**1. Introduction**

Despite the high success rate of dental implants [1,2], early and late implant failures are still encountered [3,4]. It is known that the surgical approach is one key-factor for successful implant treatment [5]. It was advocated that an optimal surgical technique should provide initial mechanical implant stability necessary for the initiation of the osseointegration process [6,7]. Simultaneously, implants should be installed with a gentle and atraumatic surgical technique, avoiding excessive biomechanical and thermal stresses to the bone [8].

Undersized drilling is one of the most common surgical techniques for increasing primary implant stability. With this technique, an implant is installed in a substantially smaller osteotomy than its diameter [9]. The rationale of such a procedure is to maximize the initial implant contact with the bone locally and, thus, secure the implant stability [10]. This approach increases the implant rotational resistance, measured as the insertion torque value (ITV) [11]. This condition is often considered desirable [12], especially when immediate or early loading protocols are applied [13].

However, there are some concerns among researchers and clinicians regarding the host bone reaction to increased lateral compression, especially when the cortical bone layer is involved [14]. Excessive stresses and strains beyond bone physiological limits can have disadvantageous effects on the local microcirculation and bone cellular responses, leading to so-called bone compression necrosis [15]. In vivo studies and clinical research reported an extensive area of apoptotic osteocytes, tissue damage, and ultimately peri-implant bone loss [16–18]. Moreover, previous consensus reports indicated compression necrosis as a possible risk factor for peri-implant tissues disease [19,20].

Besides the over-compression of the pristine bone, a thermal injury may be an additional factor inducing bone necrosis. When the bone is heated above 53 ◦C, irreversible tissue damage was observed [21], while 47 ◦C for 1 min is considered as the border condition for the occurrence of an injury [22]. Although the risk of bone overheating during the drilling procedure was extensively investigated [23], the increase of temperature during implant installation, was seldom reported [24]. During the seating into an osteotomy site, energy is supplied to the bone and part of it is transferred as frictional heat [25]. According to thermodynamics, thermal energy is partially absorbed and conducted by the implant itself, and by the bone, in the form of temperature increase [26].

It is unknown whether the frictional heat generated during implant installation can cause an increase in bone temperature exceeding the threshold of initiating irreversible tissue damage. The temperature may be influenced by several factors, including implant-osteotomy size discrepancy and implant micro-design. One could postulate that the installation of an implant in an undersized osteotomy and the use of a moderately rough surface would generate a greater temperature increase in the bone than a larger osteotomy and a turned surface.

However, the in vivo intraosseous temperature during implant installation was never previously evaluated in a controlled experimental setting. Besides that, the effect of such temperature on histomorphometric parameters is unknown.

The primary aim of this in vivo study was to investigate the influence of the drilling protocol and implant surface on the intraosseous temperature change during dental implant installation. The secondary aims were to evaluate the influence of the temperature on osseointegration and peri-implant bone healing and to calculate the heat distribution in cortical bone.
