410 >CLINICAL REVIEW
Dentists need to consider various factors when choosing
restorative materials, with the longevity of restorations be-
ing one of the most important criteria. Replacement of failed
restorations constitutes over 60% of operative procedures,
leading to high annual costs. This literature review compares
the survival rates of different restorative materials used for
both direct and indirect restorations. A literature search
was carried out using Pubmed to identify all articles on re-
storative materials published from 1974 to 2014, of which 22
were included in this review. For direct restorations, amal-
gam showed the highest survival rates (22.5 years), with
an average survival rate of 95% over 10 years, followed by
composite resins (90% over 10 years), and glass ionomer
cements (65% over 5 years). For indirect restorations, gold
restorations are still the “gold standard” with a 96% over
10 years survival rate, followed by porcelain-fused-to-metal
crowns (PFM) (90% over 10 years), and all ceramic crowns
(75-80% over 10 years). Amongst the ceramic restorations,
eMax shows the longest survival rate (90% over 10 years),
and Zirconia the lowest (88% over five years). The longevity
of restorations depends on many factors, including: materi-
als used, type of restorative procedure, patient parameters,
operator variables, and local factors.
A wide variety of materials are used by dentists in the
restoration of teeth. Many factors need to be considered
by both the dentist and the patient when choosing the
optimal restorative material for each procedure, with the
longevity of that particular restorative material being one
of the most important.1, 2
Restoration success is the demonstrated ability of a resto-
ration to perform as expected, whereas the length of time
that a restoration survives (survival rate), is often used as a
measure of clinical performance. Replacing failed restora-
tions constitutes about 60% of all operative procedures car-
ried out by dentists, with estimated annual costs of around
$5 billion in the USA alone.1 Restorations have a limited
lifespan and once a tooth is restored, a “restorative cycle”
commences, where the restoration will likely be replaced
many times throughout the lifetime of the patient.3 Dentists
are obliged to inform their patients about the survival rates
of different materials and restorative procedures. This will
allow the patients to make informed decisions regarding
their treatment options. The United States Public Health
Service (USPHS) criteria have been used most widely to
determine the clinical performance of restorations. This
requires two independent examiners and uses a grading
system based on a number of observations (eg. retention,
colour match, secondary caries, etc.). For each observation
there is a grading from Alpha (perfect), Bravo (less perfect),
to Charlie (complete failure).1 The majority of the articles re-
viewed in this paper used these criteria in their evaluation,
with the main focus being on survival rates.
DETERMINANTS OF RESTORATION
A wide variety of both patient and clinician variables will
influence the longevity of restorations.4 These include:
Caries index, where a high index is often associated with a
low restoration longevity, usually due to recurrent caries.5
Restoration size, with larger restorations having great-
er failure rates due to their greater surface area, making
them more susceptible to recurrent caries, fracture, and
Tooth position, with molars having lower restoration sur-
vival rates than anterior teeth.5 This relates to restorations
being larger on posterior teeth and sustaining greater oc-
clusal forces, affecting their longevity.
SADJ October 2015, Vol 70 no 9 p410 - p413
NA Fernandes1, ZI Vally2, LM Sykes3
The longevity of restorations -
a literature review
NA Fernandes: 1. BDS. Registrar, Department of Prosthodontics,
School of Dentistry, Faculty of Health Sciences, University of Pretoria.
ZI Vally: 2. BDS, MDent (Pros). Senior Specialist, Department of
Prosthodontics, School of Dentistry, Faculty of Health Sciences,
University of Pretoria.
LM Sykes: 3. BDS, MDent (Pros). Head of Clinical Unit and Associate
Professor, Department of Prosthodontics, School of Dentistry,
Faculty of Health Sciences, University of Pretoria.
Corre spondi ng author
Department of Prosthodontics, School of Dentistry, Faculty of Health
Sciences, University of Pretoria. E-mail: firstname.lastname@example.org
CEREC: Chairside Economical Restoration of Esthetic
FPD: Fixed partial dentures
GIC’s: Glass ionomer cements
PFM: Porcelain fused to metal
YST: Yttrium-stabilized tetragonal type
www.sada.co.za / SADJ Vol 70 No. 9
Clinician variables: more experienced clinicians have
higher restoration survival rates.
Patient parameters may also play a role. Studies found
that those who regularly change dentists had their resto-
rations replaced more frequently, while restoration failures
are highest among older patients and lowest in the 4-18
year age group. This may purely be due to older patients
having older restorations, however, caries incidence is
also higher in the elderly due to changes in their stoma-
tognathic system, impaired motor function, and reduced
salivary flow rates, amongst others.5
HOW LONG SHOULD RESTORATIONS LAST?
A literature search was undertaken using Pubmed in the
identification of relevant articles published from 1974 up
to and including 2014.The following keywords were used:
longevity, restorations, prosthodontics, crowns, all ce-
ramic, zirconia, CAD/CAM, amalgam, composite, lifespan,
survival. Twenty two articles have been included in this
review, which covers both direct and indirect restorative
materials as well as different manufacturing techniques.
