Abstract

Aim

It is the aim of this paper to present data on the survival of glass ionomer restorations by analysis of the time to re-intervention on the restorations and time to extraction of the restored tooth, and to discuss the factors which may influence this.

Methods

This study examined the recorded intervals between placing a glass ionomer restoration and re-intervention on the tooth, this being obtained from a data set consisting of General Dental Services' (GDS) patients treated in the GDS of England and Wales between 1990 and 2006. The data consist of items obtained from the payment claims submitted by GDS dentists to the Dental Practice Board (DPB) in Eastbourne, Sussex, UK.

Results

Data for more than three million different patients and more than 25 million courses of treatment were included in the analysis. Included were all records for adults (aged 18 or over at date of acceptance). Overall, 1,592,566 glass ionomer restorations were included, of which 711,581 had a re-intervention over the duration of the dataset. The Kaplan-Meier analysis indicated that 28% had survived without re-intervention at 15 years. When glass ionomer restorations are compared with the survival curves for other types of restoration, it is apparent that these restorations perform less well in terms of time to re-intervention than other treatment groups overall. They also perform less favourably in the charts dealing with time to extraction, with 23% of teeth restored with GI being extracted at 15 years.

Conclusions

The survival of glass ionomer restorations to re-intervention and in time to extraction of the restored tooth was found to be less good than other restoration types. This was particularly influenced by the age of the patient and the position of the restored tooth in the mouth.

Introduction

Satisfactory survival of restorations is of importance to patients, dental professionals, epidemiologists, third-party funders, governments, and other interested parties. It is also important that the data are derived from general dental practice (as opposed to secondary care), given that it is in this arena that the majority of dental treatment, worldwide, is provided and it is where the majority of dentists operate and where the majority of restorations are placed. Using the methodology described in Paper 1 in this series,1 it has been possible to produce precise information regarding the survival of glass ionomer restorations and all the known factors which may influence this.

Glass-ionomer (GI) cements were developed in the early 1970s.2 These materials comprised a fluoro-alumino-silicate (FAS) glass, initially being derived from the FAS glass used in silicate materials, but with the phosphoric acid used in silicate being substituted by a polyacrylic acid.3 Their popularity increased through the 1980s, and in 2000, these materials were used in the placement of circa 1.7 million restorations in the NHS in England and Wales, mainly in Class V non-load-bearing cavities.4 Principal advantages of GI materials include their good compressive strength, their reliable adhesion to tooth substance (which, in turn, reduces the need for the clinician to cut sound tooth substance to create retention for the restoration), and release of fluoride, which was once considered to inhibit the progress of caries around the restoration, although the literature on this is by no means unequivocal.5 Disadvantages of conventional GI materials included poor tensile/flexural strengths and suboptimal wear resistance (which precluded the use of these materials in loadbearing cavities), moisture sensitivity, and poor aesthetics, because of their opacity.3 The most recently developed generation of GI materials have been termed fast-setting, high-strength, or reinforced glass ionomers, examples being Fuji IX (GC, Tokyo, Japan) or Ketac-Molar Universal (3M, MN, USA). Manufacturers claim improved early physical properties and resistance to dissolution over conventional GIs,6 this improvement being due to a reduction in the size of the glass particles in the matrix, allowing a faster speed of reaction between the glass and the polyacrylic acid. These materials are stiffer when mixed and have been termed 'packable' as a result. Manufacturers have considered that a reinforced GI material may be suitable as a long-term temporary restoration of Class I and II cavities in permanent teeth (Chemflex), or permanent small Class I restorations,7 notwithstanding its suggested use in Class III and V cavities, Class I and II cavities in primary teeth, fissure fillings, core build-ups and atraumatic restorative treatment (ART) technique. However, under the regulations relating to the General Dental Services in force at the time of this study, GI materials were precluded from use in loadbearing cavities.

It is therefore the purpose of this paper to investigate the following:

  • Survival of glass ionomer restorations, by assessing time to re-intervention, and the patient and dentist factors associated with this

  • Time to extraction of teeth restored with glass ionomer restorations and the factors which influence this.

Results

More than three million different patient IDs and more than 25 million courses of treatment were included in the analysis, each of which includes data down to individual tooth level.8 Included were all records for adults (aged 18 or over at date of acceptance). Regarding GI restorations, 1,592,566 were included, of which 711,581 had a re-intervention. The Kaplan-Meier analysis (Fig. 1 and Table 1) indicates that 28% had survived without re-intervention at 15 years.

Figure 1
figure 1

Overall survival to re-intervention by treatment type

Table 1 Overall survival to re-intervention by treatment type

However, when GI restorations are compared with the survival curves for other types of restoration, it is apparent that these restorations perform less well in terms of time to re-intervention than other treatment groups overall (Fig. 1). They also perform less favourably in the charts dealing with time to extraction (Fig. 2), with 23% of teeth restored with GI being extracted by the 15-year mark, compared with 16% of teeth restored with an amalgam restoration (Table 2).

