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.

Influence of etching ability of one-step self-etch adhesives on bonding to sound and non-carious cervical sclerotic dentin

The purpose of this study was to evaluate influence of etching ability of one-step self-etch adhesives on bonding to non-carious cervical sclerotic lesion. Forty-eight human maxillary premolars with and without natural non-carious cervical sclerotic lesions at buccal surfaces were used in this study. Artificial wedge-shaped lesions were prepared in sound premolars. All lesions were bonded with Bond Force (BF; pH=2.3) or G-Bond Plus (GBA; pH=1.5) according to the manufacturers' instructions. After water storage for 24 hours at 37°C, bonded specimens were subjected to microtensile bond test to measure bond strength to the gingival wall in each lesion. The μTBS of BF to the natural lesion was significantly lower than that of artificial lesion (p<0.05), while for GBA, there is no significant difference (p>0.05). There was no difference in μTBS to artificial lesion between these two adhesives, however in case of non-carious cervical sclerotic lesion, the μTBS of GBA was statistically higher than that of BF.

Effect of light units on tooth bleaching with visible-light activating titanium dioxide photocatalyst

This study evaluated the influence of different light sources on the efficiency of an office bleaching agent containing visible-light activating titanium dioxide photocatalyst (VL-TiO(2)) using an artificial discoloration tooth model. Extracted bovine teeth were stained by black tea. The CIE L*a*b* values were measured before and after nine consecutive treatments by the VL-TiO(2)-containing bleaching agent (TiON in Office, GC, Tokyo, Japan). A halogen light unit (CB; CoBee, GC) or an LED unit (G-light, GC) with two modes (blue and violet: GL-BV, blue: GL-B) were used to activate the bleaching agent in three groups (n=8). Brightness (ΔL) and color difference (ΔE) increased as bleaching repeated in all groups. Two-way ANOVA showed that both number of treatments and light sources significantly affected ΔE (p<0.05). GL-BV showed better bleaching effect than GL-B. In measurement of irradiation spectra, CB showed a wide spectrum (380-530 nm), GL-B had a sharp peak at 470 nm and GL-BV showed an additional peak at 405 nm. It was concluded that the light source influenced the efficiency of the tooth bleaching with VL-TiO(2).

Effect of functional monomers in all-in-one adhesive systems on formation of enamel/dentin acid-base resistant zone

This study aimed at evaluating the effect of functional monomers in all-in-one adhesive systems on formation of acid-base resistant zone (ABRZ) in enamel and dentin. Experimental adhesive systems containing one of three functional monomers; MDP, 3D-SR and 4-META were applied to enamel or dentin surface and light-cured. A universal resin composite was then placed. The specimens were subjected to a demineralizing solution (pH 4.5) and 5% NaClO for acid-base challenge and then observed by SEM. The ABRZ was clearly observed in both enamel and dentin interfaces. However, enamel ABRZ was thinner than dentin ABRZ in all adhesives. Morphology of the ABRZ was different between enamel and dentin, and also among the adhesives. Funnel-shaped erosion was observed only in the enamel specimen with the 4-META adhesive. The formation of enamel/dentin ABRZ was confirmed in all adhesives, but the morphology was influenced by the functional monomers.

Bonding durability of dual-curing composite core material with different self-etching adhesive systems in a model complete vertical root fracture reconstruction

PURPOSE

This study evaluated a dual-curing composite along with different dentin adhesive systems for 1 year under water storage, as a new bonding method of root fragments in complete vertical root fracture.

MATERIALS AND METHODS

Bovine root fragments were bonded with the dual-curing resin composite Clearfil DC Core Automix (DCA) and one of three adhesive systems: two-step self-etching adhesive Clearfil SE Bond (SE), one-step self-etching adhesive Tokuyama Bond Force (BF), one-step dual-curing self-etching adhesive Clearfil DC Bond (DC). Microtensile bond strength (µTBS)/ultimate tensile bond strength (UTS), FE-SEM ultramorphology of fracture modes, and adhesive dentin interface were observed after water storage for periods of up to one year. The data were analyzed with two-way ANOVA.

