7 yo x-ray showed crowding on canine and molars and peg lateral incisors. referred to orthodontist for initial consultation. what should i expect? are two-phase treatments worth it at that age? also, what causes peg teeth?

Peg laterals are usually caused by genetics or they're just a developmental anomaly. Not common, but not unheard of. Multiple phase treatment is often necessary since all of his teeth have not yet erupted, yet the ones that are present need treatment now to help guide the rest of his dentition and influence his facial bones. Adults with straight teeth have less periodontal issues. It's worth it.

At Initial Examination Orthodontist will discuss severity of malocclusion (bad bite) with you and appropriate treatment modalities. Amer Dent Assn, Amer Acad of Pediatric Dent, & Amer Assn of Orthodontists recommend all children be evaluated by 7th b'day. Peg shaped laterals are relatively common developmental anomalies, as is crowding. Orthodontists are trained to resolve these issues.