A kit for use in teeth whitening, the kit comprising: a teeth whitening device comprising a tray unit; an electric power source unit; and a peroxide-free whitening substance; said tray unit comprising: at least one dental tray comprising a recess configured for receiving therein at least one tooth of a dental arcade and for holding a whitening substance, thereby defining a teeth-substance contact region in said recess; an electrode unit extending along at least part of said recess and configured and operable to create an AC electric field region within said recess in a range of a few hundreds of kHz to few tens of MHz; and a substance measurement circuit located in the tray; said electric power source unit comprising: an electric signal generator configured and operable for generating an alternating current signal and controllably applying a corresponding AC activation signal to said electrode unit during a treatment session; and a control unit configured for modifying said AC signal of the electric signal generator by a predetermined control function to create said activation function of the AC signal in a range of a few hundreds of kHz to few tens of MHz, said control unit comprising a substance controller associated with and connectable to said substance measurement circuit for monitoring of one or more parameters of the whitening substance being indicative of a treatment process; wherein: said electrode unit comprises at least one pair of spaced-apart electrodes; said AC activation signal having a profile corresponding to a predetermined activation function of frequency and time selected such that said AC electric field acts on the whitening substance and causes an electrochemical reaction within the whitening substance that breaks down the components thereof and at least one of these components causes the tooth whitening effect and thus causes improvement of white shade grade of said at least one tooth being in contact with the whitening substance in said recess. a teeth whitening device comprising a tray unit; an electric power source unit; and a peroxide-free whitening substance; at least one dental tray comprising a recess configured for receiving therein at least one tooth of a dental arcade and for holding a whitening substance, thereby defining a teeth-substance contact region in said recess; an electrode unit extending along at least part of said recess and configured and operable to create an AC electric field region within said recess in a range of a few hundreds of kHz to few tens of MHz; and a substance measurement circuit located in the tray; an electric signal generator configured and operable for generating an alternating current signal and controllably applying a corresponding AC activation signal to said electrode unit during a treatment session; and a control unit configured for modifying said AC signal of the electric signal generator by a predetermined control function to create said activation function of the AC signal in a range of a few hundreds of kHz to few tens of MHz, said control unit comprising a substance controller associated with and connectable to said substance measurement circuit for monitoring of one or more parameters of the whitening substance being indicative of a treatment process; said electrode unit comprises at least one pair of spaced-apart electrodes; said AC activation signal having a profile corresponding to a predetermined activation function of frequency and time selected such that said AC electric field acts on the whitening substance and causes an electrochemical reaction within the whitening substance that breaks down the components thereof and at least one of these components causes the tooth whitening effect and thus causes improvement of white shade grade of said at least one tooth being in contact with the whitening substance in said recess.