Silver Diamine Fluoride and Glass Ionomer: Dr. Geoff Knight’s Role in the Rise of Minimally Invasive Dentistry
For most of modern restorative dentistry, caries was treated as a mechanical problem. Find the decay, remove it, replace what was lost, and hope the restoration outlives the disease that created it. Dr. Geoff Macdonald Knight helped push dentistry toward a different question. Instead of asking only how much carious tissue could be removed, he asked how much tooth could safely be preserved if the biology of the lesion could first be changed.
Knight did not invent silver diamine fluoride, and he did not invent glass ionomer cement. SDF traces back to Japan in the 1960s, where Professor Mizuho Nishino and colleagues at Osaka University developed and studied 38 percent SDF. Glass ionomer cement came from Alan Wilson and Brian Kent, who introduced the material in the early 1970s. Knight’s contribution came later, at the intersection of those technologies.
His work explored whether silver fluoride, potassium iodide, and glass ionomer could be combined into a tooth preserving approach to caries management. His 2008 PhD at the University of Adelaide, The pharmacological management of dentine to protect against plaque microorganism degradation, formalized that idea. Rather than viewing demineralized dentin simply as infected material that had to be drilled away, Knight investigated whether it could be biologically modified, stabilized, remineralized, sealed, and preserved.
The laboratory evidence was intriguing. In 2005, Knight and colleagues exposed demineralized dentin to Streptococcus mutans and found that silver fluoride, with or without potassium iodide, significantly reduced bacterial growth compared with untreated controls. The treatment did not sterilize the dentin or create an impermeable barrier, but it changed the microbial environment. That was the important point.
Knight then asked whether this biological treatment could coexist with restorative dentistry. In a 2006 study, he examined the bond of conventional glass ionomer to dentin treated with silver fluoride and potassium iodide. When the reaction precipitate was left on the surface, bond strength fell. When it was washed away before placing the glass ionomer, bond strength was comparable with conventionally conditioned dentin. The implication for dentists was practical. The chemistry could work, but the clinical sequence mattered.
Another 2006 study examined ion movement between glass ionomer and treated dentin. Silver fluoride and potassium iodide did not significantly interfere with strontium transfer from the glass ionomer, and treated dentin showed greater fluoride uptake. In 2009, Knight’s group reported that silver fluoride treated dentin resisted visible Streptococcus mutans biofilm formation under laboratory conditions and was more resistant to further demineralization. Silver and fluoride could be detected hundreds of micrometers into the dentin.
These were not large clinical trials. They were laboratory experiments using extracted teeth, artificial demineralization, bacterial cultures, and materials testing. They established biological plausibility, not proof of superior patient outcomes. But they were asking questions that would later become central to minimally invasive dentistry. Can we suppress disease without removing every bit of altered dentin. Can we preserve more tooth structure. Can the restorative material become part of the biological strategy rather than simply fill the hole.
Knight was also one of four named inventors, along with Hien Ngo, Graham Craig, and Toshihiro Sekiguchi, on a 2001 patent involving silver compounds followed by potassium iodide or related salts. The goal was to reduce silver associated discoloration while preserving the caries inhibiting benefits of the treatment. The patent also described subsequent restoration with glass ionomer. This does not make Knight the inventor of SDF or the sole inventor of the silver fluoride and potassium iodide concept, but it confirms that his role was more than simply adopting an established technique.
Modern evidence has validated part of what Knight was investigating. A 2022 systematic review and meta analysis of 22 laboratory studies found that SDF pretreatment did not significantly reduce glass ionomer bond strength to dentin. That broadly supports Knight’s early conclusion that silver treatment and glass ionomer can function together at the restorative interface.
Potassium iodide is where the story becomes more complicated.
The appealing clinical narrative is obvious. Use SDF to arrest caries, add potassium iodide to reduce staining, then restore with glass ionomer. The dentist gets antimicrobial activity, fluoride, adhesion, less drilling, and a better looking result. Unfortunately, real world evidence is not that clean.
A 2021 systematic review found that adding potassium iodide generally preserved antimicrobial activity, but the evidence that it reliably prevents staining was inconsistent. A small randomized clinical study found that KI significantly reduced immediate discoloration, but by later follow up the difference between SDF and SDF plus KI largely disappeared.
A larger clinical trial in Cambodian children found that KI improved appearance but was associated with lower caries arrest. At 12 months, SDF without KI arrested about 77 percent of lesions compared with about 65 percent when KI was added. In another silver fluoride formulation, arrest fell from about 75 percent without KI to about 51 percent with it.
That trial does not settle the question for every patient, tooth, or product. But it raises an important possibility. The chemistry that reduces black staining may also reduce some of the therapeutic silver available to arrest the lesion.
That matters enormously in patient communication. Potassium iodide should not be presented as a guaranteed way to eliminate SDF staining without tradeoffs. A better explanation is that KI may improve appearance, particularly initially, but the benefit may not last and its effect on caries arrest remains uncertain.
The same caution applies to SMART, silver modified atraumatic restorative treatment, in which SDF is applied before glass ionomer. The biological rationale is strong, and Knight’s work clearly anticipated much of it. Yet a 2026 systematic review and meta analysis of six randomized clinical trials found no statistically significant difference in overall clinical success between SMART and conventional ART. SMART appears clinically viable, but current evidence does not show that adding SDF beneath glass ionomer consistently produces better outcomes.
The larger story is more important than whether one technique wins.
The 2023 American Dental Association restorative guideline conditionally favors selective carious tissue removal for many moderate and advanced lesions. The goal is to preserve tooth structure and reduce the risk of pulp exposure rather than aggressively excavating every area of altered dentin. In 2026, the World Health Organization strongly recommended 38 percent SDF twice yearly for appropriate cavitated lesions in primary teeth and root caries in permanent teeth without pulpal involvement.
Those guidelines do not validate every detail of Knight’s protocols. They do confirm that the larger philosophy he was investigating has moved into mainstream dentistry. Caries is a disease process, not simply a hole. A successful restoration does not require sterilizing the tooth. Deep lesions do not always require complete excavation. Preserving pulp vitality and healthy tooth structure may matter more than reaching perfectly hard dentin everywhere.
For practicing dentists, that changes the operatory conversation. The question is no longer only, How much decay can I remove. It is also, What tissue must I remove, what can I preserve, how can I control the disease, and what treatment gives this tooth the best chance to survive.
For a cooperative adult with excellent isolation, conventional adhesive dentistry may remain the best choice. For a young child, an older patient with root caries, a medically complex patient, or someone with limited access to care, SDF and glass ionomer can create options that involve less anesthesia, less tooth removal, shorter appointments, and fewer pulpal exposures.
The mistake is turning minimally invasive dentistry into another ideology. SDF is not magic. Glass ionomer is not the best material for every restoration. Potassium iodide does not reliably erase the staining problem. SMART has not been proven superior to ART. Teeth with spontaneous pain, necrosis, abscess, or irreversible pulpal disease need more than a bottle of SDF and a glass ionomer restoration.
Knight’s contribution is best understood within those limits. He was an early translational researcher who helped connect silver fluoride pharmacology with preservation of demineralized dentin and glass ionomer restorative chemistry. He did not invent SDF, glass ionomer, or minimally invasive dentistry. He helped build a scientific bridge between them.
When you encounter a deep carious lesion tomorrow, will your first question be what you can remove, or what you can safely save.
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