Microleakage in alloy-glass ionomer lined amalgam restorations after thermocycling

Fracture resistance of amalgam/glass-polyalkenoate open sandwich Class II restorations: an in vitro study

OBJECTIVE

To investigate the effect of two glass-polyalkenoate restorative materials used as root-dentin replacements on the fracture strength of Class II amalgam restorations.

MATERIALS AND METHODS

Class II slot preparations extending 2mm apical to the cemento-enamel junction were made in 30 teeth and randomly assigned to three groups. Group 1 (Control): restored entirely with amalgam (Tytin, Sybron Kerr, Orange, CA, USA). Group 2: The root-dentin area was restored with a viscous conventional glass-polyalkenoate restorative material (Fuji IX GP, GC America, Alsip, IL, USA), and the remainder of the preparation restored with amalgam. Group 3: The root-dentin area was restored with a resin-modified glass-polyalkenoate restorative material (Fuji II LC, GC America) and the remainder restored with amalgam. The amalgam restorations were loaded in compression to failure and the data analyzed using one-way ANOVA (alpha=0.05).

RESULTS

No significant differences in fracture strength were found.

CONCLUSION

Root-dentin replacement with the tested glass-polyalkenoate materials did not affect the fracture strength of Class II amalgam restorations.

Three-dimensional evaluation of gap formation of cervical restorations

OBJECTIVES

In some studies gap formation has been evaluated in just one section of the restorative. This in vitro study aimed to design a quantitative three-dimensional method for evaluation of the contraction gap in restoratives.

METHODS

Cervical cavities were prepared on buccal, palatal or lingual surfaces in human extracted molars and were then filled with resin composites. Specimens were reduced every 100 microm in a direction parallel to the tooth axis, and perpendicular to the cavity floor from one proximal side to the other. The sequence of reducing the sections by 100 microm, image taking (250x) and observation of these images (maximal 2500x) were repeated. Three-dimensional images of the contraction gap were made using analytical software and the proportions of the interface with gap formation calculated.

RESULTS

The mean proportions of the interface with gap formation of the self-etching system (Clearfil Liner Bond II Sigma) was 41.7+/-6.3% and that of the self-priming system (Single Bond) was 38.2+/-3.9%; there was no significant difference.

CONCLUSIONS

Approximate three-dimensional images of the in vitro contraction gap could be drawn and the mean proportions of the interface with gap formation could be more precisely calculated than by previous methods.

The sealant restoration: indications, success and clinical technique

In this paper we have considered the available literature which demonstrates that sealant restorations perform at least as well as amalgam restorations and are more conservative. Success depends on retention of the overlying sealant and if this is fully retained it is unlikely that any residual caries will progress. The diagnosis of occlusal caries and indications for sealant restorations are discussed and the clinical technique is described. We have concluded that sealant restorations are the optimum restoration in small and discrete occlusal cavities.

A new electrical method for detecting marginal leakage of in vitro resin restorations

OBJECTIVES

Ingress of bacteria at sites of marginal leakage has been suggested to cause pulpal inflammation. The purpose of this in vitro study was to evaluate the validity of a new electrical method to detect marginal leakage of restoratives by comparing the results obtained with those of a dye penetration test.

METHODS

After cavities were prepared on the buccal coronal surfaces and root surfaces of 16 extracted non-carious human molar teeth, eight specimens were treated with a dentin bonding system (bonding group) and the other eight specimens were not treated (non-bonding group). Resin composites were filled in the cavities of all specimens, and physiological saline was applied to the margin of the restorative. Any excess saline was wiped off, leaving only the electrolyte, which had penetrated into the marginal gap. The change in conductance was measured continuously across the margin of each specimen during this process. The marginal leakage of specimens was confirmed using the dye penetration test, and the results were evaluated by the microleakage score.

RESULTS

In both coronal and root surface cavities, the changes in conductance in the non-bonding group after filling were significantly larger than those of the bonding group (p<0.05). The change in conductance of each specimen correlated with the microleakage score (p<0.05).

CONCLUSIONS

It was concluded that the relative electrical method could detect marginal leakage in both coronal and root surface cavities.

