Dental Literature Watch · RCT · Implants
Zirconia vs PFM implant crowns: the gum cannot tell the difference
TL;DR
- Monolithic zirconia and PFM implant crowns behaved the same at 6 months — clinically, radiographically, and under the microscope.
- The histology is the point. Soft-tissue biopsies were taken between the implant and the adjacent tooth and scored for inflammatory cells and fibroblast density. Crown material had a negligible effect.
- Tissue region, not material, drove everything (p < 0.001). Where you look in the tissue matters far more than what the crown is made of.
- Incidental but useful anatomy: inflammatory infiltrate peaked in the sulcular epithelium around implants and the junctional epithelium around teeth. Fibroblast density peaked in the junctional epithelium at both.
- Clinical parameters — plaque, probing depth, bleeding on probing, keratinised mucosa width, marginal bone level — were stable to 6 months in both groups.
- This is a pre-specified secondary analysis the authors themselves call exploratory: 67 of the original 83 patients, single molar implants only.
The study
| Element | Detail |
|---|---|
| Design | Pre-specified secondary analysis of an RCT; authors describe it as exploratory |
| Population | 83 patients randomised with single-tooth implants in the molar region; 67 analysed (37 ZrO2, 30 PFM) |
| Intervention | Monolithic zirconia vs porcelain-fused-to-metal single implant crown |
| Outcomes | Clinical (plaque, PD, BoP, keratinised mucosa width, marginal bone level) at implant and adjacent tooth; soft-tissue biopsy scored for inflammatory cells and fibroblasts across 4 regions |
| Follow-up | 6 months |
| Result | Comparable clinical and radiographic outcomes. Histologically, region significantly affected infiltrate and fibroblast density (p < 0.001); material did not |
| Registration / funding | NCT02272491 · implants and abutments supplied in kind by Straumann; ITI Foundation unrestricted support |
A histological null result is worth more than a clinical one here
Six months of stable probing depths could simply mean six months is too short.
A biopsy showing no material-driven difference in inflammatory infiltrate closes off the mechanism by which a difference would eventually appear — which is a stronger form of reassurance than the clinical numbers on their own.
Six months of stable probing depths could simply mean six months is too short.
A biopsy showing no material-driven difference in inflammatory infiltrate closes off the mechanism by which a difference would eventually appear — which is a stronger form of reassurance than the clinical numbers on their own.
💎 Insight — what this means chairside
The soft-tissue argument for PFM has now been tested directly
The long-running claim was that zirconia is kinder to peri-implant mucosa than metal-ceramic.
Biopsied at 6 months, that difference is not there. Neither material is punished by the tissue.
Which means the choice reverts to the criteria you can actually see: aesthetics, occlusal space, antagonist wear, cost, and what your laboratory does well.
The long-running claim was that zirconia is kinder to peri-implant mucosa than metal-ceramic.
Biopsied at 6 months, that difference is not there. Neither material is punished by the tissue.
Which means the choice reverts to the criteria you can actually see: aesthetics, occlusal space, antagonist wear, cost, and what your laboratory does well.
Peri-implant sulcular epithelium is where the inflammation sits
Around implants the infiltrate concentrated in the sulcular epithelium; around natural teeth it concentrated in the junctional epithelium.
That is a different tissue architecture, and it is a reasonable histological correlate of why implant sulci are less forgiving of plaque than tooth sulci.
Around implants the infiltrate concentrated in the sulcular epithelium; around natural teeth it concentrated in the junctional epithelium.
That is a different tissue architecture, and it is a reasonable histological correlate of why implant sulci are less forgiving of plaque than tooth sulci.
Six months of stability at the adjacent tooth too
The design measured the neighbouring natural tooth as well, and it stayed stable.
Useful when a patient asks whether the crown will affect the tooth next to it.
The design measured the neighbouring natural tooth as well, and it stayed stable.
Useful when a patient asks whether the crown will affect the tooth next to it.
