The Assessment and Minimally Invasive Management of Existing Restorations

Introduction

All dental restorations will ultimately suffer deterioration and degradation in clinical service.^1,2,3 It has been suggested that the management of deteriorating restorations, that is restorations with localized defects (henceforth, partially defective restorations), is a common occurrence in clinical practice and, as a consequence, practitioners spend much of their chair-side time on the management of partially defective restorations.⁴ In fact, it has been reported that over half of all direct restorations placed by practitioners in adults in general dental practice worldwide are replacements of existing restorations rather than the treatment of new lesions of caries.^3,5 Globally, the cost of restoration replacement runs to many millions of pounds sterling.⁶

The most recent Adult Dental Health Survey highlighted that 84% of dentate adults in the UK have at least one restoration.⁷ Of these adults, each had, on average, 7.2 filled teeth. Such figures are of concern when one considers that patients maintain their dentition for longer and with an increasingly ageing population, often presenting with increasingly complex medical histories, the challenge for managing deteriorating restorations is likely to increase in general dental practice. Typically, the strategy for early deterioration may involve implementing a prevention regimen and monitoring. If progression is apparent, and localized defects of the restoration are diagnosed clinically or radiographically, the application of minimal intervention approaches to treatment, ie restoration repair, is recommended as a safe, effective, tooth-conservative and cost-effective approach.^8,9,10 Thus, demand for restoration repair (ie partial replacement of the restoration, allowing preservation of the portion of the restoration that presents no clinical or radiographic evidence of failure) is high and is likely to increase in primary dental care, leaving teeth with repaired restorations more able to withstand loading in function and with an enhanced prognosis.¹¹

The decision-making process for reliably assessing a partially defective restoration remains problematic given ongoing debate and an ever-expanding evidence base on criteria for intervention.⁶ The decision to intervene in an existing restoration may be highly subjective on the part of the clinician. Factors, such as the age of the patient, caries risk, and the size and location of the restoration, can influence the rate at which existing restorations receive further intervention, as can changing dentist.^12,13 In fact, an illustrative example of this can be seen from UK and US settings where patients who change dentists are more likely to experience restoration replacement than those who do not.^12,14,15 However, there is potential for over-treatment. The risk of iatrogenic effects with over-treatment, notably the needless replacement of existing restorations, is significant, and inherently associated with an increase in the size of the cavity owing to the inevitable, unnecessary sacrifice of intact, healthy and salvageable tooth tissue distant from the site of defect, resulting in weakening of the tooth, and potentially irreversible harmful effects on the dental pulp.^1,2,4,6 These detrimental effects can lead to an acceleration of the restorative downward spiral of the restored tooth.⁴ The effects on the dentition may be many and varied, including the need for extensive endodontic intervention or even the premature loss of the restored tooth, resulting in progressive deterioration in dental attractiveness and loss of occlusal function, possibly influencing quality of life.⁶

Assessment of restorations

Assessing an existing restoration can be difficult as there are many clinical factors to be considered. In an attempt to address this problem, in 1971, Cvar and Ryge¹⁶ proposed five assessment criteria for the clinical evaluation of dental restorations: colour match; cavosurface marginal discoloration; anatomical form; marginal adaptation; and caries. These criteria, generally referred to as the US Public Health Service (USPHS) criteria, had a remarkable impact on clinical dental research and provided certain criteria for the failure of, or need to replace, restorations: the so-called Charlie ratings. These criteria were extended (‘modified’) in 1980 and were called ‘modified Ryge criteria’ or ‘modified United States Public Health Service (USPHS) criteria’.¹⁷ In addition to the initial five criteria, new categories, such as occlusion, postoperative sensitivity, fracture, retention and others, were taken into account. For each category, different items allow scoring of the restoration as follows:

Researchers from the UK were involved in the running of the largest, multicentre clinical trial of a restorative material ever undertaken, the clinical trial of Occlusin (ICI Dental, Macclesfield, UK), which contributed to the development of the modified USPHS criteria for the assessment of dental restorations.¹⁸ Unfortunately, researchers did not always use the same definitions to assign the scores. Moreover, the modified USPHS criteria were developed when amalgam restorations were commonly used and when adhesive materials had a limited longevity.⁶

To detect early deterioration and signs of failure, a more sensitive and discriminative scale than the modified Ryge (USPHS) criteria was required and, in 2007, Hickel et al. proposed a new system based on three criteria categories: aesthetic, functional and biological (Table 1).^19,20,21 These new clinical criteria for the evaluation of dental restorations were approved by the FDI World Dental Federation as ‘standard criteria’ and simultaneously published in three dental journals.^20,21,22 The criteria were categorized into three groups of parameters: aesthetic (four criteria), functional (six criteria) and biological (six criteria). Each criterion could be expressed by one of five scores: three for acceptable, and two for non-acceptable – one for repairable or one for replacement. Subsequently, the initial uses and resulting feedback on the use of the standard criteria led to modifications of some criteria and scores.²³

Translation into clinical practice

While widely used in the evaluation of restorations in clinical research, the USPHS Charlie ratings and the FDI World Dental Federation's ‘clinically poor (replacement necessary)’ criteria have never been promoted, let alone adopted, as criteria for the replacement of restorations in the everyday clinical practice of dentistry.⁶ This has left practitioners making traditional, empirical decisions about the clinical acceptability of restorations in clinical service, with all the variability that this brings.⁶ It is suggested that most practitioners practise what they were taught in dental school, typically tempered by experience in clinical practice and acquired skills, developed largely through self-learning, in assessments of risk of failure (need for urgent treatment) before the next time they anticipate the patient returning for routine dental care.⁶