Thermal cycling procedures for laboratory testing of dental restorations

OBJECTIVES

Exposure of restorations in extracted teeth to cyclic thermal fluctuations to simulate one of the many factors in the oral environment has been common in many tracer penetration, marginal gap and bond strength laboratory tests. Temperature changes used have rarely been substantiated with temperature measurements made in vivo and vary considerably between reports. Justification and standardization of regimen are required.

DATA, SOURCES AND STUDY SELECTION

An assessment of reports describing temperature changes of teeth in vivo is followed by an analysis of 130 studies of laboratory thermal cycling of teeth by 99 first authors selected from 25 journals. A clinically relevant thermal cycling regimen was derived from the in vivo information, and is suggested as a benchmark standard.

CONCLUSIONS

Variation of regimens used was large, making comparison of reports difficult. Reports of testing the effects of thermal cycling were often contradictory, but generally leakage increased with thermal stress, although it has never been demonstrated that cyclic testing is relevant to clinical failures. However, should this be done, the standard cyclic regimen defined is: 35 degrees C (28 s), 15 degrees C (2 s), 35 degrees C (28 s), 45 degrees C (2 s). No evidence of the number of cycles likely to be experienced in vivo was found and this requires investigation, but a provisional estimate of approximately 10,000 cycles per year is suggested. Thermal stressing of restoration interfaces is only of value when the initial bond is already known to be reliable. This is not the case for most current restorative materials.

Dentine permeability and tracer tests

OBJECTIVES

This paper reviews the evidence for dentine's permeability in order to clarify and emphasize its confounding effect on leakage test measurements, and hence the need to use special test designs to avoid its effects.

METHODS

The literature on the subject between 1887 and 1997, including 249 articles.

CONCLUSIONS

The prerequisite condition for any tracer penetration test is that unflawed specimens are themselves impermeable to tracer. Entry of tracer then can be used to indicate correctly the location or severity of flaws. The relative impermeability of intact dental enamel permits such testing of the enamel-restoration interface seal, but the same is not true when using dentine, which is usually frankly porous to most tracers through its tubules. False positive results are very likely. Recent intense interest in dentine bonding agents has increased the need and frequency of these tests with dentine, but this serious confounding factor has so far generally remained unstated, and has only been controlled adequately in one study. If tracer penetration test results are to be meaningful, then adequate control is required.

Enamel surface roughness analysis after laser ablation and acid-etching

Laser-roughened enamel surfaces have been shown to provide for greater acid-resistance and enhanced restorative material/enamel bond strength. Extracted tooth enamel was irradiated with several lasers: CO2/Nd:YAG (CW), CO2 (RSP), Nd:YAG (CW), Nd:YAG (Q-switched), Argon (CW), and Ar:F excimer. Additional teeth were acid-etched. Energy densities were standardized at 25.47 J/cm2 for all mediums. Surface profile analyses were conducted with a profilometer to determine the amount of enamel surface roughness. The acid-etched samples exhibited both a greater amount of surface roughness and a qualitatively different type of enamel surface morphology than the laser-treated specimens. Independent use of the CO2 and Nd:YAG beams exhibited a moderate amount of roughness, while the coaxial CO2/Nd:YAG beam displayed surface roughness approaching that of the acid-etch samples. Different laser mediums produce enamel surface morphologies that are characteristic of a variety of inherent lasing parameters.

The effects of low-level energy density Nd:YAG irradiation on calculus removal

This study assessed the effects of using an Nd:YAG laser to remove dental calculus from root surfaces. Human extracted molar teeth, with extensive calculus attachment to root surfaces, were irradiated with an Nd:YAG beam [power densities (PD) = 1.09 W/cm 2 and 2.19 W/cm 2; energy densities (ED) = 49.2 J/cm 2 and 98.4 J/cm 2]. An additional group of teeth was instrumented with a Gracey 11/12 curette. A separate group of untreated specimens served as controls. Specimens were examined under scanning electron microscopy and rated as to the degree of calculus detachment from root surfaces. Nd:YAG irradiation at low ED did not appreciably affect the integrity of the calculus root surface attachment. The higher-ED Nd:YAG irradiation appeared to mimic the type of calculus removal depicted with conventional hand instrumentation. Root surface damage from both laser ablations was negligible.

Microleakage

A critical review of techniques used in the assessment of microleakage in dental restorations is presented. These techniques include the use of air pressure, bacteria, radioisotopes, electrochemistry, chemical tracers and dye penetration. Wide variations in methodologies are revealed.