Principle 1: The Procedure Should Have a Significant Risk for and Incidence of Postoperative Infection

To evaluate the risk for postoperative wound infection, a classification of operative wounds and risk of infection was developed by the American College of Surgeons (Committee on Control of Surgical Wound Infections). All surgical procedures were classified according to four levels of contamination and infection rates (Box 21-1). Within these classifications, it is generally accepted that all class 2, class 3, and class 4 procedures warrant the use of prophylactic antibiotics.¹²

By definition, elective dental implant surgery falls within the class 2 (clean-contaminated) category. Class 2 medical and dental surgical procedures have been shown to have an infection rate of 10% to 15%. However, with proper surgical technique and prophylactic antibiotics, the incidence of infection may be reduced to less than 1%.^13,14 In a healthy patient, risk of infection after dental implant surgery is influenced by numerous factors such as type and location of surgery, skill of the surgeon, methods of intraoperative management, patient factors, and aseptic technique.^13,15 Moreover, additional patient-related (systemic and local) risk factors that are not addressed in these classifications have also been correlated with increased susceptibility to infection. These factors must be addressed in reference to evaluation for the use and duration of antibiotic prophylaxis (Box 21-2).

One of the most significant surgical factors that may contribute to infection is poor aseptic technique. Various routes of transmission of virulent bacteria include (1) direct contact with the patient’s blood or other body fluids; (2) indirect contact with contaminated objects; (3) contact of infected nasal, sinus, or oral mucosa; and (4) inhalation of airborne microorganisms. To prevent these conditions, a controlled, well-monitored aseptic setting should be achieved for the surgical procedure. The aseptic surgical site includes proper disinfection and draping procedures of the patient, hand scrubbing, sterile gowns worn by all surgical members, and maintenance of complete sterility of the instrumentation.

Another important surgical factor related to postoperative infection is the duration of the surgical procedure. This factor has been shown to be the second most critical risk factor (after wound contamination) affecting postoperative infection rates.¹⁸ In general, surgical operations lasting less than 1 hour have an infection rate of 1.3%, whereas those lasting 3 hours increase the rate to more than 4%.^19–21 It is postulated that the rate of infection doubles with every hour of the procedure.¹⁶

The skill and the experience of the surgeon with the placement of implants have been shown to be significant in postoperative infections and implant failures. A recent study has shown that less experienced surgeons (<50 implants placed) have a 7.3% increase in failure rates in comparison to experienced surgeons.⁸

In the medical literature, it is well documented that the insertion of any prosthetic implant or device increases the chance of infection at the surgical site. A dental implant can act as a foreign body, and the host’s defenses may therefore be compromised. The surface of the implant has been shown to facilitate bacterial adherence and the presence of an implant can compromise the host’s defenses. This may result in normal flora with low virulence potential to cause infections at the implant-host interface, which has been shown to be very difficult to treat.^22–24

The probability of risk for infection for a given procedure is related to local, systemic, and surgical factors. The patient’s American Society of Anesthesiologists (ASA) score may be used as the systemic factor and then correlated with various local and surgical factors. A risk index may then be modified from the literature to correlate these factors to dental implant surgeries (Table 21-1). The probability of wound infection may then be correlated with the type of wound contamination (class 1 to 4) and the risk index. Therefore a class 2 wound and a risk index 2 has a greater risk of complications, and a class 1 wound and risk index 0 has the least risk of postoperative infection.^19,25

Principle 2: The Appropriate Antibiotic for the Surgical Procedure Must Be Selected

The prophylactic antibiotic should be effective against the bacteria that are most likely to cause an infection. In the majority of cases, infections after surgery are from organisms that originate from the site of surgery.¹¹ Most postoperative infections are caused by endogenous bacteria including aerobic gram-positive cocci (streptococci), anaerobic gram-positive cocci (peptococci), and anaerobic gram-negative rods (bacteroides)¹³ (Box 21-3).

Although oral infections are mixed infections in which anaerobes outnumber aerobes 2:1, it has been shown that anaerobes need the aerobes to provide an environment to proliferate.²⁶ Subsequent studies have shown that the early phase of intraoral infections involve streptococci that prepare the environment for subsequent anaerobic invasion.^27,28 With that in mind, the ideal antibiotic must be effective against these pathogens.

The second factor in selecting the correct antibiotic is to use the antibiotic with the least amount of adverse effects. These effects may vary from mild nausea to the extreme allergic reaction.

The final selection factor is that the antibiotic should ideally be bactericidal. The goal of antibiotic prophylaxis is to kill and destroy the bacteria. Bacteriostatic antibiotics work by inhibiting growth and reproduction of bacteria, thus allowing the host defenses to eliminate the resultant bacteria. However, if the host’s defenses are compromised in any way, the bacteria and infection may flourish. Bactericidal antibiotics are advantageous over bacteriostatic antibiotics in that (1) there is less reliance on host resistance, (2) the bacteria may be destroyed by the antibiotic alone, (3) results are faster than with bacteriostatic medications, and (4) there is greater flexibility with dosage intervals.¹³

Principle 3: An Appropriate Tissue Concentration of the Antibiotic Must Be Present at the Time of Surgery

For an antibiotic to be effective, a sufficient tissue concentration must be present at the time of bacterial invasion. To accomplish this goal, the antibiotic should be given in a dose that will reach plasma levels that are three to four times the minimum inhibitory concentration of the expected bacteria.²⁹ The minimum inhibitory concentration is the lowest antibiotic concentration to destroy the specific bacteria. Usually, to achieve this cellular level, the antibiotic must be given at twice the therapeutic dose and at least 1 hour before surgery.¹⁵ It has been shown that normal therapeutic blood levels are ineffective to counteract bacterial invasion. If antibiotic administration occurs after bacterial contamination, no preventive influence has been seen as compared with taking no preoperative antibiotic.

Principle 4: Use of the Shortest Effective Antibiotic

In a healthy patient, continuing antibiotics after surgery often does not decrease the incidence of surgical wound infections.^2,30,31 In a healthy patient, a single dose of antibiotics is usually sufficient. However, for patients or procedures with increased risk factors (see Box 21-2), a longer dose of antibiotics is warranted.¹¹ With the high degree of morbidity associated with dental implant infections, one must weigh the benefits versus risk involved for the extended use of antibiotics.