There are a lot of things to consider when purchasing a 3D printer, in fact too many to name here. One very important issue to consider is which type of 3D printing method would work best for my needs. Here are the three most typical and popular ways in which 3D printers print; PolyJet, Stereolithography, and Fused Depostition Modeling. So, which is best for Orthodontic Labs printing models for appliance fabrication? It all depends on who you ask! For the Ortho Lab world, the prefered method seems to be the PolyJet method, as research shows the Stratasys Objet Orthodesk 30 Printer, which uses PolyJet technology is in most small and medium sized Ortho labs, and can be found in some large labs as well. Here is an explaination of the three, Choose for yourself which you would prefer:

PolyJet 3D printing is similar to inkjet printing, but instead of jetting drops of ink onto paper, PolyJet 3D Printers jet layers of curable liquid photopolymer onto a build tray. The process is simple: Pre-processing: Build-preparation software automatically calculates the placement of photopolymers and support material from a 3D CAD file. Production: The 3D printer jets and instantly UV-cures tiny droplets of liquid photopolymer. Fine layers accumulate on the build tray to create a precise 3D model or part. Where overhangs or complex shapes require support, the 3D printer jets a removable gel-like support material. Support removal: The user easily removes the support materials by hand or with water. Models and parts are ready to handle and use right out of the 3D printer, with no post-curing needed. - See more at: http://www.stratasys.com/3d-printers/technologies/polyjet-technology#sthash.2hEj73Tf.dpuf

3D printers that run on FDM Technology build parts layer-by-layer from the bottom up by heating and extruding thermoplastic filament. The process is simple:

1. Pre-processing: Build-preparation software slices and positions a 3D CAD file and calculates a path to extrude thermoplastic and any necessary support material.
2. Production: The 3D printer heats the thermoplastic to a semi-liquid state and deposits it in ultra-fine beads along the extrusion path. Where support or buffering is needed, the 3D printer deposits a removable material that acts as scaffolding.
3. Post-processing: The user breaks away support material away or dissolves it in detergent and water, and the part is ready to use.

- See more at: http://www.stratasys.com/3d-printers/technologies/fdm-technology#sthash.b8gy5Xts.dpuf

Also SLA or Stereolithography printers build parts layer-by-layer using a UV laser to solidify liquid photopolymer resins. It is commonly used to produce concept models, master patterns, large prototypes and investment casting patterns. SLA is gaining popularity in the Ortho lab printing world.

See stratasys.com for more info on 3D Printing and printers. Much of this article was based off info at stratasys.com