A retrospective cohort first published in the Journal of Dentistry on 2 October 2026 (October 2026 issue) followed CAD/CAM lithium disilicate overlays on root-filled molars for a mean of 5.1 years. Sixty-two of 63 analysed overlays were still in function, no overlay was replaced or lost, and both tooth-level events were endodontic rather than restorative. The authors argue that overlays may be a conservative alternative to full crowns when enough tooth structure remains, and that "survival" and "success" should be reported separately.
Root-filled molars are often restored with full crowns. As of October 2026, a new five-year dataset adds evidence for a more conservative option. The study, by Erkan, Gündoğar and Özyürek, appeared in the Journal of Dentistry under the title "Five-year clinical performance of CAD/CAM lithium disilicate overlay restorations in endodontically treated molars: A retrospective cohort study." For dental professionals in Toronto and across Canada who place, prescribe or mill indirect restorations, the paper is worth reading less for its headline survival number than for how it separates what failed from what merely needed maintenance.
What did the study look at?
According to the abstract, the authors identified 93 lithium disilicate overlays placed between 2016 and 2021 on endodontically treated molars. Of those, 63 overlays in 59 patients attended recall and were analysed. One operator performed all procedures, and every tooth had been root-treated for irreversible pulpitis without a periapical radiolucency.
Two calibrated examiners graded the restorations using the revised FDI criteria before any intervention, with a reported weighted kappa above 0.90. Outcomes were estimated with the Kaplan-Meier method.
The design choice that sets this paper apart is its endpoints. Instead of one blended "success rate," the authors tracked three outcomes separately:
- Tooth survival — the tooth is retained (extraction counts as the event).
- Restoration survival — the original overlay is still in place.
- Restoration success — the overlay needed no intervention at all.
Non-surgical retreatment was recorded as a separate tooth-level event. That distinction matters, because a tooth can keep its overlay and still need endodontic attention, and an overlay can need a polish without anything having "failed."
What were the five-year results?
The abstract reports that 62 of the 63 evaluable restorations were in function at five years. The headline figures:
- Tooth survival: 98.4% (95% CI 89.3–99.8).
- Survival free of endodontic re-intervention: 96.8% (95% CI 87.9–99.2).
- Restoration survival: 100% — no overlay was replaced or lost.
- Restoration success: 88.8% (95% CI 77.9–94.5), or 90.4% if the one endodontic access is excluded.
Two tooth-level events occurred, both at 24 months and both endodontic: one extraction and one retreatment carried out through the overlay. No restoration was graded 5 in any FDI category.
Seven interventions were performed between 12 and 60 months: four refinishing procedures, two composite repairs and one endodontic access. No overlay was replaced or lost.
Why does separating survival from success matter?
The authors' main interpretive point is that restorative and biological outcomes "behave as separate endpoints." Both tooth-level events in this cohort were endodontic, not restorative. The interventions on the overlays themselves were refinishing and small repairs; the two tooth-level events were endodontic, not restorative.
That framing is practical for case presentation. A single survival figure tells a patient the restoration will probably still be there in five years. A success figure tells them how likely it is to need some chairside attention along the way. The authors state that reporting both "gives clinicians a more realistic picture of the maintenance such restorations are likely to require."
Pro Tip: When you present an overlay as an alternative to a crown, give the patient two numbers rather than one: the likelihood the restoration stays in place, and the likelihood it needs a polish or repair at some point. Write both into the treatment note so the expectation is documented before the first recall.
Should overlays replace crowns on root-filled molars?
The paper does not claim that. Its stated clinical significance is narrower: overlays "may offer a conservative alternative to full crowns for endodontically treated molars with sufficient residual tooth structure." The qualifier carries weight. Case selection — how much coronal structure is left, wall thickness, occlusal load — remains a clinical judgment the study cannot make for you.
Several features of the design also limit how far the numbers travel:
- Retrospective, with loss to recall. Thirty of the 93 identified overlays were not analysed. Patients who return for recall can differ from those who do not.
- One operator. All procedures were performed by a single clinician. Results from one operator may not match those of a broader group of dentists.
- A defined case mix. Every tooth was treated for irreversible pulpitis without a periapical radiolucency. Teeth with a periapical radiolucency were not included.
- Modest sample. Sixty-three restorations produce wide confidence intervals — tooth survival, for example, spans 89.3% to 99.8%.
None of this undermines the findings. It places them where they belong: as encouraging mid-term data for a specific, well-selected group of teeth, not as a universal rule.
What does this mean for Canadian practices?
For practices in Toronto, Mississauga, Markham and elsewhere in Ontario that already mill chairside or work with a lab on CAD/CAM ceramics, the study offers three takeaways.
First, case documentation. If you choose an overlay over a crown on a root-filled molar, record why: the remaining tooth structure, the endodontic status and the alternatives discussed. That record supports the informed-consent conversation and makes the reasoning clear to anyone who treats the tooth later. Follow your provincial regulator's record-keeping requirements — in Ontario, the Royal College of Dental Surgeons of Ontario (RCDSO).
Second, recall planning. The interventions in this cohort ran from 12 to 60 months. Building a check of overlay margins and surface finish into each recall visit fits what the data show patients may need.
Third, endodontic follow-up. Both tooth-level events were endodontic and both occurred at 24 months. Periodic radiographic review of root-filled teeth under overlays is also worth scheduling.
Pro Tip: Before presenting the option, check how the patient's benefit plan classifies an onlay or overlay compared with a crown. Coverage rules differ between plans, and the patient's share can affect whether they accept the plan.
EBIKO Dental will continue monitoring restorative research relevant to Canadian dental professionals. For the bonding side of glass-ceramic restorations, see the supply resources at EBIKO Dental.
Sources
- Erkan E, Gündoğar M, Özyürek T. Five-year clinical performance of CAD/CAM lithium disilicate overlay restorations in endodontically treated molars: A retrospective cohort study. Journal of Dentistry, first published 2 October 2026 (October 2026 issue). DOI: 10.1016/j.jdent.2026.107090. Record: Europe PMC 42826920.
Frequently Asked Questions
Q: How long do lithium disilicate overlays last on root-canal-treated molars?
In a 2026 retrospective study in the Journal of Dentistry, 62 of 63 analysed overlays were still in function after a mean of 5.1 years, and no overlay was replaced or lost. Kaplan-Meier restoration success — no intervention of any kind — was 88.8%.
Q: Is an overlay a replacement for a crown after a root canal?
The study's authors say overlays may offer a conservative alternative to full crowns for root-filled molars with sufficient remaining tooth structure. They do not claim overlays suit every case, and their data come from one operator and a defined group of teeth.
Q: What problems did overlays have in the five-year study?
Seven interventions were recorded: four refinishing procedures, two composite repairs and one endodontic access. The two tooth-level events — one extraction and one retreatment — were both endodontic rather than failures of the overlay itself.