Interdisciplinary Approach to an Implant-Assisted Removable Partial

A male patient visited prosthodontist Young S. Kang, DDS, FACP, for restoration of the missing front teeth (Figure 1). Three years prior to the initial visit, the patient suffered multiple fractures to the head, including bilateral subcondylar fractures and bilateral coronoid fractures, from a motor vehicle accident. During the recovery period, the patient underwent extensive dental treatments (Figure 2 through Figure 4).

For diagnostic purposes, the prosthodontist mounted diagnostic casts on a semi-adjustable articulator (Stratos 300, Ivoclar Vivadent, ivoclarvivadent.com) with a centric relation record from a Gothic arch tracing device (Massad Jaw Relator, LeeMark Dental, leemarkdental.com) (Figure 5). Additionally, in order to investigate the influence of the facial trauma on the patient's condyles, the prosthodontist performed a computerized mandibular movement analysis (Cadiax^® Compact 2, Whip Mix, whipmix.com).

Based on the diagnostic wax-up (Figure 6) and other clinical findings, the prosthodontist made the following diagnosis: (a) partial edentulism with missing teeth Nos. 3 through 5 and 8 through 12 (Kennedy Class 3 mod I¹); (b) irregular plane of occlusion due to supra-eruption of teeth Nos. 29 and 30; (c) low horizontal condylar inclination of the right condyle (5° vs. 42° of the left condyle); and (d) moderate tooth wear (Smith and Knight Class Two²).

The subsequent treatment plan was made in two phases. First was a surgical phase with three dental implant placements at the teeth Nos. 5, 9, and 12 edentulous sites, and crown-lengthening surgery around teeth Nos. 30 and 31. Second was a prosthodontic phase with occlusal equilibration, followed by an implant-assisted interim removable partial denture (RPD), porcelain-fused-to-metal (PFM) surveyed crowns on teeth Nos. 13 and 14, zirconia crowns on teeth Nos. 18, 29, 30, and 31, and porcelain veneer on tooth No. 25. Ultimately, a maxillary implant-assisted RPD with Locator^® attachments (Zest Dental Solutions, zestdental.com) was to be provided.

The treatment began with planning for dental implant surgery. A radiographic stent (Figure 7) was fabricated for the cone beam CT study. Then the prosthodontist referred the patient to a periodontist for the implant placement surgery and crown lengthening surgery mentioned above.

Four months after the implant placement (Stage 1) surgery at the sites of teeth Nos. 5, 9, and 12, the patient was examined by another periodontist because the original periodontist had relocated out of state. During the Stage 2 implant surgery, the second periodontist noted a full dehiscence on the buccal surface of the implant No. 9. In addition, after attaching healing abutments to the implants, the prosthodontist noted that the implants' angulation was not parallel to the proposed guide plane for a partial denture (Figure 8 and Figure 9). The authors and the prosthodontist changed the treatment plan to use angle-correcting attachments (Sphero Block Micro^®, Rhein 83 USA, rhein83.com) and to remove implant No. 9 with the dehiscence.

Three weeks after the Stage 2 surgery, the patient returned to the prosthodontist for occlusal equilibration (wherein centric occlusion is equal to the maximum intercuspation position) and an acrylic interim RPD, which was directly connected to implants at the Nos. 5 and 12 edentulous sites (Figure 10 and Figure 11).

Then the prosthodontist prepared teeth Nos. 13, 14, 18, 29, 30, and 31 for crowns and tooth No. 25 for a veneer. After tooth preparations, the patient developed symptoms of irreversible pulpitis on teeth Nos. 13 and 29. Therefore, the patient was referred to an endodontist for root canal therapy of the symptomatic teeth. Following the endodontic treatment, the prosthodontist built foundation restorations for teeth Nos. 13 and 29 and made final VPS impressions for the second author, Mr. Dix, for fabrication with crowns and a veneer (Figure 12). For the PFM surveyed crowns on teeth Nos. 13 and 14, the second author used noble metal alloy (SLM Noble 25, Argen, argen.com) with veneer porcelain (GC Initial^® MC, GC America, gcamerica.com). For the mandibular crowns on teeth Nos. 18 and 29 through 31, translucent monolithic zirconia (Prettau Anterior^®, Zirkonzahn, zirkonzahn.com) was used. For restoration of tooth No. 25, a lithium disilicate porcelain veneer was fabricated (GC Initial^® LiSi Press) (Figure 13 and Figure 14).

After the prosthodontist delivered the fixed prostheses with minimal adjustment, he
created rest seats on abutment teeth Nos. 2 and 6 before making a final impression for an RPD framework. The master cast was then sent to the laboratory of the first author, Mr. Kolbeck, who fabricated an RPD framework with a cobalt chromium alloy (Vitallium 2000 Plus^®, Dentsply Sirona, dentsplysirona.com) (Figure 15).