RESULTS

µTBS was influenced by "dentin adhesive system" (F = 324.455, p < 0.001) and "length of water storage" (F = 8.470, p < 0.001). SE yielded significantly higher µTBS, regardless of storage period (p < 0.05) and maintained the initial µTBS without a significant change after 1 year of water storage (p > 0.05). From 24 h to 1 month, BF showed significantly higher bond strength than DC. UTS of DCA was influenced only by the curing mode of the material (F = 5.051, p = 0.027), but not by the length of water storage (F = 0.053, p > 0.05).

CONCLUSION

Two-step self-etching adhesive systems and dual-curing composite core material can be considered as a suitable bonding method for complete root fractures.

Estimation of lesion progress in artificial root caries by swept source optical coherence tomography in comparison to transverse microradiography

This study aimed to investigate whether swept source optical coherence tomography (SS-OCT) could estimate the lesion depth and mineral loss quantitatively without the use of polarization sensitivity, and to examine a relationship between OCT data and transverse microradiography (TMR) lesion parameters. Twenty-four bovine root dentin specimens were allocated to three groups of 4-, 7-, and 14-day demineralization. Cross-sectional images of the specimens before and after the demineralization were captured by OCT at 1319 nm center wavelength. Following the demineralization, these specimens were cut into sections for TMR analysis. Correlations between the OCT data and TMR lesion parameters were examined. TMR images of the specimens showed cavitated lesions (lesion depth or LD(TMR): 200 to 500 μm, ΔZ or mineral loss: 10,000 to 30,000 vol % μm). The OCT images showed "boundaries," suggesting the lesion front. Integrated dB values before and after the demineralization and their difference (R(D), R(S), and ΔR, respectively) were calculated from the lesion surface to the corrected depth of boundary (LD(OCT)). A statistically significant correlation was found between LD(OCT) and LD(TMR) (p < 0.05, r = 0.68). Similarly, statistically significant correlations were found between ΔZ and R(D) or ΔR. The OCT showed a potential for quantitative estimation of lesion depth and mineral loss with cavitated dentin lesions in vitro.

Cytotoxicity of 45S5 bioglass paste used for dentine hypersensitivity treatment

OBJECTIVES

45S5 bioglass mixed with 50% phosphoric acid has been suggested to treat dentine hypersensitivity and incipient enamel caries. This study is going to evaluate the biocompatibility of using the aforementioned technique with the rat pulpal cells.

METHODS

The relative cytotoxicity of 45S5 bioglass on rat dental pulp cells was compared to the cytotoxicity of a temporary filling material (Caviton; GC, Japan), Type 1 glass ionomer cement (Fuji I; GC, Tokyo, Japan) and commercial desensitising agent (SuperSeal; Phoenix Dental, Fenton, MI, USA) using a transwell insert model. Cell viability was measured by means of a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The number of viable cell counts were compared using one way ANOVA (p<0.05). The morphological alterations of the pulp cells were observed directly by phase contrast microscope.

RESULTS

The results of this study indicated that cell viability recorded by the 45S5 bioglass paste group did not differ significantly from those of the Caviton, glass ionomer or superseal, moreover pulpal cells microscopic analysis revealed that 45S5 bioglass elicited minimal toxic effect.

CONCLUSIONS

45S5 bioglass paste can serve as a biocompatible material that can potentially be used safely on dentine.

