The influence of resin composite and bonded amalgam restorations on dentine permeability in Class II cavities in vitro

Effect of a new desensitizing material on human dentin permeability

OBJECTIVES

Resin-modified glass ionomers (RMGI) have demonstrated clinical success providing immediate and long-term relief from root sensitivity. RMGIs have been recently introduced as paste-liquid systems for convenience of clinical usage. The objective of this study was to measure the ability of a new paste-liquid RMGI to reduce fluid flow through human dentin, compared to an established single-bottle nanofilled total etch resin adhesive indicated for root desensitization.

METHODS

Dentin permeability was measured on human crown sections on etched dentin, presenting a model for the exposed tubules typical of root sensitivity, and permitting measurement of the maximum permeability. In the first two groups, the etched dentin was coated with either the RMGI or adhesive, and permeability measured on the coated dentin. In a third group, a smear layer was created on the dentin with sandpaper, then the specimens were coated with the RMGI; permeability was measured on the smeared and coated dentin. Specimens from each group were sectioned and examined via scanning electron microscopy (SEM).

RESULTS

Both the resin adhesive and the new paste-liquid RMGI protective material significantly reduced fluid flow through dentin, and exhibited excellent seal on dentin with either open tubules or smear-layer occluded tubules. The RMGI infiltrated the smear layer with resin during placement, penetrated dentin tubules, and formed resin tags.

SIGNIFICANCE

The RMGI was equivalent to the adhesive in its ability to reduce fluid flow and seal dentin. It is therefore concluded that the new RMGI and the adhesive show the potential to offer excellent sensitivity relief on exposed root dentin.

Real-time measurement of dentinal fluid flow during amalgam and composite restoration

OBJECTIVES

This study examined changes in the dentinal fluid flow (DFF) during restorative procedures and compared permeability after restoration among restorative materials and adhesives.

METHODS

A class 1 cavity was prepared and restored with either amalgam (Bestaloy), or composite (Z-250) with one of two etch-and-rinse adhesives (Scotchbond MultiPurpose: MP and Single Bond 2: SB) or one of two self-etch adhesives (Clearfil SE Bond: CE and Easy Bond: EB) on an extracted human third molar which was connected to a sub-nanoliter fluid flow measuring device (NFMD) under 20 cm water pressure. DFF was measured from the intact tooth state through the restoration procedures to 30 min after restoration, and re-measured at 3 and 7 days post-restoration.

RESULTS

Inward flow during cavity preparation was followed by outward flow after preparation. In amalgam restoration, the outward flow changed into an inward flow during amalgam filling, which was followed by a slight outward flow after finishing. In composite restoration, MP and SB showed an inward flow and outward flow for the rinsing and drying steps, respectively. Application of a hydrophobic bonding resin in the MP and CE systems caused a decrease in the flow rate. Air-drying of solvent for the CE and EB systems caused a sudden outward flow, whereas light-curing of the adhesive and composite caused an abrupt inward flow.

CONCLUSIONS

Each restorative step clearly changed the direction and the rate of the DFF during restoration, which could be well identified with NFMD.

Effect of a new liner/base on human dentin permeability

OBJECTIVES

Resin-modified glass ionomers (RMGI) have demonstrated clinical success in their ability to minimize post-operative sensitivity of restorations. RMGIs have been recently introduced as paste-liquid systems for convenience of clinical usage. The objective of this study was to measure the ability of a new paste-liquid RMGI liner/base to reduce fluid flow through human dentin.

METHODS

Dentin permeability was measured on human crown sections on etched dentin, using etched dentin as a model for the exposed tubules typical of root sensitivity, and permitting measurement of the maximum permeability. In the one group, the etched dentin was coated with the RMGI, and pre- and post-treatment permeability was measured on the coated dentin. In the second group, a smear layer was created on the dentin with sandpaper, then the samples were coated with the RMGI; permeability was measured on the smeared and coated dentin. Samples from each group were sectioned and examined via scanning electron microscopy (SEM).

RESULTS

The new paste-liquid RMGI liner/base significantly reduced fluid flow through dentin, and exhibited excellent seal on dentin with either a smear layer or open tubules. SEM images show evidence that the RMGI infiltrated the smear layer with resin during placement, penetrated dentin tubules, and formed resin tags in acid-etched dentin.

CONCLUSIONS

Based on these results, combined with previous research on adhesion and microleakage, it is concluded that the new RMGI liner/base should minimize post-operative sensitivity in restorations.

Evaluation of the effect of four self-etching adhesives on dentin permeability

OBJECTIVE

The aim of this study was to evaluate the effect of two two-step and two single-step self-etching adhesives on dentin permeability using a computerized fluid filtration (CFF) test method.

METHODOLOGY

Forty recently extracted sound human molar teeth were sectioned at the mid level of the crown to obtain dentin discs of 1 +/- 0.2 mm. A total of 40 discs were obtained and randomly divided into four groups (n = 10). The permeability of the discs was measured using the CFF test method before and after application of the following self-etching adhesives: Hybrid Bond, G-Bond, AdheSE, and Protect Bond. Fluid movement measurements were made at 2-min intervals for 8 min, and a mean of the values obtained was calculated for each specimen.

RESULTS

The in vitro fluid conductance of dentin discs treated with Hybrid Bond and AdheSE were lower than the dentin discs treated with G-Bond and Protect Bond (p < 0.05).

