title: Influence of reduced air pressure methods on dye penetration in standardized voids.
abstract: OBJECTIVE
  The objective of this study was to evaluate the influence of the moment when reduced pressure is applied on dye penetration patterns.
  
  
  METHODS
  Nine hundred and sixty glass capillary tubes of different inner diameter (0.3 mm and 0.8 mm), divided into 48 groups, were submerged into dye in 3 different positions (horizontally, opening upwards, and opening downwards) under different vacuum conditions (passive, 5 kPa, 35 kPa, 70 kPa reduced pressure). When reduced pressure was applied half of the groups were submerged into dye before and half of the groups after the application of reduced pressure. Linear dye penetration was measured. Univariate analysis was performed with Mann-Whitney U test and Kruskal-Wallis test to select variables to be included in the regression model. A multiple logistic regression analysis with backward elimination was performed to assess the influence of different covariates on linear dye penetration.
  
  
  RESULTS
  The multivariate linear regression showed that the moment of vacuuming had the greatest positive effect on linear dye penetration value (beta = 10.6, P < .0001). Also the level of pressure reduction had a positive effect on the outcome variable (beta = 0.2, P < .0001) while the vertical positioning of the tubes has negatively affected the outcome variable both for the open end upside (beta = -1.01, P = .024) and the open end downside (beta = -1.05, P = .019). Diameter of the tubes (P = .442) and immersion time (P = .727) had no effect on the outcome of linear dye penetration.
  
  
  CONCLUSIONS
  Even minimum air pressure reduction applied before immersion of the specimens allowed the dye to extensively penetrate the voids.
authors.affiliation: Department of Endodontics, Catholic University of Sacred Heart, Rome, Italy. gplotino@fastwebnet.it
authors.forename: Gianluca
authors.initials: G
authors.lastname: Plotino
authors.forename: Nicola M
authors.initials: NM
authors.lastname: Grande
authors.forename: Nicola
authors.initials: N
authors.lastname: Manzulli
authors.forename: Giacomina
authors.initials: G
authors.lastname: Chiaradia
authors.forename: Giuseppe
authors.initials: G
authors.lastname: La Torre
authors.forename: Francesco
authors.initials: F
authors.lastname: Somma
mesh_terms: D000399:Air Pressure; D004396:Coloring Agents; D003763:Dental Leakage / Q000175:diagnosis*; D012044:Regression Analysis; D012212:Rheology; D018709:Statistics, Nonparametric; D014618:Vacuum
chemical_list: D004396:Coloring Agents