical composition and organic functional groups on the titanium surfaces were characterized using XPS (X-ray photoelectron spectroscopy) and FTIR (Fourier transform infrared spectrometer). The adhesive strength and stability of osteoblasts on various implant surfaces were compared under flow condition.</p><p><b>RESULTS</b>The results showed that alkali/hot water aging treatment could apparently improve the content of -OH functional groups of titanium surface. The chemical reactive Ti-O-Ti bonding at the surface of titanium played a vital role in inducing the formation of organosilane SAM. GYRGDS peptide can be covalently grafted onto the surface of titanium by SAM technique. The resistance of freshly adherent osteoblasts to detachment by flow was shear time dependent. When the four groups were compared under the same flow stress condition (2.05 Pa) at three specific time spans (30 min, 1 h, 2 h), the cells retention rates in GYRGDS-grafted groups were 93.0%, 54.4%, 34.4% respectively and were much higher than those in non-coated groups.</p><p><b>CONCLUSIONS</b>It was suggested that GYRGDS might have positive effects on maintaining stability and adherence of cells onto the substrates under flow condition.</p>

Influence of different types of posts and cores on color of IPS-Empress 2 crown / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To evaluate the influence of different types of posts and cores on the final color of the IPS-Emperss 2 crown.</p><p><b>METHODS</b>Five types of posts and cores (Cerapost with Empress cosmo, Cerapost with composite resin, gilded Ni-Cr alloy, gold alloy and Ni-Cr alloy) were made. The shifts in color of three points of IPS-Empress 2 crown surface (cervical, middle and incisal) with different posts and cores was measured with a spectroradiometer (PR-650).</p><p><b>RESULTS</b>The L* a* b* values of zirconium oxide and gilded Ni-Cr alloy posts and cores with ceramic crown were the highest. The L* a* values of zirconium oxide posts composite cores were higher while the b* values were lower. The L* a* b* values of Ni-Cr alloy were lower than that of gold alloy and were the lowest.</p><p><b>CONCLUSION</b>In combination with IPS-Empress 2 crown, zirconium oxide posts are suitable for routine use in the anterior dentition, and gilded Ni-Cr alloy and gold alloy posts and cores can be recommended for clinical practice. Ni-Cr alloy posts and cores can not be recommended for clinical practice.</p>

Retention of selected cores to all-ceramic posts in post-and-core system / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To compare the retention of selected cores to all-ceramic posts in post-and-core system, in which the ceramic core was combined with the post by direct sintering, adhering, and the composite resin core was formed onto the post.</p><p><b>METHODS</b>A total of 15 all-ceramic post fabricated by alumina-zirconia nano-composite infiltrated ceramics were divided into three groups. In group A, forming and combining the ceramic core with the post by direct sintering. In group B, combining the ceramic core with the post by adhering. In group C, forming composite resin core onto the post. Each specimen was placed into a special jig along the post axis and subjected to a load on INSTRON 4302 universal testing instrument until failure.</p><p><b>RESULTS</b>There was a statistically significant difference between the groups (P < 0.01). Group A showed a significantly higher retention which was 3.04 and 2.88 times as high as group B and C respectively (P < 0.01). There was no significant difference between adhering and composite resin core (P> 0.05).</p><p><b>CONCLUSION</b>A reliable retention of the core to the post can be achieved when the alumina-zirconia nanocomposite infiltrated ceramic core is formed and combined with the post by direct sintering, which offers significantly higher retention than adhering and forming composite resin core onto the post.</p>

Microwave sintering of nanometer powder of alumina and zirconia-based dental ceramics / 华西口腔医学杂志

