Longevity and performance of materials used for the restorative management of tooth wear: a review

The longer the natural dentition is maintained, the more likely it is to gain exposure to erosive, abrasive, and attritive challenges, culminating in the progressive loss of the mineralized tissues. Tooth wear is an irreversible, non-carious and cumulative physiological process that is also related to ageing.^1,2 It has been estimated to affect between 20% and 45% of the permanent dentition.³

Primarily, tooth wear may be caused by chemical or mechanical factors, and in most cases, it will involve a combination of both. Exposure of the dental hard tissues to chemical factors will culminate in the transitional softening of tooth surfaces, rendering them susceptible to the effects of potential mechanical factors, resulting in the accelerated loss of the softened tooth structure.⁴ Chemical factors can be intrinsic, for example when the stomach's acidic content enters the oral cavity, or extrinsic, from acids in dietary or other external sources.⁵ Mechanical factors include intrinsic factors, such as contact between teeth (clenching or grinding) that can occur during functional or non-functional jaw movements, and extrinsic factors, caused by contact with external factors as biting nails, pens, etc.⁶ These factors often interact, and other processes may be concurrently involved.

As dental hard tissue surface loss progresses, the resultant tooth wear may become noticeable. In severe cases, the loss of dental structure can lead to a significant reduction of the clinical crown and even dentine exposure.⁷ Patients with tooth wear may experience a variety of symptoms, including aesthetic concerns, sensitivity, and possible negative consequences on their oral health-related quality of life.^8,9 Preventive strategies, such as counselling and monitoring, form an important component of the management of tooth wear. However, when there are clear functional and/or aesthetic concerns, or when the patient's quality of life is significantly impacted by the level of their tooth wear, restorative treatment may be indicated.⁷ The aim of the restorative management of tooth wear is to re-establish the lost function and form, while simultaneously protecting the remaining tooth tissues from experiencing further wear. This article gives an overview of the available evidence on the performance, with particular consideration of the longevity, of restorative materials commonly used in the restorative management of tooth wear.

Restorative materials used in the management of tooth wear

In the past, common treatment options for patients with tooth wear were full- and partial-coverage conventionally retained crowns. However, developments in adhesive dentistry have expanded the available restorative options for the management of such cases and include direct or indirect techniques, using resin- and non-resin-based materials. The clinical performance of different types of restorations in the management of tooth wear (to include the management of localized and generalized tooth wear) has been reported by numerous studies, and some of the outcomes of these investigations with at least 5 years of follow-up have been summarized in Table 1. It should be noted that comparison between individual investigations reporting the performance of restorations may be challenging owing to a variety of factors, which include the application of differing nomenclature, variations in treatment protocols and the criteria used to determine outcomes. The present authors are of the view that reporting of success (or failure) should include a description of the survival percentage (after a certain observation time), or documentation of the annual failure rates (AFRs). However, despite the increasing number of such studies, there remains a lack of substantial evidence about the longer-term performance of the restorations commonly prescribed for the management of tooth wear.¹⁰

Resin-based restorations

Many of the studies listed in Table 1 evaluate the performance of resin-based restorations employed the use of both direct and indirect application techniques for the rehabilitation of the worn dentition. Resin composite materials may offer a conservative and minimally invasive treatment option (Figure 1).⁷ Additionally, resin composite restorations provide further advantages:

• May be employed using an additive strategy;⁷
• Greater repair potential;²⁰
• Exhibit a satisfactory aesthetic appearance;
• Are minimally abrasive to antagonistic surfaces.²¹

Compared to other materials, such as metals or ceramics, a drawback of resin composite restorations is that, over time, they may show an accelerated wear rate and have a tendency towards discolouration and fracture,²² ultimately requiring repair or replacement.²³ However, resin composite is a relatively inexpensive material, and when applied directly, it offers the possibility of a single-visit execution without laboratory costs. Direct resin composite restorations can also be used as a diagnostic aid to help evaluate the proposed functional and aesthetic changes that accompany the placement of these restorations, especially when further treatment planning may be anticipated that may involve the prescription of indirect restorative materials, which are far less amenable to adjustment in the oral cavity. However, the placement of direct composite restorations requires demanding technical skills, knowledge on the clinical procedure and perhaps longer chair-time.

While appraising the merits of a dental material for the rehabilitation of the worn dentition, it is not only relevant success and survival data, but also the scope to offer an improvement in the patient's oral health-related quality of life OHIP that should be considered.²⁴ Direct resin composite restorations have been shown to provide an improvement in the patient's oral health-related quality of life with respect to aspects such as with speech,²⁵ and orofacial appearance.²⁶

Given the current evidence base, there is more information available for the direct application of resin composite for the purpose of treating localized and generalized tooth wear than for any other material, or application technique. However, with some exceptions (as discussed below), much of this evidence is limited because of the use of relatively small patient samples and/or shorter observation periods. Mehta et al¹⁵ reported on the performance of 1269 direct composite restorations placed in patients with moderate to severe tooth wear, with follow up for 5.5 years. Most of the reported failures were localized deficiencies that were still amenable to repair or refurbishment, and which could also be classified as a non-catastrophic type of failure. At the time of observation, 88.6% of the total restorations were free of any failure. In this study, anterior teeth were reconstructed using the ‘sandwich-technique’,²⁷ receiving a palatal/lingual veneer restoration first, and then a buccal veneer restoration. When the two veneer restorations were not placed in the same treatment session, failure rates were higher. Based on this finding, the completion of direct anterior restorations (palatal and buccal veneer restoration) within a single appointment, is encouraged.

