Morphological field emission-SEM study of the effect of six phosphoric acid etching agents on human dentin

Micro-shear bond strength of Er:YAG-laser-treated dentin

This study tested if dentin adhesion is affected by Er:YAG laser. Ninety dentin disks were divided in groups (n = 10): G1, control; G2, Er:YAG laser 150 mJ, 90 degrees contact, 38.8 J/cm(2); G3, Er:YAG laser 70 mJ, 90 degrees contact, 18.1 J/cm(2); G4, Er:YAG laser 150 mJ, 90 degrees non-contact, 1.44 J/cm(2); G5, Er:YAG laser 70 mJ, 90 degrees non-contact, 0.67 J/cm(2); G6, Er:YAG laser 150 mJ, 45 degrees contact, 37.5 J/cm(2); G7, Er:YAG laser 70 mJ, 45 degrees contact, 17.5 J/cm(2); G8, Er:YAG laser 150 mJ, 45 degrees non-contact, 1.55 J/cm(2); and G9, Er:YAG laser 70 mJ, 45 degrees non-contact, 0.72 J/cm(2). Bonding procedures were carried out and the micro-shear-bond strength (MSBS) test was performed. The adhesive surfaces were analyzed under SEM. Two-way ANOVA and multiple comparison tests revealed that MSBS was significantly influenced by the laser irradiation (p < 0.05). Mean values (MPa) of the MSBS test were: G1 (44.97 +/- 6.36), G2 (23.83 +/- 2.46), G3 (30.26 +/- 2.57), G4 (35.29 +/- 3.74), G5 (41.90 +/- 4.95), G6 (27.48 +/- 2.11), G7 (34.61 +/- 2.91), G8 (37.16 +/- 1.96), and G9 (41.74 +/- 1.60). It was concluded that the Er:YAG laser can constitute an alternative tool for dentin treatment before bonding procedures.

Evaluation of the enamel etching capacity of six contemporary self-etching adhesives

OBJECTIVES

The purpose of this study was to evaluate the capacity of six contemporary self-etch primers/adhesives to demineralize ground enamel by means of ultrastructural analysis of the etching surface under SEM and by spectroscopic measurement of the percentage of calcium and phosphate ions dissolved.

METHODS

Seventy non-carious extracted human third molars were sub-divided into 2 groups of 35 teeth each. The teeth of the first group were ground to expose flat, polished enamel surfaces 3-4mm thick. The samples thus obtained were treated with six self-etch bonding systems and a phosphoric acid gel (control group). The self-etch priming agent was then eliminated and the etched enamel surface observed by SEM. From the teeth of the second group, disc-shaped specimens were made from ground enamel and subjected to application of each of the six self-etchants. Once the etching product had been rinsed off, the rinse solution was analyzed by atomic flame spectroscopy to evaluate the percentage of calcium and phosphate ions dissolved.

RESULTS

SEM images show that AdheSE, Adper Prompt L-Pop and Xeno III, despite having a less intensive etching efficacy than phosphoric acid, gave a regular pattern over a considerable surface area and depth. iBond and One-Up Bond F gave less regular demineralization. For Clearfil SE Bond, the demineralization was ineffective. Results of the percentage of mineral loss show that Adper Prompt L-Pop and Xeno III were the most efficient self-etch products. AdheSE, iBond and One-Up Bond F, respectively exhibited decreasing demineralizing capacity. Clearfil SE Bond, however, gave low proportions of calcium and phosphate ions loss and was considered unsatisfactory.

CONCLUSION

The action on enamel was not the same for all self-etch systems tested. The etching potential of the self-etch adhesives was lower than that of phosphoric acid but some self-etch systems, particularly those with monomers containing phosphate derivatives, gave results close to those obtained with phosphoric acid.

Effects of etching time of primary dentin on interface morphology and microtensile bond strength

OBJECTIVES

To determine the influence of different etching times (5, 15 or 30 s) on the morphology and micro-tensile bond strength (muTBS) of primary dentin.

METHODS

For muTBS study, nine primary molars were randomly distributed in three experimental groups. Three Class I cavities per tooth were drilled and etched (37% orthophosphoric acid gel for 5, 15 or 30 s). Excite adhesive was applied and cavities restored with a resin composite (Tetric Ceram). Composite/dentin bars (ca. 1 mm2 section) were obtained from teeth and tested in tension until debonding. Means of muTBS results were compared with ANOVA and Student-Neuman-Keuls post hoc tests. Morphology: Three occlusal cavities were prepared in five primary molars. Each cavity was etched and restored as described for previous groups and teeth were sectioned mesio-distally. One half of each tooth was prepared for using under optical microscopy using Masson's trichromic dye technique and the other half was examined by SEM.

RESULTS

muTBS mean (S.D.) results (in MPa) were 5 s etch: 6.20 (2.81), 15 s: 13.43 (5.91), 30 s: 13.04 (5.67). muTBS groups were Excite 5 s < Excite 15 s = Excite 30 s. Masson's trichromic technique stained the demineralized dentin layer red in all specimens. The mean (S.D.) thickness of the demineralized layers (in mu) were 5 s: 3.28 (1.23), 15 s: 3.83 (1.26), 30 s: 4.44 (1.70). There is a statistically significant linear relationship between time of application of etching and mean depth of demineralized layer. This relationship was established as depth (in mu) = 3.08 + 0.05 time (in s).

SIGNIFICANCE

The minimum adequate etching time for primary dentin is 15s.

Diffusion-induced water movement within resin–dentin bonds during bonding

It is thought that water-filled channels and nanovoids in resin-dentin bonds represent potential sites for degradation of bonds or hydrolysis of collagen or both. How water gains access to bonded interfaces is not clear. This study evaluated the diffusion-induced water uptake through resin-dentin interfaces during bonding. Two light-cured total-etch adhesive systems (Excite and One-Step Plus) and a chemical-cured adhesive (Amalgambond Plus) were used in this study. Dentin disks were placed in a split-chamber device, and the fluid movement across dentin was measured, with and without a physiological pressure, during bonding procedures and 24 h after bonding. For light-cured adhesives in the experimental groups, a 6 min interval of dark storage was conducted prior to light-curing, to evaluate the diffusion of water through the uncured resin monomers, and to test the effect of prolonged infiltration time of adhesives on water permeability of bonds. Prolonged adhesive infiltration reduced the water permeability of resin-dentin bonds for light-cured adhesives. Water gradients produced by bonding systems contribute to water movement across the dentin-adhesive interfaces during bonding procedures. Differences in chemical formulations for adhesive systems may lead to differences in the extent of diffusion-induced water movement and the amount of water within the resin-dentin bonds.

Effect of Dentin Conditioning Time on Nanoleakage

Increasing dentin conditioning time did not affect nanoleakage for any of the dentin adhesives used in this study.

Resin adhesion to caries-affected dentine after different removal methods

BACKGROUND

Caries-affected dentine is the common bonding substrate when treating a patient. At present, there are many methods used for caries removal. The aim of this study was to evaluate the microtensile bond strength of two adhesives (Clearfil Protect Bond and OptiBond Solo Plus Total-Etch) to caries-affected dentine after three different caries removal methods.

METHODS

Extracted carious human third molars were used and caries-affected dentine surfaces were obtained from one of the three removal methods: (i) round steel bur in a slow-speed handpiece; (ii) Er:YAG laser; or (iii) 600-grit silicon carbide abrasive paper. Each of the adhesives was used to bond resin composite to the caries-affected dentine according to the manufacturers' instructions. Hourglass-shaped specimens were prepared and stressed in tension at 1mm/min. Data were analysed using two-way analysis of variance and least significant difference test.

RESULTS

Clearfil Protect Bond showed significantly lower bond strength than OptiBond Solo Plus Total-Etch after caries removal with round steel bur, but the opposite was found for specimens treated with silicon carbide abrasive paper. For laser-treated dentine, no significant differences between the adhesives were revealed.

CONCLUSIONS

Besides the differences in adhesives, different caries removal methods seem to influence resin adhesion to caries-affected dentine.

