Journal of Dentistry 106 (2021) 103586
Contents lists available at ScienceDirect
Journal of Dentistry
journal homepage: www.elsevier.com/locate/jdent
A retrospective clinical study on the survival of posterior composite
restorations in a primary care dental outreach setting over 11years
Constance Wong a, Igor R. Blum b, *, Chris Louca a, Martin Sparrius a, Kristina Wanyonyi a, c
a
University of Portsmouth Dental Academy, Portsmouth, United Kingdom
Faculty of Dentistry, Oral & Craniofacial Sciences, King’s College London, London, United Kingdom
c
Centre for Dental Public Health and Primary Care, Queen Mary, University of London, United Kingdom
b
A R T I C L E I N F O
A B S T R A C T
Keywords:
Survival
Posterior composites
Re-intervention
Dental students
Hygiene-therapy students
Objectives: To investigate the survival in terms of time to re-intervention of composite restorations in posterior
teeth among patients attending for treatment at a primary care dental outreach setting over an 11-year period
and to determine whether dental, patient or operator factors influenced this.
Methods: Electronic primary dental care data were collected on individual patients, including information on
their dental treatment and socio-demographics as well as service provision, key performance indicators and
student activity.
Results: A total of 1086 patients had at least one posterior composite placed between 2007 and 2018. This
amounted to 3194 restorations placed of which 308 had a re-intervention within the 11-year period. For all
restorations, the annual failure rate at 1 year was 5.73 %, at 5 years was 16.78 % and at 10 years was 18.74 %. A
logistic regression showed that when compared to the least deprived 5th quintile, the most deprived 1st and 2nd
quintiles were significantly less likely to have a re-intervention, being 49.2 % (p = 0.022) and 53.2 % (p = 0.031)
less likely, respectively.
Conclusions: The survival rates of posterior composite restorations placed at a single outreach centre providing
undergraduate dental training in the South of England, mirrors other studies. The new findings presented suggest
similar re-intervention rates between dental students and dental hygiene-therapy students. This study’s findings
around patient deprivation and rate and time of re-intervention raises important questions related to the need for
targeted dental and after care for certain groups in the population.
Clinical significance: Understanding the factors associated with re-intervention of restorations provided to patients
has an impact on patients and dental practices. Also, as we consider widening use of skill mix in dentistry to
increase access to care, parity in provision of treatments within the dental team increases opportunities for
delegation of tasks.
1. Introduction
Increasing patient demands for aesthetic tooth-coloured dental res­
torations coupled with advances in the properties of composite resin
systems and associated dental adhesive technologies, and the worldwide
phase-down of the use of dental amalgam, have led to direct composite
resin restorative materials (composites) becoming the material of choice
for the restoration of posterior teeth, also facilitating a minimally
invasive approach [1–3]. Besides the excellent aesthetic properties of
modern composites, the main advantages of such approaches to treat­
ment include avoidance of unnecessary sacrifice of intact and
salvageable tooth structure and their amenability to repair procedures,
thereby reinforcing the remaining tooth structure and leaving restored
teeth more able to withstand functional loading and with an enhanced
prognosis [4,5].
Satisfactory performance of posterior composites is critical to patient
satisfaction, to third party funders, such as the National Health Service
(NHS) in the UK and to maintaining confidence in the dental profession
[6]. Lucarotti and Burke stated that a measure of survival of a dental
restoration is the time interval from placement to the next restoration or
other intervention, i.e., re-intervention upon the same tooth [6]. Simi­
larly, failure can be defined as the requirement for a new restoration,
* Corresponding author at: Department of Restorative Dentistry, King’s College Hospital Dental Institute, Bessemer Road London, SE5 9RS, United Kingdom.
E-mail address: igor.blum@kcl.ac.uk (I.R. Blum).
https://doi.org/10.1016/j.jdent.2021.103586
Received 17 November 2020; Received in revised form 10 January 2021; Accepted 11 January 2021
Available online 16 January 2021
0300-5712/© 2021 Elsevier Ltd. All rights reserved.
C. Wong et al.
Journal of Dentistry 106 (2021) 103586
repair or other intervention on the same tooth. Thus, the longer the
interval, the better the performance of the restoration, notwithstanding
that, for any particular individual case it may be argued that the
re-intervention was unrelated to the original restoration, or that the
need for re-intervention was questionable [7].
