Restoration of a Maxillary Anterior Defect With a Rotational Path Removable Partial Denture: Clinical Report of a Patient With Cleidocranial Dysplasia

For the partially edentulous patient who has exhausted bone augmentation and implant placement options and is not a candidate for a tooth-borne fixed prosthodontic restoration, the removable partial denture (RPD) may be a predictable treatment alternative. The use of conventional suprabulge or infrabulge clasps, however, may pose an esthetic challenge when RPD abutments are in the anterior region.^1-3

Although often overlooked, the rotational path RPD permits the esthetic and functional replacement of missing anterior teeth.³ The rotational path RPD does not make use of guide planes in the edentulous site. Instead, abutment proximal contours adjacent to the edentulous space are engaged by rigid retentive elements that gain access to undercuts through a novel rotational path of RPD placement.⁴ The rotational path RPD has been described for scenarios involving mesially tilted mandibular molar abutments and missing maxillary anterior teeth.^1,3,5,6 As is the case for all RPDs, the use of a dental surveyor is essential for appropriate diagnosis and treatment planning.^3,4,6

The restoration of missing anterior teeth may be accomplished using a category II rotational path RPD, having either an anterior-to-posterior or a lateral placement design.^1,7 These RPDs use a "dual path" of placement rather than the more conventional single straight path of placement that generally occurs perpendicular to the occlusal plane.^4,7,8 The initial straight path is not coincident with the final rotational path of placement.^3,7 The initial path permits rigid metal retainers to engage proximal retentive abutment contours at the RPD's rotational center.^3,4 The RPD is then rotated through a curved or rotational secondary path to final placement, permitting traditional clasp assemblies to engage abutments remote from the edentulous space.^7,9

Specific to the lateral rotational path RPD design described here, mesial retentive contours on anterior maxillary abutments adjacent to the edentulous space are engaged using the initial path and establish the rotational center of the prosthesis.¹⁰ Then the restoration is rotated to final placement allowing a conventional clasp assembly to engage a contralateral posterior abutment.^1,8

A 36-year-old female patient presented requesting a fixed partial denture to replace her missing maxillary left central and lateral incisors (Figure 1). The patient's medical history was significant for cleidocranial dysplasia (CCD) and von Willebrand disease. CCD is attributed to an autosomal dominant mutation in the RUNX2 gene, which leads to delayed ossification, dental abnormalities, and craniofacial changes treated through a combination of orthodontic and prosthodontic therapies.¹¹ Her dental history included orthognathic surgery and orthodontic therapy at age 17 to correct severe prognathism, failed eruption requiring surgical uncovery of the maxillary left central incisor, extraction of the maxillary left central and lateral incisors, failure of particulate bone augmentation, and early implant failure in the maxillary left central incisor site.

Intraoral evaluation revealed an irregular soft- and hard-tissue defect in the maxillary anterior edentulous space that spanned 19 mm (Figure 2), a high palatal vault, and fremitus of the maxillary right central incisor (Miller class II mobility). The patient's clinical presentation was prosthodontic diagnostic index (PDI) class III partial edentulism.¹²

Treatment plan options were developed and discussed, including: (1) occlusal device therapy, additive proximal contour revision of the right central incisor abutment using bonded composite resin, rest seat preparations, and fabrication of a lateral rotational path RPD; (2) a treatment similar to the first option except that a survey crown would be used to facilitate abutment contour revisions; and (3) no treatment. The patient elected to pursue the second treatment option.

Maxillary and mandibular irreversible hydrocolloid impressions were made. Resulting diagnostic casts were mounted in a semi-adjustable articulator in centric relation. Upon closure into maximum intercuspal position, initial tooth contact involved the maxillary right central incisor. Therefore, occlusal equilibration was warranted to provide occlusal stability in centric relation and anterior coupling. Initially performed on the mounted diagnostic casts, occlusal equilibration was subsequently accomplished on the patient over the course of 3 months in conjunction with the use of an anterior occlusal device to ensure a stable and repeatable treatment position (Figure 3).^13,14 Approximately 6 months after treatment of the traumatic occlusion, the mobility of the central incisor was reclassified as class 0.

A new maxillary cast was made and surveyed using two different horizontal cast orientations. The first positioned the occlusal plane approximately parallel with the horizon (Figure 4). When surveyed in this position, abutment surfaces adjacent to the edentulous space presented proximal contours with retentive undercuts that were acceptable for engagement by the rigid metal retainers of the planned prosthesis. The second cast position oriented the anterior edentulous space slightly above posterior aspects of the cast (Figure 5). When surveyed in this tilted orientation, abutments demonstrated proximal abutment contours that would not permit simultaneous access to coincident prosthesis rotational centers. Mesial undercut of the tilted cast was evident for the maxillary right central incisor. To better coordinate access to rotational centers and permit development of an ideal rest seat on this abutment, a survey crown was placed.