Activation of gelatinolytic/collagenolytic activity in dentin by self-etching adhesives

Mild acids are known to activate dentin matrix metalloproteinase (MMPs). All self-etching dental adhesives are acidic (pH 1.5-2.7) and may activate dentin MMPs. The purpose of this study was to compare the ability of several all-in-one adhesives to activate gelatinolytic and collagenolytic activities in powdered mineralized dentin. Powdered dentin made from human teeth was mixed with all-in-one adhesives (Clearfil Tri-S Bond, G-Bond, Adper Prompt L-Pop) or a self-etching primer (Clearfil SE Bond primer) for varying times and then the reaction was stopped by extracting the adhesives using acetone. Fresh untreated mineralized dentin powder had a gelatinolytic activity of 3.31 +/- 0.39 relative fluorescent units (RFU) per mg dry weight (24 h) that increased, over storage time, to 87.5 RFU mg(-1) (24 h) after 6-8 wk. When fresh powder was treated with acidic Tri-S Bond, the gelatinolytic activity increased from 3.24 +/- 0.70 RFU mg(-1) to > 112.5 RFU mg(-1) (24 h) after 20 min and then remained unchanged. Monomers with lower pH values produced less activity. There was a significant, direct correlation between gelatinolytic activity and pH, with Tri-S giving the highest activity. Coating dentin powder with Tri-S resin prevented fluorescent substrates from gaining access to the enzyme, even though it activated the enzyme. In conclusion, self-etch adhesives may activate latent MMP and increase the activity to near-maximum levels and contribute to the degradation of resin-dentin bonds over time.

Morphological characterization of the tooth/adhesive interface

The purpose of this study was to assess the morphological characteristics of the tooth/adhesive interface using different adhesive systems in MOD restorations under scanning electron microscopy (SEM). The tested hypothesis was that the morphology of the bonding interface would vary in different areas of MOD restorations for the three adhesive systems. MOD cavities were prepared in 12 sound extracted human third molars and restored with Filtek Z250 composite resin and one of the following adhesive systems: Experimental ABF (n=4), Clearfil SE Bond (n=4) self-etching primers and Single Bond etch-and-rinse adhesive system (n=4). After 24-h storage in distilled water at 37ºC, teeth were sectioned and prepared for SEM. The interfacial morphology varied depending on the adhesive system and also on the evaluated area. The null hypothesis was accepted because the morphology of the tooth/adhesive interface reflected the characteristics of both the dental substrate and the adhesive systems.

Effect of bur type and conditioning on the surface and interface of dentine

The purpose of this in vitro study was to evaluate the surface and resin-dentine interface characteristics of permanent tooth dentine cut with diamond or carbide burs and treated with phosphoric acid (PA) or an acidic conditioner. Labial surfaces of permanent incisors were prepared into dentine with high-speed carbide or diamond burs and divided into two halves. Phosphoric acid 36% was applied on one half and non-rinse conditioner (NRC) was applied on the other half. Ten randomly selected scanning electron microscopy (SEM) fields from each specimen (n = 15) were evaluated. Occlusal surfaces of third molars were divided in two halves for evaluation of the resin-dentine interface. The halves were randomly assigned to one of each conditioner and restored with Prime & Bond NT/Spectrum. Ten specimens were analysed by SEM to evaluate hybrid layer formation and interfacial seal. We observed that surfaces prepared with carbide bur presented less residual smear plugs (P < 0.05) than surfaces prepared with diamond burs. Surfaces conditioned with NRC, which is a smear layer modifier, presented more residual smear plugs than surfaces conditioned with PA (P < 0.05). Treatment with PA resulted in more sealed interfaces than specimens treated with NRC. Within the limitations of this study the results showed that carbide burs leave a surface that is more conducive to bonding than diamond burs.

Bonding and curing considerations for incipient and hidden caries

Contemporary adhesive systems and restorative composite materials can successfully seal and restore teeth and can facilitate the use of a minimally invasive cavity preparation technique. These systems give the operator the potential to reinforce damaged teeth and preserve healthy tooth structure. The adhesion principles rely on strict adherence to excellence in clinical technique. Differences in clinical results may depend may more on the operator's adherence to good clinical technique than the specific material selected.

A challenge to the conventional wisdom that simultaneous etching and resin infiltration always occurs in self-etch adhesives

This study provided morphological evidence that discrepancies between the depth of demineralisation and the depth of resin infiltration can occur in some mild self-etch adhesives. Sound dentine specimens derived from extracted human third molars were bonded with 5 one-step and 5 two-step self-etch adhesives. One millimeter thick slabs containing the resin-dentine interfaces were immersed in 50 wt% aqueous ammoniacal silver nitrate and processed for TEM examination. A zone of partially etched but uninfiltrated dentine was identified beneath the hybrid layers in the milder versions of both one-step and two-step self-etch adhesives. This zone was characterised by the occurrence of silver deposits along the interfibrillar spaces of mineralised collagen fibrils. The silver infiltrated interfibrillar spaces were clearly identified from the one-step self-etch adhesives Xeno III, iBond, Brush&Bond and the experimental adhesive, and were thinner and only occasionally observed in the two-step self-etch adhesives Clearfil SE Bond and Clearfil Protect Bond. The more aggressive one-step and two-step adhesives that exhibit more abrupt transitions from completely demineralised to mineralised dentin were devoid of these silver-infiltrated interfibrillar spaces beneath the hybrid layers. Incomplete resin infiltration observed in some self-etch adhesives may be caused by the reduced etching potential of the acidic monomers toward the base of hybrid layers, or the presence of acidic but non-polymerisable hydrolytic adhesive components, creating potential sites for the degradation of the bonded created by these self-etch adhesives.

Adhesiveness of dental resin-based restorative materials investigated with atomic force microscopy

This study aimed to show that the polymerization contraction of dental methacrylate-based materials, when used as adhesives on hard substrate, produces voids at the material-substrate interface. This phenomenology is closely related with the nanoleakage and the sealing ability of these materials. One prime/bond system, three restorative composite resins, and one orthodontic bonding system were cured by using mirror-like glass slides as a compliance-free reference substrate. The adhesive surface was analyzed by atomic force microscopy, and the polymerization contraction of bulk material was tested by laser beam-scanning method. Nanoperiodic structure of three-dimensional (3D) images, section analysis, and roughness characteristics (R(a) and R(z)) indicated that polymerization contraction produced voids at the interface. When the adhesive surface was exposed to oral simulating fluids (water, ethanol, and lactic acid solutions), hydrolytic degradation involved some hundreds of nanometers in depth. In visible light-cured (VLC) materials, the interface porosity decreased when an irradiation pause ( approximately 2 min) was carried out during gelation.

Microleakage study of three adhesive systems

The purpose of this in vitro study was to evaluate the efficacy of three hydrophilic dentin adhesive systems to reduce class II restoration microleakage. A total of 60 human molar teeth were used in which two box cavities were made on the distal and mesial surfaces, with a cervical margin in dentin. These cavities were randomly divided into 3 groups (n = 40 each), according to adhesive system tested: G1: OptiBond SOLO®; G2: Amalgambond Plus®; G3: Etch & Prime 3.0®. The cavities were restored with the composite resin Z-100®. The groups were thermocycled 2000 times (5 ± 1ºC and 55 ± 1ºC) with a dwell time of 1 min. The teeth were then immersed in 2% methylene blue, pH 7.0, for 4 h, sectioned and observed with a stereomicroscope MEIJI 2000 (35X). The evaluation was made using scores (0-4) and the results were expressed through the sum of the ranks. G1 = 1994.00; G2 = 2294.00; G3 = 2972.00. The three groups were significantly different. The self-etching adhesive system Etch & Prime 3.0 was less effective in preventing microleakage. The OptiBond SOLO adhesive was the most effective in reducing microleakage in dentin margins when compared with Amalgambond Plus and Etch & Prime 3.0.

Resin penetration through submicrometer hiatus structures: A SEM and CLSM study

The purpose of this study was to confirm the existence of submicrometer hiatus structures and to examine the degree of resin penetration through these formations. Dentin disks 2.0 mm in thickness were sectioned from 48 human molars with the use of a microtome saw. Three different fifth-generation (total-etch, combined primer/resin) dentin adhesive systems were used to bond a light-cured, resin-based composite to the dentin disks (n = 16 each group). Bonded disks from the three groups were then sectioned. Half of each group was examined with the use of a scanning electron microscope (SEM) (n = 8), and the other half with the use of a confocal laser scanning microscope (CLSM) (n = 8). The frequency of submicrometer hiatus formation was recorded and documented with associated imaging techniques. Resin penetration within submicrometer hiati were observed in 41.7% (10/24) of SEM specimens and 83.3% (20/24) of CLSM specimens. The location and size of these structures were found to be quite uniform. Submicrometer hiati approximated 200 microm in each of the three dentin bonding systems examined. Resin penetration through submicrometer hiati does not appear to be an artifact of desiccation. These structures were clearly identified within the hybrid layer of each dentin adhesive system used in this study.

