Non-destructive characterization of voids in six flowable composites using swept-source optical coherence tomography

OBJECTIVE

The aim of this study was to evaluate the void frequency (V(F)) and void volume (V(V)) in different flowable composites using swept-source optical coherence tomography (SS-OCT).

METHODS

Standard class I cavities were prepared and filled with six different flowable composites: Clearfil Majesty LV (MJ; Kuraray), MI Flow (MW; GC), MI Fil (ML; GC), Beautifil flow plus (BF; Shofu), Palfique Estelite low flow (EL; Tokuyama) and Surefil SDR flow (SF; Dentsply). The restorations were scanned under OCT. The OCT tomograms were analyzed and average V(F) and V(V) per restoration for each composite were calculated. Scanning electron microscope (SEM) was used to observe the structure of each composite. In addition, the flowability of the materials was evaluated measuring the displacement of each material placed up-right on a glass slide. V(F) and V(V) obtained by OCT were also compared to those calculated using micro-computed tomography (micro-CT).

RESULTS

Kruskal-Wallis ANOVA and Mann-Whitney U tests revealed significantly different V(F) and V(V) values (p<0.05) among the composites. Voids ranging from 35 to 785 μm in diameter were detected in OCT tomograms. MJ showed highest V(F) and V(V) values followed by MW, but ML, BF, EL and SF showed no significant difference. Filler volume in composites showed a positive correlation with void formation, but flowability did not show a specific trend. Micro-CT evaluation validated the V(F) and V(V) calculation by OCT, with a significant correlation in void size (p<0.001, r=0.94).

CONCLUSION

The results of this study indicate the reliability of SS-OCT for real-time void characterization of composite materials and restorations. Void formation in flowable composites is material dependent.

Concurrent evaluation of composite internal adaptation and bond strength in a class-I cavity

OBJECTIVES

This study investigated class-I cavity floor adaptation by swept-source optical coherence tomography (OCT) in combination with microtensile bond strength (MTBS) using different filling methods.

METHODS

Two adhesive systems; Tokuyama Bond Force and Tri-S Bond Plus were used in conjunction with a universal composite (Estelite Sigma Quick) placed either incrementally (oblique) or in bulk with or without a flowable composite lining (Palfique Estelite LV). Ten serial B-scan images were obtained throughout each cavity by OCT (center wavelength: 1319nm). In order to evaluate adaptation defined as the cavity floor percentage showing no gap, a significant increase in the signal intensity was considered as gap at the bonded interface of the cavity floor. The same specimens were then cut into beams to measure MTBS at the cavity floor.

RESULTS

Two-way ANOVA demonstrated that the interaction of adhesive systems and filling techniques was significantly affecting both adaptation and MTBS (p<0.05). There was a significant correlation between MTBS and adaptation at cavity floor (p<0.05). Cavity floor adaptation and MTBS were improved when incremental filling technique was applied, while the outcome of lining technique was variable.

CONCLUSIONS

Quantitative assessment by OCT can non-destructively provide information on the performance and effectiveness of dental composites and restoration techniques. There was a moderate correlation between floor adaptation and bond strength in class-I cavities. Incremental application of composite restoration showed the best performance in terms of bond strength and internal adaptation.

CLINICAL SIGNIFICANCE

Incremental application of composite restoration was the most advantageous placement technique in terms of bond strength and internal adaptation. The lack of placement pressure with flowable composites may affect their adaptation to all-in-one adhesives; therefore, the outcome of cavity lining by flowable composite was variable.

Effects of 405 nm diode laser on titanium oxide bleaching activation

OBJECTIVE

The objective of this study was to evaluate the effects of a 405 nm diode laser on bleaching reaction of H(2)O(2) and VL-TiO(2) on methylene blue (MB) dye.

BACKGROUND DATA

Visible light activating titanium dioxide photocatalyst (VL-TiO(2)) may improve efficacy of hydrogen peroxide (H(2)O(2)) bleaching agents used in dentistry while contributing to their safety by lowering the required concentration of peroxide.

