Penetration depth and enamel hardness in MIH-affected molars treated with resin infiltrate and fissure sealant

Researchers from NIOM have investigated and compared interaction of two minimally invasive materials with enamel in molar-incisor hypomineralisation (MIH) diagnosed teeth.

“Early, minimally invasive intervention can make a real difference for children with MIH-affected teeth,” says Scientist Amela Tulek, NIOM.

“By understanding how these materials affect the enamel properties, clinicians can make a more informed treatment choices”, she says.

What is this about?

Molar-incisor hypomineralisation (MIH) is a developmental defect affecting children’s permanent molars and incisors. The condition weakens enamel and dentin and increases tooth sensitivity, often leading to post-eruptive breakdown (PEB). To encounter this, minimally invasive treatments—such as resin infiltration (RI) and fissure sealant (FS)—are used to reinforce enamel and protect against damage.

This study, published in the European Archives of Paediatric Dentistry, investigated how deeply these two materials penetrate MIH-affected enamel without PEB and how they influence enamel hardness. The research was a collaboration between the University of Helsinki, the University of Turku, and NIOM.

What did the researchers find out?

The team analysed extracted MIH-affected molars and compared them to healthy control teeth using scanning electron microscopy and hardness testing. RI and FS were applied under controlled laboratory conditions to determine how effectively they infiltrate and whether they strengthen weakened enamel.

RI penetrated significantly deeper—about 25 µm on average—compared to only 3 µm for FS. The resin infiltrate material spread more evenly through the porous enamel structure, while the fissure sealant mainly remained on the surface. Chemical analyses also revealed that the RI-treated enamel showed altered mineral composition, while fluoride was detected only in FS-treated samples.

Key results

The enamel treated with RI became nearly twice as hard as untreated MIH enamel, whereas FS did not significantly increase hardness. Although hardness after RI treatment did not reach that of healthy enamel, the improvement was substantial.

“Resin infiltration seems to reinforce enamel from within, not just on the surface,” says Professor and Senior Researcher Aida Mulic at NIOM and adds:

“This supports its potential as an effective, minimally invasive option for early MIH management.”
The findings suggest that RI could serve as a promising approach for stabilizing mild MIH-affected molars and preventing further harm, especially when applied before PEB has occurred.

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