An alternative orientation partial dentures M.
B. Moulding,
W.
D.
Sulik,
University University
DMD, DDS,
MSa
of nonrigid
G. A. Holland,
DDS,
MSb
connectors
in fixed
and
MSC
of Saskatchewan, of North Carolina,
College of Dentistry, School of Dentistry,
Saskatoon, Saskatchewan, Chapel Hill, NC.
Canada,
and
Nonrigid connectors have been advocated for fixed partial dentures. However, space limitations may require overreduction of the preparation or overcontouring of the retainer to place the keyway within the retainer wall. An inverted orientation of the nonrigid connector can resolve these problems, With this design, the key is attached to the distal surface of the mesial retainer in a dual-abutment fixed partial denture, and the keyway is incorporated in the mesial surface of the pontic. This inverted orientation offers several advantages with few disadvantages. (J PROSTHET DENT 1992;68:236-8.)
N ‘.
onrlgld connectors have been indicated in fixed partial dentures (FPDs) for various reasons. Unlike rigid connectors, nonrigid connectors permit an FPD to be delivered as separate segments. They are supplied in two forms: manufactured alloy connectors or plastic patterns. With either type the connector is incorporated in the wax pattern before investing and casting. Although there are various designs, all nonrigid connectors have two component parts: the key and the keyway. References will be made to the common tapering T-type connector. CONVENTIONAL
ORIENTATION
The conventional orientation of the nonrigid connectors in a dual-abutment FPD incorporates the keyway within the distal surface of the anterior retainer of the mesial segment. The keyway opening is on the occlusal surface with the taper diverging occlusally. The key is attached to the mesial surface of the pontic and posterior retainer or distal segment, and its taper also diverges occlusally. The mesial segment is seated first at delivery, and then the distal segment is seated with the key sliding in the keyway of the anterior retamer (Fig. 1). Shillingburg and Fisher1 suggested that the distal surface of the anterior abutment must be perceptively prepared to incorporate the keyway in the normal contours of the retainer. Insufficient tooth reduction will overcontour the distal surface of the retainer and can compromise periodontal health. Conversely, reduction to provide adequate space for conventional placement of the connector
eAssociate Professor, Director af Fixed Prosthodontics, of Saskatchewan, College of Dent,istry. bProfessor, Department of Fired Prosthodontics, North Carolina, School of Dentistry. “Private Practice, Chapel Hill, N.C.
1Ql1138201 236
University University
of
Fig.
1.
Traditional
orientation of nonrigid connector.
can weaken the abutment and threaten pulpal integrity. Placing keyways in retainers of small teeth or in teeth with large pulps commonly results in overcontoured distal surfaces. Conventional orientation of a connector is more arduous with a mesially inclined posterior abutment, and the dentist will often overprepare the anterior abutment or overcontour the retainer (Figs. 2 and 3). ALTERNATIVE
ORIENTATION
The alternative orientation of the nonrigid connector reverses the key and keyway. The key is attached to the distal surface of the anterior retainer and is inverted so that its taper converges occlusally. The keyway is also inverted and incorporated in the mesial surface of the pontic, with the opening positioned on the tissue surface of the pontic. The mesiai segment is seated first at delivery, followed by the distal segment, with the keyway sliding over the key of the anterior retainer (Fig. 4). There are a number of advantages to this orientation,
AUGUST1992
VOLUME68
NUMBER2
NONRIGID
CONNECTORS
IN FPDs
Fig. 2. Conventional orientation with tilted molar overtapered distal surface of premolar abutment.
and
Fig. 4. Inverted a more conservative
orientation of a nonrigid connector with preparation of the premolar abutment.
/---
and over-
Fig. 5. Inverted orientation with tilted molar, illustrating the normal abutment preparation and improved contour of retainer.
Since the key is positioned extracoronally on the anterior retainer, the anterior abutment can be prepared without additional reduction to provide space for the nonrigid connector. This conservative tooth preparation ensures retention, improves abutment strength, and minimizes pulpal irritation (Fig. 4).
be resolved with the inverted orientation. The key is cantilevered distally on a strut of metal that becomes the connector and the keyway is positioned more distally within the pontic (Fig. 5). This inverted orientation allows more flexibility in positioning the angled connector while maintaining the desired embrasures facially, lingually, and gingivally. The principles of biologic contours are then realized with physiologic emergence angles.
