Abstract
Purpose: Excessive micromotion at the implant-bone interface may result in fibrous encapsulation instead of osseointegration of dental implants. This study quantified micromotion of implants placed in polyurethane foam and sheep tibia and tried to establish correlations with histologic parameters. Method: Dental implants (n=5) were placed in the tibiae of two sheep and allowed to heal for five and twenty weeks respectively (totalof 10 implants). Identical implants were placed in polyurethane foam with densities of 10 pcf and 20 pcf and a 3 mm thick cortical layer with a density of 40 pcf (n=5 per bone type; total of 10 implants). For determining micromotion at the implant bone interface, specimens were loaded in a universal testing machine and extensometers were used for recording implant displacement during loading. Implant stability, bone mineral density (BMD) and bone to implant contact (BIC) were determined additionally. Statistical analysis was based on Wilcoxon rank sum tests and Spearman rank correlation tests with the level of significance set at p<=0.05. Results: An increase in trabecular bone density and healing time caused a basic trend towards greater implant stability (p<0.05 for polyurethane foam; p>0.05 for sheep) and less implant displacement as a consequence of loading. The histologic parameters BIC and BMD also increased with healing time, however, this effect was only significant for BMD in the cervical (p=0.02) and apical (p=0.05) part. No difference in micromotion was found between implants placed in sheep and those placed in polyurethane foam with trabecular density of 10 pcf. Only few and inconsistent correlations were found between the parameters evaluated. Conclusions: Bone quality seems to affect implant micromotion although the exact determinants remain unclear. Implants placed in cellular polyurethane foam with density 10 pcf combined with a 3 mm layer of solid foam with density 40 pcf showed biomechanical behavior comparable to implants placed in sheep tibia.
Highlights
Besides proper three-dimensional positioning, achieving primary implant stability is the major goal in implant surgery [1]
An increase in trabecular bone density and healing time respectively caused a basic trend towards greater implant stability and less implant displacement as a consequence of loading
The histologic parameters, bone to implant contact (BIC) and bone mineral density (BMD) increased with healing time, this effect was only significant for BMD in the cervical and apical part (p=0.02 for BMD cervical and p=0.05 for BMD apical; Table 2)
Summary
Besides proper three-dimensional positioning, achieving primary implant stability is the major goal in implant surgery [1]. Apart from clinical considerations, the level of primary stability achieved determines the loading protocol applied [6]. While immediate loading seems to be feasible in implants showing high stability, implants with limited primary stability are often allowed to osseointegrate prior to loading thereby significantly increasing treatment times [7]. The concept behind this clinical decision making process is to avoid potentially detrimental levels of micromotion at the implant bone interface caused by masticatory loads [8,9]. The most widely accepted threshold value for micromotion, above which fibrous encapsulation instead of osseointegration occurs, seems to lie in the range between 50 and 150 μm relative displacement between implant and alveolar bone [10,11,12,13,14]
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