|Year : 2020 | Volume
| Issue : 3 | Page : 495-499
Safeguarding the pier abutment
Rupali Patel, Trupti Dahane, Priyanka Khungar, Surekha Godbole, Seema Sathe Kambala
Department of Prosthodontics and Crown and Bridge, Sharad Pawar Dental College, Datta Meghe Institute of Medical Sciences (Deemed to be University), Wardha, Maharashtra, India
|Date of Submission||09-Jun-2020|
|Date of Decision||05-Jul-2020|
|Date of Acceptance||20-Aug-2020|
|Date of Web Publication||1-Feb-2021|
Dr. Rupali Patel
Department of Prosthodontics, Sharad Pawar Dental College, Wardha, Maharashtra
Source of Support: None, Conflict of Interest: None
In certain partially edentulous cases, the pattern of missing teeth may lead to use of fixed partial denture on pier abutment. However, it has been reported that restoration of two missing teeth and an intermediate pier abutment with a rigid FPD is not an ideal treatment option. Using rigid connector in such situation leads to concentration of stresses on pier abutment. Pier abutment in such case acts as fulcrum leading to more debonding of fixed dental prosthesis which ultimately affects the success of fixed partial denture. Non rigid connector can overcome these problems. Non rigid connector transfers shear stresses to supporting bone & permits abutments to move independently. The non-rigid connector acts as stress breaker between retainer and pontic instead of usual rigid connector. This case report presents a simple method to rehabilitate pier abutment cases.
Keywords: Pier Abutment, Non Rigid Connector, Semi Precision Attachements
|How to cite this article:|
Patel R, Dahane T, Khungar P, Godbole S, Kambala SS. Safeguarding the pier abutment. J Datta Meghe Inst Med Sci Univ 2020;15:495-9
| Introduction|| |
The goal of restorative dentistry is to regain as much of natural form and function as possible, supplemental to preventing any further oral health issues. In terms of rehabilitation of one or two teeth, the most popular treatment modality is the fabrication of a fixed dental prosthesis. The prognosis of a fixed partial denture (FPD) relies upon multiple factors such as the abutment teeth, retainer, connector, pontic design, and the edentulous span. Furthermore, biomechanical factors such as overload, torque, leverage, and flexing bring about atypical stress generation which is found to be maximum concentrated at the connector region of an FPD. Hence, the selection of type of connector plays an important role.
In general, in clinical practice, the use of rigid connectors is preferred due to ease of technical and laboratory expertise and adequate force transmission across the FPD unit. Although the literature suggests that in certain atypical cases, there may arise a need to incorporate stress-breaking mechanism. This can be related to a case of pier abutment wherein a disparity occurs in the force transmission, the retentive capacity of the retainers, and the rigid connectors, thereby making its use unfeasible. A pier abutment or intermediate abutment, as stated in Glossary of Prosthodontic Terminologies, 9th Edition GPT-9, is “a natural tooth located between terminal abutments that serve to support a fixed or removable dental prosthesis.”
Markely et al. described “The broken stress principle” which stated that stress breakers act as safety valves against the tremendous leverage forces created by the rigid attachment between two or more teeth. Progress in this area leads to the development of nonrigid connectors for the ease of incorporation of this stress-breaking mechanism. Nonrigid connectors function as a safety valve between the components so that the force transmission can be balanced throughout the FPD without debonding itself in such cases.
| Case Report|| |
A female 40 years of age came to the Department of Prosthodontics, complaining of difficulty in chewing and unpleasant esthetics. Clinical examination revealed missing teeth 15 and 17 [Figure 1] and [Figure 2]. Radiographic diagnosis revealed the presence of adequate bone support with all the teeth; hence, they can be used as abutments.
The patient denied implant as the treatment due to surgical intervention and economic constraints. Therefore, restoration with partial fixed dental prosthesis with a nonrigid connector was selected.
