Main

Tooth wear appears to be an increasingly significant problem affecting all ages.1,2 In particular there is an increased incidence of young patients presenting with moderate to severe, erosive wear caused by intrinsic and extrinsic acids.3,4,5 Erosion is the most significant cause of tooth wear and has been implicated in 89% of all cases.6

Localised tooth wear of combined erosion/attrition aetiology is often seen affecting the palatal surfaces of the upper anterior teeth. The incisal enamel may become very thin and translucent and often gives a halo effect framing the crown. Chipping of this weakened enamel and a reduction in crown height is common. Sensitivity may also be experienced by younger patients, where the pulps are large, there is little secondary dentine, and where the erosion can be rapid. At the palatal cervical margin the enamel is often preserved and this is significant if adhesive restorations are to be considered (Figs 1 and 2).7

Figure 1
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Localised anterior tooth wear — frontal view

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Figure 2
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Localised anterior tooth wear — occlusal view

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Unless wear occurs very rapidly, compensatory eruption usually takes place, maintaining the occlusal vertical dimension despite loss of clinical crown height.8 The dento-facial complex is not a static entity, but can compensate for the effects of tooth wear by continued eruption, apical cementum deposition and localised alveolar bone growth.9,10,11 Anterior occlusal contacts are maintained in intercuspal position and the resultant 'loss' of interocclusal space presents a challenge for restoration, especially when the wear is localised and the posterior teeth are unaffected.

This process can effectively be reversed using an anterior bite platform12,13 and the mandibular rest position is known to adapt to this change, re-establishing a constant freeway space.14 The original 'Dahl' appliance consisted of a removable cobalt chromium platform worn in the upper arch and retained by clasps in the canine and premolar region. It was designed to disclude the posterior teeth whilst providing even contacts for the lower anterior teeth. Re-establishment of the posterior occlusion was found to occur in a single patient after 8 months and sufficient space was created anteriorly, on removal of the appliance, to allow provision of gold pinlays with minimal tooth preparation.15

Analysis of a further 20 subjects concluded that space creation anteriorly was achieved by a combination of anterior intrusion and posterior eruption taking place between 6 to 14 months.16,17,18 Difficulties with chewing and speaking were reported but treatment was otherwise well tolerated.

Poor patient compliance has been cited as the reason the appliance evolved into a cast metal, fixed bite platform.19 Subsequently, individual nickel chromium or gold alloy veneers placed at an increased occlusal vertical dimension were also adopted to achieve the same effect.20 More recently, so as to avoid greying of thin, translucent teeth, porcelain and direct and indirect resin-based composite (RBC) veneers have also been described.21

In vivo survival studies of RBCs have invariably analysed routine restorations, with median survival rates of 8–9 years now being quoted.22 However, owing to the rapid developments of composite materials, longer-term studies are sparse because materials are quickly superceded by the next generation.23 Additionally, the huge variety of composite types, restoration types, study design, sample size, and statistical analysis makes sensible comparison of the findings almost impossible.24

Despite the lack of comparable data, it is generally accepted that RBCs and their mechanical properties have improved over the years.23,25 Combined with an increased understanding of dentine bonding, these developments now allow more predictable use of composite in situations with significant dentine exposure. RBCs placed at an increased vertical dimension have also been shown to produce similar tooth movements to other restorations.26,27 However, although there is some evidence to suggest that composites used in this demanding situation have an acceptable performance, there is little clinical evidence about survival rates and modes of failure.28 The aim of this study was therefore to analyse the survival and clinical performance of RBC restorations used in this way.

Method

Thirty-one patients treated at the Eastman Dental Hospital, London for localised anterior tooth wear were seen on review for assessment. There were 9 female and 22 male subjects whose age range is detailed in Table 2. A total of 225 restorations were included in the sample and, at the time of data collection, they varied from 5 months to 6 years old. The restorations, 37 microfilled RBC (Durafill), a hybrid RBC (Herculite — 97 direct and 18 indirect), and 73 indirect 'ceromer' (Artglass), had been placed under rubber dam by three different, experienced operators. Replacement restorations were placed using a similar technique. A full history and clinical examination was performed and the following data recorded:

  1. 1

    Patient details.

