Influence of Bone Density on Periimplant Bone Strain Distribution in an Immediately Loaded Implant

  Recently, promising results have been observed when implants were subjected to immediate functional loads. Regardless of whether an implant is put in function after an undisturbed healing or immediately after placement, the predictability and long-term success of implant treatment are greatly influenced by the biomechanical environment. Several studies have indicated a high failure rate for delayed loaded implants in low-density bone¹. Also, poor bone density has been identified as a risk factor for immediate loading of implants. Effects of bone density on the peri-implant stress/strain distribution have been largely investigated in the delay loading treatment. Previous finite element analysis studies have demonstrated that a greater cortical-shell thickness and a higher cortical and cancellous-bone density reduce the stress/strain concentrations around the implants². However, for the immediate loading treatment the effects of bone density are still unknown. The purpose of the present study was to investigate the effects of the bone densities at the implant-placement site on peri-implant bone strain distributions in an immediately loaded implant.

  The bone densities of seventy-five potential implant sites in the posterior mandible were measured using computed tomography (CT). Based on the CT data, we defined the 5th and 95th percentiles of bone density (950 HU and 1750 HU for the crestal cortical-bone, 150 HU and 850 HU for the cancellous bone) as low and high, respectively. A model of the posterior mandible with an implant was reconstructed using a finite element analysis software, simulating the various bone types. Delayed loading model with bonded interface between bone and implants and immediate loading model with frictional contact interface were prepared. A buccolingual oblique load of 200 N was applied to the top of the abutment. The principal compressive strains in the crestal-cortical bone and in the cancellous bone around the implant were calculated.

  In delayed loading models, the peak principal compressive strains in the low-density bone models were 1.4–2.3-fold higher in cortical bone and 1.7–5.6-fold higher in cancellous bone than those in the high-density bone models. In immediate loading models, peak strains in the low-density bone models were 1.4–2.7-fold higher in cortical bone and 1.3–8.6-fold higher in cancellous bone than those in the high-density bone models. Peak strains in immediate loading models were 1.5–1.8-fold higher in cortical bone and 2.0–3.7-fold higher in cancellous bone than those in delayed loading models.

  In conclusion, the results in the present study show that peri-implant bone strains are greatly influenced by the cortical and cancellous bone density for the immediately loaded implants as well as for the delayed loaded implants. Implant placement in the low-density bone for immediately loaded implants may result in high strains in the bone.

References:

1. Tolstunov L. Implant zones of the jaws: implant location and related success rate. J Oral Implantol. 2007;33:211-20.

2. Guan H, van Staden R, Loo YC, Johnson N, Ivanovski S, Meredith N. Influence of bone and dental implant parameters on stress distribution in the mandible: a finite element study. Int J Oral Maxillofac Implants. 2009;24:866-76.