Cecilia C.S. Dong

Ex vivo detection and characterization of early dental caries by optical coherence tomography and Raman spectroscopy.

Early dental caries detection will facilitate implementation of nonsurgical methods for arresting caries progression and promoting tooth remineralization. We present a method that combines optical coherence tomography (OCT) and Raman spectroscopy to provide morphological information and biochemical specificity for detecting and characterizing incipient carious lesions found in extracted human teeth. OCT imaging of tooth samples demonstrated increased light backscattering intensity at sites of carious lesions as compared to the sound enamel. The observed lesion depth on an OCT image was approximately 290 microm matching those previously documented for incipient caries. Using Raman microspectroscopy and fiber-optic-based Raman spectroscopy to characterize the caries further, spectral changes were observed in PO4 (3-) vibrations arising from hydroxyapatite of mineralized tooth tissue. Examination of various ratios of PO4 (3-) nu2, nu3, nu4 vibrations against the nu1 vibration showed consistent increases in carious lesions compared to sound enamel. The changes were attributed to demineralization-induced alterations of enamel crystallite morphology and/or orientation. OCT imaging is useful for screening carious sites and determining lesion depth, with Raman spectroscopy providing biochemical confirmation of caries. The combination has potential for development into a new fiber-optic diagnostic tool enabling dentists to identify early caries lesions with greater sensitivity and specificity.

Detection of early dental caries using polarized Raman spectroscopy

A new technique based on polarized Raman spectroscopy is demonstrated for detecting early dental caries on extracted human teeth. Sound tooth enamel exhibited strong Raman polarization anisotropy whereas early caries consistently showed a lower degree of Raman polarization anisotropy. In particular, for sound enamel, the Raman peak arising from the symmetric nu1 vibration of PO(4) (3-) at 959 cm(-1) is strongly polarized. This is in contrast to the spectra of carious lesions that displayed weaker polarization dependence at 959 cm(-1). Such difference in the degree of Raman polarization anisotropy allows for discrimination between early dental caries and sound enamel.

The flow rate and electrolyte composition of whole saliva elicited by the use of sucrose-containing and sugar-free chewing-gums

On two occasions, 12 adults collected unstimulated saliva and then eight samples of saliva over a 20-min period while chewing 3 g of either Wrigleys Spearmint sucrose-containing gum (SCG) or sugar-free gum (SFG) at 70 chews/min. The flow rates peaked initially, then fell with duration of stimulation. With the SFG they were slightly but significantly higher than with the SCG after 4 min of chewing. The sum of the concentrations of cations minus the sum of the concentrations of anions was not significantly different from zero for saliva elicited by the SCG. However, for unstimulated saliva and that elicited by SFG, there was a slight positive anion balance. A second series of saliva collections with SCG and SFG was made by the same 12 participants and these samples were analysed for lactate. For these collections the flow rates with SCG were not significantly less than with the SFG. The lactate concentration in saliva elicited by SCG peaked at 1.82 mmol/l in samples collected over 8-15 min, whereas samples of saliva elicited by SFG had a mean lactate concentration of 0.21 mmol/l. Of the lactate formed during the metabolism of sucrose by the oral bacteria, only 2% or less appeared to be derived from the metabolism of micro-organisms free in saliva, the balance presumably being formed in dental plaque and entering the saliva by diffusion. All saliva samples were supersaturated with respect to hydroxyapatite but stimulated saliva was significantly more supersaturated than unstimulated saliva.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of chewing frequency and duration of gum chewing on salivary flow rate and sucrose concentration

