Journal of Dentistry, 7, No. 2, 1979, pp. 98-l
04. Printed in Great Britain
The use of crowns to modify abutment teeth of removable partial dentures 2. Clinical and laboratory procedures C. H. Turner, BDS, FDS RCS” B. J. Smith, BDS, MSc, FDS RCS t The Dental School, The University of Newcastle upon Tyne
ABSTRACT
only be achieved by the use of restorations. Fyli crowns enable these modifications to be made in conjunction with ideal design and location of the components of removable partial dentures. Part 1 of this paper discussed these relevant components while in Part 2 the clinical and laboratory procedures are described. Major modifications of abutment teeth can
INTRODUCTION When natural teeth are selected as abutments
for removable partial dentures, it is often desirable to modify their axial and occlusal contours. Minor modifications to natural tooth contour can be made by simple grinding but major modifications can only be achieved by the use of restorations. In part 1 of this paper (Smith and Turner, 1979) the indications for crowning abutment teeth were listed, and the components of partial dentures that are relevant to full crown construction, namely, occlusal rests, retentive clasp arms and reciprocal components, were described. The location of these components for tooth-supported and tooth- and tissue-supported partial dentures was discussed and the importance of guide planes emphasized. In this part of the paper the clinical and laboratory procedures involved in the production of crowns for abutment teeth of partial dentures are described.
TOOTH PREPARATION Any standard method of tooth
preparation for full or three-quarter crowns is followed initially (Tylman and Tyhnan, 1960). Bevelled occluso-axial margins and slots may be incorporated into the preparation (Turner, 1977). Subsequently, depending on the actual design of the denture, the tooth preparation is modified to allow for the partial denture components.
GUIDE PLANES Where it is intended to incorporate guide planes into the palatal surfaces of maxillary crowns, the preparations should be finished to definite chamfer margins. It is rarely necessary to provide shoulder margins because the axial divergence of the teeth increases the space available between two contralateral teeth for the development of the guide planes within the crowns.
* Present address: University College Hospital Dental School, Mortimer Market, London. t Present address: Guy’s Hospital Dental School, London.
Turner
and Smith:
Crowns to modify
abutment
teeth
99
Fig. 1. Mirror image photograph of cingulum rest seats on crowned mandibular canine teeth. Note the distal guide planes.
In the mandible the reverse situation applies. It is a common problem to find mandibular premolars inclined lingually, sometimes to a marked extent. Provided that dentine is not exposed, the lingual overhang may be reduced by simple grinding. With more severe undercuts, the premolars can be recontoured with full or partial veneer crowns to provide lingual guide planes. Care must be taken to avoid exposure of the lingual pulp horn during tooth preparation. Where this is unavoidable a post-retained crown can be used to alter the axial inclination of the tooth up to a maximum of 40” (Pickard 1964). Mesial and distal guide planes can usually be developed without any additional tooth reduction.
OCCLUSAL RESTS For a single occlusal rest in the finished crown, additional reduction of the appropriate marginal ridge of the tooth must be carried out to allow for a sufficient thickness of wax in the subsequent wax pattern. An occlusal rest seat at least 1 mm deep may then be carved during the production of the wax pattern. It is not advisable to wait until a crown is cast before attempting to create the occlusal rest seat. Occasionally an embrasure clasp with a double occlusal rest is required, particularly where the posterior arch is intact unilaterally. Sufficient space must be provided in the crown preparation of each tooth for the clasp as well as for the two occlusal rests. This may be achieved during tooth preparation by the creation in each tooth of a curved channel of l-2 mm depth and 1 mm width at the contact area but tapering to zero buccally and lingually by the mid cusp point. Any additional reduction of tooth substance for occlusal rests must be carried out after any reduction necessary for guide planes. Reversal of this order may result in the elimination of the depression for the occlusal rest. Occasionally the placement of rest seats on anterior crowns requires additional tooth reduction. The most suitable and easily prepared rest is placed in the cingulum area (Fig. I). This requires the production of a ledge during tooth preparation which allows a corresponding ledge to be formed in the wax pattern without excessively thinning the gold. Metal lingual surfaces are essential for the development of such rest seat areas. This factor limits the choice of material for the crown to either all gold or porcelain bonded to metal. Acrylic resin-faced gold would be insufficiently resistant to wear from repeated insertion and removal of the clasp on the buccal surface. An all porcelain crown would be weakened by such a cingulum ledge and would be very susceptible to fracture during mastication.
