Response of cortical bone to local controlled release of sodium fluoride: the effect of implant insertion site

Nanofeatured surfaces in dental implants: contemporary insights and impending challenges

Dental implant therapy, established as standard-of-care nearly three decades ago with the advent of microrough titanium surfaces, revolutionized clinical outcomes through enhanced osseointegration. However, despite this pivotal advancement, challenges persist, including prolonged healing times, restricted clinical indications, plateauing success rates, and a notable incidence of peri-implantitis. This review explores the biological merits and constraints of microrough surfaces and evaluates the current landscape of nanofeatured dental implant surfaces, aiming to illuminate strategies for addressing existing impediments in implant therapy. Currently available nanofeatured dental implants incorporated nano-structures onto their predecessor microrough surfaces. While nanofeature integration into microrough surfaces demonstrates potential for enhancing early-stage osseointegration, it falls short of surpassing its predecessors in terms of osseointegration capacity. This discrepancy may be attributed, in part, to the inherent "dichotomy kinetics" of osteoblasts, wherein increased surface roughness by nanofeatures enhances osteoblast differentiation but concomitantly impedes cell attachment and proliferation. We also showcase a controllable, hybrid micro-nano titanium model surface and contrast it with commercially-available nanofeatured surfaces. Unlike the commercial nanofeatured surfaces, the controllable micro-nano hybrid surface exhibits superior potential for enhancing both cell differentiation and proliferation. Hence, present nanofeatured dental implants represent an evolutionary step from conventional microrough implants, yet they presently lack transformative capacity to surmount existing limitations. Further research and development endeavors are imperative to devise optimized surfaces rooted in fundamental science, thereby propelling technological progress in the field.

Bone healing at implants with a fluoride-modified surface: an experimental study in dogs

OBJECTIVES

The aim of the present experiment was to study early stages of osseointegration to implants with a fluoride-modified surface.

MATERIAL AND METHODS

Six mongrel dogs, about 1-year old, were used. All mandibular premolars and the first mandibular molars were extracted. Three months later, mucoperiosteal flaps were elevated in one side of the mandible and six sites were identified for implant placement. The control implants (MicroThread) had a TiOblast surface, while the test implants (OsseoSpeed) had a fluoride-modified TiOblast surface. Both types of implants had a similar geometry, a diameter of 3.5 mm and were 8 mm long. Following installation, cover screws were placed and the flaps were adjusted and sutured to cover all implants. Four weeks after the first implant surgery, the installation procedure was repeated in the opposite side of the mandible. Two weeks later, biopsies were obtained and prepared for histological analysis. The void that occurred between the cut bone wall of the recipient site and the macro-threads of the implant immediately following implant installation was used to study early bone formation.

RESULTS

It was demonstrated that the amount of new bone that formed in the voids within the first 2 weeks of healing was larger at fluoride-modified implants (test) than at TiOblast (control) implants. It was further observed that the amount of bone-to-implant contact that had been established after 2 weeks in the macro-threaded portion of the implant was significantly larger at the test implants than at the controls.

CONCLUSION

It is suggested that the fluoride-modified implant surface promotes osseointegration in the early phase of healing following implant installation.

Response of osteoblastic cells to titanium submitted to three different surface treatments

In the complex process of bone formation at the implant-tissue interface, surface properties are relevant factors modulating osteoblastic function. In this study, commercially pure titanium (cp Ti) samples were prepared with different surface characteristics using chemical attack with a sulfuric acid/hydrochloric acid based solution (treatment A); chemical attack plus anodic oxidation using phosphoric acid (treatment B); and chemical attack plus thermal oxidation followed by immersion in a sodium fluoride solution (treatment C). The samples were characterized by scanning electron microscopy (SEM), contact profilometry and contact angle. The biological performance of the prepared surfaces was evaluated using mice osteoblastic cell cultures for up to 21 days. Cells seeded on the different titanium samples showed similar behavior during cell attachment and spreading. However, cellular proliferation and differentiation were higher for samples submitted to treatments A and C (p < 0.05; n = 3), which were less rough and showed surface free energy with smaller polar components.

