ICAAC: Amalgam Dental Fillings Fend Off Bacteria Better than Composite

SAN FRANSICO, Sept. 29 -- The debate about mercury in amalgam dental fillings not withstanding, amalgam is superior to composite material in reducing adherence of caries-causing Streptococcus mutans, researcher said here.

The least bacterial adherence was seen for titanium, gold and natural enamel followed by amalgam, according to a German study of 73 samples presented in a poster session at the Interscience Conference on Antimicrobial Agents and Chemotherapy.

But materials aside, said Heinrich K. Geiss, M.D., of the University of Heidelberg, the most important preventive measure in dental health remains still frequently brushing one's teeth.

All materials besides titanium, gold and amalgam had significantly higher bacterial counts than enamel. Precious metals had less adherence even than enamel while amalgam came out similar to enamel, Dr. Geiss said. Mean bacterial counts compared without saliva were:

• 0.95 per ?m² for titanium (the most common material for dental implants),
• 1.13 per ?m² for gold,
• 1.91 per ?m² for enamel,
• 5.85 per ?m² for amalgam alloy,
• 7.08 per ?m² for cerec ceramic,
• 8.46 per ?m² for acrylate (methylmethacrylate-copolymer),
• 11.49 per ?m² for Herculite XRV composite (the most commonly used composite worldwide),
• 23.31 per ?m² for hydroxyapatite cement, and
• 34.53 per ?m² for aluminum trioxide.

Metallic ions are bactericidal, Dr. Geiss said, thereby slowing the buildup of plaque that can affect adjacent tooth surfaces. The difference with aluminum trioxide may be explained by its rougher surface that still has major crevices and fissures visible with a scanning electron microscope after polishing and grinding of the material's surface.

The addition of saliva significantly changed the bacterial adherence of all the samples. Titanium's bacterial counts decreased to 0.67 per ?m² while amalgam's counts likewise fell to 2.84 per ?m². All others had increased bacterial counts:

• 2.43 per ?m² for gold,
• 9.91 per ?m² for enamel,
• 12.59 per ?m² for cerec,
• 21.53 per ?m² for acrylate,
• 19.79 per ?m² for composite,
• 33.92 per ?m² for cement, and
• 24.55 per ?m² for aluminum trioxide.

The researchers compared in vitro specimens of the materials to human enamel from extracted teeth as a reference material. The 73 samples were immersed in two different fixatives then dehydrated in alcohol, dried and mounted on aluminum studs. The samples (36 with and 37 without saliva) were sputter-coated with cultured S. mutans. Each specimen was then examined in different areas for bacterial counts using a scanning electron microscope.

However, the study does not dilute the controversy over whether the mercury present in amalgam alloy should prevent its use.

The research may weigh in on the composite versus amalgam filling controversy, said Marylin Roberts, Ph.D., of the University of Washington in Seattle, who commented on the study. However, there are multiple types of composites used whereas the study looked at only one, she noted.

Dr. Geiss concluded that when patients do need restorative dental work, metallic materials including amalgam may be the best options from the standpoint of future caries risk.