Air-Bubble Entrapment as Affected by Investment Technique, Pattern Angle, and Use of a Surface Tension-Reduction Agent

The effect of five dental investing techniques, three angles formed between adjoining internal pattern surfaces, and the use of a surface tension-reducing agent on air-bubble entrapment during investing were assessed. One investing technique, which mechanically mixed the investment under vacuum, invested the pattern without vacuum, then subjected the setting investment to .275 mPa of air pressure, was found to produce significantly fewer air bubbles than the other four techniques (P = 0.0096, Student's t test). The volume of the air bubbles was not found to be significantly affected by the different investing techniques, but the angle between adjoining internal pattern surfaces indicated that the more acute the angle, the larger the volume of the trapped air bubbles. When a surface tension reducer was used on the surface of patterns, pattern angles of 90 degrees had fewer trapped air bubbles than those produced with more acute tooth preparation angles, but the surface tension reducer agent had no significant effect on bubble volume. The use of a surface tension-reducing agent on the pattern surface prior to investing significantly reduced air bubble numbers (P = .054).