Dentine permeability and tracer tests

Simulated Hydrostatic Pulpal Pressure Effect on Microleakage-An Initial Study

PURPOSE

This study's purpose was to evaluate the effect of simulated in vitro hydrostatic pulpal pressure (HPP) on microleakage.

METHODS AND MATERIALS

Extracted third molars (n=12) were sectioned 5 mm below the cementoenamel junction, pulp tissue removed, and the sectioned crowns mounted on a Plexiglas plate penetrated by an 18-gauge stainless steel tube. The mounted specimen mesial surface received a 2×4×6 mm Class V preparation followed by restoration with a strongly acidic, one-step dental adhesive and a flowable microfilled resin, following all manufacturers' instructions. Restorations were finished to contour, and tubing was attached to a 20-cm elevated, 0.2% rhodamine G reservoir to the specimen steel tube for 48 hours. Specimens then received a nail polish coating to within 1 mm of the restoration margins and were placed in 2% methylene blue (MB) dye for 24 hours, followed by rinsing, embedding in epoxy resin, and sectioning into 1 mm slices using a diamond saw. Controls were intact molars (n=12) processed as above but without HPP. Specimen slices were evaluated using laser confocal microscopy with images exported to ImageJ software with microleakage assessed as the MB linear penetration as a percentage of the total interfacial wall length. Mean values were evaluated with the Kruskal Wallis/Dunn test at a 95% confidence level.

RESULTS

The control specimens demonstrated significantly greater (p<0.0001) MB penetration than experimental specimens with simulated HPP. Under this study's conditions, simulated HPP significantly decreased MB dye penetration.

CONCLUSION

Studies accomplished without simulated HPP may overestimate microleakage results.

Impact of dentin conditioning and sealer modification with chitosan-hydroxyapatite nanocomplexes on the antibacterial and mechanical characteristics of root dentin

INTRODUCTION

This study aimed to characterize the effectiveness of dentin-conditioning with bio-mineralizable chitosan-hydroxyapatite precursor (CS-HA) nanocomplexes alone or associated with tricalcium silicate sealer (TCS/CS-HA) on the mechanical property and antibiofilm efficacy in root dentin.

METHODS

Flow tests were performed following ISO6876:2012-specifications. Solubility was measured. Micromorphology was assessed using Scanning Electron Microscopy (SEM). Nanohardness/elastic modulus were also determined. Fracture resistance was determined on lower premolars that were prepared, and randomly distributed among 7-groups (n=8/group), including the control, CS-HA dentin-conditioning and root canal filled groups. Similar canal preparation/distribution procedure was followed to test the antibacterial effect on Enterococcus faecalis-infected roots. Descriptive statistic was used to report SEM findings. Flowability results were analyzed using Paired t-test. Multiple comparisons from solubility, fracture and antibacterial assays were assessed by one-way ANOVA-Tukey's tests.

RESULTS

TCS/CS-HA showed optimal flow and no effect on solubility after immersion for 4 weeks (p>.05). TCS/CS-HA significantly increased nanohardness and elastic modulus (210±11.3MPa, 7.9±0.9GPa) compared to TCS (44.5±7.8MPa, 2.1±0.3GPa,p<.05). SEM revealed needle-shaped mineralized structures resulting in fewer voids and a well-adapted sealer-dentin interface in the TCS/CS-HA groups. NaOCl-EDTA irrigation resulted in reduced fracture resistance (444.34N) while CS-HA dentin-conditioning alone (928.28N, p<.05) and CS-HA dentin-conditioning plus CS-HA/TCS resulted in higher fracture resistance (1134.06N, p<.05). CS-HA dentin-conditioning also reduced bacteria by 2.04 log (4.50±0.43) from the initial bacterial load (6.54±0.07, p<.05). There was further bacterial reduction when CS-HA-conditioned root canals were filled with TCS or TCS/CS-HA (0.00 to 0.98±0.57, p>.05).

