Effect of powder/liquid ratio on the clinical and laboratory performance of resin-modified glass-ionomers

Microstructural characterization of dental zinc phosphate cements using combined small angle neutron scattering and microfocus X-ray computed tomography

OBJECTIVE

To characterize the microstructure of two zinc phosphate cement formulations in order to investigate the role of liquid/solid ratio and composition of powder component, on the developed porosity and, consequently, on compressive strength.

METHODS

X-ray powder diffraction with the Rietveld method was used to study the phase composition of zinc oxide powder and cements. Powder component and cement microstructure were investigated with scanning electron microscopy. Small angle neutron scattering (SANS) and microfocus X-ray computed tomography (XmCT) were together employed to characterize porosity and microstructure of dental cements. Compressive strength tests were performed to evaluate their mechanical performance.

RESULTS

The beneficial effects obtained by the addition of Al, Mg and B to modulate powder reactivity were mitigated by the crystallization of a Zn aluminate phase not involved in the cement setting reaction. Both cements showed spherical pores with a bimodal distribution at the micro/nano-scale. Pores, containing a low density gel-like phase, developed through segregation of liquid during setting. Increasing liquid/solid ratio from 0.378 to 0.571, increased both SANS and XmCT-derived specific surface area (by 56% and 22%, respectively), porosity (XmCT-derived porosity increased from 3.8% to 5.2%), the relative fraction of large pores ≥50μm, decreased compressive strength from 50±3MPa to 39±3MPa, and favored microstructural and compositional inhomogeneities.

SIGNIFICANCE

Explain aspects of powder design affecting the setting reaction and, in turn, cement performance, to help in optimizing cement formulation. The mechanism behind development of porosity and specific surface area explains mechanical performance, and processes such as erosion and fluoride release/uptake.

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.

Effect of radiant heat and ultrasound on fluoride release and surface hardness of glass ionomer cements

PURPOSE

The purpose of this investigation was to evaluate the influence of radiant heat and ultrasound on fluoride release and surface hardness of 3 glass ionomer cements (GICs).

METHODS

There were 3 experimental groups for each GIC; in group 1, the specimens were left to set without any treatment; in group 2, the specimens were irradiated for 2 minutes using a LED unit; and in group 3, ultrasound was applied using a scaler for 55 seconds on the specimen surface. Fluoride release measurements were performed daily for 7 days and at days 14 and 28. Surface hardness of the tested GICs was determined using Vickers method. The measurements were performed 24 hours and 7 days after mixing. Statistical analysis of the data was made using 1-way ANOVA and Tukey's and Bonferroni post hoc tests (α = 0.05).

RESULTS

Radiant heat during setting reduced the fluoride release and increased the surface hardness of GICs (p<0.05). Ultrasonic treatment also reduced the fluoride release and increased the surface hardness (p<0.05) of GICs but in lower extent. Among the GICs there were differences in fluoride release and surface hardness properties depending on their composition (p<0.05).

CONCLUSIONS

Radiant heat and ultrasonic treatments may be useful methods for GIC restorations in order to achieve faster adequate initial mechanical properties.

Comparative evaluation of the antibacterial and physical properties of conventional glass ionomer cement containing chlorhexidine and antibiotics

Objective:

To evaluate the antimicrobial efficacy and compressive strength of conventional glass ionomer cement (GIC) containing chlorhexidine and antibiotics at varying concentrations.

Materials and Methods:

Chlorhexidine diacetate and antibiotics (ciprofloxacin, metronidazole, and minocycline) were incorporated into GIC Fuji IX at 1.5% and 3% w/w ratio to form the experimental groups. The experimental GIC specimens were placed on brain heart infusion agar plates inoculated with Streptococcus mutans, and the area of inhibition was measured after 48 h. The 24-h compressive strength of the set specimens was evaluated using a Universal Testing Machine.

Results:

The control group demonstrated no zone of inhibition. All experimental groups showed inhibition against S. mutans (P < 0.05), with larger zones of inhibition found in the higher concentration groups. Compressive strength at the end of 24 h decreased in the experimental groups as compared to the control group (P < 0.05), but no difference was found between the experimental groups (P > 0.05).

Conclusion:

The present study demonstrated that experimental GICs containing chlorhexidine diacetate and antibiotics were effective in inhibiting S. mutans, and incorporation of 1.5% ABX was optimal to give the appropriate antibacterial and physical properties.

