Abstract
Objectives
The aim of this patient document-based retrospective study among 25- to 30-year-old Finnish adults was to evaluate longevity of 2- and 3-surface posterior restorations according to type of tooth, size of restoration, and restorative material used.
Methods
Data were extracted from electronic patient files of the Helsinki City Public Dental Service (PDS), Finland. A total of 5542 2- and 3-surface posterior composite and amalgam restorations were followed indirectly from 2002 to 2015. Longevity of restorations was illustrated using Kaplan-Meier curves. Annual failure rates (AFRs) of the restorations were calculated separately by type of tooth, size, and material. Differences in longevity were statistically tested with log-rank tests.
Results
Composite restorations formed the majority (93%). The longest median survival times and the smallest failure rates were found for teeth in the upper jaw, for premolars, and for 2-surface restorations. Median survival time of all restorations was 9.9 years (95% CI 9.6, 10.2) and re-intervention of restorations occurred less often in the maxilla (AFR 4.0%) than in the mandible (AFR 4.7%). Median survival time of composite restorations was greater for 2-surface than for 3-surface restorations: in premolars 12.3 vs. 9.6 years (p < 0.001) and in molars, 9.2 vs. 6.3 years (p < 0.001); for molar amalgams the difference (8.0 vs. 6.3 years) was non-significant (p = 0.38). Median survival time of 2- and 3-surface restorations in premolars exceeded that in molars (12.0 vs. 8.7 years; p < 0.001).
Conclusions
Longevity of posterior composite multisurface restoration is comparable to amalgam longevity.
Clinical significance
Regarding material choices for posterior multisurface restorations, composite and amalgam perform quite similarly in molars, 3-surface restoration being challenge for both materials.
1
Introduction
The estimates of longevity of larger dental restorations vary widely depending on the study in question . The characteristics most often associated with longevity are restoration material and extent, type of tooth and patient age. The settings range from one-dentist practices or clinic or dental schools to large Practice Based Research Network (PBRN) or insurance-based records, and the length of follow-up rarely exceeds 5 years . The changing pattern of restorative materials is evident; in the Nordic countries, the use of amalgam has dramatically decreased, and in Norway is no longer permitted . Globally, composite resins are in continuous development, with new filler sizes, combinations, and compounds being introduced regularly .
Regarding Class I and II direct restorations in posterior teeth, a review and meta -analysis of eight studies report a mean annual failure rate (AFR) of 1.7% for amalgam and 3.1% for composite , but patient ages were not available for all of the studies. A large 10-year PBRN follow-up from the Netherlands reports as a mean AFR of 5.2% for amalgam and 4.4% for composite in posterior teeth , but does not give AFRs by size of restoration or material separately for premolars and molars. A 12-year follow-up of a private practitioner reports an AFR of 2.41% for amalgam and 1.68% for composite . A cohort study from the USA based on insurance data of over 300 000 multisurface restorations in posterior teeth reports survival as 5-year rates: 94% for amalgam and 93% for composites , suggesting corresponding AFR rates of 1.2% and 1.4%. Using a cross-sectional design with a questionnaire for dentists, studies from general dental practice have reported median age of 6–16 years for failed Class II amalgam restorations and 4–6 years for failed Class II composites . A similar questionnaire study among Finnish private dentists regarding their adult patients reports a mean age of 15.5 years for failed amalgam restorations and 7 years for failed composites , but the longevity data were available for only half of the failed restorations, and types of tooth and restoration sizes were not specified.
Tooth position in dental arch has been suggested to have an influence on restoration longevity. Re-treatment of amalgam and tooth-colored restorations in adults at a one-year follow-up was more likely in molars (7%) than in premolars (5%) in an American PBRN cohort study . Also in the Netherlands the mean AFR of restorations in molars was 5.2% compared to 4.0% in premolars . Some other reports have found no association between longevity of posterior restorations and type of tooth or jaw .
Based on a vast administrative database of the NHS in England and Wales in 1991–2001, comprising data on 80 000 adult patients with over 500 000 restorations, 58% of 1-surface and 49% of 2-surface posterior amalgam restorations and 43% of 3-surface (MOD) amalgams remained without intervention over a 10-year follow-up . Another large study from the Washington Dental Service, with over 279 000 posterior restorations in adults followed retrospectively from 1993 to 2000 until censored or failed, reports longevity of 4.4 years for 2-surface and 4.3 years for 3-surface amalgam restorations, and for composites, 2.6 years for 2-surface and 2.1 years for 3- to 4-surface restorations . A recent study from Germany analyzed health insurance data of almost 15 million restorations and reports four-year-success rates for posterior teeth being 74% for 2-surface and 68% for 3-surface restorations , yet the mean and median observation times remained near two years (650-700 days).
