It is now accepted that caries infected dentin may stabilize beneath a restoration1 and, since the late 1990s, there has been an emerging bank of evidence showing that the creation of a biological seal at the cavo margin (isolating the lesion from the overlying biofilm) reduces the viability of bacteria remaining within the lesion and arrests further caries progression.2
Despite this, it is generally accepted amongst many dentists that bacterially infected dentin is irreversibly decomposed, unable to remineralize and should be removed prior to placing a restoration. This removal of softened dentin to create a firm base for a restoration has been one of the traditional cornerstones of restorative dentistry. However, if carious dentin does not have an inhibitory effect upon invading bacteria, it infers that the dentin pulp complex is the only vital tissue in the body without a front line physiological response to bacterial invasion. What are the evolutionary parameters that maintain a single point of tissue vulnerability in the body against infection?
A recent study3 has shown that demineralized dentin was more effective in reducing the viability of streptococcus mutans than dentin treated with an antibacterial substance (silver fluoride [AgF] and potassium iodide [KI]). This suggests there are substances that may be released by carious dentin that inhibit bacteria viability. When AgF and KI are applied to the surface of demineralized dentin there is a further substantial reduction in bacterial viability3 and suggests that the application of AgF and KI works synergistically with demineralized dentin in further reducing the reproductive potential of the bacteria.
ARRESTED ROOT CARIES
The presence of arrested root caries demonstrates the ability of a tooth to heal itself by the remineralization of carious tooth structure. Arrested caries are inevitably black in color as sulphur salts become incorporated into the remineralizing tissue. Once these lesions remineralize, they remain resistant to further caries attack unless there are dramatic changes in the oral environment. This is partly due to the remineralization process that transforms tooth dentin, carbonated apatite with a demineralization pH of around 5.5, into a complex of hydroxyl and fluorapatite4 (plus other ions in the oral environment) that is able to resist demineralization at a pH of around 4.5. This is a pH level that pushes the biological tolerance of many oral bacteria.
The ability of carious teeth to remineralize may be assisted by preventing biofilm formation over the lesion, without which caries are unable to progress. Both the application of ozone5 and AgF/KI6 to dentin prevents biofilm formation. This is analogous to dressing a soft tissue wound with materials such as silver ointment or iodide to assist healing.
In caries affected dentin some demineralization occurs, but the collagen matrix remains intact enabling reconstitution of a hydroxyl fluorapatite dentin.
Strontium and fluoride ions from glass ionomer (GI) cement restorations have been detected in infected dentin consistent with remineralization.7 The nature and composition of the remineralized tissues will depend upon the ions present and the extent of degradation of the supporting collagen matrix.
The hardening of carious dentin may be compared to skin scar tissue formation. Figure 1 shows arrested caries after 18 months beneath a lost GI cement restoration. There is no black staining since the lesion was isolated from the oral environment. The surface of the lesion has a cracked appearance due to the dehydration of the hydrated carious dentin during the hardening process. The surface of the lesion is obviously not remineralized dentin, but a tissue hard enough to resist marking with a sharp probe.
PHARMACOLOGICAL MANAGEMENT OF CARIES
Case Report 1: Glass Ionomer Combined With Ozone Treatment
GI cements pharmacologically assist with the remineralization of carious dentin by providing a source of fluoride, calcium, or strontium ions (depending upon the GI used). These ions can penetrate more than 100 µm into dentin to assist with the formation of hydroxyl and fluorapatite in the demineralized tissue.7,8 GI cements have further benefits when treating caries as they prevent demineralization at the perimeter of the restoration, unlike composite resins which offers no such protection.9
The following clinical case shows increased radiopacity that occurred under a self-curing GI cement restoration treated with ozone.
A patient presented with a large carious lesion on a lower second molar (Figure 2). Although the lesion was asymptomatic, a periapical radiograph showed extensive caries that may well have resulted in a pulp exposure during cavity preparation.
Overlying caries were removed and the lesion was etched with phosphoric acid for 5 seconds, then washed and dried with oil-free air. The residual softened caries were treated with ozone for 40 seconds using a HealOzone (KaVo) unit. Following this the cavity was restored with a self-curing GI cement (Fuji Triage [GC America]). Extensive radiolucency below the restoration is apparent, immediately after restoration placement (Figure 3). However, 12 months later, when the patient was recalled to have a composite resin (Ice [Southern Dental Industries]) placed over the GI, a further radiograph shows a marked improvement in radiopacity below the GI base (Figure 4).