Roughness and pH changes of enamel surface induced by soft drinks in vitro-applications of stylus profilometry, focus variation 3D scanning microscopy and micro pH sensor

This study aimed to evaluate enamel surface roughness (Ra) and pH before and after erosion by soft drinks. Enamel was exposed to a soft drink (cola, orange juice or green tea) for 1, 5 or 60 min; Ra was measured using contact-stylus surface profilometry (SSP) and non-contact focus variation 3D microscope (FVM). Surface pH was measured using a micro pH sensor. Data were analyzed at significance level of alpha=0.05. There was a significant correlation in Ra between SSP and FVM. FVM images showed no changes in the surface morphology after various periods of exposure to green tea. Unlike cola and orange juice, exposure to green tea did not significantly affect Ra or pH. A significant correlation was observed between surface pH and Ra change after exposure to the drinks. Optical surface analysis and micro pH sensor may be useful tools for non-damaging, quantitative assessment of soft drinks erosion on enamel.

Effect of resin coating and occlusal loading on microleakage of Class II computer-aided design/computer-aided manufacturing fabricated ceramic restorations: a confocal microscopic study

OBJECTIVE

To evaluate the effect of resin coating and occlusal loading on microleakage of class II computer-aided design/computer-aided manufacturing (CAD/CAM) ceramic restorations.

MATERIAL AND METHODS

Molars were prepared for an mesio-occlusal-distal (MOD) inlay and were divided into two groups: non-coated (controls); and resin-coated, in which the cavity was coated with a combination of a dentin bonding system (Clearfil Protect Bond) and a flowable resin composite (Clearfil Majesty Flow). Ceramic inlays were fabricated using the CAD/CAM technique (CEREC 3) and cemented with resin cement (Clearfil Esthetic Cement). After 24 h of water storage, the restored teeth in each group were divided into two subgroups: unloaded or loaded with an axial force of 80 N at a rate of 2.5 cycles/s for 250,000 cycles while stored in water. After immersion in 0.25% Rhodamine B solution, the teeth were sectioned bucco-lingually at the mesial and distal boxes. Tandem scanning confocal microscopy (TSM) was used for evaluation of microleakage. The locations of the measurements were assigned to the cavity walls and floor.

RESULTS

Loading did not have a significant effect on microleakage in either the resin-coated or non-coated group. Resin coating significantly reduced microleakage regardless of loading. The cavity floor exhibited greater microleakage compared to the cavity wall. TSM observation also revealed that microleakage at the enamel surface was minimal regardless of resin coating. In contrast, non-coated dentin showed extensive leakage, whereas resin-coated dentin showed decreased leakage.

CONCLUSIONS

Resin coating with a combination of a dentin-bonding system and a flowable resin composite may be indicated prior to impression-taking when restoring teeth with CAD/CAM ceramic inlays in order to reduce microleakage at the tooth-resin interface.

Relationship between perception of difficulty and clinical experience of approximal composite restorations in final-year undergraduate students at Tokyo Medical and Dental University

The aims of this study were to clarify which steps in approximal restorative procedure were difficult for the final-year undergraduate students at Tokyo Medical and Dental University, and to examine the relationship between perception of difficulty and clinical experience. At mid-term of the clinical education experience, a self-questionnaire was performed by final-year undergraduate students to clarify the difficulty of restorative procedures at the time. There were statistically significant differences in the number of clinical cases experienced at the time between students who designated the matrix application, shade selection and finishing as the easy steps and those who considered them as the difficult ones (Fisher exact test with Bonferroni correction, p < 0.05). There was a significant difference in the total number of procedures designated as difficult between students who had treated above 15 cases and those who had fewer than 15 cases (Wilcoxon rank-sum test, p< 0.05). In the final-year clinical education for operative dentistry, students might need to treat over 15 cases to gain confidence in performing approximal composite restorations independently.

Effect of hesperidin in vitro on root dentine collagen and demineralization

OBJECTIVES

Caries progress might be controlled when collagen matrix could be preserved after demineralization. The aim of this pH cycling study was to investigate the effect of hesperidin, a citrus flavonoid antioxidant, on dentine collagen and remineralization in dentine lesion, and compared with that of chlorhexidine.

METHODS

The pH cycling was employed on bovine root dentine by demineralization for 14 h, incubation in testing solutions (hesperidin or chlorhexidine) for 2 h and remineralization with bacteria-derived collagenase for 8 h, for 8 days. Calcium release was measured by means of an atomic absorption spectrophotometer, and degraded collagen matrix by collagenase was investigated by assaying hydroxyproline. The lesion depth and mineral loss was evaluated by means of transverse microradiography.

