Effect of different fluoridation regimes on the microhardness of bleached enamel.
OBJECTIVE
This in vitro study evaluated the effects of toothpaste fluoridation and toothpaste plus gel fluoridation and influence of the time period of fluoride gel application on the microhardness of bleached enamel.


METHODS
Ninety bovine enamel samples were distributed among nine groups (A-I), each having 10 samples. Half of each surface was bleached with 10% carbamide peroxide gel (8 hours/daily) for 14 days, while the remaining surface was not bleached and served as the control. Groups A-H were fluoridated with toothpaste twice daily throughout the experiment (42 days) and assigned to fluoride gel treatment during the pre-bleaching period (14 days), during the bleaching period and/or during the post-bleaching period (14 days): A: prior, B: during, C: post, D: prior+during, E: during+post, F: prior+post, G: prior+during+post, H: no gel. Group I was neither fluoridated by toothpaste nor gel. The Knoop microhardness (KHN) of each specimen was determined at baseline, after pre-bleaching (day 14), after bleaching (day 28) and after post-bleaching (day 42). Statistical analysis of the percentage of change at baseline KHN was performed by ANOVA and t-test (p < 0.05).


RESULTS
Bleaching led to a significant decrease of KHN in Group I (unfluoridated) compared to Groups A-H, where microhardness did not fall below baseline values. Fluoridation treatment in Groups A-H increased microhardness in bleached and unbleached samples, but additional supplementation of fluoride gel in Groups A-G was not superior to toothpaste fluoridation only (H). After the post-bleaching period, the microhardness of the bleached and unbleached surfaces was not significantly different in Groups A-H.


CONCLUSIONS
Regular toothpaste fluoridation prevents microhardness loss due to bleaching treatment in vitro. The additional supplementation of fluoride gel did not enhance the beneficial effect of toothpaste fluoridation, and microhardness was not influenced by the time period of gel fluoridation.
Clinic for Preventive Dentistry, Periodontology and Cariology, University of Zürich, Zürich, Switzerland. annette.wiegand@zzmk.unizh.ch
Annette
A
Wiegand
Monika
M
Schreier
Thomas
T
Attin
D000818:Animals; D002327:Cariostatic Agents / Q000008:administration & dosage*; D002417:Cattle; D003743:Dental Enamel / Q000737:chemistry / Q000187:drug effects*; D005459:Fluorides / Q000008:administration & dosage*; D006244:Hardness / Q000187:drug effects; D014073:Tooth Bleaching / Q000009:adverse effects; D014100:Toothpastes / Q000008:administration & dosage* / Q000737:chemistry
D002327:Cariostatic Agents; D014100:Toothpastes; D005459:Fluorides