"Enamel layering" using double-layered enamel-shade resin composites: The strategy to simulate the optical characteristics of human enamel.

OBJECTIVE: To evaluate the optical match between enamel and resin composites fabricated using mono-layered and double-layered techniques. MATERIALS AND METHODS: Enamel slabs were prepared from human upper incisors and canines. Mono-layered composite replicas were prepared from seven Filtek Z350XT and Estelite Sigma shades using silicone molds prepared from the respective enamel surfaces. Translucent and enamel shades (A2 or A3) of the two materials were produced from incisor molds for double-layered replicas, and the groups with the best results underwent accelerated aging. Spectrophotometric evaluation was performed using CIE color system. The differences in translucency (ΔTP) and color (ΔE00 ) between the enamel and paired composite replicas were calculated and analyzed using parametric statistics (α = 0.05). RESULTS: For the mono-layered composites, white enamel and translucent shades of Filtek yielded the lowest ΔTP for canines (4.6) and incisors (8.9), respectively. The ΔE00 of mono-layered replicas ranged from 5.1 to 11.8. Double-layered Filtek replicas displayed a better 1-day optical match with the lowest ΔTP (3.4-4.0) and ΔE00 (4.2-4.6), irrespective of each layer's thickness. CONCLUSIONS: For canines, the lowest ΔTP of Filtek white enamel was close to the acceptable threshold (4.43). For incisors, the thicker translucent double-layered Filtek composites demonstrated the greatest optical match before and after aging. CLINICAL SIGNIFICANCE: Upper incisors and canines have distinct enamel optical properties. Enamel layering using specific double-layered resin composites could achieve a better optical match with upper incisor enamel.

Delayed light activation of resin composite affects the bond strength of adhesives under dynamic simulated pulpal pressure.

OBJECTIVE: To evaluate the effect of a time delay before the light activation of resin composite on the microtensile bond strength (µTBS) of self-etch adhesives under dynamic simulated pulpal pressure. MATERIALS AND METHODS: One hundred twenty crown segments were prepared from human third molars. Dentin surfaces were prepared with coarse diamond burs and connected to a dynamic pulpal pressure device. The self-etch adhesives used were Clearfil SE Bond (CSE), G2-Bond Universal (G2B), Clearfil Universal Bond Quick (CBQ), and G-Premio Bond (GPB). Each adhesive was divided into 3 subgroups: immediate light activation of resin composite (T0), delayed light activation for 150 s (T1), and 300 s (T2). The µTBS data were obtained after 24-h water storage. Scanning electron microscopy was used to evaluate the nanoleakage at the resin-dentin surface. The µTBS data were analyzed using two-way ANOVA and Duncan's multiple comparisons. RESULTS: All adhesives demonstrated a significant reduction in µTBS at T2, except for CBQ where the bond strength was not affected by the delayed light activation times. The two-step self-etch adhesives (CSE and G2B) demonstrated higher bond strength than the one-step adhesives at all conditions. Nanoleakage was observed in all adhesives at T2; however, nanoleakage was detected only in CBQ and GPB at T1. CONCLUSIONS: Delayed light activation of resin composite adversely affected the dentin bond strength of self-etch adhesives. Two-step self-etch adhesives had better bonding performance than one-step self-etch adhesives. CLINICAL RELEVANCE: After adhesive application, resin composite should be adapted and cured as soon as possible.

Role of the smear layer in adhesive dentistry and the clinical applications to improve bonding performance.

Currently, dental adhesives can be divided into two systems; a smear layer-removal approach with etch-and-rinse adhesives or a smear layer-modified approach with self-etching adhesives. After phosphoric acid etching, the smear layer is completely removed. More attention is, however, required when using self-etching adhesives. The smear layer is partially demineralized by the weak acidic monomer and subsequently incorporated into the hybrid layer. Therefore, the characteristics of the smear layer play an important role on the bonding performance of self-etching adhesives. Such characteristics, for instance, smear layer thickness and smear layer density, are influenced by many factors, e.g., instruments used for dentin surface preparation, cutting speed, and the abrasive particle size of the cutting instruments. This review discusses the contributing factors that affect the smear layer characteristics, and the influence of the smear layer on the bonding performance of dental adhesives. Also, the application techniques regarding how to improve the bonding performance of self-etching adhesives - the smear layer removal by using chemical agents, or the modification of the adhesive application procedures - are provided.

