Evaluating the microleakage between dentin and composite materials.

BACKGROUND: For successful restoration, it is necessary to minimize the microleakage between dentin and the composite material. OBJECTIVES: The purpose of this study was to evaluate the microleakage of 2 different resin cements (self-adhesive and conventional) on dentin treated with acid, sodium hypochlorite (NaOCl), the acid-NaOCl mixture, the erbium-doped yttrium aluminum garnet (Er:YAG) laser, and their combination. MATERIAL AND METHODS: Seventy dentin specimens were divided into 7 groups (n = 10) according to the surface treatment. Then, the specimens were divided into 2 subgroups (n = 35) according to the resin cement used during cementation with prepared composite resin blocks 5 mm × 11 mm × 3 mm: self-adhesive resin cement or conventional resin cement. Microleakage was scored and recorded at the occlusal and gingival levels, along the resin-dentin interfaces. The data was analyzed with the use of univariate analysis of variance (two-way ANOVA) and the Kruskal-Wallis test for both resin subgroups. RESULTS: The obtained results revealed that self-adhesive resin cement and conventional resin cement showed similar microleakage. Etching with sodium hypochlorite, the Er:YAG laser, the acid-NaOCl mixture, and their combination resulted in microleakage comparable to that achieved in acid etching, which is the conventional method of surface treatment. CONCLUSIONS: Microleakage exhibited by self-adhesive resin cement was similar as in the case of conventional resin cement.

Three-Year Effects of Deproteinization on the In Vitro Durability of Resin/Dentin-Eroded Interfaces.

OBJECTIVE: To evaluate the effect of sodium hypochlorite on the immediate and three-year bonding properties of a resin-eroded dentin interface produced by one of two adhesive strategies. METHODS AND MATERIALS: Forty-eight molars were randomly assigned to six experimental groups, according to the combination of the adhesive strategy (etch-and-rinse and self-etch) and the dentin surface (control groups without erosion, eroded dentin surface [ED], and eroded dentin surface + NaOCl 5.2% [ED + NaOCl]). After completing restoration, specimens were stored in water (37°C) for 24 hours and then sectioned into resin-dentin beams (0.8 mm2) to be tested under tension (0.5 mm/min) immediately thereafter or after three years of water storage. To assess nanoleakage (NL), specimens were immersed in silver nitrate solution and examined by scanning electron microscopy at both time points. The dentin-etching pattern was examined under a scanning electron microscope. Data were subjected to appropriate statistical analysis (α=0.05) Results: In both strategies, a more pronounced and significant reduction of the microtensile bond strength (µTBS) values was observed for the ED groups ( p=0.0001) after three years. However, in the ED + NaOCl group, µTBS values were maintained after three years of water storage. Furthermore, application of NaOCl to eroded dentin significantly reduced the immediate NL values and also preserved these values after three years of water storage for both adhesive strategies ( p>0.05). When considering the ED group, a superficial removal of the smear layer and enlarged lumen tubules in comparison to control were present. However, for ED + NaOCl, there was a total removal of the smear layer and significant numbers of collagen fibrils were exposed. CONCLUSION: The use of NaOCl may maintain the long-term stability of a resin-eroded dentin interface formed by etch-and-rinse and self-etch adhesives.

An investigation into the effect of a resin infiltrant on the micromechanical properties of hypomineralised enamel.

