Effect of pH on tooth discoloration using food colorant in-vitro

Objective: Evaluate the effect of acidic, neutral and alkaline food colorant medium (FCM) on tooth discoloration in-vitro.  It was hypothesized acidic FCM would cause more discoloration (extrinsic and intrinsic) than neutral or alkaline FCM.

Methods:  Treatment (T, n=24) and control (C, n=24) sterile, hydrated human molars were prepared in individual, impervious holders and their color measured (Pre-test) using a non-contact spectroradiometer system.  Specimens were randomly assigned to and immersed in one of 3 buffer solutions (pH2, pH7 or pH12).  Red food color (Red40) was added to the T buffer solutions at 0.025%.  Immersed samples were incubated for four hours at 37ºC.  Colors were also measured after immersion/incubation (Post-test) and again after subsequent two-minutes of polish using a plain-pumice slurry with a slow-speed handpiece (Post-polish).  Differences in CIE a* (redness parameter) were analyzed by Repeated Measures ANOVA with Bonferroni-corrected t-tests for the pairwise comparisons of interest.

Results:  Mean Δa*(±SD) posttest to pretest

Group	pH2(n=8)	pH7(n=8)	pH12(n=8)
Control	0.322 (±0.374)a	-0.158(±0.215)	-0.136(±0.185)
Treatment	5.490(±4.632) a,b,c	0.455(±0.325)b	0.088(±0.188)c

^ap<0.001,^bp<0.001,^cp<0.001

Mean Δa*(±SD) post-polish to pretest

Group	pH2(n=8)	pH7(n=8)	pH12(n=8)
Control	-0.261(±0.346)a	-0.033(±0.125)	-0.224(±0.90)
Treatment	2.393(±2.737) a,b,c	0.241(±0.192)b	-0.039(±0.163)c

^ap<0.001,^bp<0.003,^cp<0.001

Mean Δa*(±SD) post-polish to posttest

Group	pH2(n=8)	pH7(n=8)	pH12(n=8)
Control	-0.583(±0.398)a	0.125(±0.241)	-0.088(±0.201)
Treatment	-3.097(±2.539) a,b,c	-0.214(±0.286)b	-0.127(±0.150)c

 ^ap<0.001,^bp<0.001,^cp<0.001

Conclusions: A significant change in color was not observed between C and T for neutral and alkaline FCM.  However, acidic FCM caused tooth discoloration posttest to pretest, post-polish to pretest and post-polish to posttest compared to C and T (neutral and alkaline).  Discoloration in acidic FCM represented both extrinsic (mean difference between post-polish and posttest) and intrinsic (mean difference between post-polish and pretest) stain.  Although food/beverage-pigments are associated with extrinsic stain, these preliminary results suggest that degree and type of stain are influenced by pH.