Functionalized Mouth-Conformable Interfaces for pH Evaluation of the Oral Cavity

Abstract

Oral health monitoring is highly desired, especially for in home use, however, current methods are not sensitive enough and technically convoluted for this purpose. This paper presents incorporation of bioactive materials and colorimetric chemical sensors into routinely used oral appliances transforming them into bioresponsive, conformable interfaces. Specifically, endodontic paper points and dental floss can be functionalized to locally sense and monitor pH variations within the oral cavity via color changes. Moreover, edible colorimetric indicators are developed and used to make sensing, edible devices in the form factor of candies that can dynamically and visually respond to acidity changes in saliva. These interfaces would enable early detection of caries (e.g., using dental floss and paper points) providing low-cost point of care devices that respond in real-time by detecting pH variations in biological fluids thus bringing monitoring to home settings .

Keywords: colorimetric sensors; mouth compatible interfaces; oral cavity.

Figure 1

Biomaterial‐based sensing mixes consisting of silk fibroin and pH sensing molecules (i.e., commercially available pH indicators or extracted from fruits and vegetables). The schematic shows the steps involved in the making of sensing interfaces that can be used to monitor pH variations within the oral cavity. Sensing mixes contain silk fibroin and a pH sensing molecule. The sensing mix is used to realize different types of intraoral sensing devices: i) spray coated to generate pH detecting dental floss; ii) dip coated highly absorbent paper points to detect pH in between teeth or inside teeth during root canal treatment; iii) casted into molds to realize color changing candies able to sense pH variations in user's salivary fluid.

Figure 2

Characterization of biomaterial‐based sensing mixes used a,c,e) to spray coat dental floss and b,d,f) to dip coat highly absorbent paper points able to colorimetrically detect pH variations within the oral cavity in real time. The plots and pictures show the color changes of indicators at pH values ranging between 3 and 8.5. a) Nitrazine yellow (NY) embedded into a silk‐based mix spray coated on dental floss: sensing range pH 6–8 (n = 3, error bars standard errors). Colored circles show the colorimetric response recorded at different pH (indicated by the label above circular areas). b) Mix of bromocresol green (BG)/chlorophenol red (CPR) embedded into a silk‐based mix used to dip coat highly absorbent paper points: sensing range pH 3–5.5 (n = 3, error bars standard errors). Colored circles show the colorimetric response recorded at different pH (indicated by the label above circular areas). c) Mix of BG/CPR spray coated on dental floss. The picture shows the dental floss exposed to different pH variations in three highlighted sections: enlargements at pH 4, 6, and 7.5 (i.e., from left to right). d) Highly absorbent paper points dip coated with NY embedded into silk‐based mixes. NY color changing points were exposed to pH 4, 5, 6, 7, and 8.5 (i.e., the arrow indicates the direction of paper points exposed to increased pH). Right: Enlargement of paper point at pH 6. Colored circles show the colorimetric response recorded at different pH (indicated by the label next to circular areas). e) BG/CPR embedded into a silk‐based mix used to spray coat dental floss: sensing range pH 3–6 (n = 3, error bars standard errors). Colored circles show the colorimetric response recorded at different pH (indicated by the label above circular areas). f) NY embedded into a silk‐based mix used to dip coat highly absorbent paper points: sensing range pH 3–7.5 (n = 3, error bars standard errors). Colored circles show the colorimetric response recorded at different pH (indicated by the label above circular areas). The plots allow quantifying the signal as variations in either Red (i.e., CPR/BG and NY for dental floss) or Euclidean distance (ED) (i.e., CPR/BG and NY for paper points) channel intensity versus pH.

Figure 3

Characterization of biomaterial‐based sensing mixes used to dip coat highly absorbent paper points able to colorimetrically detect pH variations within the oral cavity. The plots and pictures show the color changes at pH values ranging between 3 and 8.5. a,c) Anthocyanins extracted from blueberries (BB) embedded into a silk‐based mix. Colored circles show the colorimetric response recorded at different pH (indicated by the label below circular areas). c) The plot shows sensing ranges of pH 3–4, pH 5.5–6.5, and pH 7.5–8.5 (n = 3, error bars standard errors). b,d) Anthocyanins from BB and red cabbage (RC) (i.e., combined in ratio 1:2 v/v) embedded into a silk‐based mix. Colored circles show the colorimetric response recorded at different pH (indicated by the label below circular areas). d) The plot shows sensing ranges of pH 3–5 and pH 7.5–8.5 (n = 3, error bars standard errors). e) Highly absorbent paper points dip coated with BB anthocyanins embedded into silk‐based mixes, exposed to different pH 4, 5, 6, 7, and 8 (i.e., the arrow indicates the direction of paper points exposed to increased pH). Left: Colored circles show the colorimetric response recorded at different pH (indicated by the label next to the circular areas). Right: Enlargement of BB point exposed to pH 6. f) Highly absorbent paper points dip coated with BB/RC embedded into silk‐based mixes, exposed to different pH 4, 5, 6, 7, and 8 (i.e., the arrow indicates the direction of paper points exposed to increased pH). Left: Enlargement of RC/BB point exposed to pH 6. Right: Colored circles show the colorimetric response recorded at different pH (indicated by the label next to the circular areas). The plots allow quantifying the signal as variations in the Red channel intensity (i.e., for both types of paper points) versus pH.

Figure 4

Characterization of mouth‐conformable interfaces based on biomaterial‐based sensing mixes able to colorimetrically detect pH variations within the oral cavity. The plots and pictures show the color changes at pH values ranging between 3 and 8.5. a) Examples of colorimetric mouth‐conformable sensing interfaces that can monitor pH variations within the oral cavity. They can be realized in the format of spray coated dental aligners and edible lollipops able to evaluate the buffering capacity of saliva inside the mouth. The inset shows a dental aligner exposed to pH 3 (i.e., acid) and pH 8.5 (i.e., base). b) Lollipop based on silk fibroin embedding anthocyanins extracted from BB. The lollipop is exposed to pH variations in four highlighted sections: pH 4, 6, 7, and 8.5 (i.e., arrows point at the direction of increased pH). The enlargement shows the color changes recorded at pH 8.5 (i.e., top) and pH 4 (i.e., bottom). c) pH indicator extracted from nectarine skins (N) embedded into a silk mix molded and casted in the format of a lollipop: sensing range pH 3–3.5, pH 4–5.5, and pH 6–7 (n = 3, error bars standard errors). Colored circles show the colorimetric response recorded at different pH indicated by the label below every circular area. d) pH indicator extracted from blueberries (BB) embedded into a silk mix molded and casted in the format of a lollipop: sensing range pH 4–6 (n = 3, error bars standard errors). Colored circles show the colorimetric response recorded at different pH indicated by the label below every circular area. The plots allow quantifying the signal as variations in the Green channel intensity versus pH for both lollipops.