This study shows that the use of anterior composite resin restorations combined with posterior cast or indirect restorations is a viable mid to long term treatment option to treat generalised tooth wear at an increased OVD. However, more than 60% of all the restorations exhibited some form of failure (minor or major) over the preceding 10 years and required intervention and maintenance. Of all failures the vast majority (69%) occurred within the composite resin restorations due to fracture, wear and marginal discolouration. These commonly occurred in combination.
The overall complication rate within the extra coronal restoration group was low. Around 63% of these restorations were deemed to be successful. This low complication rate is in keeping with findings of previous studies on survival of crowns (Smales and Hawthorne, 1997) and compare well to those placed within the General Dental Services in the UK (Burke and Lucarotti, 2009). Cast gold restorations historically have been reported to have high survival rates (Bentley and Drake, 1986), however, success is less frequently reported. The complication rate in this study appears to be higher than those reported for tooth borne prostheses in a systematic review by Pjetursson et al. (2007). Given the cohort of patients selected for this study being treated for tooth wear, the difference in overall complications should be expected. However some similarities were found with Pjetursson et al. (2007). There appeared to be a greater proportion of implant restoration suffering complications than extra coronal restorations. This is likely due to the differences in the way forces are distributed between implant and tooth borne restorations in parafunctional patients. The periodontal ligament allows for a certain amount of shock absorbing capacity that implant restorations do not, which may explain the higher rates of technical complications in implant restorations.
At the major failure level requiring replacement of the restorations, the MST for all restorations pooled together was 136 months (11.33 years). For all failures (combined major and minor), the MST for all restorations was 71 months (5.9 years). A similar study by Smales and Berekally (2007), found 10 year cumulative survival estimates were 62% for composite resin restorations and 74.5% for all indirect restorations. When considering major failures, the present study found a cumulative survival rate at the 10-year mark of around 52.0% for composite resin restorations and 86.0% for cast restorations. However, given the limited number of patients presenting with treatment carried out over 10 years ago, the results may not be truly representative. More comparable would be the 5-year survival rates, which appear to be similar to those of Smales and Berekally (2007). Cumulative survivals for composite resin and cast restorations were found to be in order of 78% and 84% respectively, whereas, the present study found survivals of 78% and 96% respectively.
In a study by Gulamali et al. (2011), composite resin restorations placed in cases with localised anterior tooth wear were reported to have MST of 7 years for major failures. The MST for the composite resin group in the present study appears to be an improvement on those reported by Gulamali et al. (2011), when assessing major failures. However, it is lower when comparing combined major and minor failures within the composite resin group of the present study (52 months as opposed to 69 months). This may be attributed more severe cases being treated with potentially greater demands on the restorative material.
The prospective study by Milosevic and Burnside (2015), assessed the survival of composite resin restorations placed in patients with severe tooth wear. The authors assessed 1010 direct composite restorations placed by a one specialist practitioner over period of up-to 8 years. The prospective design involved the assessment of large volume of cases and teeth assessed however the average follow up time was 33 months. Drawing comparisons with this study remain difficult since the restorations assessed were predominantly on anterior teeth and failure determination methods were not clearly defined. The annual failure rate in the first year was estimated to be 5.4%. The present study found an estimated annual failure rate of 2% and 17% when considering major or combined major and minor failures, respectively. Interestingly, Milosevic and Burnside (2015) did find that a lack of posterior support was a significant factor associated with failure. This is in keeping with the findings of the present study and may offer some explanation for the increased survival in comparison with the studies of Gulamali et al. (2011).
At both levels of failure, major and combined major and minor, patients with attrition as the primary aetiological factor had restorations with significantly lower survival outcome when compared to erosion or combined aetiology. However, primarily attrition was diagnosed in only four patients, and it was not possible to establish one clear aetiological factor in those subjects diagnosed with combined aetiology. Interpretation of these results should be carried with caution given the disproportionate representation of different categories within the aetiological variables and large amount of right censoring.
