30-YEAR LIFE SPAN OF A SPRING CANTILEVER BRIDGE: CASEREPORTJ L. Lui. 3D-year life span of a spring cantileverbridge: case report. Annal Dent Univ Malaya 2008;15(1): 48-54.

ABSTRACT

Besides other indications, the spring cantilever bridgecan solve the difficult clinical problem of providingdiastema on either side of a pontic. Unlike theconventional bridges, it has a somewhatcontroversial design in that the anterior pontic isconnected to its retainer on a posterior abutment bya relatively long flexible palatal bar. This paperpresents a case report of a spring bridge whichfractured due to metal fatigue after 30 years ofcontinued service. Other studies reported a mean lifespan of 8-10 years for conventional bridges. Theadvantages of the spring cantilever bridge are alsodiscussed.

Key words: spring cantilever bridge; life span;serviceability; bridge fracture; metal fatigue

INTRODUCTION

The spring cantilever bridge has a somewhatdifferent design from other conventional bridges.Instead of being directly connected to its retainer(s)as in fixed-fixed, fixed-movable or cantilever bridges,it comprises of a pontic which is connected to itsretainer by a relatively long flexible palatal connectorbar (Figure 1). In short, the spring bridge resemblesthe cantilever bridge in that it is fixed on only oneend; therefore the name 'spring cantilever bridge'.The spring bridge is essentially tissue-supported butabutment tooth-retained. Thus, forces of masticationacting on the pontic are absorbed by the supportingpalatal mucoperiosteum and completely dissipitatedbefore they reach the abutment tooth which merelyacts to retain the bridge in place.

When diastemata are present between adjacentteeth, the replacement of a missing upper anteriortooth by means of a conventional design bridge isimpossible if the patient requests that a diastema bemaintained on either side of the pontic. A previousattempt to overcome this problem was the use ofgold palatal bar connectors to connect the pontic tothe retainers cemented to the abutments on bothsides as in a fixed-fixed design(l). With the adventof adhesive dentistry this same design was adoptedexcept that the fitting surfaces of the cast retainers

Case Report

J.L. Lui

Professor

Department of Conservative DentistryFaculty of DentistryUniversity of Malaya50603 Kuala LumpurMalaysia

Corresponding author: Lui 100 Loon

were etched and resin-cemented(2). More recently,the same modified method involving minimal-preparation of two fixed-fixed and two cantileverresin-retained palatal bar connector bridges werereported(3). As these palatal bar connectors wereshort, the pontics were rigidly connected to theirretainers.

In the spring bridge, the palatal bar is relativelylong because the abutment tooth is at some distancefrom its pontic; a missing anterior tooth may besupported by an abutment in the premolar or molarregion. Being long, the palatal bar is flexible andallows 'springing' of 1 to 1Y2 mm at the incisal edgeof the pontic. Besides overcoming the problem ofdiastemata in bridgework, the spring bridge can alsobe used in circumstances where the aesthetic demandis of prime consideration or where the teeth on eitherside of the edentulous anterior space are sound orare unsuitable for use as abutments(4).

In fixed prosthodontic work, besidesmaintaining health and comfort, restoration ofaesthetics and function is of paramount importance;the serviceability and longevity of the prosthesis arewithin the expectations of the patient for all the time,energy and cost involved. A study reported a meanlife span of 10.3 years for fixed prosthodonticrestorations with caries accounting for most of thefailures(5). Another study reported an even lowermean life span of 8.3 years with 22% of failure dueto caries(6). Other failures cited included porcelainfracture, uncemented restorations, poor aesthetics,defective margins, fractured root/tooth, periodontaldiseases/mobility, periapical involvement, fracturedconnector and others.

It is the purpose of this paper to present a casereport of fracture of the palatal bar connector of aspring bridge after a 30-year service following itsissue in early 1977(7).

30-year life span of a spring bridge 49

Figure 1: Spring cantilever bridge (In: Dent J Malaysia 1977; 3: 15-20).

Figure 2: Spring bridge showing detached pontic with anterior portionof the fractured palatal bar.

