(1) Temperature rise is too fast and too high during heat treatment: As mentioned in the previous heat treatment method, the temperature rise should not be too fast and too high during heat treatment, otherwise many tiny spherical pores will be formed inside the base and distributed in the thicker part of the base, and the larger the base volume, the more pores there will be.
(2) The powder-liquid ratio is out of balance: there are two main situations: 1) There is too much water in the denture base: the polymerization shrinkage is large and uneven, and irregular pores or cavities can be formed everywhere in the denture base. 2) There is too little water in the denture base: the denture base powder is not completely swollen, and tiny pores can be formed, which are evenly distributed throughout the denture base. It is more common that the tray water is insufficient, or the mixing cup is not covered properly, which makes the tray water volatilize, or the model absorbs the tray water because it is not soaked in water and coated with isolation agent.
(3) Filling time is not allowed. 1) Premature filling: It is easy to bring in bubbles artificially due to wire sticking when filling too early, and the mixture is too fluid to be compacted, which is easy to form irregular pores in various parts of the base. 2) Filling is too late: the mixture hardens, plasticity and fluidity decrease, and defects may be formed.
(4) Insufficient pressure: irregular pores or pores will be generated on the surface of the base, especially irregular defective pores will be formed in the subtle parts of the base. (1) Improper packing and excessive pressure: If the upper and lower boxes are stressed only by gypsum contact, if the pressure is too high, the gypsum model will be easily deformed, and the base will also be deformed. Therefore, it should be packed in strict accordance with the regulations.
(2) Too late filling: the mixture exceeds the dough stage and loses plasticity. If the plastic injection molding is forced, the model will often be deformed or damaged, which will lead to the displacement of various parts of the denture and the deformation of the denture base.
(3) Excessive temperature rise: the base resin is a poor heat conductor. If the temperature rises too fast, the polymerization speed of the surface layer of the base layer is faster than that of the inside, which leads to uneven shrinkage of the polymerization volume and deformation of the base layer.
(4) The thickness difference of base course is too large: the shrinkage of polymerization volume varies from place to place, which will also change the shape of base course.
(5) Too fast cooling and too early unpacking: too fast cooling and too early unpacking will lead to too large temperature difference between the inside and outside of the base, which will lead to inconsistent temperature contraction of the base, and will release potential stress in the base after the base is taken out of the box, leading to deformation of the base. If the box is opened too early, it is easy to make the base that has not been fully cooled and hardened be stretched and deformed.