Endodontics may be considered the treatment or prevention of apical periodontitis, which translates into the elimination or control of root canal infection. Over the years, medicaments used for this purpose have changed from strong and toxic chemicals to more selective and effective, yet tissue tolerant agents. Antibiotics have found limited use in root canal treatment, but may be useful in the treatment of immature teeth. The bacterial flora of different types of root canal infections is variable, and so is their susceptibility to conventional medicaments; this has led to alternatives, or combinations of, medicaments that show promise in managing persistent and recurrent infections. A better understanding of factors influencing the local availability and potency of medicaments has helped facilitate improved means of application. Medicaments are also used with the intention of controlling pain and supporting the tissue healing process; however, they are always secondary to their main, antimicrobial function. While irrigation with sodium hypochlorite and dressing with calcium hydroxide remain standard treatment protocol, chlorhexidine and iodine compounds are emerging as alternatives or supplements to these classical medicaments.

Endodontic success or failure is related to the absence or presence of signs and symptoms of apical periodontitis. ¹ Root canal treatment can, therefore, be considered the prevention or cure of this disease. ² Apical periodontitis includes periapical granuloma and radicular cyst as well as acute manifestations of inflammation. The aetiology of apical periodontitis is, primarily, a bacterial infection of the root canal system;^{3.4.5. and 6.} consequently, the technical and pharmacological aspects of prevention and treatment are mainly aimed at controlling infection. Thus, preventive endodontics entails treatment of a tooth without previous signs of apical periodontitis by aseptic pulp extirpation. Curative endodontics is the chemomechanical elimination of infection in the root canal system of a tooth with signs of apical periodontitis. Both procedures are completed by the placement of a bacteria-tight filling to prevent new infection.

The use of intracanal medicaments is an adjunct to the prevention, and essential for, the treatment of apical periodontitis. The primary function is to prevent root canal infection where none is present, and/or to inactivate bacteria already infecting the root canal space. Intracanal medicaments would include any agent with intended pharmacological action introduced into the root canal space. Antibacterial and other active compounds currently used as irrigating solutions during instrumentation rightly belong in this category. Intracanal dressings more concisely describe medicaments left in the root canal space to exert their effects over a longer time period.

The role of microorganisms in pulpless teeth was recognized more than a century ago, ⁷ and strong, caustic antiseptics were popular as intracanal medicaments at the turn of the twentieth century. Formaldehyde-containing materials, e.g. formocresol, ⁸ and iodoform pastes⁹ belong to this category and remained popular for decades. Formulations with sulphonamides¹⁰ and later antibiotics were tried as intracanal medicaments; Grossman’s polyantibiotic paste¹¹ and Ledermix®¹² (Haupt Pharma GmbH, Wolfratshausen, Germany) are examples of these types of dressings.

The reduction of pain through pharmacological control of the inflammatory process has also been attempted in endodontics by the application of eugenol, ¹³ and later corticosteroids and other anti-inflammatory drugs, ¹⁴ as dressings. The focus on the possible adverse toxic effects of medicaments^15,16 led to a more systematic selection from the list of disinfectants available for use. Phenol derivatives and iodine formulations gained popularity as medicaments in endodontics; sodium hypochlorite was confirmed as a suitable irrigant.

Calcium hydroxide, while advocated since 1930, ¹⁷ has gained popularity in endodontics in the last three decades. Calcium hydroxide has had success in a variety of clinical situations including pulpotomy, root resorption, root-end closure, control of exudation and root canal infection. ¹⁸

The primary function of endodontic medicaments is to provide antimicrobial activity. In a few instances, other, secondary functions are desirable (Table 8.1). The rationale for applying intracanal medicaments in various clinical situations has been reviewed. ¹⁹

Following pulpal necrosis, sooner or later, the entire root canal system will become infected. A long-standing infection will have bacteria not only in the main, but also in accessory canals, and for a distance into the dentinal tubules. ²¹ If apical periodontitis has progressed to the point where resorption of the cementum occurs, bacteria may be found throughout the length of the dentinal tubules. ²²

The source of the infecting bacteria may be dental caries, salivary contamination through fractures, cracks or leaking fillings, or contamination of the pulp space during dental, including endodontic, treatment. The microbial flora will vary with the clinical condition, and endodontic infection may be one of three types: primary, secondary, or persistent infection. Infected canals typically contain 2–10 different cultivable species; the total number of microorganism ranging from 10³ to 10⁷. ²³ The exact number of microorganisms is not known as they vary from tooth to tooth, and because of a lack of established quantitative methods of determination.