CONCLUSION

Dentin modification with CS-HA increased the fracture resistance of root dentin, and decreased the residual bacterial burden. TCS/CS-HA potentiated the nanomechanical and physical properties of TCS.

Marginal, Internal Fit and Microleakage of Zirconia Infrastructures: An In-Vitro Study

Fitting accuracy and microleakage dominate prognostic covariates for the long-term durability of crown restorations. The fitting accuracy and microleakage potential of zirconia infrastructures might be influenced by manufacturing technology.

Assessment of different dyes used in leakage studies

The goal of this in vitro study was to identify the most suitable dye for endodontic dye leakage studies, which could be a further step towards standardisation. The root canals of 70 extracted, single-rooted human adult teeth were enlarged to apical size 50 using hand instruments. The teeth were divided into seven groups (n = 10 each), and all root canals were completely filled by injection with one of the following dyes: methylene blue 0.5% and 5%, blue ink, black ink, eosin 5%, basic fuchsin 0.5% and drawing ink. Transverse root sections from the coronal, middle and apical part of the roots were examined, and the percentage of the dentine penetrated by dye was evaluated by software-supported light microscopy. In addition, the range of particle size of drawing ink particles was evaluated. There were conspicuous differences in the relative dye penetration into the root dentine and the penetration behaviour in the different root sections (two-way ANOVA, both p < 0.0001). One dye (drawing ink) penetrated less into the root dentine compared with all the others (p <0.0001). The particle size of this agent (0.1-2 microm) corresponds best with the size range of a representative selection of 21 species of pathogenic endodontic bacteria. Compared to the other dyes tested, drawing ink appears to be superior for use in endodontic dye leakage studies. The penetration behaviour into the root dentine of all the other dyes tested might be one factor that limits the applicability of these dyes in dye leakage studies.

Lack of correlation between ex vivo apical dye penetration and presence of apical radiolucencies

OBJECTIVE

The aim of this study was to determine if there is a significant correlation between the in vivo presence of periapical radiolucency and ex vivo apical dye penetration on the same human teeth.

STUDY DESIGN

Eighty-four endodontically filled teeth that were scheduled for extraction were classified into 2 groups according to the presence or absence of a periapical radiolucency and further divided into 2 subgroups according to the quality of the root canal filling. After extraction, the apical filling was evaluated by a dye penetration method.

RESULTS

The dye extraction evaluation showed no correlation between apical dye penetration and the presence of a periapical radiolucency (not significant), but a statistically significant correlation with the quality of the root canal filling (P = .03).

CONCLUSION

The results of the dye penetration study were correlated to the quality of the root canal filling but had no predictive value for the development of periapical radiolucency.

Influence of the methodology and evaluation criteria on determining microleakage in dentin–restorative interfaces

This in vitro study compared microleakage along the dentin-restorative interface using a spectrophotometer protocol and two conventional single-surface methods (scores and percentages), using an organic dye (0.5% buffered methylene blue) or a tracer (50% silver nitrate). Occluso-proximal preparations with gingival margins in dentin were made in 40 human teeth. The teeth were divided into four groups (n=10) according to the solution dyes and adhesive system used: group 1, single bond/methylene blue; group 2, single bond/silver nitrate; group 3, Clearfil SE Bond/methylene blue; and group 4, Clearfil SE Bond/silver nitrate. The dye penetration measurements were made in all groups, using scores and percentages. Groups 1 and 3 were also assessed by UV spectrophotometer. For percentage measurement, the data were submitted to ANOVA and Tukey's test. For the material factor, there was a statistically significant difference between groups 1 and 3. For the dye factor, there was a statistically significant difference between groups 3 and 4. The score results were submitted to Kruskall-Wallis test and showed differences between groups 1 and 3 and groups 2 and 3. For spectrophotometer measurement, no significant difference was observed between groups 1 and 3. The results of dye penetration suggest that there was a difference between dyes and measurement methods, and this should change the interpretation of microleakage tests.