CASE REPORT

A 56-year old male Chinese patient returned fromTaiwan to the Dental Clinic, Faculty of Dentistry,University of Malaya complaining that his bridgehad fractured. He was biting on an apple when hesuddenly felt that the pontic portion of his springbridge was displaced forward and upwards.Instinctively, he pressed the pontic back into placeand found that it just dropped onto the floor of hismouth. He brought along the pontic with itsattached portion of the fractured connector palatalbar (Figure 2).

The bridge was placed 30 years ago in earlyJanuary 1977 when he was a 26-year old who hadrequested for a fixed appliance in place of his looseupper partial denture replacing the upper left centralincisor. A spring bridge was indicated for him at thattime because of his expressed request to maintain allthe diastemata in his mouth; the presence of whichwere attributed to his congenitally missing uppercanines and diminutive upper lateral incisors (Figure3). There was also some loss of labial alveolar tissuesat the edentulous 21 region but he had a low lip line.Following issue of the spring bridge, good oralhygiene was emphasized especially with flossing

50 Annals of Dentistry, University of Malaya, Vol. 15 No.1 2008

Figure 3: Anterior diastemata present in the upper arch due to congenitally missingcanines and diminutive laterals (In: Dent J Malaysia 1977).

Figure 4: Flossing of the spring bridge.

under the palatal bar (Figure 4) and regular follow-up reviews (Figures 5 & 6) were carried out.

The last review was five years ago in 2002 whenthe bridge was in service for 25 years. There were nountoward sign and symptoms and the general oralhygiene was well maintained. The gingival healtharound the second upper left premolar abutment wasgood and no defect was detected at the three-quartergold crown retainer. The attached palatal barconnector carrying the 21 pontic were all in good

condition and the patient had adapted very well tothe presence of the palatal bar which had settledonto the mucoperiosteum. The bar still possessed theflexibility to allow I to I Y2 mm up and downspringing action with respect to the pontic incisaledge. The supporting mucosa beneath the pontic andpalatal bar was healthy, of normal colour and therewas no ulceration. Mechanically, the integrity of thebridge was intact and there was no observablematerial failure in both porcelain and alloy. Oral

30-year life span of a spring bridge 51

Figure 5: One-week review: the patient was satisfied with the provision of the naturaldiastemata and the overall aesthetics (In: Dent J Malaysia 1977).

Figure 6: One-year review of the spring cantilever bridge.

52 Annals of Dentistry, University of Malaya, Vol. 15 No.1 2008

hygiene was reinforced and the patient was dismissedto be reviewed in the next five years at 30 years ofserVIce.

Just as the bridge was due for review after 30years of service, the patient e-mailed from overseason 14 January 2007 to inform of its fracture andrequested attention upon his immediate return a fewdays later. On examination, the palatal bar hadfractured at the straight portion from the ponticleading towards the curved part as the bar turnedtowards the retainer. Except for the fracture, thedetached portion of the bar and the porcelain ponticwere in good condition. The remaining portion ofthe bar was still attached to its retainer and bothwere also found to be in good condition (Figure 7).The palatal mucosa and the gingiva at the abutmentappeared healthy and the abutment tooth was firmand there was no mobility. The retainer was still inplace and was well cemented. The apposing fracturedends of the bar appeared clean and there was nofragmentation.

Various treatment options including partialdentures, bridges, implants and integrated fixedremovable prostheses incorporating precisionattachments were discussed with the patient. As aninterim measure, the still attached portion of thebridge was removed by cutting the three-quarter

crown with a water-cooled transmetal bur and theabutment protected by cementing a temporaryacrylic crown. An intermediate partial denture wasissued within a matter of days so that the patientcould presentably continue with his overseasassignments. When the patient returned two monthslater and after thinking long and hard, he againopted for the spring bridge which he deemed best inhis circumstance and banked on the hope that thenew spring cantilever bridge would last him another30 years (Figure 8).

DISCUSSION

This spring bridge which lasted 30 years had a lifespan three to almost four times that of other fixedbridges reported(5,6). A meta-analysis of 42publications on conventional bridges between 1970and 1992 covering 4118 bridges showed an overallsurvival rate of 74% after 15 years(8). Though thespring bridge is a controversial prosthesis in that anarea of mucosa is permanently covered by the ratherlong flexible palatal bar, when judiciously indicatedand well maintained, it can provide many years ofcontinued service functionally and aesthetically.

