Pathology

Subpontic osseous hyperplasia: A case reportEduardo R. Lorenzana, DDSi/William W. Hallmon, DMD, MS'

Subpontio osseous hyperplasia is an ectopic growth ot bone occurring on the edentuious ridge beneath afixed partial denture replacing a mandibuiar first molar. A 56-year-oid woman experienced an eniargementol the hard and soft tissues beneath the pontic region ot a fixed paniai denture replacing her mandibularleft first molar. Following removal of the fixed partial denture, the bony enlargemeni was surgicallyremoved, and the bony fragments were submitted tor histologie analysis, which demonstrated maturelamellar bone and appositionai growth. One year posfoperatively, there has been no recurrence of thelesion. The possible etiologies and treatment modalities are reviewed and a rationaie for treatment is pre-sented. (Quintessence Inf 2000:31 •57-61 )

Key words: ecfopic growth, tixed partiai denture, subpontic osseous hyperplasia

Living bone is a dynamic tissue, characterized byinteractive states of résorption and deposition that

result in periodic remodeling. This remodeling isimportant because it enables response to increasedstress, realigns bony morphology in accordance withmechanical stresses, and deposits new organic matrixto maintain the required strength and integrity ofbone.' Although normal remodeling maintains anequilibrium that keeps bone mass constant, certainconditions may affect the equilibrium, causing eitherexcess résorption or excess deposition of bone matrix.

Intraorally, increased deposition cf bone usuallymanifests as single or multiple exostoses. However,growth of bone has occasionally been observedbeneath the pontic of fixed partial dentures (FPDs)that replace lost or missing portions of the dentition.Such bone formation has been the subject of a limitednumber of case reports and reviews in the literature-'^and continues to evoke speculation among investiga-tors regarding its cause.

Subpontic osseous hyperplasia was first describedby Caiman et al, in 1971. as a painless, slow-growinglesion on the edentulous ridge beneath a fixed partialdenture replacing a mandibular first molar. A ciinicaidiagnosis of osteoma was rendered, and the authorsspeculated that the FPD was the stimulating factoraccounting for bone formation.^ This type of exostosishas been described in the dental literature; reportshave used the following terms: plateauitization,^ sub-

'Department ot Periodontics, Baylor Coliege ot Dentistry, Texas ASMUniversity Syslem. Daiias, Texas

Reprint requests: Dr Wiiliam W. Hailmon, Department ot Penodortics,Bayior College o( Dentistry. Texas ASM University System. PO Bo«660677, Dallas, Texas 753S6-0677. E-mail. WHallmon@TAMeCD.edLi

pontic osseous proliferation.'^ subpontic hyperosto-sis,^'' hyperostosis.'^ reactive subpontine exostoses,^and subpontic osseous hyperplasia.''"-'^ As a result ofthe lack of consensus on terminology for this condi-tion, subpontic osseous hyperplasia (SOH) will be theterm used in this report, because it addresses the clini-cal, radiographie, and microscopic characteristics ofthe lesion.'"

The purpose of this article is to report a case of sub-pontic osseous hyperpiasia, including related clinicaldata and histopathologic observations. An approachto treatment and the prevailing theories related to theetiologi' of this phenomenon will also be discussed.

CASE REPORT

A 56-year-Dld woman was referred with chief com-plaints of a swelling around her fi.xed paniai dentureand discomfort associated with the swelling. A r e ^ wof the patient's medical history revealed that she hadsurgery for removal of her gallbladder and a hysterec-tomy performed in 1988. There was no prior history oftumors or growths in the head and neck region.Currently prescribed inedications included estradiol(Eslrace) and iluoxetine hydrochioride (Prozac) fordepression. The patieni stated that the FPD replacingher mandibular left first molar had been placedapproximately 25 years ago and that she was unawareof the enlarged tissue around her prosthesis untilrecently, at which time she began to experience dis-comfort beneath the pontic.

Clinical examination revealed a gold FPD, span-ning the second premolar to the second molar, with asaucer-shaped enlargement of the hard and soft tissuescircumscribing the pontic area (Fig 1). The affected

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Fig 1 Initial presentation ol a gold fixed partiai denture replacingtine mandibuiar ielt first moiar. inflammation and suppurationare associated with the excess tissue m intimate contact with thepontic.

Fig 2 tiiiLiai periapicai radiograph. The bony iesion appearsmore radiopaque than does the surrounding alveolar bone Notethe styius-snaped pontic design.