Fig. 3. Common contoured
orientation premolar retainer.
Conservative
Physiologic
tooth
axial
with tilted
molar
prepa.ration
contours
The nonrigid connector is entirely within the contours of the pontic using this inverted orientation, and overcontouring of the distal axial surface of the anterior retainer can be controlled. A flat emergence profile and physiologic contour of the gingival one third can be developed (Fig. 4).
Flexibility
of angulation
The problems with paralleling the nonrigid connector to a mesially inclined posterior abutment (Figs. 2 and 3) can
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
Esthetic
potential
The inverted orientation of a nonrigid connector can be more esthetically pleasing in porcelain fused-to-metal (PFM) FPDs. Since the keyway opening is on the tissue surface of the pontic, the only visual evidence of the connector is the interface between the metal guiding planes of the two segments. This surface can be concealed by placing the guide planes at the occlusal embrasure between the retainer and pontic. However, with porcelain coverage,
237
MOULDING,
caution must be exercised to ensure that no contact occurs between the porcelain of the two segments. The porcelain can fracture as a result of shear stresses because of the slight unavoidable movement of the nonrigid connector. The keyway seat of the inverted orientation is farther from the long axis of the anterior abutment, so concern may arise about distal torquing of this tooth. In a photoelastic stress analysis that evaluated nonrigid connectors in a five-unit FPD with a pier abutment, no significant differences in stress patterns were observed between the normal and inverted orientations placed at the distal surface of the pier.2 Also, if the contact between the two segments is precise, there will be limited movement before the guide planes of the two segments resist any “bending effect” of the FPD, minimizing the distal torquing of the anterior abutment. There is one disadvantage to inverting the orientation of the nonrigid connector. With the inverted orientation, the opening of the keyway and the porcelain-to-metal junction (with a metal/ceramic pontic) are positioned on the tissue surface of the pontic. With tissue-contacting pontics, the space between the key and the keyway is an area for plaque retention and resultant tissue irritation. This problem is avoided with the use of nontissue-contacting pontics, although this is not always possible. However, the poten-
umes
tial for minor irritation ter when one considers entation.
HOLLAND,
AND
SULIK
of the ridge mucosa is a small matthe advantages of the inverted ori-
SUMMARY An alternative orientation of nonrigid connectors in FPDs has been described that has the following advantages: (1) conventional tooth abutment preparations with less reduction; (2) suitable axial contours; (3) simplified angulation and placement of the nonrigid connector with a mesially inclined posterior abutment, and (4) improved esthetics with porcelain. REFERENCES 1. Shillingburg HT, Fisher DW. Non-rigid connectors for fixed partial dentures. J Am Dent Assoc 1973;87:1195-8. 2. Moulding MB, Holland GA, Sulik WD. Photoelastic stress analysis of supporting alveolar bone as modified by non-rigid connectors. J PROSTHET DENT
1988;59:263-74.
Reprint requests to: DR. M. B. MOULDING DENTAL CLINIC BUILDING UNIVERSITY OF SASKATCHEWAN SASKATOON, SASKATCHEWAN S7N OWO CANADA
avai
Bound volumes of THE JOURNAL OF PROSTHETIC DENTISTRY are available to subscribers (only) for the 1992 issues from the publisher at a cost of $55.00 ($68.00 international) for Vol. 67 (January-June) and Vol. 68 (July-December). Shipping charges are included. Each bound volume contains a subject and author index, and all advertising is removed. Copies are shipped within 30 days after publication of the last issue in the volume. The binding is durable buckram with the journal name, volume number, and year stamped in gold on the spine. Volumes 65 and 66 are also available. Payment must accompany all orders. Contact Mosby-Year Book, Inc., Subscription Services, 11830 Westline Industrial Drive, St. Louis, MO 63146-3318, USA; phone (800) 325-4177, ext. 4351, or (314)453-4351. Subscriptions must be in force to qualify. Bound volumes are not available in place of a regular JOURNAL subscription.
238
AUGUST
1992
VOLUME
68
NUMBER
2
B. Moulding,
W.
