Disintegration of visible light-cured composite resins caused by long-term water immersion

The purpose of this study is to clarify a cause of disintegration of composite resins by long-term immersion in distilled water. Three kinds of visible light-cured composite resins (Heliosit, Plurafil Super and Visio Dispers) and one conventional composite resin (Clearfil F II) were prepared as the specimens with a 20 mm diameter and 1 mm thickness. These specimens were immersed in distilled water at 37 +/- 1 degree C for 3 years. These specimens were analysed and observed by a comprehensive multi analyzer and scanning electron microscope. The other hand residues in distilled water were analysed by infrared (IR) and nuclear magnetic resonance (NMR) spectrometers. The surface layer of all four composite resins showed signs of disintegration. The composite resins with abundant dissolved substances had disintegrated markedly, and such disintegration occurred deep inside the specimens. In IR and 1H-NMR spectra of dissolved substances, two visible light-cured composite resins (Heliosit and Plurafil Super) could be detected unreacted monomers, but one visible light-cured composite resin (Visio Dispers) and one conventional composite resin (Clearfil F II) could not be detected them. In 1H-NMR spectra of dissolved substances of all four composite resins, new signals not composed originally were observed. The progress of disintegration were demonstrated clearly. The dissolved substances were shown as the disintegrated substance between resin matrixs and silane coupling agents. It is suggested that the disintegration of composite resins by long-term water immersion is derived from hydrolysis.     

Flexural properties of denture base resins subjected to long-term water immersion

Abstract

Objective. The aim of this study was to investigate the flexural properties of denture base resins subjected to long-term water immersion. Materials and methods. Four denture base resins (one conventional heat-processed, one microwave energy-processed and two pour-type autopolymerizing) were selected for this study. The specimens of each denture base material tested were fabricated according to the manufacturers' instructions (n = 10). The flexural properties of the denture base resins were measured according to ISO 20795-1. The ultimate flexural strength, the flexural strength at the proportional limit and the elastic modulus of the specimens were evaluated. Results. The ultimate flexural strengths of the heat-processed resin and the two pour-type autopolymerizing resins significantly decreased after 6 months water immersion. The flexural strength at the proportional limit of the heat-processed resin significantly decreased after 6 months water immersion, but the microwave energy-processed denture base resin and two pour-type autopolymerizing resins did not change after 6 months water immersion. The elastic moduli of the heat-processed resin, the microwave energy-processed denture base resin and one pour-type autopolymerizing resin significantly increased after 6 months water immersion. Conclusion. The flexural properties of denture base resins significantly changed after long-term water immersion.     

Hardness of heat-polymerized acrylic resins after disinfection and long-term water immersion

STATEMENT OF THE PROBLEM: In selecting a disinfectant for dental prostheses, compatibility between the disinfectant and the type of denture base material must be considered to avoid adverse effects on the hardness of the acrylic resin. PURPOSE: This study investigated the hardness of 2 denture base resins after disinfection and long-term water immersion. MATERIAL AND METHODS: Thirty-two disk-shaped specimens (13 mm in diameter and 8 mm thick) were fabricated from each resin (Lucitone 550 and QC-20), polished, stored in water at 37 degrees C for 48 hours, and submitted to hardness tests (Vickers hardness number [VHN]) before disinfection. Disinfection methods included scrubbing with 4% chlorhexidine gluconate for 1 minute, immersion for 10 minutes in 1 of the tested disinfectant solutions (n=8) (3.78% sodium perborate, 4% chlorhexidine gluconate, or 1% sodium hypochorite), and immersion in water for 3 minutes. The disinfection procedures were repeated 4 times, and 12 hardness measurements were made on each specimen. Control specimens (not disinfected) were stored in water for 56 minutes. Hardness tests (VHN) were also performed after 15, 30, 60, 90, and 120 days of storage in water. Statistical analyses of data were conducted with a repeated measures 3-way analysis of variance (ANOVA) and Tukey post-hoc test (alpha=.05). RESULTS: Mean values +/- SD for Lucitone 550 (16.52 +/- 0.94 VHN) and QC-20 (9.61 +/- 0.62 VHN) demonstrated a significant (P <.05) decrease in hardness after disinfection, regardless of material and disinfectant solutions used (Lucitone 550: 15.25 +/- 0.74; QC-20: 8.09 +/- 0.39). However, this effect was reversed after 15 days of storage in water. Both materials exhibited a continuous increase (P <.05) in hardness values for up to 60 days of water storage, after which no significant change was observed. CONCLUSION: Within the limitations of this in vitro study, QC-20 and Lucitone 550 specimens exhibited significantly lower hardness values after disinfection regardless of the disinfectant solution used.     

Three-year study of two light-cured posterior composite resins

Two visible light-cured composite resins, Ful-Fil and X-55, were used to restore 136 Class I and Class II cavity preparations in adult teeth. After three years, the ratings for color matching, interfacial staining, secondary caries, and marginal adaptation remained good using USPHS criteria (ranging from 72% to 100% Alfa). The average surface loss due to occlusal wear was 145 and 164 micrometers for Ful-Fil and X-55, respectively. These results indicate that Ful-Fil composite resin meets the current ADA Council on Dental Materials specifications for provisional acceptance in adult posterior teeth.     