Fig 3 F\xeü partiai denture sectioned for removal, showing therelationship between the pontic and the underiying osseous tissue.

Fig 4 Removai of the fixed partial denture, reveaiing a bonycrypt continuous with the surrounding alveolar bone.

tissues were in intimate contact with the pontic,obscuring its apical extent. The soft tissues were char-acterized by marginal erj thema and bleeding on gentleprobing between the enlargement and the pontic.Plaque accumulation was evident buccoiingually. Thepatient also had FPDs replacing the maxiliary rightsecond premolar and the mandibular right first molar,but the associated subpontic tissues were clinicallynormal.

Radiographie evaluation revealed a stylus-shapedhygienic pontic, which approximated the supra-alveo-lar bony iesion. The adjacent alveolar ridge was con-tiguous with the bony lesion in the subpontic area,although a difference in their densities was observed.The hyperplastic bone was more radiopaque than wasthe adjacent alveolar ridge, and there was little evi-dence of trabeculation within the lesion compared tothat within the adjacent bone (Fig 2).

The treatment plan included surgical removal of thelesion and associated recontouring of the alveolarridge. A full-thickness buccal flap was reflected priorlo removal of the FPD, allowing observation of therelationship of the pontic to the underlying soft andhard tissues (Fig 3). The bone directly beneath thepontic was indistinguishabie from the adjacent alveo-lar bone, sbowing a definite homogenous appearance.Removal of the restoration and reflection of a full-thickness tlap lingually revealed a saucer-shaped bonycrypt that followed the contours of the pontic (Fig 4).

Rongeurs were used to remove large bony frag-ments, and the ridge was subsequently reshaped withchisels and high-speed handpiece instrumentation,used under profuse irrigation with sterile water (Fig 5).The bony fragments were collected in 10% neutralbuffered formalin for submission for histopathologicexamination.

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Fig 5 Osteopiasty performed using rongeurs, round bur, andchisels.

Fig 6 One-year pos(operative photograph. There is no evidenceot recurrence of the lesion

Fig 7 Low-magnification view of biopsied osseous tissue Notethe presence of viable bone with osteocytes m iacunae, the pres-ence of vascular channels, and the lack of an infiammatory infii-trate, (Hematoxylin and eosin stain.)

Fig 6 High magnification ot osseous lissue (Hematoxylin andeosin stain,)

Following removal and recontouring of the bone,the flaps were reapproximated over the edentulousarea. The pontic was reshaped so that it did not con-tact the surgical site. The FPD was relined mth acrylicand used as a provisional restoration during initialhealing. Four months later, the preparations on theabutment teeth were refined, and a new provisionalrestoration was fabricated. One year postoperatively,there has been no recurrence of the lesion, and thepatient is awaiting delivery of her permanent fixedpartial denture (Fig 6),

The tissues submitted for histologie exammationwere decalcified, sectioned, and staitied with hema-toxylin and eosin. The sections revealed multiple irreg-ular fragments of mature, lamellar, viable bone withevidence of appositional growth. Some osteoblasticlayering was present with evidence of small amountsof new osteoid (Figs 7 and S),

DISCUSSION

This report describes the 37th case of SOH reported inthe literature. All of the subjects of these case reportswere adults, men and women, between 29 and 81years of age. Ali SOH lesions bave occurred in associ-ation with mandibular FPDs, ''

Fixed partial dentures are commonly used toreplace a missing tooth or teeth by "bridging" thespace between the remaining teeth adjacent to theedentulous area. Numerous pontic designs exist; thesehave varying effects on function, hygiene, and esthet-ics,'•* The hygienic, or sanitary, pontic facilitates thepatient's hygiene efforts and may therefore favor thehealth of the periodontium. It has a convex, roundedinferior surface and does not contact the underlyingridge, providing the patient ample access for clean-ing,''' The pontic in the case presented appeared to

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have this design intent in mind. However, it had amuch sharper form, resembling a stylus; this may havecontacted the ridge, creating a functional stimulus atrest and/or during occlusal contact, resulting in theformation of bone around the pontic. However, SOHhas been reported in association with other ponticdesigns that clearly were not in eontact with the alve-olar ridge. •' At this point, tbe influence of ponticdesign on SOH remains inconclusive.

