Process for producing a workpiece with low translucency

A process for producing a dental restoration made of glass ceramics, comprising the following steps in the order:

• a) a first thermal treatment of a workpiece at a first temperature T1 within a range of from 400 to 700° C. for a period of 10 to 180 minutes;
• b) a second thermal treatment of the workpiece at a second temperature T2 within a range of from 500 to 800° C. for a period of 10 to 400 minutes, the second temperature T2 being higher than the first temperature T1;
• b-1) cooling the workpiece to room temperature and forming the workpiece to a dental restoration;
• c) a third thermal treatment of the dental restoration at a third temperature T3 within a range of from 600 to 1100° C. for a period of 2 to 90 minutes for forming the final crystal phase of the dental restoration, the third temperature T3 being higher than the temperature T1 and the temperature T2;
• d) cooling the dental restoration down to a temperature Tcool, which is below the glass transition temperature of the glass ceramic after the third heat treatment;
• characterized in that
• e) there is a fourth thermal treatment of the dental restoration, after the cooling step d), at a fourth temperature T4 within a range of from 600 to 1100° C. for a period of 2 to 30 minutes, the temperature T4 being higher than the temperature T1 and the temperature T2;
• and
• wherein after the fourth thermal treatment,
• f) cooling of the dental restoration to a temperature Tf as desired by the user is effected,
• wherein the dental restoration is obtained from a starting melt comprising 55-64% by weight SiO2, 10-20% by weight Li2O, 8-20% by weight of a stabilizer, 0-5% by weight K2O, 0.1-5% by weight Al2O3, and 0-10% by weight additives, based on the total weight of the starting melt, and there is no change in the crystalline phase of the workpiece after the fourth heat treatment of step e) relative to the crystalline phase present after the third thermal treatment in step c).