100
Journal of Dentistry, Vol. ~/NO. 2
Fig. 2. Pin-retained root cap cemented on a’ mandibular right second molar. (See Fig. 3 for the occlusal view.) Note the wear facet from the opposing tooth.
A rest seat may also be placed near the proximal gingival margin of a crown, but this necessitates a reduction in the mesiodistal width of the crown. This type would have a limited use on anterior teeth, for instance, because of the poor aesthetics. PARTIAL OVERDENTURE ABUTMENTS It has been mentioned that where exposure of the pulp was unavoidable, a post-retained crown could be used. An alternative would be to cut the tooth down to the gingival level after endodontic therapy and then place a post with a dome-shaped root cap. This arrangement may be suitable for teeth with a poor periodontal condition since it reduces applied leverage to the tooth, allows slight movement of the denture base under load and retains the proprioceptive pathways controlling mandibular movement (Kay and Abes, 1976). In certain situations the size of the pulp may have been reduced by the formation of secondary dentine. Where this has caused complete obliteration of the pulp in the clinical crown, it is commonly accompanied by severe narrowing of the radicular pulp chamber. Access for conventional endodontics is often difficult and may involve removal of considerable coronal tooth substance to reach the root canal. If the root canal has additionally become tortuous the prognosis for a satisfactory root filling is diminished. Where this has happened an alternative to a root filling and a post-retained root cap may be a pin-retained root cap (Fig. 2). The tooth may be safety decoronated and a truncated crown preparation with chamfer margins cut. Finally, to improve retention one or more parallel pin holes may be placed. THE HEMISECTED MOLAR In cases where periodontal disease has involved the bifurcation or trifurcation areas, or endodontic therapy to all the roots of a multi-rooted tooth has not been successful, part of the tooth and root may still be retained (Richard et al., 1977). Usually the distal root of mandibular molar teeth and the palatal root of maxillary molar teeth may be kept, as these have straighter and usually wider root canals which increase the chances of successful endodontic therapy. Once this therapy is completed, the tooth may be divided and the other root or roots extracted. The remaining root can then have either a post and core or a screwor pin-retained amalgam core built up and a crown placed to restore the root to function in
Turner
and Smith:
Crowns to modify
abutment
101
teeth
the form of a premolar. Such a coronal restoration is ideally suited to the development, within the gold, of rest seat and reciprocal component areas, and the ideal buccal contour for a retentive clasp arm. By the use of such a method a distal edentulous area may be avoided.
IMPRESSIONS AND JAW RELATION
RECORDS
The operator should use the Impression technique that gives the best results in his hands. The master cast should be poured as soon as possible in die stone, or the impression electroplated, depending on the actual technique followed. An alginate impression of the opposing arch taken in a well-designed stock tray should also be made. This cast must be poured almost immediately in hard dental stone. Unless the casts can be occluded precisely (provided that the intercuspal position is the position to which the restorations are to be constructed) a jaw relation record must always be made. The choice between centric relation (the most posterior relation of the mandible to the maxillae at the established vertical relation) and the intercuspal position (the position of the mandible at which maximum intercuspation of the teeth occurs) should have been made at the treatment planning stage. The selected jaw relationship is recorded using an interocclusal record between the natural teeth or between occlusion rims. The interocclusal record must be made at the desired vertical relation.