A between-patient disinfection method to control water line contamination and biofilm inside dental units

The aim of the present study was to evaluate the efficacy of a between-patient disinfection procedures to maintain low bacterial counts in dental unit water line (DUWL) effluents, and control dental water line biofilms. Six dental units already in use, that had never been cleaned, were monitored for three weeks. During the first week only baseline contamination levels were assessed with no treatment of the system. In the second week lines were flushed with water for 30 s before treating each patient. During the third week, a disinfection procedure with 0.26% peracetic acid, followed by a water flush, was implemented before treating each patient. DUWL samples were collected both at the beginning and at the end of 216 dental procedures (72 during each period), plated on R2A agar and incubated at room temperature for seven days to obtain total bacterial counts in colony forming units per millilitre. To assess biofilm control, nine dental units (five never used and four old dental units with established biofilm) were used for 30 days in routine dental practice undergoing five between-patient DUWL disinfecting cycles every day. Water line samples were removed at baseline and at the end of the study and examined by scanning electron microscopy to determine the presence or absence of biofilms. A significant difference (P < 0.01) in mean DUWL bacterial counts was found between the three sets of observations. Biofilms were not present in any of the new dental units and a demonstrable reduction in the biofilms from the four dental units with previous presence of established biofilms was observed at the end of the study. In this study, a between-patient disinfection procedure consisting of flushing DUWL with peracetic acid with use of water was efficacious in the control of both microbial contamination of dental treatment water and dental water line biofilms.

Effect of acid etching time and technique on interfacial characteristics of the adhesive-dentin bond using differential staining

Dentin bonding using the total-etch method has been claimed to be technique-sensitive. The aim of this study is to examine the effect of acid-etch variations on the dentin demineralization and interfacial structure of the adhesive-dentin bond using a differential staining technique. Single Bond adhesive with 35% phosphoric acid gel was used. The occlusal one-third of the crown was removed from 60 extracted, unerupted human third molars. Smear layers were created by abrading the dentin with 600 grit SiC under water for 30 s. The prepared teeth were randomly assigned to four groups according to etching time (Group 1, 10 s; Group 2, 15 s; Group 3, 30 s; Group 4, 60 s). In each group, the etching gel was: (i) applied and spread to the dentin surface and left to stand undisturbed; (ii) applied and gently agitated during etching; (iii) applied without using dispensing tips for the syringe and left for the same period as above. After rinsing, the etched dentin was then treated with the adhesive per manufacturers' instructions. 3-5 micro m thin sections of the adhesive/dentin (a/d) interface were cut with a microtome and stained with Goldner's trichrome. Stained, thin sections from each prepared tooth were imaged with light microscopy. The depth and extent of dentin demineralization, and the a/d interdiffusion zone were clearly visible by this differential staining microtechnique. The thickness of the interdiffusion zone increased as a function of etching time. However, the etchant gel application methods have a significant influence on dentin demineralization. Although agitating acid gel facilitates the penetration and etching into dentin, it should not be recommended, especially for longer etching time. These results indicated that the etching technique has a large effect on the profile of both dentin demineralization and interfacial structure.

Ultramorphological analysis of resin-dentin interfaces produced with water-based single-step and two-step adhesives: Nanoleakage expression

This study evaluated the nanoleakage patterns in bonded interfaces using two single-step, self-etching adhesives (Adper Prompt-AD, and One-up Bond F-OB), two two-step, self-etching primers (Clearfil SE Bond-CF, and Unifil Bond-UB), and one two-step, total-etch adhesive (Single Bond-SB). Dentin surfaces were bonded with the adhesive systems and stored in water at 37 degrees C for 1 week and 6 months. After storage periods, teeth were sectioned into 0.8 mm-thick slabs, coated with nail varnish except for the bonded interfaces, and immersed in ammoniacal AgNO(3) for 24 h. After immersion in photodeveloping solution, bonded sections were prepared and observed under a SEM using the backscattered electron mode. Undemineralized, unstained, epoxy resin-embedded sections were prepared for TEM. Nanoleakage patterns were qualitatively compared between periods. Nanoleakage was observed in all bonded specimens at both periods. CF and UB presented silver deposits predominantly restricted to the thin (0.5 microm) hybrid layer (HL) at both periods. Although no evident differences were observed in the nanoleakage pattern of UB at 7 days and 6 months, CF presented enlarged areas of silver impregnation after 6 months. SB presented accumulation of silver particles mostly within the HL at 7 days, which was intensified after 6 months. AD and OB presented massive silver accumulation within the HL and the overlying adhesive layer. No evident differences were noticed between storage periods. Silver impregnation increased for all adhesive systems from 7 days to 6 months, except for UB.

Total-etch versus self-etch adhesive

BACKGROUND

Self-etching adhesives are believed to prevent postoperative sensitivity when used under posterior resin-based composite restorations. The authors tested a twofold hypothesis: a self-etch, or SE, adhesive would result in less postoperative sensitivity than a total-etch, or TE, adhesive; an SE adhesive would result in poorer enamel marginal integrity than a TE adhesive.

METHODS

Patients were selected on the basis of requiring Class I and II restorations in molars and premolars. The authors placed 30 restorations with the SE material (Clearfil SE Bond, Kuraray America, New York) and 36 restorations with Prime & Bond NT (Dentsply Caulk, Milford, Del.), which uses 34 percent phosphoric acid to etch enamel and dentin simultaneously. Preparations were of standard design, with all margins in enamel without beveling. Upon rubber dam isolation, the authors conditioned the enamel and dentin walls with the self-etching primer (for Clearfil SE Bond) or etched with the proprietary 34 percent phosphoric acid (for Prime & Bond NT), followed by application of the corresponding dentin adhesive. Teeth were restored with the proprietary hybrid resin-based composite indicated for posterior restorations: Clearfil AP-X for Clearfil SE Bond or Esthet-X Micro Matrix Restorative for Prime & Bond NT. The restored teeth were evaluated preoperatively and at two weeks, eight weeks and six months postoperatively for sensitivity to cold (ice), air and masticatory forces, as well as for marginal discoloration.

RESULTS

Analysis of variance revealed no statistically significant differences in postoperative sensitivity between the SE and TE materials at any recall time. Marginal discoloration was rated as "absent" for all restorations at six months. Only one tooth displayed sensitivity to occlusal forces at six months.

CONCLUSION

The SE adhesive did not differ from the TE adhesive in regard to sensitivity and marginal discoloration.

CLINICAL IMPLICATIONS

Postoperative sensitivity may depend on the restorative technique rather than on the type of dentin adhesive used.

Formation and Decontamination of Biofilms in Dental Unit Waterlines

BACKGROUND

Biofilms are a natural occurrence in aquatic environments, including community drinking water systems. The interior of small-diameter tubings in dental unit waterlines (DUWL) are also sites of biofilm formation. In the lumen of the tubings, the flow is minimal, and the water becomes stagnant when the units are not in use. Molecules precipitate from the water onto the interior wall and promote the adherence of planktonic microorganisms from the water. Once they become sessile, the microorganisms change their phenotype. After adherence, there is a so-called surface-associated lag time, and the organisms then enter a growth phase and produce exopolysaccharides that coat the organisms in a slime layer. Within the biofilm, the microorganisms can signal one another, transfer nutrients, and exchange genetic material. The insoluble exopolysaccharides shield the microorganisms from displacement and from penetration by predator organisms, antibiotics, and disinfectants. The external surface layer of microorganisms is faster growing and may detach as "swarmer" cells. Detachment of microorganisms from dental unit biofilm flushed into the oral cavity could theoretically infect the patient. Splatter and aerosols from dental procedures may possibly infect health care personnel.

METHODS

This study compared three DUWL cleaners (an alkaline peroxide product, a freshly mixed chlorine dioxide product, and a buffer-stabilized chlorine dioxide product) in 16 dental units with self-contained water systems, 6 months after installation in a periodontal teaching clinic. One unit treated by flushing and drying served as a control. Units were sampled daily for 10 days with heterotrophic plate count (HPC) sampler plates. The plates were incubated for 7 days at room temperature, and colonies were counted at 10.5x magnification. Samples of internal water tubing before and after the use of waterline cleaners were processed and examined by scanning electron microscopy.

RESULTS

The estimated mean HPC was derived from original and replicate independent counts of two investigators of undiluted and diluted samples, reported as colony forming units (CFU)/ml. Shock treatments with the alkaline peroxide product (n = 5) reduced the HPC from baseline, but in the ratio of daily counts to control, there was a large variance and a trend to return of high counts as days passed. The mean daily HPC was significantly better than the control for only 3 of the 9 days of treatment and exceeded the goal of 200 on 3 days. Freshly mixed chlorine dioxide (n = 4) and the buffer-stabilized chlorine dioxide (n = 5) both reduced HPC to near 0 on all days. Their ratios of daily estimated means to that of the control were significantly (P < 0.001) better at all times. In comparing treatments, the freshly mixed chlorine dioxide was better (P < 0.001) than the alkaline peroxide on 8 of 9 days. The buffered chlorine dioxide treatment was better than the alkaline peroxide at all times. The two chlorine dioxide treatments each had so many HPC counts of 0 that a meaningful statistical difference between them was not calculated. Scanning electron microscopy of plastic waterline tubing samples taken before and after treatments showed reductions in biofilm coverage, but the differences were not statistically significant.

