Li Jianying, Fok Alex S L, Satterthwaite Julian, Watts David C
Minnesota Dental Research Centre for Biomaterials and Biomechanics, University of Minnesota, Minneapolis, MN 55455USA.
Dent Mater. 2009 May;25(5):582-8. doi: 10.1016/j.dental.2008.11.001. Epub 2008 Dec 20.
The aim of this study was to measure the full-field polymerization shrinkage of dental composites using optical image correlation method.
Bar specimens of cross-section 4mm x 2mm and length 10mm approximately were light cured with two irradiances, 450 mW/cm(2) and 180 mW/cm(2), respectively. The curing light was generated with Optilux 501 (Kerr) and the two different irradiances were achieved by adjusting the distance between the light tip and the specimen. A single-camera 2D measuring system was used to record the deformation of the composite specimen for 30 min at a frequency of 0.1 Hz. The specimen surface under observation was sprayed with paint to produce sufficient contrast to allow tracking of individual points on the surface. The curing light was applied to one end of the specimen for 40s during which the painted surface was fully covered. After curing, the cover was removed immediately so that deformation of the painted surface could be recorded by the camera. The images were then analyzed with specialist software and the volumetric shrinkage determined along the beam length.
A typical shrinkage strain field obtained on a specimen surface was highly non-uniform, even at positions of constant distance from the irradiation surface, indicating possible heterogeneity in material composition and shrinkage behavior in the composite. The maximum volumetric shrinkage strain of approximately 1.5% occurred at a subsurface distance of about 1mm, instead of at the irradiation surface. After reaching its peak value, the shrinkage strain then gradually decreased with increasing distance along the beam length, before leveling off to a value of approximately 0.2% at a distance of 4-5mm. The maximum volumetric shrinkage obtained agreed well with the value of 1.6% reported by the manufacturer for the composite examined in this work. Using irradiance of 180 mW/cm(2) resulted in only slightly less polymerization shrinkage than using irradiance of 450 mW/cm(2).
Compared to the other measurement methods, the image correlation method is capable of producing full-field information about the polymerization shrinkage behavior of dental composites.
本研究旨在使用光学图像相关法测量牙科复合材料的全场聚合收缩率。
将横截面约为4mm×2mm、长度约为10mm的条形试样分别用450 mW/cm²和180 mW/cm²两种辐照度进行光固化。固化光由Optilux 501（ Kerr公司）产生，通过调整光尖端与试样之间的距离实现两种不同的辐照度。使用单相机二维测量系统以0.1 Hz的频率记录复合材料试样30分钟的变形情况。在观察的试样表面喷涂颜料以产生足够的对比度，以便跟踪表面上的各个点。将固化光照射在试样的一端40秒，在此期间涂漆表面被完全覆盖。固化后，立即移除覆盖物，以便相机记录涂漆表面的变形。然后用专业软件分析图像，并确定沿光束长度的体积收缩率。
在试样表面获得的典型收缩应变场高度不均匀，即使在距辐照表面距离恒定的位置也是如此，这表明复合材料的材料组成和收缩行为可能存在异质性。最大体积收缩应变约为1.5%，出现在距表面约1mm处，而不是在辐照表面。达到峰值后，收缩应变随后沿光束长度随着距离增加而逐渐减小，在4 - 5mm的距离处趋于平稳，达到约0.2%的值。获得的最大体积收缩率与制造商报告的本研究中所检测复合材料的1.6%的值吻合良好。使用180 mW/cm²的辐照度导致的聚合收缩仅比使用450 mW/cm²的辐照度略少。
与其他测量方法相比，图像相关法能够提供有关牙科复合材料聚合收缩行为的全场信息。
