Analysis of the thickness and structural homogeneity of the adhesive interface in composite resin and glass ionomer cement restorations of wedge-shaped non-carious cervical lesions

Relevance. Despite the high prevalence of wedge-shaped non-carious cervical lesions (NCCLs), treatment outcomes frequently remain unsatisfactory, with dentin hypersensitivity, poor esthetics, chipping, and restoration loss. These limitations highlight the need to investigate bonding to the affected dental hard tissues. The available literature lacks laboratory data directly comparing the dentin interfaces formed by composite resin used with the most widely employed fifth- and seventh-generation adhesive systems and by glass ionomer cement (GIC) in wedge-shaped NCCLs. This knowledge gap prompted the present study. Objective. To compare the thickness and structural homogeneity of the material–dentin interface formed with a fifth-generation (two-step etch-and-rinse) adhesive, a seventh-generation (one-step self-etch) adhesive, and GIC in wedge-shaped NCCLs.

Materials and methods. Forty-eight extracted permanent teeth with wedge-shaped NCCLs were allocated to three groups (n = 16 per group): Group 1, restored using a fifth-generation (two-step etch-and-rinse) adhesive; Group 2, restored using a seventh-generation (one-step self-etch) adhesive; and Group 3, restored with GIC. Histological ground sections were prepared and examined by polarized light microscopy at ×200 magnification to assess interfacial thickness and morphology. Descriptive statistics included the mean, standard error of the mean (SEM), and coefficient of variation (CV); between-group differences were assessed using Student’s t test.

Results. Interfacial thickness (mean ± SEM) was 4.26 ± 0.04 μm in Group 1 (CV = 14.6%), 2.20 ± 0.01 μm in Group 2 (CV = 7.21%), and 0.730 ± 0.003 μm in Group 3 (CV = 6.29%). Intergroup differences were statistically significant (p < 0.0001). Group 1 showed poorly defined hybrid-layer boundaries and focal areas of structural heterogeneity. Group 2 showed more uniform layer thickness, with only isolated areas of poorly defined margins. No conventional hybrid layer was observed in Group 3; instead, a uniform GIC–dentin interface was present, without penetration into the dentinal tubules.

Conclusion. The fifth-generation adhesive system produced the thickest hybrid layer; however, it showed greater variation in layer thickness and less consistent interfacial morphology. The seventh-generation adhesive system produced a thinner hybrid layer with more consistent thickness and morphology. In the GIC group, no conventional hybrid layer was formed; however, GIC produced the thinnest and most morphologically uniform interface.

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