Ultra-morphological characteristics of dentin surfaces after different preparations and treatments.

Using transmission electron microscopy (TEM), this study investigated the characteristics of smear layers after preparation of dentin surfaces using different methods. In addition, this study analyzed, using scanning electron microscopy (SEM), the interactions of smear layers with the various acidic agents used subsequently to treat the dentin surface. Mid-coronal dentin surfaces were prepared according to one of five instrumentation methods: fracture; grinding with carbide bur; grinding with regular-grit diamond bur; grinding with superfine-grit diamond bur; or grinding with 600-grit silicon carbide (SiC) abrasive paper. Then, each prepared dentin surface was further divided into control (no further treatment) or treatment with one of the following agents: phosphoric acid solution (PAS); phosphoric acid gel (PAG); Clearfil SE Bond 2 Primer (SE2); or Scotchbond Universal Adhesive (SBU). Longitudinal ultra-thin sections were made for TEM observations. Dentin discs, representing each surface preparation and treatment method described above, were created, and the morphology was examined by SEM. The TEM results revealed differences in thickness and denseness of the smear layer, according to the different methods of instrumentation used to prepare the dentin surface. The two forms of phosphoric acid completely removed the smear layer in all groups. Agglomerated silica particles were observed on the top of the collagen layer after etching with PAG. For all dentin surfaces, except for that prepared with SiC, SE2 demonstrated better etching efficacy on different smear layers, whereas SBU provided only superficial interaction.

Bond strength of self-etching adhesives to dentin surface after smear layer removal with ultrasonic brushing.

This study determined the micro-shear bond strength (µSBS) of two self-etching adhesives to dentin surface after smear layer removal with a novel ultrasonic brushing method. Ninety-five dentin discs were ground flat with diamond burs and divided into 5 groups; no treatment (control), brushing with a custom-made brush for 10 and 30 s without and with ultrasonic application. The smear layer thickness was evaluated using SEM. The 24 h µSBS of Clearfil SE Bond (CSE) and Clearfil Tri S Bond (CTS) to these dentin surfaces were evaluated. Smear layer thickness decreased significantly from control, brushing without, and brushing with ultrasonic groups, respectively. The µSBS of CSE were higher than CTS in all groups. The µSBS were improved with ultrasonic brushing for 30 s for both adhesives. Ultrasonic brushing is the effective method in mechanical smear layer removal which can improve bond strength of self-etching adhesives to ground dentin.

Effect of smear layer and surface roughness on resin-dentin bond strength of self-etching adhesives.

The purpose of this study was to evaluate the effect of surface roughness and smear layer on the micro-shear bond strength (µSBS) of two self-etching adhesives, Clearfil SE Bond (SE) and Clearfil Tri-S Bond (S3). Flat dentin surfaces were prepared with SiC papers (600-, 180- and 120-grit) and diamond burs (extra fine, medium and coarse). They were further divided into smear-covered and smear-free surfaces and bonded with respective adhesives. µSBS test was performed after water storage at 37ºC for 24 h. Smear layer thickness measurement was evaluated by scanning electron microscope (SEM). Surface roughness was examined by contact stylus profilometer. Smear layer thickness and surface roughness were significantly different among all groups (p<0.05). No difference in µSBS was observed among surface prepared by SiC whereas bur-cut smear layer had negative effect on µSBS, especially for S3. Surface roughness from different surface preparations had no influence on µSBS (p<0.05).

Changes in the permeability and morphology of dentine surfaces after brushing with a Thai herbal toothpaste: A preliminary study.

