Sharanbir K. Sidhu

Effect of different power parameters of Er,Cr:YSGG laser on human dentine

The aim of this work was to determine the optimal power setting of an Er,Cr:YSGG laser for cutting human dentine to produce a surface that remains suitable as a foundation on which to build and bond a dental restoration. The cutting efficiency and resulting microhardness of the dentine were evaluated for various laser power settings, and representative samples were examined by SEM. The microhardness of the dentine was significantly reduced by 30–50% (p < 0.05, paired t test) after laser irradiation, irrespective of the power setting used. The mean ablation efficiency increased in proportion to the power setting of the laser. Although the laser power setting did not affect the extent of reduction in microhardness, it did affect the microstructure of human dentine.

Glass‐ionomer cement restorative materials: a sticky subject?

Glass-ionomer cement (GIC) materials have been in clinical use since their inception 40 years ago. They have undergone several permutations to yield different categories of these materials. Although all GICs share the same generic properties, subtle differences between commercial products may occur. They have a wide range of uses such as lining, bonding, sealing, luting or restoring a tooth. In general, GICs are useful for reasons of adhesion to tooth structure, fluoride release and being tooth-coloured although their sensitivity to moisture, inherent opacity, long-term wear and strength are not as adequate as desired. They are useful in situations where they are not disadvantaged by their comparatively lower physical properties, such as where there is adequate remaining tooth structure to support the material and where they are not subject to heavy occlusal loading. The last decade has seen the use of these materials being extended. However, they are likely to retain their specific niches of clinical application.

Water sorption in resin-modified glass-ionomer cements: An in vitro comparison with other materials

The pattern of water uptake into a polyacid-modified composite resin (compomer), Dyract (D), was assessed using gravimetric analysis and tritiated water absorption. The results were compared with a resin composite, Herculite (H), a resin-modified glass-ionomer, Fuji II LC (FL), and a conventional glass-ionomer, Fuji II (F). Samples were stored in tritiated water for periods varying between 6 h and 6 months. The resulting change in gravimetric weight and dimensions was recorded. The tritiated water content was then assessed using liquid scintillation counting and this was compared to the gravimetric changes. The inherent water content of each material was also established. D and H showed a slow steady net uptake to 3% and 1.3% weight by volume (WV) respectively at 6 months. FL showed a rapid uptake reaching 8.9% WV at 7 days and 9.3% WV at 6 months. F showed a steady, less dramatic water uptake reaching 5.3% WV by 6 months. For the glass-ionomer materials, values for gravimetric water uptake and tritium release differed due to the ongoing acid base reaction and an increase in firmly bound water. This phenomenon was noted in D suggesting evidence of a similar reaction in this material.

The Effects of Maturity and Dehydration Shrinkage on Resin-modified Glass-ionomer Restorations

The dimensional change, including hygroscopic change, of adhesive dental materials is a clinically important topic, since excessive changes could cause debonding from tooth structure. The water balance of glass-ionomer cements arises mainly from their sensitivity to the environment; depending on the surroundings, they can gain or lose water, either of which can be potentially damaging. These effects become less noticeable as the cement ages. The effects of maturity of the newer resin-modified glass-ionomer materials and their responses to changes in moisture are unknown. Using confocal microscopy, we examined the effects of dehydration stress on the glass-ionomer/tooth interface in specimens of various degrees of maturity. Wedge-shaped cervical cavities in extracted teeth were restored with one of three resin-modified glass-ionomer restorative materials. The control specimens were restored with a conventional glass ionomer. The samples were left to mature, then sectioned and examined at 1 day, 1 wk, 1 mo, 3 mos, 6 mos, and 1 yr. After being sectioned, each specimen was examined immediately with a confocal microscope with water-immersion objectives so that the subsurface interfacial characteristics could be studied. The specimen was then allowed to dehydrate under the microscope, with further examinations at 15, 30, and 60 min. Generally, gap formation at the interface occurred within 15 min of dehydration. All materials showed a different pattern of gap change with maturity, probably due to the different setting mechanisms involved. All of them were susceptible to dehydration shrinkage up to 3 mos of maturity. At 6 mos and 1 yr, Fuji II and Fuji II LC showed insensitivity to dehydration. Vitremer and Photac-Fil showed less sensitivity to dehydration at 1 yr than at 6 mos. The results of this study of the maturing polymerized resin-modified cements have potential clinical implications in the handling of these materials; the addition of resin has not significantly reduced the glass ionomers susceptibility to dehydration problems.

Radiopacity of potential root-end filling materials

OBJECTIVES In recent years various root-end filling materials have been suggested for clinical use. The purpose of this study was to assess the radiopacity of some potential materials according to ISO specification 6876. STUDY DESIGN Radiographs were taken of 1-mm thick specimens of eight materials (amalgam, Kalzinol, IRM, Super EBA, Vitrebond, Fuji II LC, Chemfil, gutta-percha); light transmission was assessed densitometrically and related to equivalent thickness of aluminum. RESULTS Commercial glass ionomer cements (Vitrebond, Fuji II LC, Chemfil) had radiopacities below the international standard for root canal sealers (< 3-mm aluminum); three zinc oxide-eugenol cements (Kalzinol, Super EBA, IRM) had radiopacities equivalent to 5 to 8 mm aluminum; and gutta-percha had a radiopacity equivalent to 6.1-mm aluminum. CONCLUSIONS We recommend that root-end filling materials should have a radiopacity greater than that for root canal sealers.