This aspect of survey and design for the lateral rotational path prosthesis cannot be over-emphasized. While proximal abutment contours adjacent to edentulous spaces in conventional RPD design are adjusted to serve as guiding planes (parallel to the single prosthesis path of placement), abutment surfaces adjacent to the edentulous space for the lateral rotational path RPD design must present an undercut contour to serve in retention of the prosthesis.^15,16

The design cast received two sets of tripod marks to designate both the horizontal and tilted cast orientations. The carbon marker was then used to indicate heights of contour on abutments. Finally, a 0.01-in. undercut gauge was used to plan conventional retentive features on a posterior abutment tooth (maxillary right second molar). With the survey completed, the RPD framework design was indicated on the cast.

A wax pattern for the maxillary right central incisor abutment was developed and analyzed for appropriate contours as indicated above. A deep cingulum rest seat was included, and a metal-ceramic survey crown was fabricated and placed. Great care was taken to replicate planned abutment contours during porcelain application, finishing, and polishing. A deep cingulum rest seat was prepared on the maxillary left canine abutment. A mesial occlusal rest seat was prepared on the maxillary right second molar.

An irreversible hydrocolloid impression of the maxilla was used to produce the definitive working cast for RPD framework fabrication. The articulator-mounted definitive cast, the RPD design cast (Figure 6), an index of the denture tooth set-up, and a fully executed work authorization form were submitted to the laboratory for framework fabrication.

While conventional clasp assemblies require block-out of proximal surface undercuts (Figure 7), no block-out was provided in the location of planned rigid retainers (Figure 8). Care was taken to limit facial extension of the rigid metal retainers and the denture tooth retentive components to optimize esthetics.

Framework try-in was accomplished (Figure 9), which included verification that the rigid metal retainers contacted the designated undercut areas (Figure 10). Prosthetic teeth were arranged in wax, assessed clinically, and approved by the patient. The trial rotational path RPD was invested, and denture base resin was subsequently injection-molded. The prosthesis was divested, subjected to laboratory remount adjustments, recovered from the cast, finished, and polished (Figure 11). The definitive prosthesis was placed (Figure 12), and the patient was instructed on prosthesis placement and removal. Home care instructions were provided. At the time of this writing, routine aftercare has been ongoing for more than 2 years.

When carefully diagnosed, appropriately planned, and accurately fabricated, a rotational path RPD permits acceptable prosthesis support, stability, retention, comfort, and function. The design advantage of a rotational path RPD is the elimination of the use of clasping in esthetically demanding areas as well as black triangles adjacent to anterior abutment teeth.^1,7 Generally less expensive and less invasive than implant restorations, the rotational path RPD also can involve minimal reduction of tooth structure. Additionally, because surgical intervention and the potential complications related to it is avoided, treatment time can be shortened and morbidity decreased.

Clinicians and laboratory technicians, however, must be mindful of the potential disadvantages and risks of rotational path RPDs. Denture teeth may be difficult to match with adjacent natural teeth and restorations. Abutments must be critically evaluated for appropriate contours, and rest seats must be well-prepared to allow positive abutment engagement by the prosthesis to prohibit abutment drift away from the framework under occlusal loading.^16,17 With little tolerance for error, the accuracy of framework fit is essential to success. Any adjustment of the rigid retentive components is extremely difficult and often impossible, and requires careful finishing and polishing if attempted.¹⁶ If abutment restorations require replacement, the rotational path RPD will also need to be remade. Moreover, individuals with poor manual dexterity may struggle with the very specific nature of prosthesis placement and removal. Finally, patient compliance with post-restorative occlusal splint therapy and maintenance is paramount for a predictable and durable outcome. Any tooth movement that occurs when the RPD is not in place can cause fit problems moving forward.

As with all prosthodontic treatment, patient selection and diagnosis are critical. The treatment approach described herein provided esthetic and functional replacement of missing maxillary anterior teeth. Clinical findings included traumatic anterior occlusion, missing maxillary incisors, horizontal restorative space discrepancy, and an irregular defect of the edentulous site. Occlusal equilibration and occlusal device therapy provided resolution of deleterious interarch contacts and resulted in stable tooth and intermaxillary relationships. The success of the definitive removable prosthesis and prognosis of the abutment teeth is dependent upon the maintenance of the equilibrated occlusion. In conjunction with a single anterior survey crown, a lateral rotational path RPD was used to restore the patient's missing teeth to her comfort, function, and esthetic satisfaction.

Angela Gullard, DMD, PhD, MDS
Assistant Professor and Director, Implant Prosthodontics, Department of Prosthodontics, University of Tennessee Health Science Center, Memphis, Tennessee

David R. Cagna, DMD, MS
Professor and Director, Graduate Prosthodontics, Department of Prosthodontics, University of Tennessee Health Science Center, Memphis, Tennessee; Past President, American Board of Prosthodontics