There are many variables that can influence the performance of
posterior composites, including patient and operator factors. Patient
factors including age, caries risk and socioeconomic status whilst oper­
ator factors include experience, moisture control and correct imple­
mentation of the sensitive operative placement technique [2].
Substantial evidence now exists from numerous recent worldwide sur­
veys on the teaching of posterior composites, indicating that dental
students are familiar and competent with minimal intervention tech­
niques and the use of composites for the restoration of posterior teeth, as
a viable and predictable alternative to dental amalgam [8–12]. In fact,
many dental schools are exclusively teaching the placement of com­
posites as definitive restorations in posterior teeth [1,10,12]. It has been
shown that dental students can achieve acceptable clinical results with
posterior composites with a mean annual failure rate of 2.8 % [13].
While several survival studies with varying observation periods have
been reported on the clinical performance of posterior composites with a
wide range of annual failure rates of between 1 and 6% [13–20] many of
these included calibrated operators trained in the operator sensitive
techniques under evaluation, and trained observers using standardised
operative and examination protocols. In addition, restorations were
mostly placed in a selected patient population with a high level of dental
motivation and low caries risk which do not reflect the ‘real world’
primary care dental practice environment. In contrast, dental restora­
tions placed in the primary care setting are often placed by operators
who are not calibrated when it comes to placing and assessing the
restoration. Moreover, patients are more representative of the average
population including a variety of caries risk-patients. Assessments of the
performance of posterior composites placed under the conditions pre­
vailing in primary care may therefore be of value as indicators of
restoration survival in the ‘real world’, in other words, effectiveness
rather than efficacy. This study reports such a performance.
Whilst the existing literature includes many studies reporting on the
survival of posterior composites little information exists, to date, on the
link between restoration failure and number of surfaces of the failed
restoration, tooth type, operator skill, and patient factors such as age
and sociodemographic deprivation. Furthermore, no information exists,
to date, on the performance of posterior composites placed by under­
graduate students in an outreach training centre in the UK. Outreach
dental clinical training in the UK is delivered in a community based
primary dental care setting. It offers undergraduate dental students
exposure to a real-life working environment simulating general dental
practice and the chance to work closely as a team with other dental care
professionals delivering integrated oral care to patients [21]. The
outreach dental teaching model is now well accepted and widely re­
ported in the literature [22] and the educational advantage of commu­
nity based dental programmes has been extensively discussed in the USA
and the UK [23].
The aim of this retrospective clinical study is to evaluate key findings
in relation to the survival of posterior composites received by patients in
an NHS funded primary care dental outreach training centre in England,
by assessing the interval to re-intervention and associated factors.
Further objectives were to obtain an insight into restoration failure
analysed by the number of restoration surfaces and tooth type, with
cross analysis by patient age, patient deprivation and operator skill mix.
The null hypothesis was that there was no association between posterior
composite re-intervention and patient age, patient sex, operator skill
mix, tooth type, tooth restoration surface, tooth position, age or pa­
tients’ deprivation status as derived from post-code of residence.
2. Materials and methods
Electronic patient files from the University of Portsmouth Dental
Academy (UPDA), a state-funded NHS primary care service and training
centre attended by patients for treatment by final year dental students of
a London based dental school and dental hygiene & therapy students of
UPDA working together in a team based primary dental care setting,
were used for collecting data for this study. The design and protocol
were approved by the NHS Research Ethics Committee (REC 18/SC/
0296) and Higher Research Authority (HRA 18/SC/0296). Data from all
patients attending UPDA who had a posterior composite placed between
April 2007 and March 2018, were recorded in this study. Treatment at
the UPDA is free at the point of delivery for patients utilising this service.
Prior to accessing the data for research, the data were pseudoanonymised and housed in a data warehouse. The methods used to
retrieve the data have been described previously [24].
From the files, the data consisted of all those records containing
directly placed Class I and Class II posterior composite restorations
which related to courses of treatment between 1 st April 2007 and 31
March 2018. For each tooth treated with a posterior composite resto­
ration, the subsequent history of intervention on that tooth was con­
sulted and the next date of intervention (re-intervention), if any, was
identified in the extended data set. The data variables recorded for each
restoration placed in the study and their descriptors are shown in
Table 1. Composite restorations placed with a lining material and pa­
tients under the age of 18 at the time of restoration placement were
excluded from the study.