This is still one of the most commonly used restorative ma-
terials in posterior teeth in some countries. It’s use is how-
ever declining due to higher aesthetic demands of patients
and their concerns over mercury toxicity.6 It has a unique
ability to seal itself over time by a phenomenon known as
“c ree p”,7 which has been defined as “the deformation of
a metal under a load that is below its proportional limit”.8
Dental amalgams have been shown to “creep” as a con-
sequence of low-frequency cyclic stresses resulting from
mastication and from thermal changes during ingestion of
hot and cold food. The material expands with internal cor-
rosion and phase changes, which will fill in the microscopic
space at the tooth-amalgam interfaces. The median surviv-
al time of amalgam has been estimated to be 22.5 years,2
with some studies showing annual failure rates of 3%.4
Early composite resin materials showed failure rates as
high as 50% after 10 years.2 This has drastically improved
with the introduction of newer products. These materials
can currently be classified as nanofilled, microfilled, or mi-
cro/nanohybrid materials with filler quantities varying from
42-55%. Of these, the hybrid composites performed the
best with annual failure rates of 1.5-2%, most often as
a result of restoration fracture.9 The major drawbacks of
these materials are polymerization shrinkage and polym-
erization stress. These have the potential to initiate fail-
ure at the composite-tooth interface which will result in
post-operative sensitivity and the opening of pre-existing
enamel microcracks. Newer low stress flowable base ma-
terials can overcome some of these problems by reducing
the amount of stress generated during polymerization (1.4
MPa compared with 4 MPa for other flowable compos-
ites).10 Such restorations should be followed up periodi-
cally for early detection of problems as once failures e are
initiated there is usually a rapid progression. The place-
ment of glass ionomer cement liners under composites
further improved their success rates and is now regarded
as a “gold standard” procedure especially in posterior
teeth. These cements resist caries formation in the adja-
cent tooth structure by maintaining the pH at levels above
those required for demineralization to occur.11 Current ap-
proaches have seen the introduction of new nanocom-
posite materials which release fluoride (F-), calcium (Ca2+),
and phosphate (PO4) ions. These calcium and phosphate
ions combine to form hydroxyapatite [Ca10(PO4)6(OH)2],
thus strengthening the tooth and combating secondary
caries.12 More studies and further development of these
new materials is however needed.
GLASS IONOMER CEMENTS (GIC’S)
As mentioned, GIC’s make an excellent dentine replace-
ment as a lining or base when managing dentinal caries
but lack the physical properties needed to be used alone
for posterior restorations.2 In addition, they are more read-
ily lost interproximally where reduced saliva flow leads to
sustained low pH levels. Improved saliva flow on other
tooth surfaces helps restore the resting pH levels.11 These
materials are most effective buffers in acidic environments
and are also excellent luting agents. Their primary use is
for restoring Class V cavities, primary teeth, and in the ART
technique (atraumatic restorative treatment). In primary
teeth GIC’s have a 93-98% survival (over the longevity span
of the tooth), and a median survival of 30-42 months in per-
manent teeth. Their annual failure rate when used alone as
a restorative material is estimated to be 7%.4
412 >CLINICAL REVIEW
Gold crowns and inlays
These are considered the “gold standard” against which
all other restorations are measured in terms of longev-
ity. The most common biological reason for their failure
is secondary caries, with retention loss being the most
common technical cause of default. Studies have shown
survival rates to range from 96% over 10 years, 87% over
20 years, to 74% over 30 years2 with a mean failure rate of
1.4% in the posterior permanent dentition.4
Porcelain fused to metal (PFM) crowns
These restorations have been repor ted to have a 97% 10
year survival rate.2 The majority of failures (65%) occur in
the anterior region (traumatic zone), and have been attrib-
uted to eccentric chewing forces, iatrogenic factors, ac-
cidents, and inadvertent contact with instruments during
ALL CERAMIC CROWNS
Many different types of materials are available for all-ce-
ramic restorations. These can be chosen depending on the
properties required for a particular clinical situation (such as
aesthetic concerns versus the need for strength).2
The lifetime of these materials depends on the presence
of incidental cracks and their propagation under intra-oral
conditions.14 There are substantial differences in material
properties of the different ceramics, and thus they should
be considered separately.
Heat pressed, reinforced ceramics
Leucite-reinforced (eg. IPS Empress I) is reported to have
a 99% survival rate after 3.5 years, and a 95% survival
after 11 years, with better success reported for ante-
rior restorations.2 The IPS EMax system is comprised of
lithium disilicate (Li2O2SiO2) glass ceramic and zirconium
dioxide (ZrO2) materials which are suitable for pressing,
but can also be used with the CAD/CAM technologies.