Indirect posterior composite resins

The use of indirect posterior composite restorations has facilitated the generation of ideal anatomic form, marginal adaptation, and appropriate proximal contact and contour. Unfortunately, however, the use of post-cure heat treatments has done little to enhance the overall clinical performance of the restoration. The development of new curing techniques in conjunction with modifications of the formulae have contributed to a substantial improvement in both the mechanical characteristics and long-term clinical performance of indirect posterior composite resins.     

Influence of water on the transverse strength of posterior composite resins.

In an attempt to evaluate the influence of water on the mechanical properties of composite resin, the transverse strengths of 15 commercially available composites were determined in water at 37 degrees C and compared with the strength measured in air after storage in water for periods of 1 day to 3 months. Some of the composites, including two which contained a blend filler, showed remarkable reduction of transverse strength when measured in air, according to the procedures specified in ISO 4049, in comparison with transverse strength measured in water. The change of water content in the material can predominantly affect the mechanical behavior of composite resin.     

Porosity in posterior composite resins

The percent pore area and the mean pore size were measured in specimens made of nine brands of composite resin restorative materials. The overall percent porosity ranged from 0.01 to 4.5%. The specimens for the study were prepared in two ways; by condensation or by pressure. Most of the materials, including all those chemically activated, showed more porosity in the condensed than in the pressure specimens. Reversed results emerged for two of the materials, and for another two, the specimens were similar in this respect. The mean pore sizes were smaller in the condensed than in the pressure specimens. Neither mean pore size nor total amount of porosities could be correlated to the curing method of the materials.     

Porosity in posterior composite resins

Abstract – The percent pore area and the mean pore size were measured in specimens made of nine brands of composite resin restorative materials. The overall percent porosity ranged from 0.01 to 4.5%. The specimens for the study were prepared in two ways; by condensation or by pressure. Most of the materials, including all those chemically activated, showed more porosity in the condensed than in the pressure specimens. Reversed results emerged for two of the materials, and for another two, the specimens were similar in this respect. The mean pore sizes were smaller in the condensed than in the pressure specimens. Neither mean pore size nor total amount of porosities could be correlated to the curing method of the materials.     

Three-year clinical study of UV-cured composite resins in posterior teeth

Four proprietary composite resins cured with ultraviolet light were inserted into Class I and II cavity preparations. The restorations were evaluated over a 3-year period for color match, interfacial staining, secondary caries, loss of anatomic form, marginal adaptation, and surface texture. The percent of restorations exhibiting no generalized loss of anatomic form ranged from 47% to 93%.     

Wear rates of posterior composite resins

The wear rates of nine posterior composite resins were determined for a period of up to 3 years. The wear rates observed depended on the method used for evaluation. A quantitative method of evaluation showed that the wear rates decreased with time. With the use of the quantitative measurements obtained at the end of 6 months after insertion, it was possible to predict the average annual rates of wear at the end of 3 years.     

Radiopacity of light-cured posterior composite resins

Radiographic images of teeth and restorations were used to evaluate the radiopacity of 11 light-cured posterior composite resins. The radiopacity of these composite resins provided enough variation on radiographs so that clinicians distinguished the images of the restoration from adjacent tooth structure.     

Impact strength of denture base and reline acrylic resins subjected to long-term water immersion

Water may influence the mechanical properties of the acrylic resins. Thus, the effect of water storage on the impact strength (IS) of one denture base (Lucitone 550 - L) and four reline resins (Tokuyama Rebase II - T; UfiGel Hard - U; Kooliner - K; New Truliner - NT) was evaluated. Bars of L were made (60 x 6 x 2 mm) and relined (2 mm) with T, U, K, NT and L. Intact specimens of each material (60 x 6 x 4 mm) were also fabricated for comparative purposes. Specimens were submitted to Charpy impact tests without water storage (control) and after immersion in water for 7, 90 and 180 days. Data (kJ/m(2)) analyzed by two-way ANOVA and Tukey's test (p=0.05) revealed that after 90 days, U exhibited an increase in the IS (0.93) compared to 7 days (0.58). K (1.48) and L/K (7.21) exhibited a decrease at the 7-day period (1.01 and 3.23, respectively). NT (0.60) showed an increase in the IS after 180 days (1.52), whereas L/NT (7.70) showed a decrease (3.17). Water immersion improved the IS of U and NT, and decreased the IS of K, L/K, and L/NT. Water may affect differently the IS of acrylic resins and, consequently, the resistance to fracture of relined denture bases.     

Marginal fracture of posterior composite resins

This study assesses the early cavomarginal breakdown of the newer posterior composite resin restorations compared with that of amalgam restorations. A total of 432 posterior composite restorations and 73 amalgam restorations were examined: 121 composite restorations (28%) and 44 amalgam restorations (60%) clinically showed a marginal crevice at some point on the cavosurface margin of the restoration at 6-month, 1-year, and 2-year recalls. The largest single reason for poor marginal adaptation was marginal fracture. Up to 2 years, the marginal integrity of the studied posterior composites was superior to that of an amalgam alloy. It was determined that smaller cavities, greater bulk of resin at the margin (especially at functional cusp areas), and well-finished margins without overfiling seem to reduce the occurrence of marginal fracture on composite resin restorations.