BACKGROUND: Resin infiltration may alter the mechanical properties of enamel hypomineralised lesions (HL); however, variable surface layer (SL) thickness may affect resin penetration. AIMS: To determine the thickness of the SL of HL and to investigate the effect of resin infiltration on the mechanical properties of HL. DESIGN: The thickness of the SL over HL was determined using polarised light microscopy. Etching time using 15% HCl gel to remove the SL of 52 samples was determined. Selected HL and control areas of 21 teeth were infiltrated with Icon® resin infiltrant, and cross-sectional Knoop microhardness (KHN) measurements were recorded before and after resin infiltration. RESULTS: Ninety-six point five per cent of HL had a detectable SL with mean thickness of 58 ± 29 µm. Application of HCl for 120 s produced a mean MIH erosion depth of 58 ± 12 µm. Eleven of 21 samples had evidence of infiltration using visual examination. The infiltrant penetrated some of the HL leading to an increase in KHN (111 ± 75 KHN) which, when compared to adjacent non-infiltrated HL (96 ± 52 KHN), was not statistically significantly different (P = 0.56). CONCLUSIONS: There was marked variation in the SL thickness of HL. Resin infiltration of HL did not increase microhardness significantly.

Effect of cavity depth on dentine sensitivity in man.

OBJECTIVE: To determine if dentine at the enamel-dentine junction (EDJ) in man is more sensitive to hydrostatic pressure stimuli then deeper dentine. DESIGN: Cavities (1mm diam.) were cut at the tips of the buccal and lingual cusps of 8 premolars in 3 subjects (ages: 22-25 years). Both cavities were initially deepened to expose the EDJ then one (the test cavity) was deepened in steps of 0.5mm to a maximum of 2.0 mm below the EDJ. The cavities were tested at each stage, before and after etching, with 5s, hydrostatic pressure stimuli between 400 mm above, and 400 mm below atmospheric. The intensity of any pain produced was recorded on a VAS scale and electrodes were placed in both cavities in an attempt to monitor any action potentials evoked in intradental nerves. RESULTS: In all the teeth, the intensity of the pain produced by a stimulus tended to increase as the cavity was deepened, as did the number of action potentials recorded (in 6 of the 8 teeth). The responses were greater from etched than unetched dentine, and negative pressures evoked greater responses than the corresponding positive pressures. CONCLUSION: There was no evidence that dentine close to the EDJ was more sensitive to hydrostatic pressure stimuli than deeper dentine. It may however be more sensitive to mechanical stimuli as it is more compliant.

Effects of different orthodontic primers on enamel demineralization around orthodontic brackets.

AIM: The purpose of this work is to evaluate the effectiveness of one self-etching and two filled orthodontic primers on enamel demineralization around orthodontic brackets. METHODS: Brackets were bonded to 84 bovine teeth and the vestibular enamel surfaces covered with acid-resistant nail varnish exposing 1 mm of space on each side of the bracket base. The teeth were allocated to four groups, using either Transbond XT conventional primer on etched enamel (group 1), Transbond Plus Self-Etching Primer on untreated enamel (group 2), Pro Seal filled resin primer on etched enamel (group 3), or Opal Seal filled resin primer on etched enamel (group 4). Each tooth was subjected to 15,000 strokes of brushing followed by exposure to an acid challenge. Calcium-ion release from each sample was calculated using atomic absorption spectrophotometry. Data were analyzed using one-way ANOVA and a post hoc Tukey test. Differences were considered statistically significant at p ≤ 0.05. RESULTS: Statistically significant differences were observed between the four groups (p < 0.001). No significant difference was found between the controls (group 1) and the Opal Seal group. Higher calcium release was observed in the Pro Seal group and the self-etching primer group compared to the controls. The highest calcium release was recorded in the self-etching primer group. CONCLUSION: Filled sealants may not have a protective effect against enamel demineralization. Transbond Plus Self-Etching Primer should be used cautiously, considering the risk of demineralization involved in its application.

Demineralization adjacent to orthodontic brackets after application of conventional and self-etching primer systems.

