~cbid mans u&g d@tde hydrocdd?) impression material
(irmwdtAe
William R. Scott, D.D.S. Vancouver, B.C., Canada
T
his article, the result of 20 years of experience, discusses why alginate (irreversible hydrocolloid) impression material is ideal for occlusal registrations in partially edentulous mouths and explains how this material should be used to produce optimum results. Making such occlusal registrations is always difficult (Figs. 1 and 2). Customary occlusal registration materials such as plaster, thyocal, silicone, zinc oxideeugenol (ZOE) paste, and wax have limitations which make their use inadvisable in certain situations. Alginate too has limitations, but it also has some advantages over the other materials that make it more valuable. DISADVANTAGES OF CUSTOMARY OCCLUSAL REGR%RATION MATERIALS Wax, perhaps the most frequently used occlusal registration material, is subject to distortion from temperature changes and from improper storage, e.g., occlusal registrations resting unsupported on the laboratory bench. Also, its lack of resiliency makes it more liable to permanent distortion during the mounting procedure. In making registrations of teeth and edentulous areas using baseplates, wax causes displacement of soft tissues and movement of the teeth. This is especially true when a patient repeatedly taps his teeth into a thin wafer of wax. The resulting distortion is compounded when the dentist attempts to fit working casts into a registration which mars the detail in the wax, distorting the registration. This problem is compounded further when occlusal registrations are made with plaster or ZOE materials, since they record minute details more accurately and am even less resilient than wax. Presented to the Pacific Coast Society of Pmsthodontists, Francisco, Calif.
CKC2-3913/78/110517+ 03$K0O/Od 1978 The C. V. Mosby Co.
San
Hence minute imperfections in the working casts result in inaccurate mountings. Furthermore, the occlusion rims in the edentulous areas have a tendency to displace the underlying mucosa., causing the casts to be mounted with a alight vertical opening. These erras are common for occluaal registrations made with the materials commonly used.
Because of its extreme fluidity before setting and its resiliency after atting, alginate causes minimal tooth and tissue displacement when occluaal registrations are made with it. Moreover, because zilginate is similar to those materials used for making impressions for working casts, any displacement of soft tissue areas and mobile teeth will be closely replicated in the alginate occlusal registration. Equalization in these two operations permits the dentist to fit working casts into the occlusal registration without permanently distorting it, and minor twisting or torque movements of the casts during orientation and mounting on an articulator can be minimized. PROCEDURE Thin alginate sections, which are exceedingly fragile and elastic, would be of little value in supporting the working casts (Fig. 3). Hence the success of alginate in making accurate occlusal registrations depends upon the use of this material in bulk. Indeed, the greater the bulk, the greater the resiliency and resistance to displacement and the greater the area of support of the casts. Therefore it is necessary to place as much alginate as possible in the patient’s mouth when making the occlusal registration (Figs. 3 and 4). With .practice, the dentist will learn to place the alginate in the vestibule below the tongue on each side and in the
NOVEMBER 1978
VOLUME 40
NUMBER 5
517
Figs. 1 and 2. Two mirror images. The large vertical space between the prepared maxillary and mandibular teeth, the edentulous spaces,and the posterior cross-bite relationship create a difficult problem for making an occlusal registration.
Fig. 3. The maxillary side of the alginate occlusal registration with large facial and lingual regions of support for the maxillary cast. The metal stop (MS) was placed between the teeth to obtain a predetermined vertical opening (1.5 mm) before the alginate registration was made. Thin incisal and occlusal sections are unsuitable to support casts. Fig 4. The mandibular side of the alginate occlusal registration.
poet&or region, so as to get the maximum support in this area. Usually, most of the material placed in the mouth will flow naturally into the palatal area above the tongue, where the material should cover the palatal area of the maxillary teeth and soft tissues. Althaugh some patients gag when any foreign material is placed in their mouths, few patients Seem to be bothered by this method of registration, in spite of the amount of material used. The setting of the mate&al can of course be speeded up by using warm water and warm mixing bowls to lessen the time the alginate must remain in the mouth. Storage of a&ate occlusal registrations can be a problem. If left for any time in room atmosphere they will shrink from evaporation. If left to soak in a water solution they will absorb moisture, which will cause distortion. Accordingly, alginate occlusal mgistmtions should be kept in a suitable humidor and we-d as soon as possible.