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.

Clinical evaluations of resin-modified glass-ionomer restorations

OBJECTIVES This paper collates some of the existing data on the clinical evaluations of resin-modified glass-ionomer cements (RMGICs) since their introduction two decades ago. METHODS The relevant literature was considered and data reviewed under the headings of retention, marginal characteristics, material deterioration, secondary caries, color stability, as well as pulpal and biological effects. RESULTS The retention for RMGICs is generally good, with an annual failure rate over 13 years reported as being under 3%. However, more data is required on their performance in carious situations. Regarding marginal characteristics, they exhibit margins that are likely to deteriorate over time. From the limited data on the surface characteristics, they appear to exhibit some wear and loss of anatomic form, particularly in the mid to long term. Despite the fact that the studies reviewed for secondary caries varied in the initial caries status of lesions restored, the overwhelming conclusion is that this does not seem to be a problem. While their initial color match may be favorable, it appears that they change over time and may not be color stable. In the absence of more clinical data, it is difficult to draw conclusions on the pulpal and biological effects. The existing information primarily reports postoperative sensitivity, which fortunately does not seem to be an issue with RMGICs, and limited histopathology of the pulp, with mixed opinions. SIGNIFICANCE The RMGICs appear to perform well in terms of retention, and secondary caries as well as postoperative sensitivity are not a problem. However, this is not necessarily true of their marginal characteristics, surface properties and color stability. More and long-term clinical research is required to establish compelling evidence of their behavior, particularly in terms of retention in carious cavities, surface properties and biological effects.

Change of Color and Translucency by Light Curing in Resin Composites

OBJECTIVE This study evaluated color and translucency changes caused by light curing resin composite materials. METHODS The CIELAB parameters (L*, a* and b*) of disks of A2 and opaque A2 shades of Charisma (Heraeus-Kulzer), Solare (GC) and Filtek Supreme (3M) were evaluated on the backings of black, white and the material itself both before and after light curing to evaluate color and translucency changes (by means of calculating deltaE* and the translucency parameter, respectively). RESULTS Solare and Filtek Supreme showed significantly smaller color changes during light curing than Charisma; however, the value of deltaE* of all the products/shades was still in the clinically unacceptable range. Regarding translucency changes during light curing, the A2 and opaque A2 shades of Charisma showed a statistically significant increase, although no difference was observed in the other products. CONCLUSIONS Solare and Filtek Supreme tended to show less changes in translucency and color during light curing compared to Charisma. Nevertheless, the changes in color during light curing were still in the range of unacceptable color change. Therefore, direct shade matching of these materials for a precise shade match should be performed by using the cured material.

A Review of Glass-Ionomer Cements for Clinical Dentistry

This article is an updated review of the published literature on glass-ionomer cements and covers their structure, properties and clinical uses within dentistry, with an emphasis on findings from the last five years or so. Glass-ionomers are shown to set by an acid-base reaction within 2–3 min and to form hard, reasonably strong materials with acceptable appearance. They release fluoride and are bioactive, so that they gradually develop a strong, durable interfacial ion-exchange layer at the interface with the tooth, which is responsible for their adhesion. Modified forms of glass-ionomers, namely resin-modified glass-ionomers and glass carbomer, are also described and their properties and applications covered. Physical properties of the resin-modified glass-ionomers are shown to be good, and comparable with those of conventional glass-ionomers, but biocompatibility is somewhat compromised by the presence of the resin component, 2 hydroxyethyl methacrylate. Properties of glass carbomer appear to be slightly inferior to those of the best modern conventional glass-ionomers, and there is not yet sufficient information to determine how their bioactivity compares, although they have been formulated to enhance this particular feature.

Water-dependent Interfacial Transition Zone in Resin-modified Glass-ionomer Cement/Dentin Interfaces

The function of the interfacial transition zone (absorption layer) in resin-modified glass-ionomer cements bonded to deep dentin remains obscure. This study tested the hypotheses that the absorption layer is formed only in the presence of water derived from hydrated dentin and allows for better bonding of resin-modified glass-ionomer cements to dentin. Ten percent polyacrylic acid-conditioned, hydrated, and dehydrated deep dentin specimens were bonded with 2 resin-modified glass-ionomer cements and sealed with resins to prevent environmental water gain or loss. A non-particulate absorption layer was identified over hydrated dentin only, and was clearly discernible from the hybrid layer when bonded interfaces were examined with transmission electron microscopy. This layer was relatively more resistant to dehydration stresses, and remained intact over the dentin surface after tensile testing. The absorption layer mediates better bonding of resin-modified glass-ionomer cements to deep dentin, and functions as a stress-relieving layer to reduce stresses induced by desiccation and shrinkage.