ABSTRACT
<p><b>OBJECTIVE</b>To evaluate the influence of veneer application on failure behavior and reliability of lithium disilicate glass-ceramic (LDG) crowns of maxillary first molar, and thus to reveal the failure mechanism of bilayered LDG crowns.</p><p><b>METHODS</b>Twenty-six LDG maxillary first molar crowns were fabricated in a dental laboratory using IPS e. max Press or IPS e. max Press/Ceram. The crowns were randomly assigned into two groups (with or without veneer application) with thirteen in each group. The crowns were cemented on composite resin dies. After storage in water for one week, the sliding-contact fatigue test was performed by sliding the steatite ceramic ball indenter (6 mm in diameter) from central fossa up to the lingual surface of disto-buccal cusp, cyclic loaded 1 200 000 times with a weight of 100 N at 2 Hz with a fatigue chewing simulator. Survived specimens were subjected to single-load-to-fracture testing using a steatite ceramic ball of 6 mm in diameter at a cross-head speed of 0.5 mm/min in a universal testing machine. Fracture load values were recorded and analyzed with t test. Weibull modulus was calculated to evaluate structure reliability. Fractographic analysis was carried out to determine fracture modes of the failed specimens by a stereomicroscope and a scanning electron microscope (SEM).</p><p><b>RESULTS</b>Statistical analysis results indicated a significant difference of the fracture load values between monolithic group [(2071.23 ± 397.05) N] and bilayered group [(1483.41 ± 327.87) N] (P < 0.001). Monolithic and bilayered groups present similar Weibull modulus (95% confidence interval) as 6.15 (5.15 ∼ 7.15) and 5.54 (4.01 ∼ 7.08) respectively, with no significant difference (the confidence bounds overlapped with each other). Bulk fracture initiating from the middle of oblique ridge of the first maxilla molar was the primary failure mode of monolithic/bilayered LDG crowns. Crack propagation initiated from core-veneer interfacial defects was another major failure mode of bilayered all-ceramic crowns.</p><p><b>CONCLUSIONS</b>Veneer application has some influence on fatigue failure of LDG crowns, but shows no effect on structure reliability. Accumulated damage combined with tensile stress concentration on the surface of veneer layer and defects within core-veneer interface lead to initiating of cracks. The mechanical property of veneering materials should be increased, and procedure of veneer application should be standardized and improved in order to reduce the failure rate of LDG molar crowns.</p>
Subject(s)
Crowns , Dental Porcelain , Chemistry , Dental Restoration Failure , Materials Testing , MolarABSTRACT
<p><b>OBJECTIVE</b>To investigate the binding effect of the short peptide SY1 to the multidrug-resistant gastric cancer cell line SGC7901/VCR cells and its reversing effect on those cancer cells.</p><p><b>METHODS</b>The cultured cells were divided into two groups named SGC7901 and SGC7901/VCR. The SGC7901/VCR group was co-cultured with vincristine (VCR). SY1 was obtained from cyclic 7-mer peptide library by differential screening. Immunofluorescence technique was used to detect the capacity of SY1-containing positive phage specifically binding to SGC7901/VCR cells, compared with that of the negative phage and unrelated phage. MTT assay in vitro was performed to analyze the alteration of drug resistance of SGC7901/ VCR cells, using the positive phages and the chemically synthesized SY1 peptide. Flow cytometry assay was performed to detect the accumulation and retention of adriamycin (ADM) in the SGC7901/VCR cells.</p><p><b>RESULTS</b>Immunofluorescence analysis showed that the SY1-containing positive phages could bind to the SGC7901/VCR cell surface but not to its parent cell line SGC7901 cells. The unrelated phage and negative phage did not bind to SGC7901/VCR cells. These results indicated that SY1 could specifically bind to SGC7901/VCR cells. MTT assay in vitro showed that the survival rate of SGC7901/VCR cells was reduced considerably by the positive phages and the chemically synthesized SY1 peptide (P <0. 05), indicating that SY1 enhanced the sensitivity of SGC7901/VCR cells to chemotherapeutic drug VCR. Flow-cytometric detection showed that SY1 enhanced the accumulation of ADM in the SGC7901/VCR cells, compared with that of the negative phages and the unrelated phages (P <0.05).</p><p><b>CONCLUSION</b>SY1 not only is able to bind to SGC7901/VCR cells specifically, but also can partly reverse the resistance of SGC7901/VCR cell line to chemotherapeutic drug VCR. Those findings might be important to open a new approach to reverse the gastric cancer MDR.</p>