Effect of wider implant/abutment mismatching: an histological study in dogs

Background: Clinical studies extensively demonstrated positive effect of platform switching restorations, concluding that the degree of marginal bone resorption was inversely correlated with the degree of the implant/abutment mismatch. However, several histologic animal studies questioned the validity of platform switching in the maintenance of crestal bone levels. Aim: the aim of the present study was to histologically evaluate the influence of wide implant/abutment mismatching on the peri-implant hard tissue remodeling and the soft tissue dimensions. Material & methods: The research protocol was submitted and approved by the local Ethical Committee for Animal Research at the University of the State of São Paolo. Mandibular premolars and first molars of 6 Labrador dogs were extracted bilaterally. After 3 months of healing, 1 tapered implant was installed on each side of the mandibular molar region with the implant shoulder placed at the level of the alveolar buccal bony crest. On the right side of the mandible, a reduced in diameter abutment was used creating a mismatch of 0.85mm (test), while a matching abutment was affixed in the left side of the mandible (control). The flaps were sutured to allow a non-submerged healing. After 4 months, the animals were sacrificed and ground sections were obtained for histometric assessment. The following landmarks were identified: implant shoulder (IS), most coronal bone-to-implant contact (B), top of the adjacent bony crest (C), top of the peri-implant mucosa (PM), apical portion of the junctional epithelium (JE). The following measurements were performed: vertical distance along the long axis of the implant between IS and B (IS-B), and IS and C (IS-C); vertical distance between PM and C (PM-C) and PM and JE (PM-JE). The distances PM-B, JE-B and PM-IS were extrapolated. Results: At the end of the study, all implants resulted osseointegrated. Bone resorption was greater at the control than at the test sites. However, statistically significant differences were found only at the buccal and inter-implant aspects (Tab.1). The soft tissue vertical dimension was higher at the control compared to the test sites. However, no statistically significant differences were demonstrated for any of the variables evaluated (Tab.2). Conclusions: The present study demonstrated differences in peri-implant (buccal and inter-implant) hard tissue dimensions as a result of an implant/abutment mismatch of 0.85mm, when the implant shoulder was placed at the level of the buccal bony crest.