Collar length is the distance between the implant platform and the gingival margin. Sometimes, significant vertical space that has not been corrected with vertical ridge augmentation may necessitate selection of longer abutments, which would lead to an increased vertical cantilever. Furthermore, selection of the length of abutment collar would be affected if different distances between the implant platform and the gingival margin exist. Despite consistent occlusogingivial dimension, the thickness of soft tissue around the abutment affects abutment collar length selection. Therefore, in posterior regions where reduction of surrounding soft tissues thickness does not interfere with esthetic results, this reduction may be beneficial from a biomechanical point of view [9]. Selection of the suitable abutment collar length from a prosthetic/esthetic point of view is influenced by the length of the implant collar used. Abutment collar length is determined based on the height of the emergence profile and prosthetic restoration type (cemented, screw-retained, or overdenture) [16].

Abutment selection according to collar length index is a critical mechanical factor; selection of longer abutments leads to an increased vertical cantilever which acts as a force magnifier [8]. Vertical cantilever designs increase forces on screws due to the lever effect and, therefore, should be avoided [17, 18]. Although increased restorative vertical space with longer collar length could play a role in screw loosening, there is no certain evidence that increase in abutment collar length can affect screw loosening. However, considering the abutment height from implant platform to the top of abutment (including abutment collar), an increase in the collar length might result in an increase in the vertical cantilever. To reduce the possibility of screw loosening, reducing the cantilever length has been recommended [9].

The application of dynamic cyclic loading is used to simulate masticatory function mimic oral cavity that might lead to a failure of implant–abutment connection. Also, it is a reliable method to test the effect of mechanical fatigue on the implant–abutment stability [4].