Purpose: Mandibular deformation during function in patients with implant-supported prostheses is associated with increased strain at the bone-implant interface when dental implants are connected by a relatively rigid superstructure. Whilst there is a body of evidence concerning deformation as measured between the corpora, there are little data on its effects in the midline. This study measured 3 types of midline mandibular deformation during nonmasticatory functional mandibular movements in edentulous subjects with dental implants. Materials and Methods: A range of custom displacement transducers was fabricated for 5 edentulous subjects who had been treated with dental implants in the anterior mandible. These transducers were mounted on contralateral implant abutments adjacent to the midline to measure medial convergence, corporal rotation, and anteroposterior shear. Their output was recorded for offline analysis by a personal computer. Results: The values of medial convergence ranged from 15 to 42 µm during opening, from 10 to 21 µm during lateral excursions, and from 18 to 53 µm during protrusion. Corporal rotation varied from 0.05 to 0.11 degrees during opening, from 0.03 to 0.08 degrees during lateral excursions, and from 0.03 to 0.15 degrees during protrusion. Anteroposterior shear varied from 38 to 93 µm during opening, from 28 to 56 µm during lateral excursions, and from 52 to 103 µm during protrusion. Discussion and Conclusions: Nonmasticatory physiological mandibular movements cause the jaw to deform about the midline in at least 3 directions. It is important for the clinician to be aware of the phenomenon of mandibular deformation, which should be taken into consideration in the design and monitoring of mandibular prostheses. Keywords: dental implants, edentulous subjects, mandibular deformation