Mechanical properties and clinical survival of bulk-fill composites: A systematic review with mAFR analysis

The objectives of this study were to investigate the longevity and quality of restorations placed with bulk-fill composites compared to conventional composites. Both material categories were characterized by in-vitro properties (Part I) and by their longevity in short and long-term clinical studies (Part II).

Part I: A systematic literature search was carried out for the period of 2010-2025 in PubMed, Embase, Web of Science und Scopus and structured according to the PRISMA flow diagram. Studies that examined the following mechanical properties of bulk-fill composites compared to conventional composites were included: Flexural strength according to the 3-point bending test, polymerization shrinkage according to ISO 17304 and shrinkage stress, using "Bioman" developed by D.C. Watts. In addition, the following inclusion criteria were applied: studies published in English or German, exclusively in-vitro studies, and use of standardized sample preparation for specific tests. Only studies with direct restorative materials and with at least one commercially available composite were included. Following the screening process, n = 88 studies were included. Data analysis was performed using weighted regression. The risk of bias in in-vitro dental material studies was assessed with the RoBDEMAT tool. Part II: Four different databases PubMed, MEDLINE via Ovid, Embase and Cochrane Library were used for a systematic literature retrieval of clinical trials between 2010 and 2025 regarding their longevity of bulk-fill composites in comparison to conventional composites, structured according to the PRISMA flow diagram. The inclusion criteria required that studies were reported in English, involved clinical trials with patients aged 18 and older and assessed only direct restorations examined according to World Dental Federation (FDI) and/or US Public Health Service (USPHS) methodology. Subsequently, n = 38 trials. were evaluated in terms of Esthetic, Functional and Biological properties and a calculation of the mean Annual Failure Rate (mAFR) was performed. Data analysis was performed using weighted regression. The Risk of bias tool for randomized trials (RoB 2) and the GRADE tool (Grading of Recommendations Assessment, Development, and Evaluatiodn) were also applied to enhance transparency in evaluating the evidence.

Part I: All bulk-fill composites had a flexural strength well above 80 MPa and can therefore be used in the posterior region including occlusal surface in accordance with ISO 4049. The polymerization shrinkage of 'Flowable base' bulk-fill materials (3.2%) was significantly lower than of conventional flowables (3.5%) and that of 'Full-body' bulk-fill composites (1.9%) was significantly lower than that of viscous universal composites (2.3%). The Flowable base bulk-fills achieved the significantly lowest shrinkage stress (2.4 MPa), followed by the Full-body bulk-fills (2.6 MPa), despite higher volume shrinkage compared to conventional composites. Part II: Bulk-fill composites showed a lower mean mAFR (0.8%) than conventional composites (1.4%). The findings of the short-term studies (< 2 years) indicated the following sequence of reasons for failures of bulk-fill materials, ranging from most to least significant: Retention > Marginal staining > Fractures > Marginal adaptation > Patients's view > Anatomic form > Postoperative (hyper-) sensitivity. The order for long-term studies (> 2 years) was: Restoration integrity > Color stability and translucency > Anatomic form > Marginal adaptation > Fractures > Tooth integrity > Surface luster/gloss > Recurrence of caries, Erosion and abfraction > Retention > Marginal staining > Surface staining > Postoperative (hyper-) sensitivity. Bulk-fill composites showed slightly higher 'Alpha' and 'Bravo' scores, and lower 'Charlie' scores compared to conventional composites.

This review shows that the investigated 'Flowable base' and 'Full-body' bulk-fill composites had a flexural strength comparable to conventional composites and lower polymerization shrinkage and shrinkage stress ('Flowable base' bulk-fill 2.4 MPa, 'Full-body' bulk-fill 2.7 MPa, 'viscous conventional' 3.0 MPa). Their mAFR was 0.6 %age points lower than that of conventional composites. These results suggest that Flowable base and Full-body bulk-fill composites, which require less placement time, lead to clinical outcomes comparable to conventional composites.