Objective:To employ a laser triangulation method for measuring the dynamic shrinkage of composite resins during polymerization, and to investigate the maximum shrinkage rate (Smax) and the time at maximum shrinkage rate (tmax). Methods: A novel experimental set-up based on laser triangulation was utilized which was capable of real-time shrinkage strain measurements. Uncured composite was condensed into a FFFE mould and irradiated for 40 s. The laser signals obtained from lateral composite surfaces were monitored using a laser triangulation measuring system and were converted into the displacement of the tested surface. The volumetric shrinkage derived from the linear shrinkage was calculated by multiplying 3. Total volumetric shrinkage (%S) of the five restorative materials (AP-X, Charmfill, Charisma , Durafill VS, and Herculite Precis) was measured using three methods ( laser triangulation method, Acuvol, and buoyancy method). Smax and tmax were measured using the laser triangulation method. Statistical analyses were done using the two-way ANOVA ( P ＜ 0. 05 ) and post hoc test. Results: The highest shrinkage value was measured by Acuvol, followed by laser method, and the lowest was by buoyancy method. All the three methods of measuring % S generated the same, statistically secured ranking for the five light-cured restorative materials: DurafillVS＜AP-X ＜Herculite Precis＜Charisma ＜Charmfill. % S measured by laser triangulation method varied between 2.06% and 3. 37% . Smax varied between 4. 39 μm/s and 29. 25 μm/s. Tmax varied between 0. 77 s and 1. 59 s. Significant differences in Smax ( F = 734. 87, P＜0. 01) and tmax ( F = 53. 24, P ＜0. 01 ) for five composite resins were found. Conclusion: Laser triangulation method offers several advantages over the conventional methods of measuring polymerization shrinkage. It is simple, compact, non-invasive and suitable for measuring the dynamic polymerization shrinkage in real time without delay. Therefore, it can be used to characterize the shrinkage kinetics in a wide range of visible-light-cure materials.%目的:开发一种能够实时监测复合树脂早期动态固化收缩的测量系统,并且研究不同复合树脂之间收缩速率的差异.方法:本测量系统基于激光测距技术,采用激光位移传感器和特制的材料固化腔.固化灯可以在固化腔上方直接照射,与此同时激光位移传感器可以无接触地监测复合树脂侧方(即与光照方向垂直)固化收缩的全过程.利用此实验方法获得了5种复合树脂(AP-X,Charmfill,Charisma,Durafill VS,Herculite Precis)的总线性收缩率,并换算为体积收缩率(线性收缩率×3),采用双因素方差分析与Acuvol法及密度法的结果进行了对比.此外,还获得了5种复合树脂固化收缩速率峰值,以及达到峰值的时间.结果:3种方法的测量结果之间差异有统计学意义(P＜0.001):Acuvol法＞激光法＞密度法.5种复合树脂体积收缩率之间差异有统计学意义(P ＜0.001).每种测量方法内测得5种树脂体积收缩率顺序趋势一致:DurafillVS＜ AP-X＜ Herculite Precis＜ Charisma＜ Charmfill.激光法测得5种树脂的体积收缩率在2.06％～ 3.37％之间,固化收缩速率峰值在4.39 ～ 29.25 μm/s之间,达到峰值的时间在0.77～1.59 s之间.5种复合树脂之间固化收缩速率峰值(p＜0.01)以及达到峰值的时间(P＜0.01)差异有统计学意义.结论:本方法是一种非接触性的无延迟实时动态测量方法,不仅可以测得体积收缩率,还可以测得固化收缩速率峰值和达到峰值的时间,此外还具有设备简单、操作方便、测量结果稳定且能够重复的优点,是一种可以推广的测量复合树脂固化收缩的方法.
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