The effect of variability in the powder/liquid ratio on the strength of zinc phosphate cement

Aim. To investigate (a) variability in powder/liquid proportioning and (b) effect of variability on diametral tensile strength (DTS), in a zinc phosphate cement. Statistical analyses (α = 0.05) were by Student's t-test in the case of powder/liquid ratio and one-way ANOVA and Tukey HSD for pair-wise comparisons of mean DTS. The Null hypotheses were that (a) the powder-liquid mixing ratios would not differ from the manufacturer's recommended ratio (b) DTS of the set cement samples using the extreme powder/liquid ratios would not differ from those made using the recommended ratio. Methodology. 34 dental students dispensed the components according to the manufacturer's instructions. The maximum and minimum powder/liquid ratios, together with the manufacturer's recommended ratio, were used to prepare samples for DTS testing. Results. Powder/liquid ratios ranged from 2.386 to 1.018. The mean ratio (1.644) was not significantly different from the recommended value of 1.718 (P = 0.189). DTS values for the maximum and minimum ratios were both significantly different from each other (P < 0.001) and from the mean value obtained from the recommended ratio (P < 0.001). Conclusions. Variability exists in powder/liquid ratio for hand dispensed zinc phosphate cement. This variability can affect the DTS of the set material.

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.

Clinical Performance of Viscous Glass Ionomer Cement in Posterior Cavities over Two Years

In this controlled prospective clinical study the highly viscous glass ionomer cement Ketac Molar was clinically assessed in Class I and Class II cavities. Forty-nine subjects (mean age 32.3 years) received 108 restorations placed by six operators in conventional Black I and II type cavities with undercuts after excavating primary lesions or after removing insufficient restorations. At baseline, and after 6, 12, and 24 months, restorations were assessed by two independent investigators according to modified USPHS codes and criteria. Impressions of the restorations were taken and epoxy replicas were made. Between the baseline and the 24-month recall, 51 representative samples were analyzed at 130 × magnification by use of a stereo light microscope (SLM). Recall rates were 83% after 6 months, 50% after 12 months, and 24% after 24 months. Failure rates after 24 months were 8% for Class I and 40% for Class II fillings, mainly due to bulk fracture at occlusally loaded areas (Kaplan Meier survival analysis). Significant changes over time were found for the criteria “surface roughness”, “marginal integrity”, “restoration integrity”, and “overall judgement” (P < .05; Friedman test). SLM analysis revealed statistically significant differences for the following criteria over time (baseline/6 months/12 months (in % of entire evaluable margin length); P < .05; Friedman 2-way ANOVA): perfect margin 37/19/11, negative step formation 26/49/57, gap formation 2/7/9, and overhang 24/11/8. Replicas exhibited mainly negative step formation as main finding due to apparently inferior wear resistance (P < .05). Gap formations were more frequently observed in Class II restorations than in Class I (12% versus 3% after 12 months; P < .05, Mann-Whitney-U test). The evaluated margin lengths were not statistically different (P > .05, Friedman 2-way ANOVA).

Kinetics of fluoride release from and reuptake by orthodontic cements

INTRODUCTION

The purposes of this in-vitro study were to compare the fluoride-release profiles and the fluoride release, reuptake, and rerelease characteristics of orthodontic cements before and after topical fluoride treatment.

METHODS

The orthodontic cements tested were 2 resin-modified glass ionomers (Vitremer [3M Dental Products, St Paul, Minn] and Fuji Ortho LC [GC Dental, Tokyo, Japan]), a glass ionomer (Ketac-Cem [Espe-Premier Dental Products, Norristown, Pa]), and a composite (Concise [3M Dental Products]). Fifteen specimens of each material were stored in plastic vials containing deionized water at 37 degrees C. Fluoride release was measured daily for the first 15 days and then weekly for a 57-day period. After initial elusion, specimens were exposed to 1.23% acidulated phosphate fluoride gel, and the fluoride release was monitored daily for 7 consecutive days. The fluoridation/elution procedure was repeated once, and the specimen surfaces were then examined with a scannning electron microscope.

RESULTS

Kinetic release profiles of the test materials were deduced. All materials except Concise had similar fluoride-release profiles. Vitremer demonstrated the highest fluoride release, followed by Fuji Ortho LC and then Ketac-Cem in the time period of the study (P <.01). All glass-ionomer cements, but especially Fuji Ortho LC, showed enhanced uptake and release on repeated exposure to the topical fluoride treatment. Nevertheless, Vitremer showed the greatest surface degradation after refluoridation.

CONCLUSIONS

All resin-modified and conventional glass ionomers studied exhibited the capacity for fluoride release and reuptake after fluoridation, but the subsequent fluoride release was transitory. Thus, the benefit from fluoride reuptake in these orthodontic cements should be balanced with the risk of weakening them after repeated fluoridation.

Viscoelastic behavior and fracture toughness of six glass-ionomer cements

STATEMENT OF PROBLEM

Viscoelastic behavior can influence the fracture properties of glass ionomers, which is of clinical relevance. Glass-ionomer cements can display viscoelastic behavior, defined as having displacement rate- or strain rate-dependent mechanical properties. Understanding and describing the viscoelastic behavior of glass ionomers is important to understanding their clinical behavior.

