Abstract Modern insert systems have been available on the dental market since the late 1980s. In general, two major systems can be distinguished: those with and those without preparation instruments in combination with matching standardized inserts. It is claimed that one of the advantages of insert systems is the better marginal adaptation of insert/composite restorations compared to mere composite restorations: the integration of inserts re- duces the polymerization shrinkage stress and lowers the overall coefficient of thermal expansion. In vitro data in- dicate that adapting the insert size to the most precise fit produces a quality of marginal adaptation comparable to that of ceramic inlays. Inserts also facilitate the establishment of a proximal contact. With respect to wear, no significant differences are detected between composite and insert restorations. The bond between in- sert and composite is susceptible to contamination dur- ing operative procedures. Short-term clinical investiga- tions confirm in vitro findings regarding improved mar- ginal adaptation and increased wear resistance. Long- term controlled clinical studies are in progress, but data are not yet available. Based upon the present in vitro and in vivo data it can be concluded that the insert technolo- gy shows promising results, but further investigations re- garding, for example, stability of the insert/composite bond, fracture resistance of the overall restoration, and wear behavior are necessary to predict the clinical suc- cess of this alternative restoration procedure. Key words Class II composite restorations · Marginal adaptation · Ceramic inserts · Ceramic inlays · Tooth preparation instrumentation Introduction The minimal invasive restoration of primary lesions with composite resin, following the guidelines of the adhesive technique, is an accepted method of treatment today. Data presented in the scientific literature also support the use of resin-based composites for restoring medium-sized class I and II cavities [3]. However, clinical shortcomings are associated with the placement of medium-sized class I and II composite restorations, including polymerization shrinkage stresses and differing coefficients of thermal expansion between tooth structure and restorative materi- al, which may both affect marginal adaptation. Further- more, establishing a physiological proximal contact area is difficult with composite resins especially in more ex- tended lesions. Lutz et al. [31] introduced the increment technique to prevent these shortcomings and to meet the demands of gap-free marginal adhesion and proper estab- lishment of proximal contact areas. Other approaches to improving composite resin materials and adhesive tech- niques focus upon: (a) further reduction in polymeriza- tion shrinkage, (b) improvement in bonding techniques, and (c) improvement and development of curing methods [3]. In this context, new products such as compomers, or- mocers, polyglass, and smart materials have been intro- duced [19], curing methods have been modified (soft- start technology, plasma-arch curing devices), and recent- ly the use of prefabricated ceramic inserts in combination with composite resins has been advocated for the esthetic and cost-effective restoration of medium-sized class I and II cavities [5, 6, 18, 23, 30, 32, 37]. Modern insert systems have been available on the dental market since the development of Beta-Quartz in- serts by Bowen et al. [7] in the late 1980s. Among the restorative techniques now available, inserts have so far received only little attention. However, insert technology has recently become the focus of increased interest with regard to the development of new dental materials and restorative techniques in the search for an alternative to amalgam and following patients’ demands for esthetic, tooth-colored, and cost-effective restorations. M. Federlin ( ✉ ) · B. Thonemann · G. Schmalz Department of Operative Dentistry and Periodontology, Dental School, University of Regensburg, Franz Josef Strauß Allee 11, 93042 Regensburg, Germany Tel.: +49-941-9446024, Fax: +49-941-9446025 Clin Oral Invest (2000) 4:1–8 © Springer-Verlag 2000 REVIEW M. Federlin · B. Thonemann · G. Schmalz Inserts – megafillers in composite restorations: a literature review Received: 30 November 1999 / Accepted: 12 December 1999