Minimally invasive management of partially defective direct restorations

State-of-the-art resin composites are widely accepted as the evidence-based, minimal intervention restorative material of choice for the direct restoration of teeth. This has been driven by advances in adhesive technology, patients' demand for tooth-coloured restorations and the phase down of dental amalgam owing to the Minamata convention. The partially defective direct restorations in this article are limited to resin composite restorations. The reasons most commonly cited for replacement of a resin composite restoration include:²

While some restorations will inevitably require replacement, by employing state-of-the-art adhesive procedures, many deteriorating yet serviceable restorations may be given extended life through repair procedures, especially if the defect is localized and accessible.²⁴ For example, many non-carious marginal defects can be simply managed by refurbishing – a procedure that should normally pre-empt and delay repair or replacement.²⁴ Refurbishment procedures typically involve removal of overhangs, surface recontouring, removal of discolouration and smoothening or glazing of surface, including sealing of pores and small gaps, without adding new restorative material except glaze or bonding (Figures 1 and 2).

Caries adjacent to the margin of a composite restoration (secondary caries) should be treated as a new primary lesion.²⁵ As with all patients who present with a new lesion, preventive measures should be initiated, followed by operative intervention as, and when, the lesion is shown to be active and progressing through dentine, or cavitation has occurred.⁸ Operative intervention should be minimally interventive, coupled with partial replacement of that portion of the adjacent composite restoration that is undermined by caries, or hinders the access required for necessary caries removal and the placement of an effective repair (Figures 3 and 4). The portion of the composite restoration that presents no clinical or radiographic evidence of failure should be left in place, unless there is good clinical indication to resort to total restoration replacement, with its various consequences. With a tendency to practise ‘defensive dentistry’ in a society that is increasingly litigious, it is regrettable that restorations affected by early forms of secondary caries, which are amenable to repair, may continue to be managed by total replacement.⁸

A recent systematic review concluded that direct restorations treated by minimally invasive alternative techniques, that is repair and refurbishment, did not present a significant difference in longevity in long-term clinical studies^26,27,28 in comparison to the replacement technique in permanent teeth.²⁹ It is clearly preferable, therefore, to perform restoration repair techniques, as an alternative to restoration replacement, wherever possible to preserve healthy tooth tissue distant to the site of defect. Thus, current evidence should help and encourage practitioners during the decision-making process to consider repair techniques as a useful alternative to replacement. The advantages of performing repair techniques have been reported^2,8 as follows:

The clinical procedure for performing a composite restoration repair is outlined below:

Alternatively, a composite repair may be performed using sandblasting with silica-coated particles, a technique described elsewhere.⁸

Minimally invasive management of partially defective indirect restorations

Ceramic fracture and chipping have been reported to be the major cause for the replacement of both all-ceramic and ceramic fused to metal restorations.⁹ Blum et al⁹ proposed a classification of fractures occurring in metal–ceramic restorations, differentiating between simple and complex fractures. Simple fractures are those involving only the ceramic, originating from intra-ceramic defects, trauma and parafunctional habits.^9,30,31 Complex fractures are associated with exposure of the metal substructure, resulting from failures at the metal–ceramic interface, an improper design, an inadequate framework support for the ceramic, fatigue of the metal substructure or internal stresses induced by incompatibilities between the coefficients of thermal expansion of ceramic and metal.⁹

An example of a complex fracture where ceramic had fractured from the labial surfaces of the patient's maxillary right lateral incisor and canine teeth is shown in Figure 5. Clinical and radiographical examination indicated that the crown margins were sound, although some gingival recession was present. The patient stated that she was satisfied with the appearance of the crown margins as they were not visible on smiling and it was therefore decided to repair the crowns. The shade of the crowns was noted. With personal protective equipment measures for the dental team and patient in place, the defective crowns were isolated using a rubber dam. The exposed metal was sandblasted using an intra-oral sandblaster (Microetcher, Danville Engineering, USA) filled with CoJet sand (3M ESPE, Germany) at 40 psi for 15 seconds, which had resulted in a matt appearance of the exposed metal surface (Figure 6). Silane (ESPE-SIL) was then applied to the treated metal surface and allowed to dry for 30 seconds. The powder and liquid of the opaquer (Visio Gem, 3M ESPE, Germany) were mixed and applied in a thin layer to the exposed metal and light cured for 10 seconds. A layer of unfilled resin (Visio Bond, 3M ESPE) was then applied to the opaquer and light cured for 20 seconds, following which the defect was repaired using a composite resin restorative material (Figure 7).

Criteria for repair of restorations

Dentally motivated patients who attend on a regular basis, and maintain a good standard of oral health, have been deemed good candidates for restoration repair procedures.⁴ Patients who have complex medical histories or limited capacity to co-operate may also be viewed as suitable candidates for the repair rather than the replacement of defective restorations, in particular, if operating time needs to be kept to a minimum. In contrast, patient reluctance to accept a repair as an alternative to restoration replacement, irregular attenders, high caries risk patients or the presence of caries undermining the restoration and a history of failure of a previous repair should be viewed as contraindications for repair. In addition, repairs should not be contemplated if there is uncertainty about the procedure to be followed to ensure a satisfactory clinical outcome.

Conclusion

Proper clinical assessment and minimally invasive management of partially defective restorations increases the longevity of the remaining part of the restoration, and that of the restored tooth. Repair approaches should be carried out, wherever possible, as a viable minimally interventive treatment option. Restoration replacement should be considered as the last resort when there are no other viable alternatives.