Analysis of cariogenic biofilms by using a swept-source optical coherence tomography in vitro.

OBJECTIVE: The objective was to measure the thickness of Streptococcus mutans (S. mutans) biofilms forming in an oral biofilm reactor (OBR) by using a noninvasive swept-source optical coherence tomography (SS-OCT) system at every 4 h time interval until 20 h and analyze the correlations with the amounts of biofilms. METHODS: S. mutans biofilms were formed on square-shaped bovine enamel blocks inside an OBR. Biofilms were analyzed at every 4 h stage (4 h, 8 h, 12 h, 16 h and 20 h) using a SS-OCT system and a laser scanning confocal microscope (LSCM). The amounts of biofilms were measured at each stage by separating the water insoluble glucan (WIG) and bacterial cells. Co-relationships between the SS-OCT measured biofilm thickness and the amounts of adhered biofilms were analyzed. RESULTS: The thickness of biofilms detected on SS-OCT images at 4 h stage was 0.059 ± 0.029 (Av ± SD) mm which increased time-dependently in a linear fashion after 8 h stage and reached to 0.435 ± 0.159 mm at 20 h stage and the correlation coefficient was about 0.89. The amounts of biofilms; bacterial optical density (OD) and WIG concentration increased time-dependently were 0.035 ± 0.008 / mm2 and 10.328 ± 2.492 µg/ mm2 respectively at 20 h stage. Correlation coefficients of 0.66 between 'the amounts of bacteria' and 'biofilm thickness on OCT' and 0.67 between 'the amounts of WIG' and 'biofilm thickness on OCT' were obtained, suggesting that there was a relatively positive correlation between them. CONCLUSION: The SS-OCT can be a useful tool to measure time-dependent growth of biofilms. Further studies are needed in order to assess biofilms using SS-OCT more accurately.

Optimal Surface Pre-Reacted Glass Filler Ratio in a Dental Varnish Effective for Inhibition of Biofilm-Induced Root Dentin Demineralization.

A unique type of dental varnish (DV) containing surface pre-reacted glass (S-PRG) fillers of different concentrations was evaluated to determine the unpresented optimal ratio for inhibiting root dentin bio-demineralization. S-PRG DVs (10% to 40%)­10%-S, 20%-S, 30%-S, and 40%-S­were applied to bovine root dentin blocks and compared with controls­0%-f (no S-PRG) and 5%-NaF (5%-NaF). The Streptococcus mutans biofilm challenge was executed inside and outside an oral biofilm reactor for 7 days. The specimens were examined using a confocal laser scanning microscope and swept-source optical coherence tomography. Furthermore, they were observed using a scanning electron microscope and analyzed using energy-dispersive X-ray spectroscopy. The roughness (SzJIS) due to leaching of DV materials and demineralization depth were significantly less in the S-PRG groups than the control groups (p < 0.05). Complete or partially plugged dentinal tubules (DTs) were observed in 20%-S, 30%-S, and 40%-S, while wide-open DTs were observed more in controls. Cylindrical tags were present in groups containing more than 20% S-PRG. F, Na, Al, and Sr were detected in a higher percentile ratio in the 20%-S, 30%-S, and 40%-S groups compared to 0%-f and 10%-S. Nonetheless, it is suggested that incorporating 20% to 30% S-PRG fillers in DVs would be effective enough as an anti-demineralization coating, together with supplementing minerals; further evaluation is required to validate these findings.

Evaluation of the cariogenic potential of a probiotic candidate strain Lactobacillus gasseri YIT 12321.

OBJECTIVE: This study was designed to evaluate the cariogenic potential of Lactobacillus gasseri YIT 12321. DESIGN: L. gasseri YIT 12321 was isolated from the human oral cavity as a probiotic candidate strain. Three types of experimental biofilm formations on bovine enamel specimens were assessed using Streptococcus sobrinus ATCC 33478, L. gasseri YIT 12321, and a co-culture of S. sobrinus and L. gasseri YIT 12321 in vitro. L. gasseri YIT 12321 was analyzed for its ability to utilize seven carbohydrates. L. gasseri YIT 12321 was cultured in tryptic soy broth without dextrose and containing a test carbohydrate at 37 °C for 16 h. RESULTS: The decrease in pH in the region under the biofilm produced by L. gasseri YIT 12321 was unusually slow, and the pH was maintained above 5.5 for 16 h. The amount of biofilm and the reduction in enamel hardness were minimal in the L. gasseri YIT 12321 group among the three experimental groups. The amount of co-culture-derived biofilms was less than that of S. sobrinus biofilms. When S. sobrinus was grown using sucrose, the pH decreased to 3.98. In contrast, L. gasseri YIT 12321 cultures maintained the pH above the critical pH for dentin demineralization. CONCLUSIONS: L. gasseri YIT 12321 is suggested to have a low cariogenic potential. The application of this strain as a probiotic may contribute to oral safety.