CROWN CONSTRUCTION The master casts are mounted on an articulator using the split-cast technique described by Iaurizten and Wolford (1964). The master casts must be removable since they will be placed on a surveyor table. Removal of the entire cast, plaster and mounting plane assembly from the articulator is not usually satisfactory because of the difficulty of holding it firmly on the surveyor table. The wax patterns are made on the dies of the master cast using either an incremental or a carving technique. The contact areas and occlusal surface are refined on the articulator. The master cast is then placed on the surveyor table and the required guide planes carved parallel to the selected path of insertion using a wax carver in the surveyor chuck (Fig 3). The lengths of the desirable interproximal guide planes were detailed in part 1. The lingual guide planes on maxillary crowns usually have to be associated with ledges because of the inclination of the maxillary teeth. Finally, the buccal retentive area should be created using undercut gauges to obtain the exact degree of horizontal undercut at the correct distance from the gingival margin (Fig. 4). In premolar and canine teeth this distance is usually as little as possible to avoid an unaesthetic appearance. When the crown has a facing the retentive tip of the clasp should rest on gold rather than on the facing. Ideally, and when aesthetics allow, the entire path of insertion of the retentive tip of the clasp should be on gold. It is essential that the crown is not made excessively bulky in order to produce the required degree of undercut. Parkinson (1976) has shown that increased bulk of crowns predisposes to the retention of plaque. Rather, the undercut may be enhanced by means of a small depression at the point of retention. The occlusal rest seats may now be carved in the wax pattern. For the reasons mentioned earlier, this step must follow the creation of the guide planes to avoid the necessity of recarving the rest seats should they be obliterated by the guide planes.
102
Journal of Dentistry, Vol. ~/NO. 2
Fig. 3, Initial stages in carving a guide plane in wax pattern. Wax carver is parallel to the path of insertion.
Fig. 4. Undercut gauge is used to check the correct buccal contour of wax pattern for a molar crown.
Fig. 5. Mirror image photograph showing full crowns cemented on a maxillary left first molar and right first premolar. Note the prepared rest seats and lingual and proximal guide planes. A root cap has been placed on the maxillary right second premolar and an inlay in the maxillary left second premolar.
When the crowns have been cast, they can be replaced on the master cast and then all guide planes and undercuts rechecked on the surveyor. CROWN PLACEMENT The abutment crowns are tried in the mouth and examined carefully for correct fit and occlusion. The authors prefer to cement the crowns on to the abutment teeth before making
Turner
and Smith:
Crowns to modify
fig. 6, Mirror image photograph partial denture in place.
abutment
teeth
of a maxillary
Fig. 7. Mandibular partial denture showing cingulum rests and framework covering a pin-retained root cap. Clasps are wrought gold and engage mesial undercuts.
the impressions for the denture construction (Fig. 5). This arrangement reduces the time the patient is required to wear temporary crowns. Some clinicians prefer to use the crowns as copings on to which the denture is fabricated after an overall impression is made. Where changes in the vertical relation of the jaws have been made, it may be necessary to modify existing dentures with self-cured acrylic resin or to construct all acrylic resin temporary partial dentures to avoid damage to the one or two teeth that may be in occlusion at this stage.
PARTIAL
DENTURE CONSTRUCTION
Rarely, the special trays used for making the crown impressions can be used for the final denture impressions. More often a new tray, spaced for the intended impression material, will have to be made. The authors prefer to use alginate impression material inside a correctly spaced tray for making the impression for the removable partial denture framework. Alginate will tear rather than distort permanently and this can be seen easily. The various synthetic rubber impression materials do not have this advantage. Additionally, alginate impression materials are generally very much cheaper than the synthetic rubber materials. Occasionally, however, alginate impressions tear repeatedly in the same place. If this happens a synthetic rubber impression material should be substituted. The partial denture framework is made on the master cast. The framework is tried in, the jaw relations are again recorded using the framework as a carrier for the record or occlusion rims and the casts mounted on an adjustable articulator. The artificial teeth are set up and the denture tried in and finished (Figs. 6, 7). Processing and deflasking changes in the occlusion are corrected, preferably by remounting the dentures on an articulator. Where only a few teeth are replaced on an entirely tooth-borne partial denture, the use of articulating paper directly in the patient’s mouth may be acceptable.
