Interaction of glass-ionomer cements with moist dentin.

Glass-ionomer cements (GICs) are regarded as aqueous gels made up of polyalkenoic acid salts containing ion-leachable glass fillers. The consequence of water permeation across the GIC-dentin interface is unknown. This study used SEM, field-emission/environmental SEM (FE-ESEM), and TEM to examine the ultrastructure of GIC-bonded moist dentin. Dentin surfaces bonded with 6 auto-cured GICs were examined along the fractured GIC-dentin interfaces. Additional specimens fractured 3 mm away from the interfaces were used as controls. SEM revealed spherical bodies along GIC-dentin interfaces that resembled hollow eggshells. FE-SEM depicted similar bodies with additional solid cores. Energy-dispersive x-ray analysis and TEM showed that the spherical bodies consisted of a silicon-rich GIC phase that was absent from the air-voids in the controls. The GIC inclusions near dentin surfaces result from a continuation of the GI reaction, within air-voids of the original polyalkenoate matrix, that occurred upon water diffusion from moist dentin.

Mechanical properties of an improved visible light-cured resin-modified glass ionomer cement.

This study investigates the mechanical properties (hardness, flexural strength and compressive strength) of a new light-cured resin-modified glass ionomer cement (Fuji II LC Improved). Effects of the increased powder:liquid ratio on mechanical properties and the correlation between different mechanical properties were also studied. Mechanical properties of the cement at manufacturer's recommended powder:liquid ratio (F), 2% (F2) and 4% (F4) increased powder weight were measured after one day, one week and one month storage in distilled water at 37 degrees C. Hardness testing (KHN; n = 5) was done with a digital microhardness tester (load = 500 g, dwell time = 15 seconds). Flexural and compressive strength testing (MPa; n = 5) were conducted based on ISO 4049 and BS6039, respectively. Results were analyzed using ANOVA/Scheffe's test (p < 0.05) and Pearson's correlation (p < 0.01). The maximum mechanical properties of Fuji II LC Improved were achieved at one week. The hardness, flexural and compressive strength at one week was significantly higher than at one day. A decrease in all mechanical properties was observed at one month. Mechanical properties were significantly affected by increased powder:liquid ratio. After one month storage, significance was as follows: Hardness--F, F2 > F4; Flexural strength--F4 > F, F2 and F > F2; Compressive strength--F, F2 > F4 and F2 > F. A significant very strong and negative correlation was observed between flexural and compressive strengths (r = 0.97).

Marginal sealing ability of three cervical restorative systems.

The purpose of this in vitro study was to evaluate the enamel and dentinal marginal sealing ability of three different cervical restorative systems. Class V preparations were made at the cementoenamel junction of 36 freshly extracted premolars. The teeth were randomly divided into three groups of 12 and restored with either a polyacid-modified resin composite ("compomer"), resin composite, or resin-modified glass-ionomer cement. The restored teeth were stored in saline at 37 degrees C for 1 week, thermally stressed for 500 cycles, and subjected to dye penetration testing. The results showed that there was no significant difference in dentinal margin sealing ability among the three materials evaluated. When the margins were in enamel, the resin composite restorations had significantly less leakage than did compomer or resin-modified glass-ionomer cement restorations. The marginal sealing ability of all three materials was significantly poorer in dentin than in enamel.

Non-carious cervical tooth loss. Part 2: Management.

The aetiology, prevalence, diagnosis, prevention and monitoring of non-carious cervical tooth loss (NCTL) has been covered in the first article of this series. The aetiology of NCTL is usually multifactorial and may not be attributable to any single factor. Central to the successful management of NCTL is a correct diagnosis of the cause. This article will focus on the management of NCTL.

Non-carious cervical tooth loss: Part 1.

Non-carious cervical tooth loss is not always attributable to a single causative factor, as evidenced by the numerous terminologies used. In this, the first of two articles, the aetiology and prevalence of non-carious tooth loss are discussed. Guidelines are suggested as to how it may be diagnosed, prevented and monitored. A further article will cover the restorative management.

Shear bond strength of orthodontic brackets using Panavia: an in-vitro study.

In this study, Panavia (a phosphonated Bis-GMA resin which is known to develop very high bond strengths with resin-bonded bridges) is compared to a conventional no-mix orthodontic Bis-GMA bracket adhesive. Results showed that there was no statistically significant difference in the shear bond strengths between the two resins when used as adhesives for bonding orthodontic brackets. Coupled with the fact that Panavia requires an anaerobic environment for complete polymerization, its routine use as a bracket adhesive in direct bonding of orthodontic brackets is not indicated.

Effects of polymerization techniques on uniformity of cure of large-diameter, photo-initiated composite resin restorations.

The polymerization effectiveness of various methods of exposing large-diameter, light-activated composite resin samples is reported. Results of Knoop hardness testing showed that highest mean hardness was achieved by using a wide tip (13 mm) with either the spot cure or overlap method for 60 seconds. More uniform hardness resulted from the wide-tip with scanning methods and 60-second cure than resulted from the narrow-tip (8 mm) with the spot or overlap method and 20-second cure.