A root-analogue dental implant (RAI) – also known as a truly anatomic dental implant, or an anatomical/custom implant – is a medical device to replace one or more roots of a single tooth immediately after extraction. In contrast to common titanium screw type implants, these implants are custom-made to exactly match the extraction socket of the specific patient. Thus there is usually no need for surgery. As the root analogue dental implant matches the dental alveolus (tooth socket) it can only be placed immediately after the tooth extraction. If the tooth has been already lost and the soft and hard tissue is already healed, an RAI can no longer be placed. The basic principle of endosseous implants is a biological process described as osseointegration, in which materials such as titanium or ceramic form an intimate bond to bone. There are no particular differences between the osseointegration of a root analogue implant and a conventional screw type implant.
Disadvantages of conventional implants
As technology has improved, so has implant success rate. Conventional titanium dental implants typically have success rates of 90–95% for 10-year follow-up periods, but this is based on questionable definitions of success. The fundamental problem with conventional implant technology is that the patient must be altered to fit the screw or cylinder implant, rather than the other way around. A tooth has one or more roots. Even a single-rooted tooth is nearly twice as wide in one direction as in the other. A cylindrical screw-type implant does not resemble a tooth, so invasive surgery is needed to make it fit into an existing tooth socket. Such surgery involves drilling into healthy bone, filling gaps between implant and bone either with bone or bone substitutes, and frequently sinus lift procedures. Titanium screws are prone to peri-implantitis and plaque accumulation, leading to further interventions. The grey colour of titanium tends to show through gums, and in case of gum and bone recession, esthetic outcome is often highly unpredictable. Moreover, there are concerns over possible long-term corrosion and release of ions to the body environment, so researchers are evaluating non-metallic alternatives.
Root analogue implants
RAIs are custom made to perfectly fit the tooth socket of a specific patient immediately after tooth extraction. Therefore every implant is unique. As an optimised root-form it is much more than a simple 1:1 replica of a tooth. Since it exactly fills the gap left after the tooth is extracted, surgery is rarely needed. The implant can be produced from a copy of the extracted tooth, an impression of the tooth socket, or from a CT scan or CBCT scan. The advantage of a CBCT scan is that the implant can be produced before extraction. With the former methods, it takes one or two days to fabricate an implant. A root analogue implant can be fabricated from zirconium dioxide (zirconia) or titanium. Successful titanium RAIs have been three-dimensionally printed as porous one-piece implants, using CAD software. However, zirconia is the preferred material, because it is more esthetic in colour, with no grey discolouration visible through gums. Zirconium dioxide is doped with small amounts of yttria, which results in a material with superior thermal, mechanical, and electrical properties, and enhanced fracture toughness – ideal for surgical implants. Zirconia is metal free and is biocompatible, and has low bacterial affinity in comparison to regular titanium. An alternative technique uses a titanium root fused to a zirconia abutment by a sintering process that eliminates any possible microgap (which could cause peri-implantitis, leading to bone loss around the implant). True 'root-form analogue' or 'anatomic' dental implants have been attempted in the past. Those early attempts failed because of insufficient knowledge of healing of cortical and spongy bone, method, material, tooling, and technology. The principle of differentiated osseointegration, in conjunction with suitable material and technology, has enabled the first success in this field
The principle of "differentiated osseointegration" Differentiated osseointegration describes the guided equilibrium of bone-to-implant distance, contact and compression, taking into account spongy or cortical bone, in order to achieve secure osseointegration of individual anatomical dental implants. The design of the implant surface is crucial in integrating all three possible primary bone-to-implant contact scenarios:
Contact in the area of the exact root replica, for an immediate start of primary osseointegration without bone trauma; Distance at the thin buccal and lingual cortical plates, to safely avoid fracture and pressure resorption of this sensitive bone; Compression with macro retentions only in areas of spongy bone to maintain safe primary stability during the entire osseointegration phase. The combination of all these factors is the most important condition for osseointegration of anatomically shaped dental implants.
Technique
Treatment consists of three steps:
Obtain the 3D form of the tooth to be replaced. This is done either through careful tooth extraction and scanning of the root, taking an impression of the tooth socket, or a pre-op CBCT scan. The root analogue implant is produced using modern CAD/CAM technology, based on the principle of differentiated osseointegration; Atraumatic extraction of the hopeless tooth; Placement of the root analogue implant by tapping it in. In general, no surgery is necessary. In particular, no sinus lift or invasive surgery is ever necessary. The implant is placed immediately if it has been produced beforehand from a CBCT scan, or the next day if root has to be scanned or an impression of the socket is used. A protective splint is fitted to protect the implant during the healing period. Recovery time is very fast as neither soft nor hard tissue is traumatised. Typically, even the day after implant placement there is no swelling, bruising or pain. After 8–12 weeks' healing period, the final crown may be fitted by a family dentist.
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