In some cases, bacteria persist and produce symptoms of inflammation despite apparently optimal cleansing and disinfection procedures. ⁹¹ They may either be inaccessible to the cleaning instruments or to the medicaments, or they may be resistant to the medicaments used. ⁵⁷ Special interest has recently focussed on streptococci, enterococci and yeasts in persistent infections; these have been shown to be relatively resistant to calcium hydroxide^{84.90.92. and 93.} and occur in high frequency in retreatment cases.^{27.33. and 94.} Organic and inorganic debris in the root canal system will also affect and limit the antimicrobial activity of irrigating solutions and interappointment dressings. ⁹⁵

Given the infectious nature of apical periodontitis, any clinical procedure should be based on the ability of each step to prevent contamination and to eliminate infection. A standard procedure should, furthermore, be based on a worst-case scenario, which would be the infected root canal with associated chronic apical periodontitis. Individual treatment steps have been assessed for their efficacy in eliminating bacteria from infected root canals^{23.91.96.97.98.99. and 100.} (Fig. 8.1).

The process of creating a hard tissue barrier at an open apex or at a grossly over-instrumented apex is termed root end closure or apexification.^{119. and 120.} When calcium hydroxide is used in long-term treatment of traumatized young permanent incisors and infection is controlled, a barrier of bone/cementum-like tissue at the apex is formed with a high degree of predictability^120,121 (Fig. 8.4). This barrier allows mechanical compression of the root filling, and any toxic responses of the tissues to the filling materials are minimized by this intervening barrier. While it may not be essential that calcium hydroxide be used as a dressing for this purpose, its clinical application is the most extensively documented. Similar principles apply in the formation of a hard tissue barrier more coronally, e.g. at the line of a horizontal root fracture or at a pulpotomy or pulp-capping wound surface. ¹²² Mineral trioxide aggregate (MTA) is now the material of choice for these purposes; it is a filling or sealant material rather than a medicament, and thus falls outside the scope of this chapter¹²³ but is covered elsewhere in this book (see Chs 9& 12).

Endodontic pain is mainly associated with both inflammation and infection.^{124.125.126.127.128. and 129.} The inflammatory responses to the trauma of pulp extirpation and instrumentation may elicit pain of lesser magnitude and duration than pain following bacterial activity. ^29,130 The rationale behind pain control by interappointment dressings is thus, primarily, to combat infection. This is reflected also in the finding that interappointment pain is significantly more frequent in infected, necrotic teeth than in vital cases. ^131,132 There are strong psychological components to the clinical expression of pain of endodontic origin. ^133,134 Clinical pain is further confounded by the concomitant presence of microbial and iatrogenic and other factors. The quantification of pain clinically is also very difficult to standardize for comparative purposes.

The incidence of interappointment or post-treatment pain seems to be very much dependent on the criteria defining pain.^{135.136. and 137.} As an operating definition, the incidence of patients requiring an extra, non-scheduled visit following self-reported pain may have some merit. It would not include the discomfort sometimes associated with, the practical necessities of the treatment itself (local anaesthetic injection, rubber dam clamp placement, severance and laceration of the pulp). By such criteria, no significant advantage of one medicament over another has been reported.^{138.139.140. and 141.}

Due to the lack of precise knowledge of the source of pain in individual cases, the introduction of medicaments in dressings to alleviate inter- and post-treatment pain has been by theoretical considerations, and by trial and error, rather than by clinical research. Most interest has focused on the use of corticosteroids in the interappointment dressing; particularly, the use of Ledermix containing triamcinolone, has been popular.^{12.51.142. and 143.} It is doubtful whether initial concerns about the systemic effects of locally administered corticosteroids are justified; there is no indication that harmful side-effects are associated with its use in dentistry, and the doses applied are rather small compared with other medical indications. ¹⁴⁴ However, while concerns for side-effects may have been exaggerated, the clinical benefits, if any, over calcium hydroxide medication remain questionable. ¹⁴³ Non-steroidal anti-inflammatory drugs have also been tested clinically as intracanal dressings, ¹⁴ but any clinical advantages again remain obscure.

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