METHODS

The experimental solution was prepared with H(2)O(2), VL-TiO(2), MB, and pure water. The final concentration of H(2)O(2) was 3.5% and that of MB was 10 ppm. The experimental solution of 3 mL in a quartz cell was irradiated by a 405 nm diode laser with various powers, duty cycles, and pulse durations for 7 min.

RESULTS

In all irradiation conditions, the increase in laser irradiation time gradually decreased the MB concentration. Irradiation by higher output power showed more reduction of MB concentration. Pulse durations as short as 5 ms with duty cycle reduced to 25% did not affect the degree of the reduction in MB concentration compared with continuous wave irradiation at the same average output power.

CONCLUSIONS

It was concluded that using 405 nm diode laser, the bleaching effects of VL-TiO(2) depended upon the irradiation time and the average output power, regardless of pulse duration or duty cycle.

Effect of waiting interval on chemical activation mode of dual-cure one-step self-etching adhesives on bonding to root canal dentin

OBJECTIVES

The purpose of this study was to evaluate the effect of waiting interval on the chemical activation of dual-cure one-step self-etching adhesives before placing resin core materials on the regional bond strength to root canal dentin.

MATERIALS AND METHODS

Forty-eight post spaces prepared in human lower premolars were applied with four dual-cure one-step self-etching adhesives Estelite Core Quick: ECB/ECQ, Clearfil DC Core Automix: CDB/CDC, Unifil Core EM: UNB/UNC, BeautiCore: BTB/BTC as the manufacturers' instructions. These adhesives were cured with light activation for 10 s, or chemical activation with 0, 10, and 30 s waiting intervals prior to placing resin core material. Resin core materials were then placed into the post space and light-cured for 60 s. After 24h water storage, each specimen was serially sliced into 8, 0.6 mm × 0.6 mm thick beams for the μTBS test. The regional μTBS data were analyzed using three-way ANOVA and Dunnett's T3 test (p < 0.05).

RESULTS

For the chemical activation with 10 and 30 s waiting intervals, ECB and CDB exhibited significantly improved μTBS, whereas for UNB and BTB, the μTBS were not significantly different but increased with waiting interval. On the other hand, light-activation of all the adhesives produced significantly higher μTBS to root canal dentin than chemical activation (p < 0.05), except for the UNB group.

CONCLUSIONS

For the chemical activation of dual-cure one-step self-etching adhesives, a waiting interval prior to placing resin core material improved μTBS to root canal dentin. Polymerising the adhesives before polymerisation reaction of resin core material would be effective for bonding to root canal dentin.

CLINICAL RELEVANCE

For chemical activation mode as well as light activation mode, pre-curing of adhesive layer before proceeding polymerisation of resin filling material would produce higher bonding performance to dentin in the cavity.

Light transmission characteristics of dentine and resin composites with different thickness

OBJECTIVE

The purpose of this study was to evaluate the light transmission characteristics of dentine and resin composites with different thickness.

METHODS

Disks of bovine dentine and three resin composites (Estelite Σ, Beautifil II and Clearfil Majesty) of OA2 shade were prepared with various thicknesses (0.5, 1.0 and 2.0mm). Using a goniophotometer, the distribution graphs of the light transmission intensity of each specimen were obtained, and diffusion factor (DF) as an indicator for a diffuse transmission property and peak-gain (G0) for a straight-line transmission property were calculated. Their colors were measured on black and white backings using a reflection spectrophotometer to calculate translucency parameter (TP). The data of each value (G0, DF and TP) were analyzed by two-way ANOVA and Dunnett's T3 for post hoc test (p=0.05). Regression analyses were used to determine the correlation between G0, DF, TP values and the thickness.