On ten separate occasions, unstimulated saliva was collected from 12 adults and then eight samples of saliva over a 20-min period while chewing, in random order, 3 g of either Wrigleys Spearmint chewing-gum or gum-base at frequencies of 35, 50, 70, 90, or 130 chews/min. With both stimuli, flow rates peaked in the first minute of stimulation and then fell with time. A repeated-measures analysis of variance showed that for both the gum and the gum-base, flow rates were independent of chewing frequency, except during the first minute with the chewing-gum. The gum elicited a significantly higher flow rate over the first 4 min of chewing, while the base elicited a significantly higher flow rate over the 8-20-min period of chewing. The sucrose concentration in saliva was also independent of chewing frequency. The salivary sucrose concentration peaked during the second minute of chewing (mean +/- SE = 424.7 +/- 20.0 mM) and the concentration then fell progressively with time. However, sucrose was still being released into saliva during the 15-20 min period of chewing (12.6 +/- 0.8 mM). Gum-base which had been chewed without access to saliva was softer than unchewed base but showed no change in filler content or a reduction in the average molecular weight. The decrease in hardness of the chewed gum-base may have resulted from improved mixing of heterogeneous phases and increased dispersion of plasticizing agents.

Anomalous mandibular premolars: a mandibular first premolar with three roots and a mandibular second premolar with a C-shaped canal system

AIM To describe unusual variations in the root morphology and root canal systems of mandibular first and second premolar teeth extracted for orthodontic reasons. SUMMARY Normally mandibular first and second premolar teeth have single roots with single canals. A 15-year-old patient presented for orthodontic treatment and two mandibular premolar teeth were examined post-extraction. The mandibular first premolar exhibited three distinct, separate roots and the mandibular second premolar exhibited a C-shaped root canal system. The coronal morphology of each of the mandibular premolars revealed dimensions and anatomy within normal limits. The incidence of a three-rooted mandibular first premolar is approximately 0.2%. KEY LEARNING POINTS * Thorough clinical and radiographic interpretation is important in recognizing anomalous root and root canal systems. * The most common forms of root and canal systems and its aberrations must be understood to realize variations from normal do occur. * Successful root canal treatment requires an accurate diagnosis of the root canal system using all available aids. * Value of microcomputed tomography in the study of anatomy ex vivo and cone-beam tomography in clinical endodontics of complex premolar cases is increasing.

Early dental caries detection using a fibre-optic coupled polarization-resolved Raman spectroscopic system

A new fibre-optic coupled polarization-resolved Raman spectroscopic system was developed for simultaneous collection of orthogonally polarized Raman spectra in a single measurement. An application of detecting incipient dental caries based on changes observed in Raman polarization anisotropy was also demonstrated using the developed fibre-optic Raman spectroscopic system. The predicted reduction of polarization anisotropy in the Raman spectra of caries lesions was observed and the results were consistent with those reported previously with Raman microspectroscopy. The capability of simultaneous collection of parallel- and cross-polarized Raman spectra of tooth enamel in a single measurement and the improved laser excitation delivery through fibre-optics demonstrated in this new design illustrates its future clinical potential.

Determining the Effect of Calculus, Hypocalcification, and Stain on Using Optical Coherence Tomography and Polarized Raman Spectroscopy for Detecting White Spot Lesions

Optical coherence tomography (OCT) and polarized Raman spectroscopy (PRS) have been shown as useful methods for distinguishing sound enamel from carious lesions ex vivo. However, factors in the oral environment such as calculus, hypocalcification, and stain could lead to false-positive results. OCT and PRS were used to investigate extracted human teeth clinically examined for sound enamel, white spot lesion (WSL), calculus, hypocalcification, and stain to determine whether these factors would confound WSL detection with these optical methods. Results indicate that OCT allowed differentiating caries from sound enamel, hypocalcification, and stain, with calculus deposits recognizable on OCT images. ANOVA and post-hoc unequal N HSD analyses to compare the mean Raman depolarization ratios from the various groups showed that the mean values were statistically significant at P < .05, except for several comparison pairs. With the current PRS analysis method, the mean depolarization ratios of stained enamel and caries are not significantly different due to the sloping background in the stained enamel spectra. Overall, calculus and hypocalcification are not confounding factors affecting WSL detection using OCT and PRS. Stain does not influence WSL detection with OCT. Improved PRS analysis methods are needed to differentiate carious from stained enamel.