Figure 7: Spring bridge showing cemented three-quarter crown retainerwith the posterior portion of the fractured palatal bar still in place.

30-year life span of a spring bridge 53

Figure 8: Mirror view of new spring bridge after I-week post-cementation.

When a diastema is required on either side of thepontic, the spring bridge is the answer as its retaineris placed on a posterior abutment and not connectedto the adjacent teeth. The spring bridge can also beindicated if the adjacent teeth to the edentulousanterior space are not suitable as abutments; such as(a) small conical peg-shaped clinical crownsproviding reduced retention, (b) small root surfacearea and/or poor periodontal condition renderingthem incapable of carrying the extra load, (c) goodsound adjacent anterior teeth wl!ich are notjustifiable to be mutilated. The spring'bridge is notindicated in the lower jaw as the mucosa here isthinner, the shape of the jaw will have the barcoming close to the gingival margins, the bar will notbe supported by the mucosal tissue as the bite isgenerally reverse and there is a greater tendency forcalculus formation.

To solve the problem of maintaining a diastemaon either side of the pontic, two palatal bars runningfrom the pontic to the adjacent retainers on bothsides had been designed(1). This design was furthermodified with the use of minimal preparation resin-bonded retainers(2) and also as in both fixed-fixedand cantilever resin-retained bridges(3). Since thesepontics were connected to their adjacent abutmentteeth, the connector bars placed on the palatalmucosae were short and stiff. These would be bulkyand uncomfortable for the patients. For the springbridge, the palatal bar is embedded in palatalmucoperiosteum to a depth of lY2to 2 mm clinicallyby cutting the palatal surface of the working modelto half the depth of a No. 10 round bur following

the proposed line of the bar and waxing the bar inits embedded position. For all the 30 years ofcontinued service, the patient did not experience anydiscomfort from the palatal bar. To give a better lineto the bar, the abutment of choice for replacing theupper central or lateral incisor is the first or secondpremolar and as to the canine, the upper first molaris the preferred abutment. The portion of the barwhich runs straight back from the pontic to the bendis the tissue bearing portion and it absorbs most ofthe masticatory forces(7).

The advantages of a spring bridge include: (a)readily achieved aesthetics, (b) relatively shortclinical chairside time, (c) provision of diastema oneither side of the pontic, (d) usually only oneposterior abutment is required to support the bridgeand (e) the flexible palatal bar acting as a shockabsorber reduces the chances of pontic ceramic fromfracturing. The flexible palatal connector bar of thespring bridge, as reported, finally fractured frommetal fatigue after 30 years of continuous service.

SUMMARY

The spring bridge when judiciously indicated andwell designed was able to satisfy the demands of thepatient to preserve the personal feature ofdiastemata. Good oral hygiene, patient motivationand regular follow-up reviews contributed to animpressive life span of 30 years which far exceededmost mean life span of other conventional bridges.

54 Annals of Dentistry, University of Malaya, Vol. 15 No.1 2008

REFERENCES1. Myers GE. Textbook of crown and bridge

prosthodontics. Saint Louis. The C V MosbyCompany. 1969; pp.147-8.

2. McCann KI The use of a cast etch bridge in adiastema situation. J Can Dent Assoc 1987; 9:687-9.

3. Gibson CI A modified technique for minimal-preparation, resin-retained bridges: four casereports. Dent Update 2001; 28: 442-8.

4. Roberts DH. Fixed bridge prostheses. JohnWright & Sons Ltd, Bristol. 1973; pp. 165-76.

5. Schwartz NL, Whitsett LD, Berry TG, StewartJL. Unserviceable crowns and fixed Partialdentures: Life span and causes for loss ofserviceability. J Am Dent Assoc 1970; 81: 1395-401.

6. Walton IN, Gardner FM, Agar JR. A survey ofcrown and fixed partial denture failures: lengthof service and reasons for replacement. JProsthet Dent 1986; 56: 416-20.

7. Lui JL. The spring bridge. Dent J Malaysia 1977;3: 15-20.

8. Creugers NHJ, Kayser AF, van-t Hof MA. Ameta-analysis of durability data on conventionalfixed bridges. Community Dent oral Epidemiol1994; 22: 448-52.