RESULTS

Regardless of the thickness, dentine had lower TP values than the resin composites. 0.5 mm-thick specimens of dentine and resin composite produced various G0 and DF values, with dentine exhibiting significantly lower G0 and higher DF than the resin composites (p<0.05), whereas with the 1.0 and 2.0mm-thick specimens, they were closely aligned. For dentine, G0 and DF increased in inverse proportion to the thickness (G0: R(2)=0.962, p<0.001; DF: R(2)=0.891, p<0.001).

CONCLUSIONS

Dentine had different light transmission characteristics from resin composite, depending on the thickness.

CLINICAL SIGNIFICANCE

Dentine has different light transmission characteristics (straight-line and diffusion) from resin composite, depending on thickness. Resin composite restoration might be different to accurately reproduce light transmission characteristics of dentine substrate.

Effect of air-drying dentin surfaces on dentin bond strength of a solvent-free one-step adhesive

The purpose was to evaluate the effect of air-drying dentin surfaces on the microtensile bond strength (μTBS) of a solvent-free onestep adhesive (Bond 1 SF). Twelve human molars were ground with 600-grit SiC paper. Before applying bonding agent, the dentin surface was rinsed with distilled water and blot-dried with tissue paper, followed by air-drying for 0, 3, 30, and 60 s using with a dental air syringe. After applying and curing Bond 1 SF, resin composite was incrementally built up. Specimens were then stored in distilled water for 24 h and then μTBSs were measured at a cross-head speed of 1 mm/min. Higher μTBS were observed when the dentin surface was air-dried for 3 s (33.2±6.8MPa)>0 s (26.7±4.5MPa)>30 s (22.6±5.5MPa)=60 s (20.4±5.0MPa). The results suggested that prolonged air-drying of the dentin surface removed water and decreased the bond strengths of Bond 1 SF.

Ultramorphological evaluation of the dentin acid-base resistant zone of two-step self-etching systems after long-term storage in water

PURPOSE

To evaluate the morphological changes in the acid-base resistant zone (ABRZ) at the resin/dentin interface after long-term storage in water.

MATERIALS AND METHODS

Two-step self-etching adhesive systems, Clearfil SE Bond (SE) and Clearfil Protect Bond (PB) (Kuraray Medical) were used. Human dentin disk sandwiches with resin composite were prepared, sectioned, and embedded in epoxy resin. The specimens were stored in water for 1 day, 1, 3 or 6 months, and then subjected to demineralizing solution and 5% NaOCl. The specimens were finally sectioned again, polished, argon-ion etched, and observed with SEM.

RESULTS

The outer lesion (OL) thickness at 1 day ranged from 10 to 15 µm but increased to approximately 30 µm after 6 months, suggesting gradual loss of dentin stored in water. A lower electron density was noted in the adhesives at the locations that were exposed to water. The ABRZs were observed clearly in all groups; the thickness of the ABRZ at the mid-point of the OL gradually decreased with time for SE. For PB, the thickness was stable up to 1 month, but decreased after 3 months. The bottom of the ABRZ in SE formed a right angle with dentin; in contrast, in PB, it sloped down toward dentin with a broadening bottom.

CONCLUSIONS

Water storage resulted in changes both in the dentin substrate and the adhesive layer. An ABRZ was observed beneath the hybrid layer after long-term storage in water in both SE and PB. The ABRZ was thicker and relatively more stable in PB, probably due to fluoride release.

The effects of aging on shear bond strength and nanoleakage expression of an etch-and-rinse adhesive on human enamel and dentin

PURPOSE

To evaluate the effects of increasing thermocycling regimens on bond strength and nanoleakage of an etch-and-rinse adhesive.

MATERIALS AND METHODS

Adper Single Bond (3M ESPE) was used for bonding resin composite to human enamel and dentin. Specimens were stored in water (37°C, 24 h) and subjected to thermocycling (5°C and 55°C) in five groups: 1. control (no thermal cycling), 2. 100, 3. 500, 4. 2000, or 5. 10,000 cycles. The microshear bond test was performed at a crosshead speed of 1 mm/min (n = 16). Nanoleakage specimens were immersed in silver nitrate and FE-SEM micrographs were digitally analyzed to calculate silver penetration in three samples.

