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Creating perfect direct composite restorations has been for long time a strict challenge due to many materials' limitations impacting either shade integration or surface quality, and possibly colour stability. Next to technological drawbacks, a certain complexity and lack of predictability in clinical application was inherent to the technique and made it elitist for a long time. Shading and layering concepts then progressively evolved from a simplistic, non histo-anatomical, bilaminar technique to a multi-layering approach (3 to 4 or more layers), following the Vita Classic system. One of the most achieved concepts is polychromatic layering which makes use of a variable number of layers (basically VITA or non-VITA opacious dentin, chromatic enamel and translucent/opalescent enamel), driven by the natural tooth optical composition. In parallel with this evolution, a simplified, non-VITA shading system was developed with a reduced number of layers (basically dentin &enamel layer, plus effect shades if required) known as the natural layering concept, aiming to the same optimal esthetic integration and natural colour reproduction/emulation. The latest improvements appear all driven by the same view of improved reliability and clinical simplification.

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Composite inlays are indicated for large cavities, which frequently extend cervically into dentin. The purpose of this study was to compare in vitro the marginal and internal adaptation of class II fine hybrid composite inlays (Herculite, Kerr) made with or without composite bases, having different physical properties. Freshly extracted human molars were used for this study. The base extended up to the cervical margins on both sides and was made from Revolution (Kerr), Tetric flow (Vivadent), Dyract (Detrey-Dentsply) or Prodigy (Kerr), respectively. Before, during and after mechanical loading (1 million cycles, with a force varying from 50 to 100 N), the proximal margins of the inlay were assessed by scanning electron microscopy. Experimental data were analysed using non-parametric tests. The final percentages of marginal tooth fracture varied from 30.7% (no base) to 37.6% (Dyract). In dentin, percentages of marginal opening varied from 9.2% (Tetric Flow) to 30.1% (Prodigy), however, without significant difference between base products. Mean values of opened internal interface with dentin varied from 11.06% (Tetric Flow) to 28.15% (Prodigy). The present results regarding dentin adaptation confirmed that the physical properties of a base can influence composite inlay adaptation and that the medium-rigid flowable composite Tetric Flow is a potential material to displace, in a coronal position, proximal margins underneath composite inlays

The use of composites in the smile frame has evolved and gained maturity. However, ceramics remain the preferred aesthetic option for many clinicians because bonding techniques are still considered intricate, sensitive and, to a certain extent, unpredictable. These drawbacks, essentially related to the complexity of many composite systems, can be overcome today by the application of the 'natural layering concept', which makes use of only two basics masses, dentine and enamel, perfectly mimicking natural tooth structure. There are plentiful indications for the use of such a simplified but aesthetically uncompromised treatment modality. Actually, this approach is highly suitable for young and post-orthodontic patients where conservation of tissue is a must and in general for all patients with rather healthy dentitions

The present study evaluated the influence of different composite bases and surface treatments on marginal and internal adaptation of class II indirect composite restorations, after simulated occlusal loading. Thirty-two class II inlay cavities were prepared on human third molars, with margins located in cementum. A 1-mm composite base extending up to the cervical margins was applied on all dentin surfaces in the experimental groups; impressions were made and composite inlays fabricated. The following experimental conditions were tested: no liner (control group), flowable composite treated with soft air abrasion (experiment 1), flowable composite sandblasted (experiment 2) and restorative composite sandblasted (experiment 3). All specimens were submitted to 1,000,000 cycles with a 100-N eccentric load. Tooth-restoration margins were analysed semi-quantitatively by scanning electron microscopy before and after loading; internal adaptation was also evaluated after test completion. The percentage of perfect adaptation in enamel was 79.5% to 92.7% before loading and 73.3% to 81.9% after loading. Perfect adaptation to dentin was reduced before loading (54.8% to 77.6%) and after loading (41.9% to 63%), but no difference was found among groups for pre- and post-loading conditions. No debonding occurred between the base and composite luting. A significant, negative influence of cyclic loading was observed. The results of the present study support the use of flowable or restorative composites as base/liner underneath large class II restorations. Soft air abrasion represents a potential alternative to airborne particle abrasion for treating cavities before cementation. The application of a composite base underneath indirect composite restorations represents a feasible non-invasive alternative to surgical crown lengthening to relocate cavity margins from an intra-crevicular to supra-gingival position.