Cast accuracy obtained from different impression techniques at different implant angulations (in vitro study)

Background: Angulated implants may result in inaccurate impressions, and the impression technique may affect the accuracy of the definitive cast. This study was designed to compare the dimensional accuracy of casts obtained from three impression techniques for three definitive lower casts with implants at different angulations. Methods: Three Osseolink implants were placed in three reference models with different angles (parallel, 15 degrees and 30 degrees). Impressions of each model were made with three techniques (n = 10 per group): indirect, unsplinted direct, and acrylic resin-splinted direct technique. Impressions were poured with type IV dental stone. Inter-implant distances were measured for casts using a coordinate measuring machine, and the deviations from the reference models (Delta r) were calculated. Data were analyzed using one-way ANOVA followed by post hoc tests to detect significance between groups (alpha = 0.05). Results: This study showed that the deviations in micrometers from the reference model were the least for acrylic resin-splinted direct technique (Delta r1 = 49.96, Delta r2 = 50.36) versus indirect (Delta r1 = 93.8, Delta r2 = 90.9) and unsplinted direct techniques ((Delta r1 = 67.07, Delta r2 = 68.66) in 30 degrees angulated implant situation (p value < 0.0001* for both Delta r1 and Delta r2). In 15 degrees angulated implants, both the acrylic resin-splinted direct (Delta r1 = 44.64, Delta r2 = 45.58) and unsplinted direct techniques (Delta r1 = 47.39, Delta r2 = 55.28) were more accurate than indirect technique (Delta r1 = 64.8, Delta r2 = 68.3) (p value < 0.0001* for both Delta r1 and Delta r2). While in parallel condition, no difference was found between all three techniques (p value = 0.085, 0.056 for Delta r1 and Delta r2, respectively). Conclusions: The impression technique affected the accuracy of definitive casts. The acrylic resin splinted direct technique produced the most accurate casts, followed by direct unsplinted and indirect techniques. Furthermore, implant angulation affected the impression accuracy. When implant angulation increased from parallel implants to 30 degrees, the forces of deformation increased, which resulted in increased distortion.