CONCLUSIONS In part 1 of this papgr the components of partial dentures that are relevant to full crown construction were discussed and the importance of guide planes emphasized. Part 2 has described the clinical and laboratory procedures involved in the production of the crowns. In summary, it is essential that the tooth preparation of the abutment teeth incorporates space
104
Journal of Dentistry,
Vol. ~/NO.
2
for the partial denture components that will be involved with the subsequent crowns. The crowns themselves should be waxed up on a surveyor to be in harmony with the prepared path of insertion and design of the partial denture. Finally, the partial denture itself can be constructed with the knowledge that crown contours will already be correct.
Acknowledgements We are grateful to Professor D. N. Allan and Professor Roy Storer for their helpful comments, to Mr Brian Hill of the Department of Photography of the Newcastle upon Tyne Dental Hospital for the illustrations and to Mr R. Allen of the Department of Operative Dental Surgery for constructing some of the restorations illustrated. REFERENCES Kay W. D. and Abes M. S. (1976) Sensory perception in overdenture patients. J. Prosthef. Dent. 35,615-619. Laurizten A. G. and Wolford L. W. (1964) Occlusal relationships: the split cast method for articulator techniques. J. Prosthet. Dent. 14, 256-265. Parkinson C. F. (1976) Excessive crown contours facilitate endemic plaque niches. J. Prosthet. Dent. 36,424-429.
Pickard H. M. (1964) Variants of the post crown. Br. Dent. J. 117, 5 17-524. Richard G. E., Sarka R. J., Arnold R. M. et al. (1977) Hemisected molars for additional overdenture support. J. Prosth. Dent. 38, 16-2 1. Smith B. J. and Turner C. H. (1979) The use of crowns to modify abutment teeth of removable partial dentures. 1. Introduction and partial denture design. J. Dent. 7,52-56. Turner C. H. (1977) Bevels and slots in full crown preparations. Dent. Update 4, 16 l-l 67. Tylman S. D. and Tylman S. G. (1960) Theory and Practice of Crown and Bridge Prosthodontics, 4th ed. St Louis, Mosby, pp. 694-703.
04. Printed in Great Britain
The use of crowns to modify abutment teeth of removable partial dentures 2. Clinical and laboratory procedures C. H. Turner, BDS, FDS RCS” B. J. Smith, BDS, MSc, FDS RCS t The Dental School, The University of Newcastle upon Tyne
ABSTRACT
only be achieved by the use of restorations. Fyli crowns enable these modifications to be made in conjunction with ideal design and location of the components of removable partial dentures. Part 1 of this paper discussed these relevant components while in Part 2 the clinical and laboratory procedures are described. Major modifications of abutment teeth can
INTRODUCTION When natural teeth are selected as abutments
for removable partial dentures, it is often desirable to modify their axial and occlusal contours. Minor modifications to natural tooth contour can be made by simple grinding but major modifications can only be achieved by the use of restorations. In part 1 of this paper (Smith and Turner, 1979) the indications for crowning abutment teeth were listed, and the components of partial dentures that are relevant to full crown construction, namely, occlusal rests, retentive clasp arms and reciprocal components, were described. The location of these components for tooth-supported and tooth- and tissue-supported partial dentures was discussed and the importance of guide planes emphasized. In this part of the paper the clinical and laboratory procedures involved in the production of crowns for abutment teeth of partial dentures are described.
TOOTH PREPARATION Any standard method of tooth
preparation for full or three-quarter crowns is followed initially (Tylman and Tyhnan, 1960). Bevelled occluso-axial margins and slots may be incorporated into the preparation (Turner, 1977). Subsequently, depending on the actual design of the denture, the tooth preparation is modified to allow for the partial denture components.
GUIDE PLANES Where it is intended to incorporate guide planes into the palatal surfaces of maxillary crowns, the preparations should be finished to definite chamfer margins. It is rarely necessary to provide shoulder margins because the axial divergence of the teeth increases the space available between two contralateral teeth for the development of the guide planes within the crowns.
* Present address: University College Hospital Dental School, Mortimer Market, London. t Present address: Guy’s Hospital Dental School, London.
