Traditional operative caries management relies upon complete excavation of carious tissue followed by modification of the resulting cavity in terms of its surface finish and overall internal shape to aid restoration retention. The extent of this modification is dictated by the nature of the direct, plastic restorative material used to fill the cavity. Classically, for many years, non-adhesive dental amalgam has been the material of choice for most clinicians, so much so that predetermined cavity shapes are associated erroneously with GV Black’s caries classification, classes 1–5, by many dental professionals.

With improved knowledge and understanding of the patho-physiology of the caries process and the subsequent defence reactions of the dentine-pulp complex, scientific and clinical evidence now shows clearly that not all carious tissue requires excavation during interventive operative surgical procedures (Banerjee and Watson 2015). The peripheral seal of restorations with healthy enamel and dentine close to the enamel-dentine junction (EDJ) is of paramount importance to ensure the tooth-restoration complex survives (Banerjee and Watson 2015). This is in conjunction with primary preventive methods instigated by the patient to disturb and/or remove the plaque biofilm, so preventing it from stagnating and becoming cariogenic in nature. Maximum tissue preservation along with maintaining pulp vitality (sensibility) is the tenet of minimally invasive dentistry, and the development of adhesive dentistry has promoted the MI philosophy into mainstream operative care.

Glass-ionomer cements (GICs) are an important part of the contemporary restorative armamentarium for MI operative dentistry. Since their introduction by Wilson and Kent (1971), glass-ionomer cements have had a wide range of clinical uses due to their naturally adhesive, tooth-coloured nature and fluoride-leaching properties, their low coefficient of thermal expansion and ultimate biocompatibility with mineralised tissues (Burke and Lynch 1994; Olivia et al. 2000). Clinically, they have proven to be useful in restorative, lining, luting and sealing applications.

Remineralization of demineralized carious dentine using various types of GICs has been demonstrated in several laboratory and clinical studies (Creanor et al. 1998; Ngo 2002a, b). Remineralization can be defined as the deposition of mineral in demineralized defects at a molecular level (Arends and ten Bosch 1986). It has been suggested that the mineral deposited should be apatitic in nature and should not be different from the mineral structure of natural, sound enamel and dentine. Ngo et al. (2006) studied the chemical interaction between a highly viscous GIC and demineralized dentine in vivo to determine the level of ion exchange between them. The material they used was Fuji IX GP (GC Corp, Tokyo, Japan), which includes a strontium-containing glass as opposed to the more conventional calcium-based glass in other GICs. They found that a substantial amount of both strontium and fluoride ions crossed the interface into the partially demineralized caries-affected dentine subjacent to the GIC. As the freshly mixed material is placed against the cavity wall, there is a release of ions from the enamel and dentine also leading to the exchange of ions, termed ‘ion exchange adhesion’. It is suggested that the same ion exchange can occur in the presence of the partially demineralized carious dentine (Ngo et al. 2006). The ions released from both the GIC and the tooth structure will combine to buffer the low initial pH until such time that it rises to a level where ion activity ceases. During this period of activity there will be both fluoride and strontium ions available to promote mineral deposition in areas of demineralized dentine where the calcium ion levels are low, with strontium ions substituting them. It was suggested that this occurs through a diffusion process driven partly by the concentration gradient which exists between the GIC and the dentine with respect to these two elements. As both strontium and fluoride are apatite-forming elements, they react with the demineralized dentine. If the process is controlled purely by diffusion then one would expect to see the level of ionic strontium and fluoride to be highest at the GIC-dentine interface and lowest deeper towards the sound dentine. The above clinical findings support the laboratory evidence that glass-ionomer can contribute directly to the remineralization of carious dentine. However, there are two important requirements for this to happen: firstly, the restoration has to provide a total seal against the external environment, and secondly, there must be intimate contact between the glass-ionomer and the partly demineralized dentine.

