As the name indicates one has contoured walls (pre-contoured) while the other has straight walls. NuSmile SSC’s allow you to obtain a classic "snap fit" when the tooth is properly prepared and the crown size is correctly selected. This allows the crown to grab onto the tooth to achieve mechanical retention, regardless of the cement being used. The "snap fit" also helps to insure a good marginal seal over time, especially if a pure glass ionomer cement is used, since glass ionomer cements are water soluble and can wash out over time if the margin is open. Although straight-walled crowns can be trimmed, shaped and contoured by a skilled clinician to achieve the same result, doing so is time-consuming and technique sensitive. Most clinicians have switched from using straight-walled stainless steel pediatric crowns to using pre-contoured crowns since the price difference is small (if any) and the time savings using a pre-contoured crowns is very significant, more than compensating for any difference in price.