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 Table of Contents  
Year : 2020  |  Volume : 27  |  Issue : 4  |  Page : 391-393

Breaking the stress with a non-rigid connector

Department of Prosthodontics, SGT University, Gurugram, Haryana, India

Date of Submission17-Jun-2020
Date of Decision23-Jun-2020
Date of Acceptance24-Sep-2020
Date of Web Publication04-Nov-2020

Correspondence Address:
Dr. Priyanka Rani
Department of Prosthodontics, SGT University, Gurugram, Haryana
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/npmj.npmj_184_20

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Lone standing abutments or pier abutments have usually been restored with a conventional fixed partial denture (FPD) using a rigid connector between the pontics and the retainers. However, such fixed and rigid restorations have been associated with a higher rate of debonding, microleakage, caries, etc., The aim of the modern day prosthodontics is the preservation of what remains as given by M.M Devan. As a result, a non rigid connector (NRC) may be the connector of choice in situations of pier abutment. A NRC acts as a stress breaker so that the anterior and posterior segments can move independent of each other. This case report presents a simple method of rehabilitating a patient with a pier abutment in the upper right posterior region of the mouth. Rehabilitation was done by FPD with an inverted key-keyway type NRC. Follow up was done up to 11 months.

Keywords: Inverted key-keyway, non-rigid connector, pier abutment

How to cite this article:
Rani P, Malhotra P. Breaking the stress with a non-rigid connector. Niger Postgrad Med J 2020;27:391-3

How to cite this URL:
Rani P, Malhotra P. Breaking the stress with a non-rigid connector. Niger Postgrad Med J [serial online] 2020 [cited 2021 Mar 3];27:391-3. Available from: https://www.npmj.org/text.asp?2020/27/4/391/299903

  Introduction Top

Pontic, retainer and connector constitute the parts of a fixed partial denture (FPD). Besides pontic and retainer, the selection of the right type of connector is of utmost importance to the success of the treatment. A rigid connector design is most commonly used in fixed Prosthodontics however; at times, in situations of the alone free standing abutment, the rigid connector may not be suitable as the amount of force exerted on the anterior segment may be different than the posterior segment, resulting in a higher rate of debonding, microleakage and caries.[1] Pier abutment is a natural tooth located between terminal abutments that serve to support the FPD prosthesis (GPT). For example, second premolar serves as pier abutment when first premolar and first molar are missing. If these teeth are restored with FPD using a rigid onnector, it may result in failure of FPD.[1] The reason for this failure has been cited as the difference in the physiologic teeth mobility of anterior and posterior segments.[2] Due to this difference in mobility, the extrusion of the weaker retainer of FPD may occur (anterior segment). Non-rigid connector (NRC) plays an important role in the prevention of this failure. It breaks the stress and also directs it along the long axis of the abutment tooth.[3] NRC is a connector that permits limited movement between otherwise independent members of a FPD (GPT 8). The first NRC was invented in (1886).[4]

Different types of NRCs are loop connector, split connector, key-keyway (dovetail) or Tenon-Mortise connector (pier abutments) and cross pin and wing connector.

NRC may be fabricated by the incorporation of prefabricated plastic/metal inserts into the wax pattern (precision attachments) or through a custom milling process after the first casting has been obtained (semi-precision attachment). These attachments can be intracoronal and extracoronal and can be used with pier abutment, malaligned teeth, long-span bridges and questionable distal abutment. It should not be used with a mobile abutment, cases where pontic space is > one teeth, the opposing arch is having anterior natural teeth and posterior removable partial denture.

