J Adv Prosthodont.  2017 Dec;9(6):453-462. 10.4047/jap.2017.9.6.453.

Investigation of the cytotoxicity of thermoplastic denture base resins

Affiliations
  • 1Institute of Tissue Regeneration Engineering (ITREN), Dankook University, Cheonan, Republic of Korea. ducious@gmail.com, haelee@dku.edu
  • 2Department of Biomaterials Science, College of Dentistry, Dankook University, Cheonan, Republic of Korea.
  • 3Department of Removable Prosthodontics, Tsurumi University School of Dental Medicine, Tsurumi-ku, Yokohama-shi, Japan.

Abstract

PURPOSE
The purpose of this study was to investigate the in vitro cytotoxicity of thermoplastic denture base resins and to identify the possible adverse effects of these resins on oral keratinocytes in response to hot water/food intake.
MATERIALS AND METHODS
Six dental thermoplastic resin materials were evaluated: three polyamide materials (Smile tone, ST; Valplast, VP; and Luciton FRS, LF), two acrylic materials (Acrytone, AT; and Acryshot, AS), and one polypropylene resin material (Unigum, UG). One heat-polymerized acrylic resin (Vertex RS, RS) was chosen for comparison. After obtaining extracts from specimens of the denture resin materials (Φ=10 mm and d=2 mm) under different extraction conditions (37℃ for 24 hours, 70℃ for 24 hours, and 121℃ for 1 hour), the extracts (50%) or serial dilutions (25%, 12.5%, and 6.25%) in distilled water were co-cultured for 24 hours with immortalized human oral keratinocytes (IHOKs) or mouse fibroblasts (L929s) for the cytotoxicity assay described in ISO 10993.
RESULTS
Greater than 70% viability was detected under all test conditions. Significantly lower IHOK and L929 viability was detected in the 50% extract from the VP (70℃) and AT (121℃) samples (P < .05), but only L929 showed reduced viability in the 50% and 25% extract from LF (37℃) (P < .05).
CONCLUSION
Extracts obtained from six materials under different extraction conditions (37℃, 70℃, and 121℃) did not exhibit severe cytotoxicity (less than 70% viability), although their potential risk to oral mucosa at high temperatures should not be ignored.

Keyword

High temperature incubation; Thermoplastic denture base resins; Immortalized human oral keratinocyte; L929; Cytotoxicity

MeSH Terms

Animals
Denture Bases*
Dentures*
Fibroblasts
Humans
In Vitro Techniques
Keratinocytes
Mice
Mouth Mucosa
Nylons
Polypropylenes
Water
Nylons
Polypropylenes
Water

Figure

  • Fig. 1 Cell viability results (A) and confocal microscopy images of live and dead cells (B to E) for thermoplastic Smiletone (ST) according to extraction condition (37℃ for 24 hours, 70℃ for 24 hours, and 121℃ for 1 hour) and extract percentage in co-culture with IHOKs (0, 6.25, 12.5, 25, and 50%). Different letters indicate significant differences among the extraction conditions (P < .05). Live cells (green) and dead cells (red) were observed by confocal microscopy. The red line indicates 70% cell viability. Representative means ± standard deviation (n = 6) and images are shown; the experiments were independently performed in triplicate.

  • Fig. 2 Cell viability results (A) and confocal microscopy images of live and dead cells (B to E) for thermoplastic Valplast (VP) according to extraction condition (37℃ for 24 hours, 70℃ for 24 hours, and 121℃ for 1 hour) and extract percentage in co-culture with IHOKs (0, 6.25, 12.5, 25, and 50%). Different letters indicate significant differences among the extraction conditions (P < .05). Live cells (green) and dead cells (red) were observed by confocal microscopy. The red line indicates 70% cell viability. Representative means ± standard deviation (n = 6) and images are shown; the experiments were independently performed in triplicate.

  • Fig. 3 Cell viability results (A) and confocal microscopy images of live and dead cells (B to E) for thermoplastic Luciton FRS (LF) according to extraction condition (37℃ for 24 hours, 70℃ for 24 hours, and 121℃ for 1 hour) and extract percentage in co-culture with IHOKs (0, 6.25, 12.5, 25, and 50%). Different letters indicate significant differences among the extraction conditions (P < .05). Live cells (green) and dead cells (red) were observed by confocal microscopy. The red line indicates 70% cell viability. Representative means ± standard deviation (n = 6) and images are shown; the experiments were independently performed in triplicate.

  • Fig. 4 Cell viability results (A) and confocal microscopy images of live and dead cells (B to E) for thermoplastic Acrytone (AT) according to extraction condition (37℃ for 24 hours, 70℃ for 24 hours, and 121℃ for 1 hour) and extract percentage in co-culture with IHOKs (0, 6.25, 12.5, 25, and 50%). Different letters indicate significant differences among the extraction conditions (P < .05). Live cells (green) and dead cells (red) were observed by confocal microscopy. The red line indicates 70% cell viability. Representative means ± standard deviation (n = 6) and images are shown; the experiments were independently performed in triplicate.

  • Fig. 5 Cell viability results (A) and confocal microscopy images of live and dead cells (B to E) for thermoplastic Acryshot (AS) according to extraction condition (37℃ for 24 hours, 70℃ for 24 hours, and 121℃ for 1 hour) and extract percentage in co-culture with IHOKs (0, 6.25, 12.5, 25, and 50%). Different letters indicate significant differences among the extraction conditions (P < .05). Live cells (green) and dead cells (red) were observed by confocal microscopy. The red line indicates 70% cell viability. Representative means ± standard deviation (n = 6) and images are shown; the experiments were independently performed in triplicate.

  • Fig. 6 Cell viability results (A) and confocal microscopy images of live and dead cells (B to E) for thermoplastic Unigum (UG) according to extraction condition (37℃ for 24 hours, 70℃ for 24 hours, and 121℃ for 1 hour) and extract percentage in co-culture with IHOKs (0, 6.25, 12.5, 25, and 50%). Different letters indicate significant differences among the extraction conditions (P < .05). Live cells (green) and dead cells (red) were observed by confocal microscopy. The red line indicates 70% cell viability. Representative means ± standard deviation (n = 6) and images are shown; the experiments were independently performed in triplicate.

  • Fig. 7 Cell viability results (A) and confocal microscopy images of live and dead cells (B to E) for conventional heat-polymerized acrylic resin (Vertex RS: RS) according to extraction condition (37℃ for 24 hours, 70℃ for 24 hours, and 121℃ for 1 hour) and extract percentage in co-culture with IHOKs (0, 6.25, 12.5, 25, and 50%). Different letters indicate significant differences among the extraction conditions (P < .05). Live cells (green) and dead cells (red) were observed by confocal microscopy. The red line indicates 70% cell viability. Representative means ± standard deviation (n = 6) and images are shown; the experiments were independently performed in triplicate.


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