Anti-Demineralization Effects of Dental Adhesive-Composites on Enamel-Root Dentin Junction.

Oral biofilm reactor (OBR) and pH cycling (pHC) artificial caries model were employed to evaluate the anti-demineralization effects of four composite filling systems on enamel-root dentin junction. Sixty-four enamel-root dentin blocks (6 mm × 6 mm × 2 mm) each with a cylindrical cavity were randomly assigned to the pHC and OBR group, then four subgroups (n = 8) and filled with either the Beautifil II (BEF, SPRG-filler-containing) or Estelite (EST) composite after the adhesive (either Single Bond Universal (SBU) or FL Bond II (FL, SPRG-filler-containing)). The demineralization lesions of filling interface were examined by micro-computerized tomography (µCT) and swept-source-optical coherence tomography (SS-OCT). According to the degree of interface damage, the caries lesions were sorted into four types: Type A and B (no attachment loss); Type C and D (attachment loss). EST/SBU showed the worst demineralization lesion and attachment loss (100% Type D), while BEF/FL exhibited the shallowest lesion depth (p < 0.05, 145 ± 45 µm on enamel, 275 ± 35 µm on root dentin) and no attachment loss (75% Type A and 25% Type B). Using FL adhesive alone does not effectively reduce enamel demineralization. BEF plays a leading role in acid resistance. The combination of BEF and FL showed a cumulative synergistic effect on anti-demineralization.

Tetracycline, an Appropriate Reagent for Measuring Bone-Formation Activity in the Murine Model of the Streptococcus mutans-Induced Bone Loss.

Tetracycline is used as a fluorescent reagent to measure bone formation activity in bone histomorphometric analyses. However, there is a possibility to lead a different conclusion when it is used in a bacteria-infected murine model since the tetracycline is considered to work as an antibiotic reagent. There are non-antibiotic fluorescent reagents such as alizarin and calcein for measuring bone formation activity. The purpose of this study was to clarify whether tetracycline could be an appropriate reagent to measure bone formation activity in a murine bacterial model in the same way as a non-antibiotic fluorescent reagent. We used Streptococcus mutans (S. mutans), a normal inhabitant in the oral cavity and tetracycline-sensitive bacteria, for inducing the bacterial model. The murine bacterial model was generated by intravenously inoculating S. mutans to the tail vein, followed immediately by the injection of the first fluorescent reagent, and the second one was injected 2 days prior to euthanization. After one day of inoculation with S. mutans, the subcutaneously injected alizarin had a similar colony count derived from the liver and the bone marrow tissue compared to the phosphate buffered saline (PBS)-injected control group. On the other hand, subcutaneous injection of tetracycline led to a significantly lower colony count from the liver compared to alizarin- or calcein-injected group. However, on day seven, after S. mutans intravenous injections, bone mineral density of distal femurs was significantly reduced by the bacteria inoculation regardless of which fluorescent reagents were injected subcutaneously. Finally, S. mutans inoculation reduced bone-formation-activity indices in both the tetracycline-alizarin double-injected mice and the calcein-alizarin double-injected mice. These results suggested that a one-time injection of tetracycline did not affect bone formation indices in the S. mutans-induced bone loss model. Tetracycline could be used for measuring bone formation activity in the same way as non-antibiotic fluorescent reagent such as calcein and alizarin, even in a tetracycline-sensitive bacterium-infected model.

Effect of advanced periodontal self-care in patients with early-stage periodontal diseases on endothelial function: An open-label, randomized controlled trial.

