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.