Figure 2
figure 2

Overall survival to extraction by treatment type

Table 2 Overall survival to extraction by treatment type

Influence of tooth position

GI restorations have been found to perform more favourably in the lower arch than in the upper (Fig. 3 and Table 3). With regard to tooth position, it is apparent that GI restorations survive optimally in premolar and lower incisor teeth and least well in upper incisor teeth (Fig. 4 and Table 4).

Figure 3
figure 3

Survival to re-intervention by mouth quadrant

Table 3 Survival to re-intervention by mouth quadrant
Figure 4
figure 4

Survival to re-intervention by tooth type

Table 4 Survival to re-intervention by tooth type

With regard to time to extraction of the restored tooth, it is apparent that teeth restored with GI in the lower arch survive circa five percentage points better at 15 years than those in the upper arch (Fig. 5 and Table 5). This may be further explored in Figures 6 and 7 which present the influence of individual tooth position, indicating that performance of GIs is best in first premolar teeth and least good in incisor teeth (Fig. 6 and Table 6). The variation between upper and lower jaw within tooth type (Table 7 and Figure 7) demonstrates that performance of glass ionomer is highly tooth-dependent.

Figure 5
figure 5

Survival to extraction by mouth quadrant

Table 5 Survival to extraction by mouth quadrant
Figure 6
figure 6

Survival to extraction by tooth position

Figure 7
figure 7

Survival to extraction by tooth type

Table 6 Survival to extraction by tooth position
Table 7 Survival to extraction by tooth type

Influence of dentist factors

Gender of dentist was not found to have any influence with regard to overall survival of GI restorations, with age of dentist having only minimal influence, with younger dentists' restorations surviving slightly longer than dentists in older age groups. When time to extraction is investigated, it is apparent that there was minimal influence of dentist age or gender.

Influence of patient factors

There was no difference in survival of GI restorations among male or female patients up to 10 years, after which restorations placed in females performed better.

However, as observed with many other restoration types, GI restorations performed optimally in younger age groups of patients (Fig. 8 and Table 8).

Figure 8
figure 8

Survival to re-intervention by patient age

Table 8 Survival to re-intervention by patient age
Table 9 Survival to extraction by patient age

With regard to time to extraction of the restored tooth, this is two percentage points less in female patients than in male patients and a substantial difference of about 30% was observed between the youngest and oldest patient groups (Fig. 9).

Figure 9
figure 9

Survival to extraction by patient age

Did the patient have to pay for treatment?

Patients who were exempt from charge or whose charge was remitted had restorations which survived two percentage points better at 15 years than those who paid the appropriate patient charge. However, with regard to time to extraction of the restored tooth, there was minimal difference between those who were charge payers and those who were not, although initially, and up to 12 years, patients who were non-payers received restorations which performed better in terms of years to extraction, with the graphs reversing at around 12 years.

Patient's state of oral health

Two different proxies for the patient's state of oral health have been considered: the annual average cost of GDS dental treatment for the patient, and the median interval between courses of treatment for the patient, given that it may be considered that patients with high treatment need will attend more often, and will have additional emergency attendances.

Average annual fees

Figures 10 and 11 clearly show that the patient's history of dental treatment is a major factor in determining the likely survival of GI restorations, both to time to re-intervention (Fig. 10) and time to extraction (Fig. 11). For time to re-intervention, the difference, at fifteen years, is between 58% for those with low annual expenditure on dental treatment, and 17% for those with high annual dental treatment fees (Table 10). Looked at in terms of tooth loss, patients with high annual dental expenditure face a 31% prospect of losing any GI-restored tooth within 15 years, compared with 9% for patients with low annual dental fees (Table 11).

Figure 10
figure 10

Survival to re-intervention by patient mean annual fees

Figure 11
figure 11

Survival to extraction by patient mean annual fees

Table 10 Survival to re-intervention by patient mean annual fees
Table 11 Survival to extraction by patient mean annual fees
Table 12 Survival to re-intervention by patient median attendance interval
Table 13 Survival to extraction by patient median attendance interval

Median interval between courses of treatment

Figures 12 and 13 show that patients who attend more frequently than once every six months have worse outcomes by ten percentage points or more, in terms of survival of GI restorations over periods of up to 15 years, than those who attend at longer intervals.

Figure 12
figure 12

Survival to re-intervention by patient median attendance interval

Figure 13
figure 13

Survival to extraction by patient median attendance interval

Other factors

When the data are analysed with regard to year of placement of the glass-ionomer restoration, no major differences are apparent, either in terms of time to re-intervention or time to extraction of the restored tooth, between restorations placed in 1990 and those placed in 2006, and the years between these (Fig. 14). In particular, there is no indication of any improvement over that time period.