518
Mounting casts In order to see that the casts are seated properly and completely in the alginate occlusal registration, the labial and buccal material is cut away with a sharp knife (Figs. 5 and 6). The incisal edges or cusp tips of the teeth of both upper and lower casts should completely contact the alginate registration. If a space is evident the alginate should be cut away in those areas where the cast does not coincide with the registration. This space is the result of disparities between the working cast and the occlusal registration in the tongue area of the mandibular cast and in the tuberosity or muscle regions of the maxillary cast. Once these disparities are removed, the casrs should be ready for the articulator, but care must be taken in mounting to avoid pressing either cast in such a way as to create a torque or twist, for such motion will distort the relationship of the opposing casts. To avoid this, the dentist should lock the two casts together with a number of supporting sticks
NOVEMBER
1978
VOLUME
40
NUMBER
5
Figs. 5 and 6. Alginate occlusal registration material (shaded area) has been cut away buccally and labially to expose the in&al and buccal edges of the teeth to ensure the castsfit accurately into their respective impressions. Sticks attached to the casts with sticky wax stabilize them for mounting on the articulator. waxed around the casts (Figs. 5 and 6). These rods are attached to both casts when one is resting passively and vertically over the other, with the supporting alginate occlusal registration placed between them. The casts can then be mounted safely on the articulator without distortion.
APPLICATIONS The alginate occlusal registration can be used in many different procedures: in partially edentulous mouths needing fixed and/or removable partial dentures (Figs. 1 and 2); in completely edentulous mouths to obtain a preliminary relationship of the casts so as to orient a central bearing pin and opposing plate to occlusion rims for a more accurate occlusal registration; in mouths having a complete dentition; in mouths with extreme malocclusions (Class II or III occlusal relationships); and along
THE KXJRNAL
OF PROSTHETIC
DENTISTRY
with anterior wax or metal stops in mouths with “open-bite” relationships (Figs. 1 and 2).
SUMMARY AND CONCLUSION Alginate impression material can be used to make occlusal registrations. It is probably most useful for occlusal registrations of partially edentulous mouths, although it can be so used for complete edentulous mouths, mouths with no missing teeth, and for mouths having severe malocclusions. A brief discussion of some of the limitations of other materials used for occlusal registrations was presented. Refnirttrequeststo: R. SCOTT 1006-925 W. GEORGIA VANCOUVER, B. C. V6C lR5
DR. WILLIAM
CANADA
519
(irmwdtAe
William R. Scott, D.D.S. Vancouver, B.C., Canada
T
his article, the result of 20 years of experience, discusses why alginate (irreversible hydrocolloid) impression material is ideal for occlusal registrations in partially edentulous mouths and explains how this material should be used to produce optimum results. Making such occlusal registrations is always difficult (Figs. 1 and 2). Customary occlusal registration materials such as plaster, thyocal, silicone, zinc oxideeugenol (ZOE) paste, and wax have limitations which make their use inadvisable in certain situations. Alginate too has limitations, but it also has some advantages over the other materials that make it more valuable. DISADVANTAGES OF CUSTOMARY OCCLUSAL REGR%RATION MATERIALS Wax, perhaps the most frequently used occlusal registration material, is subject to distortion from temperature changes and from improper storage, e.g., occlusal registrations resting unsupported on the laboratory bench. Also, its lack of resiliency makes it more liable to permanent distortion during the mounting procedure. In making registrations of teeth and edentulous areas using baseplates, wax causes displacement of soft tissues and movement of the teeth. This is especially true when a patient repeatedly taps his teeth into a thin wafer of wax. The resulting distortion is compounded when the dentist attempts to fit working casts into a registration which mars the detail in the wax, distorting the registration. This problem is compounded further when occlusal registrations are made with plaster or ZOE materials, since they record minute details more accurately and am even less resilient than wax. Presented to the Pacific Coast Society of Pmsthodontists, Francisco, Calif.
CKC2-3913/78/110517+ 03$K0O/Od 1978 The C. V. Mosby Co.
San
Hence minute imperfections in the working casts result in inaccurate mountings. Furthermore, the occlusion rims in the edentulous areas have a tendency to displace the underlying mucosa., causing the casts to be mounted with a alight vertical opening. These erras are common for occluaal registrations made with the materials commonly used.
