Due to their improved success rate, there has recently been a large increase in the use of dental implants. Several types have been imported from foreign countries in order to obtain improved masticatory function and esthetics. In addition, in the field of maxillofacial surgery here in Japan certain implant materials such as Co-Cr, titanium, ceramics and other artificial materials have been applied together with autogenous bone grafts for reconstruction of the mandible following excision of tumors. The criterion for success is essentially the same whether for mandibular reconstruction or for a preprosthetic dental implant in that they both must provide oral rehabilitation and comfort for the patient.
Satisfactory, long-term results cannot be obtained in every case due to postoperative infection, the exposure of the implant to intra- and extra-oral sites, and resorption of the underlying grafted bone. For these reasons we have carried out reconstruction of the mandible with a vascularized osteomyocutaneous flap using a microvascular anastomoses technique to reconstruct large defects and prevent bone resorption. Nonetheless, even when the reconstruction has been successful, postoperative problems such as difficulties with mastication, deglutition, and speech often remain due to the loss of soft tissues and teeth, and due to deformities of the alveolar ridge and contours of the mandible.
Attempts have therefore been made in reconstruction of the edentulous mandible in certain countries to apply various dental implants which eliminate these postoperative dysfunctions. The Transmandibular (TM) Implant devised by Dr. Hans Bosker of the Netherlands is one such device. We were the first in Japan to apply this implant to the reconstruction of two mandibles resected due to oral carcinomas.
The first case reconstructed a segmentally resected mandibular defect with revascularized iliac bone. The second case involved a mandible which was marginally resected due to a tumor. Both cases were reconstructed with major flaps such as a deltopectoral flap combined with a pectoral major myocutaneous flap, and a forearm flap for soft tissue defects at the primary surgery. Both of the TM-Implant cases showed significant elimination of oral dysfunction due to the stability of the dentures placed during the second phase of treatment.
Dental implants can be expected to improve function for the patients who have had surgery for oral carcinomas. In order to avoid postoperative complications when implants are performed, it is necessary to carry out careful surgical procedures as well as careful diagnosis of the pre-operative condition of the bone using periapical and panoramic radiographs, tomography, CT, MRI, and bone scintigraphy. In addition, since the perfect dental implant system has as yet not been developed, it is very important to the future development of dentistry that each practitioner maintain detailed records of all of his cases.

View full abstract

The IMZ Implant is a submersible one based on the concept of osteointegration. The IMZ implant system utilizes a two phase surgical procedure. The first phase includes the surgical implantation of the implant cylinder followed by a three to four month healing period during which time the implant is in a stress-free environment covered by mucosa. The second phase involves uncovering the implant, preparing for and fabricating the appliance, and the final attachment of the prosthesis to the implant.
The concentration of occlusal forces must be dispersed in order to avoid bone resorption around the osseointegrated implant. Therefore an insert of (IME) is placed between the prosthesis and the implant. IME is fabricated from polyoxymethylene (POM) which is a viscoelastic material. Due to its mechanical properties, POM protects the bone/implant interface from high stresses in a manner similar to natural dentition. The physiological mobility is very similar to that of the periodonal ligament of natural teeth; it operates to avoid concentration of stresses.
POM was developed in 1960 and has been used in medical devices for nearly 20 years, having been applied to implant products ranging from orthopaedics to cardiovascular medicine. POM has the physical properties of wear resistance, toughness and high density. However, since plastics are not as durable as metal, in time the IME implant will need to be replaced. It is recommended that it be replaced at least once per year during a routine check-up.
The pure titanium cylinder has a titanium plasma flame spray surface coating which increases the surface area of the implant six fold, encouraging rapid initial implant fixation and improved osseointegration as compared with a smooth surface implant.
The cylindrical shape of this implant is created in the bone by a precision drill system. The drills for the IMZ implant system consist of a marking drill, a spiral drill, a round drill and a cannon drill. The cannon drill has three diameters, 2.8mm, 3.3mm and 4.0mm. The spiral and cannon drills have specially adapted internal irrigation systems for atraumatic preparation of the implant receptor site. The specially designed IMZ drills minimize thermal and mechanical trauma to the bone at the implant site, creating a receptor site which precisely fits the implant. A smooth, highly polished titanium transmucosal implant extension (TIE) permits the healthy adaptation of the soft tissue to the implant and facilitates oral hygiene.
IMZ implants are indicated for free standing, free end and edentulous cases. The IMZ implant system can also be used in totally edentulous patients where fixed prostheses are indicated and desired. It is recommended that 6 implants be incorporated into the treatment plan for patients where multiple implants are positioned between the mental foramina. Otherwise, the edentulous mandible can be restored with a standard IMZ bar and clip assembly with an IMZ implant in each cuspid region.

View full abstract