Strain Distribution of Immediately Loaded Implants With Fixed Prosthesis Using The “All-on-4” Protocol in the Edentulous Mandible: Nonlinear Three-dimensional Finite Element Analysis
Implant-supported fixed full-arch prostheses are being established as a treatment option for the edentulous mandible. In edentulous patients, anatomic limitations of the residual alveolar bone such as mandibular canal may cause problems for insertion of dental implants. In recent years, so-called All-on-Four concept, where only 4 implants are inserted in the interforaminal region in placing a fixed prosthesis on an edentulous mandible, has shown a high clinical success rate1. Previous biomechanical studies reported that All-on-Four configuration resulted in a favorable reduction of stresses in the bone, framework, and implants for delayed loading2. However, to date, there has been little well-documented evidence for immediately loaded implants according to the All-on-Four concept. In addition, controversy exists regarding a framework material. Some authors recommended using metal frameworks because of its high rigidity as compared to all-acrylic resin prostheses. On the other hand, other authors have reported high survival rates of all-acrylic resin prostheses. The purpose of this study was to evaluate peri-implant bone strain distribution in immediately loaded implants according to the All-on-Four concept, and to examine the effect of a framework material on the bone strain in an edentulous mandible.
A 3D-finite elementmodel of an edentulous mandible was constructed from computerized tomographic scan data of a 62-year-old male. Four implants with a diameter of 4.1mm and a length of 10mm were placed between the bilateral mental foramen according to All-on-Four concept. A framework between bilateral first molars was modeled. Delayed loading model with bonded interface between bone and implants and immediate loading model with frictional contact interface were prepared. The framework was assumed to be made of titanium or acrylic resin. Two types of loading were simulated: 1) cantilever loading; a vertical load of 200 N was applied in the right first molar region, and 2) non-cantilever loading; a vertical load of 200 N was applied in the right second premolar region. The principal compressive strains in bone around implants were calculated.
The principal compressive strains were concentrated in the bone around the neck of the distal implant in all models. Peak strains in the immediate loading models were 27.0−41.3% higher than those in delayed loading models. Peak strains in the non-cantilever loading models resulted in 43.9−53.8% reduction compared with the cantilever loading models. Peak strains in the acrylic resin framework models were at most 20% higher than those in titanium framework models. Peak principal compressive strain in the immediate loading model without cantilever was lower than that in the delayed loading model with cantilever.
In conclusion, loading condition contributes the peri-implant bone strain in immediate loading models. The results in the present study suggest that there is a biomechanical rationale for immediately rehabilitation of edentulous mandible using the All-on-Four concept in the situation without cantilever loading. A framework material did not affect the peri-implant bone strain so much.
References:
Crespi R, Vinci R, Capparé P, et al: A clinical study of edentulous patients rehabilitated according to the “All on Four” immediate function protocol. Int J Oral & Maxillofac Implants 27:428, 2012
Fazi G, Tellini S, Vangi D, et al: Three-dimensional finite element analysis of different implant configurations for a mandibular fixed prosthesis. Int J Oral & Maxillofac Implants 26:752, 2011