Natural Enamel Caries: A Comparative Histological Study on Biochemical Volumes

Abstract

This study aimed to test the hypothesis that organic volume is the main variable for explaining the optical properties and predictive degree of diffusion of enamel histological points at zones of natural enamel caries (NEC; surface layer, SL, n = 30, and body of the lesion, BL, n = 58) and normal enamel (NE, n = 131). Molars with either NEC or NE were quantitatively analyzed regarding the mineral, organic and water volumes (considered as effective pore volume), opacity (predicted in 94% of cases by water volume in NEC), and water volume more easily available for diffusion, α_d (squared water volume divided by the nonmineral volume; related to permeability). NEC presented lower mineral volumes and higher organic volumes, effective pore volume and opacity than NE. External origin of organic volume in NEC was evidenced by an organic gradient decreasing from the surface inward (R² = –0.7), which was not detected in teeth with NE only; α_d values of the SL and NE were similar and both were lower (p < 0.0001) than that of the BL. Comparing the SL from both NEC and artificial enamel caries (AEC; published data; n = 71), with similar mineral volumes, against developing enamel (published data), AEC showed more effective pore volume (3 times higher), higher α_d and opacity than NEC mainly due to differences in organic volumes. Our results reasonably matched widely known features of NEC histological zones, and confirmed the organic volume as the main variable for explaining optical properties and α_d (related to permeability).

High Amount of Organic Matter during Caries Formation Reduces Remineralization and Resin Infiltration of Enamel Caries

“…The difference between the experimental and the predicted [Sousa et al, 2009] organic volumes for a given mineral volume -Δorganic -was calculated as before [Barbosa de Sousa et al, 2013]. The difference in the pore volume available for remineralization (Δremineralizable = experimental total water volume minus predicted total water volume) (with opposite sign to Δorganic) was the dependent variable of hypothesis 1.…”

“…Organic matter from the external environment is incorporated into enamel pores during caries initiation and progression [Bibby, 1971;Van Der Linden et al, 1987; Barbosa de Sousa et al, 2013]. For a given pore volume in enamel caries, the volumes available for remineralization and infiltration are inversely proportional to the organic pore volume [Barbosa de Sousa et al, 2013].…”

“…70% in the surface layer and 50% in the body of the lesion) in natural enamel caries (NEC) in humans [Barbosa de Sousa et al, 2013]. At the surface layer, the water pore volume in NEC was lower than in artificial subsurface enamel caries induced by an acid gel [Barbosa de Sousa et al, 2013].…”

“…70% in the surface layer and 50% in the body of the lesion) in natural enamel caries (NEC) in humans [Barbosa de Sousa et al, 2013]. At the surface layer, the water pore volume in NEC was lower than in artificial subsurface enamel caries induced by an acid gel [Barbosa de Sousa et al, 2013]. This is consistent with the deeper infiltration of resin infiltrants into artificial enamel caries lesions compared to NEC lesions [Meyer-Lueckel and Paris, 2008], and with the improved caries infiltrantion [Kielbassa et al, 2017] and remineralization [Robinson et al, 1990] in NEC after surface treatment with organic solvents.…”

“…This is consistent with the deeper infiltration of resin infiltrants into artificial enamel caries lesions compared to NEC lesions [Meyer-Lueckel and Paris, 2008], and with the improved caries infiltrantion [Kielbassa et al, 2017] and remineralization [Robinson et al, 1990] in NEC after surface treatment with organic solvents. Due to the inclusion of NEC lesions of unknown age [Barbosa de Sousa et al, 2013], it is not known whether the difference in water pore volume was a result of different amounts of organic matter in the external environment or in the caries induction time. Previously, induction of artificial enamel caries with increasing amounts of organic matter (albumin) in the demineralizing solution was shown to increase protein uptake into bovine artificial enamel caries' pores and reduce subsequent mineral loss in the lesions [Van Der Linden et al, 1987], but quantitative volumetric data at histological layers were not obtained.…”