CONCLUSIONS

Chlorine dioxide waterline cleaners are effective in decontaminating DUWL biofilm. Chlorine dioxide has advantages over other chlorine products. Controlling DUWL biofilm may have beneficial effects on nosocomial infections.

Immunocytochemical analysis of dentin: A double-labeling technique

Immunocytochemical analysis is a fundamental and selective technique for identifying different molecular components of human dental structure. The hypothesis tested here is that the application of different etching solutions on dentin does not hinder collagen fibrils and proteoglycans from maintaining their immunochemical antigenicity. Human dentin disks were treated with 0.5M of EDTA, citric acid, maleic acid, or phosphoric acid (for 15 or 30 s). A double-immunolabeling technique was performed to identify, simultaneously, collagen fibrils and chondroitin sulfate. The use of different acids resulted in different degrees of labeling. Maleic and citric acids revealed a diffuse and intense labeling for both collagen fibrils and proteoglycans. The use of phosphoric acid on dentin showed a massive coagulation of the proteoglycans (15 s) or very low labeling (30 s). These data clarify that the use of acids on dentin components is able to modify their antigenicity. Moreover, the double-labeling immunocytochemical technique allows understanding of the spatial relationships between the collagen fibrils and proteoglycans of the dentin matrix.

Effect of dentinal pretreatments on coronal dentin primary carious lesions: a field emission SEM study

The aim of the study was the morphological analysis of coronal dentin caries and the modifications induced by different pretreatments with phosphoric acid or sodium hypochlorite. Carious dentin specimens were obtained from human molars affected by carious lesions. Specimens were divided in four groups and submitted to: (1) untreated; (2) 35% phosphoric acid for 15 s; (3) 35% phosphoric acid for 15 s and 5% sodium hypochlorite for 2 min; (4) sodium hypochlorite for 5 min. Specimens were observed under high-resolution SEM. Different areas were identified within the carious lesion: a deeper, inner region revealing closed highly mineralized tubules, and a more superficial outer layer showing an increasing demineralization rate toward the surface of the lesion. Phosphoric acid followed by NaOCl treatment removed all collagen fibrils from greatly altered carious outer-dentin layer. The 5-min treatment with sodium hypochlorite affected both inner and outer dentin, removing all collagen fibrils and increasing the porosities of deeper intertubular hypermineralized dentin. FEISEM analysis confirmed that only inner carious dentin after phosphoric acid treatment may be considered a suitable substrate for dentinal bonding system. On the contrary, the outer dentin is an unstable substrate for any type of bonding systems and must be avoided/removed from any surface before conditioner application.

SEM and TEM analysis of water degradation of human dentinal collagen

Recently several long-term studies have reported evidence of the hydrolytic degradation of collagen fibrils based on fractured surface observations after bond testing. Those studies suggested that one cause of the decline in the bond strength was the degradation of the collagen fibrils within the bonds. However, one concern has been raised that the dentinal collagen fibrils may be stable in water that does not contain oral bacteria or enzymes. Therefore, the present study aimed to clarify the micromorphological change in naked collagen fibrils after 500 days of water storage. To prepare exposed collagen fibrils, sectioned and polished human dentin surfaces were acid conditioned for 15 s with the use of two commercially available acid conditioners: All-Etch (10% phosphoric acid) and Uni-Etch (32% phosphoric acid) (Bisco, Inc.). Those specimens were stored in distilled water at 37 degrees C for 1 day (control) for 500 days. After the storage periods, the samples were examined with the use of SEM and TEM. Under SEM and TEM examination, micromorphological alterations (disarrangement of collagen web, widening the interfibrillar space, and the thinning diameter of collagen fibrils) were found in the specimens after 500 days in water.

Six-month storage-time evaluation of one-bottle adhesive systems to dentin

PURPOSE

The goal of this study was to evaluate the 1-week, 3-month, and 6-month performance of eight commercially available one-bottle adhesive systems to dentin.

MATERIALS AND METHODS

Lingual and buccal surfaces from human third molars were ground wet on 600-grit SiC paper to obtain a flat dentinal surface. The specimens were randomly divided into 24 groups (n = 10), which were established to measure the shear bond strengths of Bond-1 (B1), ONE-STEP (OS), OptiBond SOLO (OP), Prime & Bond 2.1 (PB), Single Bond (SB), STAE (ST), Syntac Sprint (SS), and Tenure Quick (TQ) after 1-week, 3-month, and 6-month water storage at 37 degrees C. One-bottle adhesives were applied according to manufacturers' instructions and Z100 composite cylinders were applied on the bonded dentinal surfaces. The 3-month water-storage groups were thermocycled for 1500 cycles at 5 degrees C and 55 degrees C and 6-month groups for 3000 cycles. After storage periods, specimens were tested in shear in a universal testing machine (0.5 mm/min).

RESULTS

were statistically analyzed by analysis of variance and Tukey test. Results: The changes in shear bond strengths were not uniform over time. Over the test period, OS, PB, SB, and SS exhibited bond strength stability, however, SS presented low bond strengths on all tested periods. A significant decrease in bond strength was observed for B1, OP, ST, and TQ after the 6-month storage period.

Effect of smear layer on root demineralization adjacent to resin-modified glass ionomer

The cariostatic effect of resin-modified glass ionomer (RMGI) on secondary root caries is well-documented. However, this beneficial effect may be dependent upon the mode of cavity surface treatment. To investigate this relationship, we studied 4 cavity surface treatments prior to the placement of RMGI: no treatment (None), polyacrylic acid (PAA), phosphoric acid (H(3)PO(4)), and Scotchbond Multi-Purpose adhesive (SMP) as a control. Specimens were aged for two weeks in synthetic saliva, thermocycled, and subjected to an artificial caries challenge (pH 4.4). Polarized light microscopy (PLM) and microradiography (MRG) showed significantly less demineralization with the H(3)PO(4) cavity surface treatment as revealed by ANOVA and Tukey's multiple comparisons (p < or = 0.05). Dentin fluoride profiles determined by electron probe microanalysis (EPMA) supported PLM and MRG findings. It may be concluded that removal of the smear layer with phosphoric acid provides significantly enhanced resistance to secondary root caries formation adjacent to RMGI restorations.

Characterization of sound human dentin particles of sub-millimeter size

OBJECTIVES

To obtain small dentin particles to provide material for the characterization of dentin. To study the interaction of etchants with dentin not covered by a smear layer and bonding agents.

METHODS

Sound human dentin particles of sub-millimeter sizes were obtained by room temperature high-pressure fragmentation. Smear-layer free particles of three different average sizes were obtained by sieving. Surface areas were measured by the BET method. Simultaneous thermogravimetric and differential thermal analysis was carried out on all specimens and etched samples. Densities were measured by helium pycnometry.

RESULTS

On average, the water, organic and mineral contents show the expected proportions. The more dense particles tend to be in the smaller sized fractions. Thus dentin particles of average size 100 microm have a density of 2.482(0.002) g/ml which is statistically different from the 300 microm average sized particles with 2.306(0.002) g/ml. However, the respective measured specific surface areas of 2.54(0.01) and 2.50(0.02) m(2)/g are not found to be statistically different. The specific surface areas of dentin particles increase upon etching, the increase being related to acid strength. Thermal analysis of acid-etched 200 microm diameter particles shows up to 75% loss of carbonate and only 30% loss of phosphate.

SIGNIFICANCE

Smear-layer free dentin particles which have not been exposed to heat by grinding can be obtained by room temperature high-pressure fragmentation. Such sub-millimeter sized dentin particles can be acid-etched to significantly increase their specific surface area. Thermogravimetry used to analyze carbonate and phosphate contents gives new insight to the buffering action of human dentin.

