Objective:To study the antibacterial properties of pure titanium treated with benzalkonium chloride solution.Meth-ods:10 mm ×10 mm ×1 mm titanium specimens were processed by the benzalkonium chloride solution at 1%,0.5% and 0.1%respectively followed by treatment in the cultured bacterial suspension,and then the antibacterial properties of the titanium plates were examined.Additionally,the thermal cycling test was carried out for the 1% benzalkonium chloride-treated titanium plates, and subsequently put the plates into cultured bacterial suspension,the duration of antibacterial properties was observed.Results:0.5% and 1% benzalkonium chloride solution-treated titanium plates significantly inhibited the growth of candida albicans(P <0. 05),1% solution was more effective than 0.5% solution.After 1 000 and 2 500 thermal cycling,the pure titanium still retained the antibacterial ability,but the plates treated by 5 000 cycling showed no antibacterial effect.Conclusion:A certain concentration of benzalkonium chloride can make the pure titanium obtain antibacterial properties.The treated plates may maintain the antibacte-rial properties for a minimum of 3 months.

Objective:To evaluate the effect of different shoulder width on the compressive strength of full-contour zirconia crowns.Methods:A computer aided design and computer aided manufacturing(CAD/CAM) system was used to prepare 24 full-contour zirconia crowns of the mandible first molar.1 mm occlusal thickness crowns with 4 shoulder width of knife-edge(group A),0.3 mm(group B),0.5 mm(group C) and 1.0 mm(group D) (n =6).The Co-Cr alloy PFM crowns made by the die of group C were used as the controls (n =6).All the full-contour zirconia crowns were bonded to the corresponding die using 3 M glass ionomer cement (GIC) and the compressive strength were measured by an universal testing machine.Based on the statistical analysis,crowns with the shoulder width of 0.5 mm were treated by the thermocycling test under cycling of 10000 times(group C1),20 000 times(group C2) and 30000 times (group C3) respectively(n =6).One-way ANOVA method was used for the statistical analysis.Results:The mean compressive strength(N) of group A,B,C,D and E was 3855.00 ± 305.47,2731.70 ± 261.80,3698.30 ± 276.87,3841.70 ± 544.88 and 2992.17 ± 168.41 respectively.The strength of group B and E were lower than that of group A,C and D(P ＜ 0.05),B vs E P ＞0.05.The compressive strength(N) of group C1,C2 and C3 was 3220.00 ± 504.38 (group C1),3148.33 ± 425.60(C2) and 2992.17 ±168.41 (C3) respectively (P＞0.05).Conclusion:For the full-contour zirconia crowns,both the knife-edge shoulder and the shoulder wider than 0.3 mm can meet the thermoclinical needs.The cycling times used in this study have no influences on the compressive strength.

Objective:To observe the artifacts produced by dental metal crown made from different materials on magnetic resonance imaging (MRI).Methods:Mental crows made from Co-Gr,Ni-Gr,low-Ti alloy and Pure-Ti were respectively fabricated for upper right second premolar of a ripe crossbreed dog.The 4 different casting crowns were respectively put on experimental tooth and head MRI scan was carried out with 4 sequences of 1.5 T and 6 sequences of 3.0 T MRI respectively.The existence and extent of the arti-facts were assessed and compared.Results:On both 1.5 T and 3.0 T MRI,the Go-Gr alloy crown exhibited significantly wider arti-facts than the others (ANAVO analysis,P<0.01).There were no significant differences among Ni-Gr,low-Ti alloy and Pure-Ti on 1.5 T MRI(P>0.05).On 3.0 T MRI the artifacts produced by Ni-Gr was larger than that by low-Ti alloy or Pure-Ti(P<0.05,be-tween low-Ti alloy and pure-Ti,P>0.05).By any of the test sequence either on 1.5 T or on 3.0 T,the Co-Gr alloy produced arti-facts in the most slices of MRI imaging and Pure-Ti in the least.Conclusion:Go-Gr alloy may produce larger artifacts than Ni-Gr, low-Ti alloy and Pure-Ti on MRI.

OBJECTIVEThis study aimed to observe and evaluate six 3.0 T sequences of metallic artifacts produced by metal dental crowns.

METHODSDental crowns fabricated with four different materials (Co-Gr, Ni-Gr, Ti alloy and pure Ti) were evaluated. A mature crossbreed dog was used as the experimental animal, and crowns were fabricated for its upper right second premolar. Each crown was examined through head MRI (3.0 T) with six sequences, namely, T₁ weighted-imaging of spin echo (T₁W/SE), T₂ weighted-imaging of inversion recovery (T₂W/IR), T₂ star gradient echo (T₂*/GRE), T2 weighted-imaging of fast spin echo (T₂W/FSE), T₁ weighted-imaging of fluid attenuate inversion recovery (T₂W/FLAIR), and T₂ weighted-imaging of propeller (T₂W/PROP). The largest area and layers of artifacts were assessed and compared.

RESULTSThe artifact in the T₂*/GRE sequence was significantly wider than those in the other sequences (P < 0.01), whose artifact extent was not significantly different (P > 0.05).

CONCLUSIONT₂*/GRE exhibit the strongest influence on the artifact, whereas the five other sequences contribute equally to artifact generation.

Alloys ; Animals ; Artifacts ; Crowns ; Dogs ; Magnetic Resonance Imaging ; Titanium