Although a significant association between periodontal disease and atherosclerotic cardiovascular disease has been reported, their cause-to-effect relationship remains controversial. This randomized controlled clinical trial aimed to investigate the effect of advanced self-care on atherosclerotic cardiovascular disease-related vascular function markers flow-mediated brachial artery dilatation (FMD) and serum asymmetric dimethylarginine (ADMA) level in patients with early-stage periodontal disease. The study was designed as a parallel group, 3-month follow-up, open-label, randomized controlled trial. The control group received standard care for periodontal diseases, whereas the test group additionally applied disinfectant using a custom-fabricated prescription tray for advanced self-care twice a day. Overall, 110 patients provided data for FMD and serum ADMA level. No significant improvements in FMD were observed in the control (mean increase, -0.1%; 95% confidence interval [CI], -1.0-0.8; P = 0.805) or test (mean increase, -0.3%; 95% CI, -1.1-0.4; P = 0.398) group. No significant changes in serum ADMA levels were observed (mean reduction, 0.01 µmol/L; 95% CI, -0.00-0.02; P = 0.366 and mean reduction, 0.00 µmol/L; 95% CI, -0.01-0.01; P = 0.349, respectively). No significant between-group differences were found in FMD (mean difference, -0.2%; 95% CI, -1.4-0.9; p = 0.708) or serum ADMA levels (mean difference, 0.01 nmol/L; 95% CI, -0.00-0.03; p = 0.122). Significant improvements in the average probing pocket depth were observed in the control and test groups. The bleeding on probing score in the test group was significantly reduced, while that in the control group was reduced, although not significantly. Periodontal care for a 3-month duration did not provide better endothelial function although improvements of periodontal status in patients with early-stage periodontal diseases. This trial is registered in UMIN Clinical Trials Registry (www.umin.ac.jp/ctr/; ID: UMIN000023395).

Characteristics of biofilm-induced degradation at resin-dentin interfaces using multiple combinations of adhesives and resins.

OBJECTIVE: We aimed to evaluate morphological, mechanical and chemical characteristics at resin-dentin interfaces using multiple combinations of adhesives and resins after a short-term biofilm-induced degradation. METHODS: Cervical cavities were prepared in bovine incisors, treated by Clearfil SE Bond 2 (SE) or FL-Bond II (FL), restored by Clearfil Majesty ES Flow (ES) or Beautifil Flow Plus (BFP) and grouped into SE-ES, SE-BFP, FL-ES and FL-BFP. After biofilm challenge, interfacial gaps and dentin wall lesions were examined by optical coherence tomography (OCT). Gap depth (GD), gap pattern scale (GPS) and dentin wall lesion depth (WLD) were evaluated from confocal laser scanning microscope. Microhardness of dentin lesions was measured with a Vickers microhardness tester. Chemical elements in resins and dentin wall lesions were analyzed by scanning electron microscopy and energy dispersive X-ray spectrometry (SEM/EDS). Morphological structures of interfacial gaps were observed by SEM. RESULTS: OCT could detect adhesive-dentin-bonded and adhesive-dentin-debonded gaps. SE-containing groups showed significantly lower GPS than FL-containing groups. FL-BFP showed significantly lower WLD than FL-ES. Microhardness of dentin wall lesions was higher than that of outer lesions and they showed significant differences in FL-BFP. SE-BFP showed a lower GPS curve and higher intensities of Ca and P in the upper half of dentin wall lesions than other groups. From SEM, microgaps between filler and matrix, break and loss of matrix, separation of adhesive matrix with hybrid layer occurred at interfacial gaps. SIGNIFICANCE: The morphological, mechanical and chemical characteristics of resin-dentin interfacial degradation depend on the component and chemistry of restorative materials.

Effects of silver diamine fluoride preparations on biofilm formation of Streptococcus mutans.

