# Comparison Between Titanium and Thermally Activated Prostheses in Stages Surgery
## 1 Introduction  
Otosclerosis is a progressive multifocal disease affecting the middle and inner ear characterised by bone resorption and deposition of pathological slcetric or spongiosis bone leading to fixation of the stapes base [1, 2]. Otosclerosis most commonly causes conductive hearing loss, while a minority of patients develop mixed hearing loss as a consequence of otosclerosis [1]. Although certain aetiological factors contributing to thedevelopment of tosclerosis are known (genetic component, biochemical, immune and hormonal disorders, and measles virus), the exact pathogenesis remains unknown, and it is not known why otsclerosis occurs only in the temporal bone, while the rest of the ossicles remain unaffected [3]. Nowadays, stapedotomy is the leading surgical therapy, which improves hearing but does not eliminate the cause of deafness, otosclerosis [3,4]. Studies show that, despite not removing the cause of otosclerosis, long-term results for patients after stapedotomy are satisfactory [5]. In stapedotomy, the prosthesis is placed on a mobile incus and the fixation methods can be manual or thermal [6]. Results of the study by [PERSON] et al. [1] have shown that differences in the angular position of the prosthesis relative to the base of the tapes do not cause significant variation in the movement of the prosthesis up to a certain angle at which the prosthesis is placed (with crimping location 0.5-1.5 mm from the tip of the incus, the tolerance is 26.9 degrees for a prosthesis of 0.4 mm diameter and fenestration hole of 0.5 mm in diameter). When this angular position threshold is reached, the movement of the prosthesis is sharply limited. Adequate fixation of the prosthesis to the long process of the incus during stapedotomy is an important factor determining the surgical success of the operation. Incomplete fixation leads to loosening of the prosthesis and consequent conductive hearing loss [1,4,7,8]. The most commonly used material for the prosthesis today is titanium, which has low density, electrical and thermal conductivity, non-ferromagnetic properties, high stiffness, and is well tolerated in the middle ear [7,9]. Ten years ago a Matrix titanium prosthesis was introduced to the market. This prosthesis has low mass and high rigidity. Its loop is perforated and is band-shaped (Figure 1). Such design enables more consistent manual crimping with larger surface area, allowing acoustic signal to be conducted with minimal loss [2]. A band-shaped loop prevents an S-shaped deviation as can occur in wire loop after crimping. To avoid late necrosis of the long process of the incus, a prosthesis which covers much less of the mucosal surface of the long process was developed, NiTiBOND (Heinz Kurz company, Dusslingen, Germany) (Figure 2: Thermo-Dummy NiTiBOND prosthesis with dummy prosthesis already tested with the laser on the upper right corner and real prosthesis on the lower left corner prepared to be inserted into the stapedotomy). The loop can be activated thermally with the laser because nitinol, a titanium-nickel alloy returns to its original shape when heated, allowing the prosthesis to seal sufficiently and precisely around the long process of the incus, thus avoiding manual tightening (Figure 3). Additionally, this reduces the complications of the surgery [4,9,10]. The attachment loop  
Figure 1: Matrix titanium prosthesis in place manually crimped on the long process of the incus. consists of three different zones: four thermo-block zones in direct contact with the incus, which are separated by three thermo-active zones made of nitinol not in contact with incus, and three elastic zones, which allow for defined pressure on the incus. The elasticity of the individual zones ensures that the pressure is as even as possible. The flat wide band reduces the risk of pressure points. Prosthesis stem is made of pure titanium. It is not completely clear whether a non-crimping stages prosthesis gives better hearing results.