OBJECTIVES: The aim of this study was to evaluate dentine permeability after brushing with Twin Lotus(®), Thai herbal toothpaste by comparing with Sensodyne Rapid Relief(®), a commercial desensitizing toothpaste, and also after artificial saliva (AS) immersion or citric acid challenge. MATERIALS AND METHODS: Dentine discs from human mandibular third molars were divided into three groups (n = 20) and brushed with either experimental toothpaste or water (control) for 2 min with an automated toothbrush. Then, 10 discs were immersed in AS, and the other 10 discs were immersed in 6% citric acid to simulate the conditions of the oral environment. The dentine permeability of each specimen was measured before brushing and after each treatment using a fluid filtration system. Morphological changes in the dentine were observed using scanning electron microscopy (SEM). RESULTS: Both toothpastes significantly reduced dentine permeability, and a crystalline precipitate was observed on the dentine surface under SEM observation. No significant difference was found between the two toothpaste groups with regard to dentine permeability after brushing and AS or acid immersion. CONCLUSIONS: The dentine permeability reduction caused by the two toothpastes did not differ after brushing or after AS or citric acid immersion.

Self-etch or etch-and-rinse mode did not affect the microshear bond strength of a universal adhesive to primary dentin.

This study evaluated the microshear bond strength (µSBS) of resin composite to primary dentin using a universal adhesive in etchand-rinse mode or self-etch mode. Flat ground dentin surfaces were created on forty extracted human primary incisors and randomly assigned into four groups (n=10): Adper Single Bond II (ASB), Clearfil SE Bond (CSE), Single Bond Universal etch-and-rinse (SBUER) and Single Bond Universal self-etch (SBU-SE). Adhesive was applied on the dentin surface, which was subsequently bonded with a resin composite. The µSBS test was performed using a universal testing machine at a crosshead speed of 1 mm/min. The ASB group generated a lower mean µSBS (19.1±3.4 MPa) than those of the other groups [SBU-ER (24.3±2.7 MPa), SBU-SE (25.1±2.4 MPa), and CSE (25.3±2.7 MPa)]. Adhesive failure was the most common failure mode in each group. In conclusion, SBU used in etch-and-rinse or self-etch mode resulted in similar bond strength to primary dentin.

Mechanical properties of experimental silicone soft lining materials.

The purpose of this study was to evaluate the mechanical properties of experimental silicone elastomers, Silastic(®) MDX 4-4210 reinforced with silica fillers, to assess its potential as a denture soft lining material. The mechanical properties measured included tensile strength, percentage elongation, tear strength, and Shore A hardness. Using one-way ANOVA and Tukey's HSD test, the results indicated that silicone elastomers with filler loadings of 6, 8, and 10 phr had significantly greater tensile strength, percentage elongation, tear strength with a softer surface compared with commercial materials (p<0.001). In conclusion, the experimental silicone elastomers revealed acceptable mechanical properties to be used as denture soft lining materials.

Shear bond strength between autopolymerizing acrylic resin and Co-Cr alloy using different primers.

This study aimed to examine the shear bond strength between cobalt chromium alloy and autopolymerizing acrylic resin using experimental primers containing 5, 10, and 15 wt% of 4-methacryloxyethyl trimellitic anhydride or 1, 2, and 3 wt% of 3-methacryloxypropyl-trimethoxysilane comparison to 5 commercial primers (ML primers, Alloy primer, Metal/Zirconia primer, Monobond S, and Monobond plus). Sixty alloy specimens were sandblasted and treated with each primer before bonded with an acrylic resin. The control group was not primed. The shear bond strengths were tested and statistically compared. Specimens treated with commercial primers significantly increased the shear bond strength of acrylic resin to cobalt chromium alloy (p<0.05). The highest shear bond strength was found in the Alloy primer group. Among experimental group, using 10 wt% of 4-methacryloxyethyl trimellitic anhydride -or 2 wt% of 3-methacryloxypropyltrimethoxysilane enhanced highest shear bond strength. The experimental and commercial primers in this study all improved bonding of acrylic resin to cobalt chromium alloy.

Shear and micro-shear bond strengths of four self-etching adhesives measured immediately and 24 hours after application.

This study measured the immediate and 24 h shear (SBS) and micro-shear bond strengths (MSBS) to dentin of four self-etching adhesives. A resin composite was bonded using each adhesive to the area of 5-mm diameter for SBS test or 0.75-mm diameter for MSBS test of flat bovine dentin. The bond strengths of all adhesives at 10 min were lower than at 24 h for both tests. The mean SBS (MPa, 10 min, 24 h) were similar in ranking order at both time periods that is: Clearfil SE Bond (21.2, 25.3) >Clearfil TriS Bond (12.7, 19.5)=i Bond (11.7, 19.5)=G Bond (11.1, 16.6). For the MSBS test, G Bond provided equivalent mean bond strength (35.0) to Clearfil SE Bond (36.9) and higher than the other adhesives at 24 h [i Bond (26.3), Clearfil TriS Bond (28.5)]. In conclusion, the MSBS test was slightly more discriminating than the SBS test.

