[Manufacture of a titanium full crown by CAD/CAM--tolerance of the cutting tool].
OBJECTIVE
We investigated the durability of the cutting tool(bar)that is used when creating a dental crown by using the CAD/CAM system of a computer-assisted NC machine tool.


METHODS
We used the chamfer type as the shape of the dental cervical margin of the support tooth model. We also used a mold model whose shaft surfaces on both sides had an 8-degree taper. We used the CAD/CAM system of DENTAL Cadim (Advance Inc.). First, we manufactured a nonocclusion dental crown of the resin-pattern on top of the support dental model, and measured its 3-dimensional shape. Upon measuring the 3-dimensional shape, we created a pure-titanium block by using cutting bars continuously for rough processing and for finishing processing separately. Upon completion of the pure-titanium block, we measured the time required for each processing and measured the surface roughness after each processing.


RESULTS
The surface roughness Ra of the rough processing became significantly worse after the fifth processing (p<0.01). Rmax became significantly worse after the sixth processing(p<0.05)and after the seventh processing (p<0.01). The surface roughness of both Ra and Rmax of the finishing processing became significantly worse after the fifth processing (p<0.05) and after the seventh processing (p<0.01).


CONCLUSIONS
From the viewpoint of quality of the crown's finished surface and compatibility fitness, the number of cuttings, the number of rough processing and the number of finishing processing using the same cutting tool for making a full crown of a molar tooth should be limited to four times.
Uno
Mitsunori
M
Division of Prosthetic Dentistry, Department of Oral Rehabilitation, Asahi University School of Dentistry, Mizuho, 501-0296 Gifu. uno@dent.asahi-u.ac.jp
Furuya
Masayoshi
M
Kurachi
Masakazu
M