RESULTS

The mean bond strength to enamel was not significantly affected by thermocycling. However, artificial aging decreased dentin bond strength in groups 4 and 5 compared to control. Weibull analysis indicated that the characteristic strength decreased gradually with aging in both substrates. All groups exhibited some nanoleakage, and a significant increase in silver penetration compared to the control was observed in enamel and dentin groups 2 to 5.

CONCLUSION

A nanoleakage increase was detected in an earlier stage of aging than when a significant drop in bond strength was observed, with the dentin bond being more susceptible to deterioration.

Contemporary adhesives: marginal adaptation and microtensile bond strength of class II composite restorations

PURPOSE

To evaluate the marginal adaptation (in terms of % continuous margin) and microtensile bond strength (microTBS) of the enamel and dentin of direct class II composite restorations.

METHODS

32 standardized class II cavities were prepared with the gingival margin of one box occlusal to the cementum-enamel junction (CEJ) and one gingival floor extended beyond the CEJ. The teeth (n= 8) were restored using one of four adhesive systems [Adper Scotchbond Multi Purpose (SMPP), Adper Scotchbond 1 XT (S1XT), Clearfil SE Bond (CSEB), or Clearfil Tri-S Bond (CTSB)] with incrementally placed composite restorations before being stored in water (24 hours), thermocycled (2,000 cycles, 5 to 55 degrees C) and mechanically loaded (50,000 cycles, 50 N). Marginal adaptation was evaluated by SEM. Additionally, the teeth were sectioned and trimmed to obtain specimens for microTBS testing.

RESULTS

All adhesive systems exhibited "continuous margins" in enamel over 95.4%, whereas "continuous margins" in dentin ranged from 60.2 to 84.8%. CSEB and CTSB yielded significantly more "continuous margins" between the adhesive restoration and dentin than SMPP or S1XT (P< 0.05). The mean microTBSs (MPa) for enamel were 40.5 (SMPP), 37.3 (S1XT), 30.8 (CSEB) and 23.2 (CTSB), and for dentin, they were 37.7 (SMPP), 33.0 (S1XT), 37.3 (CSEB) and 29.0 (CTSB).

Scrubbing effect of self-etching adhesives on bond strength to NaOCl-treated dentin

PURPOSE

To evaluate the scrubbing effect of self-etching adhesive systems on the microtensile bond strengths to sodium hypochlorite-treated dentin.

MATERIALS AND METHODS

The occlusal surfaces of 36 extracted human third molars were horizontally cut to expose sound dentin. The dentin surfaces of the teeth were treated with 6% NaOCl aqueous solution for 30 s or none. After water rinsing for 10 s and air drying, a 2-step (Clearfil Protect Bond) or 1-step (Clearfil S3 Bond or Bond Force) self-etching adhesive was applied with or without a scrubbing technique, and resin composite (Clearfil AP-X) crowns were built up. The bonded specimens were stored in water for 24 h and then subjected to the microtensile bond test at a crosshead speed of 1.0 mm/min. Data were analyzed using three-way ANOVA and Bonferroni multiple comparisons (p < 0.05).

RESULTS

The NaOCl-treated dentin exhibited significantly lower bond strength with the tested self-etching adhesive systems than did the normal dentin (p < 0.05). Using a scrubbing technique for the tested self-etching adhesive systems significantly improved the µTBS to NaOCl-treated dentin (p < 0.05), whereas there was no significant difference in µTBS to normal dentin between a scrubbing and nonscrubbing technique (p > 0.05).

CONCLUSION

Using a scrubbing technique for applying self-etching adhesive systems to NaOCl-treated dentin was effective in improving the compromised bonding.

Color shifting at the border of resin composite restorations in human tooth cavity

OBJECTIVES

The purposes of this study were to evaluate color shifting at the boarder of resin composite restorations after placement in human tooth cavities in vitro.

