Axial displacement of the suprastructures at the conical implant — abutment interface

BACKGROUND: The inconsistency of the congruence of the surface of the implant–abutment interface leads to the impaired communication of the implant shaft with the oral cavity, breakdown of the structure, including the implant, and changes in the occlusal relationships because of axial displacement.

AIM: This study aimed to investigate the degree of axial displacement of abutments made relative to implants and analogs. Specific tasks were as follows: (1) to make various abutments for implants with a conical connection obtained from MIS, (2) to study the value of axial displacement of abutments of each type relative to the implant with load modeling, and (3) to examine the value of the axial displacement of abutments of each type relative to the analog of the implant from the tightening force of the screw.

MATERIALS AND METHODS: Axial displacements were tested using implants and analogs of MIS implants with conical joints. Original and non-original abutments were chosen as suprastructures. The original abutment was presented by CS-CPK62. Abutments for the conical connection C1 were made by milling, laser sintering, and casting according to burned models. The fastening of implant analogs and implants was made in a block of plaster of the 4th class. The study was conducted in a simulation complex we have developed, which creates a cyclic load within 30 kg. The study was divided into two stages. In the first stage, axial displacements on analogs from the force of screw tightening were examined. Abutments were attached with various forces: 7 Ncm (tightening force with a simple screwdriver), 15 Ncm, and 30 Ncm. After each screw tightening, vertical measurements were made with a micrometer. In the second stage, axial displacements on implants under load in the original simulation complex were assessed. The screw was tightened with a force of 30 Ncm, as recommended by the manufacturer, and load simulation was performed. Measurements were made both before and after the load simulation.

RESULTS: The original abutments and those made by milling showed the greatest deviation (0.056 mm and 0.066 mm, respectively), and abutments obtained by casting had deviations of 0.047 mm. The smallest deviation was found in the abutment made by laser sintering (0.032 mm). The values obtained in the second stage were as follows. Original abutments and abutments obtained by milling showed the smallest axial displacement when modeling the load (0.00167 mm each). Moreover, the abutments obtained by casting and laser melting showed significant displacements (0.007 mm and 0.004 mm, respectively).

CONCLUSIONS: A pattern was revealed: the smoother the surface of the conical parts, the stronger the axial displacement on the analog implants in the range of 7–30 Ncm, whereas an uneven surface gives the smallest axial displacement, and fixation according to the protocol provided resistance to chewing loads on the implants in the original and milled abutments. The use of a platform with a conical system to create high-precision orthopedic structures has certain limitations because an error in the height of the restoration is created in laboratory conditions. The use of non-original suprastructures leads to the accumulation of errors. Thus, it is necessary to further evaluate conical systems from other manufacturers and improve the accuracy of restorations based on dental implants.