Oral viscous lidocaine 2% solutions or benzocaine solutions should not be used to treat infants and children with teething pain because of serious health risks.  The US Food and Drug Administration (FDA) said, “Use in infants and young children can cause serious harm, including death."

"Topical pain relievers and medications that are rubbed on the gums are not necessary or even useful because they wash out of the baby's mouth within minutes. When too much viscous lidocaine is given to infants and young children or they accidentally swallow too much, it can result in seizures, severe brain injury, and problems with the heart,” the FDA warns.

In 2011, the FDA warned that  using OTC benzocaine gels or liquids for teething or mouth pain can cause a rare but serious condition called methemoglobinemia.  It is life-threatening and can result in death.  Benzocaine containing medications are sold under names such as Anbesol, Hurricaine, Orajel, Baby Orajel, Orabase.

The FDA advises parents and caregivers to follow the American Academy of Pediatrics' recommendations for treating teething pain: use a teething ring chilled in the refrigerator (not frozen) or gently rub or massage the child's gums with your finger to relieve the symptoms.

Edited from the article: Oral Lidocaine for Teething Pain May Cause Harm, FDA Says. Medscape. Jun 26, 2014.