Ultrasound Investigation of Tongue Movement During Mastication for Completely Edentulous Patients Rehabilitated by Mandibular Implant Retained Overdenture

Each patient received a newly constructed conventional complete denture. To construct the radiographic stent, the mandibular denture was duplicated in clear acrylic resin and modified by placing multiple holes filled with radiopaque gutta-percha points. A stereolithographic surgical guide was then constructed using a dual scan technique with cone beam computerized tomography (CBCT, i-CAT Vision®, Imaging Sciences International, Hatfield, PA). Two dental implants were inserted in the patient's mandibular arch at the canine region using guided surgery and a delayed loading protocol. Patients were instructed to rinse their mouth with Chlorohexidine mouthwash just before the implant surgery and continue for one week. A prophylactic antibiotic (Amoxicillin and Clavulanic acid 125 mg) was administered one hour before the surgery and continued for one week after surgery. To control pain, a nonsteroidal anti-inflammatory drug (Ibuprofen 600 mg) was prescribed. After surgery, patients were prohibited from using the complete denture and were advised to follow a soft diet.

After one week, the mandibular denture was relieved and relined with soft relining material (Softliner; PROMEDICA) and delivered to the patient. After 3-4 months, the dental implants were exposed and ball abutments were screwed into the implants (Fig.1A). The housing of the ball attachments were incorporated into the fitting surface of the mandibular denture using a direct pick-up technique (Fig. 1B). The mandibular overdenture was then inserted into the patient's mouth and occlusal adjustment was done using articulating paper to remove any occlusal interferences. Follow-up visits were scheduled.

Tongue movement measurement The evaluation of tongue movement was conducted using an ultrasound imaging system (Toshiba Medical Systems Corporation, Tokyo, Japan) with a 3.1-MHz convex probe. A layer of ultrasound jelly (Sono Jelly, Toshiba Medical Systems Corporation) was applied to the patient's skin under the probe. The patient was instructed to sit in upright position, and the probe was placed under the chin area to allow the beam to pass through the distal surfaces of the second premolars on both the right and left sides. The probe was secured in place using a microphone stand (Panasonic System Networks Co., Ltd., Tokyo, Japan) with adjustable height and angle. The position of the tongue was confirmed on the B-mode image of the sagittal plane, which provided a two-dimensional recording of the slice through the oral cavity. The recording rate was 0.0476 seconds (21 frames per second). Ultrasound images were taken while the patient chewed 1/4 of a cookie in a normal manner until it was swallowed.

The ultrasound images were taken at two different oral conditions: 3 months after complete denture insertion and 3 months after mandibular implant overdenture insertion. The ultrasound data were exported from the imaging system via a USB port and transferred to a personal computer. The Articulate Assistant Advanced (AAA) software program version 221.2.0 was used to analyze the data. The software program provides a measurement fan, which is used to automatically set control points at the intersection of the tongue-surface spline and each radial axis. This is done using the AAA edge-detection algorithm, which detects dark-bright discontinuities in the image. (28) The spline was then fitted to the visible surface of the tongue in each relevant video frame (Fig. 2). From the start time (the beginning of mastication) to the end time (when the tongue moved up towards the palate at the start of swallowing), the tongue surface was traced in AAA.

The following items were measured: