Peri-Implant Bone Organization under Immediate Loading Conditions: Collagen Fiber Orientation and Mineral Density Analyses in the Minipig Model

Mechanical properties of bones are greatly influenced by percentages of organic and mineral constituents. Nevertheless, information about mineralization level on a microscopic scale and collagen fiber organization in peri-implant bone after immediate loading is scarce. The aim of this work was to analyze and compare the degree of mineralization and collagen fiber orientation in alveolar bone (AB) and peri-implant bone of immediately loaded (IL) and unloaded (NL) implants. A total of 25 dental implants of 3.8 mm in diameter and 11 mm in length were used in the present study. In five minipigs, three premolars and the first molar were removed from the left side of the mandible. Three months later, five implants for each animal were inserted. Four implants were loaded immediately with a fixed restoration, while one implant was left unloaded. After a 4-month healing period, all implants were retrieved. Circularly polarized light and scanning electron microscope with backscattered electron imaging were used to analyze both peri-implant and AB retrieved 5 mm from the implant. The bone/implant contact ratio (BIC %) was 77.8 +/- 5.9% for the IL implants and 78.0 +/- 5.8% for the NL implants; the difference was not statistically significant (p = 0.554). In the peri-implant bone, the area related to transverse collagen fibers was 112,453 +/- 4,605 pixels for IL implants and 87,256 +/- 2,428 pixels for NL implants. In the AB, the area related to transverse collagen fibers was 172,340 +/- 3,892 pixels. The difference between groups was statistically significant (p < .001). The degree of mineralization of peri-implant bone was 137 +/- 19 gray level for IL implants and 115 +/- 24 gray level for NL implants, while in the AB, the degree of mineralization was 125 +/- 26 gray level. This difference was statistically significant (p < .001). In this study, it was found that IL and NL implants showed the same degree of osseointegration. The bone matrix around IL implants had a higher quantity of transverse collagen fibers and presented a higher level of mineralization.