Effects of silver diamine fluoride preparations (SDFs) on cariogenic biofilm formation on root dentin (RD) were investigated. Streptococcus mutans (S. mutans) biofilms were formed on bovine RD blocks coated with one of three the SDFs (38%-SDF, 3.8%-SDF and 35%-SDF+potassium-iodide; SDF+KI) and a non-coated Control which were quantified (spectrometric-measurement) and thickness measured (optical coherence tomography) after 20 h. Bacterial viability test (BacLight) and biofilm-morphometry (SEM) of 2 h biofilms were also performed. The amounts of biofilms (bacteria and water insoluble glucan) and the thickness of biofilm were minimum on 38%-SDF specimen; 3.8%-SDF and SDF+KI had significantly more than that, but had significantly less than Control (p<0.05). Most S. mutans cells found dead and morphology damaged by 38%-SDF. Some dead bacteria and remarkably damaged biofilms were observed in case of 3.8%-SDF and SDF+KI. Inhibition potential of 3.8%-SDF and SDF+KI on S. mutans biofilm formation is almost similar, although not equivalent to 38%-SDF.

Detection and analysis of early degradation at resin-dentin interface by optical coherence tomography (OCT) and confocal laser scanning microscope (CLSM).

OBJECTIVE: To evaluate early degradation at resin-dentin interface using non-invasive swept-source optical coherence tomography (SS-OCT) and confocal laser scanning microscope (CLSM). METHODS: Self-etch adhesives and resin-composites containing bisphenol-glycidyl-dimethacrylate (Bis-GMA), which is one of the most widely used monomers in restorative materials, were investigated in this study. Forty cervical cavities were prepared in bovine incisors and applied by the adhesive with/without Bis-GMA (AdhesiveBG/Adhesive), filled by the resin with/without Bis-GMA (ResinBG/Resin) and then challenged by cariogenic biofilm (37 °C, 24 h). Gap Formation and dentin demineralization around resin-composites were observed by SS-OCT and CLSM. RESULTS: Three types of resin-dentin interfacial degradation could be detected from SS-OCT. Type I-dentin demineralization around resin without gap, showing feather-shaped dark zones without bright scattered lines at resin-dentin interfaces. Type II-dentin demineralization around resin with adhesive-dentin bonded gaps, showing feather-shaped dark zones with bright scattered lines at resin-dentin interfaces. Type III-dentin demineralization around resin with adhesive-dentin debonded gaps, showing edge-shaped dark zones with bright scattered lines at resin-dentin interface. From CLSM, the groups were compared in gap scale (GS), gap depth (GD), gap width (GW) and dentin wall lesion depth (WLD). Bis-GMA-containing adhesive groups showed significantly lower GS than Bis-GMA-free adhesive groups. Bis-GMA-containing resin groups showed significantly lower WLD than Bis-GMA-free resin groups. However, they did not show significant differences in GD and GW. CONCLUSION: Three types of early degradation at resin-dentin interface can be noninvasively detected by SS-OCT. Bis-GMA-containing and Bis-GMA-free restorative materials show differences in gap scale and dentin wall lesion depth. CLINICAL SIGNIFICANCE: SS-OCT can nondestructively detect early resin-dentin interfacial degradation. Gap scale can be used as a parameter to evaluate the risk factor of gaps.

Effects of a surface prereacted glass-ionomer filler coating material on biofilm formation and inhibition of dentin demineralization.

OBJECTIVES: This study investigated the ability of a surface prereacted glass-ionomer (S-PRG) coating material to inhibit the biofilm formation and demineralization of dentin. METHODS AND MATERIALS: Dentin specimens were randomly divided into three groups: (1) no coating (control), (2) S-PRG filler-containing coat, and (3) a nonS-PRG filler-containing coat. Streptococcus mutans biofilms were grown on the dentin surfaces in a microcosm for 20 h. Then, the quantity of bacteria and water-insoluble glucan in the retained biofilm on the dentin surface were measured. Regarding demineralization inhibition test, specimens were demineralized for 5 days then sectioned into halves and observed under confocal laser scanning microscope (CLSM). One-way ANOVA and Tukey's HSD were used for statistical analysis. RESULTS: The estimated mean surface roughness for specimens in the S-PRG group was statistically significantly higher than the estimates for both the nonS-PRG and the control group specimens. The quantity of bacteria and water-insoluble glucan/mm2 revealed that the S-PRG group prevented biofilm formation and bacterial adhesion to the dentin surface compared with the control and nonS-PRG groups. The S-PRG group recorded the highest acid-resistance ability with no surface loss. CONCLUSION: Application of S-PRG barrier coat on dentin surfaces can inhibit biofilm formation as well as protecting the dentin surface against demineralization. CLINICAL SIGNIFICANCE: Coating material containing S-PRG fillers might be used for caries prevention, through inhibiting biofilm formation, enhancing mineralization, and reducing acidic attack by cariogenic bacteria.

