IJSS Case Reports & Reviews | September 2014 | Vol 1 | Issue 4 1

Spring Cantilever: When and Why – A Clinical Report

H S Kiran Kumar1, Sudhakara Bhat2, Sanjay Gouda Patil3, Sankar Madhavan4, Rahul Kulkarni5

1Assistant Professor, Department of Prosthodontics, Sri Hasanamba Dental College and Hospital, Hassan, Karnataka, India, 2Professor and Head, Department of Prosthodontics, Sri Hasanamba Dental College and Hospital, Hassan, Karnataka, India, 3Professor, Department of Prosthodontics, Sri Hasanamba Dental College and Hospital, Hassan, Karnataka, India, 4Assistant Professor, Department of Prosthodontics, Sree Anjaneya Institute of Dental Sciences, Modakkallur, Atholi, Kozhikode, Kerala, India, 5Post-graduate, Department of Prosthodontics, Sri Hasanamba Dental College and Hospital, Hassan, Karnataka, India

A fi xed partial denture is routinely done for the replacement of the missing natural teeth. In the case of anterior missing teeth, conventional cantilever type of fi xed partial denture is more conservative depending upon the case selection. Replacements of anterior teeth are challenging when there is a generalized spacing between the maxillary anterior teeth. Shape and size of the pontic, which replaces the missing teeth has to be in proportion with natural anterior teeth (golden proportion). In such cases, to achieve acceptable esthetics there may be a need to involve more number of teeth by regular fi xed partial denture. Spring cantilever is an ideal solution in these situations. Th e present article covers the case selection, advantages and disadvantages of spring cantilever type of fi xed partial denture.

Keywords: Partial denture, Pontic, Teeth

surgery for implant placement and wanted an immediate fi xed alternative for the right lateral incisor.

Instead of conventional fixed partial denture, to avoid unnecessary involvement of sound adjacent tooth, and posterior tooth needs crowning as well, a bar type of spring cantilever bridge was planned to cover the edentulous space. Thus, second premolar was decided as the abutment support due to caries involvement.

PROCEDURE

Restoration and tooth preparation done in relation to the right second premolar, with slight sub gingival fi nish line. Retraction procedures were carried out, a polyvinyl siloxane impression was made using the pu y reline technique in a rim-lock impression tray and cast was poured.

Keeping in mind, that the palatal bar connector should be long, thin, and resilient, it should extend from the posterior region, closely adapting to the palatal surface so that it is partly supported by soft tissue.6,7 The wax pa ern for the connector was fabricated using 0.8 mm × 4 mm casting strip wax, extending from second premolar towards edentulous space (Figure 3).

The rest of the laboratory procedures were common with that of conventional metal-ceramic fi xed partial denture construction. Metal try-in was performed to verify the extension, adaptation, fi t of the casting (Figure 4). Ceramic

INTRODUCTION

With the advance in material science and bonding technologies, restoration of missing anterior teeth can be dealt with implants and conventional porcelain-fused-to-metal and resin-bonded fixed partial dentures.1,2 In cases where edentulous space is excessive, and there are surgical limitations, then a variant of fixed partial denture the cantilever principle can be considered.3 Cantilever fixed dental prosthesis, also known at various times as the flying pontic, direct extension bridge, a free end, swing-on or throw-off bridge.4 It is the type of fixed partial denture in which the pontic is cantilevered, i.e., is retained and supported only on one end by one or more abutment.5

CASE REPORT

The case we present here is about a 40-year-old female patient reported to the Department of Prosthodontics, with a missing right maxillary lateral incisor (Figure 1). On intraoral examination, the anterior edentulous space with missing lateral incisor had increased mesio-distal width, caries involving right second premolar and compromised crown root ratio of sound adjacent teeth (Figure 2).

A single tooth implant and removable partial denture was a viable alternative. However, the implant would entail surgery and a more protracted treatment. However, the patient was neither willing for removable prosthesis nor

Corresponding Author:Dr. H S Kiran Kumar, Department of Prosthodontics, Sri Hasanamba Dental College and Hospital, Hassan, Karnataka, India. Phone: +91-9986047747. E-mail: dr.kiranhs@gmail.com

Case Report

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absorbed by the supporting palatal mucoperiosteum and completely dissipitated before they reach the abutment tooth.8 The spacing between the teeth can be maintained or even altered based on the patient’s preference. However in adhesive dentistry, this same design can be used except that the fi ing surfaces of the cast retainers have to be etched, and resin cemented.9,10 According to recent literature two fi xed-fi xed and two cantilever resin-retained palatal bar connector bridges have been reported, but the palatal bar connectors were short and the pontics were rigidly connected to their retainers.11

The popularity of spring cantilever fi xed partial denture began from Essig in 1897 and various modifications (Thompson in 1947, Kantorowicz in 1957, Heigeiway and Williams in 1962, Lemmer in 1963, Roussel in 1906 and Johnstone in 1971) have been carried out ever since.12-14

build up was completed, and the bridge was cemented (Figure 5).