To manage patient care, the UPDA uses a live patient management
system (Clinical +) developed by Carestream Limited, UK from which
data for this study were extracted. The extracted data constituted
courses of care, which had either been completed or closed within the
eleven-year period, including both emergency and planned care. Cour­
ses of care were “closed” when patients failed to return for care but could
not be distinguished from “completed” courses in the system.
The descriptive analysis of the data using frequencies and pro­
portions is presented in the format reported by Lucarotti and Burke [6].
Statistical analyses were performed using SPSS 25. Kaplan-Meier anal­
ysis was used to create survival curves to quantify the distribution of
survival times, both overall and according to the characteristics of the
restoration, the patient and the operator. Differences in re-intervention
were statistically tested with log-rank tests. Logistic regression was
carried out on patients’ sociodemographic data to predict the likelihood
of re-intervention based on their socio-demographic characteristics and
the type of operator skill mix. The data on operator skill mix only
included restorations completed on introduction of the dental student
programme post 2010. While some patients contributed multiple res­
torations to this study, the method described by Chuang et al. [25]
utilising all restorations, assuming independence among restorations
Table 1
Data variables and descriptions.
Variable
Descriptions
Patient sex
Operator
Male or Female
Restoration was completed by either Dental Student
(DS) or Hygiene-Therapy student (HTS)
1, 2 or 3+ surfaces
Maxillary or mandibular tooth, premolar or molar
By decade groups
Quintiles of deprivation status derived from postcode
(zip code) of patient’s residence*.
Re-interventions were defined as operative
interventions, i.e., replacement or repair involving at
least one of the same, if not more restoration surfaces
on the same tooth**.
Restoration surfaces
Tooth position
Patient age
Deprivation
Time interval to reintervention in months:
*
740 out of 1086 patients had provided a postcode that could be converted to
deprivation.
**
Tooth extractions and root canal treatments were excluded.
2
C. Wong et al.
Journal of Dentistry 106 (2021) 103586
from the same patient, was used to produce statistically valid standard
errors for the estimates of survival.
Table 3
The characteristics of individual composite restorations that had at least one reintervention.
3. Results
Restoration
Characteristic
3.1. Patient based characteristics
In total, 1086 patients (597 males, 489 females; age range 18–93
years; mean age 38 years (sd 15.13)) received 3194 posterior composite
restorations. Of these 3194 restorations, 1789 (56 %) and 1405 (44 %)
were placed in male and female patients, respectively. Of the 1086 pa­
tients, 308 (28.4 %) were found to have at least one re-intervention
during the observation period. There was a slightly higher proportion
of re-intervention in males. A higher proportion of re-intervention was
also noted in older age groups. Patients in the least deprived quintiles
had a higher proportion of re-interventions than those in more deprived
quintiles. A summary of the characteristics relating to patients with at
least one re-intervention is shown in Table 2.
Subcategories
Overall
Female
Male
1 st quintile
2nd quintile
3rd quintile
4th quintile
5th quintile
Total
18− 19
20− 29
30− 39
40− 49
50− 59
60− 69
70− 79
80+
1 Surface
2 Surfaces
3 Surfaces
Premolar
Molar
LL4 and LR4
LL5 and LR5
LL6 and LR6
LL7 and LR7
LL8 and LR8
UL4 and UR4
UL5 and UR5
UL6 and UR6
UL7 and UR7
UL8 and UR8
DS
HTS
Sex
Deprivation
status
(n = 2815)
Age
3.2. Restoration based characteristics
Tooth surface
Of the 3194 restorations evaluated, 1840 (58 %) composites were
placed in molar teeth and 1354 (42 %) in premolars. Over the 11-year
observation period, 501 composite restorations (15.7 %) required one
or more re-interventions, mostly in the older age groups. Most in­
terventions occurred in maxillary premolar teeth. Multi-surface com­
posite restorations performed less well than single surface occlusal
restorations in terms of time to re-intervention and number of reinterventions required.
With regard to posterior composite restorations that were placed by
dental students and hygiene-therapy students, no notable difference was
found in terms of re-intervention between the different operator student
groups.