METHODS

Twenty extracted human premolars with an A2 shade were used in this study. Cylindrical shaped cavities (3.0mm or 1.5mm depth; 2.0mm diameter) were prepared in the center of the crowns. One of four resin composites of A2 shade (Clearfil AP-X, AP; Clearfil Majesty, MA; Tetric N Ceram, TNC; Ceram X mono, CX) was placed in the cavity, and the color was measured at four points (0.4mm × 0.4mm) on the restored teeth (area 1: tooth area 1.0mm away from the border of resin composite restoration; area 2: tooth border area 0.3mm away from margin of resin composite restoration; area 3: resin composite border area 0.3mm away from margin of resin composite restoration; area 4: resin composite area at the center of resin composite restoration) using a spectrophotometer (Crystaleye). The color of each area was determined according to the CIELAB color scale. Color differences (ΔE*) between the areas of 1 and 2, 2 and 3, 3 and 4, and 1 and 4 were calculated, and also the ratio of ΔE*23 to ΔE*14 as a parameter of the color shifting at the border of resin composite restoration, was determined. The data were statistically analyzed using two-way ANOVA, and Dunnett's T3 and t-test for the post hoc test.

RESULTS

For all materials, the Δ*23 were significantly lower than ΔE*14, in which ΔE*23 were significantly influenced by the materials although there were no significant differences in the ΔE*14 between the materials. Additionally, ΔE*12 were significantly higher than ΔE*34. For the 3.0mm cavity depth group, the lowest ΔE*23/14 ratio was seen in CX = <TNC<AP. For the 1.5mm cavity depth group, TNC dramatically reduced the ΔE*23/14 ratio, and the lowest ratio was seen in TNC = CX<MJ<AP.

SIGNIFICANCE

All resin composite restorations in the tooth cavities produced the color shifting of resin composite and tooth at the border. For deep cavity, resin composites with higher diffused light transmission property showed higher color shifting at the border, while for shallow cavity, the straight-line as well as diffused light transmission of resin composite affected the color shifting at the border. Clinically, diffused light transmission property of resin composites may contribute to the color shifting at the border of resin composite restoration regardless of cavity depth, resulting in better color matching.

Effect of lining with a flowable composite on internal adaptation of direct composite restorations using all-in-one adhesive systems

The purpose of this study was to evaluate the effect of lining with a flowable composite on internal adaptation of composite restorations using three all-in-one adhesive systems; Bond Force (BF), G-Bond Plus (GP), and OptiBond All-in-one (OP), and a two-step self-etching adhesive system; Clearfil SE Bond (SE). They were applied to each cylindrical cavity prepared on the human dentin. The cavity surface was lined with/without a flowable resin composite prior to filling with a resin composite (FL/NL). After water storage for 24 h, the specimens were sectioned and polished, and internal adaptation of the restorations was assessed using a confocal laser scanning microscopy. For SE, a perfect cavity adaptation was recognized in both FL and NL. For BF, GP and OP, cavity adaptation was material dependent in NL, whereas no gap formation was observed in FL. However, voids formation was observed at the composite-adhesive-dentin interface in every all-in-one adhesive system.

In vitro effect of hesperidin on root dentin collagen and de/re-mineralization

The aims of this study were to investigate the effects of hesperidin, a citrus flavonoid, on human root dentin demineralization and collagen preservation, and compare it with chlorhexidine and grape seed extract. Specimens were assigned to different treatment groups: hesperidin, chlorhexidine and grape seed extract. Specimens were subjected to pH cycling by demineralization for 14 h, incubation in testing solutions for 2 h and remineralization in presence of bacterial-derived collagenase for 8 h, for 8 days. Calcium release was measured by means of an atomic absorption spectrophotometer, and degraded collagen matrix was investigated by hydroxyproline assay. Specimens were assessed longitudinally with transverse micro-radiography to investigate lesion depth and mineral loss. In hesperidin and grape seed extract groups, demineralization was reduced when the collagen matrix was preserved. The hesperidin group showed the lowest value in lesion depth and mineral loss, indicating that hesperidin inhibited demineralization and probably enhanced remineralization even under fluoride-free conditions.

