Restoration of the access cavity and postoperative radiograph.
Following bleaching, the access cavity should be restored with a composite which is adhesively attached to enamel and dentine. This avoids re-contamination with bacteria and staining substances and improves the stability of the tooth. A sound restoration with sealed dentinal tubules is a prerequisite to create a successful bleaching therapy (Baratieri et al. 1995, Abou-Rass 1998). Some authors (Glockner et al. 1997, Abou-Rass 1998) recommend the use of composites with light colours, in case the bleaching therapy does not result in complete success. The adhesion of composites to bleached enamel and dentine is temporarily reduced (Titley et al. 1988b, 1992, Murchison et al. 1992, Garc|. a-Godoy et al. 1993, Toko & Hisamitsu 1993, Dishman et al. 1994, Josey et al. 1996, Swift & Perdigao1998). Glass-ionomer cement also has a reduced adhesion to bleached dentine (Titley et al. 1989). It is assumed that remnants of peroxide or oxygen on the surface or pores of the tooth inhibit the polymerization of composite (Torneck et al.1990, Dishman et al. 1994). It is less likely that changes in the enamel structure may influence composite adhesion (Ruse et al. 1990, Torneck et al. 1990). The formation of composite tags in bleached enamel is less regular and distinct than in unbleached enamel (Titley et al. 1991). This could explain why access cavities of bleached teeth, which are filled with composite, occasionally show marginal leakage (Barkhordar et al.1997). The negative influence of H2O2-containing bleaching agents on adhesion can be clearly reduced by moderate beveling of the cavity before acid etching (Cvitko et al.1991). The same can be achieved by pretreatment of enamel with dehydrating agents such as alcohol and the use of acetone-containing adhesives (Kalili et al.1993, Barghi & Godwin 1994). To dissolve remnants of peroxide, the cavity can also be cleaned with catalase or sodium hypochlorite (Rotstein 1993, Attin & Kielbassa 1995). A contact time of at least 7 days with water is recommended to avoid the reduction of adhesion of composites to enamel (Torneck et al. 1991, Adibfar et al.1992,Titley et al.1993). Optimal bonding to prebleached dental hard tissue could be achieved after a period of about 3 weeks (Cavalli et al. 2001, Shinohara et al. 2001). During this period, the colour stability of the bleached tooth should be controlled and a calcium hydroxide dressing should be placed in the pulp cavity for buffering the acidic pH which can occur on cervical root surfaces after intracoronal application of bleaching agents (Kehoe 1987, Baratieri et al. 1995). The calcium hydroxide suspension temporarily placed into the pulp chamber after completion of the bleaching procedure does not interfere with the adhesion of composite materials used for final restoration of the access cavity (Demarco et al. 2001).
A radiograph of the bleached tooth should be taken after treatment in order to diagnose cervical resorption as early as possible. No information is available in the literature regarding the time intervals for taking postoperative radiographs after bleaching. In accordance with the recommendations for postoperative radiographic controls of endodontically treated teeth, given by the European Society of Endodontology (1994), a radiographic inspection within the first year after bleaching is suggested.
Prognosis and complications during internal bleaching of non-vital root-filled teeth.
Despite many clinical reports, there are few evidence based studies on aesthetic dentistry (Niederman et al. 1998). Most reports present initial results following bleaching (Table 2). Complete colour matching of the bleached tooth with the adjacent teeth is regarded as an optimal result. However, darkening after internal bleaching can be observed occasionally (Friedman 1997) that is caused presumably by diffusion of staining substances and penetration of bacteria through marginal gaps between the fillings and the tooth. It is worth noting that the opinion of the patient regarding the success of the therapy is often more positive than the opinion of the dentist (Anitua et al. 1990, Glockner et al. 1995,1999).
Some have presumed that teeth with a discolouration existing for several years do not respond as well to bleaching therapy as teeth that are stained for a short period of time (Brown1965, Howell1980). Howell (1981) could not confirm this claim. Furthermore, it is uncertain whether darkening after bleaching is more probable when the tooth is heavily or mildly discoloured (Brown 1965, Howell 1980, 1981). Discolouration caused by restorative materials has a dubious prognosis (van der Burgt & Plasschaert 1986). Certain metallic ions (mercury, silver, copper, iodine) are extremely difficult to remove or alter by bleaching. No scientific study has yet directly compared the bleaching efficacy in differently (for example grayish or yellowish) discoloured non-vital teeth. However, Brown (1965) reported that trauma or necrosis induced discolouration can be successfully bleached in about 95% of cases compared to lower values for teeth discoloured as a result of medicaments or restorations (Brown 1965). There are differing opinions on whether teeth that respond rapidly to bleaching have a better long-term colour stability (Howell 1981, Feiglin 1987, Holmstrup et al. 1988). Some studies report that stained teeth can be more easily bleached in young patients than in older patients (Chandra1967, Hodosh et al.1970, Feiglin1987, Glockn er et al.1996), as the wide open dentinal tubules of young teeth enable a better diffusion of the bleaching agent. However, not all studies confirm the age dependency of bleaching success (Brown1965,Howell1981).Teeth with internal discolouration caused by root-canal medicaments, root-filling materials or metallic restorations such as amalgam have a poor prognosis regarding bleaching success (Brown1965).Anterior teeth with several approximal restorations occasionally show a less optimal result than teeth with a palatal access cavity only (Glockner et al.1996,1999). This may be because of the fact that composites cannot be bleached (Monaghan et al.1992). In these cases, replacing the existing restorations after finishing the whitening treatment is recommended in order to get an optimal result.
Table 2. Studies concerning the success rate of internal whitening treatment of non-vital root-filled teeth.