Turner
and Smith:
Crowns to modify
abutment
teeth
99
Fig. 1. Mirror image photograph of cingulum rest seats on crowned mandibular canine teeth. Note the distal guide planes.
In the mandible the reverse situation applies. It is a common problem to find mandibular premolars inclined lingually, sometimes to a marked extent. Provided that dentine is not exposed, the lingual overhang may be reduced by simple grinding. With more severe undercuts, the premolars can be recontoured with full or partial veneer crowns to provide lingual guide planes. Care must be taken to avoid exposure of the lingual pulp horn during tooth preparation. Where this is unavoidable a post-retained crown can be used to alter the axial inclination of the tooth up to a maximum of 40” (Pickard 1964). Mesial and distal guide planes can usually be developed without any additional tooth reduction.
OCCLUSAL RESTS For a single occlusal rest in the finished crown, additional reduction of the appropriate marginal ridge of the tooth must be carried out to allow for a sufficient thickness of wax in the subsequent wax pattern. An occlusal rest seat at least 1 mm deep may then be carved during the production of the wax pattern. It is not advisable to wait until a crown is cast before attempting to create the occlusal rest seat. Occasionally an embrasure clasp with a double occlusal rest is required, particularly where the posterior arch is intact unilaterally. Sufficient space must be provided in the crown preparation of each tooth for the clasp as well as for the two occlusal rests. This may be achieved during tooth preparation by the creation in each tooth of a curved channel of l-2 mm depth and 1 mm width at the contact area but tapering to zero buccally and lingually by the mid cusp point. Any additional reduction of tooth substance for occlusal rests must be carried out after any reduction necessary for guide planes. Reversal of this order may result in the elimination of the depression for the occlusal rest. Occasionally the placement of rest seats on anterior crowns requires additional tooth reduction. The most suitable and easily prepared rest is placed in the cingulum area (Fig. I). This requires the production of a ledge during tooth preparation which allows a corresponding ledge to be formed in the wax pattern without excessively thinning the gold. Metal lingual surfaces are essential for the development of such rest seat areas. This factor limits the choice of material for the crown to either all gold or porcelain bonded to metal. Acrylic resin-faced gold would be insufficiently resistant to wear from repeated insertion and removal of the clasp on the buccal surface. An all porcelain crown would be weakened by such a cingulum ledge and would be very susceptible to fracture during mastication.
100
Journal of Dentistry, Vol. ~/NO. 2
Fig. 2. Pin-retained root cap cemented on a’ mandibular right second molar. (See Fig. 3 for the occlusal view.) Note the wear facet from the opposing tooth.
A rest seat may also be placed near the proximal gingival margin of a crown, but this necessitates a reduction in the mesiodistal width of the crown. This type would have a limited use on anterior teeth, for instance, because of the poor aesthetics. PARTIAL OVERDENTURE ABUTMENTS It has been mentioned that where exposure of the pulp was unavoidable, a post-retained crown could be used. An alternative would be to cut the tooth down to the gingival level after endodontic therapy and then place a post with a dome-shaped root cap. This arrangement may be suitable for teeth with a poor periodontal condition since it reduces applied leverage to the tooth, allows slight movement of the denture base under load and retains the proprioceptive pathways controlling mandibular movement (Kay and Abes, 1976). In certain situations the size of the pulp may have been reduced by the formation of secondary dentine. Where this has caused complete obliteration of the pulp in the clinical crown, it is commonly accompanied by severe narrowing of the radicular pulp chamber. Access for conventional endodontics is often difficult and may involve removal of considerable coronal tooth substance to reach the root canal. If the root canal has additionally become tortuous the prognosis for a satisfactory root filling is diminished. Where this has happened an alternative to a root filling and a post-retained root cap may be a pin-retained root cap (Fig. 2). The tooth may be safety decoronated and a truncated crown preparation with chamfer margins cut. Finally, to improve retention one or more parallel pin holes may be placed. THE HEMISECTED MOLAR In cases where periodontal disease has involved the bifurcation or trifurcation areas, or endodontic therapy to all the roots of a multi-rooted tooth has not been successful, part of the tooth and root may still be retained (Richard et al., 1977). Usually the distal root of mandibular molar teeth and the palatal root of maxillary molar teeth may be kept, as these have straighter and usually wider root canals which increase the chances of successful endodontic therapy. Once this therapy is completed, the tooth may be divided and the other root or roots extracted. The remaining root can then have either a post and core or a screwor pin-retained amalgam core built up and a crown placed to restore the root to function in
Turner
and Smith:
Crowns to modify
abutment
101
teeth
the form of a premolar. Such a coronal restoration is ideally suited to the development, within the gold, of rest seat and reciprocal component areas, and the ideal buccal contour for a retentive clasp arm. By the use of such a method a distal edentulous area may be avoided.
