The effect of contact time between alginate impression material and type III dental stone on the surface properties of stone casts

Background: Alginate impression material is the irreversible hydrocolloid material that is widely used in dentistry. The contact time between alginate and gypsum cast could have a detrimental effect on the properties of the gypsum cast. The objective of this study is to evaluate the impact of various contact time intervals of Alginate impressions & type III dental stone on surface properties of stone cast. Materials and Methods: Time intervals tested were 1hour, 6 hours and 9 hours. Surface properties of stone cast evaluated were surface detail reproduction, hardness and roughness. Surface detail reproduction was determined using cylindrical brass test block in accordance with ISO 1563. Surface roughness was measured by profilometer and hardness was measured by Durometer (Shore D). Results: The detail reproduction showed significant difference (P<0.05), at 6 hr., and 9 hr. showed better results. While surface roughness significantly decreased (p<0.01) with prolonged contact time. However, surface hardness increased significantly (p<0.01) with increased contact time. Conclusions: Surface detail reproduction increased with increasing the contact time and this was noticed at (6, 9 hours). However, 1hour time interval showed decreased surface detailed reproduction. Roughness decreased when the contact time was increased between type III dental stone and alginate impression whereas, hardness was improved significantly with increasing contact time.

Influence of expiration date on detail reproduction of dental elastomers

Elastomers are synthetic rubber materials formed by polymers, which are joined by a small number of cross-links that form a three-dimensional network. The aim of the current study was to compare the surface detail reproduction of polyvinyl siloxane and polyether-based elastomeric impression materials (2 years after their expiration date) to the ones that have not exceeded this period-of-time. Four groups comprising 5 samples, each (n = 5), were divided based on material (polyvinyl siloxane – Express and polyether – Impregum Soft) and expiration date (expired, or not). The manipulated material was placed on a tray in a way to fully cover its inner part. Later on, it was placed on a metal matrix presenting 20-, 50- and 75-μm lines. Molds were removed after polymerization and surface detail reproduction was measured in comparator microscope (Stereozoom Microscope), along the 20 μm line (25 mm in length), at 4x-magnification, in compliance with ISO 4823. Surface detail reproduction values were subjected to descriptive analysis - results were expressed in percentage (%). All groups presented 100% of surface detail reproduction, regardless of impression material or expiration date. Surface detail reproduction of the investigated materials was not influenced by the evaluated elastomers’ expiration date.

The accuracy of gypsum casts obtained from the disinfected extended-pour alginate impressions through prolonged storage times

Background Manufacturers of the extended-pour alginates claimed their dimensional stability through prolonged storage. No data confirmed the ability of these materials to maintain their dimensions and the reproduced oral details following their chemical disinfection. Therefore, this study evaluated the dimensional stability and surface detail reproduction of gypsum casts obtained from disinfected extended-pour alginate impressions through different storage time intervals. Methods Two hundred and forty three hydrocolloid impressions were made from one conventional (Tropicalgin) and two extended-pour (Hydrogum 5 and Chromaprint premium) alginates. These impressions were subjected to none, spray and immersion disinfection before their storage in 100% humidity for 0, 72 and 120 h. The dimensional stability and the surface detail reproduction were indirectly evaluated under low angle illumination on the resulted gypsum casts. At α = 0.05, the parametric dimensional stability data were analyzed using One-Way ANOVA and Tukey’s comparisons, while the nonparametric detail reproduction data were analyzed using KrusKal Wallis and Mann–Whitney's tests. Results All gypsum casts exhibited a degree of expansion; however, the recorded expansion values did not differ between test categories (P > 0.05). Generally, casts obtained from spray-disinfected impressions showed lower detail accuracy (P < 0.05). Immersion-disinfected extended-pour alginates produced casts with better detail accuracy following 120 h of storage (P < 0.05). Conclusion All alginates materials offer comparable cast dimensions under different testing circumstances. Extended-pour alginates offer casts with superior surface details following their immersion disinfection and 120 h of storage. Spray-disinfection using 5.25% sodium hypochlorite affects the surface details of casts obtained from conventional and extended-pour alginates adversely.

“EVALUATION OF SURFACE DETAIL REPRODUCTION OF BD IMPRESS AND NEXUS MEDODENT THERMOPLASTIC IMPRESSION MATERIALS” - AN IN VITRO COMPARATIVE STUDY

Impression making is the primary step in the process of fabrication of prosthetic restoration. Dimensional stability, Surface detail reproduction, and compatibility with gypsum products is an essential prerequisite for a successful restoration. Clinically, the accuracy of impressions depends on two major aspects: 1) Ability to ow and adapt intimately to the relevant surfaces while making the impression, and 2) the wetting of the polymerized impression material by the gypsum. The purpose of this study is to evaluate and compare the surface detail reproduction of BD Impress and Nexus Medodent impression material. The results showed signicant difference in surface detail between the two thermoplastic impression materials with p-value <0.05. It was observed that comparison of mean scores obtained by BD Impress and Nexus Medodent impression material are 2.7556 and 2.2222 respectively. The materials with minimum mean score value is considered as the material with good surface detail reproduction. Thus one can conclude that Nexus Medodent thermoplastic material has the good surface detail reproduction compared to BD Impress thermoplastic material.

A Comparative Evaluation of Dimensional Accuracy and Surface Detail Reproduction for Polyvinyl Siloxane and Vinyl Siloxane Ether under Dry and Moist Conditions- An In-vitro Study

Introduction: The conventional impression procedure plays a major role in prosthodontics inspite of advancement in intra- oral scanning devices and 3D imaging procedures. Dimensional accuracy and surface detail reproduction are important for recording an impression. Aim: The study evaluated and compared the dimensional accuracy and surface detail reproduction of Polyvinyl Siloxane (PVS) and vinyl siloxane ether impression materials when used under dry and moist conditions. Materials and Methods: An in-vitro study was conducted in the Department of Prosthodontics, Rural Dental College, Pravara Institute of Medical Sciences, Loni, Ahmednagar, Maharashtra, India, for a period of two years from October 2018 to September 2020. A total of 60 impressions were made with PVS (Group A) and vinyl siloxane ether (Group B) under dry (A1, B1) and moist (A2, B2) conditions of stainless steel dies which had lines engraved on superior surface of the die. Using a Harloc’s Tool maker’s microscope, dimensional accuracy was measured by comparing the width of line Y in each impression. Surface detail reproduction was evaluated by American Dental Association (ADA) specification no. 19 where it stated continuous replication of at least any two lines out of the three lines inscribed on the die. Data analysis processing was performed in the SYSTAT version 12 (made by Crane’s software, Bangalore). Student’s unpaired t-test and Chi-square test were performed to determine statistical difference between PVS and vinyl siloxane ether where the level of significance was set at 5% and 1%. Results: The mean dimensional change and SD values for PVS under dry condition ranged from 21.93±2.46 to 22.40±2.89 (in mm). The mean dimensional change and SD values for PVS under moist condition ranged from 22.87±3.20 to 23.33±3.42. The mean dimensional change and SD values for vinyl siloxane ether under dry condition ranged from 21.93±3.61 to 24.73±5.20. The mean dimensional change and SD values for vinyl siloxane ether under moist condition ranged from 21.93±4.48 to 22.87±4.15. No statistical difference was found under dry and moist conditions within 2 hours and after 24 hours for both the materials. Conclusion: The study revealed no significant difference between dimensional accuracy and surface detail reproduction for PVS and vinyl siloxane ether. Both the materials can reproduce the details under dry and moist conditions satisfactorily and remained dimensionally stable till 24 hours after impression making.