PURPOSE

The purpose of this study was to evaluate the viscoelastic behavior of 6 glass-ionomer cements and determine whether there was a correlation to fracture toughness.

MATERIAL AND METHODS

Three conventional glass-ionomer cements (alpha-Silver, alpha-Fil, and Ketac-Molar) and 3 resin-modified glass-ionomer cements (Vitremer, Fuji II LC, and Photac-Fil Quick) were evaluated using measurements of compressive strength (CS), flexural strength (FS), and diametral tensile strength (DTS) at displacement rates of 0.5, 1.0, 1.5, and 2.0 mm/min. The CS and DTS specimens were cured in glass tubes and cut to 4 x 6-mm and 4 x 2-mm disk-shaped specimens, respectively. The FS specimens were cured in bar molds (2 x 2 x 15 mm). The fracture toughness (FT) specimens were cured in a minicompact mold to obtain precracked specimens. The mechanical testing results were compared statistically using generalized linear model/analysis of covariance and the Ryan-Einot-Gabriel-Welsch multiple range test at the alpha=.05 level.

RESULTS

For all 3 mechanical properties, there was a displacement-rate dependence on the mechanical property. However, there were no differences in the displacement-rate dependence based on the type of material-conventional glass ionomer or resin-modified glass ionomer-for any of the mechanical properties. Only for FS test was there a significant difference based on the brand of material. There was no statistical difference in FT among the glass-ionomer cements tested, although the resin-modified glass ionomers tended to display higher FT.

CONCLUSION

A larger sample size and a much wider range of crosshead speeds are necessary to support a correlation between viscoelastic behavior and FT.

Longevity of a resin-modified glass ionomer cement and a polyacid-modified resin composite restoring non-carious cervical lesions in a general dental practice

BACKGROUND

Long-term prospective survival studies of resin-modified glass ionomer cements (RMGICs) and polyacid-modified resin composites (compomers) placed in non-carious cervical lesions (NCCLs) are lacking from general dental practice. Short-term studies have shown an unsatisfactory clinical performance for several materials.

METHODS

One practitioner placed 87 compomer (Compoglass, Vivadent-Ivoclar) and 73 encapsulated RMGIC (Fuji II LC, GC Int.) restorations in NCCLs for 61 adults. Compoglass was placed using SCA primer, and Fuji II LC using GC Dentin Conditioner. No cavity preparation was undertaken. The Kaplan-Meier method was used for estimating the cumulative survivals for those restorations that were replaced, with the probability level set at alpha = 0.05 for statistical significance.

RESULTS

Restorations were judged unsatisfactory (by the practitioner and the subjects) because of surface and marginal loss of material (68.8 per cent), dislodgement (18.8 per cent) and discoloration (12.4 per cent), these modes being similar for both materials (P = 0.35). Unsatisfactory restorations were replaced in 121 (75.6 per cent) instances. After periods of up to five years, cumulative survival estimates were 14.9 (5.8 Standard Error) per cent for Compoglass and zero per cent for Fuji II LC (P = 0.74). Median survivals were 30 months for Compoglass and 42 months for Fuji II LC.

CONCLUSION

Both materials had high long-term unsatisfactory performances when placed in non-prepared NCCLs in a general dental practice.

Interaction of resin-modified glass-ionomer cements with moist dentine

OBJECTIVES

The objective of this study was to report on a novel phenomenon that occurs when resin-modified glass-ionomer cements (RMGICs) are bonded to moist human dentine.

METHODS

Dentine surfaces from extracted third molars were abraded with 180-grit SiC paper. Ten teeth were prepared for each of the two RMGICs tested (Fuji II LC, GC Corp. and Photac-Fil Quick, 3M ESPE). RMGIC buildups were made according to the manufacturers' instructions. After storage at 37 degrees C, 100% humidity for 24 h, the bonded specimens were cut occlusogingivally into 0.9 x 0.9 mm beams. Dentine surfaces bonded with the two RMGICs were examined along the fractured RMGIC/dentine interfaces. Additional beams fractured within the RMGICS and at 3 mm away from the interfaces were used as controls. The fractured beams were examined using scanning electron microscopy (SEM), field emission-environmental SEM (FE-ESEM) and transmission electron microscopy (TEM).

RESULTS

SEM and FE-ESEM revealed numerous solid spherical bodies along the RMGIC/dentine interfaces. By contrast, no spherical bodies could be identified within the RMGIC fractured 3 mm distant from the bonded interface. TEM and energy dispersive X-ray analyses performed on carbon-coated ultrathin sections showed that these solid spherical bodies consisted of a thin aluminum and silicon-rich periphery and an amorphous hydrocarbon core within the air voids of the original resin matrix.

CONCLUSION

The spherical bodies probably represent a continuation of GI reaction and poly(HEMA) hydrogel formation that results from water diffusion from the underlying moist dentine. Their existence provides evidence for the permeation of water through RMGIC/dentine interfaces.