IMPRESSIONS AND JAW RELATION
RECORDS
The operator should use the Impression technique that gives the best results in his hands. The master cast should be poured as soon as possible in die stone, or the impression electroplated, depending on the actual technique followed. An alginate impression of the opposing arch taken in a well-designed stock tray should also be made. This cast must be poured almost immediately in hard dental stone. Unless the casts can be occluded precisely (provided that the intercuspal position is the position to which the restorations are to be constructed) a jaw relation record must always be made. The choice between centric relation (the most posterior relation of the mandible to the maxillae at the established vertical relation) and the intercuspal position (the position of the mandible at which maximum intercuspation of the teeth occurs) should have been made at the treatment planning stage. The selected jaw relationship is recorded using an interocclusal record between the natural teeth or between occlusion rims. The interocclusal record must be made at the desired vertical relation.
CROWN CONSTRUCTION The master casts are mounted on an articulator using the split-cast technique described by Iaurizten and Wolford (1964). The master casts must be removable since they will be placed on a surveyor table. Removal of the entire cast, plaster and mounting plane assembly from the articulator is not usually satisfactory because of the difficulty of holding it firmly on the surveyor table. The wax patterns are made on the dies of the master cast using either an incremental or a carving technique. The contact areas and occlusal surface are refined on the articulator. The master cast is then placed on the surveyor table and the required guide planes carved parallel to the selected path of insertion using a wax carver in the surveyor chuck (Fig 3). The lengths of the desirable interproximal guide planes were detailed in part 1. The lingual guide planes on maxillary crowns usually have to be associated with ledges because of the inclination of the maxillary teeth. Finally, the buccal retentive area should be created using undercut gauges to obtain the exact degree of horizontal undercut at the correct distance from the gingival margin (Fig. 4). In premolar and canine teeth this distance is usually as little as possible to avoid an unaesthetic appearance. When the crown has a facing the retentive tip of the clasp should rest on gold rather than on the facing. Ideally, and when aesthetics allow, the entire path of insertion of the retentive tip of the clasp should be on gold. It is essential that the crown is not made excessively bulky in order to produce the required degree of undercut. Parkinson (1976) has shown that increased bulk of crowns predisposes to the retention of plaque. Rather, the undercut may be enhanced by means of a small depression at the point of retention. The occlusal rest seats may now be carved in the wax pattern. For the reasons mentioned earlier, this step must follow the creation of the guide planes to avoid the necessity of recarving the rest seats should they be obliterated by the guide planes.
102
Journal of Dentistry, Vol. ~/NO. 2
Fig. 3, Initial stages in carving a guide plane in wax pattern. Wax carver is parallel to the path of insertion.
Fig. 4. Undercut gauge is used to check the correct buccal contour of wax pattern for a molar crown.
Fig. 5. Mirror image photograph showing full crowns cemented on a maxillary left first molar and right first premolar. Note the prepared rest seats and lingual and proximal guide planes. A root cap has been placed on the maxillary right second premolar and an inlay in the maxillary left second premolar.