Dentin proteoglycans: an immunocytochemical FEISEM study

Dentin proteoglycans are fundamental constituents of the dentin matrix and are distributed ubiquitously both in dentin and cement. They have several important functional properties; in particular, they have a fundamental role in the maintenance and the correct stabilization of collagen fibers. The use of phosphoric acid on dentin, as proposed in most common dental adhesive systems to establish a reliable bond, may affect the molecular structure of proteoglycans. The aim of this study was to evaluate, after the application of EDTA or phosphoric acid on dentin, the dentin proteoglycans with an immunocytochemical approach with high resolution SEM. For this purpose, dentin disks obtained from recently extracted human molars were etched with a 35% water solution of phosphoric acid for 15 s, 30 s, and 60 s. Control specimens were conditioned with EDTA. Specimens were immunolabeled with a monoclonal antibody antichondroitin sulfate and visualized with a gold-conjugated secondary antibody. Conditioning dentin with EDTA resulted in a distinct labeling of the proteoglycans, as visualized on branching fibrillar structures in the order of 10-20 nm. The use of 35% phosphoric acid on dentin revealed a coagulation of proteoglycans after etching for 15 s while a very low labeling signal was detectable after 30 s. No labeling was obtained after etching dentin with phosphoric acid for 60 s. These results suggest that the use of 35% phosphoric acid on dentin is able to produce significant structural modifications of the dentin proteoglycans even after short application times. Additionally, when applied on the dentin surface for more than 30 s, phosphoric acid produces a dramatic decrease in proteoglycans' antigenicity, probably due to structural modifications of the three-dimensional conformation of these molecules.

In situ atomic force microscopy of partially demineralized human dentin collagen fibrils

Dentin collagen fibrils were studied in situ by atomic force microscopy (AFM). New data on size distribution and the axial repeat distance of hydrated and dehydrated collagen type I fibrils are presented. Polished dentin disks from third molars were partially demineralized with citric acid, leaving proteins and the collagen matrix. At this stage collagen fibrils were not resolved by AFM, but after exposure to NaOCl(aq) for 100-240 s, and presumably due to the removal of noncollagenous proteins, individual collagen fibrils and the fibril network of dentin connected to the mineralized substrate were revealed. High-aspect-ratio silicon tips in tapping mode were used to image the soft fibril network. Hydrated fibrils showed three distinct groups of diameters: 100, 91, and 83 nm and a narrow distribution of the axial repeat distance at 67 nm. Dehydration resulted in a broad distribution of the fibril diameters between 75 and 105 nm and a division of the axial repeat distance into three groups at 67, 62, and 57 nm. Subfibrillar features (4 nm) were observed on hydrated and dehydrated fibrils. The gap depth between the thick and thin repeating segments of the fibrils varied from 3 to 7 nm. Phase mode revealed mineral particles on the transition from the gap to the overlap zone of the fibrils. This method appears to be a powerful tool for the analysis of fibrillar collagen structures in calcified tissues and may aid in understanding the differences in collagen affected by chemical treatments or by diseases.

Morphological study of demineralized dentine after caries removal using two different methods

BACKGROUND

Caries-affected dentine is the usual substrate bonded to in everyday clinical practice. The first step for most of the current dentine adhesive systems is etching or conditioning. It is therefore important to understand the effect of etchant/conditioner on caries-affected dentine.

METHODS

Twelve extracted carious permanent molars were examined. Six teeth had caries removed using burs after staining with a caries detector dye, and caries from the other six was removed using Carisolv. After caries removal, three teeth from each group were left untreated. The remaining teeth were sectioned to obtain two normal dentine samples and two caries-affected dentine samples from each tooth. One half of the normal dentine samples and one half of the caries-affected dentine samples were treated with 35 per cent phosphoric acid, and the remaining samples were treated with 20 per cent polyacrylic acid/3 per cent aluminium chloride. The samples were observed using field emission scanning electron microscopy (FE-SEM).

RESULTS

Phosphoric acid treated samples showed more obvious intertubular dentine microporosity and greater depth of demineralization in caries-affected dentine. Polyacrylic acid treated samples showed some residual smear layer. However, the peritubular and intertubular collagen network was easily observed in Carisolv treated dentine. The depth of demineralization was not as distinct as that of the phosphoric treated samples.

CONCLUSIONS

From this study it was shown that etched 'normal' dentine and etched caries-affected dentine had different surface appearances. Furthermore, the two caries removal techniques resulted in different caries-affected dentine surfaces after acid treatment that may influence the longevity of bonds from adhesive restorative materials.

Dentin bonding as a function of dentin structure

The traditional principles of operative dentistry have been challenged since Dr. Buonocore introduced the aid-etch technique in 1955. In spite of the numerous changes in clinical protocols and adhesive techniques, adhesion to dentin remains difficult. The importance of micromechanical bonding to dentin has been recognized over the last decade. Researchers now believe that dentin adhesion relies primarily on the penetration of adhesive monomers into the filigree of collagen fibers left exposed by acid etching. Two main strategies are currently in use for bonding to enamel and dentin: the self-etch technique and the total-etch technique. The efficiency of either bonding strategy depends very much on the dentin substrate used for bonding. Laboratory tests use ideal dentin from extracted teeth, which does not reflect the clinical reality. Clinical studies are the ultimate test for any dental adhesive material.

Morphology and thickness of the diffusion of resin through demineralized or unconditioned dentinal matrix

The formation of a hybrid layer is the main bonding mechanism of current dentin-bonding systems. This study evaluated the morphology and thickness of the resin-infiltrated dentinal layer after the application of adhesive systems. The dentin-bonding agents were evaluated on flat dentinal preparations confected on the occlusal surfaces of human teeth. The test specimens were prepared and inspected under scanning electron microscopy at a magnification of X 2,000. The adhesive systems were responsible for different hybrid layer thicknesses (p < 0.05), and the mean values were: for Scotchbond MP Plus (SM), 7.41 +/- 1.24 micrometer for Single Bond (SB), 5.55 +/- 0.82 micrometer for Etch & Prime 3.0 (EP), 3.86 +/- 1.17 micrometer and for Clearfil SE Bond (CB), 1.22 +/- 0.45 micrometer. The results suggest that the conventional three-step adhesive system (SM) was responsible for the thickest hybrid layer, followed by the one-bottle adhesive (SB). The self-etching adhesives, EP and CB, produced the formation of the thinnest hybrid layers.

Fractured surface characterization: wet versus dry bonding

OBJECTIVE

Fractographic analysis was conducted to evaluate the resin-dentin bond structures made under wet and dry conditions.

METHODS

Resin-dentin bonded specimens were prepared using two adhesive resin systems (Single Bond/SB; 3M and All Bond 2/AB2; Bisco Inc) under wet and dry conditions. The specimens were sectioned perpendicular to the adhesive interface to produce a square bar-shaped specimen (adhesive area: 0.9 mm(2)) by means of a diamond saw. The mean bond tensile test was then conducted at a crosshead speed of 1.0 mm/min. The mean bond strengths were statistically compared with two-way ANOVA and Fisher's PLSD test (p<0.05). Subsequently, the fractured surfaces of all specimens were examined using SEM and the area fractions of failure modes (%) were measured using an image analyzer on SEM microphotographs.

RESULTS

No significant differences in tensile-bond strength were observed between SB (60.1+/-16.4MPa) and AB2 (69.8+/-17.4MPa) (p>0.05) under wet conditions. However, the bond strength either of SB or AB2 made under wet conditions was significantly greater than those made under dry conditions (SB: 26.2+/-12.5MPa and AB2: 6.8+/-3.3MPa) (p<0.05). Under fractographic analysis, the major portion at the fractured surface was occupied by the cohesive failure of bonding resin and the resin composite for the wet conditions, and the top of the hybrid layer for the dry conditions in both systems.

SIGNIFICANCE

The interaction between the top of the hybrid layer and the bonding resin influenced the bond integrity.

The extent to which resin can infiltrate dentin by acetone-based adhesives

The combined methodologies of fractography and laser-Raman spectroscopic analysis were used for evaluation of the resin-dentin bonds made with wet and dry bonding. Resin-dentin-bonded beams were produced by means of 2 acetone-based adhesives (One-Step and Prime & Bond NT). The micro-tensile bond test was conducted, and the fractured surfaces of all specimens were examined by SEM and an image analyzer. The amount of resin infiltration within the hybrid layer was quantified by means of a laser-Raman spectroscope. In Raman analysis, the amount of resin impregnation within the hybrid layer of the dry bonding was found to be significantly lower (approximately 50%) than that in the wet one. Under fractographic analysis, a correlation was found between the bond strength and the failure mode. Based on those findings, it was suggested that the integrity between the bonding resin and the top of the hybrid layer played a major role in bond strength.