Microleakage in bonded amalgam restorations using different adhesive materials

The aim of this study was to verify the ability of different adhesive materials to prevent microleakage in bonded amalgam restorations. Standard cavities were prepared in both buccal and lingual surfaces of 35 bovine incisors. The gingival wall was located in cementum/dentin and the occlusal wall in enamel. Teeth (n=35) were divided into 5 groups, according to material employed (one glass-ionomer cement, two resin cements, one adhesive system, and Copalex varnish as a control). Following restoration, the teeth were submitted to thermal cycling. The teeth were subsequently immersed in methylene blue dye and sectioned to allow assessment of microleakage. Non-parametric statistical analysis indicated that all materials demonstrated less leakage than the control group (p<0.01). No leakage was found using the resin-modified glass-ionomer cement, which was significantly different from the other adhesive materials (p<0.05). Leakage in enamel was lower than in cementum/dentin margins. It was concluded that bonded amalgam was an effective technique, since all materials prevented microleakage in enamel and cementum/dentin, when compared to the control group, except Panavia in cementum/dentin margins.

Comparison of two methods to measure permeability of dentin

Dentin permeability was measured alternatively with two methods: a 10-microl capillary method with visual evaluation (PC) and a motorized automatic measuring device (Flodec, FD), both interposed in a simulated perfusion system. Eight human third molar coronal fragments were connected to systems, and their permeability to distilled water measured at 0, 5, 10, 15, 20, 25, and 29 cm H(2)O pressure. Resultant permeabilities (in microl/s) for both techniques were interrelated with the use of the Passing and Bablok nonparametric method, which gives information about the range of constant and proportional errors and their 95% confidence intervals (95CI). The relationship between the methods is described by the regression formula: FD = -0.0003 + 0.945.PC, with 95CI for constant (-0.0015-0.0009) and for slope (0.738-1.168), indicating that both methods are interchangeable, although not identical.

Surface coating and leakage of dentin-bonded resin composite restorations

OBJECTIVES

To compare the marginal leakage of dentin-bonded resin composite restorations in tooth sections coated with nail varnish and similarly restored sections coated with cyanoacrylate cement.

METHODS

MO and DO cavities were prepared with the gingival floor below the CEJ in 11 non-carious extracted human molars. Each cavity was restored with a dentin adhesive and resin composite. Sectioning yielded four specimens per tooth (N=44). One specimen from each restoration was coated with varnish. The other specimen was coated with cyanoacrylate cement. The coatings were applied to all surfaces except that a 1mm window on either side of the interproximal gingival margin was left uncoated. Specimens were thermocycled and stained with silver nitrate. Silver penetration into the gingival margin of each section was measured with a measuring microscope. The predominant leakage path for each coating type was determined by scanning electron microscopy.

RESULTS

There was no significant difference between the leakage of the varnish-coated and cyanoacrylate-coated specimens. No marginal gaps were observed either by optical or by electron microscopy. However, the both optical and electron microscopy revealed leakage in nearly all specimens. This leakage was confined to either the dentin/hybrid layer interface or the adhesive resin/hybrid layer interface.

CONCLUSIONS

The results suggest that these coating materials are not confounding factors in laboratory investigations of marginal leakage along dentin-bonded interfaces of resin composite restorations. Although marginal gaps were undetectable even at high magnification, leakage was observed along the gingival margin of almost all of these Class II resin composite restorations.

Comparison of three types of fiber-reinforced composite molar crowns on their fracture resistance and marginal adaptation

