A study of bubbles in a rubber elastomer manipulated under clinical conditions

Addition Silicone Impressions in Fixed Prosthodontics: Clinical Standpoints

Addition silicones have revolutionized the field of fixed prosthodontics because of their dimensional stability, sufficient tear strength and excellent detail reproduction. This review study aims to provide a detailed description of the essential variables to be taken into account during the process of making addition silicone impressions in fixed prosthodontics. These variables include the selection of appropriate tray type, size, and fabrication; the use of tray adhesive; gingival displacement techniques; manipulation of the impression material; the choice of the impression material's viscosity; impression techniques; and the proper insertion, removal, disinfection, and pouring of the cast. Additionally, this review aims to help doctors produce high-quality impressions by empowering them to critically assess the impressions to spot mistakes and motivating them to redo impressions that have serious problems before submitting them to the laboratory.

Assessment of preference of mixing techniques and duration of mixing and tray loading for two viscosities of vinyl polysiloxane material

STATEMENT OF PROBLEM

Information regarding operators' preferences for different impression mixing techniques and duration of mixing and tray loading is limited.

PURPOSE

The purpose of this study was to assess operators' preferences, and the duration of mixing and tray loading using different mixing techniques.

MATERIAL AND METHODS

Thirty dentists, 30 dental assistants, and 30 inexperienced dental students evaluated mixing heavy-body vinyl polysiloxane material (VPS) using electronic mixing compared to automixing, and extra-heavy-body material using electronic mixing compared to hand mixing. Participants rated their level of preference using a scale from 0 to 10 for ease of mixing, control of loading, quality of mixing, level of cleanliness, and overall rating. The duration of mixing and tray loading was also measured. Mean values were compared within participant groups using the paired t test (alpha=.05) and between groups using 1-way analysis of variance (ANOVA) (alpha=.05). Holm's procedure was used to adjust the level of significance for the multiple comparisons.

RESULTS

The paired t test showed that mean values of level of preference for electronic mixing were significantly higher (P<.001 to .033) than those for automixing or hand mixing. The mean values of duration of mixing and tray loading with electronic mixing were significantly higher (P<.001 to .002) than those with automixing or hand mixing, except for students using heavy-body materials (P=.31). One-way ANOVA showed that there were no significant differences between the 3 participant groups in preference and duration of mixing and tray loading, both of heavy-body and extra-heavy-body VPS impression materials.

CONCLUSIONS

All participant groups preferred electronic mixing to automixing or hand mixing. Electronic mixing was significantly slower for all groups except for students using heavy-body materials. There was no significant difference between the 3 participant groups in the preference or duration of mixing and tray loading for the mixing techniques tested.

In vitro study of the number of surface defects in monophase and two-phase addition silicone impressions

STATEMENT OF PROBLEM

Monophase addition-cured silicone impression materials in stock trays are considered to be alternatives to two-phase systems used with custom trays.

PURPOSE

This study compared the number of surface defects in addition-cured silicone impressions recorded with monophase materials in stock trays and two-phase impressions in custom trays.

METHODS

The number of voids visible on the surface of impressions recorded in vitro were counted. Two monophase impression materials. (President Monobody system 75, Bayer Cutter) in stock trays were compared with impressions recorded with two-phase addition silicone materials (President Plus light-body/regular-body and Zhermack Elite light-body/medium-body) in custom trays. A total of 200 automixed impressions, 50 with each material, were recorded of 50 dentoform molar teeth prepared for full veneer crowns. Impressions were examined for surface voids anywhere on the prepared part of the tooth by a trained examiner.

RESULTS

Mean number of voids observed for the monophase impressions were 3.0 +/- 2.2 for President Monobody system and 3.4 +/- 2.0 for Bayer Cutter system. Mean number of voids for the two-phase materials were 0.8 +/- 1.0 for President Plus, and 1.0 +/- 1.1 for Zhermack Elite. No significant differences were observed for number of voids between the monophase materials or between the two-phase systems (ANOVA and Neuman-Keuls p > 0.05). However, both two-phase materials in custom trays had significantly fewer surface voids than the two-monophase materials (ANOVA and Neuman-Keuls, p < 0.001) used in stock trays.

CONCLUSION

Monophase addition-cured impression materials in stock trays carries an increased risk of void formation on the surface of the impression when compared with two-phase addition silicone materials in custom trays.

Effect of loading and syringing on void formation in automixed addition silicone elastomers

The effect of loading and syringing on void formation in five automixed addition silicones was evaluated by determining the voids created in the first and second halves of material loaded and dispensed from a metal syringe. Impressions were made of a model with six stainless-steel cylinders. The voids were counted at a predetermined site on 3 separate days using a binocular microscope at x 7 magnification. Automixed addition silicones did not confirm the 'last out-fewer bubbles' phenomenon and specific loading and syringing technique did not appear to have a consistent effect on void formation in automixed elastomers.

Bending strength of Fuji and Ketac glass ionomers after sonication

Glass ionomer cements mixed by conventional methods contain voids that can decrease their overall strength. This study evaluated the effect of sonication on the reduction of air entrapment by measuring the bending strength in glass ionomer cements (Fujj-II and Ketac-fil). Glass ionomer cement was placed in identical-test vials and sonicated for 45s, 10s, or 0s. The bending strengths were measured (0.005 in min-1) after setting times of 1 or 2 weeks. Mean bending strengths (MPa +/- SD) for the 12 treatment both cements (P < 0.001) and sonication times (P < 0.001). The effect of setting time produced minimal increases in bending strength (P < 0.218). The sonication of freshly mixed glass ionomer cements is a possible solution for reducing voids to increase bending strength.

Effect of operator variability on void formation in impressions made with an automixed addition silicone

This study examined voids produced in impressions of an automixed addition-reaction silicone. Two operators took the impressions using material dispensed from either intra-oral tips or an impression syringe. The material was also hand-mixed for comparison. There were no differences in the number of voids in the automixed material dispensed using the intra-oral tip or impression syringe. Automixing produced substantially fewer voids than hand-mixing. There was a significant difference in the number of voids in the impressions made by the two operators.

Defects in automixed addition silicone elastomers prepared by putty-wash impression technique

Voids presenting in impressions of five automixed addition silicone elastomers were investigated. Impressions were prepared with the putty-light body impression technique on stainless-steel cylinders with acrylic spacers. The number of voids was counted at a predetermined site on three separate days using a stereomicroscope at x7 magnification. Impression specimens of a hand-mixed addition silicone, and from hand-mixing of the automixed materials, were made for comparison. Express gave a significantly higher number of voids than other automixed materials, with President Jet having the lowest void count. Automixed materials generally produced impressions with significantly fewer voids than the hand-mixed material. Automixing was effective in reducing void defects in elastomeric impressions.

Relationship of viscosity to porosities in automixed elastomeric impressions

Porosities commonly presenting as voids have been recognized as an inherent problem in elastomeric impressions. Automixing of the impression has been found to be effective in reducing voids. The purpose of this study was to compare formation of voids in medium-viscosity and putty-wash materials in four automixed addition silicone elastomers. Impressions of a master model were made according to manufacturers' recommendations on manipulation of materials. Voids presenting on a predetermined surface were counted under a binocular microscope at a magnification factor of 7x. Results showed that Express exhibited a significantly higher number of voids than other materials in both categories. Putty-wash impressions generated significantly less voids than medium-viscosity impressions for all materials except Reprosil. The findings of this study suggested that putty-wash impressions produced significantly less porosities than medium-viscosity impressions and, consequently, offer better tear strength for impressions.