Esthetic Partials are difficult to fabricate for a patient when:
1. The patient has no posterior abutments. The shape of centrals, laterals, and cuspids make it difficult to hide the retentive arm without crowning or significantly preparing the abutment teeth. Consult with Armstrong Laboratory to see if an Esthetic Partial can be applied to such a case. ClearClasp or The Virginia Partial may be an alternative if the abutments can’t be used for an Esthetic Partial.
2. The patient has an extremely deep overbite where the lower teeth touch the upper lingual gingival tissue. There may be no room for minor connectors. The problem must be corrected by crowning or selective grinding the lowers.
See Figures below. Rest preparations (A) should be deep enough to allow a rest thickness of at least 1.5 mm. Rest seats should be prepared with relatively parallel walls (not spoon shaped) so the rest provides bracing for the appliance.
Brassler makes two F.G. diamond burs that are good for preparing rests: #845.KR.018 for bicuspids and #845.KR.025 for molars.
Distal Free-End Saddle Design
Prepare a guide plane (B) on the lingual half of the mesial surface, making it as tall as possible and as wide as possible without destroying the contact area. Note that all guide planes used for the appliance must be as parallel to one another as clinically possible. These guide planes are fitted with proximal plates on the casting, which act as reciprocation for the retentive arms.
On the distal surface, prepare a narrow, flat, “positioning guide plane” (C) in the occlusal ¼ of the distal surface. This guide plane is wide from buccal to lingual but only 1-2 mm tall from occlusal toward gingival. This guide plane moves the undercut gingivally and provides room for the artificial tooth to contact the abutment occlusal to the clasp arm.
There should be at least an 0.010 undercut on the distal-facial surface near the facial line angle that is adjacent to the saddle area. This is the undercut where the clasp will engage the tooth. If there is doubt about adaquate undercut in this area, prepare a dimple at the junction of the middle and gingival thirds of the tooth surface.
Mesial Free-End Saddle Design
(Bicuspids and Anterior Teeth Missing to the Midline)
The preparations are similar but the mesial-distal orientation of the rest (A), guide plane (B), and positioning guide plane (C) are switched. Move the rest preparation (A) to the distal side, the guide plane (B) to the distal side, and the positioning guide plane (C) to the mesial side.
Additional support and retention can be gained by clasping the posterior abutment. However, if there are any doubts about the periodontal health of the posterior abutment, it’s still advisable to use the Distal Free-End design. This way, if the posterior abutment is subsequently lost, it can be added without having to redesign and remake the partial.
Diagnostic Support Services
To assist you in designing Esthetic Partials, Armstrong Laboratory provides a free diagnostic service. Send in your study models and we will survey them, suggest a design, and prepare the cast approximately as you would need to prepare the patient’s teeth. The models are then returned to you for your approval.
This focus sheet is intended only to provide an overview of the concept of Esthetic Partials and explain the most common preparation requirements. There are a number of other designs that could not be described for lack of space.
Armstrong Laboratory provides an RPD Syllabus that explains all the different designs available, esthetic and standard, with extensive illustrations and descriptions of the preparation requirements. This Syllabus is provided complimentary with your first Chrome case.