Strains Recorded in a Combined Tooth-Implant Restoration: An In Vivo Study

Strains Recorded in a Combined Tooth-Implant Restoration: An In Vivo Study
March 2005
Ormianer, Zeev DMD*; Brosh, Tamar PhDÇƒÜ; Laufer, Ben-Zion DMD*; Shifman, Arie DMD
Implant Dentistry: Volume 14
Abstract TOP
Implant-supported fixed prosthesis is a treatment option to restore missing teeth. Occasionally, it is necessary to connect teeth and implants as abutments for these restorations. Whether such restorations can be recommended is a matter of debate. This in vivo study measured strains involved in connecting implants to a natural tooth and compared rigid and nonrigid tooth/implant connections. A patient was treated with mandibular unilateral fixed prosthesis supported by two implants and one proximal tooth. Strain gauges were cemented to the experimental framework restoration. Recordings were obtained from the restorations while the patient bit on a wooden stick on the day of placement and after 2 weeks in function, using both rigid and nonrigid attach-ment connections. A significant differ-ence was found in horizontal deformation of the tooth/crown between day 1 and 2 weeks later. Vertical deformations were smaller than horizontal ones. After applying biting forces, horizontal and vertical deformations were maintained. Strain recorded in a clinical setting revealed mostly horizontal strains generated in a combined tooth/implant device. These strains were maintained after a 2-week recording. Within the limitation of this study, combined tooth/implant restorations could be a potential complication and could cause an intrusion of a natural abutment regardless of the type of connection (rigid or nonrigid).
Implant-supported fixed prostheses are a treatment option to restore missing posterior teeth. Occasionally, it becomes necessary to connect teeth and implants as abutments for these restorations because of anatomical limitations or implant failure to osseointegrate. Whether such restorations can be recommended is a matter of debate. In a 10-year clinical study, no adverse effects were found in combined tooth/implant restorations in the posterior mandible.1 However, intrusion of the natural teeth is reported as a major clinical complication of such a design, with incidence ranging from 3.4 to 37%.2-5
Several theories have been proposed to explain this phenomenon, of which the force-distribution theory is the most plausible.6-8 It has been suggested that intrusion could be caused through energy absorption by the implants. Part of this energy is transmitted to the tooth and induces stresses that initiate intrusion because of the differences in mobility between tooth and implant.
The use of nonrigid semiprecision attachments for implant/tooth connection has been suggested to overcome the differences in tooth and implant mobility.8 However, a rigid connector may be more suitable for controlling forces transferred from implants to the teeth.9-11 The purpose of the present study was to compare rigid and nonrigid tooth/implant connections by recording strains generated by occlusal forces.
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