OBJECTIVES: The goal of this work was to compare the demineralization of enamel associated with two different self-etching primers and traditional acid etching. MATERIALS AND METHODS: A total of 15 volunteers (23-32 years, 8 male and 7 female) were provided with a removable archwire/resin appliance to be worn 20 h/day for 28 days. The device was attached to the mandibular posterior teeth and included samples of human enamel (from extracted third molars) located in both posterior vestibules. Both sides featured the same distribution of samples, including one untreated control sample (group A) and three samples with brackets (Victory™ APC II) bonded to their surface after conditioning with a self-etching non-fluoride primer (iBond™ Gluma® Inside; group B), a self-etching fluoride-releasing primer (Transbond™ Plus; group C), or traditional acid-etching with 35% phosphoric acid and Transbond™ XT (group D). Mineral loss was assessed extraorally under standardized conditions using quantitative light-induced fluorescence (QLF) with a specialized camera system (Inspektor Pro). Results were expressed as relative fluorescence loss (ΔF in %). A baseline measurement (T0) was taken before the appliance was first inserted but with the brackets already bonded. Fluorescence loss was analyzed after 3 (T1), 7 (T2), 14 (T3), and 28 days (T4) and compared to the baseline loss (T0) for each of the four study groups (A to D). Kruskal-Wallis and Mann-Whitney U tests were used to compare the results for statistical significance. RESULTS: The lowest percentages of fluorescence loss both at baseline and during the follow-up assessments was found in group C. While all three experimental groups (B, C, D) presented total decreases in fluorescence loss after 28 days, indicating remineralization, the decrease in group C was the largest. The Kruskal-Wallis test yielded no significant differences between the three groups other than a significantly lower percentage of fluorescence loss in group C than in group D during the last assessment (T4). The untreated samples of control enamel (group A) revealed increasing percentages of fluorescence loss over the entire study period. CONCLUSION: Use of the self-etching primers (groups B and C) was not associated with patterns of enamel demineralization different from those noted after traditional etching with phosphoric acid (group D). The only significant difference we observed was between the self-etching fluoride-releasing primer (group C) and traditional etching (group D) at the final assessment (T4). Thus, the fluoride-releasing system Transbond™ Plus was advantageous.

Inactivation of matrix-bound matrix metalloproteinases by cross-linking agents in acid-etched dentin.

OBJECTIVES: Published transmission electron microscopy analysis of in vitro resin-dentin bonds shows that, after 44 months, almost 70% of collagen fibrils from the hybrid layer disappear. Matrix metalloproteinases (MMPs) play an important role in that process and are thought to be the main factor responsible for the solubilization of dentin collagen. Therefore, this study aimed to evaluate the inactivation of matrix-bound MMPs by two different cross-linking agents, carbodiimide (EDC) or proanthocyanidin (PA), or the MMP-inhibitor, chlorhexidine (CHX), on acid-etched dentin using a simplified MMP assay method. MATERIALS AND METHODS: Dentin beams (2×1×6 mm) were obtained from mid-coronal dentin of sound third molars and randomly divided into six groups (G) according to the dentin treatment: G1: Deionized water (control); G2: 0.1 M EDC; G3: 0.5 M EDC; G4: 0.5 M EDC + 35% hydroxyethyl methacrylate (HEMA); G5: 5% PA; and G6: 2% CHX. The beams were etched for 15 seconds with 37% phosphoric acid, rinsed, and then immersed for 60 seconds in one of the treatment solutions. The data were expressed both in absorbance values at 412 nm and in MMP-9 activity equivalents. The total MMP activity of dentin was analyzed for one hour by colorimetric assay (Sensolyte). Data were submitted to Wilcoxon nonparametric test and Mann-Whitney tests (p>0.05). RESULTS: All experimental cross-linking solutions significantly reduced MMP activity from 79.8% to 95.2% when compared to the control group. No difference was observed among 0.1 M EDC (84.8%), 5% PA (87.6%), and 2% CHX (79.8%). Addition of 35% HEMA to 0.5 M EDC produced inactivation (95.2%) that was similar to that of 0.5 M EDC alone (92.7%). CONCLUSION: Dentin treatment with cross-linking agents is effective to significantly reduce MMP activity. Mixing 0.5 M EDC and 35% HEMA did not influence EDC inhibitor potential.

