Replace® Select Abutments

New
Evaluation of the Precision of Fit Between the Procera Custom Abutment and
Various Implant Systems

Abstract: The bearing surface of the implant and the opposing bearing surface of the implant abutment form a screw joint that must remain stable throughout the life of the implant restoration. The fit tolerance between the external hexagon of the implant and the internal hexagon of the abutment has been suggested as a factor in the stability of the abutment/implant screw joint. Therefore, a study was designed to assess the precision of fit of the CAD/CAM produced Procera® abutment (Göteborg, Sweden) onto the external hexagon and bearing surfaces of implants from various implant manufacturers, and to determine the interchangeability of the Procera abutment screw with these systems. The following implants were evaluated for precision of fit of their external hexagons with the platform internal hexagon bearing surface of the Procera custom abutment: 1) BRÅNEMARK® System - Conical Self-Tapping 3.75 X 10 mm implants (Nobel Biocare, Göteborg, Sweden), 2) Lifecore Restore - 3.75 X 10 mm implants (Lifecore Biomedical, Chaske, MN), 3) Implant Innovations Inc. (3I) System - 3.75 X 10 mm implants (West Palm Beach, FL), 4) ImplaMed - 3.75 X 10 mm implants (Sunrise, FL), and 5) Paragon - Taper-Lock 4.0 X 10 mm (Encino, CA). A direct measurement was made of the external hexagon and the bearing surface of each implant, and the internal hexagon and bearing surface of each Procera abutment. The mean flat-to-flat hexagon dimensions of the implants ranged from 2.67 to 2.69 mm. The Procera abutment’s flat-to-flat dimension was 2.73 mm. The height dimension of the implant systems external hexagon ranged from 0.69 to 0.81 mm. The height of the Procera abutment blanks was 0.90 mm. From the measurement data, the Procera abutment fit all of the implants measured in this study. Thirty Procera abutments were produced by CAD/CAM with a uniform collar and height. Each implant and its Procera abutment formed one sample. Each sample was placed in a rigid device to ensure solid fixation without rotation for tightening of the abutment screw. The Procera custom abutment was tightened using the abutment screw specific to each of the five different implant systems. Each abutment screw was tightened to 32 Ncm using a calibrated electro-torque controller and using the internal counter torque device (Nobel Biocare, Göteborg, Sweden). During the abutment connection procedure, the Procera-Paragon assembly could not be tightened. Radiographic examination of the Lifecore Restore and 3I samples demonstrated that the manufacturers screws did not fit appropriately within the internal screw bore of the Procera abutment and these assemblies could not be acceptably tightened. All screw threads have a standard profile or geometry and are usually made according to the International Organization for Standard (ISO). Two widely used standards are the American National (Unified) thread and the metric threads. The basic profile of metric screw thread is specified in ISO 68 and on ANSI/ASME B1.13M-1983 (R1989) American National Standard. Three abutment screws and three implants from the Procera, Brånemark system, Lifecore Restore, Implamed, 3I, and Paragon implants systems were examined for interchangeability based on ANSI/ASME B1.13M-1983 (R1989) American National Standard. This standard assesses the major determinants of interchangeability by the screw profile (ANSI/ASME B1.21M), the pitch and tolerance. The standard contains general metric criterion for a 60-degree symmetrical screw thread with a basic 68 designated profile . The basic thread profile is the cyclical outline in an axial plane of the boundary between the external and internal threads. The ISO 68 basic profile for metric screw threads is the basic M profile with 60o symmetric threads. The basic M profile indicates that the thread angle is 60o and a thread form in which the crest form of the major external thread is flat, permitting corner rounding. This profile is used where a high fatigue strength is required as is the case with an implant abutment screw. These are expressed by the metric M value. It was determined that the internal screw bore of all implant systems studied had a metric thread designation of M2 X 0.4 – 6H. The metric thread designation of all abutment screws examined was M2 X 0.4 – 6g. The greatest variations in the dimensions of the abutment screws measured were seen in the diameter of the screw head. The diameter of the screw head of the Procera abutment screw was 2.52 mm. The diameter of the screw head of the abutment screws for Implamed (2.59 mm.), and 3I (2.69 mm.) were larger than the Procera abutment screw head diameter, while the diameter of the Lifecore Restore (2.43 mm.) and the Paragon (2.15 mm.) abutment screw heads were smaller. The Paragon UCLA-type abutment screw head diameter had the largest variation from the Procera screw. It was 0.37 mm. smaller than the diameter of the Procera abutment screw.
Conclusions: Since the measurement data regarding the Procera abutment screw indicated a thread designation of M2 X 0.4 – 6g, which should fit into the thread bore designation M2 X 0.4-6H of all the implant systems evaluated, it was concluded that The Procera abutment screw, which was designed to fit the Procera abutment internal bore, would also fit into the internal threading of all of the external hexagon implants studied.