D.
Sulik,
University University
DMD, DDS,
MSa
of nonrigid
G. A. Holland,
DDS,
MSb
connectors
in fixed
and
MSC
of Saskatchewan, of North Carolina,
College of Dentistry, School of Dentistry,
Saskatoon, Saskatchewan, Chapel Hill, NC.
Canada,
and
Nonrigid connectors have been advocated for fixed partial dentures. However, space limitations may require overreduction of the preparation or overcontouring of the retainer to place the keyway within the retainer wall. An inverted orientation of the nonrigid connector can resolve these problems, With this design, the key is attached to the distal surface of the mesial retainer in a dual-abutment fixed partial denture, and the keyway is incorporated in the mesial surface of the pontic. This inverted orientation offers several advantages with few disadvantages. (J PROSTHET DENT 1992;68:236-8.)
N ‘.
onrlgld connectors have been indicated in fixed partial dentures (FPDs) for various reasons. Unlike rigid connectors, nonrigid connectors permit an FPD to be delivered as separate segments. They are supplied in two forms: manufactured alloy connectors or plastic patterns. With either type the connector is incorporated in the wax pattern before investing and casting. Although there are various designs, all nonrigid connectors have two component parts: the key and the keyway. References will be made to the common tapering T-type connector. CONVENTIONAL
ORIENTATION
The conventional orientation of the nonrigid connectors in a dual-abutment FPD incorporates the keyway within the distal surface of the anterior retainer of the mesial segment. The keyway opening is on the occlusal surface with the taper diverging occlusally. The key is attached to the mesial surface of the pontic and posterior retainer or distal segment, and its taper also diverges occlusally. The mesial segment is seated first at delivery, and then the distal segment is seated with the key sliding in the keyway of the anterior retamer (Fig. 1). Shillingburg and Fisher1 suggested that the distal surface of the anterior abutment must be perceptively prepared to incorporate the keyway in the normal contours of the retainer. Insufficient tooth reduction will overcontour the distal surface of the retainer and can compromise periodontal health. Conversely, reduction to provide adequate space for conventional placement of the connector
eAssociate Professor, Director af Fixed Prosthodontics, of Saskatchewan, College of Dent,istry. bProfessor, Department of Fired Prosthodontics, North Carolina, School of Dentistry. “Private Practice, Chapel Hill, N.C.
1Ql1138201 236
University University
of
Fig.
1.
Traditional
orientation of nonrigid connector.
can weaken the abutment and threaten pulpal integrity. Placing keyways in retainers of small teeth or in teeth with large pulps commonly results in overcontoured distal surfaces. Conventional orientation of a connector is more arduous with a mesially inclined posterior abutment, and the dentist will often overprepare the anterior abutment or overcontour the retainer (Figs. 2 and 3). ALTERNATIVE
ORIENTATION
The alternative orientation of the nonrigid connector reverses the key and keyway. The key is attached to the distal surface of the anterior retainer and is inverted so that its taper converges occlusally. The keyway is also inverted and incorporated in the mesial surface of the pontic, with the opening positioned on the tissue surface of the pontic. The mesiai segment is seated first at delivery, followed by the distal segment, with the keyway sliding over the key of the anterior retainer (Fig. 4). There are a number of advantages to this orientation,
AUGUST1992
VOLUME68
NUMBER2
NONRIGID
CONNECTORS
IN FPDs
Fig. 2. Conventional orientation with tilted molar overtapered distal surface of premolar abutment.
and
Fig. 4. Inverted a more conservative
orientation of a nonrigid connector with preparation of the premolar abutment.
/---
and over-
Fig. 5. Inverted orientation with tilted molar, illustrating the normal abutment preparation and improved contour of retainer.
Since the key is positioned extracoronally on the anterior retainer, the anterior abutment can be prepared without additional reduction to provide space for the nonrigid connector. This conservative tooth preparation ensures retention, improves abutment strength, and minimizes pulpal irritation (Fig. 4).
be resolved with the inverted orientation. The key is cantilevered distally on a strut of metal that becomes the connector and the keyway is positioned more distally within the pontic (Fig. 5). This inverted orientation allows more flexibility in positioning the angled connector while maintaining the desired embrasures facially, lingually, and gingivally. The principles of biologic contours are then realized with physiologic emergence angles.
