Ultrafine midway filled composites

Objectives. The aim of this study was to compare a large set of resin composites suitable for application in stress-bearing areas on the basis of their consistency. Methods. A variety of posterior resin composites were tested using an apparatus that was originally designed for determination of the consistency of elastomeric impression materials (ISO 4823,1992)*The consistency of a standardized volume of resin composite was tested in a dark room at 23°C by loading the samples during 60 s with 1625 g. After loading, the circumference of each sample was determined by a digitizer. Results were analyzed usingTukey-HSD multiple comparisons test and Student's t-tests. Results. The consistency of different brands of composites varied considerably. P50 was the material with the thinnest consistency. Significant differences (p < 0.05) in consistency were found between the same brands of material which were applied directly out of the syringe or out of a preloaded tip. Loading a Centrix tip with one composite out of a syringe resulted in a thinner consistency of the material than when taken directly from the syringe. Significance. A ranking of posterior resin composites is presented to enable a material selection based on consistency. INTRODUCTION Classification of resin composites is often based on morphological properties. Although the size and distribution of filler particles and the filler amount are important factors, mechanical properties should also be included in a classification (Willems et al, 1992). However, for a successful restorative procedure, the handling characteristics of a material are important as well. Dentists often have a preference for a composite with a specific consistency, as this parameter will affect the application and manipulation of the material. However, the consistencies of resin composites for posterior restorations have not been previously compared. In a study by Van Meerbeek et ah (1994), resin composite cements were compared. This study reported a large variation in consistency among materials. The current processes of inserting a composite into a cavity can sometimes lead to voids and porosities in the restoration. In a clinical study by Rreulene£ al. (1992) on the performance of posterior composites, the presence of voids in restorations was frequently demonstrated using radiographic evaluation. In that study, 52.9% of the restorations had voids, and a significant difference was found between various brands of composites. Nordb0 et al. (1993) also reported the detection of voids on radiographs in a clinical study on posterior composites. In the clinical situation, the presence of voids and porosities can lead to discoloration, decreased wear resistance (O’Brien and Yee, 1980; Leinfelder and Roberson, 1983) and even replacement of the restoration (Nordb0 et al., 1993). One of the important factors that influences the introduction of voids is the consistency of the material when inserted and manipulated during the restorative procedure. During clinical application, the currently available composites show a large variation in consistency Some authors recommend the use of i£high-viscosity” or “condensable” composites in posterior restorations but provide no objective criteria to compare consistency (Jordan and Suzuki, 1992). In a proper restorative procedure, the composite is placed and cured in layers. The influence of manipulation of a resin composite on the adaptation to the cavity wall was investigated by Hansen andAsmussen (1989). They found that extensive manipulation of composites in the cavity resulted in increased marginal porosity. At the same time, the width and extent ofthe contraction gap increased. Therefore, the authors recommended carefi.il manipulation of a resin composite when the material is applied in the cavity Tire consistency of the composite will certainly influence the manipulation required for correctly shaping the material. A composite can be applied in the cavity either by injecting the composite or by application with a hand instrument. Resin composites can be injected in a tip preloaded by the manufacturer, or in a Centrix tip (Hawe Neos, Bioggio, Switzerland) which can be filled in the dental office. A study by Gjerdet and Hegdahl (1978) found that 50 Opdam et af./Consistency of resin composites : '.-.‘ i ’ : ;-s: v "•> <' lV 's’s i v ' v ' f v s i 1 ✓*!.vy.;:i-.\y:';’ s ’ *.’ • * • S \ s . t <\: I I V , •: : '':V'' ̂ V ^ ' i ’ f ,:V