A summary of the characteristics of individual composite restora­
tions by the proportion that had at least one re-intervention is shown in
Table 3.
Tooth type
Tooth position
Skill mix
N = 2232
For all the restorations, the annual failure rate (defined as no need for
re-intervention) at 1 year was 5.73 %, at 5 years was 16.78 % and at 10
years 18.74 %. The logistic regression analysis in terms of number of
annual re-interventions and cumulative re-interventions over the 11year period with cumulative re-intervention as a percentage is shown
Table 2
The characteristics of patients with at least one re-intervention.
Sex
Deprivation
status
Age groups
Subcategories
Posterior composite
re-intervention
Frequency
%
Total
Overall
Female
Male
1 st quintile (most
deprived)
2nd quintile
3rd quintile
4th quintile
5th quintile (least
deprived)
18− 19
20− 29
30− 39
40− 49
50− 59
60− 69
70− 79
80+
308
134
174
58
28.4
12.3
16.0
28.2
1086
489
597
206
83
85
32
37
28.6
37.6
32.7
38.5
290
226
98
96
5
84
65
52
58
34
10
0
17.2
22.5
27.1
28.7
41.1
40.0
38.5
0
29
374
240
181
141
85
26
10
%
Total
501
216
285
88
134
155
49
61
487
10
147
119
84
80
46
15
0
210
210
81
249
252
32
62
65
46
11
82
73
76
52
2
105
212
15.7
15.5
15.8
15.0
15.6
20.7
15.5
19.8
17.3
11.6
11.9
15.8
18.1
22.2
21.1
24.2
0.0
11.3
20.0
29.0
18.4
13.7
13.7
18.2
15.0
11.0
9.8
20.7
19.1
15.6
15.4
3.6
14.5
14.1
3194
1391
1803
586
858
747
316
308
2815
86
1333
752
464
262
218
62
17
1865
1050
279
1354
1840
234
341
432
417
112
396
383
486
437
57
724
1508
in Table 4.
When the data were analysed with regard to patient age in terms of
cumulative median restoration survival, more re-interventions were
noted over a shorter period of time in terms of months in the over 40
years age group (Fig. 1). It is noteworthy that the 60− 69 age group had
the lowest survival rate out of all the age groups with half of the res­
torations requiring re-intervention by 16.4 months. In contrast, resto­
rations in the 20− 29 age group appeared to have the highest survival
rate with 50 % of restorations requiring re-intervention at 25.9 months.
In terms of patient sex, no notable statistically significant differences
were identified in the Kaplan-Meier analysis regarding the cumulative
median survival of restorations (p = 0.214) (Fig. 2).
3.3. Survival rates of restorations
Patient
Characteristic
Posterior
Composite
Re-intervention
Frequency
Table 4
The number of yearly re-interventions and cumulative re-interventions over the
11-year period with cumulative % re-intervention.
3
Age of
restoration in
years
No of intact
restorations
No of reinterventions
Cumulative reinterventions
% reintervention
0
1
2
3
4
5
6
7
8
9
10
3194
3021
2910
2830
2764
2735
2719
2704
2696
2693
2690
0
173
111
80
66
29
16
15
8
3
3
0
173
284
364
430
459
475
490
498
501
504
0
5.73
9.76
12.86
15.56
16.78
17.47
18.12
18.47
18.60
18.74
C. Wong et al.
Journal of Dentistry 106 (2021) 103586
Fig. 1. Survival of composite restorations to re-intervention, in relation to
patient age in years.
Fig. 3. Time to re-intervention of composite restorations with respect to type
and position of tooth.
Fig. 2. Survival of composite restorations to re-intervention, in relation to
patient sex.
With regard to tooth type and position, the Kaplan-Meier analysis
revealed that maxillary premolars demonstrated shorter median sur­
vival times of composite restorations to re-intervention. Median survival
times were overall longer for restorations in mandibular molars than
maxillary molars, with mandibular third molars having the highest
mean survival rate of 35.2 months compared to maxillary first molars,
which had the lowest median survival time of 15.3 months. Posterior
composite restorations in mandibular second molars were found to have
longer survival times than in maxillary second molars. Although all
differences were found, these did not achieve statistical significance (p =
0.753) (Fig. 3).
