At the beginning of the class a teacher calls the register and designates a student on duty, names the topic and purpose of the class, finds out unclear questions, which appeared during independent work of students.
Then the teacher analyzes subject questions, tasks of students’ research work and methods of practicing skills in accordance with the methodologic instruction, by means of actively questioning all students of the group.
The teacher is guided by the extent of knowledge obtained by the students during their independently studying the material in the textbooks, lecture notes and methodologic instructions, as well as preparing students’ research work in the albums for independent work.
Besides, the teacher can choose to check the hometask in oral or written form, as well as in mixed and oral-and-written form. The teacher can use situational tasks and test questions in addition to routine subject questions.
Having controlled the students’ knowledge for the class, the teacher demonstrates to the students methods of preparation and obtaining of a print thermoplastic impression material.
After the demonstration the students start to independently train practical skills on each other under supervision of a senior laboratory assistant or the teacher.
At the end of the class the teacher gives marks for oral answer or written work, for independent students’ work, signs the protocol of the laboratory work, as well as names the next topic and questions for study.
Processing the denture
After the trial dentures (Acrylic base, wax and teeth) have been waxed, they are prepared for denture processing to substitute the acrylic record base and the wax with a hot cure denture base attached to the teeth. This is done in the following steps:
2) Wax elimination.
7) Shaping and Polishing.
Flask: Is a metal case or tube used in investing procedures.
Flasking: The process of investing the cast and a waxed denture in a flask to make a sectional mould used to form the acrylic resin denture base.
The flask is made of 3 major parts, (1) lower half (which contains the cast), (2) upper half and (3) the cover or lid. The lower half may have a round plate, covering a round hole in the base of the lower half.
Molding or flasking Techniques:
1- Compression technique:
The stone cast with the record denture base, wax and teeth are secured to the lower half of the flask with gypsum investment material (plaster or stone). Then the upper half of the flask is put in place and gypsum is poured to the occlusal surfaces of the teeth. Finally the top portion of the flask is poured with investment and the lid is placed on the flask.
2- Injection molding technique:
It is a complicated procedure requiring special flask and equipment. In this technique the wax pattern is sprued and the material is injected into the mold. This process allows injection of further material during polymerization to compensate for the polymerization shrinkage.
The procedure of flasking a denture in compression technique is as follows:
Acrylic resin dough is made by mixing the powder (polymer) and liquid (monomer) to form 'dough' which is packed into a gypsum mold for curing. The ratio of powder to liquid is important since it controls the workability of the mix as well as the dimensional changes on setting.
The mixing should be done in a clean jar which should be covered to prevent evaporation of the monomer.
It should be done when the mixture reaches dough stage, as the dough is rolled into a rod-like form and placed in the upper half of the flask then a polyethelen (nylon sheet) is placed over the dough in the upper half and then the two halves of the flask are closed until they are almost in approximation, this is done to spread the dough evenly throughout the mold. Then the two halves of the flask are separated, the excess material at the borders of the denture is removed by a wax knife, and additional resin is added at any places that are deficient. At least two trial closures are done and before the final closure a thin layer separating medium is applied on the cast and the 