The treatment of deep carious lesions approaching a vital pulp presents a significant challenge to the practitioner. The traditional management of carious lesions dictates the removal of all infected and affected dentine to prevent further caries progress and to provide a sound base of dentine to support the overlying definitive restoration. In order to prevent, or at least minimize, the serious complications of complete excavation of carious dentine close to the pulp (the dreaded pulp exposure), the minimally invasive, tooth-preserving operative ‘stepwise’ excavation approach was developed. This involves initially excavating the more superficial soft, wet, necrotic infected dentine, followed by sealing the lesion with calcium hydroxide and a GIC provisional restoration. Some months later the clinician would revisit the lesion and finally remove all or most of the underlying arrested, dry and often darkly stained dentine. The rationale for this is that by this point, any residual bacteria will not have survived, the residual affected dentine will have remineralized and tertiary, reparative dentine will have been deposited. This will make it easier for the dentist to remove any remaining carious tissue without the risk of exposing the vital pulp (Thompson et al. 2008; Banerjee and Watson 2015). As it became increasingly clear that it is the effective peripheral seal of the restoration that is important in preventing the caries process from continuing within an existing cavitated lesion, a fully minimally invasive or ultraconservative approach was developed; this is also referred to as ‘partial/selective caries removal’. In this method, all of the infected dentine is removed, the peripheral enamel and dentine are prepared to optimize adhesion and the cavity is sealed (with or without indirect pulp protection) with the definitive adhesive restoration. The ‘trade-off’ for avoiding pulp exposure, which more often clinically leads to pulp death (Bjørndal et al. 2010), is retaining a layer of potentially radiolucent, affected dentine beneath the definitive restoration (see Fig. 4.2e). This can be defended by citing the substantial evidence that exists in the literature showing that cariogenic bacteria isolated from their source of nutrition by a restoration of sufficient integrity either die or remain quiescent and thus, given a vital pulp, pose no risk to the health of the dentition (Ricketts et al. 2013). Foley et al. (2004) compared the cariostatic effectiveness of alternative restorative materials in both selective and complete removal of carious tissue. They used a split-mouth design in 44 patients (aged 3.7–9.5 years) who had at least one pair of previously unrestored primary molars that had no pulp involvement. One tooth of each pair underwent complete caries removal, and the other had incomplete, selective caries removal followed by restoration using copper phosphate cement, GIC or a material ‘of the operator”s choice’ (such as amalgam). At 24 months post treatment, teeth that had undergone selective caries removal followed by restoration with copper phosphate cement exhibited greater abscess or sinus formation than did teeth that had undergone other treatments. Teeth treated with GIC alone after selective caries removal exhibited a durability and effectiveness comparable with those placed in teeth that had undergone complete caries removal.

Marchi et al. (2006) studied the effectiveness of two materials as indirect protective pulp liners, a setting calcium hydroxide and a RMGIC, in the treatment of 27 primary molars with deep caries. Four years post treatment, the success rate using the former was 88.8 % and using the GIC was 93 %. The investigators defined ‘success’ essentially as the absence of any ‘clinical or radiographic signs or symptoms of irreversible pulp pathologies or necrosis’. The authors concluded that ‘indirect pulp capping in primary teeth arrests the progression of the underlying caries, regardless of the material used as a liner’. In order to provide evidence that the caries process was arrested in the sealed lesions, they sampled teeth for bacterial culture at periods ranging from 1 week to 2 years; at the latter stage, they found a substantial decrease in the number of cultivable micro-organisms in sealed lesions when compared with the unsealed control teeth. Interestingly, they found the greatest amount of bacterial reduction within 2 weeks after treatment. In another microbiological study of dentine samples taken from 40 carious lesions before and after undergoing atraumatic restorative treatment (ART), Bonecker et al. (2003) found significant reductions in the frequency and proportions of the total viable mutans streptococci (but not lactobacilli) in restorations sealed with GIC.

A more recent randomized clinical trial has compared the use of GIC and a calcium silicate cement to restore deep carious cavities in patients (Hashem et al. 2015). The affected teeth were symptomatic with acute pulpitis. Baseline periapical radiographs, CBCT (cone beam CT) and a full clinical examination were carried out before minimally invasive selective caries removal was performed using burs and hand instruments, assisted with Carisolv™ gel. No pulp exposures occurring at this stage of treatment were included in the study. These deep cavities were restored either with a high-viscosity GIC, Fuji IX (GC Corp, Tokyo, Japan), or a setting calcium silicate cement, Biodentine™ (Septodont, Saint-Maur-des-Fossés, France). They were reviewed after 1 month, and assuming the clinical signs and symptoms indicated healing, these provisional restorations were veneered with a resin composite (a layered definitive restoration – see Fig. 4.2). At the 1 year review, it was clear that both materials had a similar 83 % success rate in maintaining tooth structure as well as pulp vitality and the layered restorations were faring well. Thus, on the basis of the evidence cited, it can be reasonably concluded that the removal of all infected dentine in deep carious lesions is not required for successful caries treatment, provided that the restoration can seal the lesion from the oral environment effectively.

A number of countries have already banned or are considering banning the use of dental amalgam, partly in response to the Minamata Treaty agreed by the United Nations Environment Programme (UNEP 2013). Since then, both the International Dental Federation (FDI) and the World Health Organization (WHO) have called for alternatives to amalgam to be developed for use to operatively manage carious lesions. One alternative is to use currently available glass-ionomer cements. Its high-viscosity variant has become the material of choice for atraumatic restorative treatment (ART). This minimally invasive caries management approach, involving the use of hand instruments only and the placement of a high-viscosity glass-ionomer cement (HVGIC), is considered an alternative to the more traditional maximally invasive restorative treatments (Raggio et al. 2013; Holmgren et al. 2013). In terms of restoration survival, a systematic review concluded that ART/HVGIC and amalgam restorations of the same size, type of dentition and follow-up period are equally successful clinically. However, because of the limited number of suitable data sets for the analysis, the authors of the review suggested that further studies should be carried out to confirm these findings (Mickenautsch et al. 2010).