Biodegradation of all-in-one self-etch adhesive systems at the resin-dentin interface.

This study evaluated the effects of two exogenous enzymes on the resin-dentin interface. Collagenase (Col) and acetylcholinesterase (Ach) were used to simulate salivary enzymes and accelerate the aging process of the bonding interfaces. Four adhesives, Adper Single Bond 2 (SB), Clearfil SE Bond (SE), Clearfil tri-S Bond (S3) and G-Bond (G), were bonded to the dentin surfaces. After storage in water with collagenase or acetylcholinesterase, the specimens were examined using a microtensile bond strength test (MTBS). Nanoleakage patterns were observed with a scanning electron microscope (SEM). The MTBS results demonstrated significantly lower bond strengths in the groups stored with either enzyme than in water. SB exhibited severe degradation after exposure to collagenase, while G showed severe degradation after exposure to acetylcholinesterase. All of the self-etch systems (SE, S3 and G) exhibited water-tree patterns within the adhesive layer when immersed in water for three months. The etch-and-rinse system (SB) showed nanoleakage within the hybrid layer and the adhesive.

Non-destructive assessment of cavity wall adaptation of class V composite restoration using swept-source optical coherence tomography.

The purpose of this study was to evaluate gap formations under class V restoration using swept-source optical coherence tomography (SS-OCT). Wedge-shaped cavities were prepared on the buccal surface of 40 extracted premolar teeth at 2 locations; 1) cemento-enamel junction (CEJ) with enamel and cementum margin and 2) root surfaces with cementum margin. The cavity was treated with Clearfil S(3) Bond, restored with Clearfil Majesty and polished with abrasive disks. The specimens were kept in water at 37°C for 24 hours and subjected to a thermocycling procedure. Gap formations at the tooth-restoration interface were measured with SS-OCT image and conventional dye leakage under a microscope. There was no effect of the locations of the cavity and the margins of the cavity on the gap formation. Therefore, a significant effect of the observational methods was observed. The gap formation was 0.89±0.48 mm with the SS-OCT, and the gap formation was 0.34±0.41 mm with the dye leakage. The observation with SS-OCT demonstrated a greater degree of gap formation than the observation with dye leakage.

Posterior resin composite restorations with or without resin-modified, glass-ionomer cement lining: a 1-year randomized, clinical trial.

AIM: To investigate the effect of resin-modified, glass-ionomer cement lining on the quality of posterior resin composite restorations, bonded with a two-step, total-etch or self-etching adhesive, at 1 year. METHODS: Patients with 1-4 moderate-to-deep, primary occlusal caries in molars were informed and recruited. A total of 110 composite restorations were placed in 75 participants, with one of four restorative procedures: (a) bonded with a total-etch adhesive (Single Bond 2); (b) lined with glass-ionomer cement (Fuji Lining LC), and then bonded with total-etch adhesive; (c) bonded with a self-etching adhesive (Clearfil SE Bond); and (d) lined with glass-ionomer cement, and then bonded with self-etching adhesive. RESULTS: At 1 year, 57 patients (86 restorations) attended the recall. Each of the restorations was evaluated and scored from 1 (clinically excellent) to 5 (clinically poor) using the following criteria: (a) patient satisfaction; (b) fracture and retention; (c) marginal adaptation; (d) recurrent caries; and (e) post-operative sensitivity. At 1 year, the qualities of the restorations were not significantly affected by the placement of glass-ionomer cement lining, regardless of the adhesive used (P > 0.05). Most of the restorations were scored 1 for all criteria. CONCLUSIONS: The benefit of placing a glass-ionomer cement liner in resin composite restoration is questionable.

Dynamic viscoelastic properties of experimental silicone soft lining materials.

