Biofilm models are important tools to study the impact of bacterial metabolism and the effect of therapeutic measures on the caries process. Laboratory models consisting of few bacterial species are useful for high-throughput testing, but in-situ models reflect the complexity of the oral environment much better. The increased complexity typically results in a large variation in the amount of biofilm produced, not only between individuals but also between biofilms collected from the same person. Here, we designed a lower-jaw-splint with 3D-printed silicon inserts that protect the biofilm samples during growth and provide a standardized recession for each individual biofilm sample. We hypothesized that a standardized splint geometry reduces variation between replicate biofilm samples from the same individual and increases the amount of biofilm produced, compared to an in-situ-model without standardized geometry. The splints consisted of a 3D-printed metallic arch and two acrylic vestibular extensions. The extensions contained 3D-printed silicon inserts for biofilm carriers (4x4x1.5 mm). Each individual carrier was surrounded by silicon walls, recessed by 1.5 mm and kept in place by an undercut. 48-h biofilms were collected in 6-tuplicate (2 technical, 3 biological replicates) from five healthy participants, both with standardized splints and with ‘traditional’ splints where the carriers were fixed with sticky wax. The biovolume was determined by confocal microscopy. The coefficient of intra-individual variation was high for both systems, but slightly lower for the standardized splints (69 vs. 80). The average amount of biofilm was slightly lower on the standardized splints (124599 µm3±70284 SD vs. 163616 µm3±135033 SD), with no statistically significant difference (p=0.33, 2-sample t-test). The use of silicon inserts eased the handling of the biofilm samples.