Determination of Surface Roughness and Accuracy of Alginate Impression Material Disinfected by Immersion

Background: This study was conducted to evaluate the surface roughness and dimensional accuracy of commercially obtainable alginate impression material in terms of imbibition after immersion in two different media. Materials and method: Two disinfecting agents, ethanol 70% and povidone-iodine 4%, were used to access the dimensional accuracy and surface roughness of alginate impression material. Weights of specimen discs of alginate impressions were measured before and immediately after immersion to gain a measure of imbibition. For surface roughness, disinfected specimens rectangle was examined before and after disinfection. Results: Minimal changes in weight were observed after disinfection, but a statistically non-significant difference was found before and after immersion. It did not affect the surface roughness of alginate impression material Conclusion: Disinfection of alginate impression material with ethanol and povidone iodine had no significant effect on dimensional accuracy and surface roughness.


Introduction
Alginate impression is one of the highly contaminated materials between dental laboratory workers and patients. Infectious agents are transferred from saliva and blood to the casts via dental impression (1,2) . It has been found that 67% of dental material forward from a dental clinic to the lab is contaminated (3) . Dental materials must be disinfected after making an impression (4,5) . Various disinfection protocols related to the type and method of disinfection have been proposed for alginate and dental cast (3) . Immersion and spray application are two different chemical disinfection processes that are carried out on impression (6) . American Dental Association for control guidelines infection advised immersion disinfection of hydrocolloid irreversible impression because it was more reliable and effective. Various solutions, such as sodium hypochlorite, formaldehyde, synthetic phenol, iodine, and alcohol, are applied to the chemical disinfection of dental material (7) . The seen changes in the dimensional stability and surface chemistry of the impression depend on the type of disinfectant used. One of the adverse effects of disinfection solution is the dimensional change of the impression due to physical and chemical reactions between impression and disinfecting substance (8,9) . Alginate impression has an imbibition phenomenon that absorbs water within a certain time so it will expand. In addition, alginate can experience syneresis which is a continued reaction because of its ability to expand which may lead to more deformation of impression (10) . Various types of research studied the effect generated by imbibition on the surface detail reproduction and dimensions of impression. Some studies have agreed that the effect produced is negligible, others have shown that a significant dimensional change is caused by immersion (11) .The time for which the disinfection happens is also a contributing factor (12) . Immersion of impression in disinfectant solutions for a longer time causes changes in the impression, transferred to the cast (13) . Changes in the properties of gypsum cast, containing dimensional stability, hardness, surface detail reproduction and roughness will affect the accuracy of complete restoration after increasing the time of immersion of an impression (7) . This study was designed to access the dimensional accuracy due to imbibition phenomena and surface roughness of alginate material immersed in two different chemical disinfectant solutions.

Materials and Methods
In this study, alginate material (Zhermack, Hydrogum) was used. Forty specimens were prepared, 20 specimens for the surface roughness test, and 20 specimens for the dimensional accuracy test. Each test has two groups (consisting of 10 specimens, each n =10) The study groups were as follows: 1-Impressions were immersed in ethanol 70% for 3 minutes 2-Impressions were immersed in povidone-iodine 4% for 3 minutes A rectangular silicon mold measuring (521 cm) was used (14) . Figure (1) A round disk-shaped silicon mold measuring (4mm H, 6 mm W) is used for the dimensional accuracy test (3) .Figure (2).Following the water-powder ratio (18gm / 36 ml) recommended by manufacturer instructions After applying the alginate to the impression mold, a glass slab was placed over the alginate material to ensure the accurate contact of alginate with the mold and a uniform flat surface (15) . All of the alginate specimens were allowed to sit for five minutes at 37 Cᴼ. After setting, the impression was separated, removed from the mold, and immersed in disinfecting solution (3) . Figure (3,4) . Testing procedure

Dimensional accuracy test
After specimens were constructed, the initial weight for each was measured using an electronic balance (KERN ,ALS 220.4, Germany) and was indicated as w1. The specimens were weighed again after immersion. Change in percentage weight for each specimen in two different media was calculated.Figure (5).

Surface roughness test
The specimens' surface was evaluated using a Profilometer (600 S , China), a measurement length of 5 mm /s. The device was adjusted according to the instructions before the measurement and the evaluated measures of each specimen surface; Ra's gained surface roughness values were averaged.    (7) for the alcohol and povidone iodine groups.
The mean values of alcohol specimens were decreased after immersion while increased in a povidoneiodine group after immersion. The F-test results were accounted for non-sig differences before and after immersion in the povidone iodine solution group while significant in the alcohol group before and after immersion. The t-test revealed non -significant before and after immersion for both groups, as in table (2).   Table (3) presents descriptive statistics. The surface roughness values of alcohol and povidone iodine groups were decreased after immersion-figure (8). The results of the F-test and t-test were accounted for non-sig differences before and after immersion in povidone-iodine and alcohol solution groups as in table (4).

Discussion
When making an impression, pathogens were transmitted in the oral cavity to the outer environment. The spread of infectious diseases can be prevented due to contamination (16) .
Disinfection of impressions is considered a topic of significance for several years (17) . The effect of disinfection treatment on the properties of dental impression and disinfecting solution in removing the pathogen is the main requirement (18) . The most workable and dependable method is chemical disinfection by immersion, which does not affect dental impressions and dimensional accuracy (19) . Irreversible hydrocolloids tend to be hydrated by ethanol. Therefore, it should be disinfected for a short time because of imbibition (absorption of water), resulting in inaccurate impressions and casts (20) .In this study comparison of alcohol, and disinfectant occurs with povidone-iodine. The observed alginate is a minimum dimensional change in weight immediately after immersion in two media but is statistically non-significant. This is in accordance with the results of the previous study (3) which concluded that disinfection of alginate material with Clorax will cause minimal dimensional changes related to imbibition and syneresis, but after thirty minutes, it observed the overall minimal change in weight. The activity of disinfecting agent is not essentially the same for all impressions, depending on the thickness and texture of the impression. To provide maximum accuracy, a uniform thickness of 4-6 mm was proposed for irreversible hydrocolloid Rudd and Morrow. In this study, the alginate disc was used to measure the dimensional accuracy before and after disinfection with a uniform thickness of 4 mm. The conclusion does not give a significant change in dimensional accuracy.
The disinfection procedure should not cause alteration in the surface roughness of impression material. Several studies were conducted to estimate the surface roughness of hydrocolloid impression materials. Kotha et al.(2017) concluded that chemical disinfection did not significantly affect surface roughness. In this study, no significant differences were found before and after immersion for two disinfectant solutions. This result agrees with AI Kheraif (2013), who evaluated polyvinyl siloxane material's surface roughness after various disinfection procedures.

1-
The dimensional accuracy of Hydrogum alginate material was not affected by immersion in either ethanol or povidone-iodine.
2-The immersion time or disinfecting agents did not have a significant effect in terms of surface roughness.