INTRODUCTION
Dental
implant treatment has been clinically used since 1970 in dentistry, and
implant design, surface properties, abutment–implant connection style,
and superstructure–abutment connection style have evolved over time.
Recently, a two- or three-piece implant design has been introduced and
demonstrated high survival rates.1 However, biological
and prosthetic complications have frequently occurred2that require the development of new implant and prosthetic designs that
do not induce biological and prosthetic
complications.3
Generally, superstructure–abutment connection modes are screw fixing
and cement fixing. Cement fixation poses a risk of infection due to
residual cement, and screw fixation is often selected. Due to the hollow
structure of the screw fixation, bacteria invade inside, outside of the
component, and the microleakage causes peri-implant bone
loss,4,5 Further, in the case of multiple implant
treatments, it takes time to remove all the screws and superstructure,
so a connection style that allows easy removal is required. In the past,
a method of attaching the superstructure by frictional force has been
reported6; however, it was difficult to manufacture
because custom abutments and electroformed telescopic crowns had to be
created. Therefore, a reverse-taper lock system using existing
components: a connection system by friction force was proposed. The
reverse-taper lock system allows the establishment of new prosthetic
designs that do not require cement and screws. This case report
describes implant treatment of the reverse-taper lock system and
two-stage implant.
CASE
1
A 42-year-old woman was given one-step-type implant treatment (Figure
1). Although the width of the mandible was narrow, informed consent was
obtained for performing implant treatment with a narrow diameter without
performing bone graft. We performed two implant placement surgeries, one
in the upper jaw and another in the lower jaw. All the surgeries were
performed using standard procedures. After administering local
anesthesia, the mucoperiosteal flap was elevated, and the osteotomy for
the implant bed was prepared as per the manufacturer’s protocol. All
one-step-type implants (Figure 2) (IT-implant; Platon Japan, Co., Ltd.,
Tokyo, Japan) were inserted using a hand driver at an initial torque of
35 N. Four months after the implant was placed, the implants
demonstrated successful osseointegration. Impression was performed using
the impression abutment (Platon Japan). Zirconia crown made by a milling
machine (DWX-52DC; Roland, Shizuoka, Japan) was luted to the metal
frame. The superstructure was created by bonding zirconia to a straight
abutment. The superstructure was attached to the abutment by friction
force without cement or screws. No mechanical or biological
complications including inflammation of the peri-implant soft tissue or
resorption of the peri-implant bone (Figure 3, 4) were observed during
the 4-year follow-up period after fitting.