MySweetSmile's Hyaluronic Gum Serum normally retails for £29.99 but has been cut in price to £24.99. MySweetSmile's Hyaluronic Gum Serum is powered by high-concentration Hyaluronic Acid (HA+) and has been specially formulated to offer deep hydration, all while soothing inflammation and strengthening gum tissue. Meanwhile at Holy Mouthwash, The Halo Gum Serum is priced at £23 down from £31 and claims to h ydrate thinning gum tissue and strengthen the gum line. Bought the enamel repair, gum serum, whitening strips and whitening powder. Someone else raved: "The hyaluronic gum serum is fantastic.