This study aimed at investigating longevity of 2- and 3-surface restorations in posterior teeth among 25- to 30-year-olds across 13 years at the Helsinki City Public Dental Service. Our working hypotheses were that longevity of restorations in premolars exceeds that in molars, longevity of 2-surface restorations exceeds that of 3-surface restorations, and no difference exists in longevity according to the restorative material of amalgam or composite.
2
Materials and methods
2.1
Background
In Finland, Public Dental Services (PDS) are available for all citizens, but more than half of adults use private services. Adults visiting public dentists pay highly subsidized fees. Both in the public and private sector, the recording of treatments is based on the official codes given by the National Institute for Health and Welfare, an agency under the Finnish Ministry of Social Affairs and Health. Filling out the patient documents is strictly regulated. In PDS, all patient documentation is recorded and stored in electronic format. The patients are identified using their personal identification number.
2.2
Ethics considerations
Our data are based on patient documents from the database of the Helsinki City PDS, the original recordings having been made at each appointment. Before providing us with the data, a PDS officer removed the identification numbers, replacing them with consecutive numbers to ensure confidentiality. The City of Helsinki Department of Social Services and Healthcare approved the study protocol.
2.3
Study design
The baseline cases were restorations of Class II or larger placed in 2002 in posterior teeth of patients aged 25–30 years visiting the Helsinki City PDS. We followed the fate of the restorations indirectly via the database as long as the patient in question continued visiting the Helsinki City PDS, but no longer than the end of 2015.
2.4
Data collection
For each restoration, we collected information about the tooth, numbered according to the ISO 3950 system, and later categorized as premolar or molar, and as upper or lower tooth. Based on the size of the restoration, we coded three types: Class II mesial (MO), Class II distal (DO), and larger (MOD). MO and DO were 2-surface restorations and MOD 3-surface ones. The restoration materials included composite, amalgam, and glass-ionomer. A further inclusion criterion was that after the placement of the restoration the patient had visited the Helsinki City PDS at least once. We recorded the dates of the placement and the re-intervention of the restoration and the patient’s most recent dental visit. The patient’s background data included gender, age in years, and dental indices (DMFT and DT) in 2002.
In total, the database included 6528 restorations, but for 926 restorations the patients made no further visits to the Helsinki City PDS. In addition, we considered the number of glass-ionomer restorations (n = 60) too small for estimating their longevity. After excluding these incompatible cases, a total of 5542 restorations remained for analyses.
Longevity of a restoration was the interval from the placement to the re-intervention if any; in case no such incident occurred, the follow-up time ended at the last visit made by the patient before the end of 2015. These intervals indicated the longevity for survivals. We calculated the intervals to an accuracy of one day.
2.5
Statistical methods
The data were prepared for analyses using Survo MM . Descriptive statistics included Chi-squared tests for comparison of frequencies and t -test for comparison of mean values. Further statistical analyses were performed using R version 3.2.3 and its survival package . The survival curves were created using Kaplan-Meier analysis , and the differences in longevity according to type of tooth and size of restoration were statistically tested with log-rank tests. The R package plotrix was used to refine the graphs. Pointwise confidence intervals for the survival functions were computed based on the cumulative hazard of the logarithm of the survival function . The mean AFR for the restorations were calculated using the formula (1−y) z = 1−x, where y stands for the mean AFR and x is the total failure rate at z years . Differences in longevity were statistically tested with log-rank tests.
2
Materials and methods
2.1
Background
In Finland, Public Dental Services (PDS) are available for all citizens, but more than half of adults use private services. Adults visiting public dentists pay highly subsidized fees. Both in the public and private sector, the recording of treatments is based on the official codes given by the National Institute for Health and Welfare, an agency under the Finnish Ministry of Social Affairs and Health. Filling out the patient documents is strictly regulated. In PDS, all patient documentation is recorded and stored in electronic format. The patients are identified using their personal identification number.
