Hyperbranched polycoumarates with photofunctional multiple shape memory.

In good shape: The films of hyperbranched polycoumarate derivatives can undergo a reversible [2+2] cycloaddition under irradiation of UV light and behave like photomechanical elastomers. From a predetermined original shape A the photonically and thermally memorized shapes B and C were obtained. The original shape was recovered by photoirradiation (see picture; Tg =glass transition temperature).

[Comparison of the shear bond strength by using nano silica sol to zirconia basement and veneer porcelain].

PURPOSE: To investigate the feasibility of using sol gel technique to produce thin layer nano silicon dioxide on zirconia ceramic surface and the effect of improving shear bond strength between zirconia and veneer porcelain. METHODS: The presintered zirconia specimen was cut into a rectangle block piece (15 mm×10 mm×2.5 mm), a total of 40 pieces were obtained and divided into 4 groups, each group had 10 pieces. Four different treatments were used in each group respectively. Pieces in group A (control group) were only sintered at 1450°C to crystallization; pieces in group B underwent 30% nano silica sol infiltration first and then were sintered at 1450°C to crystallization; piece in group C underwent crystallization first at 1450°C, then 30% nano silica sol infiltration and were sintered at 1450°C again; pieces in group D was coated by nano silica sol and then sintered at 1450°C to crystallization; ten rectangle block pieces (12 mm×8 mm×2 mm) in group E were made. Cylinder veneers 5 mm in diameter and 4 mm in height were produced in each group and the shear bond strength was tested. Data were statistically analyzed by SPSS 19.0 software package. RESULTS: The shear bond strength of the 5 group specimens were: (28.12±2.95) MPa in group A, (31.09±3.94) MPa in group B, (25.60±2.45) MPa in group C, (31.75±4.90) MPa in group D, (28.67±3.95) MPa in group E, respectively. Significant differences existed between the 5 groups, and group C had significant difference compared with group B and D. CONCLUSIONS：① Use of nano silicon sol gel on presintered zirconia surface to make thin layer of nano silicon dioxide can improve the shear bond strength between zirconia and veneer; ②Using nano silicon sol gel on crystallization zirconia surface to make thin layer of nano silicon dioxide will decrease the shear bond strength between zirconia and veneer; ③ Zirconia veneer bilayer ceramic has the same shear bond strength with porcelain fused to Ni Cr alloy; ④Use of sol gel technique to produce thin layer nano silicon dioxide on zirconia ceramic surface is feasible and can improve shear bond strength between zirconia and veneer porcelain.

Effects of background, direction and intensity of ambient light, measuring position, and adjacent teeth, on anterior tooth colour measurement in vitro.

OBJECTIVE: to investigate the effects of different background colours (black, white or pink), direction and intensity of ambient light, measuring position, and the adjacent teeth, on the in vitro colour measurement of maxillary anterior teeth, using the Minolta CR-321 colorimeter. METHODS: ten extracted human maxillary central incisors were selected. A fibre-optic light MI-150 was used as the ambient illuminant. Teeth were irradiated from a 3- or 12-o'clock direction. L*a*b* values of seven sites on the labial surfaces were obtained by means of the Minolta CR-321 colorimeter, using three background colours, with or without the adjacent teeth. The recorded data were analysed with two-tailed Student t tests and analysis of variance (α = 0.05). RESULTS: the ambient light did not affect the colour measurement of anterior teeth, regardless of the presence or absence of the adjacent teeth. There were no statistically significant differences in L*a*b* values at the same position under different background colours, except ΔE12 (colour difference between site 1 and site 2) between black and white backgrounds. ΔE12 (under black background), ΔE13 and ΔE15 were greater than 1.5, while the others were lower than 1.5. CONCLUSION: the background, ambient light and the presence of adjacent teeth did not affect the colour measurement of anterior teeth using the Minolta CR-321 colorimeter in vitro. The inherent disadvantages of using the naked eye during clinical visual shade assessment may be overcome by the colorimeter.

[Influence of MgO and TiO2 on mechanical properties of zirconia toughened alumina ceramics formed by gel-casting technique].

