| Objective To evaluate and compare the radiographic outcomes in functional loading or non-functional loading with platform-switching (PLS) implants and butt-joint implants. To investigate the factors leading to margin bone loss around PLS.Methods Six adult dogs were selected and numbered randomly. Firstly, we have extracted the second, third and fourth premolars in mandible bilateral side of each dog. 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:Ankylos (Group A), GS-â…¡(Group G) and US-â…¡(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 every dog, right side only, the abutments were installed and impression was taken. Then, after 2 weeks, the dental prostheses were put on the right side. All dogs were executed at the end of the 12th month. X-Ray was taken at the 3rd,6th,9th and 12th month, as well as the moment of the 1st surgery (baseline). Measurements were made between the implant shoulder (IS) and:-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 separately by statistic software.Results 1. All experimental animals were healthy without any postoperative inflammation and no sudden death, and all implants were fixed without any clinical mobility. X-ray showed the excellent interface between implants and mandibles. The survival rate was 100 percent.2. For three kinds of implants, as compared with each other, the mean IS-CLB and IS-BC values of A, G were significantly different with those of U at the 6th,9th and 12th month, while there was no significant difference between those of group A and G.3. No matter they were loading or not, the self-comparison of each kind of implant exits no significant difference.4. For the three groups when compared with themselves at different times, there were no significant differences between every kind of implant on their self-comparison during the first three month; while, the differences were significant during the next 9 months.Conclusion 1. Both of PLS implants and butt-junction implants could be used to treat edentulous patients well.2. PLS could be beneficial of reducing the absorption of the crest bone around implant and it can maintain the crest at a high level during the first 12 months of implant functional loading from the moment it was implanted.3. For Ankylos and GS-â…¡system, both of which could be used to treat edentulous patients and the influence on crest bone during the first 12-month functional loading from the moment they were implanted was no significant different.4. The bone absorption was not related to functional loading or not.5. The most significant changes in the absorption of margin bone around two stage submerged implant can be observed after three months of implanting.6. Further investigation and observation are needed to clarify the mechanism and influence of PLS on marginal crest bone absorption around implants.
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