Case Report 2: Glass Ionomer Used With Silver Fluoride and Potassium Iodide
The following case report describes a pharmacological approach to managing a carious lesion using AgF/KI and GI cement:
The patient presented with occlusal caries on a lower molar in Figure 5.
Enamel was removed to gain access to the lesion. A moat was then prepared in sound dentin with a No. 3 slow speed round bur, at the dentin-enamel junction (DEJ) around the perimeter of the caries (Figure 6). Next, the preparation was etched with 37% phosphoric acid for 5 seconds, washed with water, and dried with oil-free air. AgF was then applied to the preparation, followed by KI until the precipitation turned from cloudy white to clear. The cavity was washed and dried again with oil-free air (Figure 7).
After isolating the preparation from moisture with strategically placed cotton rolls, a self-curing GI cement (Riva [Southern Dental Industries]) was placed into the preparation to slightly overfill the preparation. AgF/KI enhances the bond strength between self-curing GI and dentin.10 A 3 cm square piece of a plastic freezer bag was placed over the GI and the patient asked to close in into centric occlusion for 4 minutes until the GI had cured (Figure 8). After curing, minimal contouring was required to complete the restoration (Figure 9).
INFORMED CONSENT IS IMPORTANT
Intentionally leaving caries under a restoration may have the potential to lead to legal problems if a patient is unaware of the nature of procedure. This is especially true if another practitioner should have to radiograph the restoration and be unaware of this treatment protocol. Dentists who carry out remineralization procedures are well advised to provide their patients with written explanatory notes about the procedure and the benefits that can be achieved.
Restoration of teeth by amputation is a caries management model that often leads to the ongoing iatrogenic destruction of the dentition. The pharmacological management of caries is a conservative alternative that enables the remineralization of caries infected teeth to form a decay resistant layer at the base of a restoration.
AgF has been used to arrest caries, primarily in deciduous teeth since the early 1970s. After application, free silver ions react with oral sulphides to form silver sulphide, staining the teeth black. The application of KI immediately after AgF application forms silver iodide. This is a low-solubility creamy-white precipitate with significant antibacterial properties that inhibits silver staining.
- Mertz-Fairhurst EJ, Curtis JW Jr, Ergle JW, et al. Ultraconservative and cariostatic sealed restorations: results at year 10. J Am Dent Assoc. 1998;129:55-66.
- Kidd EA. How “clean” must a cavity be before restoration? Caries Res. 2004;38:305-313.
- Knight GM, McIntyre JM, Craig GG, et al. Differences between normal and demineralized dentine pretreated with silver fluoride and potassium iodide after an in vitro challenge by Streptococcus mutans. Aust Dent J. 2007;52:16-21.
- Chow LC, Vogel GL. Enhancing remineralization. Oper Dent. 2001;26(suppl 6):27-38.
- Knight GM, McIntyre JM, Craig GG, et al. The inability of Streptococcus mutans and Lactobacillus acidophilus to form a biofilm in vitro on dentine pretreated with ozone. Aust Dent J. 2008;53:349-353.
- Knight GM, McIntyre JM, Craig GG, et al. Inability to form a biofilm of Streptococcus mutans on silver fluoride- and potassium iodide-treated demineralized dentin. Quintessence Int. 2009;40:155-161.
- Ngo HC, Mount G, Mc Intyre J, et al. Chemical exchange between glass-ionomer restorations and residual carious dentine in permanent molars: an in vivo study. J Dent. 2006;34:608-613.
- Knight GM, McIntyre JM, Craig GG, et al. Electron probe microanalysis of ion exchange of selected elements between dentine and adhesive restorative materials. Aust Dent J. 2007;52:128-132.
- Knight GM, McIntyre JM, Craig GG, et al. An in vitro investigation of marginal dentine caries abutting composite resin and glass ionomer cement restorations. Aust Dent J. 2007;52:187-192.
- Knight GM, McIntyre JM, Mulyani. The effect of silver fluoride and potassium iodide on the bond strength of auto cure glass ionomer cement to dentine. Aust Dent J. 2006;51:42-45.
Diclosure: Drs. Knight and Craig are named on a process patent associated with the use of silver fluoride and potassium iodide. Dr. Knight was associated with the development of Fuji Triage and has a financial interest in this product.
Disclosure: Dr. McIntyre reports no conflicts of interest.
Diclosure: Drs. Knight and Craig are named on a process patent associated with the use of silver fluoride and potassium iodide.
Disclosure: Dr. Mulyani reports no conflicts of interest.