Osseointegration of implants with different surfaces placed during sinus grafting procedure. A histological and histomorphometric study in humans

Background: Sinus lift is a common procedure to ensure adequate bone height for implant fixation in the posterior maxilla. Sinus grafting and implant placement can be accomplished as either a “one-stage” (simultaneous) or “two-stage” (delayed) procedure, usually depending on the residual bone height.. Implant success rates following sinus floor elevation vary between 83% and 100%. The failure rate of machined surface implants is significantly higher than that for rough surface implants inserted in combination with sinus floor elevation. The implant surface with CaP nano-crystals have shown marked improvements in histological early-healing outcomes. After implantation, calcium and phosphate ions gradually dissolve in the biological medium; the increased saturation of surrounding fluids induces the precipitation of a biological apatite onto the implant surface. This apatite, containing endogenous proteins, might serve as a matrix for osteogenic cell attachment and growth. Aim/Hypothesis: The present study was carried out to histologically investigate and compare the bone to implant contact rate (BIC) of implants with a sand-blasted acid-etched surface with (NT) or without (OT) deposition of calcium-phosphate crystals, placed simultaneously with graft material during sinus lifting procedure. Study (null) hypothesis under test considered the same BIC rate for NT and OT implants. Material and methods: This was a monocentric, prospective, randomized-controlled, longitudinal study. Twenty qualified patients (n = 20) with partial edentulism and atrophic maxillary ridges were enrolled in the study. Each patient was treated for a mono- or bilateral-sinus lift augmentation with anorganic bovine bone (ABB). During surgery one half of the patients (n = 10) received two small dimensional (2 9 10 mm) site evaluation implants (SEI) as randomly indicated. One SEI had a nanoscale CaP enriched surface (NT), while the other one had a sandblasted acid-etched (SLA) surface (OT). A randomization scheme was followed for the placement of SEI implants. After 4 months of healing, the SEIs were removed, and implants were placed. Histological Processing: The retrieved specimens were fixed, dehydrated and embedded in resin. Undecalcified sections of 20 10 lm were prepared and stained with toluidine blue and acid fuchsin. Histomorphometric analysis: the bone implant contact rate (BIC %) was measured in both groups using a transmitted brightfield light microscope. Bone mineral density was evaluated under scanning electron microscope (SEM) using back scattering electrons detector and X-Ray spectrometry. After normal distribution evaluation, BIC rates were compared for both the surfaces using a parametric t-test. A p-value of <0.05 was considered statistically significant. Results: One OT implant showed a complete detach of the bone from the implant surface during the retrieving process, without clear cause. Histologic results: In the augmented area, the bone growth takes place around and between the ABB particles before reaching the implant surfaces. Isolated areas of osseointegration are present between apical implant threads, irrespective of the group. NT implants showed increased osseointegration in the native bone portion. Histomorphometric results: The BIC rate (mean SD) was 19.8 13.3% for NT and 15.8 11.1% for OT implants, without statistically significant difference. Mineral density: ABB particles appeared almost completely surrounded from bone; around the SEIs, the bone was present only in some areas, irrespective of surface topography. The calcium/phosphorus rate was 1.91 0.06 for ABB particles, while its value for newly formed bone around both the ABB and SEIs was 1.57 0.27. Conclusions and clinical implications: In this study the simultaneous placement of biomaterials and implants with CaP nanocrystals enriched surface did not change significantly the amount of BIC rate after 4 months of healing; histological findings confirm and support the conclusions reported in a previous investigation.