⚠️ The catch
Exploratory secondary analysis — the authors' own word
The parent RCT was not powered to detect a histological difference between materials, and a secondary analysis of 67 patients cannot rule out a small one.
"Negligible effect" here means no signal at this sample size and timepoint, which is not the same as proof of equivalence. This is why the item sits at 2 rather than higher.
The parent RCT was not powered to detect a histological difference between materials, and a secondary analysis of 67 patients cannot rule out a small one.
"Negligible effect" here means no signal at this sample size and timepoint, which is not the same as proof of equivalence. This is why the item sits at 2 rather than higher.
Six months is short for a peri-implant question
Peri-implantitis is a multi-year problem. Marginal bone level changes were limited in both groups, but limited change at 6 months is the expected result regardless of material.
The histology partly compensates by looking at mechanism rather than waiting for the endpoint — partly, not fully.
Peri-implantitis is a multi-year problem. Marginal bone level changes were limited in both groups, but limited change at 6 months is the expected result regardless of material.
The histology partly compensates by looking at mechanism rather than waiting for the endpoint — partly, not fully.
Sixteen of 83 randomised patients are missing from the analysis
Sixty-seven had complete clinical, radiographic and histological data. The abstract does not explain the attrition.
Requiring a biopsy for inclusion is a plausible and fairly benign reason, but it is not stated.
Sixty-seven had complete clinical, radiographic and histological data. The abstract does not explain the attrition.
Requiring a biopsy for inclusion is a plausible and fairly benign reason, but it is not stated.
Industry in-kind support is declared
Straumann supplied implants and abutments; the ITI Foundation gave unrestricted funding. The authors state the funder had no role in design, analysis or interpretation.
The finding is a null result on crown material, which is not the kind of finding a component manufacturer benefits from — but the declaration belongs on the record.
Straumann supplied implants and abutments; the ITI Foundation gave unrestricted funding. The authors state the funder had no role in design, analysis or interpretation.
The finding is a null result on crown material, which is not the kind of finding a component manufacturer benefits from — but the declaration belongs on the record.
⚡ Bottom line
- Choosing between monolithic zirconia and PFM for a molar implant crown → peri-implant soft tissue does not give you a reason to prefer one.
- Patient asks which is "healthier" for the gum → at 6 months, histologically, neither.
- Deciding on other grounds → aesthetics, occlusal clearance, antagonist wear, cost and laboratory capability now carry the decision.
- Tempted to treat this as settled → exploratory secondary analysis, 67 patients, 6 months. Reassuring, not definitive.
🧪 Questions
Tap an answer — instant grade, deciding line, and the trap.
In this RCT secondary analysis, what was the dominant determinant of inflammatory infiltrate and fibroblast density in the peri-implant soft tissue?
Tissue region significantly affected both outcomes (p < 0.001), while crown material had only a negligible effect — that contrast is the paper's central finding. Crown material is the hypothesis the study set out to test and the one it failed to support. Keratinised mucosa width and probing depth were recorded as clinical parameters and remained stable; neither was reported as a driver of the histological outcomes.
A patient needs a single molar implant crown and asks which material is better for the health of the surrounding gum. Based on this trial, what is the most accurate answer?
Comparable clinical, radiographic and histological outcomes is exactly what the trial reports, which moves the decision to aesthetics, occlusion, wear, cost and laboratory. Zirconia for less plaque is the widely repeated claim this trial did not confirm — plaque control record was among the comparable parameters. PFM better tolerated is the same error in reverse. Zirconia produced less infiltrate states the opposite of the histological result.
Why does this study warrant caution despite a clean null result?
Exploratory secondary analysis, 67 of 83 patients, 6-month timepoint — the study was not powered to exclude a small material effect, and absence of a signal is not proof of equivalence. Unregistered is false: it is NCT02272491. Materials no longer used is false — monolithic zirconia and PFM are both current. No histological outcome inverts the study's main strength; the biopsy data are precisely what makes the null result interesting.