# Bone Temperature Variation Using a 3D-Printed Surgical Guide with Internal Irrigation
## 1 Introduction  
Overheating is a possible cause of implants failure during the early phases of healing, due to an excessive thermal stress to the bone [1, 2, 3].  
Frictional heat is always generated during implant site preparation with cutting tools at high speed [4, 5] and during implant insertion [6]. When bone is exposed to excessive heat, tissue necrosis can be triggered [7]. It has been demonstrated that the threshold temperature for bone tissue viability is 47 \({}^{\circ}\)C for 1 min and a linear relationship between time of exposure and the extent of the damaged area has been observed [8].  
Heat causes a dehydration of the tissue, a denaturation of membrane proteins, a decrease in osteoblastic and osteoclastic activity, and interrupts the microcirculation contributing to cells necrosis [9, 10]. Besides, necrotic tissue is more prone to bacterial infections [10]. Ultimately, a thermal injury induces an irreversible bone resorption [7], which can impede the osseointegration process. Several factors that influence overheating during implantsite preparation have been identified, including the drill characteristics [9; 11; 12], the host bone [13], operator-related variables [14; 15], and the surgical technique [16; 17; 18].  
Computer-guided surgery allows accurate implant positioning and results in less postoperative discomfort [19]. However, there are some concerns regarding the risk of bone overheating during a guided surgery. Previous studies have found that a drilling procedure with the use of a surgical guide can cause a greater increase of temperature compared with a conventional drilling method [11; 16; 20].  
As reported in previous studies, increased drill length and physical barriers, represented by the sleeve and the guide itself, could block the irrigation fluid flow to the drilling site, thus resulting in a deficient irrigation [11; 21]. Moreover, the possible friction between drills and the sleeve may increase heat generation. For this reason, various strategies have been advocated, including a copious and continuous irrigation, a frequent intermittent drill movement, the renovation of the drill kit after a certain usage and procedures for an improved cooling [16; 19]. Other surgical strategies are pilot-drill guided surgery, half-guided surgery with a free-handed implant insertion and an open-flap guided surgery [22; 23].  
In the recent years, the huge advancements in the three-dimensional (3D) printing technology have offered alternative techniques to the conventional stereolithography for the production of surgical guides [24; 25]. In this context, a novel type of 3D-printed surgical guide characterized by a supplementary built-in internal irrigation has been proposed, aiming to provide an additional irrigation to the surgical field. This type of guide may be a viable option to decrease the risk of bone overheating, however, its efficacy has never been tested. It is hypothesized that, during a guided implant surgery, the use of this supplementary irrigation may reduce the bone temperature increase when compared with a conventional external irrigation.  
The purpose of this ex vivo study was to investigate the effect of a supplementary built-in irrigation in terms of bone temperature variation during dental implant osteotomy. For this purpose, surgical guides provided with supplementary built-in irrigation tubes were produced for guided osteotomies in bovine ribs. Different irrigation methods were tested, and the bone temperature was recorded during the drilling procedures in three fixed positions.