A simple solution to recycle and reuse dental CAD/CAM zirconia block from its waste residuals

Purpose: To seek a simple solution that can recycle and regenerate dental CAD/CAM zirconia green blanks from its waste residuals. Methods: Waste residuals (3M (R) Lava (TM) Plus HT) were pulverized after dry milling and cutting, and subsequently sieved before pickling in a 0.5 M nitric acid. These powders were then dry-pressed and pre-sintered into blocks at seven different temperatures in the range 800-1100 degrees C. New zirconia blocks flagged with the same batch numbers were used as control. These blocks were cut into bars before subjected them to manufacturer-recommended sintering at 1450 degrees C. Crystalline phases (by XRD). elemental compositions (by EDX), surface morphologies (by SEMI), machinability, linear shrinkage rate. relative density. and Knoop microhardness were evaluated before and after sintering, and four-point flexural strengths were also evaluated for the sintered zirconia bars. Results: Only tetragonal phases were found in both pre- and fully-sintered recycled zirconia blocks. SKI results showed that pre-sintered samples at 950 degrees C had smooth and flat surfaces with evenly distributed particles. Recycled and control zirconia blocks had similar elemental compositions. Results from machined surface, linear shrinkage rate, relative density, and Knoop microhardness established that 950 degrees C and 1000 degrees C were suitable pre-sintering temperatures for recycling zirconia. Pre-sintered recycled zirconia had no significant differences in flexural strengths, however, samples pre-sintered at 1000 degrees C exhibited the closest value (897 MPa) compared to that of the control (904 MPa). Conclusions: Dental CAD/CAM zirconia can be recycled and reused from its waste residuals by adopting a simple method that requires a pre-sintering at 950 or 1000 degrees C.

Automated summary

This study found that dental CAD/CAM zirconia can be recycled and reused from its waste residuals by adopting a simple method that requires pre-sintering at 950 or 1000 degrees Celsius. Pre-sintering at these temperatures resulted in recycled zirconia with similar properties to control samples, showing that it is a feasible and effective recycling method.