[Influence of platform switching on crest bone maintenance around implants: a radiographic investigation in dogs].

PURPOSE: To evaluate and compare the dynamic changes in functional loading or non-functional loading with platform-switching (PLS) implants and butt-joint implants,and to refine the factors leading to marginal bone loss around PLS. METHODS: Six adult dogs were selected and numbered randomly.The second,third and fourth premolars in bilateral mandible of each dog were extracted. After 3 months, the implantation operation was carried out. There were 3 kinds of implants, 36 implants in total, which were divided in to 3 groups: Group A,Group G and Group U. In particular order, A, G and U were placed on each side of every dog. Three months later, the 2nd surgery was begun. At the 4th month from the 1st surgery, for each dog, on the right side only, the abutments were installed and impression was taken. Then, after 2 weeks, the dental prostheses were put on. All dogs were executed at the end of the 12th month. X-ray film was taken at the 3rd, 6th, 9th and 12th month and the moment of the 1st surgery (baseline). Measurements were made between the implant shoulder (IS),the most coronal level of bone in contact with implant (CLB), and the level of alveolar bone crest (BC). According to the different groups of implants (A, G, U), all records were analyzed with paired and Wilcoxon's signed rank test using SPSS11.5 software package. RESULTS: The mean IS-CLB and IS-BC values of group A, G were significantly different with those of group U at the 6th, 9th and 12th month, while there was no significant difference between group A and G. No matter they were loading or not, the self-comparison of each kind of implant presented no significant difference. There was no significant difference between every kind of implant on their self-comparison during the first three months; while, the differences were significant during the next 9 months. CONCLUSIONS: The most significant changes in the absorption of marginal bone around two stage submerged implant can be observed after 3 months of implanting. The bone absorption was not related to functional loading or not.