Key messages
- If damaged teeth are filled with a "bulk-fill" (material placed in one large layer) or a standard resin-based composite (RBC) material (placed in multiple layers), there is probably little or no difference in failure between the filling materials.
- Older evidence found that dental amalgam (silver-coloured fillings) may have fewer material failures than RBC. But this finding was based on older studies. Modern RBCs are better, dentists have more experience using them, and there are likely fewer failures.
Why do we need fillings and what are they?
Sometimes the tooth tissue becomes damaged, and holes (cavities) may form in the teeth. Cavities are caused by tooth decay, which is mainly a preventable disease if people adopt good oral hygiene and limit sugary foods and drinks.
When tooth decay leads to permanent damage, dentists may use a filling in the cavity to restore the tooth's shape and function.
What are the different materials used for fillings?
Traditionally, cavities were filled with amalgam. This silver-coloured filling material (made mainly from tin, silver and copper, and mixed with liquid mercury) is low cost and easy to use. But, it is now known that mercury can be harmful to people's health and the environment. At an international meeting, agreement was reached to reduce (or stop) the use of mercury, including in dental fillings. Alternative mercury-free filling materials that can be placed in a single dental appointment include:
- RBC: standard white or tooth-coloured material, applied in layers or in bulk.
- glass ionomer cement (GIC): sometimes used as a temporary filling, not as strong in some situations, so not suitable for chewing surfaces of teeth.
- resin-modified GIC (RMGIC): a hybrid GIC, stronger than GICs but not as strong as RBC.
- compomers: alternative to RMGIC but closer to composite than GICs.
RBC, RMGIC and compomers use an adhesive system to fix the material to the teeth, and need light-curing to harden the material. These are not needed with GIC.
What did we want to find out?
We wanted to find out:
- the benefits of one filling material compared to another for reducing tooth loss (because the filling has failed), failure (when the filling does not work as intended), length of time to failure, and tooth sensitivity after the procedure.
- whether one filling material is more cost-effective than another.
What did we do?
We searched for systematic reviews that looked at materials used for dental fillings in people's permanent back teeth. These reviews collect all the available evidence from published studies and analyse their results. We summarised the results of reviews alongside ratings of confidence (based on factors such as review or study methods and sizes) in the evidence that they reported.
We also looked for economic studies about the cost-effectiveness of these materials.
What did we find?
We found 14 reviews with 57 studies. The studies were undertaken between 1980 and 2023; one study had follow-up for 10 years but generally follow-up was much shorter. Some reviews did not report results for our critical outcomes, and sometimes the same studies were included in more than one review. We prioritised evidence from six reviews, with 25 unique studies.
We found seven studies about cost-effectiveness.
Main results
We found no reviews with evidence for tooth loss or length of time to failure.
- Although amalgam fillings may lead to fewer failures than RBC fillings (8 studies, 3486 fillings), the studies started in the late 1990s. RBCs, and dentists' experience using them, have improved since then. Failure with RBC is more likely to be 5% today (compared to 15% in the older studies). This means that older evidence comparing amalgam with RBC is less useful in modern settings.
- There is probably no difference between bulk-fill and standard RBC at reducing failures (7 studies, 511 fillings). It is likely that most people will experience no tooth sensitivity after either type of RBC material (5 studies, 510 fillings).
- There may be no difference between standard RBC and GIC at reducing failures (1 study, 60 fillings) or tooth sensitivity (4 studies, 311 fillings). RMGIC may be more likely to reduce failures than GIC (1 study, 50 or 38 fillings). We found reviews comparing GIC with amalgam and compomer, but these did not report failures or postoperative sensitivity.
- Most economic studies gave no overall conclusions about the cost-effectiveness of any of the materials. One economic study found that amalgam fillings were likely to last longer and be more cost-effective than RBC fillings, though this was based on an older study (from the late 1990s).
What are the limitations of the evidence?
Most reviews did not meet the highest standards. We judged only two reviews to be well-conducted. However, reviews mostly reported very similar results, even when they included different studies.
We were less confident in the evidence including GIC and RMGIC because studies were often small with few participants.
How current is this evidence?
The evidence is current to April 2025.
Read the full abstract
Direct-placement dental restorative materials are required to replace the loss of tooth substance and restore the functional structural integrity of damaged posterior teeth. Whilst dental amalgam was traditionally used for these restorations, there are concerns about toxicity to human health and the environment. The Minamata Convention on Mercury recommends a phase-down of amalgam use in dentistry. Alternative mercury-free direct-placement restorative materials are available and have been evaluated in systematic reviews.
Objectives
To summarise the evidence from Cochrane and other systematic reviews evaluating the clinical effectiveness and longevity of restorative materials for direct-placement coronal restoration in the permanent posterior dentition.
To summarise the evidence from economic studies for the cost-effectiveness of restorative materials for direct-placement coronal restoration in the permanent posterior dentition.
