Is a crown lengthening for effective than a tooth extraction?

No: They are two different ways to address a problem, with different outcomes. An extraction means the tooth is no longer there. Crown lengthening leaves the tooth in place, but if it fails later on it may be hard to replace the tooth with an implant.

Crown lengthening : Crown lengthening is a procedure to expose more sound tooth so a new crown can be placed. Consideration needs to be given to the adjacent teeth as well as the length of the remaining tooth. Also, which tooth is important as well is the tooth going to be used as an anchor for some other dental work. A crown lengthening is very common and can save your tooth, but sometimes there are better options.