title: Influence of residual surface investment material on crystallization shrinkage of a mica-based glass-ceramic.
abstract: OBJECTIVE
  It has been reported that residual surface investment material induced precipitation of a second phase in the surface of a mica-based castable glass-ceramic. The objective of this study was to investigate the influence of this precipitate on the crystallization shrinkage of the glass-ceramic.
  
  
  METHODS
  In experiment 1, six glass bars were cast. The whole surface of three of the six bars was ground to remove residual surface investment material. Then, the six bars were treated thermally to induce crystallization. Dimensional change in the bars during the treatment was recorded. In experiment 2, 14 glass specimens were assigned to two groups. Seven specimens in the one group would form the second phase. The length of each specimen was measured pre- and post-crystallization, and the crystallization shrinkage value calculated.
  
  
  RESULTS
  In experiment 1, all specimens showed shrinkage during thermal processing. The majority of crystallization shrinkage began around 620 degrees C and finished at 750 degrees C. Specimens with the residual investment showed less net shrinkage than those without the investment. In experiment 2, mean shrinkage values and standard deviations were 1.11 (0.05)% for the group without the investment and 0.93 (0.11)% for the group with the investment. There was a significant difference between the groups (P<0.01).
  
  
  CONCLUSIONS
  The residual surface investment material decreases the crystallization shrinkage, and must affect the strength of the mica-based glass-ceramic and the fit of this ceramic restorative to the prepared cavity.
authors: Department of Operative Dentistry, Tsurumi University School of Dental Medicine, Yokohama, Japan. yamamoto-tk@tsurumi-u.ac.jp
authors: Takatsugu
authors: T
authors: Yamamoto
authors: Masaaki
authors: M
authors: Takamizu
authors: Atsushi
authors: A
authors: Kohno
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry; D002516:Ceramics / Q000737:chemistry*; D003460:Crystallization; D003734:Dental Casting Investment / Q000737:chemistry*; D003735:Dental Casting Technique; D006358:Hot Temperature; D007284:Inlays
chemical_list: D000538:Aluminum Silicates; D003734:Dental Casting Investment; C464482:OCC glass; C011934:mica