## 1 Introduction  
In dental implant restorations, implant and prosthetic elements are usually held together by means of a screw [1]. A tightening torque is applied to the screw head in order to create a tension load known as preload [2] and ensure a good structural integrity among the components [3, 4]. The recommended torque is provided by manufacturers based on different implant design factors [5]. Nevertheless, during their life span dental implants are subjected to variable loads; biting, mastication and bruxism loads to name a few. Axial loads are generally predominant but are always accompanied by lateral forces [6]. These loads can cause the screw to untighten or loose preload; this is known as screw self-loosening phenomenon and is produced by the lateral external force that generate a rotational movement of the screw. As a result, gradual preload loss may occur, leading to micro-movements and eventual structural failure of the dental implant assembly [7, 2, 8, 9, 10, 11]. Screw loosening is one of the major mechanical cause of tooth implant replacement [12], affecting between 4.3% and 12.7% of dental implants according to specialized literature [13; 14; 15]. It is well established that screw loosening depends on a large number of parameters, such as tightening torque, preload, occlusal forces, thread embedment and geometrical misfits [10; 16; 17]. In this sense, screw loosening is generally the result of an inadequate tightening torque, incorrect implant design, manufacturing defects or unexpected load conditions, amongst others [18; 19; 20]. Many works have studied the influence of different parameters of screw self-loosening. [PERSON] et al. concluded that lubrication reduces friction and consequently increases the clamping force while reducing the loosening torque [21]. [PERSON] et al. studied the effect of screw coatings that decreases the friction coefficient, agreeing with [PERSON] et al. in terms of preload and untightening torque [22]. [PERSON] et al. recommend the clinical use of gold-plated screws to prevent screw loosening. Teflon coating is also recommended by these authors as well as avoiding repeated tightening [23]. In several works, a significant reduction of removal torque after cyclic loading was noticed, demonstrating that screw preload decreases with the number of cycles due to screw self-loosening [9; 24]. [PERSON] et al. studied the influence of the screw tightening torque and consequently the screw preload level and recommended a tightening torque above 30 Ncm to minimize screw self-loosening [25]. In this sense, [PERSON] et al. stated that the preload should be 75% of the yield strength of the screw [26]. [PERSON] et al. concluded that anti-rotation strategies may be used to reduce screw self-loosening problems [16]. Along this line, [PERSON] et al. proposed adding an adhesive to the screw joint interface [19]. The effect of other parameters on the screw self-loosening, such as abutment type, has also been studied in dental implant applications [27]. Researchers agree that transverse loading is a major source of self-loosening in bolted joints in general [28; 29; 30; 31; 32; 33] and in dental implants in particular [6; 9; 16; 24]. In this sense, [PERSON] et al. [31; 32] presented a mathematical model to estimate self-loosening under transverse cyclic loads, and validated it using an experimental setup with two sliding plates. [PERSON] et al. [33] found some limitations in these mathematical model such as the difficulty to analytically obtain the bending stiffness under the bolt head and nut, and further developed a model that includes the effect of plate thickness on self-loosening. In general, this model is very useful to understand the mechanical foundations of the phenomenon and the effect of different design parameters. Some conclusions were derived from this work; the thickness of the clamping parts increases self-loosening and so does the amplitude of the transverse vibrations.