CONCLUSION

1-Treating dentin discs with self-etching adhesives caused significant reduction of dentin permeability. 2-All self-etching adhesives allowed diffusion of distilled water. However, AdheSE and Hybrid Bond showed the lowest permeability.

The repeatability of human dentine permeability measurement in vitro

OBJECTIVE

The aim of this study was to determine the repeatability of apparatus designed to assess dentine permeability at two different pressures.

METHOD

Forty-five human coronal tooth portions were prepared and permeability was measured at two separate time points, 5h apart, at 14 cm H2O pressure and then at 100 cm H2O pressure. Repeatability was determined using the limits of agreement (LOA) method.

RESULTS

The results showed equal mean permeability of 0.6 microl at both time 1 and time 2 at 14 cm H2O pressure, and 2.7 and 2.5 microl at time 1 and time 2, respectively, at 100 cm H2O pressure. At 14 cm H2O pressure, the LOA were (-0.4, 0.4)microl and at 100 cm H2O pressure the LOA were (-0.2, 0.6)microl.

CONCLUSION

Although repeatability measurement at 14 cm H2O pressure appeared to be acceptable, the higher permeability values at 100 cm H2O pressure may make the latter the pressure of choice despite the small bias.

Fluid movement across the resin-dentin interface during and after bonding

This study evaluated the extent of water penetration through resin-dentin interfaces before and after being sealed with adhesives. Four adhesive resin systems (2 total-etch adhesives and 2 self-etching primer adhesives) were used in this study. Dentin disks were placed in a split-chamber device, and in situ fluid movement across dentin was measured, with and without physiological pressure, during bonding procedures or 24 hrs after bonding. The fluid movement across dentin occurs via dentin tubules after acid-etching. Large outward or inward fluid shifts across dentin were observed during air-drying and light-curing for resin application. The amount of fluid movement across resin-bonded dentin when total-etch adhesives were used was significantly greater than that with self-etching adhesives. The milder acid-etching effects of self-etching primers may retain hybridized smear plugs within the tubules that reduce outward fluid flow, resulting in superior dentin sealing.

Effect of dentin perfusion on the sealing ability and microtensile bond strengths of a total-etch versus an all-in-one adhesive

OBJECTIVES

To test the null hypothesis that perfusion of dentin has no effect on the sealing or bond strength in Class V resin composite restorations using a two-step total-etch (Scotchbond 1), or a one-step self-etch (all-in-one) (Prompt L-Pop) adhesive.

METHODS

Dentin permeability in Class V cavity preparations cut into extracted human third molars was measured in a fluid transport setup. Resin composites were placed using either Scotchbond 1, or Prompt L-Pop with or without dentin perfusion at 1.47 kPa. Permeability was re-measured, and the reduction in permeability was calculated as a percentage of the initial value. Additionally, microtensile bond strength (microTBS) to dentin was measured.

RESULTS

Whereas the ability of Scotchbond 1 to seal dentin was significantly decreased due to dentin perfusion (p = 0.00025), that of Prompt L-Pop was not affected (p = 0.099). Scotchbond 1 produced significantly less dentinal seal than Prompt L-Pop only in the restorations carried out with perfusion (p = 0.0003), in the absence of perfusion, however, the difference was not significant (p = 0.343). Dentin perfusion significantly decreased the microTBS of Scotchbond 1 to dentin (p = 0.001). Due to excessive premature failure during sectioning, microTBS test could not be performed with Prompt L-Pop.

SIGNIFICANCE

Dentinal fluid flow may have detrimental effects on the sealing ability of dental adhesives depending on the type of adhesive used. Studies aiming to rank adhesives in relation to their sealing ability in vitro should not disregard dentin perfusion.

Pulpal uptake of mercury from lined amalgam restorations in guinea pigs

The aim of the present study was to examine pulp in amalgam-restored teeth of guinea pigs with respect to the presence of mercury, and to evaluate whether lining of cavities with resin modified glass ionomer cements had any effect on the penetration of mercury. Class V cavities were prepared in 63 incisor teeth of 21 guinea pigs. Three amalgam restorations were placed per animal, one without base liner and two with different resin-modified glass ionomer cements (GC Lining LC and Ionoseal). Following observation periods of 1, 7 or 30 d, teeth were extracted and the mercury concentration in the pulp tissue was evaluated using atomic absorption spectrophotometry. It was found that resin-modified glass ionomer cements significantly diminished the transport of mercury into the pulp between day 7 and day 30 after amalgam insertion.

The effects of post-extraction time on the hydraulic conductance of human dentine in vitro

The permeability characteristics of dentine have been used in many in vitro studies to evaluate longitudinally the efficacy of various restorative and preventative procedures. However, the permeability of human dentine increases over time after tooth extraction. The aim here was to determine if there is a steady phase in dentine permeability in vitro over time. The convective permeability of dentine discs cut from extracted human third molars to 0.8% albumin solution was measured initially on day 7 after extraction using a fluid-transport model and the hydraulic conductance was calculated. The permeability of each disc was then re-measured de- and re-mounting the split-chamber 1h after the initial measurement as well as on days 8, 9, and 37 after extraction. No significant difference was found between the initial and 1h hydraulic conductances. A significant increase in hydraulic conductance was seen from day 7 to 9, but there was no significant difference between the hydraulic conductances on days 9 and 37. These results suggest that the measurements were reproducible and that a steady phase of dentine permeability is established 9 days after extraction under these study conditions in vitro.