Bone as an effect compartment : models for uptake and release of drugs

"Bone-seeking agents" are drugs characterised by high affinity for bone, and are disposed in bone for prolonged periods of time while maintaining remarkably low systemic concentrations. As a consequence, the bone becomes a reservoir for bone-seeking agents, and a site of both desirable and adverse effects, depending on the pharmacological activities of the specific agent. For some agents, significant systemic effects may also be produced following their prolonged release from bone, a process that is governed mostly by the rate of bone remodelling. This review covers the pharmacokinetic and pharmacodynamic features of bone-seeking agents with different pharmacological properties, including drugs (bisphosphonates, drug-bisphosphonate conjugates, radiopharmaceuticals and fluoride), bone markers (tetracycline, bone imaging agents) and toxins (lead, chromium, aluminium). In addition, drugs that do not possess bone-seeking properties but are used for therapy of bone diseases (such as antibacterials for treatment of osteomyelitis) are discussed, along with targeting of these drugs to the bone by conjugation to bone-seeking agents, local delivery systems, and other approaches. The pharmacokinetic and pharmacodynamic behaviour of bone-seeking agents is extremely complex due to heterogeneity in bone morphology and physiology. This complexity, accompanied by difficulties in human bone research caused by ethical and other limitations, gave rise to modelling approaches to study bone drug disposition. This review describes the pharmacokinetic models that have been proposed to describe the pharmacokinetic behaviour of bone-seeking agents and predict bone concentrations of these agents for different doses and patient populations. Models of different types (compartmental and physiologically based) and of different complexity have been applied, but their relevance to drug effects in the bone tissue is limited since they describe the behaviour of the "average" drug molecule. Understanding of the cellular and molecular processes responsible for the heterogeneity of bone tissue will provide better comprehension of the influence of microenvironment on drug bone disposition and the resulting pharmacological response.

Effect of controlled local release of sodium fluoride on bone formation: filling a defect in the proximal femoral cortex

To assess the effect of sodium fluoride (NaF) in the healing of a defect in cortical bone, an experimental model was created by the drilling of 5.0 mm holes in the proximal ends of both femora of 12 adult male New Zealand White rabbits. An interlocking intramedullary implant constructed of poly(d,l-lactic acid) containing NaF was placed in the right femur and an identical implant without NaF (sham), in the left. The implant in the right femur was designed to release NaF in a controlled manner over the duration of the experiment. Ten weeks after implantation, the specimens were removed and were tested in torsion. The mechanical properties were not significantly different between the groups. The femora exposed to NaF had an 18.6% increase in intact cortex near the defect (p = 0.023), however, the deposition of mineralized bone within the defect was not significantly greater. In fact, healing appeared to be impaired by the presence of NaF. There was complete closure of the defect in all but one of the femora with a sham implant, but the tissue had not yet calcified. In contrast, only one femoral defect exposed to NaF had closed. Examination of the material filling the defects of the femora exposed to NaF showed that it was predominantly uncalcified osteogenic mesenchymal tissue.

Effect of controlled local release of sodium fluoride on trabecular bone

Systemic sodium fluoride has been used in the treatment of osteoporosis. Recent studies have shown that it has a positive risk/benefit ratio for use in increasing spinal trabecular bone density. However, thinning of the cortices of the long bones with a resulting increase in fracture incidence has been observed. This study was designed to determine the response of bone to sodium fluoride released from a biodegradable polymer matrix, a technique which could potentially deliver it locally to a site of need in the skeleton which has a positive response to fluoride. In one group of mature New Zealand white rabbits, cylindrical poly(D,L-lactic acid) (PLA) implants, with or without impregnated sodium fluoride, were implanted into the contralateral femoral trochanters and tibial metaphyses. In a second group, similar implants were placed in adjacent vertebrae. Four weeks postimplantation, the femora, tibiae, and vertebrae were removed, sectioned, cleaned of all but mineralized tissue, and the surfaces of the sections stained. The stained surfaces were imaged and analyzed for morphometric properties of the trabeculae. Comparing contralateral vertebrae, those exposed to sodium fluoride had significantly thickened trabeculae, with decreased spacing between them and a greater bone fraction. A similar increase in trabecular width was found in the subchondral bone of the proximal tibiae exposed to local release fluoride. Femoral sections showed no difference, possibly due to the lack of extensive trabecular bone in the region chosen for study.