Dental Materials FAQ.
Short answers to recurring questions about restorative materials — the ones that come up chairside, often with a patient waiting for a response.
Can a fractured ceramic restoration be repaired in the mouth?
Sometimes, and always as a temporizing measure rather than a definitive solution. Composite repair depends on surface treatment appropriate to the substrate, which differs between a glass ceramic and zirconia — hydrofluoric acid and silane will bond to lithium disilicate but do essentially nothing to zirconia, which needs air abrasion and a phosphate-monomer primer.
The bond achieved is considerably weaker than the original material, and the repair is visible under most lighting. It buys time, particularly where a patient cannot be seen for definitive treatment immediately.
More usefully, a fracture is information. Ask why it happened — clearance, occlusal loading, unsupported ceramic — because replacing it without answering that produces the same result again.
Do zirconia restorations stain or discolour over time?
Zirconia itself is stable and does not take up stain the way an acrylic or composite surface does. What can change is the applied surface — extrinsic stains and glaze can wear, particularly on occlusal surfaces in function.
Where a restoration relied heavily on surface characterization to achieve its shade, that characterization diminishes as it wears, and the restoration trends toward the underlying blank shade. This is one of several arguments for shade being intrinsic to the material where possible rather than painted on.
Surface roughening from wear can also make a restoration accumulate extrinsic staining from diet more readily than a polished one.
Are metal-free restorations inherently better?
Not inherently. Metal-free is a preference many patients express and a reasonable one to accommodate, but it is not a clinical superiority claim.
Metal-ceramic and cast gold restorations have the longest clinical track records of any restorative option, perform in situations where ceramics struggle, and remain the right answer for certain long spans, non-ideal preparations, and cases involving attachments or existing partial dentures.
Where a patient has a genuine sensitivity, or where aesthetics govern, all-ceramic is clearly indicated. Where the choice is being made on a general impression that metal is outdated, it is worth a conversation.
Can patients be allergic to dental alloys?
Yes, and nickel is by far the most common. Nickel sensitivity is reasonably prevalent, more so in women, and often already known to the patient through reactions to jewellery.
It is worth asking directly before prescribing a base-metal alloy, and worth recording the answer on the prescription. Reactions to high noble alloys are uncommon.
Where sensitivity is known or suspected, high noble alloys or all-ceramic options avoid the question entirely. Alloy identification certificates provide a record of what was actually used.
How long should a restoration last?
There is no single answer, and any specific figure quoted without qualification should be treated with suspicion. Longevity depends on the material, the preparation, the occlusion, the patient's function and hygiene, and the quality of the margin far more than on the material alone.
What can be said usefully is that the dominant failure modes differ. Restorations fail through secondary caries at the margin, through fracture, through loss of retention, and through periodontal or endodontic problems in the underlying tooth — and different materials shift the balance between those.
For a patient asking, the honest framing is that a well-made restoration on a well-prepared tooth in a well-maintained mouth lasts a long time, and that the variables they control — hygiene, splint wear, review attendance — matter considerably.
Can zirconia be bonded, or must it be cemented?
It can be either, which is one of its practical advantages. Zirconia has sufficient strength that it does not depend on an adhesive bond the way lithium disilicate does, so a retentive preparation can be conventionally cemented with a resin-modified glass ionomer perfectly predictably.
Where bonding is wanted — a short preparation, limited retention form — the protocol is air abrasion with fine alumina followed by a primer containing a phosphate monomer such as MDP. Hydrofluoric acid does not etch zirconia.
The most common error is treating zirconia as though it were an etchable glass ceramic, which produces a bond that is essentially decorative.
Will a ceramic crown wear the opposing tooth?
It can, and how much depends more on surface finish than on the material's hardness. A well-polished restoration is considerably kinder to opposing enamel than a rough one, and polished monolithic zirconia performs better in this respect than its hardness would suggest.
The practical risk is adjustment. A restoration ground at delivery and not properly repolished presents a rough surface to the antagonist for the life of the restoration.
Where preserving intact opposing enamel is a specific concern — heavy function, an unrestored antagonist — cast gold remains the kindest option available.
Can the shade be altered after a restoration is made?
Within limits. Extrinsic staining and re-glazing can shift shade modestly, usually toward higher chroma or lower value, and can add characterization. Making a restoration lighter is considerably harder than making it darker.
For a layered restoration, more substantial change means removing and rebuilding ceramic, which is effectively a remake of the aesthetic work. For a monolithic restoration milled from a shaded blank, the intrinsic shade cannot be changed at all.
This asymmetry is a reason to try in demanding anterior cases before final glazing, while the ceramist can still alter both form and colour.
What happens to restorations when a patient bleaches?
Nothing. Bleaching agents lighten natural tooth structure and have no effect on ceramic, composite or metal restorations.
The consequence is that a patient who bleaches after restorative work will end up with restorations that are now darker than their natural teeth. Where bleaching is planned, it should be completed first, with an interval for the shade to stabilize before the definitive shade is taken.
This needs raising with the patient before treatment. A patient who bleaches six months later and finds their anterior crown no longer matches will reasonably feel they were not warned.
In short
- Ceramic repair is temporizing; a fracture is information about the cause
- Ask about nickel sensitivity before prescribing base-metal alloys
- Zirconia can be bonded or conventionally cemented — but not HF-etched
- Making a restoration lighter after fabrication is far harder than darker
- Complete bleaching and let the shade stabilize before taking a definitive shade
More on clinical
Discuss a case
Where a case sits between options, a short conversation before preparation is usually quicker than resolving it afterwards.