Statement of problem

The dimensional stability of alginate dental impressions is a key factor for the reliability of delayed gypsum pouring and digital scanning. However, studies of the dimensional stability of alginates with conventional methods that consider the dimensional variations of large impressions are lacking.

Purpose

The purpose of this in vitro study was to investigate and compare 2 digital methods for the analysis of dimensional stability of large impressions made with 5 different extended-pour alginates and to assess dimensional stability up to 5 days.

Material and methods

Impressions of a simplified master maxillary model were made with Alginoplast, Blueprint, Hydrogum 5, Orthoprint, and Phase Plus and then analyzed at different time points. Digital scans of the alginate impression surfaces were obtained with a desktop scanner and analyzed by evaluating the linear measurements between reference points and by using a novel method that consists of the analysis of the entire scanned surface to evaluate the expansion and contraction of the impressions.

Results

The first method revealed that the dimensional changes did not exceed 0.5%, with the exception of Phase Plus at day 3 (-0.6 ±0.7%), and the average dimensional variation was always lower than or equal to 0.2 mm. Blueprint was the most stable material (-0.2 ±0.6%). The second method revealed dimensional variations always lower than 0.03 mm and confirmed Blueprint as the best performing material (0.001 ±0.006 mm) and Phase Plus the worst (-0.019 ±0.006 mm).

Conclusions

Both the methods used to evaluate alginate stability showed that the analyzed materials remain stable over time; the dimensional variations showed a similar trend, with differences in the absolute values depending on the applied method. Linear measurements are affected by the operator and choice of reference points; however, by evaluating the average variations of the entire structure surfaces, local variations should be minimized. The evaluation of the average variations with the second method offers the advantage of a rapid visual representation of these variations.

中文翻译：

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使用光学扫描和数字方法评估长效海藻酸盐印模材料的稳定性

问题陈述

藻酸盐牙科印模的尺寸稳定性是延迟浇注石膏和数字扫描的可靠性的关键因素。然而，缺乏利用考虑大压痕的尺寸变化的常规方法对藻酸盐的尺寸稳定性的研究。

目的

这项体外研究的目的是调查和比较2种数字方法，以分析由5种不同的延时浇注藻酸盐制成的大型印模的尺寸稳定性，并评估长达5天的尺寸稳定性。

材料与方法

使用Alginoplast，Blueprint，Hydrogum 5，Orthoprint和Phase Plus制作简化的上颌模型的印象，然后在不同的时间点进行分析。用台式扫描仪获得藻酸盐压印表面的数字扫描，并通过评估参考点之间的线性测量值并使用一种新颖的方法进行分析，该方法包括对整个扫描表面进行分析以评估压印的膨胀和收缩。

结果

第一种方法表明，尺寸变化不超过0.5％，第3天的Phase Plus除外（-0.6±0.7％），并且平均尺寸变化始终小于或等于0.2 mm。蓝图是最稳定的材料（-0.2±0.6％）。第二种方法显示尺寸变化始终小于0.03 mm，并确认Blueprint是性能最好的材料（0.001±0.006 mm），而Phase Plus是最差的材料（-0.019±0.006 mm）。

结论

两种用于评估藻酸盐稳定性的方法都表明，所分析的材料会随时间保持稳定。尺寸变化显示出相似的趋势，其绝对值取决于所采用的方法。线性测量受操作员和参考点选择的影响；但是，通过评估整个结构表面的平均变化，应将局部变化减到最小。使用第二种方法评估平均变化的优势在于可以快速直观地表示这些变化。