Obtaining Models, Transfer to Occlusor and Die Materials PDF

Obtaining Models, Transfer to Occlusor and Die Materials Assist.Prof.Delâl Bozyel Learning Outcomes • Determines the occlusor and die materials which used in laboratories • Because direct fabrication of patterns for extracoronal restorations in the mouth is inconvenient, difficult, time consumin...

Obtaining Models, Transfer to Occlusor and Die Materials Assist.Prof.Delâl Bozyel Learning Outcomes • Determines the occlusor and die materials which used in laboratories • Because direct fabrication of patterns for extracoronal restorations in the mouth is inconvenient, difficult, time consuming, and next to impossible, practically all wax patterns are made in the dental laboratory. This technique requires an accurate reproduction of the prepared tooth, the surrounding soft tissues, and the adjacent and opposing teeth. • A solid cast-and-die system captures the necessary information so the laboratory has all necessary information to fabricate the prescribed restoration. • A solid definitive cast (or master or working cast) is a replica of the prepared teeth, ridge areas, and other parts of the dental arch. • The die is the positive reproduction of the prepared tooth and consists of a suitable hard substance of sufficient accuracy. The cast must meet certain requirements: • It must be an exact reproduction of both prepared and unprepared tooth surfaces. • The unprepared teeth immediately adjacent to the prepared tooth or teeth must be free of voids. • All surfaces of any teeth involved in anterior guidance and the occlusal surfaces of all unprepared teeth must allow for precise articulation of the opposing casts. • All relevant soft tissues should be reproduced in the definitive cast, including all edentulous spaces and residual ridge contours that will be involved in the fixed prosthesis. The die for the fixed restoration also must meet certain requirements: • It must be an exact reproduction of the prepared tooth. • All surfaces must be accurately duplicated, and no bubbles or voids can be accepted. • The remaining unprepared tooth structure immediately cervical to the finish line should be easily discernible on the die, ideally with 0.5 to 1 mm visible (enough must be present to help the technician establish the correct cervical contour of the restoraton). • Adequate access to the margin is imperative. Definitive Casts Gypsum • The two crucial characteristics of cast-and-die materials, dimensional accuracy and resistance to abrasion while the wax pattern is being formed, are adequately achieved with gypsum. • This material is inexpensive, is easy to use, and produces consistent results. Surface detail reproduction with type IV and type V gypsum products is acceptable for fixed prosthodontics. Available Methods (Removable Dies) • In a removable die system, the die is an integral component of the definitive cast and can be lifted from the cast to facilitate access. • Precise relocation of the die in the definitive cast is crucial to the success of this system and is usually accomplished with brass pins or dowels. • The location and orientation of the dowels are critical; if they are improperly placed, the dowels do not allow the die of the prepared teeth to be withdrawn from the cast. • Dowels may be positioned in the stone of the initial pour before it is set. An alternative method is to drill controlled holes into the set stone cast and then cement the pins into the stone base. Available Methods (Solid Cast with Individual Die) • The solid cast–individual die system, also referred to as the multiplepour technique, has certain advantages over the removable die system; its primary advantage is its simplicity. It may also be slightly more accurate. • In this technique, once the impression is judged to be satisfactory, type IV or V stone is poured only in the area of the preparations. When set, it is separated. A second pour is then made of the entire arch. Available Methods (Solid Cast with Individual Die) Disadvantages of the solid cast technique: • It may be difficult to transfer complex or fragile wax patterns from cast to die. • The technique can be used only with elastomeric impression materials (if reversible hydrocolloid is used, separate impressions are needed for definitive cast and die). Available Methods (Di-Lok system) In the Di-Lok system, a specially articulated tray is used for precise reassembly of a sectioned definitive cast. The impression is poured, and the cast is trimmed into a horseshoe configuration that fits in the special tray. The tray is filled with a second mix, and the cast is seated. When the stone has set, the tray is disassembled, saw cuts are made on each side of the preparation, and the resulting die is trimmed. Available Methods (Di-Lok system) The cast and die can be reassembled in the tray, which is then mounted on an articulator. A disadvantage of this system is that the overall size of the tray can make articulation and manipulation awkward and difficult. Articulators To able to make an analysation of functional relationships. For such analysis, the diagnostic casts need to be attached to an articulator, a mechanical device that simulates mandibular movement. • Small Nonadjustable Articulators • This instruments do not have the capacity to reproduce the full range of mandibular movement. • Occlusal interferences and associated neuromuscular disorders may result. Articulators • Semiadjustable Articulators They are about the same size as the anatomic structures they represent. Therefore, the articulated casts can be positioned with sufficient accuracy so that arcing errors are minimal and usually of minimal clinical significance. There are two basic designs of the semiadjustable articulator: the arcon & the nonarcon An advantage of the arcon design is that the condylar inclination of the mechanical fossae is at a fixed angle to the maxillary occlusal plane. With the nonarcon design, the angle changes as the articulator is opened, which can lead to errors when a protrusive record is being used to program the articulator. Arcon Non-arcon References [1] Contemporary Fixed Prosthodontics, chapter 2, pages (35- 42). [2] Contemporary Fixed Prosthodontics, chapter 17, pages (457- 462). Thank you