There are several theories about the nature andonset of SOH, Although all have some validity, nonecan fully explain this phenomenon, which mayinvolve a number of factors. First, the aforemen-tioned functional stresses or stimuli have beendescribed as a possibie etiology for SOH ' " and otherbony exostoses, such as palatal or mandibular tori."Support for tbis theory exists from Appleby,^ whoreported a case of subpontic osseous hyperplasia thatspontaneously disappeared following loss of theinvolved pontic.

Photoelastic studies have found the first molarregions to be subjected to distinct stresses on openingand occlusal loading,"*'' The placement of an FPDcould alter these stresses and, at least in theory, induceosteogenesis.'^ However, if this were the case, patientswith multiple FPDs would have multiple occurrencesof SOH, in parts of the dentition other than the poste-rior mandible." This was not the case in this patient,who had 3 FPDs bul only 1 occurrence of SOH andno other bony exostoses. To date, no report has everdescribed SOH anywhere other than the posteriormandible.-'^

A second theory suggests that the presence of amild, chronic irritation beneath the pontic may be thestimulus for bone formation.-^ After examining 500FPDs, Stein'' reported that the soft tissues underlyingthe pontics were inflamed in 95% of the cases.Although no inflammatory cells were found in thebiopsied bony fragments in the present report, signs ofgingival irritation were readily detected during the ini-tial clinical examination.

Another possible etiology of exostoses is theorizedto be genetic predetermination.^'''^' This may also be afactor contrihuling to the incidence of SOH. Whilesome authors have noted the presence of exostoses inpatients with SOH,'-''' ' SOH in the absence of otherexostoses or tori'' leads one to speculate on the likeli-hood of a multifactorial etiology.

Last, a theory based on research by Bassett et aP^and Bassett and Becker" proposes that bone undercompression develops negative electric potentials,which have been associated with bone growth. In fact,certain forms of electrical stimulation that promoteosteogenesis have been used to enhance healing offractures. '' This suggesfs that, if bone beneath an FPD

is subjected to occlusal or functional stresses, a nega-tive electric potential may occur, which can inducebone formation as seen in O > ' f

TREATMENT MODALITIES AND RATIONALE

The most common treatment modality of SOH isremoval of the FPD, surgical resection and recontour-ing of the alveolar ridge, and fabrication of a newFPD. Occasionally, if the existing FPD is well madeand can be retrieved without damage fo its contourand marginal adaptation, recontouring and recemen-tation of the original FPD is a viable, conservativetreatment alternative. Patients should be informed,however, that the potential for recurrence of SOHdoes exist.' Applcby'-" reported spontaneous remissiotiof SOH following loss of the pontic by the patient andsuggested removal of the pontic as another conserva-tive treatment modality. He also discussed 2 othertreatment options, including the use of a semiprecisionattachment to decrease stresses in the area or restora-tion of the edentulous space with an implant and animplant-supported restoration, to avoid recurrence.'

Although spontaneous remission on removal of theFPD has been reported, the most efficient and pre-dictable treatment remains surgical exposure andosseous recontouring. Restoring the edentulous spacewith a new, hygienic, properly contoured and polishedFPD is the most economic alternative followingsurgery. If the patient or the operator is concernedwith recurrence, however, an implant-supportedrestoration would be the treatment of choice to main-tain function and occlusal stability. Regardless of fhetreatment modality chosen, the rationale for treatmentshould include (1) the restoration of phonetics, esthet-ics, and function; (2) biopsy to rule out malignancy;(3) control of chronic irritation and/or trauma; (4)access for oral hygiene maintenance of the area by theoperator and the patient; (5) treatment of associatedinflammatory periodontal disease, both locally andcomprehensively; and (6) prevention of any displace-ment of the restoration. ' -"

ACKNOWLEDGMENTS

The authori grateriilly acknowledge Dr William H. Birinie and Dr E.James Cundiff II, Baylor College of Dentislry-Tesas A&M Univer-sity System, Division of Pathology, for their help with the prepara-tion and miero,icopic description of the histologie specimens. Specialthanks to Dr Terry D. Rees, Baylor College of Denti.stry-Texas A&MUniversity System, Department of Pcriodontics, for reviewing themanuscript prior to submission.

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24. Brighton CT, McCluskey WP. Cellular responses and mech-anisms of action of electrically induced osteogenesis. In:Peck WA (ed). Bone and Mineral Research, vol 4. NewYork: Elsevier Science, 1986:213-254

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Quintessence International 61