BioFlex vs Stainless Steel Hall Crowns: 12-Month Trial

A 12-month randomized trial in Clinical Oral Investigations found no statistically significant difference in success between BioFlex crowns and stainless steel crowns placed with the Hall Technique on primary molars (91.9% vs. 94.6%). Children and parents rated BioFlex higher, but plaque was higher and the only two perforations were in the BioFlex group, and the authors describe this use of BioFlex as off-label.

BioFlex crowns, which the trial's authors describe as tooth-coloured crowns made from a hybrid resin polymer, are now being tested with the Hall Technique. The authors call this application off-label, and the manufacturer's website says the crowns are not recommended for the Hall Technique. As of November 2026, a two-arm randomized trial by Ramadan, Baraka, Dean and Wahba, published online on October 22, 2026 in Clinical Oral Investigations (volume 30, issue 11, article 544), offers 12-month data on the comparison. For dental professionals in Toronto, the GTA and across Canada who treat young children, the result is interesting but narrow: one tooth type, one age band and one year of follow-up.

This summary is based on the full open-access article and the trial's ClinicalTrials.gov registry record.

What Is the Hall Technique?

A 2022 systematic review in the Japanese Dental Science Review describes the Hall Technique as cementing a preformed metal crown over a carious primary molar, with no carious tissue removal, no tooth preparation and no local anaesthesia. The authors add that success depends on an effective marginal seal, which arrests the caries.

The new trial keeps that placement approach and asks how a BioFlex crown (NuSmile, which spells the product "BioFlx") compares with a 3M stainless steel crown when both are placed this way. The authors say the off-label use was disclosed to parents or guardians during informed consent.

How Was the Trial Designed?

• Participants: 74 healthy, cooperative children aged 4 to 6 years without bruxism, at moderate to high caries risk, treated at one centre: Alexandria University in Egypt.
• Teeth: asymptomatic mandibular second primary molars with active ICDAS 3 to 5 lesions (ICDAS 3 only with radiographic dentine involvement), with one tooth per child.
• Allocation: random assignment, 1:1, to a BioFlex crown or a stainless steel crown.
• Cement: resin-modified glass ionomer in both groups.
• Primary outcomes: clinical and radiographic success.
• Secondary outcomes in this report: plaque and gingival indices, plus child and parent satisfaction.
• Registration: NCT06847646, with Alexandria University listed as lead sponsor. The authors note that it was registered retrospectively, after recruitment began.

The registry record shows what the team counted as failure. Crown perforation and crown loss where the tooth could be re-treated were minor failures. Pulpitis or a fistula or abscess requiring pulpotomy, pulpectomy or extraction was a major failure. Radiographic success meant no radicular radiolucency, no internal or external root resorption and no widening of the periodontal ligament space. Teeth that failed clinically were not assessed radiographically and counted as failures, so the authors caution that radiographic success was not completely independent of clinical success.

What Did the Trial Find at 12 Months?

Success was 91.9% with BioFlex crowns and 94.6% with stainless steel crowns, a difference the authors report as not statistically significant (risk ratio 0.97, 95% CI 0.86 to 1.10). The gap comes down to one crown: 34 of 37 versus 35 of 37. No major failures occurred in either group, and no participants were lost to follow-up.

Read that interval carefully. The authors state that the trial was designed as a superiority trial, not a non-inferiority or equivalence trial, so this result does not show the crowns are equivalent. Applied to the 94.6% stainless steel rate, the lower end of the interval works out to about 81% success (our arithmetic). That is about 13 points below the stainless steel rate, about twice the 6.65-point difference the authors treated as clinically relevant when sizing the trial, although they set no formal non-inferiority margin.

What Happened With Perforation and Crown Loss?

• Perforation: two BioFlex crowns (5.4%) and no stainless steel crowns by 12 months (risk ratio 5.00, 95% CI 0.25 to 100.72). That is not statistically significant, and with so few events the interval is very wide.
• Crown loss: one BioFlex crown (2.7%) and two stainless steel crowns (5.4%) at 12 months, also not statistically significant.

The authors still treat perforation as a concern. They write that it occurred exclusively in the BioFlex group and that its long-term implications for restoration longevity and pulpal health remain uncertain. They suggest it may reflect vulnerability to occlusal wear, report that the affected children often ate hard foods such as popcorn, and caution that the risk may increase beyond one year. These are the authors' interpretations, not tested findings.

Where Did the Two Crowns Differ?

The gaps appeared in the secondary outcomes, and they do not all point the same way.

The authors conclude that BioFlex crowns may be considered an acceptable short-term esthetic alternative, and that the findings should be interpreted with caution until longer studies report. They suggest BioFlex may be a reasonable option for teeth needing short- to medium-term coverage rather than long-term restorations, and their abstract calls for careful case selection.

