Chemicals Disinfections and Their Effects on The Dimensional Stability of Alginate: Systematic Review

Background: Dental practice involves a risk of exposure to microorganisms causing many infectious diseases. The risk of contamination starts at the beginning of the prosthetic workflow through impressions. Various chemical disinfection protocols for dental impressions are reported in the literature.

Objective: This study aimed to systematically review the literature regarding the dimensional stability of alginate impressions, disinfected with different chemical agents.

Methods: The Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) checklist was used to structure this systematic review. The inclusion criteria were as follows: clinical trials, in vitro studies, studies in English or French, papers published from 2010 to 2022, disinfection done by immersion or spray and studies focusing on the effects of chemical disinfection products on the dimensional stability. An electronic search was performed in the following databases: PubMed/ MEDLINE, Scopus, Cochrane and Dentistry & Oral Sciences Source. we also conducted a manual search for articles published in specific journals of dental prostheses and references from selected electronic articles.

Results: Twenty-six studies included in this systematic review. According to the findings, Alginates are generally subject to dimensional changes during disinfection. The most widely used disinfectant was sodium hypochlorite. Immersion methods were the most studied in 19 studies, while spay methods were used in 12 studies.

Conclusion: Spraying is the disinfection method with the least dimensional alteration for alginates. The duration of disinfection and the concentration of the disinfectant are essential parameters leading to a change for immersion disinfection method.

Keywords:Dental Impression Materials; Alginate; Chemical disinfection; Immersion; Spraying; Dimensional stability

Dental practice involves a risk of exposure to microorganisms causing many infectious diseases. The risk of contamination starts at the beginning of the prosthetic workflow through impressions [1]. Impression procedure consist to the introduction of impression material into the oral cavity in order to record details of the oral cavity. It is a major communication element with the dental laboratory during the fabrication of an indirect restoration but it is too the main vectors of infection in the prosthetic workflow [2].

The contact between these materials and the oral environment leads to their contamination by saliva and oral flora [3]. Many microorganisms associated to several infectious diseases such as hepatitis B, AIDS, herpes infection and tuberculosis have been found on dental impressions [2]. In order to prevent cross-contamination with infectious diseases, dental impression disinfection’s is required.

The first recommendations from the ADA to reduce the risk of contamination from impressions was to perform rinsing [4]. However, rinsing reduces the microbial load, but does not completely eliminate the infectious potential of impressions [4, 1]. Since then, many protocols for disinfection of impressions have been established.

Nowadays, there is no consensus on disinfection methods and no miracle solution for optimal disinfection of impressions. The difficulty in developing a single protocol is explained by the various impression material families and the several number of disinfection solutions. Moreover, each impression material families have different reactions and alterations depending on the chemical nature and the method of disinfection [2]. The possibility of damaging the dimensional stability and the surface roughness leads to the option of performing no treatment on dental impression [5]. Indeed, disinfection methods lead to physicochemical changes in impression materials. However, several studies show that chemical disinfection induces dimensional and surface changes which can be compatible with the clinical applications and still provide sufficient disinfection [3, 6].

Chemical disinfection is the gold standard for the disinfection of dental impressions with two methods, immersion and spraying. Disinfection remains an essential step to reduce the risk of cross-contamination [5].

The emergence of new infectious pathologies particularly contagious should encourage dentists to be more careful in the treatment of impressions. If no decontamination procedures are applied to transferred items from dental clinic to dental laboratory, the latter may become a significant place in cross-contamination chain by getting and sending contaminated items [1, 4].

The aim of this study was to examine the effect of immersion or spray disinfection on the dimensional stability of alginate impressions through a systematic review from papers published from 2010 to 2022.

The Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) checklist was used to structure this literature review.

Selected studies were designed in accordance with the PICO strategy:

(P) stands for population, which includes alginate dental impression;

(I) stands for intervention, which means alginate disinfected with different chemical agents by immersion and spraying;

(C) stands for comparison or control which was other disinfection methods or immersed in distilled water or no treatment;

(O) stands for outcome, which was measurement of dimensional stability.

The review question was: " What is the effect of decontamination by immersion or spray on the dimensional stability of alginate impressions?”

The inclusion criteria were as follows:

• clinical trials (randomised controlled trial, prospective, retrospective);
• in vitro studies;
• studies in English or French;
• papers published from 2010 to 2022;
• disinfection by immersion or spray;
• studies focusing to the effects of chemical disinfection on the dimensional stability.

An electronic search was independently performed by two authors (MMS and PIK) in the following databases: PubMed/MEDLINE, Scopus, Dentistry & Oral Sciences Source and Cochrane Library, using MeSH and keywords with the following search strategy (Table 1).

The search parameters were restricted the period of publication from 2010 to 2022. In each database, studies were selected based on the title, keywords and abstract. To determine inclusion, each article was read entirely.

The choices made by the two authors (MMS and PIK) were analysed by a third author (NT), and a consensus was reached through discussion. A manual search for articles published in specific journals of dental prostheses and dental materials was conducted using resources such as the International Journal of Prosthodontics, Journal of Dental Research, Journal of Oral Rehabilitation, Journal of Prosthodontics, The Journal of Prosthetic Dentistry, Dental Materials, and Materials Science & Engineering. Also, prosthetic books were used and pertinent references from selected electronic articles (Figure 1).

One author (MMS) collected the information from the articles, and another author (PIK) reviewed the results. A third author (NT) analysed the choices made by the two evaluators, and a consensus was agreed upon via discussion.