Oral tissues and orthodontic treatment: common side effects.

The aim of this paper was to provide a literature review about the problems that can occur during orthodontic treatment. Using the PubMed database we collected items that would provide information regarding the direct consequences of the placement of an orthodontic appliance: coming to the discussion of the following topics: candida infections, the effects on the soft tissues, the effects on periodontal tissues and effects on hard tissues. The presence of appliances in the oral cavity increases the prevalence of people with candida, specifically the species Candida Albicans is the most frequently isolated. The balance between the clearance of the microorganism, the colonization and the state of candidiasis depends both on the virulence of the fungus, and the competence of the host immune system. On soft tissues, cases of ulceration of the upper jaw by a rapid palatal expander and pyogenic granuloma due to quad helix appliance have been reported. The second one is mostly observed on vestibular gingiva. The first one was found, however, in patients suffering from diabetes mellitus type 1 because of the tissue modifications induced by this pathological condition. The more severe periodontic effects are those caused by incorrect use of orthodontic elastic separators. Finally, the White Spot Lesions are the direct consequences of a wrong conditioning of enamel when attaching the bracket. They represent a first stage of caries in the positioning area of the bracket. The orthodontist is required to intercept these issues not to affect the success of the treatment.

Shear bond strength after multiple bracket bonding with or without repeated etching.

The purpose of the study was to measure the in vitro shear bond strength (SBS) of metal brackets after multiple bonding and debonding with and without repeated etching. One hundred and twenty extracted premolars were divided into three equal groups. In group 1, the brackets were bonded and debonded three times with repeated enamel etching and in groups 2 and 3 without repeated etching. In group 2, all composite remnants were removed before bonding, while in group 3, the remnants were levelled. Analysis of variance was used to determine significant differences in SBS with Bonferroni adjustment for the multiple testing procedures. The results showed that in group 1, the mean SBS was 11.69 MPa (SD 2.65) at the first, 14.30 MPa (SD 2.69) at the second, and 12.19 MPa (SD 2.26) at the third debonding. In group 2, SBS decreased from 12.57 MPa (SD 2.54) to below 8.0 MPa. In group 3, SBS remained constant from the first (11.93 MPa; SD 2.14) to the second (12.06 MPa; SD 1.65) debonding and only decreased significantly to 9.74 MPa (SD 1.80) at the third debonding. Less composite remained on the teeth after each debonding sequence. This was characterized by a shift from adhesive remnant index (ARI) scores 2 and 3 after the first debonding to ARI scores 1 and 2 after the second debonding to predominantly scores 0 and 1 after the third debonding. After bracket loss and levelling of composite remnants, the SBS is sufficient for application of orthodontic forces. Repeated etching may involve a higher risk of enamel tear-outs during debonding.

In vitro evaluation of microleakage under orthodontic brackets using two different laser etching, self etching and acid etching methods.

This study evaluated the microleakage of brackets bonded by four different enamel etching techniques. Forty freshly extracted human premolars were divided randomly into four equal groups and received the following treatment: group 1, acid etching; group 2, self-etching primer (SEP); group 3, erbium:yttrium-aluminum-garnet (Er:YAG) laser etching; and group 4, erbium, chromium:yttrium-scandium-gallium-garnet (Er,Cr:YSGG) laser etching. After photopolymerization, the teeth were kept in distilled water for 1 month and then subjected to 500 thermal cycles. Then, the specimens were sealed with nail varnish, stained with 0.5% basic fuchsin for 24 h, sectioned, and examined under a stereomicroscope. In addition, they were scored for marginal microleakage at the adhesive-enamel and bracket-adhesive interfaces from the incisal and gingival margins. Statistical analyses consisted of the Kruskal-Wallis test and the Mann-Whitney U test with Bonferroni correction. Microleakage occurred between the adhesive-enamel and bracket-adhesive interfaces in all groups. For the adhesive-enamel surface, a significant difference was observed between group 1 and groups 2 (P = 0.011), 3 (P = 0.002), and 4 (P = 0.000) on the gingival side. Overall, significant differences were observed between group 1 and groups 3 (P = 0.003) and 4 (P = 0.000). In dental bonding procedures, acid etching was found to result in the least microleakage. Since etching with a laser decreases the risk of caries and is time-saving, it may serve as an alternative to acid etching.

