Replacing crowns and bridges: when it is needed and what to assess first

Many patients arrive at their first visit with a precise question: ‘my crowns are twenty years old, do they need redoing?’. It is a fair question, but put this way it contains a misunderstanding. The age of a prosthesis is not, in itself, a reason to replace it. The real reasons lie elsewhere: a biological problem in the teeth that support it, a mechanical failure, an aesthetic integration that no longer suits the patient’s face. Above all, we need to understand why the existing prosthesis has deteriorated.

This article deals with fixed prostheses on natural teeth, that is, single crowns and bridges: what patients often call ‘caps’. We look at what the literature says about how long they last, the most common causes of ‘failure’, when repair makes more sense than replacement, and what is worth assessing before deciding.

How long does a fixed prosthesis on natural teeth last?

Let us start with the finding that might seem to make this article unnecessary: fixed prostheses on natural teeth last a long time. A systematic review published in 2004 in Clinical Oral Implants Research, pooling nineteen studies with a mean clinical follow-up of at least five years, estimated a ten-year survival probability of 89.1% for bridges (1). A later review by the same research group, in 2007, confirmed similar values: 93.8% at five years and 89.2% at ten years for conventional bridges, those anchored to a tooth at each end (2).

Nine bridges out of ten, then, are still in the mouth after ten years. That is a solid result and should not be played down. But the figure hides a distinction that changes how it should be read.

What is the difference between a ‘surviving’ prosthesis and a healthy one?

In the literature, ‘survival’ simply means that the prosthesis is still in the mouth. It says nothing about its condition. A crown with decay beneath its margin, a bridge supported by a tooth that has lost its vitality, chipped ceramic: all of these are ‘surviving’ prostheses.

This is why reviews also measure ‘success’, meaning a prosthesis that has remained in place without any complication. In the same 2004 study, against a survival rate of 89.1%, ten-year success was 71.1% (1). The most recent meta-analysis, published this year in the International Journal of Prosthodontics, found that only 71% of bridges reach five years without complications (3). The two figures are not directly comparable, since they come from different sets of studies, materials and time frames (ten years in the first case, five in the second), but they tell the same story: there is a gap between the prosthesis that holds and the prosthesis that is healthy, and that gap is where the decision whether and how to intervene is made.

There is also an observation that numbers alone do not convey. An old prosthesis is also a record: it bears witness to the choices of whoever designed it, the diagnosis made at the time, the limits of the materials then available. Reading it carefully before removing it is often the quickest way to understand what has happened.

Why do crowns and bridges ‘fail’?

The causes are of two kinds, biological and technical, and the distinction is not academic: they call for different responses.

In conventional bridges the most frequent complications are biological, particularly decay in the abutment teeth and loss of pulp vitality, that is, of the nerve (2). Both can develop silently, beneath a prosthesis that looks intact from the outside. The 2004 review estimated a ten-year risk of 2.6% of losing the bridge to decay and 0.7% to recurrent periodontitis (1). These percentages are low when they refer to loss of the prosthesis, but complications that stop short of loss are far more frequent, as the gap between survival and success shows (1).

Among technical causes, the same review reports ten-year risks of 6.4% for loss of retention (the prosthesis comes unstuck), 3.2% for material fracture and 2.1% for fracture of the abutment tooth (1).

The design of the prosthesis matters. Bridges with a cantilevered unit, anchored on one side only, showed ten-year survival of 81.8% and success of 63%, lower than conventional bridges (4). Loss of vitality in the abutment teeth was the most frequent biological complication. This does not mean a cantilever bridge should be ruled out: it means that, when one is chosen, it is chosen knowing the safety margin is smaller.

Does a margin below the gum really make a difference?

This is one of the most interesting questions, because it concerns a detail the patient never sees. A longitudinal study that followed 160 middle-class Scandinavian men for twenty-six years, with good to moderate oral hygiene and regular check-ups, compared sites where a restoration had been placed with its margin below the gum against similar sites with no restoration or with a margin more than one millimetre from the gum (5). Subgingival restorations were associated with greater loss of periodontal attachment, that is, of the tooth’s support, clinically detectable as early as one to three years after placement.

The finding should be read with caution: it comes from a single cohort, made up of men only, and the study concerned restoration margins in general, not specifically those of crowns. But it is consistent with a principle well known in prosthodontics: the margin of a crown is where mechanics meets biology, and any imprecision there produces a cost that is paid over time. When assessing a prosthesis for replacement, the position and quality of the existing margins are among the first things to examine, and correcting them is often one of the primary reasons to intervene.

Redo everything or repair?

A prosthesis with a problem does not always need replacing in full. A small chip in the ceramic, a margin that can be corrected, decay that can be reached without removing the crown: in some cases repair is a reasonable option.

The evidence supporting this choice, however, is thin. A 2022 systematic review and meta-analysis found no difference in failure risk between repaired and replaced restorations, but the certainty of evidence was very low and the study covered only direct composite and amalgam fillings, not crowns or bridges (6). For fixed prostheses, good-quality direct comparisons are lacking.

