| Objective:The aim of the present study was to investigate the influence of different implant-abutment junction design on crestal bone resorption at titanium implants by histomorphology, on loaded and unloaded condition. The implant animal model was established, in order to optimize implant-abutment junction design and to provide an evidence for clinical application.Methods:Six healthy adult dogs were chosen. Their second, third, fourth premolars of mandibles were extracted, and after three months healing,36 implants were placed after general anesthesia. With control for comparision, all the implants were grouped in three by different implant-abutment junction. A: Osstem-US system (conventional design, external hex); B:Osstem-GS system (platform switching, internal hex); C: Ankylos system (platform switching, internal hex).3 months later, second stage surgery was performed to connect healing abutment.1 month later, implants located in right were connected with metal crowns and functioned loaded, while implants located in left were unloaded. The animals were killed after 8 months. Ground sections of bone with dental implant were made for histomorphometrical analysis. IS (implant shoulder),CLB (the most coronal level of bone in contact with the implant),BC (the level of the alveolar bone crest) and aJE (the apical extension of the long junctional epithelium) were located, measurements were made between IS-CLB,IS-BC and IS-aJE. Data were statistically analyzed.Results:(ⅰ) All experimental animals were no postoperative inflammation and no sudden death; all implants had a perfect osseointegration.(ⅱ) In group A: IS-CLB is 1.16±0.26mm (loaded) and 1.15±0.37mm (unloaded), IS-BC is 0.76±0.32mm (loaded) and 0.72±0.59mm (unloaded), IS-aJE is 0.94±0.29mm (loaded) and 1.07±0.35mm (unloaded).(ⅲ) In group B:IS-CLB is 0.33±0.33mm (loaded) and 0.34±0.51mm (unloaded), IS-BC is 0.21±0.31mm (loaded) and 0.21±0.50mm (unloaded), IS-aJE is 0.17±0.34mm (loaded) and 0.07±0.34mm (unloaded).(iv) In group C:IS-CLB is -0.10±0.63mm (loaded) and -0.07±0.44mm (unloaded), IS-BC is 0.04±0.42mm (loaded) and 0.14±0.30mm (unloaded), IS-aJE is -0.01±0.11mm (loaded) and -0.02±0.18mm (unloaded).(v) The difference in IS-CLB,IS-BC and IS-aJE had high statistical significance between conventional design group A and each tow platform switching groups (P< 0.01). Therefore, the difference in IS-CLB,IS-BC and IS-aJE had no statistical significance between platform switching group B and C (P> 0.05).(vi) The difference in IS-CLB,IS-BC and IS-aJE had no statistical significance between the buccal and the lingual aspects, nor between load and unloaded condition in each group (P> 0.05).(i) There is obvious margin crestal bone resorption around conventional design titanium implants, and it has no relation with loaded or unloaded condition.(ii) Compared with conventional design implant system, platform switching can reduce the margin crestal bone resorption effectively and keep the crestal bone level stability.(iii) The main mechanism of margin crestal bone preservation by platform switching implant may be:the injurious of bacteria and inflammatory cells down along the implant surface is stopped, and the adjunction of biological width is restricted on the implant platform effectively.
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