Figure 14
figure 14

Survival to extraction by year of acceptance

However, when the effect of placement of a root canal filling in the same course of treatment as the GI restoration is examined, the charts indicate substantial effects with regard to time to re-intervention and time to extraction of the restored tooth. The probability of re-intervention within fifteen years is increased by five percentage points (Fig. 15 and Table 14) and that of extraction of the root filled restored tooth is increased by eight percentage points (Fig. 16 and Table 15).

Figure 15
figure 15

Survival to re-intervention by whether a root filling was placed

Table 14 Survival to re-intervention by whether a root filling was placed
Figure 16
figure 16

Survival to extraction by whether a root filling was placed

Table 15 Survival to extraction by whether a root filling was placed

Discussion

With 25 million courses of treatment being linked over 15 years, the dataset used in this work is the largest ever to become available for work on dental treatment. This is the first publication on glass ionomer restorations related to the interrogation of this dataset. Because of the size of the dataset, not only can complex interactions be explored, but the robustness of resultant models and algorithms can be tested by replication.

When interpreting the results, it should be borne in mind that the GDS regulations in force at the time of the present study precluded the use of glass ionomer (GI) materials in loadbearing situations, in other words, the cavity types under investigation were Class III and Class V, thus rendering direct comparison with amalgam restorations (which may be placed in loadbearing situations) inappropriate, although it may be considered that restorations placed under the forces of occlusal loading may be more prone to failure than those which are not. Notwithstanding this, GI restorations were found to perform suboptimally when compared with other restoration types and it may be considered that this is related to (a) the material's properties and (b) the clinical situations in which these materials are used. With regard to the properties of GI, its modulus of elasticity is low, at least in comparison to resin composite and amalgam, thus precluding its use under conditions of heavy occlusal load, but making them appropriate for Class V restorations, given that it has been considered that this area of the tooth may flex under occlusal load.9 Notwithstanding that, however, GI restorations have performed suboptimally overall. One saving grace might be that such restorations may be placed in Class V non-carious cervical cavities with no or minimal preparation; in other words, no preparation damage to the tooth has occurred and the restoration may be replaced at no or minimal cost, in terms of tooth substance, to the tooth. There is also a consideration that dentists may use GI in clinical situations where they consider that the prognosis of the tooth is uncertain,10 or, anecdotally, as a last resort, thereby reducing the overall data on survival, this factor possibly being reflected in the results from the present work which indicated that about 23% of teeth restored with GI were extracted at 15 years.

The results indicate better performance of GI restorations in the lower arch than in the upper and that GI restorations survive optimally in premolar and lower incisor teeth and least well in upper incisor teeth. This may relate to the placement of GI, a fluoride-releasing material, in upper incisor teeth rather than resin composite for patients with high perceived caries activity, despite the fact that the effect of GI materials upon cariostasis has been called into doubt.5 Nevertheless, it is clear that, for GI restorations at least, tooth position and dental arch interact in their relationship with restoration survival.

There is little influence of patient gender and dentists' gender in survival of GI restorations either per se or in years to extraction, but large differences are apparent with regard to patient age in respect of years of the restored tooth to extraction, with around 30% percentage points difference between younger and older patients. This again might be considered to indicate that clinicians place GIs in situations in older patients where they consider that the prognosis of the tooth is guarded.

With regard to patients who are exempt from payment for treatment, the data with regard to GI bucks the normally seen trend of patients who are non-payers having restorations which perform less well. This might relate to patients in the lower socio-economic groups (who may be exempt from payment) also having poorer oral health.10 In the present work on GI restorations, patients who were exempt from charge had restorations which survived better at up to 12 years than those who paid the appropriate patient charge, albeit with restorations in the non-payer group finishing worse at 15 years. This trend is repeated in the chart relating to time to extraction of the restored tooth, again with the graphs reversing at circa 12 years. This is an interesting finding, although it should also be noted that the difference between charge-payers and those with exemption or remission was small.

Regarding the type of GI material employed by clinicians in the present study, the collection of data commenced in 1991 and continued until 2006. This would tend to indicate that the GI materials utilised will more likely have been conventional GIs at the commencement of the study, rather than the more recently-introduced resin-modified (RMGI) and reinforced GIs later in the work. However, as is indicated in Figure 14, there is no improvement in the performance of GI restorations placed at the start of the data collection compared with those placed later. This might be considered surprising, given the improvements in GI materials during that time (as described in the introduction), but might also indicate that the majority of dentists in the study had not implemented the use of newer materials into their clinical practice. In this regard, the result of recent research,12 in which 1,000 Class V restorations were followed for five years in dental practices in the West Midlands (England), restorations formed in RMGI outperformed conventional GIs in terms of restoration survival by over 20%.

Conclusions

The survival time of GI restorations to re-intervention and in time to extraction of the restored tooth was found to be less good than other restoration types. This was influenced by the age of the patient and the position of the restored tooth in the mouth, with restorations in lower premolar teeth performing best.