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.