Comparison of bleaching effects when applied to white-spot lesions before or after resin infiltration: An in vitro study

Bleaching as a complement to fluoride-enhanced remineralization or resin infiltration in masking white spot lesions

OBJECTIVE

There are many suitable strategies for addressing caries, which is an ongoing worldwide problem. Although white spot lesions (WSLs) can be either remineralized naturally or treated with non- or micro-invasive strategies, their whitish and opaque appearance may persist. To evaluate the effects of tooth bleaching as a complement to fluoride-enhanced remineralization or resin infiltration in masking WSLs, as well as in enamel surface roughness relative to that of the adjacent enamel.

METHODOLOGY

Flattened rectangular bovine enamel fragments (6×3×~2.9 mm length, width and thickness) were divided into six groups (L/N, F/N, F.BL/BL, I/N, I.BL/BL, N/N; n=15). Treatments applied to the 3×3 mm left half included: L (Lesion) - WSL simulation with 50 mM acetate buffer, 96 hours, 37ºC; F (Fluoride) - WSL treatment with 2% NaF neutral gel, 1x/week, 8 weeks; I (Infiltration) - WSL treatment with H3PO4 37%/10 s; Icon®-Dry/30 s; Icon®-Infiltrant/3 min+1 min; N (Nothing) - sound enamel/control. Treatments applied to both halves after F and I included: BL (Bleaching) - Opalescence Boost 40%, 3×/20 min each; N (Nothing) - control. The differences in color (ΔE00, ΔL, Δa, Δb) and surface roughness (ΔRa) between the left and right halves were measured. Kruskal-Wallis/post-hoc tests were applied to ΔE00, ΔL, Δa and ΔRa, and 1-way ANOVA/Tukey tests to Δb (α=0.05).

RESULTS

The factor under study significantly influenced ΔE00 (p=0.0001), ΔL (p=0.0024), Δb (p=0.0015), and ΔRa (p<0.001), but not Δa (p=0.1592). Both fluoride-enhanced remineralization and resin infiltration were able to mask WSL, regardless of subsequent bleaching. However, when bleaching was performed, ΔE00 median values did not exceed the acceptability threshold for color difference. Only resin infiltration reduced ΔRa between WSL and the adjacent enamel.

CONCLUSIONS

Both remineralization and infiltration, particularly if complemented by bleaching, fostered satisfactory esthetic results. Only infiltration without bleaching led to really good results in surface roughness.

Effect of Bleaching on Resin-Infiltration-Masked Artificial White Spots In Vitro

Resin infiltration is an effective method to mask vestibular white spots. If needed, external bleaching is usually recommended before infiltration, whilst in clinical practice, this sequence may not always be feasible. This in vitro study evaluated the effect of bleaching after resin infiltration regarding surface roughness and color using bovine incisors. Unlike for the untreated specimens (control, n = 25), artificial caries lesions were created within the test group (n = 25) using a demineralization solution at 37 °C for five days (pH = 4.95). The lesions were subsequently infiltrated using a resin infiltrant (Icon, DMG, Hamburg, Germany), followed by polishing. Afterwards, all specimens were bleached with a 10% carbamide peroxide gel (Opalescence, Ultradent, South Jordan, UT, USA) for 8 h/day over a ten-day period. Between bleaching treatments, specimens were stored in an opaque container with moistened paper tissues at 37 °C. Surface roughness was measured using a profilometer, and color in the L*a*b* space was assessed spectrophotometrically before and after bleaching. Bleaching increased the L*-values of both infiltrated (mean ± SD; ΔL* = 3.52 ± 1.98) and untreated (control) specimens (ΔL* = 3.53 ± 2.30) without any significant difference between the groups (p = 0.983). Bleaching also induced a significant increase in the mean surface roughness of both infiltrated (p < 0.001) and untreated (p = 0.0134) teeth. In terms of clinical relevance; it can be concluded that bleaching resin-infiltrated enamel is as effective as bleaching sound enamel.

Aesthetic impact of resin infiltration and its mechanical effect on ceramic bonding for white spot lesions

BACKGROUND

Treating white spot lesions (WSLs) with resin infiltration alone may not be sufficient, raising questions about its compatibility with other treatments amid controversial or incomplete data. Therefore, this study aimed to assess the aesthetic feasibility of resin infiltration combined with bleaching, as well as its potential mechanical effect on ceramic bonding to WSLs.

METHODS

One hundred and fifty flat enamel surfaces of bovine incisors were prepared. Ninety specimens were deminerailized and randomly assigned to three groups(n = 30): post-bleaching resin infiltration (Bl-R), pre-bleaching resin infiltration (R-Bl), and only resin infiltration (R). Color, surface roughness and microhardness were assessed in immediate, thermocycling and pigmentation tests. The remaining sixty samples were randomly assigned to three groups (n = 20): control (Ctrl), bonding (Bo), pre-bonding resin infiltration (R-Bo). Shear bonding strength, failure mode, micro-leakage depth and interface morphology were evaluated after ceramic bonding. The Tukey test and analysis of variance (ANOVA) were used for statistical analysis.

RESULTS

For the effect of resin infiltration and bleaching on WSLs, the R-Bl group showed the worst chromic masking ability, with the highest |ΔL|, |Δa|, |Δb|, and ΔE values after treatment. Compared with those in the Bl-R group, the R-Bl and R groups showed significant time-dependent staining, which is possibly attributed to their surface roughness. For the effect of resin infiltration on the adhesive properties of WSLs, resin infiltration reduced the staining penetration depth of WSLs from 2393.54 ± 1118.86 μm to 188.46 ± 89.96 μm (P < 0.05) while reducing WSLs porosity in SEM observation.

CONCLUSIONS

Post-bleaching resin infiltration proved to be advantageous in the aesthetic treatment of WSLs. Resin infiltration did not compromise bonding strength but it did reduce microleakage and enhance marginal sealing. Overall, resin infiltration can effectively enhance the chromatic results of treated WSLs and prevent long-term bonding failure between ceramics and enamel. Based on these findings, the use of post-bleaching resin infiltration is recommended, and resin infiltration before ceramic bonding is deemed viable in clinical practice.