In April 2025, we searched the Cochrane Library, MEDLINE, Embase, Epistemonikos and PROSPERO for systematic reviews that compared restorative materials for direct-placement coronal restoration in the permanent posterior dentition in children and adults. We included reviews reporting quantitative syntheses and comparing at least two restorative materials, from: resin-based composite (RBC), resin-modified glass ionomer cement (RMGIC), glass ionomer cement (GIC), compomer, dental amalgam, or other material. For RBC, we also compared bulk-fill with incremental-layered (conventional) RBC.
We used Cochrane methodology to conduct an overview of the evidence from eligible reviews, and assessed the methodological quality of reviews using ROBIS. We prioritised data from selected reviews when we found a high degree of overlap of primary studies between reviews.
Critical outcomes were: tooth loss (owing to restoration failure), restoration failure, time to failure, and adverse effects.
Additionally, we searched for relevant economic evaluations of direct-placement restorative materials and developed a brief economic commentary.
Main results
Overall, we found 14 reviews including 57 primary studies; only one was a Cochrane review. Very few primary studies (about 10%) were conducted in general practice. We prioritised data at the longest time point from six reviews, including 23 primary studies. Two reviews were at low risk of bias, and the others were at high risk. However, results across all reviews were largely comparable.
RBC compared with dental amalgam. One Cochrane review reported low-certainty evidence that the risk of restoration failure may be 7% less with dental amalgam than RBC (RD 0.07, 95% CI 0.05 to 0.09; 2 studies, 3010 restorations; 5 to 7 years follow-up; class I and II restorations). Studies in this review began recruitment in the late 1990s, which may affect the generalisability of this evidence to contemporary practice, and the failure rate for RBC in these studies was higher than in contemporary evidence of RBC in other reviews (almost 15% compared with approximately 5%). Although there was similar evidence of restoration failure from two other reviews, the certainty of this evidence was very low and, therefore, we had little confidence in the risk reductions reported in these reviews. Only one review reported postoperative pain and discomfort (about 5% in both groups), which reviewers judged to be very low-certainty evidence.
RBC compared with GIC. In one review, there may be little or no difference in the risk of restoration failure between RBC or GIC (RD -0.07, 95% CI -0.17 to 0.04, favours RBC; 1 study, 60 restorations; 10 years follow-up), or the risk of postoperative sensitivity (RD 0.03, 95% CI -0.03 to 0.10, favours GIC; 2 studies, 118 restorations); low-certainty evidence in a small sample size. Evidence for postoperative sensitivity in another review was very low certainty (overall events ranging from zero to 10%) and therefore we are uncertain of any benefit for either restorative material. Whilst this evidence included class I and II restorations, most reported were class I restorations (occlusal non-load bearing).
Bulk-fill compared with incremental-layered RBC. We found the most reviews for this comparison (n = 8), all reporting similar risk differences, and therefore this evidence was judged to be of moderate certainty. The risk of restoration failure is likely to be low, and no different between groups, at less than 5% (RD 0.00, 95% CI -0.03 to 0.03; 7 studies, 511 restorations; 1 to 10 years follow-up). In one review, there was almost no postoperative sensitivity for either type of RBC (RD 0.00, 95% CI -0.01 to 0.02; 5 studies; 510 restorations; 2 to 3 years follow-up). Overall, more restorations were in class II restorations (multiple-surface load bearing).
RMGIC compared with GIC. In one review, RMGIC may be more likely to reduce the risk of restoration failure than GIC in class I restorations (RD -0.19, 95% CI -0.37 to -0.02; 1 study, 50 restorations), and class II restorations (RD -0.71, 95% CI -0.93 to -0.48; 1 study, 38 restorations), both at two years follow-up from low-certainty evidence in a very small sample.
GIC compared with dental amalgam, and GIC compared with compomer. No reviews reported critical outcome data for these comparisons.
Brief economic commentary: Six economic reports identified no strong conclusions regarding the cost-effectiveness of mercury-free restorative materials. One report, using data from older studies, found that amalgam lasted longer and was less costly than RBC; however, we identified no economic evaluations based on contemporary clinical evidence for amalgam.
Authors' conclusions
Most evidence compared bulk-fill with incremental-layered RBC; there is probably no difference between these materials in restoration failure. Although we found evidence of fewer restoration failures with dental amalgam than RBC, this may not be comparable to contemporary practice owing to changes in properties of RBC materials and practitioner experience.
We identified few economic evaluations to provide strong conclusions to support the clinical effectiveness findings for mercury-free restorative materials.
Regarding implications for policy and practice, little evidence in this overview is from general practice. The results of clinical effectiveness should be considered alongside cost, acceptability, clinical presentation, time required for restoration placement (which may be technique-sensitive), and the health and environmental considerations of the materials. These conclusions emphasise that caries prevention is critical to effective and sustainable oral health.
Funding
Cochrane Oral Health (COH) is supported by a collaborative research agreement between The University of Manchester and the University of Pennsylvania.
Registration
Protocol (2025): https://www.crd.york.ac.uk/PROSPERO/view/CRD420251004182
