Fundamentals of Fixed Prosthodontics. James C. Kessler
Fig 5-72 The guide pin is closed into the soft resin.
Fig 5-73 The casts are moved through all excursions.
Fig 5-74 There is a custom anterior guidance record on the guide block.
Custom anterior guidance
A customized anterior guidance jig can be made for this articulator using a round-end incisal pin and a flat anterior table or an incisal cup. Acrylic resin or a light-cured material (Triad) is molded by the end of the incisal pin in the same manner that the anterior guidance is recorded for the other articulators. The mounted casts are examined on the articulator, and any nonworking interferences are removed. The articulator must be able to move freely with the anterior teeth in contact. If the guidance is inadequate, it is rebuilt to an optimum configuration with a diagnostic wax-up.
The incisal guide pin is raised at least 1 mm off the plastic incisal guide block in all excursions (Fig 5-70). The surface of the guide block is moistened with monomer. A half scoop of tray resin is mixed, and, while it is still free-flowing, a small amount is placed on the incisal guide. As the polymerizing resin becomes stiffer, more is added until there is about 6 mm (¼ inch) of it covering the guide block (Fig 5-71). The tip of the incisal guide pin and the occluding surfaces of the anterior teeth are lubricated with petrolatum. The articulator is closed to complete contact between the casts. The guide pin should sink into the soft acrylic resin (Fig 5-72). The articulator is moved through all excursions repeatedly, keeping the anterior teeth touching at all times (Fig 5-73). The pathways of all the movements will be imprinted by the tip of the guide pin in the acrylic resin as a permanent record (Fig 5-74). Movement of the casts is continued until polymerization is complete. The excess is removed.
Fig 5-75 To set the mechanical incisal guide, the casts are moved into a protrusive relationship. (a) The angulation of the table is increased to contact the pin. (b) The casts are moved into a right lateral excursion, and the left wing of the incisal table is raised. (c) The casts are moved into a left lateral excursion, and the right wing of the table is lifted to complete the recording.
Mechanical anterior guidance
The guidance of mandibular movement imparted by the anterior teeth also can be recorded on this instrument with a mechanical incisal guide. The mounted casts are examined. Any interferences that prevent the anterior teeth from remaining in contact in all excursions are removed from the casts. Any inadequacies in the guidance are restored by building up an optimum configuration in a diagnostic wax-up.
The lock nut under the incisal table at the front end of the lower member of the articulator is loosened. The incisal pin should be in contact with the incisal table.
The casts are protected from undue abrasion by lubrication of the contacting surfaces with petrolatum. The upper member of the articulator is gently moved back to bring the maxillary and mandibular teeth into an end-to-end position. The incisal pin will be lifted off the incisal table. The incisal guide is rotated to raise it posteriorly until it makes contact with the pin (Fig 5-75a). The lock nut is tightened to maintain this inclination of the table.
The casts are moved into a right lateral excursion. The pin will move to the left side and will again be lifted off the table. The small thumb nut under the left side of the table is loosened, and the elevating screw is used to raise the left wing of the table into contact with the corner of the guide pin (Fig 5-75b). The process is repeated by moving the casts into a left lateral excursion. The right wing of the incisal table is raised to contact the pin (Fig 5-75c).
References
1. Pruden WH. The role of study casts in diagnosis and treatment planning. J Prosthet Dent 1960;10:707–710.
2. Hickey JC, Lundeen HC, Bohannan HM. A new articulator for use in teaching and general dentistry. J Prosthet Dent 1967;18:425– 437.
3. Teteruck WR, Lundeen HC. The accuracy of an ear face-bow. J Prosthet Dent 1966;16:1039–1046.
4. Cowan RD, Sanchez RA, Chappell RP, Glaros AG, Hayden WJ. Verifying the reliability of interchanging casts with semiadjustable articulators. Int J Prosthodont 1991;4:258–264.
5. Sokolow SM. Interchangeable quick-mounted study models. J Clin Orthod 1986;20:779–781.
6. Weinberg LA. Physiologic objective of reconstruction techniques. J Prosthet Dent 1960;10:711–724.
7. Schuyler CH. The function and importance of incisal guidance in oral rehabilitation. J Prosthet Dent 1963;13:1011–1030.
8. Strohaver RA, Ryan JR. New face-bow simplifies use and dental laboratory cooperation. J Prosthet Dent 1988;60:638–641.
6 Treatment Planning for Single-Tooth Restorations
Using cast metal, ceramic, and metal-ceramic restorations, large areas of missing coronal tooth structure can be replaced while the remainder is preserved and protected. Function can be restored, and where required, a pleasing esthetic effect can be achieved. The successful use of these restorations is based on thoughtful treatment planning, which is manifested by choosing a restorative material and design that are suited to the needs of the patient. In a time when production and efficiency are heavily stressed, it should be restated that the needs of the patient take precedence over the convenience of the dentist.
In what circumstances should cemented restorations made from cast metal or ceramic be used instead of amalgam or composite resin restorations? The selection of the material and design of the restoration is based on several factors.
The first factor is destruction of tooth structure. If the amount of destruction previously suffered by the tooth to be restored is such that the remaining tooth structure must gain strength and protection from the restoration, cast metal or ceramic is indicated over amalgam or composite resin.
Esthetics is another important factor. If the tooth to be restored with a cemented restoration is in a highly visible area, or if the patient is highly discriminating, the esthetic effect of the restoration must be considered. Sometimes a partial coverage restoration will serve this function. Where full coverage is required in such an area, the use of ceramic in some form is indicated. Metal-ceramic crowns can be used for single-unit anterior or posterior crowns, as well as for fixed partial denture retainers. All-ceramic crowns are most commonly used on incisors, although they can be used on posterior teeth when an adequate amount of tooth structure has been removed and the patient is willing to accept the possibility of more frequent replacement.
Plaque control also plays a role. The use of a cemented restoration demands the institution and maintenance of a good plaque-control program to increase the chances for success of the restoration. Many teeth are seemingly prime candidates for cast metal or ceramic restorations, based solely on