Our reading, which is an interpretation rather than published data, is that the principle of minimal intervention also holds in prosthodontics: a bridge is not redone because it is old, but because repair cannot resolve the cause of the problem. If the cause is extensive decay beneath the margin, a compromised abutment tooth or an inadequate prosthetic design, repair is unlikely to be conclusive. If the cause is small, isolated mechanical damage, redoing everything may be excessive.

Which material for the replacement?

Materials have changed a great deal over the past twenty years, and ‘metal-ceramic or all-ceramic?’ is one of the most frequent questions. The honest answer is that there is no single best material: it depends on the type of prosthesis.

For single crowns, the 2026 meta-analysis found very similar five-year survival rates for the materials most used today: 98.5% for monolithic lithium disilicate, 97.3% for veneered zirconia, 97.1% for metal-ceramic and 96.8% for monolithic zirconia (7). Monolithic crowns, made from a single block without a veneering ceramic layer, showed fewer fractures and less chipping.

For bridges the picture is different. The companion meta-analysis by the same group estimated five-year survival of 92.9% for veneered zirconia, 91.3% for metal-ceramic, 87.9% for monolithic zirconia and 82.5% for lithium disilicate, the last significantly lower than metal-ceramic (3). Framework fractures were more frequent with the weaker ceramics. An earlier review, in 2015, had already found more framework fractures with reinforced glass ceramics, but rated zirconia less favourably: 90.4% at five years against 94.4% for metal-ceramic, with more chipping and loss of retention (8). The assessment of zirconia has therefore improved between the two reviews, probably reflecting in part the evolution of the materials.

In practice, a material that is excellent for a single crown can be a weak choice for a three-unit bridge. The choice has to be made case by case, taking into account the position in the mouth, chewing forces, any bruxism and aesthetic requirements. It is a clinical decision, not a catalogue one.

Is it better to replace the bridge with implants?

Many patients consider this alternative, sometimes as if an implant were automatically a step forward. The data tell a more nuanced story.

In the 2007 review, survival of bridges on implants alone was comparable to that of conventional bridges on natural teeth: 95.2% against 93.8% at five years, 86.7% against 89.2% at ten (2). The difference lay in complications. At five years, 38.7% of patients with implant-supported bridges had experienced some complication, against 15.7% of patients with conventional bridges; technical complications, such as ceramic chipping or screw loosening, were significantly more frequent on implant reconstructions (2). With similar survival, then, implant reconstructions more often require maintenance. Combined bridges, anchored partly to teeth and partly to implants, had a lower ten-year survival of 77.8%.

The same authors place conventional bridges, bridges on implants alone and single crowns on implants among the first choices, and list combined and cantilever bridges as second choices (2). In practice, when the abutment teeth are healthy and well supported, redoing the bridge on those teeth is often the most conservative solution. When the abutments are compromised, implants are a fully valid option, to be planned with the maintenance they will require in mind. For cases involving a whole arch, we have written a dedicated article on full-arch rehabilitation on implants.

What should be assessed before deciding?

Before redoing a prosthesis, the question to ask is not which new prosthesis to make, but why the existing one no longer works. Answering it requires a complete diagnosis.

First, radiographs are needed to see what is happening beneath the prosthesis: decay at the margins, infection at the root, bone loss around the abutments. Each abutment tooth needs an assessment of its vitality and prognosis, because a new bridge resting on a tooth that will not last much longer is a fragile investment. A periodontal examination is needed, because periodontitis or reduced support changes the outlook. And the occlusion, the way the teeth meet, needs analysing, because excessive forces or unrecognised bruxism can contribute to fractures; we discuss this in our article on bruxism and worn teeth.

When replacement involves many teeth, the sequence matters as much as the technique: active disease is brought under control first, then the prosthesis is designed. We describe this process in our article on full mouth rehabilitation, the clinical term for what patients call ‘having all my teeth redone’.

If you have been advised to redo an extensive prosthesis and the plan does not seem clear to you, a structured second opinion is a reasonable choice: not out of mistrust, but to have a written causal diagnosis on which to base your decision.

Questions patients often ask

How often does a fixed prosthesis need redoing?

There is no expiry date. A well-designed, well-maintained prosthesis can stay in the mouth for many years; one with a biological problem may need attention after a short time. Regular check-ups matter more than age, because they allow decay, gum problems or material damage to be noticed early.

If the prosthesis does not hurt, does it still need redoing?

Not necessarily. The absence of pain, however, does not guarantee that all is well beneath the prosthesis: decay and loss of vitality in the abutment teeth can progress without symptoms. This is why the decision rests on examination and radiographs, not on how the patient feels.

Can a single crown in a bridge be replaced?

A bridge is a single prosthetic device, so as a rule one unit cannot be replaced without working on the whole bridge. If the teeth are restored with single crowns, however, only those that need it can be redone.

Does a replacement prosthesis last as long as the first?

That depends mainly on the condition of the abutment teeth and on whether the cause that led to the replacement has been corrected. A tooth that has been treated several times has less structure and a smaller safety margin: one more reason to plan the new work carefully.