“Elucidating the Problem of Pier Abutment through the Use of a Fixed Movable Prosthesis – A Clinical Case Report”

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Placement of non-rigid connector has been advocated by many and different authors have suggested different locations like terminal retainer, ^[10] distal of the pier and one more at distal of anterior retainer ^[11].

Figure 2. Stress breaking effect with use of non-rigid connector

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Some have recommended non usage of non-rigid connectors, ^[12] while many other authors also have recommended that a stress breaking mechanical union of pontic and retainer ^{[14, 15]}

Though there are numerous attachments that can provide the required stress breaking effect in a long span bridge supported in the middle by a pier abutment, this article describes a simple and innovative method of fabricating a dowel type semi precision attachment by utilizing the design of an intra-coronal semi precision rest. It provides the clinician with the benefits of being less costly, ease of fabrication and less tooth reduction.

2. Clinical Case Report

A female patient, aged 42 years, came to the department of Prosthodontics, with a chief complaint of difficulty in mastication since last 2 years due to missing maxillary rear teeth, lost due to tooth decay. The sequence of loss of teeth was right second molar, followed by left first molar and then the right second premolar. A detailed medical, dental, social, climacteric and diet history was obtained. Inspection of the oral cavity revealed good oral hygiene with a class I molar relationship. The edentulous areas were examined for severity of bone loss. Maxillary left first molar acted as a pier abutment. Palpation of the teeth and in particular the potential abutments, did not reveal any sign or symptom of periodontal disease. Percussion of the teeth also did not reveal any significant abnormality of pulp or periapical area. Evaluation of the functional occlusion revealed presence of wear facets in relation to maxillary canines. Occlusal examination revealed a mutually protected occlusion with canine’s discluding the posteriors and anteriors in lateral excursions. Individual examination of the potential abutments on both sides revealed an adequate crown length. Radiographic examination revealed an adequate crown root ratio, favorable root morphology, healthy periodontal ligament space, positive long axis relationship, favorable gingival margin location, ideal occlusal morphology, occlusal plane and no evidence of any periapical or periodontal pathology (Figure 3). Upon analysis of the pericemental areas of all the abutments, a tentative treatment plan that included a fixed fixed (rigid) prosthesis for restoring the missing right first molar and a fixed movable prosthesis for the missing left second premolar and left second molar. Other treatment modalities that were discussed with the patient for management of pier abutment included single tooth implant for each edentulous space or a combination of single tooth implant and a fixed fixed prosthesis or a resin bonded prosthesis or a removable partial denture.

After making preliminary impressions of maxillary and mandibular partially edentulous arches with irreversible hydrocolloid (Thixotropic, Zhermach, Italy), the impressions were poured with Type III dental stone (Elite Model; Zhermack, Badia Polesine, Rovigo, Italy). Centric and protrusive interocclusal records were made using interocclusal wax records (Metrowax; Metrodent Ltd, Huddersfield, West Yorkshire, UK). The diagnostic casts were mounted on a Hanau Widevue semi adjustable articulator (Waterpik, Ft Collins, CO, USA) using a Hanau spring bow. The articulator was programmed and the entire diagnosis and fabrication of prosthesis was done on the programmed articulator.

Prosthetic rehabilitation was carried in two stages. In the first stage the abutments on the right side were prepared to receive a porcelain fused to metal, fixed fixed prosthesis with buccal facing and occlusal metal. In the second stage, all the planned abutments for fixed movable prosthesis were prepared. The posterior segment was fabricated first which contained a dove tail design for the anterior part of the prosthesis (Figure 4). A box preparation was made on the mesial aspect of the retainer in relation to the pier abutment during wax up and the two separate wax patterns were cast separately. After cementing the posterior part of the fixed movable prosthesis first, a temporary restoration was given in relation to the anterior part (Figure 5).

Figure 3. Preoperative radiograph showing the position of the pier abutment

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Figure 4. Fabrication of anterior fixed partial denture with a semi rigid connector on the distal aspect of the pontic

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Figure 5. Temporization of a fixed movable prosthesis

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In the next stage the anterior component of the fixed movable prosthesis was cemented after careful evaluation for fit and marginal integrity (Figure 6). The patient was given instructions regarding maintenance and was put on a strict follow up protocol, which included long term regular checkups after every three months. The patient was educated about the fact that due to loss of maxillary posteriors, she had developed a habit of bringing the mandible forward while mastication and this habit needed to be rectified. A demonstration on how to eat was given to the patient. After a period of 5 years the patient’s prosthesis continues to be in a healthy state (Figure 7). Radiographs show no evidence of bone loss around the pier abutment (Figure 8).

3. Discussion

Dynamic occlusal examination in such cases is essential and it should foresee the current events that are taking place and what led to those events. In this case the wear facets on the canines are one such example. These wear facets had started developing only after the posterior maxillary teeth were lost. In case the wear facets are severe and the canines no longer disclude the posteriors, then the treatment plan include restoration of anterior guidance with crowns in relation to maxillary canines. The reason that canines were undergoing wear in this case was because of the posterior loss of the teeth due to which the tendency of the patient was to masticate with the lower teeth by bringing the mandible forward, a term what can be called as protrusive mastication. This collaborated with other findings in the examination of occlusion.

Figure 6. Fixed movable bridge in place with non-visible semi rigid connector

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The need for stress breakers on a pier abutment which is supporting prosthesis on both ends is based on the fact that the vertical resilience of a normal, healthy tooth in its socket is approximately 0.1 mm to 0.2 mm. Non Rigid Connector transfers shear stresses to supporting bone rather than concentrating them in connectors. It minimizes mesiodistal torquing of abutments and permits them to move independently. When incorporated in the mandibular pier abutment situation, it allows mandibular flexure during opening and closing movements. According to a study, ^[16] the stress distribution and values of a fixed partial denture and pier abutment are affected by the presence and location of a non-rigid connector. The area of minimum stress concentration occurs in pier abutments when a non-rigid connector is located in the distal region of the pier abutment for a 5 unit fixed partial denture with a pier abutment ^[17].

Figure 7. Fixed movable prosthesis after 5 years

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Figure 8. Post follow up radiographs

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