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Technique for master impressions in fixed restorations
TECHNIQUE
FOR MASTER IMPRESSIOIVS RESTORATIONS ELLJOT
E‘EISRERC,
Scarsdale.
A
IIK FIXEIJ
I).I>.s.
N, 1’.
N ACCURATE SET of full-mouth working casts are a necessary part in the construction of fixed restorations. These casts, when articulated, should have the respective dies of the prepared teeth in their correct positions in the arches. Thus, in making the original castings, as much emphasis can be placed on the size and shape and occlusion of the castings, as is placed on the gingival fit. This is extremely important from a periodontal standpoint, since all fixed restorations should function in the mouth as an integral part of the masticatory apparatus. To obtain such working casts, the materials used are : (1) wax, (2) plaster, ( 3 j alginate, and (4) modeling compound. 1. The wax “squash bite” usually results in jacket or veneer crowns which are built too high, as well as too far toward either the buccal or the lingual side of the arch. Thus, a restoration which looks perfect on the cast usually has to he changed when it is introduced into the mouth. This is due to the distortion of the wax while it is being removed from the mouth, or when the die is introduced into the was, or by changes caused by the heat developed during the setting of thtx stone. Also, it is very difficult to make sure that the patient is registering his centric relation accurately while he is biting into a large piece of wax. 2. Plaster will give a good end result, but its U.Win full impression is hard OII (a) The the operator as well as on the patient. This is due to the following: many undercuts existing where the teeth are present necessitate the removal of the impression in sections. (hi Special skill is needed to obtain a complete imprcssion of the arch. (c) The hulk of plaster necessary for a full impression produces heat, and the changes which occur while the plaster is setting arc not pleasant to the patient. Therefore, while it would be easy to use plaster for a small segment of the arch, it hecomes much more difficult when plaster is ~rsect ill obtaining full impressions. 3. The alginates can he used to reproduce the dental arches very accurately, but it is very difficult to seat the dies in their respective positions and to keep them in place while the casts are poured. 4. A modeling compound impression may be distorted upon removal from the mouth, producing an inaccurate cast. A combination of plaster and alginate in a one-piece over-all impression will reproduce the contours of the mouth both accurately and quickly. The plaster is Received
for publication
March
19. 1055.
J. Pros. Den. September, 1955
used in those areas where teeth have been prepared (in order to hold the dies j, and an alignate is used to reproduce the rest of the dental arch. The resulting cast will make it easier to develop the correct occlusion and the alignment of the structures which are so important in the construction of functionally correct abutments and fixed restorations. Fig. 1.
Fig. 2. Fig. l.-Upper and lower trays prepared for combination alginate plaster impressions. Fig. Z.-A cutout tray with wax covers. 8, A wax cover to be luted in position. B, The prepared hole in the tray which the wax piece will cover. C, A wax piece luted over the cutout area. COMBINATION
IMPRESSIONS
Use a modified tray for alginates which covers the entire jaw. Prepare the modified trays by cutting out part of the occlusal portions of the regular alginate trays. The cutout section includes the region distal to the canine tooth posteriorly, to the end of the tray, except a small strip of metal left at the distal end of the tray to
1101 tic), sty
Fig. 5.
.-I, The retained and undisturbed portion. B, The Fig. 3.-A cutout alginate impression. from the region \vhc~rc rrstoratiolls arc being m.ade. and prep ared alg :inate has been removed of plastrr. for . the introduction Fig, 4.-The completed combination irn],rc%sioll watly for pouring. ;1, The alginate part C”, The dies are in position in the R, The plaster part of the impression. of the impression. W Hngs which are held in plaster. Fig. 6.-The completed cast wit”n the dies in plare.