Apatite crystal protection against acid-attack beneath resin-dentin interface with four adhesives: TEM and crystallography evidence

OBJECTIVES

Interaction between specific functional groups and apatite crystals may contribute to adhesion. The present study investigated effects of four adhesives with different compositions on protection of crystals beneath the hybrid layer against acid-attack using transmission electron microscopy (TEM) and selected area electron diffraction (SAED).

METHODS

Human dentin was bonded with four adhesives; two with a carboxylic-based functional co-polymer (PAA): three-step etch-and-rinse Scotchbond Multi-Purpose (SMP, 3M ESPE) and one-step self-etch Adper Easy Bond (AEB, 3M ESPE), and two with a phosphate-based functional monomer (MDP): two-step etch-and-rinse Clearfil Photo Bond (CPB, Kuraray Medical) and two-step self-etch Clearfil SE Bond (CSE, Kuraray Medical). The specimens were the either left untreated (control) or subjected to acid-base challenge with demineralizing solution (pH 4.5) and 5% NaClO. All specimens were processed and observed by TEM. SAED was used to identify the presence or absence of apatite crystallites at the base or beneath hybrid layer before and after acid-base challenge.

RESULTS

An apatite-rich zone was observed beneath the partially demineralized hybrid layer of CSE. The zone was thinner in AEB, but a demineralization-susceptible area was found beneath it. The etch-and-rinse adhesives (SMP and CPB) demonstrated completely or predominantly demineralized hybrid layers, which were devoid of the acid-resistant apatite-rich zone.

SIGNIFICANCE

TEM/SAED evidence disclosed that the preserved dentin apatite crystals beneath the thin hybrid layer of the mild self-etch adhesives were protected against acid. Diffusion of reactive components beyond the hybrid layer, and their chemical bonding potential with the remaining crystals created the acid-base resistant zone.

Enamel Lesion Parameter Correlations between Polychromatic Micro-CT and TMR

Transverse microradiography (TMR) is considered as the gold standard technique for the evaluation of enamel lesions. Micro-computed tomography (µCT) has the advantage of non-destructive measurements, but the beam-hardening effect with polychromatic x-rays is a major drawback. To date, no study has validated µCT against TMR. The objective of this study was to validate µCT measurements of enamel lesions under various x-ray conditions and software beam-hardening correction (BHC) against TMR. Human molars with natural white-spot lesions were scanned for 5 min by µCT at 100 kV in different conditions: 50 µA (0.5-mm Al filter), 165 µA (0.5-mm Al/0.3-mm Cu), and 200 µA (0.5-mm Al/0.4-mm Cu), with or without BHC. Grayscale values were converted into mineral density values using phantoms. Thin sections at the same positions were then prepared for TMR. Lesion depth (LD; µm) and mineral loss (ΔZ; vol%µm) were compared between µCT and TMR by Pearson’s correlations. µCT measurements correlated well with TMR under all conditions (p < 0.001, r > 0.86 for LD and ΔZ), except for 0.5-mm Al without BHC (p > 0.05). Even without BHC, combined Al/Cu filters successfully reduced the beam-hardening effect. µCT can be used as a non-destructive alternative to TMR with comparable parameters for the study of enamel lesions.

