Resin Composites vs. Amalgam for Dental Restorations
Amalgam restorations remain superior to resin composites for posterior teeth restorations, with composite resins showing nearly double the failure rate and significantly higher risk of secondary caries, though composite materials should be selected when aesthetics is the primary concern or when the Minamata Convention phase-down requirements apply. 1
Evidence-Based Performance Comparison
Restoration Longevity and Failure Rates
Composite resin restorations have almost double the risk of failure compared to amalgam restorations (RR 1.89,95% CI 1.52-2.35) in posterior teeth based on data from 1,645 composite and 1,365 amalgam restorations. 1
The risk of secondary caries is more than twice as high with composite resins (RR 2.14,95% CI 1.67-2.74) compared to amalgam, representing the most significant clinical limitation. 1
Composite resin restorations do not show higher rates of restoration fracture compared to amalgam (RR 0.87,95% CI 0.46-1.64), suggesting comparable structural integrity despite higher overall failure rates. 1
The expected longevity of resin composite restorations in posterior teeth is approximately 8 years when used as amalgam substitutes. 2
Material Properties and Clinical Considerations
Laboratory testing shows composite materials have physical properties comparable to amalgam (except hardness), with the advantage of lower thermal conductivity and superior aesthetics. 3
The limiting factor with composite resin substitutes is the elevated risk of secondary caries resulting from marginal openings that are unavoidably associated with the operative technique. 2
Under clinical conditions, composite materials demonstrate inferior resistance to marginal percolation compared to amalgam, and their color tends to yellow over time. 3
The abrasion resistance of composite materials is unsatisfactory under clinical conditions due to failure of the bond between filler particles and resin. 3
Safety Profile
Toxicity and Biocompatibility
Very low-certainty evidence suggests no clinically important differences in the safety profile between amalgam and composite resin restorations. 1
Higher urinary mercury levels were reported in children with amalgam restorations, but levels remained below known toxic thresholds. 1
No consistent or clinically important harms were found regarding renal function, neuropsychological measures, psychosocial function, physical development, or postoperative sensitivity when comparing the two materials. 1
There was no evidence of differences in neurological symptoms, immune function, or urinary porphyrin excretion between amalgam and composite resin groups. 1
Clinical Decision Algorithm
When to Choose Amalgam
For Class I and Class II posterior restorations where aesthetics is not the overriding consideration, amalgam remains the preferred material due to superior longevity and lower failure rates. 3, 1
In settings where cost-effectiveness is paramount, particularly in low- and middle-income countries, amalgam continues to be the restorative material of choice. 4, 1
When moisture control is challenging but not impossible, amalgam provides more predictable outcomes than composite resins. 1
When to Choose Composite Resin
For Class III, Class IV, and Class V cavities where aesthetics is essential, composite resin is the material of choice. 3
When the restoration must remain imperceptible at normal talking distance, composite resin alternatives are indicated despite their higher failure risk. 2
In jurisdictions where the Minamata Convention on Mercury phase-down requirements have been ratified (127 governments as of 2021), composite resins become necessary alternatives. 1
For fractured incisors and anterior teeth restorations, composite materials are universally accepted as the most popular choice. 3
Special Considerations for Composite Resin Application
Ensure surfaces are completely dry before applying adhesive, as moisture will prevent proper adhesion. 5
Apply the least amount of adhesive necessary to avoid excess material that could cause pooling and subsequent complications. 5
Special protective measures including a no-touch technique and blue light protection are required when handling resin-based materials. 4
Use copious water spray when adjusting or removing restorative materials to minimize exposure risks. 4
Common Pitfalls and How to Avoid Them
Do not assume that composite resins can universally replace amalgam – there is no single material that can replace amalgam in all applications; different materials are needed for different situations. 4
The claim that Class II composite restorations can be placed more easily and rapidly than amalgam cannot be substantiated if comparable contour and adaptation is to be achieved. 3
Restorations using amalgam substitutes (composite resins) in permanent teeth most likely fail in some critical aspect of quality guidelines when used in stress-bearing posterior applications. 2
Cost and reimbursement policies may need to be considered when amalgam alternatives are used, and material recommendations require informed consent of the patient. 4
Contemporary Context
Composite resin materials have undergone important improvements since earlier comparative trials were conducted, though the fundamental performance gap in posterior restorations persists. 1
A patient-centered rather than purely material-centered approach is recommended, considering dental factors (dentition, tooth type, cavity class), oral aspects (caries risk profiles), and patient-related factors (systemic conditions, allergies, compliance). 4
The global phase-down of dental amalgam via the Minamata Convention is an important consideration when deciding between materials, with 127 governments committed to reducing amalgam use as of 2021. 1