OCT of early dental caries: a comparative study with histology and Raman spectroscopy

Early dental caries result from destruction of the tooths outer mineral matrix by acid-forming bacteria found in dental plaques. Early caries begin as surface disruptions where minerals are leached from the teeth resulting in regions of decreased mineral matrix integrity. Visually, these early carious regions appear as white spots due to the higher backscattering of incident light. With age these areas may become stained by organic compounds. Optical coherence tomography (OCT) examination of human teeth demonstrates a difference in penetration depth of the OCT signal into the carious region in comparison with sound enamel. However, while OCT demonstrates a structural difference in the enamel in the region of the caries, this technique provides little insight into the source of this difference. Raman spectroscopy provides biochemical measures derived from hydroxyapatite within the enamel as well as information on the crystallinity of the enamel matrix. The differences in the biochemical and morphological features of early caries and intact sound enamel are compared. Histological thin sections confirm the observations by OCT morphological imaging while Raman spectroscopy allows for biochemical identification of carious regions by a non-destructive method. Visual examination and conventional radiographic imaging of the intact tooth are used in clinical assessment prior to optical measurements. The combination of OCT, Raman spectroscopy and thin section histology aid in determining the changes that give rise to the visual white spot lesions.

THE EFFECTS OF BLINDFOLDING AND BLINDNESS ON THE UNSTIMULATED AND CHEWING-GUM-STIMULATED FLOW RATES OF WHOLE SALIVA

In the early 1970s, Shannon and his colleagues reported that blindfolding caused a reduction in the flow rate of unstimulated and stimulated parotid and submandibular saliva. A study in three parts was now made to investigate the effects of blindfolding or blindness on the flow rate of whole saliva. For the first study, unstimulated whole saliva (UWS) was collected for 5 min from 34 individuals and then eight samples of chewing-gum-stimulated whole saliva (SWS) over a 20-min period. This was carried out on four separate occasions, on two of which, in random order, the individuals collected the saliva immediately after being blindfolded. For the second study, 33 of the individuals repeated the saliva collection protocol on two occasions, with and without blindfolding, but with an accommodation period of 20 min after blindfolding before beginning collection of UWS and with only three samples of SWS being collected over a 4-min period. The flow rate of UWS while blindfolded was significantly (p < 0.0001) reduced (to 64 and 71% of the flow rate while sighted, in the first and second studies, respectively), as was the flow rate of SWS (to 81-86%, p < 0.0001; and 91-95%, p = 0.0014, respectively). For the third study, UWS and SWS were collected from 24 blind individuals, ranging in age from 13-73 years, and from 24 age- and gender-matched controls. The flow rates of UWS and SWS were not significantly different in the blind participants and controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Ex vivo imaging of early dental caries within the interproximal space

Optical coherence tomography (OCT) is emerging as a technology that can potentially be used for the detection and monitoring of early dental enamel caries since it can provide high-resolution depth imaging of early lesions. To date, most caries detection optical technologies are well suited for examining caries at facial, lingual, incisal and occlusal surfaces. The approximal surfaces between adjacent teeth are difficult to examine due to lack of visual access and limited space for these new caries detection tools. Using a catheter-style probe developed at the NRC-Industrial Materials Institute, the probe was inserted into the interproximal space to examine the approximal surfaces with OCT imaging at 1310 nm. The probe was rotated continuously and translated axially to generate depth images in a spiral fashion. The probe was used in a mock tooth arch model consisting of extracted human teeth mounted with dental rope wax in their anatomically correct positions. With this ex vivo model, the probe provided images of the approximal surfaces revealing morphological structural details, regions of calculus, and especially regions of early dental caries (white spot lesions). Results were compared with those obtained from OCT imaging of individual samples where the approximal surfaces of extracted teeth are accessible on a lab-bench. Issues regarding access, regions of interest, and factors to be considered in an in vivo setting will be discussed. Future studies are aimed at using the probe in vivo with patient volunteers.