A 3-D FEM analysis of single and multiple screw-root dental implant fixed in a mandible

Replacement of single tooth using a threaded titanium screw root coated with hydroxyapatite (HA) for faster bone apposition to implant site is common. Uncoated pure titanium is also used for osseointegration. Usually bone fixation of implant takes four to six months in either case. Quite often, a good number of teeth in a mandible or maxilla are replaced. Usually it is often said that bones appear to be well designed from the point of view of structural engineering. The "maximum-minimum law" claimed by Roux is a rational concept that states that bone provides maximum strength with a minimum of construction material. According to this proposition, stress distribution in bone will be almost uniform under a set of loading conditions. This was found to be true in the case of normal human mandibular bone as examined by some Japanese scientists. The present authors are interested in examining the stress distribution during multiple single tooth replacements using 3D-FEM technique to ascertain how the stress pattern changes with such implantation of three screws in a row in the human mandible, as we are in the process of clinical trial of hydroxyapatite coated and uncoated titanium implant. This will be of considerable interest to the dental surgeons, who prompted us to address this problem. Our results depicted the mean values of various stress in cortical and cancellous bone while applying the maximum masticatory load of 50 N in each teeth. The generated stress level is within the safe range of stress for bones. However, such screws cannot be applied to osteoporotic or other diseased mandible where bone strength may be quite low.