Effects of mechanical abrasion challenge on sound and demineralized dentin surfaces treated with SDF.

This study evaluated the effect of mechanical abrasion on the surface integrity, color change (ΔE) and antibacterial properties of demineralized and sound dentin surfaces treated with silver-diammine-fluoride (SDF). The dentin specimens were divided into two groups: sound and demineralized dentin, then divided into three sub-groups, control (no-treatment), SDF, and SDF + potassium-iodide (KI). Each sub-group was further divided into two groups, one exposed to mechanical brushing and the other without brushing. Specimens were analyzed for the ΔE, surface roughness/surface loss and antibacterial properties (CFU, optical density and fluorescent microscope). Repeated Measures ANOVA was used for statistical analysis of color change while one-way ANOVA was used for CFU analysis. SDF and SDI + KI groups showed significant reduction in ΔE with brushing in the sound dentin group unlike the demineralized group. The surface roughness values were higher for both SDF and SDF + KI groups but roughness values significantly decreased after brushing. Both SDF and SDF + KI groups revealed significantly less surface loss than control. The SDF group showed high anti-bacterial effect after brushing, unlike SDF + KI group. So, we concluded that mechanical brushing improved the esthetic outcome. While, SDF and SDF + KI could protect the dentin surface integrity. SDF-treated dentin possesses an antibacterial property even after mechanical brushing.

Effect of silver-containing agents on the ultra-structural morphology of dentinal collagen.

OBJECTIVE: This study investigated the effect of silver diammine fluoride (SDF), nano-silver (AgNPs) and nano-silver/potassium fluoride (AgNPs/KF) on the morphology of dentin collagen and color staining on the dentin. Also, we investigated the anti-caries properties in terms of anti-bacterial effects and potentiality of dentin remineralization at collagen level. METHODS: Dentin specimens obtained from bovine tooth roots were finished with #2000 SiC and sonicated for 5min. Specimens were divided into two main groups: sound and demineralized dentin. Each group was subdivided into five subgroups according to treatment solution: control (no treatment), SDF, nano-silver (AgNPs), AgNPs/KF and KF. Specimens were analyzed using transmission electron microscope (TEM), spectrophotometer, scanning electron microscope (SEM) and antibacterial test. Repeated Measures ANOVA was used for statistical analysis of color change while one-way ANOVA was used for CFU analysis. RESULTS: Regarding color change, SDF showed the highest values while the other groups exhibited insignificant changes. SDF showed alteration in the collagen fibrils while the other groups showed normal intact fibrils. Regarding antibacterial activity, SDF and AgNPs/KF showed the greatest antibacterial effect. SIGNIFICANCE: SDF altered the dentin collagen morphology and inferior ethetics, but still providing intrafibrillar remineralization. Nano-silver fluoride preparations (AgNPs/KF) can be an alternative material for SDF as it can preserve the dentin collagen, showing no color change overtime, and provide a high anti-caries property including intrafibrillar remineralization with a significant anti-bacterial effect.

Inhibitory effect of zinc-containing desensitizer on bacterial biofilm formation and root dentin demineralization.

This study compared the effect of a novel zinc containing, Caredyne Shield (CS), and a fluoroaluminocalciumsilicate-based, Nanoseal (NS) desensitizers on dentin tubule occlusion, inhibition of Streptococcus mutans (S. mutans) biofilm growth, and resistance to bacterial demineralization. Desensitizers were applied to simulated hypersensitive bovine dentin, with distilled water used as a control. S. mutans biofilms were grown on the surface of each specimen in an oral biofilm simulator. CS showed the least bacterial count and water insoluble glucan amount followed by NS. Transverse micro radiography revealed that both CS and NS showed significant reduction in mineral loss and lesion depth of the associated lesion. Scanning electron micrographs showed that the two desensitizers formed obvious depositions on the dentin surfaces, occlusion of tubules and mineral tag formation.

Effects of UVB and UVC irradiation on cariogenic bacteria in vitro.

