Materials for paediatric dentistry part 1: background to the treatment of carious primary teeth

Methodology

An electronic search of Ovid MEDLINE® (1946 to August 2014) and the Cochrane Database of Systematic Reviews was carried out, using the key words: amalgam, composite resin, glass-ionomer cement, compomer, stainless steel crown(s), preformed metal crown(s), primary teeth, deciduous teeth, Atraumatic Restorative Technique (ART), Hall Technique, Hall crowns, survival, and longevity. Only results from 1985 onwards were included, as those prior to this were not considered to be applicable to current clinical practice. The abstracts generated by the search were reviewed, and full papers were obtained for those that appeared to be appropriate to the study.

Additionally, the bibliographies of the chosen papers were searched, and key journals were hand-searched for relevant information, in order to identify all appropriate research.

Different approaches to the management of caries

Traditionally, dentists have managed carious lesions in an operative manner; that is, complete caries removal, followed by restoration with a suitable filling material. Now, a more ‘biological approach’ is beginning to be adopted (despite this approach having been reported on many years ago), which concentrates on halting the carious process through good plaque control, control of diet, fluoride supplementation and, if necessary, operative treatment.14 This approach to the treatment of primary teeth can slow or arrest caries progression, with the hope of enabling the tooth to exfoliate before it develops symptoms.15

The Scottish Dental Clinical Effectiveness Programme's document Prevention and Management of Dental Caries in Children advocates this ‘biological approach’, with five main management strategies being described.16 These are as follows:

This document is a useful aid to the general practitioner, describing the strategies that may be suitable for a variety of clinical scenarios, the advantages and disadvantages of each, and step-by-step technique guides. It is an invaluable resource, particularly for those uneasy with the management of paediatric patients.

Caries can be removed from primary teeth in a number of ways: conventional removal with burs and cutting instruments; use of the atraumatic restorative technique (ART); and by chemomechanical means.17 Each way has its own advantages and disadvantages, and should be chosen on a case-by-case basis.

Operative treatment

The morphology of a primary tooth is different from that of a permanent one. The enamel and dentine are thinner, and the pulp chambers are proportionately larger and closer to the surface.18 The primary enamel ‘has a more pronounced prismless layer than permanent enamel’,19 which requires an ‘increased etching time’20 when restoring with composite resin. Due to this difference in structure, it has been postulated that the bond strength of composite resin to primary enamel is less than that to permanent enamel. For this reason, Fleming et al21 considered that composite resin might be less appropriate for restoration of the primary dentition than the permanent dentition.

Primary teeth also have shorter clinical crown heights, with cavities tending to be wider and shallower;21 this may affect the retention of intra-coronal restorations (Figure 1).18

Any restoration that is placed in a primary tooth should, ideally, have a life span that is equal to the time remaining for the tooth in which it is placed.22 At its higher end, this is around eight years.23 Primary restorations do not need to last as long as permanent restorations, as the majority of the primary teeth restored will exfoliate. Restorations should protect the remaining tooth structure,22 be biocompatible and durable,24 and have adequate physical properties to withstand the forces of occlusion. These forces are lower than those applied to restorations in permanent teeth.21 A 2009 Cochrane Review interestingly states that ‘the ideal restorative material for the primary dentition has not yet been developed’.13

Operative treatment should aim to repair or limit the damage from caries, help to re-establish function and restore good aesthetics, and enable the patient or his/her carer to maintain good oral hygiene, with the aim of halting the carious process.18 The longevity of restorations is probably the most important way of measuring the success of restorative treatment,25 although other outcomes, such as the patient remaining pain free, are also important, especially in children.

Material choices

Many materials have been used to restore primary teeth over the years, with varying degrees of success. These include amalgam, black copper cement, conventional and resin-modified glass-ionomer cement, compomer, composite resin and preformed metal crowns. Techniques such as the ‘sandwich technique’26 and ‘modified sandwich technique’27 have also been developed, where glass-ionomer cement and composite resin are used in conjunction with each other, so that the best properties of each material can be utilized. A summary of the advantages and disadvantages of each of the restorative materials can be found in the paper following this one.

Amalgam has been used to restore teeth for over a hundred years,21 and has long been considered the ‘gold standard’28 to which other materials are compared. It has many advantageous properties, such as its high strength, durability, and ease of manipulation.

A major constituent of dental amalgam is mercury, and this has increasingly been causing concern, particularly with regard to its effect on the environment.29 Parents are frequently requesting that amalgam not be used to restore their children's teeth.29 However, despite these concerns, there is ‘no evidence that the placement of amalgam restorations causes medical harm to patients'.30 With regard to environment pollution, dental mercury consumption makes up 3–4% of the total worldwide consumption of mercury:31 in this regard, it may be considered that it is likely that the environmental impact of dental amalgam has been overestimated. Nevertheless, it must be considered that all industries have a responsibility to reduce environmental pollution, no matter how big or small their contribution. It is highly likely that, following the signing of the Minamata Convention in October 2013, the use of dental amalgam will be phased down or phased out completely.

Material scientists have long been seeking to develop an ‘ideal’ tooth-coloured restorative material and, with the future of amalgam being questionable, this is becoming increasingly important. Killian and Croll26 have suggested a number of properties that an ideal tooth-coloured material would display:

Progress continues to be made in this field, and the profession is hopeful that one day this material will be developed.

Considering the evidence

In order to provide evidence-based practice, clinicians need to be able to appraise the literature critically, and pass on the relevant information to their patients or their carers.32 This is fundamental to practising proper informed consent.24

Examining the longevity of restorations is important, as it shows us the treatments that are effective, and those which are less so. Various longitudinal studies of this nature have been carried out since 1971.33

There are many factors to consider when analysing restoration survival studies including:

It is often impossible to compare like for like as, at present, there is no standardized reporting format for this type of study.13

Assessment criteria

Restorations in survival studies are usually assessed using criteria such as the ‘Modified Ryge’ or ‘USPHS criteria’. The USPHS criteria examine a number of attributes of the restoration and its adjacent tooth tissue and grades them in the following categories:36

Each of these attributes is assessed, and given either an Alfa or Bravo score, which is deemed to be clinically acceptable, or a Charlie or Delta score, which is considered to be clinically unacceptable.32

Atraumatic restorative technique (ART) restorations are commonly assessed using the ‘ART evaluation criteria’, which are similar to the USPHS criteria.37

Factors that influence the durability of materials in primary teeth

Working with children can be extremely rewarding, but also challenging. Children are likely to have limited dental experience, and their level of co-operation may be far from ideal. Wong et al found that the age of a child at the time of treatment affected the life span of the restoration placed,33 and Espelid et al discovered that this was more pronounced if the child was under five.34

The properties of the restorative material also have a significant effect on the durability. Alves dos Santos et al felt that the most noteworthy properties of a material were its ease of use, its bonding capacity, and the application and curing technique required for its placement. How a material responds to thermal, mechanical and chemical factors is also important.32 If a material is prone to microleakage, then this may contribute to the development of recurrent caries, leading to failure of the restoration.38

Materials also appear to be less durable in Class II cavities compared to Class I cavities. Alves dos Santos et al examined the survival of compomer, resin-modified glass-ionomer cement, and composite resin, and found that a ‘Class II preparation reduced the survival of the restorations for all materials evaluated’. The study also concluded that ‘the higher the number of restored surfaces, the higher the risk for failed restorations’.32

Conclusion

This paper has provided some background to the treatment of carious primary teeth. The second paper, following on from this, will examine the literature relating to the survival of restorative materials in the primary dentition. It will also describe a more ‘biological approach’ to the management of caries.