Key-Keyway (Dovetail) or Tenon–Mortise Connector[3] is a passive attachment. The patrix, key or male component is attached to the intaglio surface of the pontic and the female component, matrix or keyway is attached at the distal surface of the pier abutment. Hence, the FPD is fabricated in two parts. Posterior teeth tend to shift mesially on occlusal forces. If the keyway is attached on the distal side of pier abutments, the key will try to seat in it on occlusal forces.[5] However, if we attach the keyway on the mesial side of the pier abutment, the effects of occlusal forces will be opposite. The disadvantage is that it is an intracoronal attachment and requires an excessive amount of tooth reduction on the distal surface of the abutment tooth, to provide adequate space for matrix attachment. Inverted key-keyway attachment [Figure 1] is the alternative of key-keyway attachment in which the key is attached to the distal surface of pier abutment and the keyway is attached on the intaglio surface of the pontic (extracoronal attachment). Moulding et al.[6] gave inverted key-keyway to solve the problem of excessive tooth reduction for attachment of female component (conservative approach) Preservation of abutment vitality, aesthetic and post operative discomfort. The disadvantage of inverted key-keyway attachment is the connector junction is towards the pontiac tissue surface which can lead to tissue irritation or can be an area for plaque accumulation, cannot be given to the short clinical crowns, and have chances of unseating of the key from keyway on mesial movements of the teeth.
Figure 1: (a) Occlusal surface of the final prosthesis with inverted key keyway attachment. (b) Intaglio surface of the final prosthesis with inverted key keyway attachment

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  Case Report Top

A 28-year old male patient reported to the Department of Prosthodontics in SGT University Gurgaon, Haryana on 16th June 2019 with the chief complaints of inability to chew food with upper right back teeth region for 1 year and wanted its replacement with a fixed prosthesis. On the extraoral examination, no abnormality was detected.

On the intraoral examination, no gross soft-tissue abnormality was detected, 14 and 16 were missing and were extracted about a year ago due to caries. Root stump was present with respect to 26 [Figure 2]. Radiographic investigation was done with orthopantomogram [Figure 3].
Figure 2: Pre operative intraoral. (a) Frontal view. (b) Right lateral. (c) Left lateral

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Figure 3: Pre operative radiographic view

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Material and Method:‑ Alginate impressions (Septodont, class A dust free and normal setting Type 2) were made with respect to maxillary and mandibular arches to obtain diagnostic cast (type 2 dental stone). The casts were articulated on the semi-adjustable articulator with the help of interocclusal records in maximum intercuspation position. The length of the axial surface of 15 was measured and was found 7 mm (minimum 4 mm connector height required for precision attachment). The options of the dental implant with respect to 14, 16 and FPD with NRCs were given to the patient. The patient opted for FPD with NRC due to financial and urgent reasons. Informed consent was obtained from the patient on July 2019.

The mockup was done on the articulated cast for the fabrication of provisional restoration. Tooth preparations were done with respect to13, 15 and 17 for full-coverage porcelain fused to metal crowns. It was done under 2% lignocaine with adrenaline 1:200,000 (LA) with a shoulder finish line on the labial surface and chamfer on the palatal surface of the concerned teeth. After achieving the complete retraction, impressions were made with addition silicon (Affinis, perfect impression, coltene – whaledent, Switzerland, double mix double consistency). The impressions were disinfected and casts were poured in die stone. Using mock up, temporization was done using a putty index with Protemp-4 (3M ESPE). Die spacer and hardener were applied and wax patterns were fabricated with respect to 13, 14 and 15 with additional wax on distal surface 15. Carving of additional wax was done (Patrix) with the help of a dental surveyor to maintain the parallelism. After that casting was done for the anterior segment. After complete casting and finishing of the anterior segment, wax coping fabrication was done with respect to16, 17 with matrix carved on the corresponding surface of 16 to ensure complete seating of matrix into patrix. Casting for the posterior segment was done. The complete metal trial was done in the patient mouth to check the fit of the prosthesis. Ceramic layering was done for both the segments and the trial was done inpatient’s mouth. All the occlusal adjustments were done and the prosthesis was luted with glass ionomer cement. The first anterior segment was luted followed by the posterior segment [Figure 4]. All the instructions for maintenance of oral hygiene were given to the patient and follow up was done after 1 week, 1 month, 3 months, 6 months and 11 months (June 2020) postoperatively and during these follow-ubridge. The use of rigid connectorsp clinical evaluation of all the teeth were done for gingivitis, pocket depth and secondary caries. Gingiva around all the prepared teeth was healthy and firm. Furthermore, the prosthesis was fixed without any teetering movement shows successful rehabilitation of pier abutment with NRC.
Figure 4: (a) Frontal view after the final prosthesis. (b) Right lateral view after final prosthesis. (c) Left lateral view after final prosthesis

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  Discussion Top

FPD is the most common way to restore Kennedys III and IV edentulous spaces. The success of any fixed partial is depends upon its type of connector, shape, size and its location.

