Oral Health Group
Feature

Hiding Denture Clasps: A Cosmetic Dilemma

April 1, 2003
by Stephen H. Abrams, DDS


Partial dentures, at times, are a forgotten alternative in replacing missing teeth. Their one major aesthetic failing is the need to use clasps for direct retention. Clasps require at least 180 encirclement of the tooth to act as an active retainer. This means that the clasp arm may be displayed on the buccal surface of the tooth and be visible in the smile. There is an ongoing struggle to provide direct retention in the anterior area without the display of any clasp arm.

There are a number of alternative clasp designs. Mesiodistal grip clasps engage only the mesial and distal surfaces of the tooth.1, 2 They rely upon sound enamel surfaces and long guiding planes. The Equipoise Clasp relies upon a mesial guide plane with clasp extending around to the distal surface.3 The RLS lingually retained clasp for distal extension partial dentures which consists of mesio-occlusal rest a distolingual “L” bar and distobuccal stabilizer.4 Dual path or rotational path of insertion involves rigid retentive components and the initial placement of one segment with the denture being fully seated by rotating the denture into place.5,6,7 These are just a few of the approaches to dealing with aesthetics and retention in partial denture fabrication.

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Over the last 15 years we have utilized the “modified hidden clasp” for clasping anterior teeth. This clasp has been used in conjunction with circumferential clasps on posterior teeth, mesio-distal grip clasp, and guide plane retention. A modified hidden clasp contains an occlusal rest and guide plane along with a bracing arm that engages an undercut on the tooth surface opposite the guide plane.

The literature describes some of the cosmetic challenges to restoring an anterior edentulous space. Some of the solutions offered are to avoid anterior clasping and utilize guide plane retention or utilize the anterior soft tissue undercuts.8,9 The hidden clasp is an ideal clasp for restoring Kennedy Class IV edentulous spaces. In figures 1 and 2 we have used the clasp on tooth 23 to provide an active retainer for the anterior edentulous space. The bracing arm emerges from the distal rest and engages a mesial undercut. The distal guide plane just breaks through the contact area to provide stabilizing action. Additional retention is achieved using circumferential clasps on teeth 17, 14, and 25 along with rests on teeth 27 and 12.

The partial denture (Figs. 3 & 4) provided the patient with a very retentive aesthetic restoration. The clasp on the posterior tooth was only visible with the cheeks retracted. The patient did not report any movement of the anterior section on chewing and no episodes of denture dislodgement. There was no evidence of caries or periodontal breakdown around the abutment teeth and this denture was replaced eight years later because of worn anterior denture teeth.

Hidden clasps can also be utilized for restoring Kennedy Class II edentulous spaces (Figs. 5-7). In these situations, we find that the clasp is extremely retentive. Tooth 23 has a hidden clasp (Fig. 5). There is a mesial guide plane with a bracing arm that extends around the lingual aspect of the tooth to engage the distobuccal undercut. The mesial guide plane extends into the contact area between teeth 22 and 23 but does not break the contact point. The guide plane is prepared so that we created a long parallel surface. In theory10 and in practice we have found that this does not create any additional torque on the tooth. The elements of this clasp eliminate any horizontal or vertical stress on the tooth.

We have also placed a distal guide plane and rest between tooth 13 and 14 to provide some additional cross-arch stabilization (Fig. 5). We were concerned about the long-term prognosis of tooth 14 and wanted to ensure that there was denture framework in the area in case we needed to add to extract this tooth.

Restoring a number of small edentulous anterior spaces introduces additional concerns (Figs. 8-11). In these situations, not only is clasp position a concern but the need to match shape and contour of natural teeth to the denture becomes a significant factor.11 We needed to design a prosthesis that would replace teeth 12 and 21 but also allow for the addition of tooth 11 to the denture if needed (Fig. 8). Tooth 11 was periodontally involved with M1 mobility, 4 mm of gingival recession and 2 mm. pocketing. We needed to utilize the tooth to provide an anterior occlusal stop but not be actively involved in retention. A hidden clasp was placed on tooth 13 with circumferential clasps placed on teeth 15, 25 and 26. A rest was placed on tooth 17 in case there was need to extract this tooth later on (Fig. 9).