When the data were analysed with regard to restoration type, an
association was noted in the number of restoration surfaces and resto­
ration survival although this did not achieve statistical significance (p =
0.753). From this association, albeit non-linear, it is apparent that single
surface posterior composite restorations out-perform multi-surface
posterior composite restorations and that restorations with at least three
surfaces are performing least favourably in terms of survival to reintervention (Fig. 4). Fifty percent of 3-surface restorations were
found to have a shorter survival than the 1- surface and 2- surface
restorations.
The Kaplan-Meier analysis did show statistical differences in median
survival times of posterior composite restorations, in terms of placement
by dental students or hygiene/therapy students although these did not
achieve statistical significance (p = 0.546) (Fig. 5).
The cumulative median survival of restorations for the different
deprivation quintiles is shown in Fig. 6. Half of restorations in the 2nd
quintile lasted 16.0 months, compared to the 3rd and 4th quintiles,
which lasted 24 and 26.1 months respectively (p = 0.608) (Fig. 6).
Fig. 4. Kaplan-Meier graph showing survival to re-intervention in months by
number of restored tooth surfaces.
Fig. 5. Kaplan-Meier graph showing survival to re-intervention in months by
operator groups of dental students (DS) and hygiene/therapy students (HTS).
4
C. Wong et al.
Journal of Dentistry 106 (2021) 103586
primary care setting in England.
A strength of this study is the use of electronic patient management
system data which included accurate charted treatment data related to
type of tooth, size/extent of restoration, and filling material used. This
added to validity of the data. A limitation is that if patients visited an
external dental practitioner during the course of care or marked study
period, no data about these treatments were available. Thus, this study
makes the assumption that restorations not restored in the practice
within the study period have indeed survived and have not failed or
replaced elsewhere.
A further strength lies in the retrospective design of the present study
which has an advantage over experimental designs, as this study relies
on real life dental observations, it saves on costs and allows the explo­
ration of a variety of real life factors influencing restorations. It should
be noted as a limitation that the study collected data from one site
(UPDA) and the findings cannot be generalized. Additionally, factors
linked to the setting may confound the findings. For example, the failure
and survival of restorations are based upon evaluation by supervising
clinical teachers and respective students rather than using the Ryge [27]
or the modified USPHS criteria [28] which are mostly used in other
experimental clinical studies assessing restorations. This can be seen as
observer bias, and as such is hard to avoid in true practice-based
research, but as it clearly reflects the real clinical situation and it
should be included as a factor of interest. In addition, it must be
emphasised that most restorations were assessed by evaluators who
were not the operators who placed the restorations i.e. the clinical tu­
tors. This should be viewed as an added advantage towards ascertaining
a valid assessment of need for reintervention.
An apparent limitation of the present dataset is that the clinical
reason for failure, diagnosis and indication resulting in the reintervention, as well as the type of re-intervention, are missing. This is
one of the drawbacks of using electronic coded data in research. Often
this type of information is held in free text and retrieving this type of
information is still challenging for researchers. There are multiple types
of re-intervention of a restoration, i.e refurbishment, repair and
replacement [29–32]. Our data does not differentiate between these
different types of re-intervention so future research is recommended for
distinguishing between these types of re-interventions. However, due to
the large number of restorations included, it is considered that the
findings of the present study provide an indication of the serviceability
of posterior composites placed by undergraduate students and should be
of immediate practical relevance in clinical practice.
Fig. 6. Kaplan-Meier graph showing survival to re-intervention in months by
deprivation quintile.
3.4. Logistic regression analysis
The logistic regression analysis (Table 5) shows that there was a
significant association between restoration re-intervention and patient
population deprivation. When compared to the least deprived 5th
quintile, the 1st and 2nd quintiles (most deprived) were less likely to have
a re-intervention within the study period, being 49.2 % (p = 0.022) and
53.2 % (p = 0.031) less likely, respectively.
4. Discussion
This study aimed to investigate patient and restoration related fac­
tors associated with survival and prediction of restoration reintervention. The study also for the first-time explores differences, if
any, in the survival of restorations placed by dental students and dental
hygiene & therapy students. Primary care dental data on a large number
of restorations over a lengthy time period is relatively rare. These data
provide valuable insight into wider determinants which may influence
the course of care such as re-intervention. To our knowledge, this is the
first study to explore the role of patients’ deprivation in in the perfor­
mance of restorations placed by dental students and dental hygiene &
therapy students.