FEINBERG
666
J. Pros. Den Srptember,
1955
Cover the cutout parts of the tray with a layer of red wax, and lute it in place on the tray, Removable metal coverings may be used for this purpose but are not necessary (Fig. 2). Fill the tray with a mix of alginate impression material and make an over-all impression of the entire jaw. Try to obtain an impression of as much of the mouth as possible, including the reflected border tissues. This is necessary so that the alginate impression will snap back into place when it is reintroduced into the mouth later. Remove the alginate impression from the mouth and cut away part of the alginate impression material in the region where restorations are being made, and remove the red wax which is over this section. Save the piece of red wax for use later. To make provision for the plaster, cut the alginate from the mesial side of the anterior abutment to the distal of the posterior abutment. Cut away enough alginate lingually to provide space for the necessary thickness of plaster to hold the copings in place. Remove all of the alginate from the buccal side in this region. This is done so that the plaster will extend to the flange of the tray and be held in position by the undercut in the tray itself. For a lower impression, all of the alginate is removed from the lingual side of the teeth so that the plaster will be held by both the buccal and lingual sides of the tray (Fig. 3). Place the transfer copings on the prepared teeth. This step is not absolutel? necessary, but it is much easier to seat the dies into the copings rather than directly into the plaster. Replace the prepared alginate impression back in the mouth. It will snap into its correct position if there is a complete impression of the tissues up to the reflected border tissues. Be sure that enough alginate has been cleared away so the region where the restorations are being made is entirely free and open for the introduction of the plaster. Make a thin mix of quick-setting plaster. With a small spatula, place the plaster through the hole in the occlusal surface of the tray so it surrounds the copings and covers the edentulous areas of the ridge. Place an excess of plaster in the opening in the tray and condense it by pressing the piece of red wax (removed before the alginate was cut out) into place over the opening in the tray. Allow the plaster to set for four minutes, and then remove the impression from the mouth. The impression will be removed easily in one piece with the transfer copings in place in the plaster part of the impression (Fig. 4). Place the dies in their copings and pour up the cast. Also, pour up a full alginate impression of the opposing jaw (Figs. 4 and 5). When these casts are occluded, the result will be a set of full-mouth impressions with each die in its correct position, and few, if any, changes will be necessary when the finished product is inserted in the mouth. This technique attains a better end-result with a minimum of effort, and saves chair-time now lost in grinding-in so-called finished restorations. HARWOOD SCARSDALE,
BLDG.
N. Y.
FOR MASTER IMPRESSIOIVS RESTORATIONS ELLJOT
E‘EISRERC,
Scarsdale.
A
IIK FIXEIJ
I).I>.s.
N, 1’.
N ACCURATE SET of full-mouth working casts are a necessary part in the construction of fixed restorations. These casts, when articulated, should have the respective dies of the prepared teeth in their correct positions in the arches. Thus, in making the original castings, as much emphasis can be placed on the size and shape and occlusion of the castings, as is placed on the gingival fit. This is extremely important from a periodontal standpoint, since all fixed restorations should function in the mouth as an integral part of the masticatory apparatus. To obtain such working casts, the materials used are : (1) wax, (2) plaster, ( 3 j alginate, and (4) modeling compound. 1. The wax “squash bite” usually results in jacket or veneer crowns which are built too high, as well as too far toward either the buccal or the lingual side of the arch. Thus, a restoration which looks perfect on the cast usually has to he changed when it is introduced into the mouth. This is due to the distortion of the wax while it is being removed from the mouth, or when the die is introduced into the was, or by changes caused by the heat developed during the setting of thtx stone. Also, it is very difficult to make sure that the patient is registering his centric relation accurately while he is biting into a large piece of wax. 2. Plaster will give a good end result, but its U.Win full impression is hard OII (a) The the operator as well as on the patient. This is due to the following: many undercuts existing where the teeth are present necessitate the removal of the impression in sections. (hi Special skill is needed to obtain a complete imprcssion of the arch. (c) The hulk of plaster necessary for a full impression produces heat, and the changes which occur while the plaster is setting arc not pleasant to the patient. Therefore, while it would be easy to use plaster for a small segment of the arch, it hecomes much more difficult when plaster is ~rsect ill obtaining full impressions. 3. The alginates can he used to reproduce the dental arches very accurately, but it is very difficult to seat the dies in their respective positions and to keep them in place while the casts are poured. 4. A modeling compound impression may be distorted upon removal from the mouth, producing an inaccurate cast. A combination of plaster and alginate in a one-piece over-all impression will reproduce the contours of the mouth both accurately and quickly. The plaster is Received
for publication
March
19. 1055.