It has also been reported that an increase of up to 5 mm in the vertical dimension of the occlusion (VDO), may be prescribed without the risk of negative effects for the patient.²⁸ In a follow up to the study above,¹⁵ using the same sample of restorations, Mehta et al²⁹ reported a significant protective effect against failure with the placement of thicker restorations (while respecting the necessary aesthetic and biological parameters). This protective effect may have been due to the enhanced fracture resistance of the restorations; furthermore, knowing that the material will wear with time, the application of a thicker layer of material (perhaps even thicker than the original form of the tooth) could potentially reduce the longer-term susceptibility to future failure. In this investigation, higher levels of anterior tooth wear (assessed using the Basic Erosive Wear Examination – BEWE) were associated with increased levels failure.²⁹ Such information may be helpful when planning care, and may support the prescription of restorative intervention before the pattern of tooth wear progresses substantially to help ensure the longevity of the restorations.²³ However, further work is required in this area.

In another study with a relatively large sample,³⁰ 1010 direct composite restorations, mainly placed at the maxillary anterior teeth using a Dahl approach, were evaluated for 8 years. With a mean follow-up time of 34 months, 7% of the restorations failed; chipping or debonding were considered failure. The authors were able to repair or replace over half of the failed restorations, corroborating the repairability of composite resin, as also observed in other studies.^14,18

The expectations for the performance of restorations for tooth wear patients should be adjusted for both clinicians and patients once the restorations will likely show early deterioration signs. Lima et al³¹ evaluated 270 anterior direct composite restorations placed in patients with moderate to severe tooth wear after 3 years. They observed that even as early as 1 month after placement, some signs of deterioration, such as surface irregularities, ditching and small chips, were visible. After 3 years, the surface irregularities had decreased, which was likely to be due to the progression of wear, while the occurrence of ditching and fractures increased. The aesthetic aspects found to be most affected by the deterioration were staining and loss of surface lustre, and for the functional criteria, the most affected were incisal contour and wear and marginal adaptation. Despite the deterioration observed, the restorations still exhibited scores considered clinically acceptable and amenable to repair or refurbishment.

The performance of indirect resin composite restorations for the treatment of tooth wear has also been documented; however, the available data is limited compared to direct restorations. One randomized controlled trial on the performance of direct and indirect restorations for the management of severe tooth wear,³² reported the absence of any significant differences in the survival of direct and indirect palatal surface maxillary anterior veneers; however, for first molar teeth, the indirect tabletop displayed a considerably higher failure rate (3.2 times) compared to direct resin restorations.³²

Promising results have been reported on the short-term use of minimally invasive, additive, indirect, nanoceramic restorations (LAVA Ultimate, 3M) on all teeth.³³ The 1-year results, which included 568 restorations, showed success rates from 97.2% to 100% (Figure 3).³² Moreover, polymer infiltrated ceramic networks (PICN), also placed in a minimally invasive, additive modality, showed favourable performance after 2 years for restorations fabricated at a mean molar tooth thickness of 0.55 ± 0.021 mm.³³ In this study, 2-year survival and success rates of 100% and 93.5%, respectively, were reported (n=192 restorations). PICN materials comprise a previously sintered ceramic network (ceramic skeleton) infiltrated with a polymeric matrix (polymer phase) and have been suggested to offer an elastic modulus analogous to dentine, high mechanical compatibility with enamel and the aesthetic value of ceramic-based materials.

Non-resin-based restorations

Adhesive-retained ceramics

Two of the studies listed in Table 1 employed the use of ceramic partial restorations for the rehabilitation of the worn dentition.^16,19 Some of the advantages of using ceramic restorations to treat cases of tooth wear are:

• Better aesthetic appearance;³⁴
• Less susceptible to surface wear and discolouration;³⁵
• Good biocompatibility and well tolerated by gingival tissues.

Ceramics are prone to failure owing to their brittleness and susceptibility to fatigue fracture.^36,37 Although it is possible to have conservative ceramic restorations with minimal preparation, some degree of tooth structure removal is often necessary, especially to provide adequate thickness for the restoration(s) to ensure they offer the required mechanical properties and aesthetic outcome. Ceramic restorations are also costly, more difficult to repair or adjust intra-orally, and inadequate polishing may lead to increased abrasive wear of antagonistic teeth.^38,39

Vailati et al¹⁹ described an approach where a palatal indirect composite veneer was combined with a buccal ceramic veneer to restore worn anterior teeth. After 6 years, they observed no major failures of the restorations. Minor marginal defects at the junction between the veneers were observed, but these restorations were still considered clinically acceptable, indicating the suitability of porcelain veneers for the improvement of the aesthetically compromised worn anterior dentition. In a prospective clinical study on the clinical performance of lithium disilicate occlusal onlays on posterior teeth exhibiting severe tooth wear,¹⁶ the authors reported a 100% survival rate over a period of up to 11 years (mean observation time: 7.9 years). The minor failures observed during the period were occlusal wear in 65% of the restorations, marginal discolouration in 3.9%, and marginal crack formation among 1% of the restorations. All these reported failures were scored as clinically acceptable. However, it is worth noting that the onlays were not placed using an additive strategy, with the need for a moderately invasive preparation form including approximal reduction and some (limited) occlusal reduction.