Information of the included studies was collected by one of the reviewers (MMS) and a second one (PIK) cross‑checked, independently, all the retrieved data (Table 2). The following data were systematically collected from each included study:

• authors and publication year;
• type of study;
• dental impression materials;
• disinfection methods;
• chemical disinfectant;
• contact time;
• experimental condition;
• conclusion.

The risk of bias in these studies was analysed using the JBI Critical Appraisal Checklist for Quasi-Experimental Studies (non-randomised experimental studies), which provides a critical analysis of the methodological quality of the studies. Each study was evaluated individually and JBI provided nine questions that were selected based on the characteristics of the studies in which the answers were "Yes," "No," "Not clear" or "Not applicable". The analysis was conducted by two examiners, and subsequently, a union score of all studies was obtained (Table 3).

The electronic search provided 1019 articles:

• 410 from PubMed/ Medline,
• 111 from DOSS
• 15 from Cochrane
• 483 from Scopus.

After removing duplicate articles, 695 articles remained. The titles, keywords and abstracts of the articles were read, which led to the removal of 480 articles. The full article of each study was read except 3 studies. Then, the eligibility criteria were applied to the 215 articles remaining. The articles were read and 188 were excluded for the following reasons: impression material not matched, another disinfection methods used or a combination of several methods of disinfection, an article written in others language, evaluation of the antimicrobial effect only, evaluation of surface roughness only. In parallel, the manual search resulted in the inclusion of 2 articles.

In total, 26 in vitro studies were included in this systematic review. The flowchart in Figure 1 details the search strategy.

All included studies were performed in vitro, only one was ex vivo. The most widely used disinfectant was sodium hypochlorite. Immersion methods were the most studied in 19 studies, while spay methods were used in 12 studies. The immersion times of the samples in the solution ranged from 30 seconds to 24 hours. The dimensional stability in all studies was measured by linear measurement (distance) except one who used the weight. The data collected from the articles are shown in Table 2.

The risk of bias analysis between the studies was low because a majority of the selected items were evaluated as "yes"; therefore, the quality of the included studies was high. Notably, the question on the follow-up period was "not applicable" for the selected studies because all selected studies were considered in vitro (Table 3).

The objective of this study was to examine the effect of immersion or spray disinfection on the dimensional stability of alginate impressions through a systematic review from papers published from 2010 to 2022.

Limited access to other databases and the lack of references to use a periodical delimitation for electronic search guide were the main limitations encountered during this work.

After reading the titles and abstracts of an initial total of 1047 articles retrieved for inclusion in the study, 26 articles were selected, as ratio of 5.4%.

The articles not included were duplicates or did not meet the selection criteria.

The risk of bias in the selected studies was low as the majority of the selected studies had a score that ranked them as such.

Alginates are generally subject to dimensional changes during disinfection. These modifications are due to the hydrophilic nature of the material and its chemical nature. Alginates are made up of alginic acid (15%), calcium sulphate which acts as a reactor (16%), zinc oxide (4%), titanium and potassium fluoride (3%), and diatomaceous particules (60%), and sodium phosphate and colouring or flavouring agents (2%) [33]. After gelification, the final product is in the form of a three-dimensional network of polymannuronic acid chains linked by calcium bonds. Between the different layers of this structure are the unreacted alkaline alginate sol, the free water, the inert charge particles, and the by-products of the reaction. The Na+, SO42-, PO43- etc. ions in the alginate will create an osmotic potential which, on contact with a solution, will produce a diffusion of ions. The ions can diffuse from the impression to the disinfection solution or vice versa depending to the osmotic potential. The water contained in the impressions will also diffuse [7]. The diffusion of water is always from the less concentrated solution to the most concentrated one. These transfers will happen until an equal balance, a buffer solution, is established. So, depending on the chemical nature or the concentration of the disinfectant and the method of disinfection, there will be exchanges: imbibition (if the exchanges are in favour of the impression) or syneresis (if the exchanges are to the detriment of the impression). This could explain the observation that all the studies investigating spray disinfection of alginates concluded that there were no significant dimensional variations [9, 10, 12, 13, 14, 15, 17, 22, 23, 26, 27, 28].

Spray disinfection does not allow ion or water transfer leading to dimensional variations, in opposite to the immersion disinfection method. Of eighteen studies reported on the disinfection of alginate impressions by immersion, ten concluded that there were significant dimensional variations [9, 11, 15, 17, 7, 21, 25, 28, 31, 32]. The studies lead by BABIKER et al., DEWI et al., HAMEDI RAD et al. or TRIVEDI et al. concluded that these changes were due to immersion in high concentration disinfection solutions.

Indeed, these studies with HS disinfectant with a concentration higher than 1% concluded that there were changes in dimensional stability. In contrast, in the seven studies that concluded that there were no significant dimensional changes [1, 16, 19, 20, 24, 25, 29, 30], the concentration of HS did not exceed 1% except for the study by SHARIF et al where HS at 5.25% was used.

Other products used were 1 or 2% GA, AQ or other products. AQ for example are salts of quaternary ammonium cations with an anion which are generally not very reactive.

From these studies it was found that the chemical composition of the alginate, the immersion time, the chemical nature of the disinfectant as well as its concentration were the factors of dimensional variations of the alginates. Spraying is the disinfection method with the least dimensional alteration. For immersion, the immersion time should not exceed 15min and the concentration of the disinfectant for HS should be less than 1%, for GA less than 2% [1, 9, 10, 12-30].

A qualitative and quantitative synthesis of the data reported in the included studies led to the following conclusions:

Spraying is the disinfection method with the least dimensional alteration for alginates.

The duration of disinfection and the concentration of the disinfectant are essential parameters leading to a change for immersion disinfection method.