DISCUSSION

A cantilever beam by defi nition (Tylman, 1970), is a beam that is supported by only one fi xed support at one of its ends. The cantilever principle has been applied in two-ways, in the development of the spring cantilever bridge, in which the pontic is supported by a bar a ached to a remotely situated retainer, and in the direct cantilever bridge, in which the pontic is a ached to an adjacent retainer.4,5

One of the designs in spring cantilever bridge is the pontic that is connected to its retainer by a relatively long fl exible palatal connector bar. Thus resembling a bridge that is fi xed only on one end, hence the name “spring cantilever bridge.” As it is essentially a tissue-supported but tooth-retained abutment, the forces of mastication acting on the pontic are

Figure 1: Pre-treatment

Figure 2: Pre-treatment close-up view

Figure 3: Wax pattern

Figure 4: Metal try-in

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Myers (1969), discuss the dangers of abutment rotation, points out that it is necessary to consider such facts as crown-root ratio, the amount of periodontal support and the relation of the maxillary and mandibular incisors during incision.15 Nally (1962) also draws a ention to the way in which anterior bridges are subject to palato-vestibular thrust which tends to result in rotation about their main axes, but makes it clear that the physiology of the jaw closing movement and the type of occlusion must be taken into consideration. Some situations are clearly less favorable than others.16

Schwei er17 and Ewing18 have wri en in a limited manner on the cantilever principle and have shed some light on such fi xed restorations. Ewing found, in many instances wherein the cantilever principle was employed in keeping within the patient’s biologic limitations that such restorations gave prolonged periods of service and did not cause tissue destruction (Table 1).

As a general principle, conventional fi xed bridgework, supported by abutments at both ends, is to be preferred if tooth structure, alignment and periodontal support permit an aesthetic and functional result. However, there are certain situations in which the fi xed bridge will not meet these requirements and where a partial denture as an alternative could not be tolerated, or would be precluded because of potential damage to periodontal tissues, or simply on the grounds that a denture would prove socially unacceptable19,20 (Tables 2 and 3).

Maintenance of health and comfort, serviceability and longevity of the prosthesis, restoration of aesthetics and function has been the main concerns in fi xed prosthesis. Schwar in 1970 had conducted a survey on life span and

serviceability of fi xed partial denture and reported that spring cantilever bridge have longer lifespan 3-4 times that of other fi xed partial denture.21 Walton in 1986 reported an even lower mean life span in conventional fi xed partial denture. Caries of the abutment tooth accounted for most of the failures, other being porcelain fracture, un-cemented restorations, poor aesthetics, defective margins, fractured root/tooth, periodontal diseases/mobility, periapical involvement and fractured connectors.22 Lui in 2008 reported that when a spring bridge is judiciously designed it is able to satisfy the demands of the patient to preserve their personal feature of spacing between the teeth.23

Though spring cantilever bridge having a permanent long fl exible palatal bar is cumbersome to the patient as well as the prosthodontist, but when cautiously fabricated and aptly maintained by the patient, it can provide many years of continued service in function and aesthetics.

SUMMARY

Drifting of teeth into the edentulous area may reduce the available pontic space; whereas a diastema existing before extraction may result in excessive mesio-distal width to the ponticspace. In such situations, the simplest approach would be to maintain the existing diastema by spring cantilever fi xed partial denture. The design and application of spring cantilever bridgework are evaluated in relation to developments in new materials and the signifi cance of the health of the periodontal tissues. Cantilever bridgework is not advanced as a preferred alternative to conventional fi xed bridgework but as a means of meeting certain clinical situations which preclude the use of abutment supports at both ends of the bridge. Lack of success in cantilever bridgework can frequently be a ributed to the abuse of design rather than failure of the underlying cantilever principle.

