**4. Discussion**

The results of the osseointegration process associated with MTIs placed in the anterior region of the mandible and immediately loaded by overdenture in humans show unprecedent evidence of the successful osseointegration of grade V titanium in the form of MTIs. The bone quality analyzed in the BAFOs showed characteristics of vascularized mature bone, with minimal evidence of bone in the resorption stage. This result is in agreemen<sup>t</sup> with the published histological findings in which the biocompatible and osteoconductive properties of substrate grade V titanium alloys were evidenced through in vivo studies [6,7,19].

The qualitative evaluation of histology indicated intimate contact between the bone and implant surface, especially in relation to cortical bone (Table 1). Bone formation around MTIs showed healing in the BAFO by an intramembranous-type bone healing pattern, and the appositional formation of new bone was observed where direct contact existed between the implant and bone immediately after placement. These findings are consistent with those described by Granato et al. [20], who observed BAFOs with woven bone appearing with a random orientation at 3 weeks, followed by the remodeling and replacement of woven bone by mature lamellar bone at 6 weeks.

The deposition of the bone matrix around the implant determines the success of the matrix, which depends directly on the process that induces the osteoblast proliferation, differentiation, secretion of extracellular matrix proteins, and tissue mineralization [21]. Along with the above, osseointegration is a dynamic process which alternates between bone formation and bone resorption. Consequently, the magnitude, direction, and period of any forces applied over the implant–bone zone will determine whether maintenance or failure of osseointegration equilibrium results [22]. The results presented here show that the properties of titanium V MTIs plus the correct surgical procedure for implant placement

achieved adequate stability, allowing a successful osseointegration process, even when an immediate load was applied through an overdenture. It is logical that osseointegration may be influenced by the biomechanical properties, surface texture, and chemical composition of dental implants [23]. Thus, the implant surface (Neoporos) may be a factor that could improve implant success. Castro et al. [24] stated that the Neoporos process is a subtractive surface treatment consisting of zirconium oxide blasting and a series of acid etching baths. Currently, roughened surfaces have been used to increase the total surface area available for osteoconductive process, which could improve bone formation around the implants [25]. Consequently, subtractive treatment of surface and implant design have been considered critical variables that affect stability and quick osseointegration of immediately loaded implants. The above, without consideration of the additive treatment applying bioactive layers on the dental titanium surface, like those performed to improve bone regeneration around degradable temporary orthopedic implants [26]. However, the potential use of additive treatments on temporary implants destined to immediate load should be considered because the advances reported have shown promising results regarding the osseointegration in early stage, the quantity of bone to implant contact, and the adhesion strength of bone-to-implant [27]. Moreover, additive treatment by biodegradable bioactive nanofilms with a sub-micrometric thickness could improve the implant surface without affecting the primary stability required during its insertion. The nanofilms can promote cell proliferation and differentiation, and play a significant role in the matrix calcification [28].

The mechanical resistance of grade V titanium ensures the load transmission to the bone tissue over a prolonged period of time, which is important when lost hard tissues are replaced with a prosthesis [29]. Therefore, the use of alloys with improved mechanical properties in orthopedics and also in implantology is important, especially considering the increasing use and validation of short [30] and small-diameter implants [3] as well as the greater longevity of the patient population [6]. Compared with Co–Cr–Mo alloys, titanium alloy is almost twice as strong and has half the elastic modulus. Compared with 316 L stainless steel, grade V titanium alloy is roughly equal in strength; however, it has half the modulus. This titanium alloy is a material that is frequently used in the orthopedic area [21] mainly because of its superior mechanical properties.

Finally, the clinician must consider several aspects for implant selection, such as patient history (parafunctional habits, implant fracture, among others) or load conditions to which the implant will be subjected [31]. The use of titanium grade V in MTIs for immediate prosthetic loading has shown good biomechanical properties and successful osseointegration, maintaining a functional temporary overdenture during the study period.
