Parameters of passive fit using a new technique to mill implant-supported superstructures: an in vitro study of a...

The objectives of this study are to describe, in vitro, a novel technique to measure the misfit of digitally designed and manufactured implant-supported frameworks according to a new concept based on computer-guided surgery in combination with previously placed mini-implants. Also, the digitally created framework and an impression-based milled structure were compared using strain gauge measurements.

Acrylic resin and plaster models were prepared to represent the edentulous mandible. After insertion of three mini-implants in the acrylic resin model, a cone-beam computed tomographic scan was performed. The data were imported to planning software, where six implants were virtually inserted. A drill guide and titanium framework were designed and milled using a fully digital computer-aided design/computer-assisted machining protocol. Six implants were inserted using the drill guide attached to the mini-implants. After an impression was made of the acrylic resin model with six implants, the second model (plaster model) was prepared. A second milled titanium structure was fabricated following optical scanning of the acrylic resin model. Strain gauge measurements were done on both structures attached to both models. To validate the results, a high-accuracy industrial optical scanning system was used to capture all connection geometry and the measurements were compared.

The accuracy of the digital superstructures was 19, 22, and 10 Microm with standard deviations (SD) of 19.2 (17.9), 21.5 (28.3), and 10.3 (10.1) Microm for the x-, y-, and z-axes, respectively. For the impression-based superstructure the measured misfit was 11, 20, and 17 Microm, with SD 11.8 (10.5), 19.7 (11.7), and 16.7 (8.2) Microm for the x-, y-, and z-axes, respectively.

The misfit of the digitally designed and produced superstructure on the digitally planned and inserted implants was clinically insignificant.