CONCLUSION

This article describes a method for replacing wide anterior edentulous space with modifi ed fi xed dental prosthesis using spring cantilever. Case selection and meticulous planning can result in spring cantilever fi xed partial denture being the most esthetic and economical answer in cases with increased mesio-distal width of anterior edentulous space where diastema has to be maintained. Good oral hygiene,

Figure 5: Post-treatment

Table 1: Essential factors of a cantilever bridgeGood periodontal attachment

Good alveolar support

Favorable root length, shape and crown length

Favorable arch-to-arch relationship

Favorable tooth-to-tooth relationship

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patient motivation and regular follow-up contribute to an impressive life span.

INFORMED CONSENT

A wri en consent was obtained from the three patients before starting the treatment. They were also informed regarding the various treatment options and the publishing protocols.

RE FERENCES

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2. Millar BJ, Taylor NG. Lateral thinking: The management of missing upper lateral incisors. Br Dent J 1995;179:99-106.

3. Thompson AR. The spring bridge. Br Dent J 1946;80:13-6.4. Crabb HS. A reappraisal of cantilever bridgework. J Oral Rehabil

1974;1:3-17.5. The glossary of prosthodontic terms. J Prosthet Dent 2005;94:10-92.6. Lemmer J. The design of spring cantilever bridge. J Dent Assoc

South Afr 1963;18:433.7. Henderson D, Blevins WR, Wesley RC, Seward T. The cantilever

type of posterior fixed partial dentures: A laboratory study. J Prosthet Dent 1970;24:47-67.

8. Lui JL. The spring bridge. Dent J Malaysia 1977;3:15-20.9. McCann KJ. The use of a cast etch bridge in a diastema situation.

J Can Dent Assoc 1987;53:687-9.10. Taggart JA. Resin bonded spring cantilever bridge. Restorative

Dent 1990;6:4-5.11. Gibson CJ. A modifi ed technique for minimal-preparation, resin-

retained bridges: Four case reports. Dent Update 2001;28:442-8.12. Thompson A. Two new abutments for the spring bridge. Br Dent

Dig 1947;1:135.13. Heigeiway HE, Williams RW. The spring cantilever bridge. Br

Dent J 1962;113:420-5.14. Johnston JF, Dykema RW, Phillip S. Modern Practice in Crown

and Bridge Prosthodontics. 3rd ed. Philadelphia: W. B. Saunders; 1971. p. 537.

15. Myers GE. Textbook of Crown and Bridge Prosthodontics. St. Louis: C. V. Mosby; 1969. p. 155.

16. Nally JN. The fi xed bridge for anterior teeth. Int Dent J 1962;12:1-6.17. Schwei er JM. Oral Rehabilitation Problem Cases; Treatment and

Evaluation. Vol. 1, 2. St. Louis: The C. V. Mosby Company; 1964.18. Ewing JE. Re-evaluation of the cantilever principle. J Prosthet Dent

1957;7:78-92.19. Cavazos E Jr. Tissue response to fi xed partial denture pontics.

J Prosthet Dent 1968;20:143-53.20. Henry PJ, Johnston JF, Mitchell DF. Tissue changes beneath fi xed

partial dentures. J Prosthet Dent 1966;16:937-47.21. Schwar NL, Whitse LD, Berry TG, Stewart JL. Unserviceable

crowns and fi xed partial dentures: Life-span and causes for loss of serviceability. J Am Dent Assoc 1970;81:1395-401.

22. Walton JN, Gardner FM, Agar JR. A survey of crown and fi xed partial denture failures: Length of service and reasons for replacement. J Prosthet Dent 1986;56:416-21.

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Table 2: IndicationsThe teeth on either side of the proposed pontic that might ordinarily

be used as abutments for fi xed bridgework are unsuitable by reason

of morphology, periodontal pathology or unfavourable angulation

Cosmetic needs cannot be met by conventional fi xed bridgework

The need to avoid unnecessary involvement of sound teeth is an

overriding factor on grounds of pulpal risk, cosmetic implications or the

temperament of the patient

Table 3: AdvantagesReadily achieved aesthetics

Relatively short clinical chairsid e time

Provision of diastema on either side of the pontic

Usually only one posterior abutment is required to support the

bridge

The fl exible palatal bar acting as a shock absorber reduces the chances

of pontic ceramic from fracturing

How to cite this article: Kumar HSK, Bhat S, Patil SG, Madhavan S, Kulkarni R. Spring cantilever: When and why - A clinical report. IJSS Case Reports & Reviews 2014;1(4):1-4.

Source of Support: Nil, Confl ict of Interest: None declared.