| Background: In contrast with the delayed loading protocol, immediate loading of dental implants is defined as a treatment procedure that the implants were loaded with a provisional restoration at the same day the implants were placed or shortly thereafter. The use of such protocols has many obvious advantages for the patient, because, for example, this immediate approach greatly increases comfort, function, speech, and stability and enhances certain psychologic factors during the transition period. Immediate loading of dental implants has received increasing interest both in the field of basic research and applications studies.According to current opinions, the primary stability of the immediately laded implants is thought to be the most important determining factor on immediate implant loading. The literature suggested that there is a critical threshold of micromotion of the bone-implant interface above which fibrous encapsulation prevails over osseointegation. And, the tolerated micromotion threshold was found to lie somewhere between 100μm and 150μm.Data from the current available literature already suggest that several methods may improve the stability of the immediately laded implants, including choosing high quality bone type, placing the implants with the press-fit technique, choosing the screw type implants and splinting the implants. Nonetheless, data from these studies are based mainly on clinical experience and limited human research. There lacks basic researches on howthe outcome of the immediately loaded implants was influenced by the factors mentioned above.Objectives: (1) To create a 3-D model of immediately laded screw-type dental implant for finite element analysis by computer. (2) To discuss the effects of press-fit surgical technique , implant dimensions and implant thread shapes on the primary stability of immediately loaded implant using the 3-dimensional finite element analysis with the models of the immediately laded implants.Methods: (1)Using the commercial code of SolidWorks, 3-D models of screw-type dental implants and a segment of mandibular bone were generated. Then using ABAQUS software, the 3-D implant-bone complex was meshed . The interfacial contact of bone and the implants was defined to be a frictional contact with the initial press-fit stress (by interference fit options). (2) Using the immediate models (with interfacial stress) and the control models (without interfacial stress),the influence of the primary interfacial stress on the stability of the implants was computed with the ABAQUS software. (3) The micromotions of the finite element models with different implant length (8mm,10mm,13mm)/width(3.7mm,4.3mm, 5.0mm) were computed with the ABAQUS software. (4)The micromotions of the finite element models with different implant thread design (V-, square-, buttress-shaped ) were computed with the ABAQUS software.Results: (1) The finite element models of the immediately loaded screw-type implant were successfully created on the computer. The bone-implant interface of the models were defined to simulate the interfacial status of immediately loaded implants which including the primary press-fit stress and the frictional contact of bone and implant. (2)The press-fit stress caused by 0.10mm interference can reduce the vertical and horizontal micromotions by 13.20% and 1.54%, respectively. (3) Increasing the length...
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