This is a highly durable, very strong (360-400MPa flexural
strength) ceramic which can overcome some of the prob-
lems encountered with the chipping off of porcelain which
is commonly encountered in zirconia restorations. Studies
have shown their survival rates to be promising, with sys-
tematic reviews showing these to be in the region of 96%
after five years.15
Slip-cast glass-infiltrated ceramics
These include magnesia, alumina, and zirconia infiltrated var-
iants, with some studies showing survival rates of 92-100%
over five years for the magnesia and alumina variants.2
Metal oxide ceramics
These materials usually contain alumina or zirconia which
confer a toughness and superior fracture resistance but
also inferior aesthetics due to the inherent opacity found in
the high-density metal oxide crystals. Clinical studies have
shown Procera Alumina crowns to have success rates of
98% over 5 years, and 94% over 10 years.2 Zirconia has
been referred to as “ceramic steel” because of its superior
material properties. It is a crystalline dioxide of zirconium,
with mechanical properties similar to those of metals and a
colour similar to that of teeth. Zirconia crystals are organ-
ized into three different patterns: monoclinic, cubic, and
tetragonal. Zirconia ceramics used in dentistry are of the
Yttrium-stabilized tetragonal type (YST), which offer excel-
lent mechanical performance, strength, and fracture resist-
ance.16 This is possible by the “phase transformation effect”
that these materials undergo (tension induced tetragonal-
to-monoclinic phase transformation).14 The net result is a
volumetric expansion which compresses cracks to prevent
propagation and enhances toughness to resist fractures.
Cracking and crazing of the veneering porcelain is of major
concern with some studies reporting this problem in as
many as 50% of cases after only two years.2 This is the
result of chewing forces being exerted on a very weak
90MPa feldspathic veneering porcelain, with the underlying
1000MPa zirconia substructure remaining intact, leading to
ultimate failure of the restoration. Such chipping can also
be attributed to rapid cooling protocols during fabrication
when firing the veneering feldspathic porcelain onto the zir-
conia substructure.14 This can be overcome to some extent
by ensuring slower cooling when the final restoration is re-
moved from the furnace.14 These restorations have survival
rates of 96% after two years, and 94% after four years,2 but
longer term clinical studies are still needed.
CERAMIC INLAYS AND ONLAYS
IPS-Empress inlays and onlays have been shown to have
survival rates of 96% after 4.5 years, and 91% after seven
years.2 With the introduction of CAD/CAM systems into
dentistry, in particular the CEREC (Chairside Economical
Restoration of Esthetic Ceramics) system, clinicians are
now able to use composite resin and ceramic materials to
fabricate indirect restorations.17 The CEREC 1 system was
mainly used for chairside fabrication of inlays and onlays
with long-term studies showing adequate survival rates of
97% over five years, and 90% over 10 years.2 The main
reasons for failure of these restorations were the result of
ceramic fracture (feldspathic porcelain), followed by frac-
tures to the underlying supporting tooth. With advances
in technology, the CEREC 2 system was capable of pro-
ducing inlays, onlays, full and partial crowns with survival
rates of 87% over seven years. The current CEREC 3 sys-
tem will manufacture veneers, shor t bridges, and implant
abutments, with survival rates for these being 95-97%
over five years.18
FIXED PARTIAL DENTURES (FPD’S / BRIDGES)
These can be divided into PFM and all ceramic. Studies
have shown survival rates to be 92% over 10 years, and 75%
over 15 years for the PFM type, 93% survival rates over five
years for zirconia, and 89% survival rates over five years for
all ceramic FPD’s. The sharp decline in survival rates after
10 years (PFM) can be attributed to material fatigue (of the
restoration or luting cements), recurrent caries, or retention
loss. FPD’s on implants have 87% 10-year survival rates.2
RESIN BONDED FIXED PARTIAL DENTURES
Longevity rates for these types of restorations vary widely,
with some studies showing 88% five year survival rates.
They are mostly lost due to de-bonding. Those in the
anterior regions seem to survive longer than those in the
posterior regions. Posterior restorations in the maxilla
survive longer than those in the mandible, possibly due to
greater masticatory forces being applied to the posterior
mandible causing more frequent de-bonding at this site.
www.sada.co.za / SADJ Vol 70 No. 9
When these restorations are re-bonded there are greater
failure rates, with 40% failing after their first re-bonding
and 60% failing after second re-bonding respectively.
Inappropriate case selection, and design flaws will not be
corrected by re-bonding these types of restorations, which
can explain their high failure rates.2
ENDODONTICALLY TREATED TEETH
When restoring endodontically treated teeth, the use of
the sandwich technique, where a glass ionomer base is
covered with overlying composite resin, is the preferred
method for minimizing coronal leakage.19 When there is
inadequate tooth structure remaining, cast post and core
restorations have been found to have success rates of
90% over 10 years.20 If pre-fabricated posts need to used,
fibre-reinforced posts offer better long-term success
compared with metal posts, as these tend to cause more
root fractures due to their higher modulus of elasticity
compared with dentine.21 Sealer selection is also impor-
tant with AH-26 (epoxy sealer) offering better resistance
to leakage than ZOE (zinc oxide eugenol) based sealers.19
Endodontically treated teeth can have survival rates of
97% over 5-8 years if adequately restored.22
The longevity of restorations is dependent on a multitude
of factors making it difficult to compare success rates.
Based on current findings, we can, however, convey evi-
dence-based information to our patients regarding antici-
pated restoration survival rates. It is essential to establish
effective communication with our patients so that they can
make informed decisions regarding their treatment.
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