Investigating filler morphology and mechanical properties of new low-shrinkage resin composite types.

Three types of low-shrinkage composites are today commercially available: Ormocers, cationic ring-opening curing systems and highly filled methacrylate-based materials, which cure via free-radical polymerization mechanisms. The aim of this study was to characterize the inorganic fraction of materials belonging to each type and to compare their mechanical properties. Two Ormocers (Admira and an experimental Ormocer V35694), one ring-opening composite (Filtek Silorane) and five methacrylate-based composites [Filtek Supreme XT, Tetric EvoCeram, Grandio, Synergy D6 (Coltène-Whaledent, Langenau, Germany) and an experimental material, V34930] were tested. Inorganic fillers were quantified by thermogravimetric analysis and morphologically characterized by scanning electron microscopy. Dynamic modulus was determined by an impulse excitation technique, static elastic moduli and flexural strength by a three-point bending method. The results were analyzed using ANOVA tests (P < 0.05) and linear correlations. Grandio, V34930 and V35694 exhibited significantly higher filler mass fractions. Both dynamic and static moduli of Grandio and V34930 were significantly higher than the other materials (P < 0.05), although no significant difference in flexural strength was observed between material type (P > 0.05). From the present findings, it was suggested that V35694 and Filtek Silorane exhibit comparable properties to conventional methacrylate-based composites, although clinically the cavity type and location must guide material choice. Under high occlusal load, the use of Grandio and V34930 might be favoured. For small cavities, alternative technologies could be preferred as the need for mechanical resistance is lower and the potential for stress generation is greater.

Meta-analytical review of factors involved in dentin adherence.

Literature data on adherence tests of dentin-bonding systems (DBS) may differ widely, even for the same DBS. The problem of bond testing is that materials are seldom compared with a standard, and experimental conditions often vary. We sought to identify the parameters that influence this variability. Using inclusion and exclusion criteria, we conducted a meta-analytical review of 75 articles, published between 1992 and 1996 in SCI reviews, that give bond strength data for 15 dentin-bonding agents of the so-called third and fourth generations. Seventeen selected parameters were classified into four groups: Group A includes factors related to the dentin substrate (i.e., nature of teeth); group B, composite and bonding area (i.e., composite stiffness); group C, storage conditions of the bonded samples (i.e., thermocycling); and group D, test design (i.e., crosshead speed). For each report, the experimental features, the bond strength means and standard deviations, and the failure mode were extracted and tabulated. Statistical Analysis System software was used to perform Pearson correlation analysis and analysis of variance, with bond strength as the dependent variable and experimental conditions as the independent variables. The meta-analytical review highlighted the significant influence of various parameters in the different groups: origin of dentin, types of teeth, pulpal pressure, tooth storage temperature, maximum storage time of teeth, and dentin depth in group A; type and stiffness of composite and bonding area in group B; storage of bonded samples (medium, temperature, and time) in group C, and testing mode and crosshead speed in group D. A significant positive correlation was observed between the mean bond strength and the rate of cohesive failure. It can be concluded from this study that some of these parameters should be controlled by the use of a standardized protocol. Unfortunately, the substrate-related variables are more difficult to control, even though their influence is consistent.

Structural integrity of resin-modified glass ionomers as affected by the delay or omission of light activation.

Since light activation of resin-modified glass ionomers as a means of polymerizing the HEMA is usually done shortly after mixing occurs, the acid-base reaction will proceed mainly within a formed HEMA-polymer matrix. Delaying or omitting light activation may alter the structure and consequently its integrity. The aim of this study was to investigate the effect on the structural integrity of Fuji II LC, Photac-Fil, and Vitremer by delaying or omitting light initiation as compared with the integrity when light activation is performed 2 min after mixing occurs. We evaluated integrity by three-body wear experiments, conducted 8 hrs after sample preparation, to establish the integrity in the early phase of hardening, as well as after 1 wk and after 4 mos, to follow the materials throughout the process of maturation. When light activation was delayed for 1 hr, the structural integrity of Fuji II LC and Photac-Fil improved significantly in the early stages of hardening. In the case of Vitremer, an hour's delay of light activation significantly decreased integrity, which declined further when light activation was omitted. Fuji II LC was not affected by the omission of light activation, while Photac-Fil was markedly weakened. After 4 mos of aging, most of the samples of each product which had been cured by the different methods attained equal integrity, with the exception of the non-light-activated Vitremer samples, which remained weaker. We concluded that the structural integrity of resin-modified glass-ionomer cements benefits from a chemical integration of the polyalkenoate and poly-HEMA networks, as in Vitremer. Improvement in the structural integrity in the early phase for cements with a mechanical entanglement of the matrices, as in Fuji II LC and Photac-Fil, requires an acid-base reaction, a considerable portion of which may take place before activation of the HEMA polymerization.

Dynamic and static moduli of elasticity of resin-based materials.

