External Connection versus Internal Connection in Dental Implantology. A Mechanical in vitro Study

Abstract

(1) Background: In today's dentistry, implantology has become a therapeutic resource of choice in certain clinical situations. The design of implants has evolved in several aspects since their inception. Dental implants were initially designed with an external hex connection, although due to force transmission and security in the adjustment of the prosthesis, later implants featured an internal hex connection. This study aims to analyse the mechanical properties of two types of implants (an internal connection and an external connection) from the same manufacturer and their different prosthetic components (union screw between implant and prosthetic abutment, and the abutment itself) when subjected to different types of load. (2) Materials and methods: Intraosseous dental implants of similar shape, design and size, although different in type of connection (external vs. internal), were studied. The specifications of the UNI EN ISO 14801 test standard were used, with all determinations being carried out three times. Finally, the dimensional characterisation of the samples analysed after the dynamic load study was carried out, and the values of both study groups were compared by means of the non-parametric Mann–Whitney U test to find statistically significant differences (p < 0.05). (3) Results: For the static characterisation test, we found between 610.9 N and 986.1 N for the external connection and between 1263.6 N and 1324 N for the internal connection (p = 0.011). All of the dynamic load tests were positive and there was no failure in any of the components studied. (4) Conclusions: After the analysis of the samples studied in vitro, satisfactory results were obtained, demonstrating that both connections can support considerable mechanical loads according to international standards (UNI EN ISO 14801).

Effect of the geometry of butt-joint implant-supported restorations on the fatigue life of prosthetic screws

“…Thus, a slightly improved fatigue response of the internal connections may be expected over the external connection if compared under the same conditions, consistent with previous studies. [52][53][54] Nevertheless, the effect of the IAC type on the fatigue life of the prosthetic screw was significantly smaller than the other 2 parameters studied, and internal butt-joint connections have other advantages, including improved esthetics, sealing, and platform switching options. 6,50 The fatigue life prediction methodology previously developed by the authors 19 provided accurate life predictions for the wide range of geometric dimensions studied.…”

“…External and internal butt-joint connections have been compared. 6,[50][51][52][53][54] From a clinical point of view, internal butt-joint connections improve sealing against microbial ingress 6 and esthetics and provide more platform switching options. 50 From a mechanical point of view, IAC type may determine not only the maximum load of the restoration but also its failure mode.…”

“…51 Thus, finite element analysis (FEA) and experimental studies have determined that internal butt-joint connections have better fatigue performance than external connections. [52][53][54] However, these studies focused on implant failure rather than prosthetic screw failure.…”

Influence of Implant-Abutment Contact Surfaces and Prosthetic Screw Tightening on the Stress Concentration, Fatigue Life and Microgap Formation: A Finite Element Analysis

“…The stress concentration in the implant-supported restoration is directly related to design and the restorative materials. It is well known that high stress magnitude may induce restoration damage and even failure [13,33]. In this study, the proposed simulation compliance provided results in terms of stress, microgap formation, lifetime prediction Under the applied loading condition, both factors (contact surfaces and torque) affected the maximum gap value.…”

“…It is important to note that some advantages of external connection implants still justify its use in some cases, such as the simpler prosthetic phase and increased versatility in the case of multiple implants [13]. However, the incidence of occlusal load can promote high stress magnitude in this type of connection.…”