Quantification and Identification of Bacteria Within Acrylic Resin Denture Bases

Objectives: It is well-known that microbial adherence to acrylic denture surfaces causes stomatitis and oral malodor. However, there is little information on microbial invasion into acrylic-resin and colonization within denture bases. Thus, this study aimed to quantify and identify microbial species within denture bases.

Methods: Acrylic-resin dentures used daily for 8-months – more than 5-years were provided from 12 patients after obtaining informed consents. The dentures were divided into two groups: group A (n=5), denture bases with visible crack at the interface to artificial teeth and/or repaired parts; group B (n=9), denture bases without any visible crack or repairing history. The denture bases were split aseptically, and resin chips were scraped from the internal layer of the split surface with sterilized steel round bur (200-rpm). The resin chips (ca. 0.1-mg) were suspended in 1-mL of buffer, and serial 10-fold dilutions (0.1-mL each) were cultured anaerobically on blood agar plates. Colonized bacterial isolates were identified by 16S rDNA sequence analysis. In addition, the denture base surfaces were observed with digital microscope (x140 and 1400).

Results: Bacteria were detected from 2 of group A (6.0x10² and 1.0x10⁴CFU/mg) and 3 of group B (4.0x10², 1.3x10³ and 1.4 x10³CFU/mg). Lactobacillus (5-species) was predominant in group A, while Actinomyces (3-species), Propionibacterium (1-species) and Streptococcus (1-species) were predominant in group B. Micro-cracks (about 10µm-in-width) were found on the used denture base surfaces, while there was little crack in unused denture bases.

Conclusions:This study revealed that several oral bacteria colonized within used acrylic-resin denture, and these bacteria seemed to invade into denture bases through micro-cracks and/or interfaces between denture base and other materials. These results suggest that acrylic-resin denture can act as a bacterial reservoir and that the bacteria and their metabolic products within the denture may cause the denture-related oral problems and accelerate the deterioration of acrylic-resin.