DISCUSSION
In this case report, implant treatment with a new implant-abutment connection mode and two-stage implant treatment were performed, and good results were obtained during the follow-up period. The new connection style attaches the superstructure to friction forces and does not require cement or screws. In addition, as it does not have a hollow structure, there was no microleakage and no marginal bone loss was observed. The two-stage implant design allows the infected area to be removed and a new abutment to be installed if the upper part is infected with bacteria. These new prosthetic designs may offer new implant treatment options.
The reverse-taper lock system boasts a solid implant body with significant mechanical strength. In typical implant, a gap exists between internal and external connections to hold the abutment screw, making the implant body hollow and reducing its strength (Figure 13). In particular, when the implant diameter is thin, the thickness of the implant’s inner diameter is also relatively thin, which increases the risk of breaking the implant body.7 Conversely, the reverse-taper lock system’s mechanical strength is attributable to its lack of a hollow structure for the abutment screw. Veneer grafting is performed in cases where the bone width is thin. However, bone transplantation is highly surgically invasive and takes time for the joining of transplanted bones; thus, the treatment period is long and stressful for doctors and patients. In addition, transplanted bone commonly resorbs over time; therefore, a narrow implant with a mechanically strong design is ideal. The reverse-taper lock system is designed for use in implant treatment without bone grafting.
The connection between the implant body and superstructure is maintained by the frictional force of the reverse-taper lock. A precisely manufactured reverse-tapered connection can be gap-free and, therefore, bacteria-resistant. As the reverse-taper lock system is not a hollow structure, it offers the greatest possible security against implant body breakage. Typically, there are two types of abutment–superstructure connection method: screw and cement fixations. Since the screw-fixing method has an access hole, the thickness of the ceramic-veneered material is uneven, and concerns about aesthetics may arise.8 When the number of implants is high, the temporary sealant and screw should be removed, requiring enough time to attach and detach the superstructure. In addition, the presence of access holes tends to induce bone resorption via microleakage. This phenomenon is promoted by a gap between implant components that allow the passage of bacteria. Several studies have reported the presence of bacteria outside, between, and within the implant components.4 These bacteria and metabolites directly affect the periodontal tissue, causing bleeding, swelling, and odors; in more advanced cases, this can also trigger the development of peri‐implantitis and peri-implant bone loss.9Conversely, the cement fixation method is more aesthetic because of not only no access hole but also a risk of infection from the leftover cement. In addition, the superstructure cannot be removed in this context. Therefore, a connection style for the superstructure using the frictional force of a reverse-taper lock was developed. Consequently, the reverse-taper lock system is aesthetic without microleakage and boasts an easy-to-remove implant design. For full arches, the prosthetic retrieval is relatively rapid and easy when using the reverse-taper lock system because it is not fixed with multiple screws, requiring the operator to only release the frictional force using the proprietary crown remover. Among others, this supports advantages in the management of elderly patients, particularly when they are physically debilitated or in care facilities (i.e., nursing homes), as special training of facility personnel is not required.
Implants are always at risk of physiological bone resorption and bone destruction due to peri-implantitis. The longer the elapsed time, the greater the risk of developing peri-implantitis.10,11When using an implant with a moderately rough surface structure, that is, an exposed surface, the biofilm tends to adhere to it and bone resorption induces further inflammation, leading to implant removal. Therefore, to prepare for such infections, an implant design that responds to bone changes is required. The two-step-type implants can be removed when the upper part of the implant body is infected with bacteria due to a unique configuration of the implant body in two stages. The first- and second-stage implant bodies are connected with a torque of 35 N via a Morse taper connection. In young patients, implant treatments face a longer functioning period, which increases the risk of peri-implantitis. Using a two-stage implant body, responding to changes resulting in peri‐implant crestal bone loss is possibly quicker or more effective. After removing the second-stage implant body, the abutment can be re-attached. Two-stage implants have not been clinically studied; therefore, their long-term prognosis is unknown and further research is needed.