The ornamental design for a biteblock, as shown and described.
FIG. 1 is a front view of a bite block showing my new design inserted into the mouth of a patient. The broken line showing of the patient's head is included for the purpose of illustrating an environment that forms no part of the claimed design.
FIG. 2 is a right side elevational view corresponding to FIG. 1.
FIG. 3 is a front perspective view of a bite block showing my new design.