Fig. 3. Common contoured
orientation premolar retainer.
Conservative
Physiologic
tooth
axial
with tilted
molar
prepa.ration
contours
The nonrigid connector is entirely within the contours of the pontic using this inverted orientation, and overcontouring of the distal axial surface of the anterior retainer can be controlled. A flat emergence profile and physiologic contour of the gingival one third can be developed (Fig. 4).
Flexibility
of angulation
The problems with paralleling the nonrigid connector to a mesially inclined posterior abutment (Figs. 2 and 3) can
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
Esthetic
potential
The inverted orientation of a nonrigid connector can be more esthetically pleasing in porcelain fused-to-metal (PFM) FPDs. Since the keyway opening is on the tissue surface of the pontic, the only visual evidence of the connector is the interface between the metal guiding planes of the two segments. This surface can be concealed by placing the guide planes at the occlusal embrasure between the retainer and pontic. However, with porcelain coverage,
237
MOULDING,
caution must be exercised to ensure that no contact occurs between the porcelain of the two segments. The porcelain can fracture as a result of shear stresses because of the slight unavoidable movement of the nonrigid connector. The keyway seat of the inverted orientation is farther from the long axis of the anterior abutment, so concern may arise about distal torquing of this tooth. In a photoelastic stress analysis that evaluated nonrigid connectors in a five-unit FPD with a pier abutment, no significant differences in stress patterns were observed between the normal and inverted orientations placed at the distal surface of the pier.2 Also, if the contact between the two segments is precise, there will be limited movement before the guide planes of the two segments resist any “bending effect” of the FPD, minimizing the distal torquing of the anterior abutment. There is one disadvantage to inverting the orientation of the nonrigid connector. With the inverted orientation, the opening of the keyway and the porcelain-to-metal junction (with a metal/ceramic pontic) are positioned on the tissue surface of the pontic. With tissue-contacting pontics, the space between the key and the keyway is an area for plaque retention and resultant tissue irritation. This problem is avoided with the use of nontissue-contacting pontics, although this is not always possible. However, the poten-
umes
tial for minor irritation ter when one considers entation.
HOLLAND,
AND
SULIK
of the ridge mucosa is a small matthe advantages of the inverted ori-
SUMMARY An alternative orientation of nonrigid connectors in FPDs has been described that has the following advantages: (1) conventional tooth abutment preparations with less reduction; (2) suitable axial contours; (3) simplified angulation and placement of the nonrigid connector with a mesially inclined posterior abutment, and (4) improved esthetics with porcelain. REFERENCES 1. Shillingburg HT, Fisher DW. Non-rigid connectors for fixed partial dentures. J Am Dent Assoc 1973;87:1195-8. 2. Moulding MB, Holland GA, Sulik WD. Photoelastic stress analysis of supporting alveolar bone as modified by non-rigid connectors. J PROSTHET DENT
1988;59:263-74.
Reprint requests to: DR. M. B. MOULDING DENTAL CLINIC BUILDING UNIVERSITY OF SASKATCHEWAN SASKATOON, SASKATCHEWAN S7N OWO CANADA
avai
Bound volumes of THE JOURNAL OF PROSTHETIC DENTISTRY are available to subscribers (only) for the 1992 issues from the publisher at a cost of $55.00 ($68.00 international) for Vol. 67 (January-June) and Vol. 68 (July-December). Shipping charges are included. Each bound volume contains a subject and author index, and all advertising is removed. Copies are shipped within 30 days after publication of the last issue in the volume. The binding is durable buckram with the journal name, volume number, and year stamped in gold on the spine. Volumes 65 and 66 are also available. Payment must accompany all orders. Contact Mosby-Year Book, Inc., Subscription Services, 11830 Westline Industrial Drive, St. Louis, MO 63146-3318, USA; phone (800) 325-4177, ext. 4351, or (314)453-4351. Subscriptions must be in force to qualify. Bound volumes are not available in place of a regular JOURNAL subscription.
238
AUGUST
1992
VOLUME
68
NUMBER
2