INSTRUCTIONS TO CONTRIBUTORSGENERAL INFORMATION

The Annals of Dentistry University of Malaya ispublished annually as the official journal of theFaculty of Dentistry, University of Malaya, KualaLumpur, Malaysia. As a general guideline, articlesintended for publication in the following year shouldbe received by the Editor by the end of Decemberof the preceding year. Original research articles andcritical reviews, pertaining to dentistry and its alliedfields will be considered for publication at thediscretion of the editors. Articles will be refereedindependently by at least two referees. Contributionsfrom all sources including from internationalcontributors are welcomed. The following guidelinesmust be strictly adhered to by intendingcontributors.

GENERAL INSTRUCTIONSAll contributions must be in English (ConciseOxford Dictionary). Authors should submit threecopies of the manuscripts (one original and twocopies) along with three sets of illustrations andfigures. The submitted manuscripts must beaccompanied by a covering letter which includes: (a)information on prior or duplicate publication orsubmission elsewhere of any part of the work, (b)the name, address, telephone number and e-mailaddress of the corresponding author responsible forcommunicating with other authors regardingrevisions and final approval of the proofs, and (c)whether the author(s) are willing to meet the cost ofreproducing colour illustrations (if any). The authorwho sends the article is responsible, in obtaining allthe authors agreement to publish and include in theletter a statement "I am submitting this paper, whichhas been approved by all authors". The manuscriptmust also be accompanied by a letter of permissionto reproduce published material or to useillustrations other than the authors of themanuscript submitted. The editorial board reservesthe right to edit all manuscripts for conciseness,clarity and stylistic consistency. Manuscripts arerefereed anonymously. Authors must keep copies ofmanuscripts sent.

CORRESPONDENCE

Address all correspondence to: The Editor, Annalsof Dentistry University of Malaya, Faculty ofDentistry, University of Malaya, 50603 KualaLumpur, Malaysia. Please include your e-mailaddress.

SUMMARY OF REQUIREMENT

Type the manuscript on white bond paper, 216 by279 mm or ISO A4 (212mm by 279mm), withmargins of at least 25mm. Type only on one side ofthe paper. Use double spacing throughout. Numberpages consecutively beginning with the title page.Type the page number in the upper right hand cornerof each page. Each manuscript component shouldbegin on a new page in the following sequence:

Title pageAbstract, Key words & Running titleText & AcknowledgementsReferencesTablesIllustrations

TITLE PAGE

This should carry: (1) Title of the article whichshould be concise but informative, (2) Initials andlast name of each author, (3) Institutional affiliation,(4) Name of department and institution should beclearly stated, (5) Name, postal address, telephonenumber and e-mail address of corresponding author.

ABSTRACT, KEY WORDS & RUNNING TITLE

The second page should carry an abstract of notmore than 250 words and should state the purposeof the study or investigation, basic procedures, mainfindings and principal conclusions. Below theabstract, provide and identify in not more than 10words the key issues of the article. Also, include ashort running title at the bottom of the page.

TEXT

The main text should include: Introduction,Materials and Method, Results, Discussion,Conclusion, Acknowledgements (if any) andReferences, in that order respectively.

INTRODUCTION

Begin with a concise introduction by outlining thepurpose of the research and making reference toprevious relevant publications. Mention anylimitation or gap in existing knowledge related to thestudy in question. Do not review the subjectextensively and do not include data or conclusionfrom the work reported.

56 Annals of Dentistry, University of Malaya, Vol. 15 No. I 2008

MATERIALS AND METHODDescribe precisely the materials/subjects used.Identify the methods, apparatus and procedures usedin sufficient detail so as to allow other workers toreplicate the study. Give references to establishedmethods, including statistical methods. Providereferences and brief descriptions for methods thathave been published but are not well known.Describe new or modified methods and give reasonsfor using them and evaluate their limitations.Identify all drugs and chemicals used includinggeneric names, dose and route of administration.

RESULTSPresent results in a logical sequence in the text, tablesand illustrations. Do not repeat in the text all thedata in the tables and illustrations. Emphasise orsummarise only important observations. Specifystatistical methods used to analyse results anddescribe them with sufficient detail to enable aknowledgeable reader with access to original data toanalyse results.

DISCUSSIONEmphasise the new and important aspects of thestudy and the conclusion that follow from them. Donot repeat in detail, data or other materials, givenin Introduction or Results section. Include in theDiscussion section the implication of the findingsand their limitations, including implications forfuture research. Relate the observations to otherrelevant studies.