The following steps were followed:
- Teeth were prepared for porcelain fused to metal prosthesis on right maxillary canine and second premolar with equigingival margins with shoulder finish line in order to enhance the esthetics [Figure 3]
- Right maxillary second molar was prepared to receive a metal crown prosthesis with supragingival margin and chamfer finish line
- Impressions were made after gingival retraction using retraction cord with elastomeric impression material following two-step putty was technique
- Bite registration material was used to obtain interocclusal record
- Tooth-colored autopolymerizing acrylic resin was used to fabricated provisional restoration which was cemented with noneugenol temporary cement
- After retrieval of the master cast, die cutting and die ditching were done, followed by mounting of the casts onto the articulator using interocclusal record
- Wax pattern was build up such that after the waxing the teeth that are canine and both the premolars, a recess was cut for the female portion to fit the prefabricated plastic dovetail on the distal aspect of pier abutment [Figure 4]
- Position and parallelism of the dovetail were determined by surveying the casts. Both the parts were separated away, and the inside of the female patter was kept free of wax [Figure 5]. Metal try-in of the anterior segment along with the female part was done after casting to verify proper seating, and the excess was trimmed according to occlusion [Figure 6]
- The wax pattern for molars was then fabricated after approximating the male part and the casted female portion. The pattern was then casted [Figure 7]
- Seating of the components was verified. Ceramic layering was done onto the canine and the premolars [Figure 8]
- The anterior segment with keyway was cemented first, followed by the posterior segment with key using glass-ionomer cement [Figure 9] and [Figure 10].
The patient was guided regarding the use of dental floss and interdental brush, and oral hygiene instructions were emphasized. Follow-up was scheduled after a week for assessment of oral hygiene status.
| Discussion|| |
Traditionally, the use of rigid connectors provides an adequate amount of stability and strength to the fixed partial prosthesis. It minimizes the atypical stresses auxiliary with the restoration, therefore, improving the prognosis and longevity of the prosthesis. However, rigid connectors may not be applicable in all clinical situations. In the case as discussed above, that is an intermediate abutment, difficulties arise due to curvature of arch, the buccolingual movement of anterior teeth with respect to posterior teeth. This tooth movement may be associated with various amount of forces, and it has been stated that these forces are directed toward the terminal retainers causing the central abutment to act as a fulcrum, leading to the failure of the prosthesis. It may cause intrusion of the pier abutment, and caries due to marginal leakage are likely to become more extensive before discovery.
For even distribution of forces, therefore, a requirement of stress breaker arises. The stress-breaking mechanism, as described by Markely et al. in 1951, theorized that the stress breaker acted as a safety valve that would prevent the concentration of forces along the abutment. It aids in transmitting the shear stresses to the supporting periodontium instead of localizing them in connectors. Furthermore, it minimizes the mesiodistal torquing of abutments and permits their independent movements.
Different types of nonrigid connectors used currently include “the tenon-mortise, the cross-pin and wing, and the split pontic.” The tenon-mortise or the keyway type of pontic is the most frequently used type of nonrigid connector. The stress-breaking mechanism provided by the connector prevents transmission of forces solely along the intermediate abutment. The connector equalizes the forces by transmitting it to the periodontium instead of directing it in the connectors, thereby minimizing the mesiodistal torquing of abutments. It helps in compensating for the difference in the resistance and retention form between the abutments. The mechanism of the connector along with its design and passive fit is crucial for the prognosis of a long-span FDP.
Sciffelger et al. compared the accuracy of multiunit one-piece casting. The greatest discrepancy was seen at the mesiogingival surface of the anterior retainer and the distolingual surface of the posterior retainer. Seating of the casting improved after sectioning. Determination and designing thus should be done keeping these observations in mind.
Ideally, according to Shillingburg, the keyway should be placed on the distal aspect of the intermediate abutment. The reason being that the posterior a slight mesial inclination of the posterior teeth has been observed upon application of occlusal load. This would lead to enhanced seating of the key in the keyway the moment occlusal loading occurs. On the contrary, if the keyway is planned on the mesial aspect, the forces will tend to dislodge the key from the keyway leading to chances of fracture of the retainer assembly. This theory is supported by findings of a finite element analysis done by Oruc et al. They observed the decreased stress concentration along the pier abutment with the help of a nonrigid connector placed distally onto the intermediate abutment. Other authors too have advocated the use of nonrigid connector along the distal aspect and, if need be, making the use of an additional retainer on the anterior retainer distally [Figure 11].,,,,,,,,
| Conclusion|| |
The use of nonrigid connector in case of pier abutment aids in elimination of the load and fulcrum-like situation. Other forms such as precision and semi-precision attachments provide room for slight movements that could prevent the loading of the pier abutment, thereby improving the longevity of the prosthesis.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11]