Dawn of Titanium dental implants
In the beginning, gold was used as dental implant material due to its corrosion resistance and good biocompatibility. However, the key drawbacks were its high cost and lower mechanical strength, which precluded its widespread use. Ever since Branemark’sserendipity of the Osseo-integrative properties of titanium (Ti), the metal has established the benchmark for dental implant materials. Titanium implants have been one of the most popular dental implants with long-term success rates of 94-97% over decades of clinical success and innovation. Commercially pure titanium (CpTi) and low interstitial Ti-6Al 4V (ELI) are the 2 most typical titanium-based materials which are about six-fold stronger compared to compact bone and thereby afford more opportunities for designs with thinner selections. However, accumulation of titanium in tissue has been observed and tissue discoloration with Ti pigments can be seen. Even though this accumulation seems to be well tolerated by the body, to overcome this local adverse tissue reaction and immunological responses niobium (Nb) has replaced vanadium, and Ti-6Al 7Nb has been proposed as an alternative.
Surface modification of implants to improve longevity and osseointegration
Osteointegration is a key concept of implant stability and retention. Though implant osseointegration takes place several months, the bone-implant contact averages 70-80% which creates a scope to devise methods for more enhanced osseointegration. Although these implants have macro-irregularities such as macroscopic threads, fenestrations, cracks, ridges, difficulty in attaining preliminary stability, and adverse interfacial bone remodeling, has led to the quest for the improvement in the surface superiority of a Ti dental implant in terms of the rate and strength of its osseointegration. Various methods have been used like polymerized nanomaterials which strongly influence the mechanical properties. Chemical methods include anodic oxidation of implants which results in a surface with micropores that demonstrate increased cell attachment. Another method is the use of blasting implant surfaces with particles of various diameters. Clinical studies have shown higher marginal bone levels and survival rates for the blasted implant than machine-turned implants. Also, etching with strong acid produces micro pits and altered surface topography which promote adhesion of osteogenic cells. Recently, plasma spraying gives a porous surface that bone can penetrate more readily and enhance osseointegration.
Along with creating micro porosities for better osseointegration other methods like biomodification, sputtering, and antibiotic coating of Titanium dental implants have also received great attention. Biomodification using Plasma sprayed hydroxyapatite (PSHA) coating on titanium implant lead to improved maturation of newly formed bone tissue. Radiofrequency magnetron sputtering deposit thin films of calcium phosphate coatings on titanium implants. Studies have shown that these coatings are more retentive, allowing the preservation of titanium’s mechanical properties while retaining the bioactivity of the coated HA. Antibacterial coatings with the use of gentamycin a tetracycline on the surface have been studied as a possible way to prevent surgical site infections.
Despite the huge success of Titanium implants and its various modifications, in recent years, patient demand for more natural esthetics has set the scene for the evolvement of various biomaterials as an alternative. The key alternative to meet such demands are ceramic dental implants.
An upsurge of ceramic implants
Due to their biodegradation inertness, high strength, physical characteristics such as color, and limited thermal and electrical conductivity, ceramic oxides were introduced for surgical implant devices. Various ceramics used as dental implant materials however, the most successful and widely studied are Zirconium dental implants which are typically marketed as a non-metal alternative to titanium implants. The addition of the oxide changes its composition structure and behavior. Zirconia’s strength and strength can be accounted for by its toughening processes, such as crack deflection, zone shielding, contact shielding, and fracture bridging. In high fatigue situations such as mastication and parafunction, the prevention of crack propagation is of vital importance. This combination of favorable mechanical properties makes zirconia an exclusive and robust material for use in situations of high stress. Multiple studies comparing Ti and Zirconium oxide implants have revealed no significant differences. However, some studies reported higher bone to implant contact (BIC) and increased proliferation of osteoblasts in zirconia compared to titanium. Periodontal aspect also showed less bleeding on probing and less amount of recession with zirconia implants. However, caution should be taken with regard to some aspects of zirconia implants, such as tensile strength and elasticity modulus, due to the lack of clinical data on long-term success rates with zirconia implants.
Another evolution came in form of Carbon-based biomaterials which elicits minimal host response and have also been used for ceramic-like coatings on metallic implants. In vitro research has demonstrated better cell attachment than an uncoated disc on carbon-coated zirconia. These carbonaceous materials do not suffer from fatigue, unlike metals, polymers, and other ceramics. In major load-bearing applications, however, their intrinsic fragility and low tensile strength restrict their use. Polymeric implants were also in use in the 1930s however, the low mechanical strength of polymers has precluded their use as implant materials.
Overall, the quest for the perfect” biomaterial for dental implants continues and ongoing research and development that is already underway in the fields of newer metal alloys and ceramic composites will see further advances in the future in a new class of binary materials-metal-ceramic formulations with highly modulated surface properties. These biomaterials could represent an optimum blend of the strength, predictability, and workability of titanium alloys and biocompatibility and aesthetics of zirconia-based composites. Regardless of the future course of dental implant biomaterials research, it is clear that the most important advances in this space will be at the cutting-edge interface of material science and will be driven by advancements in the differentiation of substrate-surface.
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