The aim of this study was to evaluate the bactericidal effect of ultraviolet (UV) light at 265-nm (UVC) and 310-nm (UVB) wavelengths from a newly developed UV light-emitting diode (LED) device against cariogenic bacteria in vitro. Suspensions of Streptococcus mutans (S. mutans) and Streptococcus sobrinus were directly irradiated by UVB or UVC for 2.5 min or 5 min. Numbers of colonies were counted and calculated as colony forming units (CFU) per milliliter. Fluorescence microscopy (FM) and optical density measurements at 490 nm (OD490) were also taken after irradiation. In addition, the bactericidal effects of irradiation against S. mutans under 0.5 mm-thick dentin were compared using culture tests and OD490 measurements. Direct UV-LED irradiation with both UVB and UVC showed strong bactericidal effects. UVB showed superior bactericidal effect through 0.5-mm-thick dentin than did UVC, especially after demineralization. These results suggest that UVB irradiation could be utilized for the prevention and management of dental caries.

Assessment of root caries under wet and dry conditions using swept-source optical coherence tomography (SS-OCT).

The purpose of this study was to compare optical properties of root caries under two observing conditions using swept-source optical coherence tomography (SS-OCT). In vitro and natural root caries were observed by SS-OCT under wet and dry conditions, followed by confocal laser scanning microscope (CLSM) and transverse microradiography (TMR). Signal intensity (SI), distance between SI peaks (SI-distance) and optical lesion depth were obtained from OCT. Lesion depth was measured from CLSM; lesion depth (LDTMR) and mineral loss (ML) were obtained from TMR. In vitro root caries under wet and dry conditions showed different OCT images and SI patterns. Lesion depth of OCT and that of CLSM, SI-distance and LDTMR, LDTMR and ML significantly correlated. Under dry conditions, half natural root caries showed similar OCT images and SI patterns as in vitro root caries. The base of demineralized dentin could be detected more clearly under dry conditions than under wet conditions.

Generation of a Gene-disrupted Streptococcus mutans Strain Without Gene Cloning.

Typical methods for the elucidation of the function of a particular gene involve comparative phenotypic analyses of the wild-type strain and a strain in which the gene of interest has been disrupted. A gene-disruption DNA construct containing a suitable antibiotic resistance marker gene is useful for the generation of gene-disrupted strains in bacteria. However, conventional construction methods, which require gene cloning steps, involve complex and time-consuming protocols. Here, a relatively facile, rapid, and cost-effective method for targeted gene disruption in Streptococcus mutans is described. The method utilizes a 2-step fusion polymerase chain reaction (PCR) to generate the disruption construct and electroporation for genetic transformation. This method does not require an enzymatic reaction, other than PCR, and additionally offers greater flexibility in terms of the design of the disruption construct. Employment of electroporation facilitates the preparation of competent cells and improves the transformation efficiency. The present method may be adapted for the generation of gene-disrupted strains of various species.

Evaluation of resin infiltration on demineralized root surface: An in vitro study.

The aim of this study was to evaluate the effect of resin infiltration on root caries induced by Streptococcus mutans biofilms. Human premolar specimens were divided to 5 groups: negative control (NC), Clearfil SE Bond (SEB), Icon-etch120s+Icon-infiltrant (HA120), Icon-etch10s+Icon-infiltrant (HA10) and K-etchant10s+Icon-infiltrant (PA10). The resin penetration was observed by fluorescent microscope. Biofilm-induced demineralization was conducted again and observed by swept-source optical coherence tomography and confocal laser scanning microscope. The maximum resin penetration depth (PDmax), lesion depth increase (∆LD), frequency of cervical enamel loss and dentinoenamel junction separation length were measured and statistically analyzed. HA120 showed 138.00±49.25 µm PDmax that was significantly larger than PA10 and SEB (p<0.05). SEB created 136.58±64.73 µm coating layers. HA120 and SEB showed significantly lower ∆LD than NC (p<0.05). Resin infiltration with 120s-HCl pretreatment has got a good penetration ability and preventive effect on root caries, however, an additional risk factor of cervical enamel loss was identified.

Optical analysis of enamel and dentin caries in relation to mineral density using swept-source optical coherence tomography.