OBJECTIVE: The objective of this study is to investigate the influence of mechanical properties and sintering performance by adding 5% weight percentage aids to nano-compound zirconia toughened alumina (ZTA) ceramics. METHODS: Micrometer Al2O3 and nanometer ZrO2 (quality ratio 4:1) were used to get 55% volume percentage slurry. Magnesium oxide and titanium oxide were taken as aids which were 5% weight percentage of the Al2O3 and ZrO2 powder. Five groups (number 0, 1, 2, 3, 4 group) were divided according to different proportion of aids. After gel-casting, the porcelain pieces were sintered at 1150, 1200, 1300, 1400, 1450, 1500, 1600 degrees C for 2 hours. Static three-point flexure strength, line shrinkage, relative density were measured and scanning electron microscopy (SEM) was used to observe section. RESULTS: Number 1 (MgO 1%, TiO2 4%) group had the highest bending strength. It was (401.78+/-19.50) MPa after sintering at 1600 degrees C for 2 hours and was higher than 0 group (380.64+/-44.50) MPa. Bending strength became lower than 0 group when MgO was more than 2% or more than that weight percentage of ZTA powder. When MgO content was higher than 2% or more than that weight percentage, there was no difference in relative density raising rate between each sintering assistants groups. When the sintering temperature was higher than 1200 degrees C, all groups showed obvious line-shrinkage and the groups which contained sintering assistants were all was higher than 0 group. CONCLUSION: Adding MgO and TiO2 aids from 1% to 4% weight percentage of ZTA will promote fritting and increase ZTA nano-compound ceramics mechanical properties. Adding 2% MgO aids or more than that weight percent will has no obvious help to increase the relative density raising rate of ZTA nano-compound ceramics and will degrade the mechanical properties of ZTA nano-compound ceramics.

[Influence of ambient light and adjacent tooth in anterior tooth color measurement].

OBJECTIVE: To investigate the influence of different intensity and directions of ambient light and adjacent tooth in anterior tooth color measurement by using colorimeter. METHODS: Fiber lite MI-150 was used as ambient illuminant and it irradiated from three or twelve o'clock direction through 45 degrees angle above. The light magnitude 0, 50, 75, 100, 125, 150 W were applied in this experiment. The values of CIE L* a* b* were measured by Minolta Chroma meter CR-321 colorimeter on the center labial surface of ten extracted human maxillary central incisors with or without adjacent teeth, then those data were analyzed statistically by using SPSS 11.5. RESULTS: Neither different intensities nor different directions of ambient light could influence the results of color measurement by using Minolta Chroma meter CR-321 colorimeter, so did the adjacent teeth whether those were exist or not. CONCLUSION: There is no influence of ambient light and adjacent teeth in the color measurement of anterior teeth under this experiment condition, and Minolta Chroma meter CR-321 colorimeter can be used to measure the color directly aside the chair with light.

[Study on the surface roughness of three dental alloys soaked in artificial saliva].

PURPOSE: The aim of this study was to investigate the corrosion behavior of three metal materials for dental use (Co-Cr alloy, Ni-Cr alloy, titanium) by measurement of their surface roughness after soaked in artificial saliva with two different pH values. METHODS: Standard samples were casted respectively from 3 different alloys and grided into the same roughness .Then the samples were exposed to artificial saliva with two different pH values. After three months,the surface roughness of the samples was tested, and the microstructure of surfaces was studied by metalloscope. The data were analyzed with SPSS11.0 software package for one-way ANOVA and t test. RESULTS: There was significant difference in surface roughness of three alloys after exposed to artificial saliva with pH5.6. The surface roughness values of three alloys were listed as follows: Ni-Cr alloy>Co-Cr alloy >titanium(P<0.01). When exposed to artificial saliva with pH7.0, Ni-Cr alloy was found rougher than Co-Cr alloy and titanium(P<0.01), while there was no significant difference in roughness between Co-Cr alloy and titanium(P>0.05).Ni-Cr alloy and Co-Cr alloy soaked in artificial saliva with pH5.6 were found rougher than the same material in artificial saliva with pH7.0(P<0.01).The microstructure of the samples' surface verified the results. CONCLUSION: Titanium was stable not only in neutral environment but also in acid environment. The corrosion resistance of Co-Cr alloy and Ni-Cr alloy was superior in neutral environment than in acid environment. The corrosion resistance of the three alloys was: Titanium >Co-Cr alloy >Ni-Cr alloy.