Paresthesia is described as a burning or prickling sensation or partial numbness caused by neurologic injury. The sensory loss may be the result of a reversible and/or irreversible nerve damage, and it can be caused by local or systemic factors. Local factors include traumatic injuries caused by impacted teeth, local injection, endodontic therapy, implant placement and exposure to toxic materials. This article reports a paresthesia by anesthetic injection. A 44-year-old man reported moderate pain during chewing and exposure to cold. Upon clinical examination, extension of the tooth fracture line was in the mesiodistal region of the mandibular left second premolar crown and was detected with 16× magnification of microscope. The diagnosis was cracked tooth syndrome, and root canal treatment was indicated. After the first appointment the patient reported altered sensation on left side of m...