<p><b>OBJECTIVE</b>The objective of the present study was to investigate the feasibility and reliability of sintering alumina and zirconia-based all-ceramic materials through a recently introduced microwave heating technique. The variation of crystal phases, the growth of grain sizes and microstructural features of these materials were evaluated after sintering.</p><p><b>METHODS</b>Four different groups of powder (l00%Al2O3, 60%Al2O3+40%ZrO2, 40% Al2O3+60%ZrO2, 100% ZrO2) were respectively press-compacted to fabricate green disk samples, 5 specimen of each group were prepared. All the samples were surrounded by refractory materials for heat containment and processed at 1 600 degrees C in a domestic microwave oven (850 W, 2 450 MHz), 1 600 degrees C/5 min for heating rate, 10 min for holding time. After sintering, the phase composition and average grain size of these ceramics were examined using X-ray diffraction (XRD). Their microstructure characteristics were studied by scanning electron microscopy (SEM).</p><p><b>RESULTS</b>All the specimens were successfully sintered with the application of microwave heating system in combination with a suitable thermal insulator. No phase change was found in alumina while monoclinic-zirconia was found to be transformed to tetragonal-zirconia. A little grain size growth of Al2O3 and ZrO2 has been observed with Al2O3 24.1 nm/before and 51.8 nm/after; ZrO2 25.3 nm/before and 29.7 nm/after. The SEM photos indicated that the microwave-sintered Al2O3-ZrO2 ceramics had a uniform crystal distribution and their crystal sizes could be maintained within the range of nanometers.</p><p><b>CONCLUSION</b>It is expected that in the near future microwave heating system could be a promising substitute for conventional processing methods due to its unparalled advantages, including more rapid heating rate, shortened sintering time, superfine grain size, improved microstructure and much less expensive equipment.</p>

Cyclic fatigue of Vita mark II machinable ceramics under Hertzian's contact / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the cyclic fatigue modes of Vita mark II machinable ceramics under Hertzian's contact.</p><p><b>METHODS</b>Hertzian's contact technique (WC spheres r = 3.18 mm) was used to investigate the cyclic fatigue of Vita mark II machinable ceramic. All specimens were fatigued by cyclic loading in moist environment, furthermore, surviving strength was examined by three point test and morphology damage observation.</p><p><b>RESULTS</b>In homogeneous Vita mark II machinable ceramics, two fatigue damage modes existed after cyclic loading with spheres under moist environment, including conventional tensile-driven cone cracking (brittle mode) and shear-driven microdamage accumulation (quasi-plastic mode). The latter generated radial cracks and deeply penetrating secondary cone crack. Initial strength degradation were caused by the cone cracks, subsequent and much more deleterious loss was caused by radial cracks.</p><p><b>CONCLUSION</b>Cyclic fatigue modes of Vita mark II machinable ceramics includes brittle and quasi-plastic mode.</p>

Influence of adhesion on the color of glass infiltrated alumina ceramic restorations / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the effects of luting agent on the final color of glass infiltrated alumina ceramic restorations.</p><p><b>METHODS</b>12 plate-shaped specimens with 12.5 mm in diameter and 0.5 mm thickness were fabricated from GI-II (color IG2). Vitadur alpha veneering porcelain (color A2) with 1.0 mm thickness was fired to GI- II glass/alumina composite. 12 plate-shaped background specimens simulating the metal alloy post-and-core 12.5 mm in diameter and 2 mm thickness were also made from Ni-Cr alloy. All-ceramic specimens were luted to the metal alloy by Zinc Phosphate cement, glass ionomer cement and composite resin. The color shifts of the specimens were measured by colorimeter.</p><p><b>RESULTS</b>Luting agents had effect on the final color of restorations. The influence of composite resin was least, followed by glass ionomer cement and Zinc Phosphate cement. The color difference between with and without Zinc Phosphate cement could be identified by the eye.</p><p><b>CONCLUSION</b>To reduce the effect of luting agents, composite resin is recommended to all-ceramic restorations' adhesion.</p>

A comparative study on cyclic and static fatigue of dental ceramic by means of Hertzian's contact / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To compare the difference in strength degradation and morphology damage of brittle dental ceramic after static load and cyclic fatigue.</p><p><b>METHODS</b>Hertzian's contact technique with a tungsten carbide sphere was used to investigate the response of feldspathic dental porcelain to static load and cyclic fatigue. All specimens were subjected to static or cyclic loading in moist environment. Furthermore the surviving strength of specimens was examined by the three-point test and the morphology damage was observed. Statistical analyses were performed with ANOVA and a P-value less than 0.05 was considered to be significant.</p><p><b>RESULTS</b>Outer cone crack and associated strength degradation simultaneously occurred both after the first cyclic loading and static loading. Up to 1,000 cycles, the specimens showed inner cone cracks and strength degradation was aggravated. No significant difference in the strength degradation among all static loading specimens and no inner cone cracks occurred in static loading specimens.</p><p><b>CONCLUSIONS</b>Both static and cyclic fatigue influence dental ceramic strength, but cyclic fatigue is more deleterious.</p>