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8 Dental Tribune Middle East & Africa Edition | September-October 2014clinical Composite restoratives suitable for the bulk-filling technique need to fulfil certain requirements. Among other things, they should demonstrate low polymerization shrinkage and ensure a high depth of cure. Esthetic rehabilitation of posterior teeth using Bulk-Fill Composite By Prof. Dr Masahi Miyazaki I n modern restorative den- tistry, a strong emphasis is placed on preserving healthy tooth structure and achieving esthetic results. The use of direct composite restoratives can assist in meeting these demands. Composite resins have become widely accepted in dentistry as direct placement restorative materials for posterior teeth. The advances made in adhe- sive technology as well as the improvement of the mechani- cal properties of composite res- ins (e.g. wear resistance) have contributed to this development. Nevertheless, the polymeriza- tion shrinkage and limited cur- ing depth of composite resins continue to be a concern to the clinician. Polymerization shrinkage of composite restora- tives has been associated with micro-leakage, de-bonding of the restoration as well as in- creased risk of secondary caries or postoperative sensitivity. To reduce the rate of polymeriza- tion shrinkage, incremental fill- ing techniques have been rec- ommended for many years. The reduced shrinkage per compos- ite layer is believed to minimize the total volumetric shrinkage [1]. Even though incremental layer- ing may be necessary to ensure adequate polymerization of the composite resin, there are also some disadvantages to this tech- nique. For example, air entrap- ment between the different lay- ers may occur. Moreover, the fact that incre- mental placement requires con- siderable time may render the restorative procedure excessive- ly long. The controversy among researchers and practitioners with regard to the appropriate placement technique, namely, incremental layering versus bulk placement, continues to persist. In recent years, dental manufac- turers have gone to considerable lengths to develop bulk-fill com- posites that demonstrate lower shrinkage stress during polym- erization and offer much greater depth of cure. The goal behind these efforts has been to shorten the duration of the restorative procedure [2]. In the meantime, several posterior composites of this type have been launched on the market. What dentists need now is some sort of guideline for their application in concrete clinical situations. Advantages and limitations of direct composite resin restora- tions A major advantage of adhesive composite restorations in pos- terior teeth is the possibility of preserving healthy tooth struc- ture. Unlike indirect procedures, the direct restorative technique with composite requires only minimal removal of sound tooth structure. Preparation to gain access to the lesion is normally limited to the affected area. Nev- ertheless, the shape of the cavity should be adjusted to match the restorativematerial.Elimination of slightly undermined enamel is not always necessary because adhesive composite resin res- torations may contribute to the stabilization of the remaining tooth structure. As a result of the shrinkage stress that occurs during the light-curing of composite resin, there are restrictions with re- gard to the placement technique employed. Studies have shown that the magnitude of the stress generated is dependent on a combination of the material properties and characteristics of the prepared cavity. Contribut- ing factors include the confine- ment conditions imposed on the composite, the volume of the restoration, the restorative tech- niques used and the suitability of the bonding substrate. When restoring cavities with a high C factor, the resultant stress puts the resin-tooth in- terface under increased tension because there is less free, non- bonded surface. An increase in the C factor is associated with potentially deleterious effects on the marginal integrity and the formation of gaps [3]. Alterna- tively, high bond strength may cause cusp deflection and crack- ing of the enamel. Methods of lowering the shrinkage stress Polymerizing low-volume in- crements may minimize the resulting shrinkage stress and maximize double bond conver- sion of the monomers to a poly- mer. Compared with bulk-filling techniques, incremental filling produces lower shrinkage stress (up to a certain threshold thick- ness of the composite layer). Incremental placement tech- niques have the advantage of maximizing the polymerization of each increment because of the reduced attenuation of light through the smaller increments of material and better adapta- tion of the composite to the cav- ity walls [4]. Nevertheless, the value of incremental placement in reducing shrinkage stress has been repeatedly questioned [5]. The contradictory conclusions at which studies have arrived might be due to differing testing methods. Apart from low residual stress and good adaptation, thorough polymerization of the composite resin is an important factor for restorative success. The main concern about the bulk-filling technique is whether the com- posite cures sufficiently in the deeper portions, as this is a pre- requisite for any filling with ac- ceptable physical and biological properties. Recently, several so-called low- shrinkage stress materials have been launched on the market. The majority of them are more translucent than conventional composites. They feature a modified initiator system which allows them to be placed in in- crements of up to 4 mm thick- ness (bulk-filling technique), but still ensures a reliable cure with short irradiation times. Bulk-fill materials have been reported to demonstrate signifi- cantly less shrinkage stress than conventional posterior compos- ite resins [6]. Trouble-free restoration In the restoration of teeth with composite resin, incremental layering is generally preferred because it reduces gap forma- tion at the adhesive interface and the postoperative sensitivi- ties associated with it. However, multiple layers of highviscos- ity composite may be difficult to place. Recent studies have sug- gested that fewer increments and even bulk filling can be equally successful. However, the unavailability of suitable bulk- fill materials has discouraged clinicians from employing such techniques [7]. Today, various dental manufacturers have ex- panded their offering to include lowershrinkage composites, al- lowing clinicians to achieve reli- able and predictable results with the bulk-filling technique. Bulk-fill composites should of- fer high depth of cure. This is Figs 1 and 2. SEM of the filler composition and surface structure of Tetric N-Ceram Bulk Fill (magnification: 200x) Fig. 3. Preoperative situation: The restoration of the upper posterior tooth shows a marginal fracture. Fig. 5. Prior to the application of the adhesive, the cavity is etched with phosphoric acid. Fig. 4. After the rubber dam has been placed, the restorationaswellascarioustissueareremoved. Figs 6 to 9. The anatomical features of the cusps are successively rebuilt until an ideal occlusal anatomy is achieved. > Page 9