Bonding to Ground versus Unground Enamel in Fluorosed Teeth

Hypermineralized surface and hypomineralized subsurface layers of fluorosed enamel might affect the bonding performance of adhesives. Objectives: To determine the micro-tensile bond strength (µTBS) of adhesives to ground versus unground enamel in fluorosed teeth and the effect of fluorosis on enamel µTBS. Methods: Human molar teeth were classified using the Thylstrup and Fejerskov index (TFI) by two investigators (Cohen's kappa statistic of 0.72). Fluorosed teeth (TFI=5) obtained from Isparta, an endemic fluorosis area of Turkey and control teeth (TFI=0) obtained from Leuven-Belgium were used. Using a depth marking diamond bur (834, Komet), 0.3mm of enamel was removed from mid-buccal and mid-palatal/lingual surfaces of the teeth, whereas the area adjacent to the ground area was left unprepared. A two-step self-etch (Clearfil Protect Bond, Kuraray) or a three-step etch&rinse adhesive (Optibond FL, Kerr) was applied and a composite resin (Z100, 3M ESPE) built-up was made. Rectangular micro-specimens with a cross-sectional area of 0.45 ± 0.07mm² were prepared and tested in tensile. Results:

µTBS (MPa±SD) (n)	TFI=5/Ground	TFI=5/Unground	TFI=0/Ground	TFI=0/Unground
Clearfil Protect Bond	45.0±12.4a (41)	15.8±15.2c (34)	40.8±10.9a (37)	27.1±14.5b (41)
Optibond FL	42.2±14.0a (20)	27.2±19.7b,c (30)	50.5±12.3a (26)	35.5±21.4a,b (15)

Same superscript letters indicate no statistical difference (Two-way ANOVA and Tukey's HSD, p>0.05), pre-testing failures were included as 0MPa.  

Lightmicroscopic/Fe-SEM fracture analysis revealed that most specimens failed mixed (interfacial and/or within resin) in all groups. Conclusions: Preparation of enamel improved the resin-enamel bond strength in fluorosed teeth (p<0.0001). Bondig effectiveness to unground enamel was lower in fluorosed teeth than in control teeth for the self-etch adhesive tested (p=0.0032).  

This study was supported by IADR.CED Visiting Scholar 2004.