The aim of this study was to evaluate the signal intensity and signal attenuation of swept source optical coherence tomography (SS-OCT) for dental caries in relation to the variation of mineral density. SS-OCT observation was performed on the enamel and dentin artificial demineralization and on natural caries. The artificial caries model on enamel and dentin surfaces was created using Streptococcus mutans biofilms incubated in an oral biofilm reactor. The lesions were centrally cross sectioned and SS-OCT scans were obtained in two directions to construct a three-dimensional data set, from the lesion surface (sagittal scan) and parallel to the lesion surface (horizontal scan). The integrated signal up to [Formula: see text] in depth (IS200) and the attenuation coefficient ([Formula: see text]) of the enamel and dentin lesions were calculated from the SS-OCT signal in horizontal scans at five locations of lesion depth. The values were compared with the mineral density obtained from transverse microradiography. Both enamel and dentin demineralization showed significantly higher IS200 and [Formula: see text] than the sound tooth substrate from the sagittal scan. Enamel demineralization showed significantly higher IS200 than sound enamel, even with low levels of demineralization. In demineralized dentin, the [Formula: see text] from the horizontal scan consistently trended downward compared to the sound dentin.

Monitoring of cariogenic demineralization at the enamel-composite interface using swept-source optical coherence tomography.

OBJECTIVES: The aim of this study was to evaluate enamel demineralization at composite restoration margins caused by cariogenic biofilm using swept-source optical coherence tomography (SS-OCT). METHODS: Sixty round-shaped cavities were prepared on the mid-buccal enamel surface of extracted human molars. The cavities were restored with Estelite Flow Quick flowable composite using either Clearfil SE Bond or Clearfil Tri-S Bond ND bonding agents. Streptococcus mutans suspension was applied to form a cariogenic biofilm on the surface. After 1, 2, or 3 weeks of incubation (n=10), the biofilm was removed to observe the carious demineralization at the cavosurface margins using SS-OCT. The gap along the enamel-composite interface was recorded on each adhesive system. Confirmatory direct observation was accomplished at the same location using confocal laser scanning microscope. RESULTS: The demineralized enamel around the restorations was observed as a zone of intensified brightness in SS-OCT. The demineralized lesion on the cervical enamel was significantly deeper than that on the occlusal enamel (p<0.05). However, the extension of enamel demineralization at the enamel-composite interface was significantly deeper at the occlusal wall than the cervical wall (p<0.05). The extension in Tri-S Bond ND group was significantly deeper than in SE Bond group (p<0.05). A significant increase in gap formation was found after the extension of demineralization compared with the baseline. SIGNIFICANCE: The carious demineralization around composite restorations were observed as a bright zone in SS-OCT during the process of bacterial demineralization. SS-OCT appears to be a promising modality for the detection of caries adjacent to an existing restoration.

Assessment of bacterial demineralization around composite restorations using swept-source optical coherence tomography (SS-OCT).

OBJECTIVE: To observe the bacterial demineralization of the enamel and dentin around composite restorations bonded with one-step and two-step self-etch adhesive systems using swept-source optical coherence tomography (SS-OCT). METHODS: Forty class V cavities (2.5-mm surface diameter, 2.0-mm maximum depth) were prepared on cervical areas of 20 human molars. The specimens were either treated with one-step adhesive (Clearfil Tri-S Bond ND Quick; TS) or two-step adhesive (Clearfil SE Bond; SE), restored with a flowable resin composite (Estelite Flow Quick). Specimens in the demineralized group were incubated for 2 weeks after Streptococcus mutans biofilm formation, while specimens in the control group were incubated for 2 weeks without biofilms. After SS-OCT observation, specimens were cut and examined under confocal laser scanning microscope (CLSM). The lesion depth (LD), interfacial gap depth (GD) and gap length (GL) obtained from SS-OCT and CLSM were analyzed by Pearson's correlation, LD by Independent-samples t-test, GD and GL by Welch t-test, the frequency of specimens with or without gap by Fisher's exact test at the 95% significant level. RESULTS: Specimens with interfacial gaps in the demineralized group showed significantly higher frequency than that in the control group (p<0.05). There was a significant correlation between SS-OCT and CLSM values of LD, GD and GL (p<0.05). SE showed significantly larger LD of dentin, but less GD and GL of enamel than TS (p<0.05). SIGNIFICANCE: SS-OCT nondestructively detected demineralization around composite restorations and interfacial gaps created by S. mutans biofilm in this in vitro model.