Adhesion/decalcification mechanisms of acid interactions with human hard tissues

In order to study adhesion/decalcification mechanisms of acid interactions with human hard tissues such as bones and teeth, the chemical interaction of five carboxylic acids (acetic, citric, lactic, maleic, and oxalic) and two inorganic acids (hydrochloric and nitric) with enamel and two synthetic hydroxyapatite (HAp) powders with, respectively, a high and a low crystallinity were analyzed using X-ray photoelectron spectroscopy (XPS), atomic absorption spectrophotometry (AAS), and spectrophotometry (S). X-ray diffraction revealed that the crystallinity of the highly crystallized HAp was considerably higher than that of enamel while the crystallinity of the poorly crystallized HAp was similar to that of dentin and bone. XPS of acid-treated enamel demonstrated for all carboxylic acids ionic bonding to calcium of HAp. AAS and S showed for both HAps that all carboxylic and inorganic acids except oxalic acid extracted Ca significantly more than P, leading to a Ca/P ratio close to that of synthetic HAp (2.16 w/w). Oxalic acid extracted hardly any Ca, but substantially more P, leading to a significantly smaller Ca/P ratio than that of HAp. AAS showed that the calcium salt of oxalic acid hardly could be dissolved, whereas the calcium salts of all the other acids were very soluble in their respective acid solution. These results confirm the adhesion/decalcification concept (AD-concept) previously advanced. Depending on the dissolution rate of the respective calcium salts, acids either adhere to or decalcify apatitic substrates. It is concluded that the AD-concept that originally dictated the interaction of carboxylic acids with human hard tissues can be extended to inorganic acids, such as hydrochloric and nitric acid. Furthermore, HAp crystallinity was found not to affect the adhesion/decalcification behavior of acids when interacting with apatitic substrates, so that the AD-concept can be applied to all human hard tissues with varying HAp crystallinity.

Dentin wetting by four adhesive systems

OBJECTIVES

To evaluate the dentin wetting by four adhesive systems and to relate the wetting properties with the adhesive efficiency.

METHODS

Scotch Bond Multipurpose Plus (3M), Syntac Single-Component (Vivadent), One-Step (Bisco) and Heliobond (Vivadent) were used. The substrate was superficial and deep human dentin. Roughness and water contact angle were measured before and after acid etching. Dentin wetting by resins was studied by contact angle measurements as a function of time to evaluate the spreading time. The shear bond strength was evaluated following a single plane method, and the microleakage was evaluated in Class V cavities.

RESULTS

Acid etching increased dentin roughness and wettability and no differences were found between acids tested. Dentin wetting and roughness was higher on deep dentin. Dentin wetting and shear bond strength of resins was similar except for Heliobond that displayed the lowest value. Microleakage was higher on the gingival wall, and the leaking was lowest for Scotch Bond Multipurpose Plus, and maximum for Heliobond. The spreading time exceeded 30s with water-based and hydrophobic adhesives, and was lower with an acetone-based adhesive. Dentin depth had some influence on contact angle and shear bond strength: contact angles obtained with SBMP and One-Step were higher on superficial dentin, and shear bond strength for One-Step was higher on superficial dentin. Dentin wetting by resins could be correlated to shear bond strength and microleakage.

SIGNIFICANCE

Dentin acid etching with different conditioners promotes similar roughness and wetting changes. On a similar substrate, the adhesion depends on the chemical and wetting characteristics of resins.

Effects of phosphoric acid and glutaraldehyde-HEMA on dentin collagen

The purpose of this study was to evaluate the effects of phosphoric acid (PA) and a proprietary glutaraldehyde-HEMA aqueous solution (Gluma Desensitizer; GD) on dentin collagen. Specimens of demineralized bovine dentin collagen were treated with either 37% or 50% PA for 1 or 5 min. An additional set of specimens was treated with 37% PA for 1 min followed by GD for 1 min. All specimens were washed with distilled water, lyophilized. reduced with standardized NaB3H4, hydrolyzed with 6 M HCl and subjected to amino acid and cross-link analyses. The results demonstrated that the treatment of demineralized dentin with PA under the conditions tested did not significantly alter the collagen cross-links. The GD-treated samples showed reduction of free lysine (Lys) and hydroxylysine (Hyl) residues, as well as a decrease in the levels of collagen reducible cross-links. In addition, unidentified reducible compounds were detected by high-performance liquid chromatography (HPLC) analysis. These compounds may be derived from cross-links formed between GD-derived aldehyde and Lys/Hyl of collagen. The findings indicate that PA treatment does not significantly affect dentin collagen amino acid and cross-link composition, and that GD treatment affects dentin collagen amino acid and cross-link composition.

A tapping mode AFM study of collapse and denaturation in dentinal collagen

OBJECTIVES

Tapping mode atomic force microscopy (AFM) was used to investigate the surface changes of collagen exposed to phosphoric acid treatment. We focus on denaturation and collapse following demineralization and exposure to air.

METHODS

Unpolished dentin disks, obtained from freshly extracted human molars, were etched in 37% phosphoric acid for 15s, rinsed ultrasonically and gently blotted with soft paper; the specimens were then continuously observed using tapping mode AFM.

RESULTS

Immediately after the removal of bulk water, the surface consisted of a porous network of banded collagen fibrils, having periodicities of 67nm. After approximately 8min of subsequent air-drying, the spacing between fibrils was lost, and the surface was observed to consist of a dense array of closely spaced fibrils. The banding periodicity was still observable.

SIGNIFICANCE

The air drying of etched dentin results in the collapse of the collagen network, but not in the denaturation of the collagen fibrils. This study indicates that collapse and denaturation are separate phenomena. It further shows that water loss occurs rapidly, and disrupts the native conformation of the collagen network. This would have adverse effects on adhesion.

Scientifically based rationale and protocol for use of modern indirect resin inlays and onlays

The desire to place esthetically pleasing, conservative, functionally stable, posterior restorative materials has steadily increased over the past 20 years. The creation of successful dentin bonding adhesives and appropriate resin luting cements has paved the way for the development of a myriad of indirect resin-based restorative materials. These materials have been specifically designed to overcome the negative attributes of their porcelain counterparts, and to simplify fabrication, insertion, and post-delivery adjustments. Possibly like no other product before, these restorative materials have met with instant clinical acceptance by many practitioners, and concern exists that these materials have not been sufficiently studied to warrant such widespread acceptance. This article presents an overview of the history and development of resin-based, esthetic, indirect systems, and offers the clinician a review of the literature supporting their role in posterior restorative dentistry. Additionally, a scientifically based protocol for preparation, impressing, provisionalization, and subsequent cementation and adjustment of indirect laboratory-processed resin inlays and onlays is presented.

Shear bond strengths of one-bottle adhesives to oil-contaminated enamel

PURPOSE

To evaluate resin bond strength to enamel contaminated with handpiece oil.

MATERIALS AND METHODS

Bovine teeth were randomly assigned to six groups of 20 teeth each for treatment with one of six different bonding systems (five one-bottle and one multibottle). For each system, 10 enamel specimens were contaminated with handpiece oil before acid-etching and 10 were contaminated after acid-etching. The enamel was etched for 15 seconds using 35% phosphoric acid. Following adhesive application, composite resin was bonded using a gelatin capsule technique. Shear bond strengths from the two contaminated groups were compared to bond strengths to uncontaminated enamel obtained from a previous study that was performed by the same group of investigators, using the same facility, materials, and methods.

RESULTS

Two-way analysis of variance (ANOVA) showed that the factor "surface contamination" did not have a significant effect on bond strength (p > .542). The type of adhesive and the interaction of adhesive and surface contamination were significant (p < .0001 and p < .003, respectively). When oil was applied before etching, mean bond strengths ranged from 18.0 +/- 4.8 MPa for OptiBond SOLO (Kerr Corp., Orange, California) to 25.3 +/- 5.6 MPa for Tenure Quik with Fluoride (Den-Mat Corp., Santa Maria, California). With oil applied after etching, bond strengths ranged from 18.4 +/- 8.0 MPa for Tenure Quik with Fluoride to 27.4 +/- 5.4 MPa for Single Bond (3M Dental Products, St. Paul, Minnesota). For the same adhesive, comparing uncontaminated and "oil-before-etch" contaminated groups, the only statistically significant difference in bond strengths was for OptiBond SOLO: 21.8 +/- 4.0 MPa (uncontaminated) versus 18.0 +/- 4.8 MPa (oil before etch). Comparing uncontaminated and "oil-after-etch" groups, the only statistically significant difference was for Tenure: 24.5 +/- 5.7 MPa (uncontaminated) and 18.4 +/- 8.0 MPa (oil after etch).

