Artificial dental implants are the most reliable restoration option available for mature tooth loss. Despite their long potential lifespan, poor integration into the jaw and a slow healing process often create implant failure. Ensuring longevity requires adequate protection of the abutment-implant interface, protection achieved with surface functionalization by biocompatible coatings or advanced surface plasma treatments. The research summarized in this article examines the effect of using titanium nitride (TiN) and diamond-like carbon (DLC) thin-film coatings for implants.
The Problem with Implants
Dental clinical research studies conducted in the United States and Europe have reported more than a 90 percent success rate for dental implant cases.1 A survey from the American Academy of Implant Dentistry shows that 9 percent of the American population have successful dental implants and estimated the future demand for implants to increase by 500,000 annually. Traditional dentures used for restoration driven dentistry have historically lasted for 7–10 years, while artificial dental implants can have an extended lifetime of about 15-20 years.2 However, several issues can reduce implant lifespan. Major factors include insufficient osseointegration, bacterial invasion on the implant, and bio-mechanical and biochemical instabilities existing within the implant system.
Dental implant components are made of various metal alloys (Co-Cr, Ni-Cr, Ti, Ti6Al4V) and consist of an implant, an abutment, and a screw. The screws hold the implant and abutment together inside the jaw. Most clinical case studies conducted at laboratories and on patients have suggested a need for improvement of the biochemical and biomechanical quality of the implant-abutment interface. The improvements would be designed to minimize any associated complications during and after implant surgery. Biochemical failure caused by insufficient bio-inertness at the implantgum-bone interface leads to loosening of the implants. This issue accounts for about 17 percent of reported implant failures.3,4 However, the failure rate caused by mechanical complications investigated are even higher at 31 percent.3
Studies on mechanical failure of implants from various sources reveal that higher friction forces and abrasive wear at the abutment-implant interface increase the loss of pre-load during the abutment-implant screw tightening procedure.5,6 Furthermore, sequential micro-movement at the abutment-implant interface during chewing and biting leads to fatigue fractures of the abutment and paves the way for bacteria.7,8 Figure 1 shows the critical functional requirements at the abutment-implant-screw interfaces and necessary coating properties needed to protect the implant-abutment-screw interface.
Technological Advances Create New Options
In the past decade, advanced plasma-based physical vapor deposition (PVD) and plasma-enhanced chemical vapor deposition (PE-CVD) nanostructured coatings have become more frequently considered for biomedical applications. Such coatings can be made very attractive for aesthetic appeal while meeting application-specific functional needs, particularly for dental implants. Using plasma coating technology, these combined possibilities can be a very effective and economical option available for dental OEM manufacturers.
Recent advances in PVD and PE-CVD technologies have also stimulated development of nanostructured coatings with various compositions and microstructures designed to achieve a wide range of properties for multisectoral applications, including biomedical and dental. These coatings are fabricated in high-vacuum chambers using a plasma-enhanced chemically reactive environment.
Figure 2 shows the VaporTech® Cadence™ system on which this research was conducted. The system is designed to fabricate a range of nanostructured coatings using Remote Anode Assisted Magnetron Sputtering (RAAMS™), a unique enhanced magnetron sputtering PVD technology for metal-based coatings. The system is also designed to operate in PE-CVD mode for diamond-like carbon (DLC) coatings. The blue space in Figure 2 is the coating zone where coating deposition on parts takes place. Table 1 shows the functional features of the coating system in PVD and PE-CVD mode.
Promising Results for Dental Implant Longevity
Potential coatings for dental implants can be classified as wear-resistant and solid lubricant coatings. The aesthetic appearance and biofunctionality of TiN and DLC coatings make them a natural choice for biomedical applications. Both coatings show promise for their wear resistance, biocompatibility, and low-friction properties compared with uncoated components in in-situ biomedical conditions.
During natural human oral movement, fatigue load generated at the jaw during biting and chewing forces occurs at between 20 and 400 N in both the lateral and vertical directions. Coated implant-abutment surfaces used for restoration purposes must be stable during high fatigue load and must act as a protective layer on implants against a corrosive attack in the natural oral fluid environment.