Composite materials for clear-aligner attachments: a narrative review of classification, composition, and material properties

Composite attachments used in clear-aligner therapy are fabricated from resin-based dental composites and are essential for effective force transmission to teeth. These materials constitute a heterogeneous group differing in resin-matrix composition, filler characteristics, viscosity, and physicomechanical, surface, and optical properties. This narrative review summarizes the classification of composite materials used for attachment fabrication and discusses the relationships between their composition and clinically relevant properties. Available evidence indicates that composite performance is influenced by multiple interacting factors, including resin chemistry, filler loading and morphology, polymerization characteristics, and degradation processes occurring during service. Laboratory studies have demonstrated material-dependent differences in attachment reproduction accuracy, surface roughness, wear resistance, volume loss, hardness, translucency, and color stability. Clinical studies have also reported attachment wear and dimensional changes during treatment. Current findings suggest that attachment behavior cannot be reliably predicted solely from material classification, viscosity, or filler content. Instead, attachment performance appears to be product-specific and multifactorial. Although individual materials may exhibit advantages in selected properties, no composite has consistently demonstrated superior performance across all evaluated outcomes. Consequently, no single composite material can currently be regarded as the gold standard for clear-aligner attachment fabrication.