A photoacoustic FTIRS study of the chemical modifications of human dentin surfaces: I. Demineralization

Acids are used to modify the structure and composition of dentin surfaces to improve bonds formed with resins. The purpose of this work is to investigate such chemical modifications using the surface-sensitive technique photoacoustic Fourier transform infrared spectroscopy (PA-FTIRS). Spectra of acid-treated samples (citric, maleic, nitric, and phosphoric at pH = 1.0) were recorded at various time intervals. Analysis of these spectra indicates a gradual increase in sample surface area with treatment time. A decrease of the bands associated with calcium hydroxyapatite (HAP) and carbonate apatite inherent to the mineral phase of dentin are also observed. A comparison of spectra of samples treated for 2 min with each acid also reveals that maleic and phosphoric acids remove more HAP than citric acid. We conclude that citric acid may cause the formation of precipitates at the etching front which inhibit etching.

Fracture resistance of dentin-composite interfaces using different adhesive resin layers

OBJECTIVES

The objective of this study was to study the effect of different adhesive layers on the interfacial fracture toughness (K(ICi)) of dentin-resin composite interfaces.

METHODS

Miniature short-rod fracture toughness specimens containing a chevron-shaped dentin-bonded interface along their midplane were used for testing. Each interface zone contained a thinned (one coat of unfilled adhesive resin, air-thinned), one-layer (one coat of unfilled adhesive resin, brush-thinned), two-layer (two coats of unfilled adhesive resin, brush-thinned), 10% filled or 45% filled adhesive resin layer. After storage in distilled water at 37 degrees C for 24h, the fracture toughness test specimens were loaded in tension at an extension rate of 0.5mm/min until fracture and the K(ICi) were determined. The results were analysed by ANOVA and Fisher's LSD test (p<0.05). Scanning electron microscopy was used to examine representative fracture surfaces.

RESULTS

There were no significant differences in mean K(ICi) among the different unfilled adhesive resin layer groups. SEM examination of these specimens showed that fracture generally occurred between the resin-infiltrated layer and adhesive resin layer during interfacial fracture toughness testing. The mean K(ICi) for the 10% filled groups was not significantly different from the unfilled groups. The 45% filled group, however, demonstrated the highest K(ICi) values, the thickest adhesive resin layer under SEM examination, and a fracture path through the adhesive resin layer.

CONCLUSIONS

There were no significant differences in K(ICi) when the unfilled adhesive resin was used despite different application methods. The 45% filled adhesive resin improved the properties of the dentin-composite interface with respect to both interfacial fracture resistance and dentinal seal after fracture.

Evaluation of ultrasonic scaling unit waterline contamination after use of chlorine dioxide mouthrinse lavage

BACKGROUND

An infection control problem in dental operatories which is not fully controlled is waterline contamination by heterotrophic mesophilic bacteria. These bacteria are present in water supplies as a planktonic phase and adhere to the lumen of tubings as a biofilm comprised of their external cell surface glycocalyx and by production of extracellular carbohydrate polymers. The adherent film is most difficult to remove. The accumulated planktonic phase can be reduced significantly by flushing water from the lines before use in patient treatment, but will return when the equipment is idle through the accumulation of more planktonic phase and by slough of the biofilm surface-adsorbed phase not yet enmeshed in the carbohydrate matrix. Chlorine dioxide has antimicrobial activity against many bacteria, spores, and viruses. It is used in water supply treatment as a disinfectant and slime preventive and has an advantage over chlorine in that carcinogenic trihalomethanes are not generated.

METHODS

This study compared use of phosphate buffer-stabilized chlorine dioxide (0.1%) mouthrinse as a lavage in ultrasonic dental scaler units with the use of tap water as a control. Sterile water flushed through the units onto heterotrophic plate count (HPC) sampler plates was cultured 7 days at room temperature and colonies were counted at 12x. One test and one control unit were used for biopsy of internal tubing and scanning electron microscopy imaging.

RESULTS

The HPC counts, in colony forming units (CFU)/ml, were reduced 3- to 5-fold by flushing tap water through the units, but they returned after units were idle overnight. When phosphate-buffered chlorine dioxide mouthrinse was used as a lavage, CFU/ml were reduced 12- to 20-fold. Holding chlorine dioxide in waterlines overnight reduced recurrent buildup compared to water (P <0.05). Scanning electron microscopy images indicated a significant reduction of biofilm coverage by chlorine dioxide as compared to water (P<0.001).

CONCLUSIONS

Phosphate-buffered chlorine dioxide mouthrinse was effective in these short-term trials for control of waterline contamination in ultrasonic dental scaling units. It should prove as useful in dental professional waterline applications as it has in industrial uses for biofilm control.

The evaluation of four conditioners for glass ionomer cements using field-emission scanning electron microscopy

OBJECTIVES

The purpose of this study was to evaluate the GIC-dentine interface morphology using FE-SEM after four different conditioners (Ketac Conditioner, Dentin Conditioner, Cavity Conditioner, and an experimental conditioner K-930), used with two RM-GICs and one self-cured GIC, and to observe the effect with an AFM of the four different conditioners on the surface of polished human dentine.

MATERIALS AND METHODS

SAMPLE PREPARATION FOR FE-SEM: Twenty-four 1-mm thick dentine discs were obtained from superficial occlusal dentine of extracted human third molars, and finished with wet 600-grit SiC paper. The discs were treated for each of the GICs using the conditioners according to the manufacturers' instructions. The specimens were kept in tap water for 24 h at 37 degrees C, and then assigned for one of two observational techniques; a fractured technique and an acid-base technique. Specimens were mounted on aluminium stubs, gold sputter-coated and observed using a FE-SEM. SAMPLE PREPARATION FOR AFM: Four rectangular dentine blocks approximately 2mm(3) were prepared from two extracted human third molars, polished and finished with diamond paste down to 0.25 microm particle size. One half of each sample was treated with one of the conditioners according to the manufacturers' instructions, and the other half was not conditioned. The samples were stored in distilled water prior to AFM contact mode observation.

RESULTS

FE-SEM: All specimens of all materials demonstrated good adaptation to the underlying dentine. However, the specimens conditioned with K-930 showed increased demineralization and a thicker acid-base resistant layer (2.8-3.4 microm) compared with the others (1-2 microm). AFM: The images of conditioned specimens showed demineralization of peritubular dentine. Funneling of dentinal tubule orifices of specimens conditioned with K-930 was observed, and was also seen for the FE-SEM specimens.

SIGNIFICANCE

The use of surface conditioners resulted in similar adaptation to the non-conditioned specimens at the GIC-dentine interface. All of the GICs demonstrated intimate adaptation to the dentine surface whether it was conditioned or not.

Interaction patterns between dentin and adhesive on prepared class V cavities in vitro and in vivo

The interface between dentin and an acetone-based single-component adhesive system (Prime&Bond 2.1, DeTrey Dentsply, Germany) was morphologically investigated by scanning electron microscopy (SEM). Interaction patterns of human teeth were correlated in vivo and in vitro. The SEM examination proved that the formation of a hybrid and an adhesive layer, the peri- and intratubular adhesive penetration, as well as hiatus and nanoleakage formation were no different on vital and nonvital dentin within the limitation of the experimental arrangement of this study.

The influence of the modification of etched bovine dentin on bond strengths

OBJECTIVE

The aim of this study was to modify demineralized bovine dentin surfaces by application of either 12.5% sodium hypochlorite (NaOCl), or 0.1% (w/w) Type I collagenase, after conditioning with phosphoric acid, to observe the demineralized surface and to investigate the effect on tensile bond strength.

METHODS

The NaOCl was applied to etched dentin for 30 s, 1 or 2 min and the collagenase for 1, 3 or 6 h. A control group was used without NaOCl or collagenase treatment. Prior to bonding, treated surfaces were examined using an Atomic Force Microscope (AFM). A 2.3 mm diameter area of dentin was conditioned, treated and bonded with either One Coat Bond or Single Bond following each manufacturer's instructions, and a resin composite rod attached. Bonds were stressed in tension at a rate of 1 mm/min until failure. Mean bond strengths were calculated (MPa) and mode of failure was determined by observation at 20x magnification. Results were analyzed using multiple regression analysis and LSD test at the 95% level of confidence (n = 12).

RESULTS

AFM results showed progressive changes of the surface collagen as the treatment time of NaOCl or collagenase increased. For both bonding systems, the bond strengths of 1 min NaOCl and 3 h collagenase treatments were significantly higher than the control or other treatment groups (p < 0.05). Bond failure consisted of mostly adhesive failure between dentin and resin combined with small regions exhibiting cohesive failure of resin.

SIGNIFICANCE

Bond strengths were not dependent on the thickness of the hybrid layer, but rather quality of the hybrid layer.