Because of its extreme fluidity before setting and its resiliency after atting, alginate causes minimal tooth and tissue displacement when occluaal registrations are made with it. Moreover, because zilginate is similar to those materials used for making impressions for working casts, any displacement of soft tissue areas and mobile teeth will be closely replicated in the alginate occlusal registration. Equalization in these two operations permits the dentist to fit working casts into the occlusal registration without permanently distorting it, and minor twisting or torque movements of the casts during orientation and mounting on an articulator can be minimized. PROCEDURE Thin alginate sections, which are exceedingly fragile and elastic, would be of little value in supporting the working casts (Fig. 3). Hence the success of alginate in making accurate occlusal registrations depends upon the use of this material in bulk. Indeed, the greater the bulk, the greater the resiliency and resistance to displacement and the greater the area of support of the casts. Therefore it is necessary to place as much alginate as possible in the patient’s mouth when making the occlusal registration (Figs. 3 and 4). With .practice, the dentist will learn to place the alginate in the vestibule below the tongue on each side and in the
NOVEMBER 1978
VOLUME 40
NUMBER 5
517
Figs. 1 and 2. Two mirror images. The large vertical space between the prepared maxillary and mandibular teeth, the edentulous spaces,and the posterior cross-bite relationship create a difficult problem for making an occlusal registration.
Fig. 3. The maxillary side of the alginate occlusal registration with large facial and lingual regions of support for the maxillary cast. The metal stop (MS) was placed between the teeth to obtain a predetermined vertical opening (1.5 mm) before the alginate registration was made. Thin incisal and occlusal sections are unsuitable to support casts. Fig 4. The mandibular side of the alginate occlusal registration.
poet&or region, so as to get the maximum support in this area. Usually, most of the material placed in the mouth will flow naturally into the palatal area above the tongue, where the material should cover the palatal area of the maxillary teeth and soft tissues. Althaugh some patients gag when any foreign material is placed in their mouths, few patients Seem to be bothered by this method of registration, in spite of the amount of material used. The setting of the mate&al can of course be speeded up by using warm water and warm mixing bowls to lessen the time the alginate must remain in the mouth. Storage of a&ate occlusal registrations can be a problem. If left for any time in room atmosphere they will shrink from evaporation. If left to soak in a water solution they will absorb moisture, which will cause distortion. Accordingly, alginate occlusal mgistmtions should be kept in a suitable humidor and we-d as soon as possible.
518
Mounting casts In order to see that the casts are seated properly and completely in the alginate occlusal registration, the labial and buccal material is cut away with a sharp knife (Figs. 5 and 6). The incisal edges or cusp tips of the teeth of both upper and lower casts should completely contact the alginate registration. If a space is evident the alginate should be cut away in those areas where the cast does not coincide with the registration. This space is the result of disparities between the working cast and the occlusal registration in the tongue area of the mandibular cast and in the tuberosity or muscle regions of the maxillary cast. Once these disparities are removed, the casrs should be ready for the articulator, but care must be taken in mounting to avoid pressing either cast in such a way as to create a torque or twist, for such motion will distort the relationship of the opposing casts. To avoid this, the dentist should lock the two casts together with a number of supporting sticks
NOVEMBER
1978
VOLUME
40
NUMBER
5
Figs. 5 and 6. Alginate occlusal registration material (shaded area) has been cut away buccally and labially to expose the in&al and buccal edges of the teeth to ensure the castsfit accurately into their respective impressions. Sticks attached to the casts with sticky wax stabilize them for mounting on the articulator. waxed around the casts (Figs. 5 and 6). These rods are attached to both casts when one is resting passively and vertically over the other, with the supporting alginate occlusal registration placed between them. The casts can then be mounted safely on the articulator without distortion.
APPLICATIONS The alginate occlusal registration can be used in many different procedures: in partially edentulous mouths needing fixed and/or removable partial dentures (Figs. 1 and 2); in completely edentulous mouths to obtain a preliminary relationship of the casts so as to orient a central bearing pin and opposing plate to occlusion rims for a more accurate occlusal registration; in mouths having a complete dentition; in mouths with extreme malocclusions (Class II or III occlusal relationships); and along
THE KXJRNAL
OF PROSTHETIC
DENTISTRY
with anterior wax or metal stops in mouths with “open-bite” relationships (Figs. 1 and 2).
SUMMARY AND CONCLUSION Alginate impression material can be used to make occlusal registrations. It is probably most useful for occlusal registrations of partially edentulous mouths, although it can be so used for complete edentulous mouths, mouths with no missing teeth, and for mouths having severe malocclusions. A brief discussion of some of the limitations of other materials used for occlusal registrations was presented. Refnirttrequeststo: R. SCOTT 1006-925 W. GEORGIA VANCOUVER, B. C. V6C lR5
DR. WILLIAM
CANADA
519