OBJECTIVES: The purpose of this study was to assess and compare the elastic moduli of 34 resin-based materials using a dynamic and a static method. The effect of water storage was also studied up to 6 months. METHODS: Five samples of each material were prepared according to ISO-4049. The dynamic moduli were first determined non-destructively from the fundamental period of the vibrating specimen, then the static moduli were determined by a three-point bending test. The percentages of fillers by weight were determined by ashing in air at 900 degrees C. RESULTS: Low values were obtained with flowable composites as well as with two packable resin composites. Correlations were found between the static and the dynamic modulus of elasticity (r = 0.94; p = 0.0001) as well as between the weight percentage of fillers and the moduli of elasticity (r = 0.82; p < 0.05 for static modulus and r = 0.90; p < 0.05 for the dynamic modulus) both at 24h. Water storage significantly affected both static and dynamic moduli of elasticity (ANOVA two factors; p < 0.05). SIGNIFICANCE: The low moduli of the flowable composites do not allow their use in posterior cavities under high stress. However, this does not exclude their use for minimally-invasive Class I cavities when the opposing tooth is stabilized to a large amount on the natural enamel. The Grindosonic method is very useful and simple for determining the dynamic moduli although it gives higher values than the static one. The elastic modulus evolution of resin-based materials after water storage is unpredictable since different patterns were observed as a function of time.

Clinical evaluation of a posterior composite 10-year report.

OBJECTIVE: The 10-year findings of one of the studies which comprised the multicentre clinical evaluation of a light-cured posterior composite restorative are reported, with special emphasis on the reasons and timing of failure of restorations included in the study. Effects of the use of rubber dam or cotton rolls and aspiration for isolation at the time of placement are considered. METHOD: One hundred Class I and II restorations of the resin composite investigated were placed by a single operator in a group of selected, predominantly young-adult patients under highly controlled conditions, with the use of rubber dam or cotton rolls and aspiration for isolation being determined according to a scheme of randomisation. The restorations were reviewed clinically after 1 week and within 1 month of placement (baseline) and, thereafter, at 6 months, 1, 2, 3, 4, 5, 6 and 10 years using modified USPHS codes and criteria. Epoxy models and photographs were obtained for retrospective analysis. RESULTS: After 10 years, 37 restorations were reviewed and 32 restorations were known to have failed. Regarding the reasons for failure, loss of occlusal anatomic form during the first 5 years and loss of approximal contacts near the end of the study accounted for most of the failures. Only two failures were attributed to recurrent caries. Few of the restorations found to be clinically satisfactory at 10 years had retained ideal functional characteristics. Location, Class and size of restoration and the method of isolation were not found to significantly influence 10-year performance and survival. CONCLUSION: The actual 10-year failure rate, estimated to have been between 40 and 50% is considered to have been high, notably given the limited incidence of recurrent caries and bulk fracture. However, the findings indicate that certain restorations of the material investigated, despite the use of outdated operative techniques, may be found to perform satisfactorily over periods in excess of 10 years.

Antibacterial activity of glass-ionomer cements, compomers and resin composites: relationship between acidity and material setting phase.

Agar diffusion testing was used with four different media to evaluate the antibacterial activity of six products (one conventional glass-ionomer cement (GIC), two light-activated glass-ionomers, two polyacid-modified resin composites and one resin composite) on Streptoccoccus mutans. Their respective antibacterial activities were also compared during and after setting. The relationship between product acidity and antibacterial activity was evaluated. All the GICs demonstrated antibacterial properties in contrast to the polyacid-modified resin composites and resin composite which did not shown any antibacterial effects. Vitrebond GIC exhibited higher antibacterial action, probably because of a cytotoxic photo-initiator diphenyliodoniumchloride. A direct relationship between material acidity and growth inhibition of S. mutans was observed.

[Dentifrices and dental hygiene]. / Dentifrices et hygiène dentaire.

The best known dentifrices are pastes. The various constituents save to respect integrity of soft and hard tissues. The abrasive must suppress coloration without enamel abrasion. The foaming agent facilitates detachment and elimination of coloration without lesion to the gingiva. Flavours, humectants, binders will not irritate the mucosa. Chlorhexidine and fluoride are among the most studied and interesting therapeutic agents.

[Release of fluoride by fluoridated amalgams and its incorporation by dental enamel]. / Libératin du fluorue par des amalgames fluorés et sa captation par l'émail dentaire.

Liberation of stannous fluoride incorporated in the alloy powder before amalgamation was demonstrated for all the amalgams tested in this study. This liberation was observed for stannous fluoride concentrations of 0.5% and 1%. Clear differences were noted in relation to the type of amalgam studied. Through the use of a non destructive method (activation with charged particles) it was possible to measure the fluoride concentration in enamel before and after the contact with the fluoridated amalgam. This analysis demonstrated that the fluoride liberated from the amalgam was trapped by enamel in contact with alloys containing 0.5% or 1% of stannous fluoride. The enrichment in fluoride was very important in the first weeks and remained high after four months. No significant difference appeared between alloys fluoridated at 0.5% and 1%. The dissolution of calcium fluoride through a KOH treatment showed that the amount of stable fluoride (fluorapatite) formed was important.

Correlation between calculus index and acid and alkaline pyrophosphatases activities of dental plaque and saliva.