The purpose of this study was to evaluate the dynamic viscoelastic properties of experimental silicone soft lining materials, Silastic MDX 4-4210 reinforced with silica fillers. Storage modulus (E'), loss modulus (E") and damping factor (tan delta) were determined using a dynamic mechanical analyzer under a deformation strain level of 0.27% at test frequency and a temperature range of 1 Hz and 0 to 60 degrees C, respectively. The degree of silica dispersion was also studied using a field emission scanning electron microscopy (FE-SEM). One-way ANOVA and Tukey's HSD test results indicated that the prepared silicone elastomers provided a significantly greater damping factor, but less storage modulus than GC Reline Soft and Tokuyama Sofreliner Tough (p<0.001). The storage moduli, loss moduli and damping factor of the experimental silicone elastomers increased with increasing amounts of fumed silica. In conclusion, the experimental silicone elastomers revealed acceptable dynamic viscoelastic properties to be used as denture soft lining materials.

Effect of dentine smear layer on the performance of self-etching adhesive systems: A micro-tensile bond strength study.

This study aimed to evaluate the effect of the smear layer on the micro-tensile bond strength when two self-etching adhesives were used with different techniques. Flat dentine surfaces were prepared using either medium grit diamond burs or tungsten carbide burs. Ten specimens from each prepared surfaces were subjected for smear layer evaluation under SEM. Forty specimens from each of the prepared surfaces were further divided into two groups, bonded with either Clearfil SE Bond (SE) or Clearfil S(3) Bond (S3) using one of four applications (as manufacturer's instructions, agitation, reapplication, and increased application time), restored with composites and subjected to a micro-tensile bond strength test. Smear layers created with diamond burs were thicker than those created with tungsten carbide burs. Surfaces prepared with tungsten carbide burs produced a higher bond strength than those prepared with diamond burs and the same type of adhesive resin. SE demonstrated a higher bond strength than S3 for all surfaces. S3 applied with the agitation technique demonstrated a higher bond strength to dentine prepared with tungsten carbide and diamond burs than that applied with other techniques. SE applied with increased time on dentine treated with carbide burs produced the highest bond strength. In conclusion, a thick smear layer decreased bond strength to dentine, and this might be improved by modification of application technique.

The influence of a local anesthetic containing vasoconstrictor on microtensile bond strengths of two adhesive systems to human dentin in situ.

PURPOSE: To evaluate the bond strengths of an etch-and-rinse adhesive and a self-etching adhesive to human dentin in vitro and under two in situ conditions: non-anesthetization and anesthetization of the teeth with a local anesthetic containing vasoconstrictor. MATERIALS AND METHODS: An in situ study was performed on 49 maxillary premolars scheduled for extraction due to orthodontic reasons. For the bond strength test, occlusal cavities were prepared either with or without a local anesthetic containing vasoconstrictor. The cavities were bonded with Adper Single Bond or Clearfil SE Bond and filled with a resin composite, Filtek Z250. The teeth were then extracted, sectioned, trimmed, and tested for microtensile bond strength. For the observation of dentin surfaces, 20 premolars were used. The impressions of the cavity floors in the anesthetized and non-anesthetized groups were taken before and after acid etching. The replicas were observed under a scanning electron microscope. In vitro, the bond strength test and the SEM observation were also carried out on 24 extracted premolars with the same procedures used in the in situ study. RESULTS: The bond strengths of the two adhesives bonded to dentin in situ were significantly lower than those in vitro. When both adhesives were tested under in situ conditions, there were no significant differences between the bond strengths to dentin of anesthetized and non-anesthetized groups (p > 0.05). No fluid droplets were found on dentin on the cavity floor prepared in vitro, either before or after acid-etching. For the unetched dentin prepared in situ, fluid droplets were found and covered on the smear layer in anesthetized and non-anesthetized groups, but the droplets were slightly larger in the non-anesthetized group. In the non-anesthetized, acid-etched group, dentin surfaces were covered with coalescent dentinal fluid in most specimens. However, in the anesthetized, acid-etched group, patent tubules and some dentinal fluid were observed on the surfaces. CONCLUSION: It was concluded that in situ, dentinal fluid had a detrimental effect on the dentin bond strengths of an etch-and-rinse adhesive and a self-etching adhesive. However, reduction in dentinal fluid due to the effect of a local anesthetic containing vasoconstrictor did not improve the bond strengths in either adhesives.

