## 4 Discussion  
In clinical practice, it is important to avoid cross-infection and it is for this reason that the drills should be treated with disinfect chemicals, thoroughly rinsed, and submitted to autoclave heat sterilization. In this study, we used two different disinfection chemicals, namely glutaraldehyde and hydrogen peroxide, which both provide high-level disinfection. The outcomes of the present research showed that zirconia drills are more resistant to the corrosive action of disinfecting chemicals. In fact, a greater difference was found in the percentages of drill covered by surface damage. SEM analysis demonstrated that repeated autoclave sterilization cycles had no effect on the zirconia and steel drills. The purpose of the present investigation was to study the influence of disinfection and sterilization on the implant drill surfaces. The authors hypothesized that zirconia drills may offer a greater resistance to the action of disinfectants commonly used in clinical practice. The contact with contaminated surfaces produces destructive hydroxyl free radicals that can attack DNA, membrane lipids, and other essential cell components. Glutaraldehyde is a saturated dialdehyde that has gained wide acceptance as a high-level disinfectant and chemical sterilization [14]. Aqueous solutions of glutaraldehyde are \"activated\" by using alkalinating agents to bring the pH to values between 7.5 and 8.5, which makes the solution sporicidal [15; 16]. Glutaraldehyde (GAA) solutions are used for the sterilization of medical devices, such as endoscopes and fibroscopes. Hydrogen peroxide has good bactericidal, sporicidal, viricidal, and fungicidal properties [17]. However, both glutaraldehyde and hydrogen peroxide are corrosive to steel instruments. Implant drills are reusable medical devices and implant bed preparation with drills is an invasive procedure involving contact of the drill with blood, bone, and other biological fluids. The major risk of all such procedures is the introduction of drill particles and transfer of pathogens, potentially leading to infection [18]. The main objective of disinfecting or sterilizing drills is to eliminate the transmission of pathogens by means of contaminated medical and surgical devices (e.g., HIV, HCV, _Mycobacterium tuberculosis_, and encephalopathies) [19; 20]. Today, the disinfection of medical devices such as implant drills is very important for preventing the emergence of transmissible spongiform, such as the encephalopathies (TSEs), which is a prion protein less susceptible to denaturation by heat and is responsible for disease such as variant Creutzfeldt-Jakob [21]. Therefore, the predicable cleaning of implant drills is believed to be a key procedure for reducing the risks of onward transmission of infectious diseases and pathogens such as human immunodeficiency virus (HIV), hepatitis B and C, gram-negative and gram-positive bacteria, fungi, and preventing the risk of mycobacteria transmission. In addition to microbial inactivation, the removal of organic or inorganic debris is crucial as it may compromise subsequent disinfection or sterilization processes [22]. The cleaning of reusable implant drills is also important in order to ensure drill longevity and efficiency in cutting bone, also making the removal of organic and chemical residues important. The effect of liquid chemical sterilant depends on cleaning to eliminate organic and inorganic material, an optimal pH, concentration, contact time, and temperature are all paramount. During chemical disinfection, it is important that implant drills are not mixed with other drills, or other instruments of different material composition in order to avoid chemical corrosion. In this study, once chemical disinfection was completed, we proceeded to heat sterilization at 134 \({}^{\circ}\)C (273 \({}^{\circ}\)F) for 35 min. It is known that the effect of disinfectants and sterilization can influence the cutting efficiency of drills [5; 23].