Previous studies have shown that dental students gain extensive
experience in the placement of posterior composites [3,8–10,13,26].
This presented study has an 11-year observation period and provides
information on the survival - in terms of interval from placement to
re-intervention of 3194 posterior composite restorations placed by both
dental and dental therapy students in an NHS funded dental outreach
4.1. Restoration failure
In the present study the annual failure rate of 5.7 % and the five-year
failure rate of 16.8 % are higher than the annual 2.8 % and five-year 13
% failure rates reported by Opdam et al. [12] which evaluated 703
posterior composites placed by undergraduate dental students. Also, the
11-year failure rate of 18.7 % in the present study is higher than the 14
% in a report by which evaluated 1695 posterior composites after 12
years of clinical service placed by dental students [33]. Another study by
Moura et al. [34], found a failure rate of 15 % for a 3-year period for 256
anterior and posterior composite restorations. The higher failure rates
observed in the present study may be attributable to the considerably
larger number of restorations included in this study, suggesting more
reliability and greater validity of this study.
Another factor which may influence the higher failure rate in the
present study is that owing to the NHS contractual arrangement within
the UPDA, which requires performance targets to be achieved annually,
patients attending the UPDA are not paying for their treatment. This is in
contrast to patients attending a primary care NHS dental practice, where
a re-intervention would lead to additional payment by the patient if
outside a one-year period. It may be hypothesised that with the payment
element being removed at the UPDA, patients with localized defects in
their restorations may have been more proactive in agreeing to
Table 5
Logistic regression results for patients who had a re-intervention (post DS
period) n = 740.
Sex
Age
Operator group (DS or HTS)
Deprivation quantiles (reference
category 5)
Quintile 1
Quintile 2
Quintile 3
Quintile 4
Odds
Ratio
95 % C.
I.
Lower
95 % C.
I.
Upper
P value
1.041
1.010
1.079
0.747
0.999
0.765
1.453
1.021
1.522
0.811
0.062
0.667
0.492
0.532
0.799
0.502
0.269
0.300
0.447
0.245
.901
.944
1.427
1.026
0.022*
0.031*
0.448
0.059
Note:*Statistically significant at α = 0.05 significance level; Reference cate­
gories:
Sex: Female = 1, Operator group: DS(Dental Student), Deprivation: Quintile 5
(Least Deprived).
5
C. Wong et al.
Journal of Dentistry 106 (2021) 103586
restoration re-intervention rather than being reactive, i.e. postponing
interventions until a complication occurs and seeking for help then.
In comparison to clinical longitudinal studies on posterior composite
survival [35], the higher failure rates observed in the present study may
be attributable to the fact that the composites in longitudinal studies are
usually placed by experienced operators. Also, patients in these studies
are often specially selected, so higher survival rates can be expected
compared to the present study in which a variety of patients were
treated by the operators with limited clinical experience. The findings of
the present study are a confirmation of the assumption by Mjör et al.
[36] that the experience of the operator in adhesive techniques plays a
critical role in the survival of composite restorations [36]. However, it
must be emphasised that many dentists who graduated before the new
millennium received limited clinical training in adhesive dentistry at
dental school. In that aspect the results of the present study should also
be compared to a study which indicated a 50 % survival rate of com­
posite restorations placed in general practice of 8 years, resulting in an
annual failure rate of 6.3 % [36]. The longevity of the restorations
placed at the UPDA could thereby be considered as satisfactory.
Demarco et al. [37] reported that there is little evidence that the
material properties of the composite used are a relevant factor in
restoration longevity. Reports have shown satisfactory survival rates for
posterior composite restorations, including hybrid materials that are no
longer available in the market [37]. Improvements in clinical perfor­
mance should address the main reasons for failure, which in clinical
studies are still secondary caries and fracture (tooth or restoration), and
neither may actually be a failure of the materials themselves.
influenced by the size of the restoration [37].