J. Pros. Den. September, 1955
used in those areas where teeth have been prepared (in order to hold the dies j, and an alignate is used to reproduce the rest of the dental arch. The resulting cast will make it easier to develop the correct occlusion and the alignment of the structures which are so important in the construction of functionally correct abutments and fixed restorations. Fig. 1.
Fig. 2. Fig. l.-Upper and lower trays prepared for combination alginate plaster impressions. Fig. Z.-A cutout tray with wax covers. 8, A wax cover to be luted in position. B, The prepared hole in the tray which the wax piece will cover. C, A wax piece luted over the cutout area. COMBINATION
IMPRESSIONS
Use a modified tray for alginates which covers the entire jaw. Prepare the modified trays by cutting out part of the occlusal portions of the regular alginate trays. The cutout section includes the region distal to the canine tooth posteriorly, to the end of the tray, except a small strip of metal left at the distal end of the tray to
1101 tic), sty
Fig. 5.
.-I, The retained and undisturbed portion. B, The Fig. 3.-A cutout alginate impression. from the region \vhc~rc rrstoratiolls arc being m.ade. and prep ared alg :inate has been removed of plastrr. for . the introduction Fig, 4.-The completed combination irn],rc%sioll watly for pouring. ;1, The alginate part C”, The dies are in position in the R, The plaster part of the impression. of the impression. W Hngs which are held in plaster. Fig. 6.-The completed cast wit”n the dies in plare.
FEINBERG
666
J. Pros. Den Srptember,
1955
Cover the cutout parts of the tray with a layer of red wax, and lute it in place on the tray, Removable metal coverings may be used for this purpose but are not necessary (Fig. 2). Fill the tray with a mix of alginate impression material and make an over-all impression of the entire jaw. Try to obtain an impression of as much of the mouth as possible, including the reflected border tissues. This is necessary so that the alginate impression will snap back into place when it is reintroduced into the mouth later. Remove the alginate impression from the mouth and cut away part of the alginate impression material in the region where restorations are being made, and remove the red wax which is over this section. Save the piece of red wax for use later. To make provision for the plaster, cut the alginate from the mesial side of the anterior abutment to the distal of the posterior abutment. Cut away enough alginate lingually to provide space for the necessary thickness of plaster to hold the copings in place. Remove all of the alginate from the buccal side in this region. This is done so that the plaster will extend to the flange of the tray and be held in position by the undercut in the tray itself. For a lower impression, all of the alginate is removed from the lingual side of the teeth so that the plaster will be held by both the buccal and lingual sides of the tray (Fig. 3). Place the transfer copings on the prepared teeth. This step is not absolutel? necessary, but it is much easier to seat the dies into the copings rather than directly into the plaster. Replace the prepared alginate impression back in the mouth. It will snap into its correct position if there is a complete impression of the tissues up to the reflected border tissues. Be sure that enough alginate has been cleared away so the region where the restorations are being made is entirely free and open for the introduction of the plaster. Make a thin mix of quick-setting plaster. With a small spatula, place the plaster through the hole in the occlusal surface of the tray so it surrounds the copings and covers the edentulous areas of the ridge. Place an excess of plaster in the opening in the tray and condense it by pressing the piece of red wax (removed before the alginate was cut out) into place over the opening in the tray. Allow the plaster to set for four minutes, and then remove the impression from the mouth. The impression will be removed easily in one piece with the transfer copings in place in the plaster part of the impression (Fig. 4). Place the dies in their copings and pour up the cast. Also, pour up a full alginate impression of the opposing jaw (Figs. 4 and 5). When these casts are occluded, the result will be a set of full-mouth impressions with each die in its correct position, and few, if any, changes will be necessary when the finished product is inserted in the mouth. This technique attains a better end-result with a minimum of effort, and saves chair-time now lost in grinding-in so-called finished restorations. HARWOOD SCARSDALE,
BLDG.
N. Y.