There's different kinds of movements in orthodontics. True, a lateral movement is best when possible. That tends to happen in the posterior teeth I think because the bone is thicker. Most often I think they just tip the teeth slightly. I think it works because the molars aren't too visible and it still provides a functional occlusion. I've read that up to 5mm expansion is considered stable without periodontal defects. I don't know how much I'm getting but I'd get 2-4mm. Relapse rates are high, up to 50%, and unpredictable in expansion surgeries, which is why up to a point some surgeons don't like them. SARME is supposed to be more stable and can provide up to 7mm expansion while a segmental LeFort can provide up to 4mm but has the advantage of vertical movements (and associated relapse risks) if desired too of course. I don't know if these numbers are per side or total and I'm just recalling from memory. Either way, with every surgery you get some loss of bone blood flow, 20% permanently according to a recent paper. It may never matter or it may not matter for a long time but there's a risk of tooth loss each time and the risks increase with repeat surgeries, prior trauma, and proximity to the osteotomy site.
I looked at slow palatal expansion too. At the surface it's appealing but look long enough and you realize why orthodontists don't do it. I found a few anecdotes of people who did it and they all seemed to seriously regret it. I don't recall the details but I saw some slides I think from an orthodontist describing all the problems that happen when it fails. I still think there's hope with osteoblast stimulators like Exogen/Acceledent (LIPUS) and Orthopulse (low-intensity near-infrared) but it'll be 5 years before anyone gets around to testing it.