CONCLUSIONSLink the conclusions to the goal of the study butavoid unqualified statements and conclusions notsupported by your data.

ACKNOWLEDGEMENTSAcknowledgements where applicable should beincluded at the end of the text. This should be keptto a minimum.

REFERENCESReferences should be carefully checked, as theiraccuracy is the responsibility of the author(s). In thetext, references should be numbered sequentially inorder of citation by bracketed numerals, ego(1,3-6).The reference list must be attached at the end of thepaper using the following format:

Journals:I) Master M, Barber TK. Action of amalgam on

dentin. J Am Dent Assoc 1980; 47: 415-22.

2) Murray AJ, Nanos JA, Fontenot RE.Compressive strength of glass ionomer with andwithout silver alloy. J Dent Res (Abstract no:215) 1986; 65: 193.

3) Kato Y, Okawa A, Hayashi S, et al. Studies onmarginal leakage of composite resin restorations.Part 2: On the leakage properties of variouscomposite resin restorations. Jpn J Conserv Dent1976; 19: 281-9.

4) Klineberg 11, Murray GM. Design ofsuperstructures for osseointegrated fixtures.Swed Dent J 1985; 28(Suppl): 63-9.

5) Lincks J, Boyan BD, Cochran DL, Liu Y,Blanchard C, Dean DD, Schwartz Z. MG63 cellsdiscriminate between surface roughness andmaterial composition. J Dent Res (Abstract no:1123) 1998; 77 (Special issue A): 246.

Books, Monographs and Agency Publications:Book - Chapter in a book:1) Zinner ID. Esthetic considerations in restorative

dentistry. In Seide LJ, ed. A dynamic approachto restorative dentistry. 1st edn. Chicago, W.B.Saunders Company 1980; pp. 520-58.

Book - personal author/s:2) Gutmann J, Harrison JW. Surgical Endodontics,

15t edn. Boston, Blackwell Scientific Publications1991.

Monograph - Book Proceeding:3) DuPont B. Bone marrow transplantation in

severe combined immunodeficiency with anunrelated MLC compatible donor. In: White HJ,Smith R, eds. Proceedings of the third AnnualMeeting of the International Society forExperimental Hematology 1974; pp. 44-6.

Monograph - thesis/dissertation:4) Tay WM. Physico-chemical properties of

aluminosilicate based dental cements. Universityof London, 1988. PhD. thesis.

Agency publication:5) Parkin DM, Whelan SL, Ferlay J, Raymond L,

Young 1. Cancer Incidence in five continents.Volume VII, International Agency for Researchon Cancer: Lyon. IARC Scientific PublicationNo 143. 1997.

Tables:

Each table should be typed on a separate sheet,numbered consecutively in Arabic numerals (eg.Table 4) and titled with a descriptive but conciseheading. Explanatory notes if any should be placedbelow the table.

Illustrations:

All graphs, drawings and photographs areconsidered figures which must be of good qualityusually 127 by l73mm (5 by 7 ins) but not largerthan 203 by 254mm (8 by 10 ins). Submit 3 copiesin a heavy-paper envelope. Authors must keep copiesof everything submitted. At the back of eachillustration, label the appropriate Figure numbercorresponding to the order of appearance as citedin the Text. Use a soft pencil to indicate the top ofthe illustration and lightly write in the running title.The author's name should not be added. Originaldrawings, figures, charts and graphs should beprofessionally drawn and lettered large enough to be

Instructions To Contributors 57

read after reduction. High quality computergenerated line diagrams or glossy prints are alsoacceptable. Photographs in general should be clearblack-and-white prints on glossy paper. Colourillustrations may be submitted if they contribute tothe value of the article but the full cost of printingmust be borne by the author(s). Prints ofradiographs should be sharp and clear.Photomicrographs must include a scale andmagnification should be clear. Consent must besubmitted with the manuscript.

Legends:

Each figure must have a legend that is clear withoutreference to the text. All legends should be typed ona single sheet with the corresponding figure numberclearly indicated.

Figures and Tables in the text:

Figures and, ta~les should be spelt out in full whenreferred to in the text e.g. Figure 2 or Table 3.