Effect of glass-ionomer cement lining on postoperative sensitivity in occlusal cavities restored with resin composite--a randomized clinical trial.

This study investigated the ability of a glass-ionomer cement (GIC) lining to reduce postoperative sensitivity in occlusal cavities restored with resin composite. In addition, the effects of a total-etch and self-etch adhesive on postoperative sensitivity were also compared. Patients who had moderate to deep occlusal caries of at least one molar were recruited. Overall, 103 restorations were placed in 70 participants, with an average age of 22.8 +/- 3.8 years. Preoperatively, each tooth was evaluated for cold-stimulated tooth sensitivity using a visual analog scale. If present, tooth sensitivity induced by cold/hot drinks or occlusal function was also noted. Caries was stained with a caries detector dye, then removed using slow-speed burs and hand excavators. The cavity was restored with one of four randomly allocated restorative procedures: 1) bonded with a two-step, total-etch adhesive (Single Bond 2); 2) lined with a resin-modified GIC liner (Fuji Lining LC), then bonded with total-etch adhesive; 3) bonded with a two-step, self-etch adhesive (Clearfil SE Bond) and 4) lined with the GIC liner, then bonded with self-etch adhesive. The cavities were incrementally filled with a nanofilled hybrid resin composite. At recall, postoperative sensitivity was evaluated at one week and one month. Overall, postoperative sensitivity in daily function was rare. No significant difference in postoperative sensitivity, either in daily function or in response to a cold stimulus, was observed between the restorative procedures with or without the GIC liner, regardless of the adhesive used (p > 0.05). In addition, no difference in postoperative sensitivity was noted between use of the self-etch and total-etch adhesive.

Microtensile bond strength of self-etching adhesive systems to differently prepared dentin.

PURPOSE: To evaluate the microtensile bond strength (microTBS) of three self-etching adhesive systems with different degrees of acidity (Clearfil SE Bond, One-Up Bond F, and Xeno III) to dentin prepared with three different methods. METHODS: Forty-five extracted human third molars were ground flat to expose occlusal dentin and polished with 600-grit abrasive paper. All teeth were randomly divided into three groups according to the preparation method: baseline surface (AP#600), steel fissure bur (SB) and regular grit diamond bur (DB). Dentin surfaces were bonded with one of the three adhesive systems; then resin composite was incrementally built up. After storage in 37 degrees C water for 24 hours, specimens were cut and trimmed to create an hourglass shape with cross sectional area of approximate 1 mm2. All specimens were subjected to microtensile bond strength testing. The bond strength data were analyzed with one and two-way ANOVA and Dunnett Multiple comparisons test at P< 0.05. RESULTS: For Xeno III and One-Up Bond F, the microTBS to dentin prepared with the different methods were not significantly different. However, the microTBS of Clearfil SE Bond to dentin prepared with the diamond bur was significantly lower than the other preparation methods. Xeno III produced the lowest microTBS that were statistically different from the other adhesive systems when each preparation method was compared (P< 0.01). SEM observation of the prepared dentin surfaces showed that the diamond bur group produced a thicker smear layer that followed by steel bur and 600-grit paper. Therefore, the smear layer from diamond burs had a greater influence in decreasing microTBS of Clearfil SE Bond that has the weakest acidity self-etching adhesive systems evaluated.

Effect of LED light-curing time for the adhesive resin on the modulus of elasticity.

PURPOSE: To evaluate the elastic modulus of successive layers where an adhesive resin was cured by different light-curing times. METHODS: Eighty dentin discs which were 2 mm thick were prepared from 40 sound third molars. The dentin discs were further divided into four groups and bonded with 3M Single Bond 2 and cured with an LED for 5, 10, 15 and 20s. Bonded specimens were restored with a microhybrid resin composite. Specimens were cut perpendicular to the resin dentin interface, embedded in epoxy resin, and polished. Polished specimens were evaluated for the elastic modulus at the layer of dentin, hybrid layer, adhesive resin, and resin composite at 24 hours after preparation. RESULTS: Light-curing times influenced the elastic modulus of hybrid layer and adhesive resin. The significant differences of elastic modulus among successive layers were found. The results suggested that extension of light-curing times of adhesive resin from 5 to 20 seconds increased the mechanical properties of the resin dentin interface.