Materials for paediatric dentistry part 2: the evidence

Glass-ionomer cements

Conventional glass-ionomer cement

Conventional glass-ionomer cement, which consists of a fluoro-alumino-silicate glass, mixed with a polyacrylic acid1 has been a popular restorative material for over 40 years. This is due to properties such as its ease of use, adhesion to tooth tissue, and its absorption and release of fluoride. It is particularly useful when working to stabilize the pre-cooperative or special care patient, and has been shown to be helpful in reducing caries progression and the need for operative treatment of adjacent tooth surfaces.2 However, conventional glass-ionomer cement does not fare well in restoration survival studies. Qvist and co-workers3 reviewed three studies of good length, plus a fourth study, examining the survival of conventional glass-ionomer cement, resin-modified glass-ionomer cement, compomer, and amalgam in primary teeth, and concluded that the survival of conventional glass-ionomer cement was significantly lower in Class II cavities, compared to all other materials tested. This backed up the conclusion that had been reached 13 years previously, that ‘conventional glass-ionomer cement is not an appropriate alternative to amalgam’.4 These results are echoed in a systematic review carried out by Chadwick and Evans in 2007.5 These findings may be related to the less than ideal flexural resistance (an important factor in Class II restorations). In this regard, Figure 2 presents a fractured glass-ionomer restoration. Qvist et al also considered that, by frequently replacing glass-ionomer restorations, the risk of iatrogenic damage to the adjacent tooth was increased; this could be a significant disadvantage of using this material.2

Conventional glass-ionomer cements do still have a place in modern dentistry, but generally not as definitive restorations. They are useful in temporization, and the stabilization of caries (Figure 3). Care should be taken to consider all alternatives to glass-ionomer, so that the best material for each clinical scenario can be chosen.

Polyacid-modified composite resins (compomers)

Compomers were developed in the 1990s in order to improve upon the difficult mixing and handling properties of RMGICs.9 Compomers may be thought of as composite resins, with the addition of a few of the characteristics of glass-ionomers.6 They contain an acid-decomposable glass, and acidic, polymerizable monomers, which substitute the polyalkenoic acid polymers.9

There are very few studies of ‘optimal’ length that consider the survival of compomers – many are so short that they are of limited use. However, Roeters et al10 examined the behaviour of Dyract® (Dentsply), the first commercially available compomer over a three-year period. The length of this study may be considered satisfactory, but the number of restorations examined was relatively small; the results should therefore be interpreted with a reasonable amount of caution. They concluded that compomer could be considered ‘a reliable restorative material in primary molars’, with ‘excellent handling characteristics’ and a ‘low failure rate’. A 48-month randomized clinical trial employing a ‘split-mouth’ design,8 established that, in Class I and Class II cavities, RMGIC, compomer and composite resin showed similar longevity, and that all three materials could be recommended equally.

The review, carried out by Qvist and co-workers3 (which is referred to throughout the present work), found a similar longevity between RMGIC, compomer and amalgam. Interestingly, they found that the application of cavity conditioner affected the longevity of compomer restorations, with 5% of Class II cavities restored without cavity conditioner failing and requiring re-treatment, compared with only 2% of those that were conditioned.3

The results from these studies pose one question, namely, is it necessary to take the additional clinical steps needed to place a composite resin restoration in a paediatric patient or, indeed, whether it is even necessary to go so far as to place a compomer, as RMGIC appears to behave so favourably.

Soncini et al followed up a considerable number of restorations placed in primary teeth for a period of up to five years, and discovered that compomer restorations had to be replaced more frequently as a result of recurrent caries than amalgam ones did.11 They also questioned the benefit of the fluoride released from compomer, and found no preventive benefit in their study.12 Qvist et al3 found that the newer brands of compomer fared worse in examined studies than the original compomer, Dyract®. This indicates that care must be exercised when choosing dental materials. In this regard, as far as tooth-coloured materials go, compomer behaves well, being easy to handle, aesthetic, and able to be placed without acid-etching.6 It is likely that, as patients and their parents continue to be more conscious of aesthetics, the compomer materials may continue to play a part in paediatric dentistry.

Resin-composite materials

The use of tooth-coloured materials in children's teeth is steadily increasing; this increase is largely being driven by parental preference.13 In this regard, a survey of American paediatric dentists in 200913 revealed that 57% of parents were most concerned about the aesthetics of the material placed in their children's teeth, above cost, toxicity and durability. The majority of dentists questioned used composite resin and preformed metal crowns (PMCs) to restore Class II lesions. Many said that they would ‘go with the parents' wishes’ when it came to material choice. Ten years ago, in California, a questionnaire revealed that non-amalgam materials were popular, with 40% of surveyed dentists using a tooth-coloured material to restore Class II cavities in primary molars.14

Opdam and colleagues assessed the 12-year survival of composite resin and amalgam restorations, and found that the composite restorations showed better longevity, with the exception of three-surface restorations, where amalgam survived better.15 Demarco et al, following a review of the literature, concluded that ‘composite restorations perform favourably in posterior teeth’,16 and Burke et al reported that the survival rates of composite resin were ‘increasingly as good as for amalgam’.17 However, the difficulty with placing composite resin in young children is achieving good tooth isolation and moisture control;18 this is often impossible when there is limited cooperation. In these situations, it may be considered that composite resin is best avoided.