Influence of etching with erbium, chromium:yttrium-scandium-gallium-garnet laser on microleakage of class V restoration.

The aim of this in vitro study was to evaluate some parameters of dental etching when irradiated with an erbium, chromium:yttrium-scandium-gallium-garnet (Er,Cr:YSGG) laser. One-hundred sound human third molars were selected and randomly distributed into ten groups (n = 10). The class V cavities of group 1 (control) were prepared with a bur and etched with 37% phosphoric acid, while groups G2 to G10, were prepared with laser (5 W, 88.46 J/cm(2), 90/70% air/water) and etched with the following powers: G3 and G4, 0.25 W; G5 and G6, 0.5 W; G7 and G8, 0.75 W; G9 and G10, 1 W. Group G2 received no laser etching. Prior to restoration, G2, G4, G6, G8 and G10 received acid etching. After restoration, all samples were submitted to a microleakage test. According to statistical analysis (Kruskal-Wallis and Dunn's tests), G10 presented the lowest microleakage values (P<0.05). The other groups showed no differences between them. Etching with Er,Cr:YSGG laser (1 W) followed by phosphoric acid was effective in reducing the microleakage of class V restorations.

Sensory transduction mechanisms responsible for pain caused by cold stimulation of dentine in man.

OBJECTIVE: To determine the effects on the sensitivity of exposed dentine to cold that are produced when dentine is etched to remove the smear layer and when the tubules are blocked again with calcium oxalate. Separate in vitro observations were made on the effects of these procedures on fluid flow through the dentine. DESIGN: The experiments were carried out on 24 premolars in 17 subjects. Dentine was exposed at the tip of the buccal cusp and cold stimuli were applied by placing the tip of an ice stick on the cavity floor for 5s under the following conditions: before etching the dentine, after etching, and after oxalate treatment. The subject indicated the intensity of any pain produced on a visual analogue scale (VAS). Fluid flow through the dentine was recorded under similar conditions in eight of the teeth in vitro. RESULTS: The mean VAS score produced by the ice before etching was 21.3+/-19.5mm (S.D.). This increased significantly to 85.4+/-15.6mm after etching (P<0.01). After oxalate treatment, it decreased significantly to 8.5+/-13.3mm. The corresponding mean rates of fluid flow through dentine were 2.15+/-1.02, 1.55+/-0.84, and 2.29+/-1.28nL/smm(2) exposed dentine, respectively. The mean after etching was significantly less than the other two values (P<0.05). CONCLUSION: If the pain was due to hydrodynamic receptors, their sensitivity to dentinal fluid flow changed when the tubules were opened or closed. Alternatively the pain was produced by receptors sensitive to some other change produced by the cold stimuli, such as specific cold receptors.

Effects of the Nd:YAG laser, air-abrasion, and acid-etchant on filling materials.

The purpose of this study was to determine any inadvertent effects of the neodymium: yttrium-aluminium-garnet (Nd:YAG) laser, air-abrasion, and ortho-phosphoric acid on some conventionally used dental filling materials [amalgam, composite resin, compomer, glass-ionomer cement (GIC), and ceromer], when they were used for purposes of margin etching and assessed according to standard enamel etching parameters using a total of five fillings. The surfaces of the filling materials were polished. One sample from each material group was exposed to laser (at 0.75 J, 15 pps) and air abrasion (with Al-oxide powder, 60 psi) for 2 s and to the 37% ortho-phosphoric acid for 60 s. The exposed materials were examined under Scanning Electron Microscopy (SEM). After laser treatment most specimens showed recrystallized areas, the GIC surface being the most affected. There were some pores and cavities on the amalgam surface following laser treatment. The abraded surfaces showed mechanical abrasions. The acid etchant showed the least effect. During the application of laser or air-abrasion, the adjacent tooth or filling surface must be protected or the dentist must be careful.