RESULTS

The effect of testing solutions had a significant difference on the results of chemical analyses (p<0.0115 for calcium release; p<0.0008 for degradated collagen). The lesion depth and mineral loss were reduced in the lesions where were incubated with hesperidin and chlorhexidine. The remineralization in deep lesions was found when the matrix was incubated in hesperidin, whilst no mineral uptake in deep lesion when incubated in chlorhexidine.

CONCLUSION

Hesperidin preserved collagen and inhibited demineralization, and enhanced remineralization even under the fluoride-free condition.

Effect of reducing agents on bond strength to NaOCl-treated dentin

OBJECTIVE

The purpose of this study was to evaluate the effect of three antioxidant/reducing agents with different application times on microtensile bond strengths to sodium hypochlorite-treated dentin.

METHODS

The occlusal surfaces of 24 extracted human third molars were horizontally cut to expose sound dentin. The teeth were divided into eight groups. The dentin surfaces of the teeth were treated as follows: group 1, no treatment; group 2, treated with 6% sodium hypochlorite (NaOCl) for 30s; groups 3-8, applications of 10% sodium ascorbate solution, 100 μM rosmarinic acid solution or Accel for 5 or 10s after the same treatment as in group 2. All treated dentin surfaces were bonded with a 2-step self-etching adhesive system (Clearfil Protect Bond) and restored with a resin composite (Clearfil AP-X). After storage in water for 24h, the bonded specimens were subjected to the microtensile bond test at a crosshead speed of 1.0 mm/min. Data were analyzed by a one-way ANOVA and Tukey test (p<0.05).

RESULTS

The NaOCl-treated group had significantly lower bond strength than the control group (p<0.05). The application of sodium ascorbate solution for 5 or 10s did not significantly increase the compromised bonding to NaOCl-treated dentin (p>0.05). On the other hand, Accel and rosmarinic acid solution had significant reversal effects with the same application times (p<0.05).

SIGNIFICANCE

The reversal effect on compromised bonding to NaOCl-treated dentin depended upon the type of antioxidant within the short application time. Applying Accel or rosmarinic acid for 5 or 10s improved bond strengths to NaOCl-treated dentin.

Nanoleakage expression and microshear bond strength in the resin cement/dentin interface

PURPOSE

The aim of this study was to evaluate dentin sealing ability and microshear bond strength of two different resin cements.

MATERIALS AND METHODS

Resin composite overlays (Estenia C&B) were fabricated and cemented to mid-dentin surfaces with either a self-adhesive resin cement (RelyX Unicem) or a resin cement with a self-etching primer (Panavia F2.0). After 24 h storage in water, the specimens were sectioned, placed into 50% (w/v) ammoniacal silver nitrate solution for 24 h, exposed to photodeveloping solution and observed using FE-SEM and EDS. Percentage distribution of metallic silver particles in the resin cement/dentin interface was calculated using digital image analysis software. In addition, small resin overlay cylinders were also bonded to dentin using either of the resin cements, and their bonding performance was evaluated with the microshear bond strength test. The statistical significance was defined as p ≤ 0.05.

RESULTS

No statistically significant difference was detected in the microshear bond strength between RelyX Unicem and Panavia F2.0 (24.9 ± 4.8 and 26.1 ± 5.3 MPa, respectively, p > 0.05). However, a significant difference was detected in silver particle penetration percentage between RelyX Unicem and Panavia F2.0 (7.4 ± 4.6 and 18.7 ± 8.7 MPa, respectively). The Kruskal-Wallis mean ranks for nanoleakage were 6.8 and 14.2, respectively (p < 0.05).

CONCLUSION

While the bond strengths of the two materials were comparable, the self-adhesive resin cement may provide better dentin sealing compared to the self-etching primer resin cement.