Internal bleaching (synonyms: Walking bleach technique; walking bleach method; internal bleaching; internal bleaching) is a procedure for whitening a discolored devitalized (market-dead) root-treated tooth, for which the bleaching agent (bleaching agent) is introduced into the tooth for a few days and allowed to develop its effect under tight seal until the desired whitening result is achieved. The discoloration of a devitalized tooth is mainly caused by blood degradation products and protein decomposition substances from the necrotically decayed pulp (the dead tooth pulp). Iron is released, which enters the dentinal tubules and reacts there with bacterially produced hydrogen sulfide (H2S) to form brownish-gray pigments. The following options are available as bleaching agents (whitening agents); the components are each freshly mixed to a paste of creamy consistency immediately before use:
- 30% hydrogen peroxide (hydrogen peroxide, H2O2) and sodium perborate; the mixture prepared here has a strongly acidic pH of 2-3.
- 3% hydrogen peroxide (1 ml) and sodium perborate (2 g); the mixture reacts with a strongly alkaline pH of 9-11.
- Sodium perborate and water; hydrogen peroxide is also split off as a reactive agent in this mixture.
The bleaching process is based on the action of hydrogen peroxide. This is a strong radical former, which converts chromogenic substances into colorless reaction products and reduces metal oxides. While the bleaching effect is delayed with the latter mixture and more frequent replacement of the bleaching insert may be necessary, the two mixtures prepared with H2O2 do not differ in terms of their effectiveness despite the large difference in concentration. However, because the risk of cervical resorption (dissolution of tooth structure in the cervical area) is associated with the use of 30% H2O2, the recommendation is to use the second mixture with only 3% H2O2 and sodium perborate.
Indications (areas of application)
Internal bleaching is suitable exclusively for devitalized (marktote) teeth that have been treated with a sufficient root canal filling and do not show any symptoms. If the loss of tooth substance in the crown area is only slight, internal bleaching may be the only treatment option. In the case of greater loss of substance and the resulting indication for restoration with a partial crown or crown, prior bleaching may be advisable, since tooth discoloration usually extends into the root area and can therefore show through the thin gingiva (gums) in the neck of the tooth.
Contraindications
If the following contraindications are present, the tooth to be whitened should first undergo appropriate therapy, unless the decision to extract (remove) the tooth is even pending:
- Radiographic abnormalities at the apex (root tip).
- Insufficient (inadequate) root filling
- Root resorptions (melting of the roots of the teeth).
- Clinical symptoms of inflammation such as percussion dolence (knocking pain) or bite sensitivity.
- Unfavorable long-term prognosis, e.g., for periodontological reasons (reasons affecting the periodontium).
Before internal bleaching
Before bleaching, the following must be diagnostically clarified:
- Condition of the root filling
- Radiographic clarification of the apex (the root tip) and the periodontium (periodontium).
- Control of the tooth structure in the crown area for enamel cracks, leaking filling restorations, size of the restorations, if necessary, planning of a subsequent crown / partial crown restoration.
- Clarify a favorable long-term prognosis.
In addition, the patient must be informed in advance about possible risks and complications, as well as his behavior during bleaching therapy in terms of increased risk of fracture (fracture).
The procedure
- If necessary, excavation of caries (removal of carious dentin with slowly rotating drills) and removal of pulp residues (remnants of dental pulp) while sparing the hard tissue as much as possible
- Installation of rubber dam
- If necessary, temporary filling replacement in case of insufficient (leaking) margins.
- Removal of the root filling material up to 1 mm apical (towards the root tip) of the root canal entrance, but not below bone level.
- Revision of the root canal filling if there are clinical leaks that remained hidden in the X-ray.
- Covering the root canal filling with phophate cement or in a dentin adhesive filling.
- Insertion of the bleaching agent
- Tight provisional closure e.g. with compomer (plastic filling).
- First control after three to five days
- Replacement of the bleaching agent, if whitening still insufficient.
- Then closer controls until the desired whitening result, which should be achieved after two to four weeks.
- After achieving the desired whitening rinses with sodium hypochlorite to neutralize remaining H2O2.
- When using the high-percentage H2O2 mixture temporary calcium hydroxide insert to neutralize the acidic pH.
- Filling care; final dentin-adhesive resin fillings that are not oral (facing the oral cavity) but in the visible area should not be placed until about four weeks after internal bleaching, as the tooth color may still change up to this point.
Possible complications
- Fracture (breakage) in the course of the bleaching procedure, as the tooth is hollow and therefore unstable as long as the bleaching agent is in place
- Root resorptions (root dissolutions) in the case of insufficiently sealed root canal filling.
- Cervical resorption (dissolution in the cervical region of the tooth); this is discussed especially in connection with the high-percentage H2O2 insert due to its strong radical formation and acidic pH value