Gum Containing Calcium Fluoride Reinforces Enamel Subsurface Lesions in situ

The aim of this study was to assess the effect of chewing gum containing phosphoryl oligosaccharides of calcium (POs-Ca) and a low concentration of fluoride (F) on the hardness of enamel subsurface lesions, utilizing a double-blind, randomized, and controlled in situ model. Fifteen individuals wore removable lingual appliances with 3 bovine-enamel insets containing subsurface demineralized lesions. Three times a day for 14 days, they chewed one of the 3 chewing gums (placebo, POs-Ca, POs-Ca+F). After the treatment period, cross-sectional mineral content, nanoindentation hardness, and fluoride ion mapping by time-of-flight secondary ion mass spectrometry (TOF-SIMS) were evaluated. Although there were no statistical differences in overall mineral content and hardness recovery rates between POs-Ca and POs-Ca+F subsurface lesions (p > 0.05), nanoindentation at 1-μm distance increments from the surface showed statistical differences in hardness recovery rate between POs-Ca and POs-Ca+F in the superficial 20-μm region (p < 0.05). Fluoride mapping revealed distribution of the ion up to 20 μm from the surface in the POs-Ca+F group. Nanoindentation and TOF-SIMS results highlighted the benefits of bioavailability of fluoride ion on reinforcement of the superficial zone of subsurface lesions in situ (NCT01377493).

Dentin bonding performance and ability of four MMA-based adhesive resins to prevent demineralization along the hybrid layer

PURPOSE

To evaluate the tensile bond durability and ability of four MMA-based adhesive resins to prevent demineralization along the hybrid layer when exposed to a demineralizing solution.

MATERIALS AND METHODS

A PMMA rod was bonded to human dentin using one of four MMA-based adhesive systems: Super-Bond C&B (SB), SBP-40TX (SBP, experimental), M-Bond (MB), and M-Bond II (MB II). Bonded specimens were sectioned into 0.9 mm x 0.9 mm beams and subjected to microtensile bond strength (µTBS) testing after water storage at 37°C for 24 h or 10,000 thermal cycles. Data were analyzed with two-way ANOVA and Bonferroni's t-test. Fracture mode analysis of the bonding interface was performed using a scanning electron microscope (SEM) and statistically analysed using the chi-square test. To disclose the demineralization inhibition potential through formation of an acid-base resistant zone (ABRZ), the bonded interface was exposed to a demineralizing solution (pH 4.5) for 90 min, and then 5% NaOCl for 20 min. After argon-ion etching, the interfacial ultrastructure was observed using an SEM.

RESULTS

µTBS values without thermocycling were not significantly different (p > 0.05) among 4 adhesive resins. After thermocycling, a significant decrease in µTBS was found in MB and MB II (p < 0.001), whereas SB and SBP showed no significant change (p > 0.05). Failure modes were significantly different (p < 0.05). An ABRZ was seen in SBP, MB, and MB II, while this protective zone was absent in SB.

CONCLUSION

Dentin bonding performance after thermocycling was material dependent in MMA-based adhesive resins. The ABRZ formation was only observed in the self-etching systems.

Potentials of mouthwashes in disinfecting cariogenic bacteria and biofilms leading to inhibition of caries

OBJECTIVES

The aim of this study was to compare the effects of certain commercially available mouthwashes on cariogenic bacteria and biofilms, following the acquisition of inhibition potentials of caries.

MATERIALS AND METHODS

Mouthwashes containing I) chlorhexidine gluconate (CHG; 0.0005% w/v), II) benzethonium chloride (BTC; 0.01% w/v), III) an essential oil (Listerine), and IV) povidone-iodine (PVP-I; 0.035% w/v) were tested on planktonic cariogenic bacteria, biofilms, and an ex vivo caries model. Bacterial aliquots were inoculated with each solution separately and vortexed for 10 seconds at room temperature. Bacterial viability was subsequently investigated by fluorescence microscopy (FM) after staining with a BacLight viability kit and the number of colony-forming units (CFUs) was counted. Similarly, mouthwash solutions were applied to artificial cariogenic biofilms, and bacterial viability of the biofilms was investigated as stated above. Inhibition potentials of two selected mouthwashes of carious lesions were investigated using biofilm-induced caries and a secondary caries model. In all steps, a phosphate-buffered saline (PBS) solution was included as a control.

RESULTS

Planktonic cariogenic bacteria and bacteria embedded in biofilms were killed in remarkably large numbers with Listerine and PVP-I treatment compared to PBS and other gargles. CFU counts also showed significant reduction after treatment with Listerine and PVP-I compared to other solutions (P<0.05). Listerine also displayed significant (P<0.05) inhibition effects in preventing the progression of demineralization.