Upon receiving the framework, the prosthodontist tried it in the patient's mouth to ensure a passive fit with the angle correcting rings (Sphero Block Micro^®) (Figure 16 and Figure 17). After the framework's fit was verified, he mounted the RPD framework on the articulator to set anterior denture teeth (Creapearl^®, Willi Geller Creation, creation-willigeller.com).

After obtaining the patient's approval for esthetics, the first author set the posterior denture teeth with group function on both sides and processed the denture base with injectable heat-cured acrylic resin (IvoBase^®, Ivoclar Vivadent, ivoclarvivadent .com) (Figure 18 and Figure 19). Finally, the prosthodontist provided the implant-assisted RPD by incorporating two clear nylon inserts chairside using a cold-cure acrylic (Figure 20).

The restorative team (the authors and the prosthodontist) wanted to create prostheses that were comfortable, functional, and esthetic for the patient.³ In order to achieve these goals, the following solutions were chosen by the team.

First, they needed to overcome the misangled implants. When the orientation of an implant abutment for attachment is not parallel to the path of insertion/removal, accelerated wear of the attachment is highly likely.^4,5 The team decided to use Sphero Block Micro attachments because (a) they have angle-correcting capability with directional rings of 0°, 7°, and 14° (Figure 21) and (b) they have small dimensions⁶ (the ball height was 1.8 mm and its stainless steel housing height was 2.5 mm). The team learned that longer attachments (cuff heights) were needed when the implants were angled subgingivally (Figure 9). In addition, it was difficult to measure precise cuff height immediately following the implant surgery due to swelling of the soft tissue. In order to confirm the accuracy of attachment seating instantly,⁷ the prosthodontist decided to pick up the attachments directly in the mouth.

Next, there was the issue of material choices. The patient's mandibular posterior teeth had short clinical crown heights in spite of the crown-lengthening surgery. Although gold alloy could be utilized, the team decided to use translucent zirconia (Prettau Anterior^®) because of better esthetics (compared to conventional zirconia and gold), adequate flexural strength (670 MPa),⁸ and its ability to be cemented with non-resin luting agents. On the other hand, the team chose to make surveyed PFM crowns with a noble metal alloy (SLM Noble 25), which was composed of palladium (25%), cobalt (42.75%), chromium (20%), molybdenum (12%), and boron (<1%).⁷ In order to create a precise fit at the margin, the SLM Noble 25 crown copings were manufactured with a selective laser melting technology.⁹ In this case, alloys for the surveyed crowns and the RPD framework contained cobalt and chromium, which enhanced compatibility between them. For example, Vitallium 2000 Plus^® and SLM 25^® alloys have similar yield strength (680 MPa for Vitallium 2000 plus and 620 MPa for SLM 25), Vicker's hardness (395 for Vitallium 2000 plus and 335 for SLM 25), and elongation (4.5% for Vitallium 2000 plus and 4% for SLM 25).^10,11

There was also the influence of trauma on the condyles to consider. The mandibular movement analysis by the Cadiax^® Compact 2 system revealed that the right condyle had a minimum of 5° of horizontal condylar inclination. Subsequently, it created minimal posterior disclusion of teeth during all the excursive movements. Therefore, the prosthodontist decided to restore the patient in group function, which required the authors' precise design for the crowns and denture teeth and meticulous occlusal adjustments in the laboratory, assisted by the accurate articulator settings dictated by the Cadiax system.

Lastly was the decision between a fixed prosthesis versus a removable one. During the initial visit, the patient desired to have a fixed prosthesis for his missing anterior teeth. However, based on the extensive loss of soft and hard tissues in the anterior maxilla,⁹ the limited time allowed for treatment, and consultations with the authors and a periodontist, the prosthodontist recommended an RPD assisted by implants. When the RPD is assisted by dental implants, there are many advantages: (a) better access for hygiene; (b) the need for fewer implants; (c) the ability to restore missing anatomical structures with acrylic resin, improving facial esthetics and articulation; (d) improved control of restoration contours, aiding deglutition and speech; (e) better control of implant loading; and (f) improved cross-arch stabilization.³

The patient was very satisfied with the end result (Figure 22 through Figure 24). This case demonstrates how a combination of detailed planning and teamwork can create a successful outcome with an implant-assisted removable partial denture in order to provide esthetics, function, and comfort to a severely compromised partially edentulous patient.

The authors thank Young S. Kang, DDS, FACP, and Kim Chappell for their encouragement and support during the writing of this manuscript.

Josef Kolbeck
Dental Technician/Dental Lab Consultant
Kolbeck Dental
Bradenton, FL

Grady Dix, CDT
Owner/Laboratory Manager
Sunwalt Dental Works
Greensboro, NC