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.

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.

Characterization of the inorganic fraction of resin composites.

The purposes of this study were to determine the weight fraction of filler in thirty-nine resin-based materials including flowable and packable composites, and to examine the morphology of the filler particles. The percentages of inorganic fillers by weight were determined by Thermogravimetric Analysis and by ashing in air technique at 900 degrees C. The size and shape of the filler particles were examined using scanning electron microscopy (SEM) after dissolution of the organic matrix. The weight fraction of inorganic fillers ranged between 41.6 and 84.6%. Wide variations were found among materials of the same category. Values found in the present study were sometimes different from those given by the manufacturers. The SEM photomicrographs showed various shapes, and sizes of inorganic fillers. Compared with universal hybrid restorative materials, flowable composites have lower filler loading and packable resin composites did not show higher values as claimed by some manufacturers. Various factors may explain the observed discrepancies between the manufacturer's data and our results. The silane treatment as well as the incorporation of organic material as part of the fillers of the composite could be responsible for those differences.

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.

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.

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.

Influence of the isolation method on the 10-year clinical behaviour of posterior resin composite restorations.

The aims of this prospective randomised clinical study were to clinically evaluate a radiopaque, highly filled, hybrid, light-activated resin-based composite for posterior teeth (Occlusin, ICI Dental, Macclesfield, UK and GC Dental, Tokyo, Japan) and compare the performance of restorations placed using rubber dam or cotton roll isolation. One clinician placed 100 (42 Class I and 58 Class II) restorations of the material under investigation. The isolation mode for each restoration was determined randomly: 52 preparations were protected from contamination with cotton rolls and aspiration, and 48 preparations were isolated under rubber dam. At baseline and periodically thereafter (0.5, 1, 2, 3, 4, 5, 6, and 10 years), each composite was evaluated by two practitioners using a modified (USPHS) rating system. After 10 years, 37 restorations were reviewed. The results showed satisfactory clinical performance with and without rubber dam after 10 years. A concern was the number of failures at 10 years due to unsatisfactory proximal contact. The evaluations for the surviving restorations were acceptable but with a large reduction in the percentage with ideal occlusal and proximal anatomy. The 10-year comparison of isolation modes showed no statistically significant differences (Kruskal-Wallis test) for each of the evaluation criteria. Furthermore, survival analysis showed no significant difference between the groups (Mantel-Haenszel method). It was concluded that the 10-year clinical behaviour of the restorations of a posterior composite placed under well-controlled, effective isolation with cotton rolls and aspiration, was not significantly different from the behaviour of restorations placed using rubber dam isolation.

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.

In vivo comparison of a microfilled and a hybrid minifilled composite resin in Class III restorations: 2-year follow-up.

An in vivo comparison was made of two different types of restorative resins over a 2-year period: a microfilled resin (-1158262462Silux Plus, 3M-1158262462, USA) and a hybrid minifilled composite resin (-1158262461Herculite XRV, Kerr-1158262461, USA); 56 restorations were placed in 28 patients by one experienced dentist and examined by two independent evaluators using the United States Public Health Service (UPSHS) rating system for marginal adaptation, marginal discoloration, surface roughness, anatomic form and modified criteria for color match (direct and indirect evaluation). Modified criteria divided the classic A score into A1 for "not detectable" filling and A2 for "slightly discernible filling". Restorations were evaluated at baseline, 1 week, 6 months, 1 year and 2 years later. After 2 years, all materials were considered satisfactory for marginal adaptation, anatomic form and surface roughness (no "Charlie", or "Delta" ratings). No recurrent caries was observed. Clinical evaluation showed a significantly higher rate of marginal discoloration for the microfilled composite resin than the other resin. Hybrid composite resin materials may be expected to perform well as an anterior restorative material. Photographic ratings confirmed the clinical evaluation. The modified evaluation for color match demonstrated differences, which are not discernible with the USPHS system and showed, more rapidly, differences that appear later with the USPHS system.

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.

[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.

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.

[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.

[From epidemiology to social epidemiology in dentistry. The example of caries]. / De l'épidémiologie à l'épidémiologie sociale en dentisterie. L'exemple de la carie.

Today, we know the caries aetiology and prevention rather well. We also know that caries-related levels of dental health are inequitably distributed among social classes: on the average, disadvantaged people experience higher DMFS then privileged people. This difference can be explained by a differential access to health care, which can be shown by the study of components of the DMFS index: proportion of filled surfaces (F/DMFS), proportion of missing surfaces (M/DMFS), and proportion of recurrent caries (secondary caries/filled surfaces). Though we are able to describe the social distribution of levels of dental care, we cannot "explain" the differences we observe. The explanation of those differences defines the field of social epidemiology. This consists in determining the social aetiology of diseases, starting from social determinants of attitudes and behaviors influencing health.

[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.

[Pulpectomy. Why? When?]. / La dépulpation. Pourquoi? A quel moment?

There are many circumstances under which the condition of the pulp calls for root canal work, due to the real or potential risk of pain, infection, inflammation or functional difficulties (acute, irreversible pulpitis, chronic pulpitic conditions, necrosis and its consequences, etc.). Other circumstances exist in which injury to the pulp is not necessarily irreversible: initial pulpitis, iatrogenic fracture of the pulp, traumatisms, dystrophic deteriorations. The high success rate for endodontic therapy could argue for elimination of impaired or necrose-prone pulp. In fact, however, unsuccessful pulpectomies often lead to loss of the dental organ and successful endodontic treatment severely weakens the whole tooth structure and often implies prosthetic restoration, with the consequent increase in tissular loss. In order to preserve pulp and crown tissues, pulpal vitality should be protected in all cases where such conservative efforts do not worsen the prognosis for maintaining the tooth on its arch or jeopardize a planned restoration. Solutions are presented for various types of situations, according to the risks encountered.

[Caries prevalence and dental hygiene in a group of school-age children]. / Le bilan carieux et l'hygiène dentaire dans un groupe d'enfants en agescolaire.

The results of a cross-sectional study of the prevalence of caries in a sample of 3,237 children aged 5 to 21 are described in relation to some objectives of the WHO program. The prevalence of caries is high in the sample: 1. 31.5% of the children aged 5 to 6 are free of caries (according to the WHO objectives, 50% of the children aged 5 to 6 should have no caries), 2. the mean number of decayed, missing and filled permanent teeth (DMF/T index) in children aged 11 to 12 is 6.6 (The DMF/T should be less than or equal to 3). The frequency of toothbrushing is distributed as follows: 23% of the children brush their teeth once a week or less, 46% brush their teeth once a day, and 31% brush their teeth twice a day or more. The purpose and the frequency of the consultations at the dentist's office have been examined: 15% of the children never consult the dentist, 44% consult the dentist in case of toothache, and 41% go to the dentist's office for screening or control. Only 3.2% of the children use regularly and appropriately fluoride tablets. Since the variance of the results is large, it is difficult to distinguish explaining variables or determinants. However, the data indicate that social groups show differences in DMF indices as well as in the behaviors associated with dental hygiene and prevention.