Crown restorations

Full coverage crowns are considered a more conventional approach, but need traditional tooth preparation to provide retention and resistance form.⁴⁰ Thus, they do not offer a conservative solution because they are likely to require the removal of tooth structure from an already compromised worn tooth. This type of restoration might seem attractive to some practitioners owing to the relatively lower requirements for maintenance and superior longevity. However, their use often results in higher initial treatment costs, and when they fail, the failures tend to be catastrophic, and are frequently not amenable to repair.¹⁸ This is why the latest European Consensus on management of tooth wear states that the restorative treatment for tooth wear patients should be additive, rather than subtractive, and such conventional approaches involving traditional preparations should not be the first restorative choice, but judiciously applied in some cases.⁷ From the studies listed in Table 1, two studies employed the use of crowns for the rehabilitation of worn dentition with good results, but the repairs were difficult to deal with.^17,18

Smales and Berekally¹⁸ reported the 10-year performance of metal–ceramic and gold crowns placed in 17 patients with worn teeth. The overall failures for metal–ceramic and gold crowns were 25.2% and only 3.6%, respectively. However, all involved major failures. Of the 65 failed metal–ceramic crowns, 13 were due to loss of restoration, in nine cases, the tooth needed a root canal treatment, and seven teeth needed to be extracted; the three gold crowns failed due to secondary caries, replacement of the crown, and root canal treatment. These types of failures related to lost restorations or pulpal problems and were probably related to the extensive tooth preparations required to accommodate the restorations.

A later clinical trial on the 6-year performance of lithium disilicate and translucent zirconia crowns for the management of 62 patients with extensive tooth wear¹⁷ reported a survival rate of 99.7% for both types of ceramic crowns, with no bulk fractures reported even though some crowns had areas of 0.6–1-mm thickness. One lithium disilicate crown exhibited loss of retention, and one tooth that received a zirconia crown exhibited a fracture at the cemento-enamel junction after 3 years. Other observed failures were the presence of apical lesions, minor ceramic fractures, or loss of the crown requiring re-bonding. Furthermore, the lithium disilicate crowns were evaluated as being more aesthetic than the translucent zirconia crowns, which might be especially significant when restoring anterior teeth.

Risk factors

Patients play a major role in the decision to select resin-based or non-resin-based materials. Moderate to severe tooth wear patients are considered patients at high risk of failure. There are known risk factors in children that could lead to tooth wear in adulthood, such as carbonated beverage drinking, the erosive potential of some medicines, gastro-oesophageal reflux and other dietary components.⁴¹ However, a clear causal relationship between the consumption of carbonated beverages factors and the progression of tooth wear is still unclear.^41–44 Awareness of these risk factors may prevent future erosion, which is the most prevalent type of wear in all ages.⁴⁵ In that regard, erosion in the primary dentition has been shown to be a predictive factor for erosive tooth wear in the permanent dentition.^46,47 It is also well documented that males are more affected, and consume more soft drinks and acidic food variants than females.⁴⁸ Several risk factors are immutable, and thus, consciousness of this group of patients is important.

Patients reported in Table 1 present a wide mean age range, from 35.3 to 64.9 years old. This means that the selection of the restorative material must take this into account. The sooner a more aggressive treatment is performed, the less sound structure will be preserved. However, if the patient, together with the clinician, decides that it is best to have a non-resin-based material to enhance aesthetic appearance, the risk of possible catastrophic failures must be carefully discussed. Where the patient may opt for direct restorative treatment, they should be clearly advised of the need for multiple repairs during their life cycle. Risk factor reduction is desirable along with the treatment plan. Discussion with the patients about those risks and how to manage future erosion may protect the remaining tooth structure.

In a similar manner, patients with a predominant mechanical aetiological factor for tooth wear (such as grinding or clenching) are most likely to continue to grind and clench after receiving restorative treatment. Among these patients, the prescription of an occlusal appliance might be advisable preventively, as a risk factor reduction strategy. However, creating consciousness of their diurnal bruxing behaviour may be an even more important factor in the preventive strategy.

Conclusions

This overview alludes to a lack of long-term evidence to support the success and efficacy of any given restorative material for the management of tooth wear. The evidence suggests that resin- and non-resin-based materials, as well as direct or indirect techniques can be used to rehabilitate the worn dentition. Restorative treatment should be delayed and executed only when appropriate, and preference should be given to additive restorative options. As per the evidence-base, the likely need for maintenance of the restorations, and the possible merits of intervention to the patient's quality of life should be clearly discussed at the outset.