The relationship of dehydration rate and transparent surface layer thickness for coronal lesions on extracted teeth

Abstract

Transparent remineralized surface zones found on natural caries lesions may reduce the permeability to water and plaque generated acids. Near-IR (NIR) reflectance imaging coupled with dehydration can be used to measure changes in the fluid permeability of lesions in enamel and dentin. Previous work demonstrated a negative association between the surface zone thickness and the rate of dehydration in simulated enamel lesions. In this study, the rates of dehydration and thickness of transparent surface layer of coronal lesions of extracted teeth were measured and correlated. Reflectance imaging at NIR wavelengths from 1695–1750 nm, which coincides with higher water absorption and manifests the greatest sensitivity to contrast changes during dehydration measurements, was used to image these enamel lesions. The remineralized surface layer thickness was determined using optical coherence tomography (OCT).

Assessment of the activity of secondary caries lesions with short-wavelength infrared, thermal, and optical coherence tomographic imaging

“…LD did not correlate with either type of dehydration measurement, which was not surprising and has been observed previously. 9 , 10 , 21 It is likely that the changes in temperature and reflectivity were limited to areas of the lesion that are near the lesion surface and deeper lesion areas have little influence on the dehydration dynamics. In addition, water loss for deeper lesions may require a longer duration for dehydration than was performed here.…”

“…Such transparent surface zones have been clearly resolved in OCT images of lesions both in vitro and in vivo on coronal and root surfaces. 9,10,27 The purpose of this study is to develop methods to assess secondary lesion activity using SWIR, thermal imaging, and OCT. We hypothesize that lesion characteristics measured with OCT such as lesion depth (LD), integrated reflectivity (ΔR), and thickness of the formation of the highly mineralized TSL correlate with the lesion permeability (fluid loss rate) and activity measured with SWIR and thermal imaging during dehydration with forced air. In this study, OCT and micro-computed tomography (MicroCT) measurements of lesion structure, depth, and severity were correlated with fluid loss rates measured with SWIR reflectance and thermal imaging.…”

“…A key indicator that lesions have become arrested due to remineralization is the formation of a highly mineralized transparent surface layer (TSL) on the outer layers of the lesions. 6 – 14 The presence of such a layer greatly inhibits the diffusion of fluids in and out of the lesion. Conversely, active lesions lack such a layer and possess a much higher permeability.…”

“…Several studies have demonstrated the utility of optical coherence tomography (OCT) for acquiring high-resolution images of lesion structure and activity in vivo . 10 When used at SWIR wavelengths, OCT is useful in determining whether lesions are active and expanding, partially arrested and undergoing remineralization, or fully arrested and remineralized. 6 – 8 , 28 , 29 This imaging method resolves the reflectivity of each layer of sound and lesion structures, as well as restorative materials.…”

“…Such transparent surface zones have been clearly resolved in OCT images of lesions both in vitro and in vivo on coronal and root surfaces. 9 , 10 , 27 …”