Composite veneers were placed on teeth 11 and 22 to allow us to create a uniform anterior shade. The anterior teeth were set on the ridge with no flange and anchored to the framework with small vertical retentive loops.

Figures 10 and 11 show the teeth and partial denture at ten years. During this time there was no further breakdown of any of the abutment teeth or need to replace the composite veneers.

Partial dentures do present a number of unique challenges in creating an aesthetic restoration. One of the major challenges is to create anterior retention without the display of any retentive element. The literature provides us with a number of techniques for designing retainers. Modified hidden clasps provides one solution for the placement of clasps on anterior teeth. Their design allows for a guide plane to reciprocate an undercut on the opposite tooth surface. This clasp design is both retentive and does not place any additional stress or torque on the abutment tooth. These clasps along with other retentive elements should provide patients with a functional and aesthetic restoration.OH

Dr. Abrams and his partner, Dr. Warren Hellen, established a group practice in Scarborough, ON, 22 years ago. He is a fellow of the Pierre Fauchard Academy and the Academy of Dentistry International. Dr. Abrams was recently awarded the Barnabus Day Award from the Ontario Dental Association for 20 years of service to the dental profession. He is the founder of Four Cell Consulting, Toronto.

Dr. Abrams has no financial interest in any of the products or techniques mentioned.

Acknowledgements

I would like to acknowledge the help and advice of Mr. Ron Klausz of Klausz Dental Laboratories Toronto Ontario. Mr. Klausz has always provided interesting and innovative advice. He has introduced me to a number of interesting materials including the Hidden Clasp. My partner, Dr. Warren Hellen, has always provided a willing ear in treatment planning and case management.

Oral Health welcomes this original article.

REFERENCES

1. Osbourne, J., Lammie, G. A., Partial dentures, Edition 4, Philadelphia, 1974, J. B. Lippincott Company.

2. Zarb, G. A., Bergman, B., Clayton, J. A., MacKay, H. F., “Prosthodontic Treatment for Partially Edentuluous Patients, St. Louis, 1978, The C. V. Mosby Company.

3. Goodman, J. J., “The Equipoise Removable Restoration, Trends Tech Comtemp. Dent. Lab., 1991, Volume 8, pages 45 – 52.

4.Aviv, I., Ben-Ur, Z., Cardash, H. S., Fatael, H., “RLS – The Lingually retained clasp assembly for distal extension removable partial dentures”, Quintessence International, 1990, Volume 21, # 3, page 221 – 223.

5.MacKay, H. F., Fenton, A. H., Zarb, G A., Cosmetics and Removable Partial Dentures, Ontario Dentist, 1978, Volume 55, # 3, pages 23 – 28.

6.Halberstam, S C., Renner, R. P., “The Rotational Path Removable Partial Denture: The Overlooked Alternative”, Compend. Contin. Educ. Dent., 1993, Volume 14, # 4, pages 544 – 552.

7.Jacobson, T. E., “Satisfying esthetic demands with rotational path partial dentures”, 1982, JADA, Volume 105, September, pages 460 – 465.

8.Zarb, G. A., MacKay, H. F., “Cosmetics and removable partial dentures – The Class IV partially edentulous patient”, J. Prosthet. Dent., 1981, Volume 46, # 4 pages 360 – 368.

9.Beaumont, A. J., “An overview of esthetics with removable partial dentures”, Quintessence International, 2002, Volume 33, # 10, pag
es 747 – 755.

10.Goodman, J. J., “The Equipoise Removable Restoration, Trends Tech Comtemp. Dent. Lab., 1991, Volume 8, pages 45 – 52.

11.Sykora, O., “Esthetic considerations in the construction of a removable partial denture”, Quintessence International, 1994, Volume 25, # 11, pages 757 – 762.


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