  2. 2

    Angles incisal relationship ( from pre-operative study casts ). See Table 3.

  3. 3

    Aetiology of wear. See Table 4.

  4. 4

    Type of RBC used.

  5. 5

    Teeth restored, date of placement, and operator.

  6. 6

    Assessment of restorations, adjacent gingival health, and patients' opinion on comfort and appearance.

  7. 7

    Details of past repairs or replacements.

  8. 8

    Date of re-establishment of posterior occlusion.

Table 2 Age distribution of patients
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Table 3 Numbers of restorations placed in different incisal relations
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Table 4 Distribution of tooth wear aetiology
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Upper and lower alginate impressions were made, disinfected, and cast in dental stone within one hour. Upper and lower occlusal, and frontal photographs were taken using a Yashica Dental Eye III camera and Kodachrome 64 slide film.

Assessment of the restorations was performed on several days by examination of projected frontal and occlusal colour transparencies and of the casts.29,30 Calibration of the single assessor was carried out and several cases were scored by a consultant in restorative dentistry to ensure correct application of the criteria. Modified United States Public Health Services (USPHS) criteria 31,32,33 were used (Table 1) and the data was entered on a spreadsheet run by the software Statistical Programme for Social Sciences (SPSS). Restorations that had been replaced were re-entered as new restorations on the date of replacement. Restorations that were entirely satisfactory were placed in category Alpha (A). Survival analysis was carried out at two different levels of failure:

Table 1 Clinical assessment criteria and criteria used to evaluate the restorations
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1. Major failure: Restorations replaced for any reason and those placed in modified USPHS category Charlie (C) for bulk fracture, margin fracture, wear, surface roughness, margin colour and surface colour.

2. Major and minor failure. All restorations in the major failure group, all those that had required refinishing or repair for any reason, and those that were placed in USPHS category Bravo (B) for bulk fracture, margin fracture, surface roughness, margin colour and surface colour. Wear scores of B were not included once it became apparent that this was an almost universal finding and would have given an inaccurate impression of overall performance.

Kaplan-Meier survival plots were charted against the following variables:

  1. 1

    Material used

  2. 2

    Aetiology of tooth wear

  3. 3

    Incisal relationship

  4. 4

    Operator

Log rank values were calculated and data was analysed pairwise over strata for significance of differences with a P-value of 0.05.

The incidence of USPHS category B, representing minor failure not requiring replacement, was calculated as a percentage of the total, to give an indication of the modes of minor failure. The time taken for posterior contact to re-establish in each subject was also recorded and a mean value calculated.

Results

Survival analysis

The survival rate for all restorations was good when only major failure criteria (C) were applied (Fig. 3). No failures had occurred in the first year but nearly half of them occurred in the fifth year. It was only possible to calculate a median survival time for Durafill (n = 37) which was 5 years 9 months. The direct Herculite (n = 97) had not had enough failures to calculate a median survival time. None of the smaller sample of indirect Herculite (n = 18) restorations had failed at this level. Artglass (n = 73) had only suffered one major failure and was surviving well up to 3 years at this level (Fig. 4).

Figure 3
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Kaplan–Meier survival function for all restorations at major failure (modified USPHS category C)

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Figure 4
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Kaplan–Meier survival function comparing different materials at major failure level (modified USPHS category C)

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At combined major and minor failure levels (B and C) the median survival rate was 4 years and 9 months for all types of material (Fig. 5). Many minor failures occurred in the first year but, as a proportion of those remaining at risk, failures occurring in the fifth year were again considerable. Durafill and direct Herculite had similar median survival times of 4 years 8 months and 4 years 9 months respectively. Despite the additional minor failures, the total was only just sufficient to calculate median survival times for indirect Herculite and Artglass. These were 3 years 8 months and 2 years 11 months respectively (Fig. 6.