In summary, a number of studies have shown that RMGIC, compomer and composite resin have similar longevity. Attin et al followed up compomer and hybrid composite restorations for three years, and found that they both showed ‘acceptable clinical results’.19 Alves dos Santos et al8 compared a RMGIC, compomer and composite resin over four years, and found them to be comparable, and Casagrande et al compared composite, RMGIC and low-shrink composite and concluded that the ‘type of material did not influence the longevity of the restorations’.20 The future certainly looks bright for these materials in restorations for paediatric dentistry.

Preformed metal crowns

Preformed metal crowns (PMCs), also known as stainless steel crowns, are ‘prefabricated crown forms which can be adapted to individual primary molars and cemented in place to provide a definitive restoration’.21 There are many situations in which their use could be considered sensible. Indications for placement of PMCs include the restoration of primary molar teeth requiring large, multi-surface restorations, the restoration of fractured primary molars, and following pulp therapy.22 They are also indicated if the failure of an alternative restorative material is likely.23 The number of contra-indications is few, but include the inability to fit the PMC. This may be due to poor cooperation, or an inadequate amount of remaining crown tissue.22 PMCs should not be placed on teeth that are close to exfoliation, or in patients who have a nickel allergy.21

The literature supports the success of PMCs. A systematic review carried out in 2000 by Randall et al24 established that PMCs survive longer and require replacement less often than amalgam restorations. A seven-year clinical study by Roberts et al, examining restorations placed under ‘optimal’ conditions, concluded that PMCs ‘continued to prove successful for the restoration of larger cavities’.7 In addition, Kindelan and colleagues state that the failure rate of PMCs is ‘very low compared to plastic restorations’.21 Should aesthetics be a concern, the facing of a PMC can be removed and replaced with a composite resin.23

PMCs are routinely prescribed and fitted by specialist paediatric dentists. However, despite a wealth of research supporting the use of PMCs in children, they have not been widely accepted by general dental practitioners (GDPs).

Threlfall and co-workers interviewed 93 GDPs about the ways in which they cared for the primary dentition.25 Only 18% of those interviewed had ever placed a PMC in practice, and many were strongly opposed to PMCs, reporting them to be ugly, expensive, inappropriate, time consuming to fit, and difficult to manipulate.

Metal-reinforced glass-ionomer cement (cermet)

Cermets differ from conventional glass-ionomer cements in that they contain silver-tin alloy fibres or flakes that have been sintered on to the glass particles.26 The addition of metal was originally thought to improve the mechanical properties and wear resistance of the cements,27 but this theory has not been supported by the literature. Indeed, studies by Kilpatrick et al28 and Espelid et al29 showed poor clinical performance of the cermet, and they were unable to support their use in primary teeth.

The research around cermets appears to be fairly damning and, as such, these materials, although still manufactured, appear to have become redundant clinically.

Black copper cements

Black copper cements were frequently used to restore primary teeth 25 years ago, but fell in popularity, as they did not display favourable characteristics. They are highly acidic when unset, do not bond to tooth substance, and commonly leak, leading to pulp death.30 Therefore, they are unsuitable for use in primary or permanent teeth.

Amalgam

The success of amalgam in primary and permanent teeth has been proven over a long period of time.31 Unfortunately, due to its colour (Figure 4), and concerns about toxicity, the popularity of this material is steadily falling, and the future of the material is now questionable. In clinical studies, materials are still compared to amalgam, as amalgam has been used for long enough to have been considered the ‘gold standard’. In this regard, Qvist et al32 did not prove that RMGICs were better as an all-round alternative to amalgam. However, Donly and colleagues33 reported that, after three years, RMGICs and amalgam fared similarly and, over a two-year period, Marks et al34 could detect no difference between compomer and amalgam restorations when using the USPHS criteria. However, both of these studies were relatively short; nevertheless they show promise for the alternative materials.

Atraumatic restorative technique (ART)

The atraumatic restorative technique (ART) was initially created for use in places where access to conventional dental treatment is limited or non-existent, such as developing countries. It involves the removal of caries with hand instruments and the placement of an adhesive material, typically a glass-ionomer cement.40 The technique is gaining in popularity elsewhere, as it is useful in the management of those with limited cooperation, such as children and special care patients.

The literature shows promising results for ART. Results from a review of the literature by van't Hof et al41 indicated high mean survival rates for single-surface ART restorations using high-viscosity glass-ionomer in primary teeth over a period of three years, and a systematic review by Mickenautsch et al42 found no difference in longevity between ART and amalgam restorations, although they did remark that more trials were needed to confirm this result. However, ART in its true form has been estimated, by Burke and co-workers, to be used by only 10% of UK dentists.43

The Hall Technique

The Hall Technique was introduced by Dr Norna Hall, a GDP working in Scotland.44 She had been placing PMCs over carious primary molars during the 1980s with no caries removal or local anaesthesia, and had found that the teeth survived well. She is to be commended for collecting sufficient data to enable the publication of her findings. Innes et al44 decided to examine this approach, and developed a study to compare the survival of teeth restored by GDPs using either the Hall Technique or the GDP's own standard restorative technique. The restorations were followed up for a minimum of four years. They found that the Hall Technique ‘significantly outperformed the GDPs standard restorations in the long term’. This was a statistically and clinically significant result. A significant advantage of the Hall Technique is how well it is accepted by the paediatric patient. Santamaria et al compared the restoration of Class II cavities using either a conventional technique or the Hall Technique and found that there was much more negative behaviour from the patients whose teeth were restored the conventional way.45 It has also been shown that the Hall Technique is much less traumatic for the patient.44