Restorative Longevity Evidence
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Direct answer
Median figures hide the message: practice-based data put the average composite at six to seven years, yet trials show annual failure rates of just 1-3 per cent — Opdam's review of posterior composites — because longevity is decided less by material than by patient risk, operator skill and cavity size. Amalgam reviews report roughly 1.6 per cent annual failure against composite's 2.9 per cent — a modest difference dwarfed by caries risk and bruxism — while secondary caries tops failure-reason lists yet is dentistry's most overdiagnosed finding: many restorations replaced for "recurrent caries" show no pathology. Hence the modern philosophy: monitor rather than replace, repair rather than re-restore, and read every number with its population attached.
What you must remember
- Headline numbers: posterior composite annual failure rate 1-3 per cent in reviews (Opdam 2014); practice-based average composite lifespan around six to seven years; amalgam about 1.6 per cent annual failure versus composite's 2.9 per cent in a common comparison.
- Failure reasons ranked: secondary (recurrent) caries first in most series, then bulk and marginal fracture, wear, and endodontic complications — with material-specific patterns (composites to fracture and secondary caries, amalgams to fracture and marginal breakdown).
- The overdiagnosis finding: a substantial share of restorations replaced for secondary caries are sound on re-examination — "replacement dentistry" — the evidence base for monitoring.
- Patient factors dominate: caries risk, bruxism, oral hygiene and socioeconomic status move survival more than material class; operator factors (isolation, matrix discipline) sit just behind.
- Cavity size penalty: failure risk rises steeply with number of surfaces — an MOD composite fails at multiples of the rate of a single-surface one; large defects belong to indirect restorations.
- Repair philosophy: repair of a localised defect (refinishing, marginal repair) extends restoration life and preserves tooth structure, and is endorsed in contemporary consensus statements over wholesale replacement.
- Evidence hierarchy: systematic reviews of practice-based networks out-predict manufacturer claims; ask who was restored, by whom, and for how long.
- Amalgam's exit: with the Minamata parties deciding in 2025 to end amalgam use by 2034, longevity comparisons increasingly answer a question about a material being retired — the contemporary framing examiners have begun to test.
Reading an annual failure rate like an examiner
A review quotes 3 per cent annual failure for posterior composites in a practice network: 97 per cent survive each year, compounding to about 74 per cent at ten years (0.97 to the power of ten) — respectable, and better than the "composites last five years" folklore. Vary the population as the exam does: high-caries-risk patients multiply the rate; single-surface restorations in low-risk adults fall toward 1 per cent (about 90 per cent at ten years). Compare materials fairly: the amalgam-composite gap (1.6 versus 2.9 per cent) is real but small beside risk-factor swings, and shrinks further with rigorous isolation — the reason reviews still endorse composite in most posterior situations. Apply the policy lens: with amalgam exiting by 2034, the question becomes "how do I make composites last" — rubber dam, matrix discipline, incremental placement, cuspal coverage for the big ones. Longevity literacy is a number, a population, a time horizon, and a decision.
Where students slip
Quoting a single survival percentage without its population is the first error — trial-condition numbers transferred to high-risk practice overpromise by years. The second is treating secondary caries as an objective finding: the diagnosis is notoriously operator-dependent, and a candidate who says "stain at a margin is not caries until it is" shows the critical reading examiners reward. The third is missing the repair option in scenario stems: a localized marginal defect on an otherwise serviceable restoration is repaired or refinished, not replaced — replacement loses tooth structure the tooth never recovers. Fourth, the arithmetic: converting an annual failure rate into a ten-year survival in one line separates candidates who understand the evidence from those who memorise it.
Frequently asked questions
What annual failure rates do posterior composites show?
About 1-3 per cent per year in systematic reviews of posterior composites, with practice-based average lifespans around six to seven years.
What is the commonest recorded reason for restoration replacement?
Secondary caries, followed by fracture — though a substantial proportion of such diagnoses are overcalls, supporting monitoring and repair.
How do amalgam and composite compare in longevity reviews?
Amalgam shows lower annual failure (about 1.6 versus 2.9 per cent for composite in a commonly cited comparison), a gap smaller than the effect of patient risk factors.
Why do practice-based and trial longevity figures differ?
Trial populations and maintenance are idealised; practice-based networks include real-world risk factors and technique variation, producing shorter survival.
What is the repair-over-replacement philosophy?
Localised defects are repaired or refinished while the sound remainder is retained, preserving tooth structure and extending restoration life — now preferred to wholesale replacement.