A Biomimetic Reinterpretation of Retention

Recommended Reading Reflection – RipeGlobal Fellowship

This week’s assigned reading, “Retention of metal ceramic crowns cemented with resin cements: Effects of preparation taper and height” (El-Mowafy et al., 1996), brings attention to a perennial challenge in restorative dentistry: how do we secure lasting, reliable retention when the tooth structure is less than ideal?

The study offers a methodical investigation into how preparation geometry—specifically taper and axial wall height—influences crown retention when using different luting agents. Using extracted molars, the authors compared the pull-off strength of crowns cemented with traditional zinc phosphate versus resin-based adhesive systems. Across both parts of the experiment, resin cements significantly outperformed zinc phosphate, especially when dealing with short or overly tapered preparations—situations that typically compromise mechanical retention.

Notably, All-Bond/All-Bond 2 yielded the highest separation forces, with results so robust that cohesive fractures of dentin were observed—something never seen with zinc phosphate. The authors concluded that resin bonding agents can compensate for less-than-ideal prep geometry, offering a valuable clinical workaround when anatomical or structural limitations prevent textbook preparation.

💡 Rethinking Retention: Enter Biomimetic Dentistry

These findings, though framed within a traditional crown and bridge context, whisper something louder beneath the surface: biomimetic principles were already beginning to show their potential.

Where traditional prosthodontics seeks mechanical resistance through long axial walls, limited taper, and often aggressive reduction, biomimetic restorative dentistry asks a different question: Can we restore teeth in a way that mimics their natural behavior instead of replacing it?

Clinicians like Pascal Magne and Matt Nejad have expanded this paradigm. In Magne’s landmark texts and clinical studies, he advocates for bonded partial restorations that rely not on retention form but on adhesive integration—respecting the structural gradient of enamel and dentin and preserving as much of the natural tooth as possible.

Similarly, Matt Nejad’s work shows how a biomimetic layering approach—often using indirect bonded restorations in combination with resin-based materials—can replace lost cusps, rebuild internal anatomy, and restore function without the need for full coverage crowns. In this view, the problem isn’t how to make short preps more retentive—it’s why we’re prepping so much in the first place.

🔍 Integrating Evidence into Practice

The El-Mowafy study becomes even more relevant when seen as a transitional piece of literature—a bridge between traditional mechanics and adhesive biomimetics. Rather than dismiss the full crown, it validates the power of adhesion as a retention mechanism. But perhaps the next step isn’t just using resin cement on compromised full-coverage preps—it’s choosing restorative designs that don’t require them at all.

A biomimetic re-interpretation of the findings might look like this:

• Short or over-tapered prep? Consider an onlay or overlay instead of a crown.

• Need retention? Use resin cement with a modern bonding protocol (e.g., Immediate Dentin Sealing).

• Want to reduce microleakage and sensitivity? Adhesively bond and preserve the internal architecture.

• Is your goal structural longevity? Mimic the elastic modulus and failure mode of natural dentin and enamel.

📘 Clinical Takeaways for the RipeGlobal Fellow

As a clinician in training for biomimetic mastery, consider these reflections:

• 🛠 Preparation design matters, but so does your material strategy. Adhesion offers a path out of mechanical compromise.

• 🧬 Tooth preservation isn’t a philosophy—it’s a technique. Your prep design, bonding protocol, and material selection must all support this goal.

• 📈 Cement choice isn’t trivial—resin cements with strong bonding systems can radically change prognosis, especially in suboptimal scenarios.

• 📚 Use studies like this one as jumping-off points—but let your philosophy be shaped by modern biomimetic evidence.

🦋 Final Word

The lesson isn’t that resin cements save bad preps. The lesson is that biomimetic thinking reframes the problem entirely. It asks us not to salvage compromised crowns—but to prevent the compromise from happening at all.

This week’s reading may be rooted in 1996, but its implications are timeless: when adhesion becomes your ally, biology becomes your blueprint.

Dr. Noor N. Ay Toghlo, BSc, DMD

El-Mowafy, O. M., Fenton, A. H., Forrester, N., & Milenkovic, M. (1996). Retention of metal ceramic crowns cemented with resin cements: Effects of preparation taper and height. The Journal of Prosthetic Dentistry, 76(5), 524–529. https://doi.org/10.1016/S0022-3913(96)90012-8