The activities of acid and alkaline pyrophosphatases were measured in human plaque of thirty subjects and saliva of twenty-two subjects. A study of correlation and analysis of variance were done between the pyrophosphatasic activity and the calculus index. A significant positive relationship has been established.

A drilling technique to improve the retention of self-threading pins.

This study determined the effect of a modification of the drilling technique on the retention of self-threading pins. The drilling technique in two stages significantly increased the retention of self-threading pins.

[Evaluation technics of the anticaries potential of fluoride-releasing materials]. / Techniques d'évaluation du potentiel anticarie des matériaux libérateurs de fluorures.

Clinical evaluation of anticariogenic potential of fluoride releasing materials seems to be the best way to evaluate products effectiveness. This is an expensive, lengthy and difficult process to realise. Yet there is a need to determine the relative effectiveness of different materials so that clinicians can make rational decision on what materials to use. Fluoride release measurement and fluoride uptake in dental tissues, antibacterial effect evaluation and caries-like lesion inhibition constitute a part of different model investigations use to study fluoride releasing materials. Even if the results of these different in vitro model systems may not be directly transposed to clinical reality, they give some useful information to determine anticariogenic potential of some dental materials. Three materials are analyzed: glass ionomer cements (conventional and resin-modified), polyacid modified resin composites and fluorated resin composites. Results obtained are different for the three kind of materials. Glass ionomer cements show much more anticariogenic properties than polyacid modified resin composites and fluorated resin composites. These two last products are more difficult to distinguish. It is probably due to their similar chemical properties. Even if these products don't have a large anticariogenic effect, it could be enough to prevent secondary caries. The anticariogenic action is principally due to the fluoride release of the materials. That's why it is necessary to define the acceptable level of fluoride release, which is required to have anticariogenic action.

[In vitro evaluation of the antibacterial activity of endodontic drugs]. / Evaluation in vitro de l'activité antibactérienne de médicaments à usage endodontique.

The antibacterial activity of camphorated phenol, iodine-potassium iodide, aqueous 2% glutaraldehyde, Rockles 4, Cresophene and Terra-Cortril has been tested in vitro against 21 species of bacteria. After 2 minutes of contact between medication and bacteria, Rockles 4, Cresophene, IKI and camphorated phenol inhibited completely all the tested bacteria. Terra-Cortril and aqueous glutaraldehyde 2% even pures were ineffective against all the bacteria species. Only Cresophene remained effective against 4 bacteria species when diluated 100 times.

Fluoride release from glass-ionomer cements, compomers and resin composites.

The short and long-term fluoride release of 16 products (seven conventional glass-ionomers, five light-activated glass-ionomers, two polyacid-modified resin composites and two resin composites) commercialized as fluoride-releasing materials were measured. A potential link between the material type and its level of fluoride release was researched. The fluoride release was evaluated after different time intervals. Initial fluoride release from all materials was highest during the first 24 h and decreased sharply over the first week. Some groups of materials appeared to be significantly different after, respectively, 7 and 91 days. However, it was impossible to correlate the fluoride release of the materials by their type (conventional or resin-modified glass-ionomers, polyacid-modified resin composite and resin composite) except if we compared the products from the same manufacturer. The link between fluoride release and an acid-base reaction seems to be confirmed. The glass-ionomer composition (glass particles and polyacid's type, powder/liquid ratio) should have more influence on fluoride release than material type.

[Dental caries in a Belgian school population of 5-to-21-year-olds]. / Etude de la carie dentaire dans une population scolaire belge âgée de 5 à 21 ans.

During the last 20 years, existing data show that caries activity has decreased in some industrialized countries, while marked increases have occurred, often rapidly, in developing countries. Changes in the prevalence of a multifactorial disease like dental caries are difficult to explain but seem to coincide either with increased intake of refined sugar-containing feeding or with the widespread availability of fluorides from many sources, more particularly in the tooth-pastes. The combination of fluorides with different other factors must be considered to explain the reduction in caries prevalence in the 1970's, but only the cariostatic effect of fluorides can be measured significantly. In spite of few studies in Belgium, a trend to a reduction of caries prevalence has been observed in temporary and permanent dentition. The aims of this study are to assess: 1. the oral health in a population of 5 to 21 old schoolchildren 2. and the effect of water naturally fluoridation on the dental caries prevalence. The dental caries prevalence is determined in each age group using the dft, dfs, D (2-4) MFT and D (2-4) MFS indices. The situation in this population is not satisfactory and there is a marked need for better oral health. The D (2-4) MFT increases from 1.67 to 11.29 between 6 and 20 years of age. In each age group, the numbers of carious and untreated surfaces in temporary and permanent dentition are more important than the number of filled surfaces. The percentage of children with caries-free teeth decreases from 27.0 to 0% between 5 and 20 years of age. A relation is recorded between the caries indices and the socio-economic category of the father, with the lowest indices among the higher educational group. The results show that the prevalence of dental caries is significantly lower in lifetime residents of the fluoridated community (Mouscron). Fluoridation reduces but does not eliminate social inequalities. The benefits of water fluoridation have been demonstrated in most countries but fluoridation alone is not sufficient to achieve total prevention.