Figure 5
figure 5

Kaplan–Meier survival function for all restorations at combined major and minor failure level (modified USPHS category B and C)

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Figure 6
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Kaplan–Meier survival function comparing different materials at combined major and minor failure level (modified USPHS category B and C)

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At both levels of failure, only those cases that were Class II Div 2 had a significantly higher probability of restoration failure. The Class II Div 1 group had the highest median survival time of 5 years 9 months.

Erosion was predominant but, for a number of subjects, it was difficult to know the precise aetiology of their tooth wear. The distribution of the suspected aetiology is detailed in Table 4. As with most materials, it is suspected that RBCs will fare less well where the aetiology of the wear is predominantly parafunctional but the results did not highlight this as a statistically significant finding.

At the major level of failure, replacement restorations appeared to have the highest probability of failure with a median survival time of 4 years. This fell considerably, when minor failures were included, to 1 year 9 months. These figures were statistically significant.

There was no statistical difference between median survival times of the restorations placed by the three different operators.

Minor failure — USPHS category B

Surface discolouration, surface roughness and bulk fracture were not common findings (Fig. 7). Restorations were more commonly placed in category B for margin fracture and discolouration. Evidence of category B wear was the most significant finding, affecting 80% of the total sample. Over 90% of the Artglass restorations were affected.

Figure 7
figure 7

Summary of minor failure, modified USPHS category B, expressed as a percentage of total number of restorations

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Just over half of the subjects had no adjacent gingival inflammation. Placement of the RBC restorations at an increased vertical dimension had been very well tolerated. Only one subject remembered having some discomfort for about three days subsequently and two other subjects recalled initial problems with phonetics. Nearly all were entirely happy with the appearance. Some had complained about visible margins following placement, but no further intervention had been considered necessary (Fig. 8).

Figure 8
figure 8

Summary of additional criteria expressed as a percentage of the sample population

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All of the subjects had some posterior contact (Fig. 9). Sixty-one per cent had firm Shimstock holds between all opposing units and 39% of the subjects had Shimstock holds on only some of the posterior teeth. This was invariably between the molar units with space remaining between the opposing premolar pairs. Time taken for re-establishment of the posterior occlusion ranged from 1.5 to 18.5 months and the mean was 7 months.

Figure 9
figure 9

Re–establishment of the posterior occlusion

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Discussion

Survival analysis

The assessment of restorations is often subjective and difficult to quantify for analysis. Arguably the most relevant factor is the clinical action subsequently taken following a certain type of failure. The use of modified USPHS criteria seeks to address this issue but it is a fairly blunt tool with which to assess restorations. Despite this, it remains popular and has been used in recent studies.22,34

There was little difference between the microfilled and hybrid RBC survival beyond the 30 month point and the median survival times for both materials were toward the upper end of the age scale for each group. The newer, ceromer material, Artglass, was exhibiting minor wear but had otherwise required virtually no clinical intervention up to 3 years.

Anatomic form

Poor anatomic form, as a result of bulk fracture requiring monitoring, refinishing or minor repair, was not a common occurrence. All four materials were involved but the samples were too small to make statistically valid comparisons.

Margin fracture

Durafill and direct Herculite appeared to have a higher incidence of marginal fracture requiring monitoring, refinishing or repair than indirect Herculite and Artglass. However, the Durafill and direct Herculite restorations were an older sample group than the other two materials and a higher incidence of marginal defects would be expected with time. These observations are in line with some in vitro studies.35,36 An overall incidence of 11.2% suggests that marginal fracture is a minor, but significant, mode of failure for these restorations.

Wear

The poor wear resistance of RBCs is well-documented23,37 and is considered to be one of the main limitations of these materials in load-bearing situations. The proportion of the sample (79.6%) placed in category B reinforces this opinion. Of particular note is the high incidence of wear in the Artglass sample (91.7%), suggesting a material less suited to load-bearing situations.

