IMMEDIATE AND EARLY LOADING OF THERMO CHEMICALLY TREATED IMPLANTS WITH DEFINITIVE ABUTMENTS AT POSTERIOR AREAS OF MAXILLA AND MANDIBLE

Abstract

The objective of this PhD project is to investigate the clinical and radiological behaviour of thermo-chemically treated implants comparing immediate and early loading protocols with definitive abutments in a functionally high-demanding clinical situation such as posterior areas of maxilla and mandible. Before starting the clinical trial a literature review on the latest scientific advances in osseointegration and physical-biochemical characteristics of the thermo-chemically treated surface used in the study has been conducted. The results of in-vitro and in-vivo studies on this surface until the present day have also been reviewed. Currently bio-engineering has enabled us to understand the different biological events that characterize osseointegration -namely, protein adsorption, clot formation, granulation tissue formation, provisional matrix formation, interface formation, bone apposition and remodelling. Protein adhesion has proven to play a key role in the earliest stages of osseointegration, where the presence of fibronectin and vitronectin favor osteoblastic cell line proliferation, while proteins such as TGF-α inhibit it. Rough implant surfaces (Sa over 1-2 μm) lead to quicker osseointegration relative to micro-rough surfaces (Sa = 0.5-1 μm) due to the phenomenon of bone neoformation, where bone starts to form from implant surface toward the periphery at greater speed. Implants presenting hydroxyapatite in their surface lead to accelerate osseointegration due to osteoblasts’ affinity to calcium phosphate. However, the surfaces produced up to date have presented long-term problems due to the bonding of this layer to the underlying titanium. Biomimetic behaviour of the investigated surface in this project has been demonstrated by current studies since -out of a chemical reaction of precipitation of plasma ions- is able to produce a crystalline hydroxyapatite layer chemically bonded to the titanium of the implant without osteoblasts taking part. Results from In-vitro assays have demonstrated a surface roughness (Sa) of 1,74μm, high hydrophilia with a contact angle of 77.6 degrees, an increased osteoblastic cellular activity and high mechanical resistance of thermo-chemical treated titanium. Augmented adhesion strength of titanium-bonded hydroxyapatite without detached areas has been observed in in-vivo assays and a BIC (bone-to-implant contact) of 80% at 3-weeks has been registered histologically. Results of the 1-year randomized clinical trial suggest that there are no statistically significant differences in terms of survival, implant stability and radiographic bone loss between implants restored with immediate or early loading protocols. 100% survival rate was registered in both groups. A mean radiographic bone loss of 0.04±0.08mm at the implant and 0.3±0.5mm at the crest in the immediate-loaded group has been observed. In the early-loaded group the means of radiographic bone loss were 0.1±0.2mm at the implant and 0.6±0.8 mm at the crest. 62.5 % of the implants showed bone contact at the abutment after 1 year. Thermo-chemically treated implants may be considered a reliable treatment option for the rehabilitation of the posterior areas of the maxilla or mandible using immediate or early loading protocols with definitive abutments placed at the time of surgery. These results must be confirmed by studies with longer follow-up.