The main aim of using NRCs is to direct the masticatory stress along the long axis of the abutment tooth. More so, in the case of pier abutment, which has to bear the occlusal load of both anterior and posterior missing teeth. Hence, it is important to break the stress posterior to the pier abutment so that both the units can move independently. There are controversies in the literature regarding the position of NRC.[7] It can be attached to the distal surface of pier abutment, both sides of pier abutments, the distal surface of the anterior retainer or the mesial side of second molar abutment. Shillingburg et al.[8] advised to attach the connector at the distal surface of the middle or pier abutment to reduce the stress concentration, also study by Oruc et al.[5] which is a finite element study supported this statement. In this case report, rehabilitation of pier abutment was done using an inverted key-keyway type of non-rigid connector.

According to the literature, the average life span of all kinds of FPDs is 8.3 years[9] and the survival rate is around 87% up to 10 years and 69% up to 15 years.[6]

A study done by Botelho and Dyson concluded that short span bridges are more successful than the pier abutment with rigid connectors.[10] Limited evidence is available in the literature regarding the use of inverted key-keyway attachment with pier abutment. Furthermore, not much evidence is available regarding the life span of pier abutment with rigid and NRCs.

  Conclusion Top

Abnormal stresses can lead to the failure of long-span bridges. The selection of connectors in FPDs plays a key role in the success and failure of such bridges. Pier abutment is one such situation of long-span bridge. The use of rigid connectors in such cases can lead to failure of the treatment, therefore NRC plays a vital role here. In this case report, the inverted key-keyway NRC was selected to preserve the vitality and conserve the tooth structure of the pier abutment. In follow-up of 11 months, it was observed that the FPD was in its place, the gingiva around the prepared teeth was healthy and firm with no apparent pockets or secondary caries of the abutment teeth.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given his consent for his images and other clinical information to be reported in the journal. The patient understand that name and initials will not be published and due efforts will be made to conceal identity, but anonymity cannot be guaranteed.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Soh NH, Jain AR. Knowledge, awareness, and practice on rigid and non-rigid connectors for management pier abutment among dental students. Drug Invent Today 2018;10:853 859.  Back to cited text no. 1
Kuruvila A, Joseph S, Jayalekshmi NL, Menon SK. The key to the management of pier abutment: An alternative approach. J Int Oral Health 2017;9:136-9.  Back to cited text no. 2
  [Full text]  
Jerkins G. Precision Attachments: A Link to Successful Restorative Treatment. London: Quintessence; 1999. p. 127-31.  Back to cited text no. 3
Kanathila H, Doddamani MH, Pangi A. An insight into various attachments used in prosthodontics; A review. Int J Appl Dent Sci 2018;4, 4:157-160.  Back to cited text no. 4
Oruc S, Eraslan O, Tukay HA, Atay A. Stress analysis of effects of nonrigid connectors on fixed partial dentures with pier abutments. J Prosthet Dent 2008;99:185-92.  Back to cited text no. 5
Moulding MB, Holland GA, Sulik WD. An alternative orientation of non-rigid connectors in fixed partial dentures. J Prosthet Dent1992;68:236-8.  Back to cited text no. 6
Kayahan ZO, Tomruk CO, Kazazoglu E. Partial edentulism and treatment options. Yeditepe Dent J 2017;13:31-6.  Back to cited text no. 7
Shillingburg HT, Hobo S, Whitsett LD, Jacobi R, Brackett SE. Fundamentals of Fixed Prosthodontics. 3rd ed.. Chicago: Quintessence; 1997. p. 85-118.  Back to cited text no. 8
Walton TR. An up to 15-year longitudinal study of 515 metal-ceramic FPDs: Part 1. Outcome. Int J Prosthodont 2002;15:439-45.  Back to cited text no. 9
Botelho MG, Dyson JE. Long-span, fixed-movable, resin-bonded fixed partial dentures: A retrospective, preliminary clinical investigation. Int J Prosthodont 2005;18:371-6.  Back to cited text no. 10


  [Figure 1], [Figure 2], [Figure 3], [Figure 4]


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