CONCLUSION

Bactericidal potencies of the mouthwashes varied significantly, suggesting that mouthwashes like Listerine can be useful for the prevention of caries and secondary caries.

Intraoral pH measurement of carious lesions with qPCR of cariogenic bacteria to differentiate caries activity

OBJECTIVES

A low pH environment is created by cariogenic bacteria. This study was aimed to measure pH of carious lesions intraorally using a micro-pH sensor, and assess predominant acid-producing cariogens by qPCR to differentiate caries activities.

METHODS

103 dentine lesions classified as active or arrested caries based on the clinical and radiological examinations were collected from patients after intraoral measurement of the lesion surface pH using a micro-pH sensor. Quantitative detection of genomic DNA copies of target cariogenic bacteria (mutans streptococci and Lactobacillus spp.) in each lesion was performed using real-time PCR. Correlation between the pH ranges and the number of bacterial species was examined by Spearman test.

RESULTS

50 samples were diagnosed as active and 53 as arrested lesions. Statistically significant difference was observed on average surface pH value between active and arrested lesions (p<0.05). Prevalence of Lactobacillus spp. was higher in active lesions than in arrested lesions (76% vs. 58% of samples, respectively). When the carious lesions were categorised into four different pH ranges (up to 5.5, from 5.6 to 5.8, from 5.9 to 6.1 and 6.2 or above), increased prevalence of Lactobacillus spp. was observed with decrease of pH levels. A significant negative relationship was found between pH value and number of Lactobacillus spp. (r=-0.209, p<0.05) but no such correlation was found for mutans streptococci.

CONCLUSIONS

Intraoral pH measurement might be clinically useful to determine acidity of the local environment of carious lesions as one aspect of the caries activity assessment.

CLINICAL SIGNIFICANCE

The population of certain bacteria may indicate activity of carious lesions. Intraoral pH measurement of the carious lesions using a micro-pH sensor may be a clinically feasible method for assessment of lesion acidity.

Effect of curing modes of dual-curing core systems on microtensile bond strength to dentin and formation of an acid-base resistant zone

PURPOSE

To evaluate the microtensile bond strength (μTBS) and acid-base resistant zone (ABRZ) of two dualcuring core systems to dentin using four curing modes.

MATERIALS AND METHODS

Sixty-four caries-free human molars were randomly divided into two groups according to two dual-curing resin core systems: (1) Clearfil DC Core Automix; (2) Estelite Core Quick. For each core system, four different curing modes were applied to the adhesive and core resin: (1) dual-cured and dual-cured (DD); (2) chemically cured and dual-cured (CD); (3) dual-cured and chemically cured (DC); (4) chemically cured and chemically cured (CC). The specimens were sectioned into sticks (n = 20 for each group) for the microtensile bond test. μTBS data were analyzed using two-way ANOVA and the Dunnett T3 test. Failure patterns were examined with scanning electron microscopy (SEM) to determine the proportion of each mode. Dentin sandwiches were produced and subjected to an acid-base challenge. After argon-ion etching, the ultrastructure of ABRZ was observed using SEM.

RESULTS

For Clearfil DC Core Automix, the μTBS values in MPa were as follows: DD: 29.1 ± 5.4, CD: 21.6 ± 5.6, DC: 17.9 ± 2.8, CC: 11.5 ± 3.2. For Estelite Core Quick, they were: DD: 48.9 ±5.7, CD: 20.5 ± 4.7, DC: 41.4 ± 8.3, CC: 19.1 ± 6.0. The bond strength was affected by both material and curing mode, and the interaction of the two factors was significant (p < 0.001). Within both systems, there were significant differences among groups, and the DD group showed the highest μTBS (p < 0.05). ABRZ morphology was not affected by curing mode, but it was highly adhesive-material dependent.

CONCLUSION

The curing mode of dual-curing core systems affects bond strength to dentin, but has no significant effect on the formation of ABRZ.