Laboratory evaluation and clinical application of a new one-bottle adhesive

PURPOSE

The purposes of this project were to compare the enamel and dentin bond strengths of a new nanofilled one-coat adhesive system with its predecessor, an unfilled two-coat adhesive system; to analyze the dentin interfacial ultramorphology, using scanning and transmission electron microscopy (SEM and TEM); and to illustrate the clinical technique associated with the use of the new nanofilled one-coat adhesive system.

MATERIAL AND METHODS

Twenty flat dentin surfaces and 20 flat enamel surfaces were polished on the labial surface of bovine incisors mounted in acrylic resin. The specimens were equally and randomly assigned to four bonding groups: (1) dentin with Prime & Bond 2.1; (2) dentin with Prime & Bond NT; (3) enamel with Prime & Bond 2.1; and (4) enamel with Prime & Bond NT. A composite post was then adapted to the treated area and light-cured. After thermocycling, shear bond strengths were determined by testing the shear strength of the specimens. The data were analyzed using one-way analysis of variance (ANOVA) and Student's t-test. For SEM and TEM, six dentin disks were obtained from middle dentin of human third molars and assigned equally to each adhesive. The adhesives were applied to dentin according to manufacturer's directions. The hybrid layer and resin penetration into dentin tubules were analyzed at an ultramorphologic level, and the observations were compared.

RESULTS

Shear bond strengths were as follows: group 1: 17.8 +/- 4.1 MPa; group 2: 20.5 +/- 3.5 MPa; group 3: 24.7 +/- 6.7 MPa; and group 4; 27.0 +/- 5.4 MPa. Electron microscopy showed that both adhesives penetrated the dentin tubules and formed a fully infiltrated hybrid layer. The nanofiller included in the new one-application adhesive penetrated the dentin tubules and infiltrated the microspaces between the collagen fibers within the hybrid layer.

CLINICAL SIGNIFICANCE

The new one-application nanofilled adhesive tested in this study resulted in bond strengths and dentin hybridization comparable to those obtained with the corresponding two-application system. The clinical sequences presented illustrate the ease of use of the newest simplified adhesives.

Porcelain veneers bonded to tooth structure: an ultra-morphological FE-SEM examination of the adhesive interface

OBJECTIVES

The porcelain veneer technique bonds a thin porcelain shell to a minimally prepared tooth surface (enamel and/or dentin) with a luting composite in combination with an adhesive system. When complete, two adhesive interfaces are formed--resin to etched porcelain and resin to tooth structure. The purpose of this laboratory investigation is to analyze the ultra-structure of these two adhesive interfaces in order to find an explanation for some clinical phenomena and/or shortcomings of bonded porcelain veneers.

METHODS

The surfaces of four porcelain disks were treated successively by sandblasting, etching with hydrofluoric acid, ultrasonic cleaning, and silanizing. The effect of each step on the surface structure of the porcelain was evaluated by field-emission scanning electron microscopy (FE-SEM). In addition, the effect of acid etching the tooth surface of veneer preparations on seven extracted upper anterior teeth was similarly determined. Finally, pre-treated porcelain veneers were luted to veneer preparations on 12 extracted upper anterior teeth by means of a contemporary total-etch adhesive system and a photo-polymerizable luting composite. The tooth/luting composite and the luting composite/porcelain interface of the veneer complex were then evaluated ultra-morphologically by FE-SEM after the specimens had been etched with an argon-ion beam to enhance the surface relief.

RESULTS

FE-SEM imaging of the tooth/luting composite/porcelain interface showed strong micro-mechanical interlocking of the luting composite in the micro-retentive pits both of the acid-etched tooth surface and in the etch pits of the acid-etched porcelain surface. From this ultra-morphological perspective, the etched porcelain surface is more retentive than the etched tooth surface. At the tooth surface, cervical aprismatic enamel and exposed dentin showed the least resin-receptive surface texture. However, in these areas, no separation of the interface was observed when a multi-step total-etch adhesive system was used.

SIGNIFICANCE

The strong interlocking of the luting composite into the retentive etch pits of both the porcelain and tooth substrates contributes to strong adhesion of porcelain veneers with good retention. This study suggests that a modern multi-step total-etch adhesive system can produce adhesion even to the less retentive cervical enamel and exposed dentin. Further clinical research is necessary to evaluate the long-term retention of porcelain veneers and to correlate these in vitro observations with clinical performance.

Surface fine structure of treated dentine investigated with tapping mode atomic force microscopy (TMAFM)

OBJECTIVES

The objective of this study was to investigate the surface morphology and roughness of human dentine treated with different dentine conditioning agents with tapping mode atomic force microscopy (TMAFM).

METHODS

Dentine samples from third permanent molar teeth were prepared as flat disks. The samples were treated with different conditioning agents for 15-30 s: aqueous phosphoric acid and those supplied with three commercial adhesive products. The surface morphology and roughness was measured with tapping mode atomic force microscopy, a highly resolving method which minimises unwanted side effects of conventional AFM.

RESULTS

The tubules, the areas between the tubules and the entire surface showed variations in surface morphology and roughness, depending on the conditioning agent used. These differences might affect the bonding properties of the agents in dentine/polymer systems.

CONCLUSIONS

The surface structure, such as the tubules diameters and depths, the local height differences of the surface between the tubules and the overall mean surface roughness Ra varies between samples treated with different conditioning agents. All conditioning agents, however, led to exposed and open tubules.

CLINICAL RELEVANCE

The direct observation of effects of conditioning agents on dentine is important in order to judge their performance under clinically relevant conditions-free of desiccation artefacts. A vast number of conditioning agents is available today. The differences in their actual effects on dentine surfaces, however, are less than clear to many users.

The durability of adhesion to phosphoric acid etched, wet dentin substrates

OBJECTIVE

The purpose of this study was to investigate the influence of remaining non-resin-impregnated, phosphoric acid demineralized dentin upon the long-term durability of specimens that were wet-bonded to bovine dentin substrates.

METHODS

Prepared bovine dentin samples were etched with 65% phosphoric acid then rinsed with water and kept wet during application of 5 wt% 4-methacryloyloxyethyl trimellitate anhydride (4-META) in acetone primer. This was followed by application of a photocured dentin-bonding agent consisting of 4-methacryloyloxyethyl trimellitate anhydride/triethyleneglycol dimethacrylate-camphorquinone/N-phenylglycine (4-META/TEGDMA-CQ/NPG). The tensile bond strength (TBS) of bonded specimens was determined after immersion in 37 degrees C water for various time intervals. Generated data were analyzed for statistical significance by one-way ANOVA and Duncan's New Multiple Range Test (p < 0.05). The dentin side of the tensile-load-fractured specimens was examined under optical and scanning electron microscopes (SEM).

RESULTS

TBS decreased from 6.6 +/- 1.0 MPa after 1-day water immersion to 3.4 +/- 1.7 MPa after 1 month of water immersion. After 6 months of water immersion, TBS was found to be 3.9 +/- 0.9 MPa and this decreased to 2.0 +/- 1.0 MPa for specimens immersed in water for 1 year, a statistically significant difference (p < 0.05). Optical microscopic and SEM observations disclosed failure patterns within demineralized, non-resin-impregnated dentin that increased with the period of water immersion.

SIGNIFICANCE

The bond durability to wet dentin was poor when demineralized dentin was not resin-impregnated, resulting in exposure of collagen fibrils which hydrolyzed during long periods of water immersion.

Regional bond strengths of self-etching/self-priming adhesive systems

The purpose of this study was to measure the regional tensile bond strengths (TBS) at various portions of human tooth enamel and dentin, and to observe the resin-dentin interfaces of two commercially available self-etching/self-priming adhesive systems by scanning electron microscopy (SEM). Twelve extracted human cuspid teeth were used to measure TBS and four additional teeth were used for scanning electron microscopy (SEM). Outer enamel and dentin were removed from the labial tooth surfaces to form a long cavity preparation into middle dentin extending from the mid-crown to the apex of the root within the same tooth. Either Clearfil Liner Bond 2 (LB 2, Kuraray) or Fluoro Bond (FB, Shofu) was bonded to the surfaces, and covered with resin-composite. The resin-bonded teeth were serially sliced at right angles to the long axis of the tooth, and the bonded surfaces were trimmed to give a bonded cross-sectional surface area of 1 mm2 for TBS tests. LB 2 and FB showed significantly higher TBS in coronal, cervical and middle root dentin than that in enamel and apical root dentin. SEM showed that the thickness of the hybrid layer of both systems was about 1.0 microm in coronal, cervical and middle root dentin, and less than 0.5 microm in apical root dentin. These results suggested that the self-etching/self-priming systems produce good adhesion in coronal, cervical and middle root dentin by creating thin hybrid and transitional layers, but bonding to enamel and apical root dentin should be improved.