When the crowns have been cast, they can be replaced on the master cast and then all guide planes and undercuts rechecked on the surveyor. CROWN PLACEMENT The abutment crowns are tried in the mouth and examined carefully for correct fit and occlusion. The authors prefer to cement the crowns on to the abutment teeth before making
Turner
and Smith:
Crowns to modify
fig. 6, Mirror image photograph partial denture in place.
abutment
teeth
of a maxillary
Fig. 7. Mandibular partial denture showing cingulum rests and framework covering a pin-retained root cap. Clasps are wrought gold and engage mesial undercuts.
the impressions for the denture construction (Fig. 5). This arrangement reduces the time the patient is required to wear temporary crowns. Some clinicians prefer to use the crowns as copings on to which the denture is fabricated after an overall impression is made. Where changes in the vertical relation of the jaws have been made, it may be necessary to modify existing dentures with self-cured acrylic resin or to construct all acrylic resin temporary partial dentures to avoid damage to the one or two teeth that may be in occlusion at this stage.
PARTIAL
DENTURE CONSTRUCTION
Rarely, the special trays used for making the crown impressions can be used for the final denture impressions. More often a new tray, spaced for the intended impression material, will have to be made. The authors prefer to use alginate impression material inside a correctly spaced tray for making the impression for the removable partial denture framework. Alginate will tear rather than distort permanently and this can be seen easily. The various synthetic rubber impression materials do not have this advantage. Additionally, alginate impression materials are generally very much cheaper than the synthetic rubber materials. Occasionally, however, alginate impressions tear repeatedly in the same place. If this happens a synthetic rubber impression material should be substituted. The partial denture framework is made on the master cast. The framework is tried in, the jaw relations are again recorded using the framework as a carrier for the record or occlusion rims and the casts mounted on an adjustable articulator. The artificial teeth are set up and the denture tried in and finished (Figs. 6, 7). Processing and deflasking changes in the occlusion are corrected, preferably by remounting the dentures on an articulator. Where only a few teeth are replaced on an entirely tooth-borne partial denture, the use of articulating paper directly in the patient’s mouth may be acceptable.
CONCLUSIONS In part 1 of this papgr the components of partial dentures that are relevant to full crown construction were discussed and the importance of guide planes emphasized. Part 2 has described the clinical and laboratory procedures involved in the production of the crowns. In summary, it is essential that the tooth preparation of the abutment teeth incorporates space
104
Journal of Dentistry,
Vol. ~/NO.
2
for the partial denture components that will be involved with the subsequent crowns. The crowns themselves should be waxed up on a surveyor to be in harmony with the prepared path of insertion and design of the partial denture. Finally, the partial denture itself can be constructed with the knowledge that crown contours will already be correct.
Acknowledgements We are grateful to Professor D. N. Allan and Professor Roy Storer for their helpful comments, to Mr Brian Hill of the Department of Photography of the Newcastle upon Tyne Dental Hospital for the illustrations and to Mr R. Allen of the Department of Operative Dental Surgery for constructing some of the restorations illustrated. REFERENCES Kay W. D. and Abes M. S. (1976) Sensory perception in overdenture patients. J. Prosthef. Dent. 35,615-619. Laurizten A. G. and Wolford L. W. (1964) Occlusal relationships: the split cast method for articulator techniques. J. Prosthet. Dent. 14, 256-265. Parkinson C. F. (1976) Excessive crown contours facilitate endemic plaque niches. J. Prosthet. Dent. 36,424-429.
Pickard H. M. (1964) Variants of the post crown. Br. Dent. J. 117, 5 17-524. Richard G. E., Sarka R. J., Arnold R. M. et al. (1977) Hemisected molars for additional overdenture support. J. Prosth. Dent. 38, 16-2 1. Smith B. J. and Turner C. H. (1979) The use of crowns to modify abutment teeth of removable partial dentures. 1. Introduction and partial denture design. J. Dent. 7,52-56. Turner C. H. (1977) Bevels and slots in full crown preparations. Dent. Update 4, 16 l-l 67. Tylman S. D. and Tylman S. G. (1960) Theory and Practice of Crown and Bridge Prosthodontics, 4th ed. St Louis, Mosby, pp. 694-703.
