Intraosseous heat generation during guided osteotomy for dental implantological purposes
Authors: Barrak Ibrahim Ádám 
Published: September 2019

Prosthodontically driven implant surgery has been subject of interest to dental professionals for the past decade. The correct positioning of implants has a number of obvious advantages, such as favourable functional and aesthetic outcomes, better occlusion and less chance of implant overload, to mention just a few. A well-positioned implant can also make it easier for the patient to maintain good oral hygiene, once the superstructure has been inserted. Thermal osteonecrosis, thermal damage As the application of metal implants has become routine in musculoskeletal trauma surgery, orthopaedic surgery, spine surgery, cranio-maxillofacial surgery, dentistry and oral implantology, drilling of bone has also become one of the most common basic surgical steps. As for the healing of the osseous structure, this can be influenced by several factors including implant design, chemical composition, the material and shape of the implant, the physiological characteristics of the host bone bed, loading conditions, the topography of the implant surface, the healing potential of the host bone, the use of adjuvant treatments, pharmacological agents and also heat generation during osteotomy. The bone tissue is very vulnerable to thermal injury, and the temperature threshold for tissue survival during osteotomy is 47˚C when drilling is maintained for more than 1 minute. Therefore, it is critical for successful osseointegration to keep heat generation under control during osteotomy. Excess heating above this limit can lead to the primary failure to of osseointegration. In the last few years a rapid development could be observed in the field of computer-assisted implant placement. Increased beneficial use of computers was made possible through the recent advances in computer technology, which allowed the planning and the execution of various steps involved in dental reconstructions during the placement of dental implants. The above mentioned novel possibilities include computer assistance for the planning of surgical interventions, for the implementation of the surgical steps, for capturing intraoral situation and also for designing temporary and final prosthetic solutions or even for the manufacturing of prosthetic components. Combining the cone-beam computed tomography (CBCT) images with an implant planning software has made it possible to virtually plan the optimal implant positions, in regard of the future prosthetic needs and the vital anatomical structures. This information can be used to fabricate a drill guide, which ultimately results in the transfer of the planned implant position from the computer to the patient, with the guide directing both the osteotomy and the insertion of the implant. The present thesis sought to find answers to the following questions: 1. How does the effect of the combination of low-speed drilling and cooled irrigation fluid influence intraosseous temperature elevation during guided and freehand implant surgery? Our hypothesis was that with the combination of low-speed and cooled irrigation fluid we can control the temperature increment in such a way that with any of the drilling procedures it will be avoidable to do thermal damage to the bony structure. 2. How does drill wear and consequent intraosseous temperature elevation during freehand and guided bone drilling change, with special attention to the effect of metal-on metal contact during guided drilling? We hypothesized that the metal-on-metal contact would damage the surface of the drilling bits, and therefore it would be associated with significantly higher temperatures during the drilling procedures. In the present thesis, we sought, first of all, to examine the effect of several factors that we believed would significantly contribute to heat generation during osteotomy: the presence of the metal sleeve in the surgical template and the combination of different drilling speed with different temperature irrigation fluids. The effect of metal to metal contact was compared with freehand osteotomy, and 3 further factors, sterilization, drilling speed, and drill wear, were also considered. To summarize the findings, at 800rpm, the intraosseous temperature never reached the necrotic threshold in any of the examined conditions during the total of 210 osteotomies. At higher drilling speeds, 90 osteotomies could be safely (i.e., without approaching 47°C) performed regardless of the applied sterilization protocol and whether the drilling was performed freehand or through a metal guide. The results also show that whether guide use led to a near-necrotic temperature increment depended largely on the applied sterilization protocol. In general, our hypothesis regarding the significant and cumulative effect of each studied factor during the experiments regarding the drill wear has been confirmed. It has been proven that the metal guide sleeve contributes significantly to heat generation during osteotomy, but this does not mean a safety risk if a soft sterilization protocol is used. As for temperature elevations in guided osteotomy our results suggest that the use of a low drilling speed of 800 rpm combined with the external irrigation fluid being cooled to 10°C can result in a mean cortical intraosseous temperature change being below 1.0°C, regardless of drill diameter or drilling method (freehand surgery or guided surgery). All in all, the literature almost unequivocally suggests that guided osteotomy (with a metal sleeve) does not pose an extra safety risk in terms of temperature elevation, which is in agreement with our results. Based on the results of the investigations that provide the basis of the present work, a low drilling speed with cooled irrigation are recommended when performing osteotomy through a surgical guide. 800 rpm and 10°C proved to be optimal in our experiments. Furthermore, drills that are used for guided osteotomy should be taken care of with extra precaution regarding the cleaning and the sterilization protocols and their use (the drill bits) should be maximized at a level of 90 osteotomies.