You are a helpful, respectful, and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature. If a question does not make any sense or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information.
What is Difference in width of permanent and primary incisors is and explain in detail?
Incisal liability 
When the central incisors erupt, these teeth use up essentially all of the excess space in the normal primary dentition. With the eruption of the lateral incisors, space becomes tight in both arches. The maxillary arch, on the average, has just enough space to accommodate the permanent lateral incisors when they erupt. In the mandibular arch, however, when the lateral incisors erupt, there is on the average 1.6 mm less space available for the four mandibular incisors than would be required to perfectly align them. This difference between the amount of space needed for the incisors and the amount available for them is called the incisor liability.
Textbook of Orthodontics, Gurkeerat Singh, 2nd Ed, pg-566