The Revolution of Dental Implants: Beyond Tooth Replacement

Dental implants have proven to be boon for the field of dentistry. In today's date there use is not just confined to replacement of few teeth but also for full mouth rehabilitation or to increase the retention for removable prosthesis. Dental implant provide many advantages over other methods for tooth replacement such as durability, improved comfort and speech, improved life like looks, improved biting force upto 450 psi(Kalidindi V) which is close enough to normal biting force exerted by a dentulous individual, biocompatibility with human bone and tissues and its mechanical properties.

These miniature gifts to the dentistry attain their stability from an ankylotic form of healing (Stelzle et al), that is, after a successful osseointegration which as defined by Branmark is a structural and functional unit of tissue and the placed implant. Osseointegration depends on quality of bone, blood supply and iatrogenic factors. (Albrektsson et al) Due to a failure in osseointegration (early failure), implants may fail in service. Heat generation during drilling an osteotomy site can be a threat to osseointegration as it results in heat induced dislocation in hydroxyapatite mineral lattice structure of the compact bone.

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Overheating of the bone while drilling the osteotomy site is most common reason behind early implant failure.

The rotating drill cuts through the bone thereby resulting in transferring of its kinetic energy to the surrounding bone, which in turn results in increase in temperature of the bone approximating the osteotomy site. This increase in temperature can result in cell death or osteonecrosis thereby resulting in delayed implant acceptance or early implant failure. The main reason for the tissue damage in bone cutting has been ascribed to the frictional heat (Thompson, 1958; Lentrodt & Bull, 1974; Rhinelander, 1974). Although other factors such as mechanical vibration and tearing of blood vessels leading to ischaemia, may well contribute to the bone injury.

Relative water content of about 35%, blood and lymph act as significant variable to protect bone from thermal injury. The thermal conductivity of fresh cortical bone in the region of 0.38-2.3 J/msK makes it a poor conductor of heat. Studies conducted by Thompson have suggested that cell death may occur. Bone temperature was noted to exceed 100 degree centigrade in absence of irrigation. Sturmer and Schuchardt by their study concluded that thermal denaturation begins when temperature change of about 5 degree centigrade above mean body temperature are noted. 44 degree centigrade has been suggested by various studies as a crucial temperature limit. (Fraser; Schubert & Bethke) and Lundskog in 1972 suggested that temperature beyond 47 degree centigrade marks an enzymatic and cellular damage. However, Eriksson suggests that a bone can withstand a threshold temperature ranging from 44°C to 47°C but only for 1 minute without impaired bony regeneration because alkaline phosphatase (AP) is denaturated beyond that level thus resulting in implant failure.

As we all know implant treatment can have high impact of patient's pocket, hence there is a need of improving results and reduce the treatment failures. The bone being sensitive to the heat changes, it's important for us to know the factors that govern the heat generation at the osteotomy site and also to manipulate these factors to get best results. Various studies have been conducted to analyse the factors and they have summed up few factors such as drill diameter (Davidson & james 2003) and sharpness, coolant delivery system, drill feed rate (Kalidindi), drill wear, drill depth (Kalidindi), drilling speed (Brisman 1996, Iyer et al, Rashad et al), drill design and diameter (Cordioli & Majjzoub, drilling status (continuous or graduated drilling) (Kalidindi), temperature of irrigation fluid, etc. (Stelzle et al)

Guided surgical stent is defined as guide used to assist in proper surgical placement and angulation of dental implants.(GPT) It can be fabricated using CAD/CAM technology such as stereolithography (Vercruyssen et al) or can be produced in laboratory using autopolymerizing resin (Talwar N). However studies have been conducted by Misir et al suggests that this surgical guide can act as an obstruction for the coolant fluid when osteotomy site is prepared. Also Miglorati in his study concludes that heat generation is more in case of guided surgery in comparison to conventional drilling and may be attributed to clogging of debris while continuous drilling and thus unavailability of irrigation and thus suggests the use of cooled irrigation. Jeong SM et al, suggested a use of an additional external irrigation manually in pumping motion to deliver saline directly at drill-bone interface to prevent increase in temperature during guided surgery.

Various factors influencing the heat generation during osteotomy site preparation have been studied before using freehand drilling however there is still lack of unanimity regarding how few of those factors regulate heat generation when a surgical guide is used. As we know that a human mandible is not a common topography for one type of density of bone but density may differ in various regions of mandible and also may differ in between patients due to age or systemic conditions.

Hence the present study targets to compare the intraosseous heat generation during guided surgical implant site preparation in two different bone densities with cooled irrigation fluids of different temperatures (10?C, 15?C and 20?C) and drill speeds of 800 rpm and 1200 rpm.