Trueness and precision of composite injection technique: Roles of index design, composite flowabilities, and...

This study evaluated the dimensional accuracy (trueness and precision) of direct composite veneer restorations fabricated using a composite injection technique by investigating the effects of clear index designs, composite flowabilities, and impression modality used for master model fabrication.

An in vitro 3 × 3 × 2 factorial design (N = 90; n = 5 per group) was used to assess three index configurations (monolayer-closed, MC; monolayer-open, MO; and bilayer-open, BO), three composite flowabilities (super-low, low, and high), and two impression modalities (conventional and digital). All specimens were digitized and superimposed onto a reference model to quantify trueness and precision using a root-mean square analysis. Data was analyzed using a generalized linear model (α = 0.05).

Trueness was significantly affected by index design and impression technique (p < 0.05), and the BO index and digital impressions achieved the highest dimensional accuracy. The digital-BO combination yielded a 48.1 % improvement over the least accurate workflow. Precision was significantly affected by all three factors (p < 0.05). Conversely, conventional impression demonstrated superior overall precision (p < 0.001) driven by a significant three-way interaction (p < 0.001) in which the digital- and conventional-MO-high groups showed poorest repeatability (111.1 µm) and highest precision (38.8 µm), respectively.

Index design and impression techniques are primary factors affecting dimensional accuracy. The rigid BO index consistently enhances both trueness and precision; digital impressions optimize trueness, and conventional impressions show superior precision.

Clinicians should prioritize rigid bilayer indices to achieve predictable veneer accuracy.