The registry also lists temporomandibular joint function and occlusal vertical dimension as secondary measures. The authors say those results will appear in a companion manuscript.

How Does This Fit With Earlier Hall Technique Evidence?

A systematic review published in Evidence-Based Dentistry (Tedesco and colleagues) reported a pooled success rate of 98% (95% CI 97% to 99%) at 12 months in randomized trials, and 95% (95% CI 91% to 100%) up to 89 months in non-randomized studies. Its authors rated the certainty of evidence as moderate to low, in part because blinding was generally not feasible with visibly different materials.

The new trial's authors acknowledge a similar problem. Blinding the operator and participants during treatment was not possible, and they say the lack of independent blinded outcome assessment may have influenced subjective measures. The review's pooled figures come from a different body of studies, so they are context, not a benchmark for this one trial.

What Should Canadian Dentists Take From It?

One short-term, single-centre trial is thin evidence on its own for changing practice in Ontario or elsewhere, and the article does not address Canadian availability, cost or insurance coverage. Four practical points follow.

• Note the off-label status. NuSmile's website currently says BioFlx crowns are not recommended for the Hall or Modified Hall technique, or for patients with bruxism, and its FAQ cites a lack of clinical data for Hall use. The trial's authors read this as an evidence gap rather than an absolute contraindication, but that is their interpretation. Read the current instructions for use before considering this.
• Keep the findings inside the study's limits. The data cover healthy, cooperative 4- to 6-year-olds without bruxism, at moderate to high caries risk, treated at one centre. Teeth were asymptomatic mandibular second primary molars with active lesions into dentine (ICDAS 4 to 5, or ICDAS 3 with radiographic dentine involvement) and no clinical or radiographic pulpal involvement. Other teeth, ages and medical histories were not part of this trial.
• Treat one year as an early read. A crown placed at age 4 may need to last much longer than the follow-up here, and the authors themselves ask for longer evaluation.
• Confirm licensing before you buy. On November 4, 2026, EBIKO Dental searched Health Canada's Medical Devices Active Licence Listing under both "BioFlex" (the trial's spelling) and "BioFlx" (NuSmile's spelling), and reviewed the licences listed under NuSmile. "BioFlx" returned no records. None of the 39 "BioFlex" device records named a crown or dental product. None of NuSmile's 14 licence records uses either name, though other NuSmile crowns are listed. A name search is not proof either way, so ask the supplier for the licence number.

Pro Tip: If a parent asks about an esthetic Hall crown, cover all of it in one conversation: parents and children rated BioFlex higher, plaque was higher at 6 and 12 months, two BioFlex crowns perforated versus none with stainless steel (not statistically significant), and the trial's authors describe this use as off-label.

EBIKO Dental will continue monitoring research on paediatric restorative care for dental professionals in Canada. More industry coverage is available at ebiko.ca.

Sources

• Ramadan Y, Baraka M, Dean JA, Wahba NA. Clinical and radiographic success of bioflex versus stainless steel crowns using the hall technique in primary molars: a 12-month randomized controlled trial. Clin Oral Investig. 2026;30(11):544.
• ClinicalTrials.gov record NCT06847646
• Hu S, et al. Hall technique for primary teeth: A systematic review and meta-analysis. Jpn Dent Sci Rev. 2022;58:286-297.
• Tedesco TK, et al. Success rate of Hall Technique for restoring carious primary molars: systematic review and meta-analysis. Evid Based Dent. 2025;26(1):65-66.
• NuSmile BioFlx product page and FAQs
• Health Canada, Medical Devices Active Licence Listing

Frequently Asked Questions

Q: Are BioFlex crowns as good as stainless steel crowns for the Hall Technique?

This trial cannot establish that. It found no statistically significant difference in success at 12 months (91.9% vs. 94.6%), but it was not designed to test equivalence or non-inferiority, and it included 74 children. The authors describe this use of BioFlex as off-label, the manufacturer's website does not recommend it for the Hall Technique, and the authors call for longer-term studies.

Q: What were the downsides of BioFlex crowns in this trial?

Plaque was higher with BioFlex at 6 and 12 months. Two BioFlex crowns perforated and no stainless steel crowns did, which was not statistically significant, but the authors say the long-term implications are uncertain and recommend careful case selection.

Q: Are BioFlex crowns available in Canada?

EBIKO Dental has not confirmed Canadian availability. Searches of Health Canada's licence listing on November 4, 2026 under "BioFlex" and "BioFlx", and of the licences listed under NuSmile, found no record using either name for a crown or dental product. That is not conclusive, so ask the supplier for its Health Canada licence number before purchasing.