An Update on Indirect Pulp Capping, with Clinical Illustration

This article is a summary of an article by Ngo et al (2006), the clinically important concepts of indirect pulp capping and margin elevation using a glass-ionomer cement base are highlighted and illustrated with a clinical case.

Prof. Hien Ngo, BDS, MDS, PhD, FRACDS

During the time of G.V. Black, the profession was taught to completely remove softened and discoloured dentine to eliminate infected tissue and create a hard foundation to support the restoration. One of the objectives of this suggested routine was to remove all soft, demineralised dentine, using aggressive hand instrumentation or a round bur, until the pulpal floor of the cavity is composed entirely of sound dentine. This was appropriate during the era of non-adhesive dentistry, as amalgam needed support from the pulpal floor of a cavity preparation. However, even today, many clinicians are still following this outdated concept.

The main risk with this traditional and aggressive approach was the possibility of accidentally exposure of the pulp, particularly in young patients. It was reported that the rate of mechanical pulp exposure, following excavation of large carious lesions in permanent molars could be as high as 40%. This would accelerate the tooth down the spiral of premature tooth loss.

As an alternative, the stepwise excavation technique was introduced by Bodecker (1938), it was designed to decrease the risk of mechanical pulp exposure. In this technique, it was recommended to partially remove the soft demineralized dentine on the cavity floor and followed by the placement of a temporary restoration using zinc oxide eugenol. The transitional restoration was expected to remain for a brief period of weeks and then replaced with a permanent restoration. According to this technique, when the transitional restoration was due for replacement, further excavation was to be carried out to completely to remove any remaining demineralised dentine. Compared with the traditional G.V. Black approach, it was found in a randomized clinical trial that the incidence of direct pulp exposure was 17.5% for the stepwise excavation method compared with 40% for the traditional method. 

Fusayama (1966) and Massler (1967) both suggested that there were two layers in carious dentine. The outer layer was heavily infected by microorganisms and was broken down to the extent that it could not be preserved. However, the inner layer, would be partially demineralised, contain some bacterial flora, but some of the original dentine tubule structure would still be present. This was identified as the affected layer and could be remineralised with glass-ionomer cements. These authors suggested that only the outer infected layer should be removed during cavity preparation and the inner affected layer be retained and treated with a therapeutic lining or base of glass-ionomer or other bioactive materials. 

Recently it has been suggested that there is no need to differentiate between the two layers and unnecessary to re-enter a properly sealed lesion. Mertz-Fairhurst et al. (1998) showed that 10 years after completely sealing a lesion the soft, wet, and demineralised dentine left on the floor of a lesion, did not progress or jeopardize the restoration placed above it. The clinical result was sound, providing a complete seal had been established and maintained. 

The advent of the glass-ionomers provided the profession with a biocompatible material, with low technique sensitivity, which allowed for the development of chemically fused seal with both enamel and dentine. We can rely of this for a reliable seal.

It was shown, in both laboratory and clinical studies, that fluoride and strontium ions are released from glass-ionomer and taken up by the adjacent sound enamel as well as the demineralized dentine. 

This study was the first to provide clinical evidence that remineralisation of a caries lesion could occur underneath glass-ionomer.  A total of 13 subjects volunteered, and the restorations were placed using Fuji IXGP (GC Corp., Tokyo, Japan) as the restorative material. These teeth were scheduled for extraction due to other clinical reasons, and upon extraction they were analyzed for remineralisation.

Findings from this clinical study support the laboratory evidence that glass-ionomer could contribute directly in the remineralisation of carious dentine. However, there were two important requirements for this to happen; firstly, the restoration had to provide a total seal to the external environment and secondly there was intimate contact between the glass-ionomer and the partly demineralized dentine.

The clinical case below demonstrated the clinical application of the above concept. It is important to point out that this technique is only applicable on teeth with reversible pulpitis.

References

• Bodecker CF. Histologic evidence of the benefits of temporary fillings and successful pulp capping of deciduous teeth. Journal of American Dental Association
• Fusayama T, Okuse K, Hosoda H. Relationship between hardness, discoloration and microbial invasion in carious dentin. Journal of Dental Research 1966;45:1033–46.
• Massler M. Pulpal reactions to dental caries. International Dental Journal 1967;17:441–60.
• Mertz-Fairhurst EJ, et al. Ultraconservative and cariostatic sealed restorations: results at year 10. Journal of American Dental Association 1998;129:55–66.1938;25:777–86
• Hien C Ngo et al Chemical exchange between glass-ionomer restorations and residual carious dentine in permanent molars: An in vivo study Journal of Dentistry 34 (2006) 604-613