IPS e.max lithium disilicate.
A glass ceramic that etches, silanates and bonds — which is both its advantage and its requirement. Tick IPS E-Max under Type of Crown.
Optical performance
Lithium disilicate remains the stronger aesthetic performer in most anterior situations. Its glass content gives optical behaviour closer to enamel: it transmits and scatters light in a way that reads as depth rather than as a uniformly bright surface.
It can be pressed or milled and then layered where a case calls for greater control of character, or used monolithically and characterized where the requirement is more modest.
For veneers, inlays, onlays and anterior crowns it is frequently the default, and reasonably so.
It depends on the bond
This is the practical difference from zirconia. Lithium disilicate is reinforced by adhesive cementation, and it does not have strength in reserve if the bond is compromised.
The protocol matters: hydrofluoric acid etch for the manufacturer's stated time, rinse and dry thoroughly, silane allowed to react, then a resin cement under proper isolation. Under-etching leaves insufficient retention; over-etching degrades the surface.
If the field cannot be isolated — a deeply subgingival margin, bleeding that will not settle — this is the wrong material regardless of its other merits, and zirconia is the better answer.
Clearance and preparation
It needs more material thickness than zirconia, particularly occlusally, and a defined chamfer or rounded shoulder rather than a feather edge.
A thin, unbonded lithium disilicate restoration compromises both requirements at once, and it is the combination that fractures.
Verify clearance before the record is taken. Zirconia versus lithium disilicate compares the thickness requirements directly.
The substrate shows through
Translucency cuts both ways. A restoration on a bright vital preparation and the same restoration on a dark post-endodontic or metal-cored preparation will not look the same however precisely the shade was matched.
Record the preparation shade with a stump guide, or photograph the prepared tooth. The technician needs it before selecting the ingot opacity — not afterwards, when the remaining options are compromises.
Pressed or milled
Lithium disilicate can be pressed from an ingot or milled from a block, and either can then be characterized on the surface or cut back and layered for greater control of internal effects.
For a straightforward posterior crown or a conservative inlay, a monolithic approach characterized on the surface is usually sufficient and stronger. For an anterior unit beside a highly characterized natural tooth, a cutback and layered approach gives the ceramist far more to work with.
Tell the laboratory which the case needs, or describe the aesthetic requirement and let the technician advise. Both are legitimate ways to prescribe.
Inlays, onlays and veneers
Much of what lithium disilicate is best at is partial coverage: inlays, onlays and veneers where the bond carries part of the load and conservation of tooth structure is the priority.
Those preparations need rounded internal line angles — sharp angles concentrate stress and are where a glass ceramic cracks — and a defined margin the laboratory can read unambiguously.
See inlays, onlays and veneers for what each asks of the preparation.
Adjusting and polishing
Lithium disilicate grinds readily with fine diamonds under water and can be polished back to a genuinely smooth surface with a conventional ceramic polishing sequence — one designed for glass ceramics rather than the diamond-impregnated instruments zirconia requires.
Repolish properly after any adjustment. Glaze does not survive grinding, and the surface left behind abrades opposing enamel for the life of the restoration if it is not brought back.
Keep separate labelled kits for glass ceramic and zirconia. Polishing zirconia covers why using the wrong one fails in both directions.
What to put on the prescription
Tick IPS E-Max, give the shade with the guide named, and mark the tooth on the design chart. Add the preparation shade for anything anterior or translucent.
Photographs with the tab in frame, taken before the teeth dehydrate, carry more than any written shade description. Use the Try In field if you want to see a demanding case before it is glazed.
More in Fixed Restorations
Send a case
Digital scans and conventional impressions are both accepted. Cases move by UPS and Purolator, and Fairmont works with practices throughout British Columbia and across Canada.