Three types of fiber-reinforced composite (FRC) molar crowns were tested on their fracture resistance and marginal adaptation under simulated oral stress conditions. Two glass fiber systems, one processed with a vacuum/pressure system, the other by manual fiber adaptation, and a polyethylene fiber system were evaluated. Every group consisted of 12 crowns. All crowns were luted adhesively on human molars and exposed to thermal cycling and mechanical loading (TCML: 6000 x 5 degrees C/55 degrees C; 1.2 x 10(6) x 50N; 1.66Hz). The marginal adaptation was evaluated through dye-penetration and analyzed semi-quantitatively with a scanning electron microscope. The fracture resistance was measured using a Zwick universal testing machine. The highest fracture resistance was observed on the glass-fiber systems (FibreKor/Sculpture 1875N +/- 596; Vectris/Targis 1726+/-542), though statistically, the polyethylene system (belleGlass/Connect 1388+/-620) was not significantly weaker. All systems exceeded the fracture resistance required to withstand the maximum masticatory forces expected in the molar region. The marginal adaptation generally had a tendency towards larger gaps after TCML. The crown/composite-cement bond deteriorated significantly after TCML with the manual fiber adaptation and the polyethylene fiber system. The cement/tooth bond strength depended on which composite-cement/dentin-adhesive system was used.

CONCLUSION

The fracture resistance of molar crowns made of glass-fiber reinforced composite was higher than those of polyethylene fiber-reinforced composite crowns. However, there was no statistically significant difference. The marginal adaptation seems to depend on the fiber systems and composite-cement/dentin adhesive system used.

Biocompatibility of resin-modified filling materials

Increasing numbers of resin-based dental restorations have been placed over the past decade. During this same period, the public interest in the local and especially systemic adverse effects caused by dental materials has increased significantly. It has been found that each resin-based material releases several components into the oral environment. In particular, the comonomer, triethyleneglycol di-methacrylate (TEGDMA), and the 'hydrophilic' monomer, 2-hydroxy-ethyl-methacrylate (HEMA), are leached out from various composite resins and 'adhesive' materials (e.g., resin-modified glass-ionomer cements [GICs] and dentin adhesives) in considerable amounts during the first 24 hours after polymerization. Numerous unbound resin components may leach into saliva during the initial phase after polymerization, and later, due to degradation or erosion of the resinous restoration. Those substances may be systemically distributed and could potentially cause adverse systemic effects in patients. In addition, absorption of organic substances from unpolymerized material, through unprotected skin, due to manual contact may pose a special risk for dental personnel. This is borne out by the increasing numbers of dental nurses, technicians, and dentists who present with allergic reactions to one or more resin components, like HEMA, glutaraldehyde, ethyleneglycol di-methacrylate (EGDMA), and dibenzoyl peroxide (DPO). However, it must be emphasized that, except for conventional composite resins, data reported on the release of substances from resin-based materials are scarce. There is very little reliable information with respect to the biological interactions between resin components and various tissues. Those interactions may be either protective, like absorption to dentin, or detrimental, e.g., inflammatory reactions of soft tissues. Microbial effects have also been observed which may contribute indirectly to caries and irritation of the pulp. Therefore, it is critical, both for our patients and for the profession, that the biological effects of resin-based filling materials be clarified in the near future.

Association between microtensile bond strength and leakage in the indirect resin composite/dentin adhesively bonded joint

PURPOSE

Develop a methodology to correlate microtensile bond strength (microTBS) and leakage within the same site of a specimen and evaluate the predominate debond and leakage pathways.

MATERIALS AND METHODS

A Class II (MO) slot cavity was prepared in 37 extracted human molars and restored with indirect resin composite restorations. The restored teeth were thermocycled 300X between 5 and 55 degrees C and then stained with silver. Two specimens per tooth were obtained by diamond saw sectioning for measurement of leakage (microm) and microtensile bond strength (MPa) at the gingival wall and then tested for association with regression analysis. Scanning electron microscopy techniques and energy dispersive spectroscopy (EDS) were used to evaluate the debond and leakage pathways.

RESULTS

Association between leakage and bond strength was not significant (t=1.31, p=0.198). All 74 samples debonded within the joint, predominantly at the hybrid layer-adhesive resin region with only one specimen including a small portion of resin cement in the debond pathway. Secondary and backscatter imaging and EDS analysis showed leakage in all samples that involved the hybrid layer.

CONCLUSION

This study demonstrates a feasible method for evaluating leakage and bond strength at the joint interface within the same specimen.