No analysis was carried out between the different types of composite resin or between direct and indirect approaches. Very few studies compare the use of direct and indirect restorations in the management of tooth wear. The statistical analysis in the present study suggested that for both major and combined failures indirect cast restorations faired significantly better than composite resin restorations. It was not possible to determine a median survival time for cast restorations since only 9 terminal events occurred through a 10-year period. Most restorations were without failures at the time of assessment thus giving an estimated cumulative survival of between 74–94%. Comparable results were reported by Smales and Berekally (2007), with a 10 year cumulative survival of 74.5% for indirect cast restorations. The authors did also suggest a strong trend for lower survivals in composite resin restorations, but, unlike the present study, did not find any statistical significance.
The nature of the incisal relationships has been reported to have an impact on the survival of restorations placed in severe tooth wear. Milosevic and Burnside (2015) found a greater proportion of failures in Class III incisal relationship but was not statistically significant. Conversely, Gulamali et al. (2011), found there was a statistically significant, better outcome in patients with Class III incisor relationships, at both levels of failure assessment. The present study found a statistically significantly difference in survival for different incisor relationships. Patients presenting with a Class III incisor relationship had a greater proportion of both major and minor failures. Possibly unfavourable, heavier shear and tensile forces on the restorative material associated with a Class III occlusions explain such a finding.
This finding should be taken with caution given that only one patient represented the Class III category. The log rank test does not allow to test the effect of the other independent variables or account for clustering of restorations within patients.
Position of the tooth within the arch may contribute to potential failures. The nature of forces exerted on a tooth vary depending on the position and the occlusal scheme. The lower anterior teeth also tend to offer reduced surface area for bonding. Restorations on anterior teeth, depending on the clinical appearance of the wear, may be placed under significant shear stresses.
In the present study, restorations placed on anterior teeth or in the mandibular arch presented with lower median survival times for combined major and minor failure. The differences although, statistically significant, were very small.
Studies assessing the role of tooth position have suggested that a greater proportion of failures appear to occur on anterior teeth and the lower arch. Smales and Berekally (2007) suggested this difference might be the result of more restorations on anterior teeth. Milosevic and Burnside (2015) demonstrated a higher proportion of failures in the mandible, but no statistical significance was found. The present study appears to reflect the findings of these two studies. Another study by Al-Khayatt et al. (2013) reported specifically on survival of restorations on lower anterior teeth. The authors found survival rate of 85% at 7 years, however a small sample size and lack of adjustment of statistical analysis to allow clustering of restorations in patient may have influenced findings.
In the present study when assessing major and minor failures combined, greater survival outcomes were observed in patients wearing post treatment splints. This was found to be to a level of statistical significance when assessed independently. The protection barrier provided by the splint may contribute to a reduction in minor failures.
Despite 18 out of the 20 subjects, including all those diagnosed with attrition, have occlusal stabilisation splints fabricated following completion of treatment, compliance appeared to be poor, with only 6 subjects still wearing the splint at the time of assessment. Most patient reported diminishing compliance with splint wearing over the first 24–36 months. The improved results reported within the 6 subjects may be attributed to the group patients being more compliant, conscientious or cautious.
The overall mean OHRQoL scores reported by participants in this study were greater than those of the British public norms (McGrath and Bedi, 2002). However, the sample was too small for separation into age categories or for any statistical analysis, therefore not allowing further interpretation of these results.
Assessment of participants’ satisfaction was carried out in four further questions. Since these questions had not been validated, they were not included in the total score reported, however, they do provide valuable information on the management of such cases.
All participants reported general improvement in their dental condition. Since the treatment lead to improvement in the patient function and appearance, this finding is as expected. Satisfaction with the treatment received was also 100%. Most subjects were happy with the dental aesthetics on completion of treatment, however two were indifferent. These were mainly related to colour match of composite restorations and subsequent discolouration of composite resin restorations.
The greatest level of dissatisfaction came from the duration of treatment, where 3 participants reported dissatisfaction. The average treatment time was 36 months. The 3 dissatisfied patients had treatment times over 71 months on average with treatment re-allocation to new postgraduates involved.