OBJECTIVETo explore the relationship between the spectrophotometric and visual methods in evaluating the color stability of denture base resin, and determine the threshold color difference of denture base resin in the spectrophotometric method.

METHODSTwo kinds of denture base resin were respectively fabricated into 33 specimens whose color differences varied from indistinguishable to obvious. Each of the specimens was assessed respectively by 30 human observers and a SP62 spectrophotometer. The results of visual assement were recorded as "indistinguishable change", "light change" or "severe change", while the spectrophotometric color differences (ΔE) were calculated. In each group, a logistic curve was explored to determine the relationship between the color difference (ΔE) and the ratio of "severe change".

RESULTSThe R squares of logistic curves were 0.93 and 0.94 respectively. The threshold color differences in the spectrophotometric method were 2.87 and 2.82 respectively.

CONCLUSIONSA high relevance between the spectrophotometric and visual methods in evaluating the color stability of denture base resin was found. The threshold color differences for different color denture base resins were similar.