4.6. Operator skill mix
For the present dataset which looked at procedures undertaken by
dental students and dental therapy students, no statistically significant
differences in restoration survival were found between the different
student groups. It was not possible to draw direct comparisons with
other studies in this respect as, to our knowledge, this is the first study
that explored the longevity of posterior composites placed by operators
from these two student groups. Nonetheless, this finding is remarkable
as dental students are subjected to more clinical experience in restora­
tion placement and, arguably, receive a more comprehensive education
in dental materials and adhesive techniques than hygiene-therapy stu­
dents. In contrast, operator-related factors have been shown in other
studies to affect restoration longevity and treatment practices. One study
has shown that more experienced third and fourth year undergraduate
dental students placed restorations with a higher longevity than second
year dental students [13] whilst another found that dentists with less
professional experience also had a shorter re-intervention time than
more experienced colleagues [45].
4.7. Deprivation
The results of this study showed that patients in the more deprived
quintiles, if they required a re-intervention, had one sooner than pa­
tients in the less deprived quintiles according to the survival analysis.
However, based on the logistic regression which controlled for con­
founding factors and looked at the prediction of re-intervention in
general, the less deprived group were statistically significantly more
likely to have a re-intervention within the whole study. A reason for this
may be that those from more affluent quintiles are more aware of health
and health needs and more likely to seek care or replacements of res­
torations, whilst indeed those who are more deprived are likely to suffer
a need for reintervention due to restoration failures, which may be
associated with poor adherence to oral health advice. Previous work has
outlined these patterns where patients from areas of higher deprivation
are more likely to have extractions rather than restorations [24] or those
from more affluent areas being more likely to seek care [46]. It is
acknowledged that in the presented study individuals without recorded
deprivation scores were not included in the logistic regression. Such
limitation, albeit non selective, is often encountered as a challenge in
studies using electronic data records. However, it must be noted that the
sample of 740 is very large and suitable for analysis to provide repre­
sentative data.
4.2. Patient age
In agreement with other studies, patient age was found to have an
impact on restoration survival as differences in failure rates were found
between different patient age groups: restorations placed in the elderly
showed a higher failure rate compared to the other age categories
[38–41]. An explanation may be that older adults who have had pre­
vious restorative treatment on the treated tooth needed further inter­
vention once the restorations failed [42,43].
4.3. Sex differences
The finding of the present study compares with previous studies that
show patient sex on its own does not seem to have an impact on the
longevity of restorations [41,44].
4.4. Position and type of teeth
The present research suggests that the survival rate is better in
mandibular molars than maxillary molars, and in mandibular premolars
than in maxillary premolars. Overall, in this study mandibular posterior
teeth fare better than maxillary posterior teeth and molars fare better
than premolars; however, this finding was not found to be statistically
significant. Previous research has found no differences in molars and
premolars in failure rates [38,39] whilst some studies have found a
positive difference in favour of premolars [40,44]. One study reported a
small but significant difference in favour of restorations in mandibular
teeth, but this combined all types of teeth including anterior teeth, and
the data did not include any posterior composites [7].
5. Conclusions
Within the limitations of this study, it is concluded that the survival
rate of composite restorations at the UPDA is similar to other values
amongst undergraduate dental students, and that socioeconomic
deprivation and age are factors that have an impact on the survival rates
of posterior composite restorations. This study also provides new in­
formation on the longevity of restorations placed by hygiene-therapy
students as well as dental students in an NHS dental outreach setting.
Declaration of Competing Interest
The authors report no declarations of interest.
4.5. Surfaces of restoration
In this study, the association noted in the number of surfaces and
median survival time of composite restorations, is in agreement with
previous studies that found survival times most favourable for single
surface restorations and shortest for multi-surface restorations, with 3surface restorations being at greatest risk for re-intervention [40,44].
This is not too surprising as it is widely accepted that longevity is
CRediT authorship contribution statement
Constance Wong: Conceptualization, Methodology, Visualization,
Investigation, Writing - original draft. Igor R. Blum: Methodology,
Resources, Writing - review & editing. Chris Louca: Project adminis­
tration, Writing - review & editing. Martin Sparrius: Investigation,
6
C. Wong et al.
Journal of Dentistry 106 (2021) 103586
Writing - original draft. Kristina Wanyonyi: Formal analysis, Data
curation.
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Acknowledgement
This research did not receive any specific grant from funding
agencies in the public, commercial, or not-for-profit sectors.
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