2.2
Ethics considerations
Our data are based on patient documents from the database of the Helsinki City PDS, the original recordings having been made at each appointment. Before providing us with the data, a PDS officer removed the identification numbers, replacing them with consecutive numbers to ensure confidentiality. The City of Helsinki Department of Social Services and Healthcare approved the study protocol.
2.3
Study design
The baseline cases were restorations of Class II or larger placed in 2002 in posterior teeth of patients aged 25–30 years visiting the Helsinki City PDS. We followed the fate of the restorations indirectly via the database as long as the patient in question continued visiting the Helsinki City PDS, but no longer than the end of 2015.
2.4
Data collection
For each restoration, we collected information about the tooth, numbered according to the ISO 3950 system, and later categorized as premolar or molar, and as upper or lower tooth. Based on the size of the restoration, we coded three types: Class II mesial (MO), Class II distal (DO), and larger (MOD). MO and DO were 2-surface restorations and MOD 3-surface ones. The restoration materials included composite, amalgam, and glass-ionomer. A further inclusion criterion was that after the placement of the restoration the patient had visited the Helsinki City PDS at least once. We recorded the dates of the placement and the re-intervention of the restoration and the patient’s most recent dental visit. The patient’s background data included gender, age in years, and dental indices (DMFT and DT) in 2002.
In total, the database included 6528 restorations, but for 926 restorations the patients made no further visits to the Helsinki City PDS. In addition, we considered the number of glass-ionomer restorations (n = 60) too small for estimating their longevity. After excluding these incompatible cases, a total of 5542 restorations remained for analyses.
Longevity of a restoration was the interval from the placement to the re-intervention if any; in case no such incident occurred, the follow-up time ended at the last visit made by the patient before the end of 2015. These intervals indicated the longevity for survivals. We calculated the intervals to an accuracy of one day.
2.5
Statistical methods
The data were prepared for analyses using Survo MM . Descriptive statistics included Chi-squared tests for comparison of frequencies and t -test for comparison of mean values. Further statistical analyses were performed using R version 3.2.3 and its survival package . The survival curves were created using Kaplan-Meier analysis , and the differences in longevity according to type of tooth and size of restoration were statistically tested with log-rank tests. The R package plotrix was used to refine the graphs. Pointwise confidence intervals for the survival functions were computed based on the cumulative hazard of the logarithm of the survival function . The mean AFR for the restorations were calculated using the formula (1−y) z = 1−x, where y stands for the mean AFR and x is the total failure rate at z years . Differences in longevity were statistically tested with log-rank tests.
3
Results
At baseline, we enrolled in the follow-up a total of 5542 restorations conducted on 3051 patients in 2002. The mean age of patients was 27.6 (SD = 1.7) years, and 63% were women. The mean DMFT was 13.2 (SD = 5.5), slightly higher for men than for women (13.5 vs. 13.0; p = 0.037). The mean DT was 3.3 (SD = 3.1), clearly higher for men than for women (4.2 vs. 2.8; p < 0.001).
Sixty-one percent of the restorations enrolled were in female patients and 39% in male patients. Table 1 provides the characteristics of the restorations enrolled in the follow-up. Molar teeth predominated over premolars, and as the material, composite predominated over amalgam. Gender differences were present with regard to the type and material of the restoration.
| Baseline characteristics | No. of teeth restored at baseline | p-value | ||
|---|---|---|---|---|
| Total N = 5542 |
In men N = 2154 |
In women N = 3388 |
||
| Type of tooth (%) | 0.051 | |||
| Premolar | 40 | 42 | 39 | |
| Molar | 60 | 58 | 61 | |
| Jaw and type of tooth (%) | 0.199 | |||
| Upper premolar | 29 | 31 | 28 | |
| Lower premolar | 11 | 11 | 11 | |
| Upper molar | 27 | 26 | 28 | |
| Lower molar | 33 | 32 | 33 | |
| Teeth by jaw (%) | 0.398 | |||
| Upper jaw | 57 | 57 | 56 | |
| Lower jaw | 43 | 43 | 44 | |
| Type of restoration (%) | 0.019 | |||
| Mesio-occlusal (MO) | 39 | 37 | 41 | |
| Disto-occlusal (DO) | 46 | 47 | 45 | |
| Larger (MOD) | 15 | 16 | 14 | |
| Material of restoration (%) | <0.001 | |||
| Amalgam | 7 | 9 | 6 | |
| Composite | 93 | 91 | 94 | |
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