Effects of Nd: YAG laser irradiation on the adaptation of composite resins to root dentin.

One of the most important goals of the restoration of endodontically treated teeth with a composite resin post system is to achieve good adaptation of the composite material to dentin walls to prevent microleakage apically and coronally. In post core systems, to avoid microleakage between the dentin wall and resin material, laser irradiation may seem to be an alternative therapy for increasing adaptation quality. The aim of this study was to investigate the adaptation of a packable composite resin to lased root canal dentin when it was used as post material. Forty-five freshly extracted human teeth were selected and post spaces were prepared. The teeth were divided into three groups. In group 1 the dentin of the post spaces were etched with 35% phosphoric acid, in group 2 the dentin surfaces were irradiated with an Nd: YAG laser, and in group 3 the dentin surfaces were initially treated with the laser and then etched. The teeth of all groups were obturated with a bonding agent and composite. The groups were divided into two subgroups: a group for the scanning electron microscope (SEM) study and a group for the microleakage study. The lased group showed poor adaptation and more microleakage was detected (p<0.05; variance analysis). The laser beam and acid-etching showed no advantage compared to the acid-etching alone (p>0.05). The Nd: YAG laser irradiation adversely affects adhesion to dentin for using composite resin as a post material and does not constitute an alternative to acid-etching.

Enamel loss at bond-up, debond and clean-up following the use of a conventional light-cured composite and a resin-modified glass polyalkenoate cement.

The aim of this study was to determine whether there was any difference in the degree of enamel loss at bond-up, debond and enamel clean-up when two different adhesive systems were tested and with four different methods of enamel clean-up. The adhesive systems were 37 per cent o-phosphoric acid with Transbond XT (group 1) and 10 per cent poly(acrylic acid) conditioner with Fuji Ortho LC (group 2). Using flattened enamel specimens, enamel loss at each stage was determined using a planer surfometer. These stages were: prior to treatment, at pumice prophylaxis, following enamel etching or conditioning and following enamel clean-up. The four clean-up methods were a high-speed tungsten carbide bur, a slow-speed tungsten carbide bur, an ultrasonic scaler and debanding pliers. The results, analysed using non-parametric tests, demonstrated that significantly more enamel loss occurred following the use of 37 per cent o-phosphoric acid than poly(acrylic acid) conditioner (P = 0.001). At debond and prior to clean-up, more adhesive remained on the enamel surface in group 1 than in group 2 (P = 0.005). During the subsequent enamel clean-up and with both adhesive systems, the least enamel loss occurred following the use of the slow-speed tungsten carbide bur and the greatest loss was seen with the ultrasonic scaler or high-speed tungsten carbide bur.Overall, the lowest enamel loss was observed with the poly(acrylic acid) conditioner and Fuji Ortho LC system (group 2) and where enamel clean-up was performed using the slow-speed tungsten carbide bur.

What's new in dentine bonding? Self-etch adhesives.

Bonding to dentine is an integral part of contemporary restorative dentistry, but early systems were not user-friendly. The introduction of new systems which have a reduced number of steps--the self-etch adhesives--could therefore be an advantage to clinicians, provided that they are as effective as previous adhesives. These new self-etch materials appear to form hybrid layers as did the previous generation of materials. However, there is a need for further clinical research on these new materials. Advantages of self-etch systems include, no need to etch and rinse, reduced post-operative sensitivity and low technique sensitivity. Disadvantages include, the inhibition of set of self- or dual-cure resin materials and the need to roughen untreated enamel surfaces prior to bonding.