Surface roughness

Surface roughness, although not a common observation, usually took the form of pitting, suspected to be due to exposure of small voids as the composite wore. There was little difference between the materials in this criterion. Surprisingly, the low incidence of roughness seen in the laboratory-made Herculite veneers was not mirrored by the indirect Artglass restorations.

Margin colour

At the time of assessment, marginal discoloration scoring B had occurred in about a quarter of the sample. The incidence of marginal staining appeared to correlate with the average age of the different groups of materials, being highest for Durafill and lowest for Artglass. Staining, as a sign of leakage, is a common finding in other types of resin restorations and may be related to the technique used and the age of the patient.38

Surface colour

Very few of the restorations had poor surface colour. Except when the incisal height had also been restored, and the restoration was visible, minor discoloration was of little significance. Intrinsic colour instability and staining due to food, drink and smoke is a recognised problem with RBCs.

Gingival health

A third of the subjects had one or more sites adjacent to the restorations that bled on probing. It is probable that a bulky composite restoration with poorly finished margins would act as a secondary plaque-retaining factor. However, all the restorations were placed with great care and gingivitis is a common finding. The results do not imply that the restorations cause gingivitis.

Pain/discomfort

As with other appliances used to produce relative axial tooth movement, complications were few. Not one subject found the restorations to be intolerable and only two subjects commented on initial, transient phonetic difficulties. One subject complained of initial tenderness and it was suspected that mild periodontal inflammation due to increased occlusal loading, prior to re-establishment of a new mandibular rest position, might have been responsible.

Appearance

In many cases there had been little loss of crown height and the appearance had not changed significantly. Those subjects who had restorations extending onto the incisal edges were generally pleased with the postoperative appearance.

Re–establishment of the posterior occlusion

Posterior tooth contact was re-established in all subjects, ranging from just under 2 months to 18 months, with a mean of 7 months. It is likely that mandibular repositioning contributed to the most rapid result. The longest case took 18 months and supports the view that, if given enough time, virtually all appliances will create space.39 However, many of the restorations showed some degree of wear and it is possible that this contributed to the re-establishment of some posterior occlusal contacts. The mean time of 7 months compares well with other studies16,39 using cast metal bite planes but differing recall intervals could influence this conclusion. Just over a third of the subjects did not achieve posterior contacts in the premolar region during the study period. Whether there is a limit to the premolar eruptive potential or whether they become impacted behind the canines is unknown.

Conclusion

The treatment of localised anterior tooth wear with resin-based composite restorations placed at an increased vertical dimension is a viable first-line option in the short to medium term (Figs 10 and 11). Directly placed Herculite and Durafill both perform well up to the fifth year of follow-up, when the probability of failure increases. The 3-year results for Artglass are encouraging although the high incidence of minor wear has been highlighted in this study (Figs 12 and 13).

Figure 10
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Artglass restorations placed at an increased vertical dimension on the upper six anterior teeth — frontal view after cementation

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Figure 11
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Artglass restorations placed at an increased vertical dimension on the upper six anterior teeth — occlusal view after cementation

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Figure 12
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Artglass restorations placed at an increased vertical dimension on the upper six anterior teeth — frontal view after 3 years

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Figure 13
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Artglass restorations placed at an increased vertical dimension on the upper six anterior teeth — occlusal view after 3 years

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Limitations in the mechanical properties of composite resins result, to a lesser extent, in marginal staining and marginal fracture. Failures such as bulk fracture, surface roughness and surface discoloration are uncommon. Maintenance of these restorations is straightforward, as localised refinishing or repairs may be all that is required. Restorations placed in a Class II Div 2 situation and those provided as replacements appear to have a higher probability of failure.

Tooth movements following this approach seem to follow the same pattern and timescale as those produced by other Dahl appliances. There is a high degree of patient satisfaction associated with these restorations. The resin can protect exposed dentine from further wear and the reversible nature of this approach may allow these patients to benefit from future materials development. The technique takes time, but it is conservative of tooth structure and may eliminate the need for conventional preparation.