International Endodontic Journal (1989) 22, 64-74

Odontiatrogenic tooth fracture

J, L, SCHWEITZER, J, E, GUTMANN* & R, d, BlASSi Department of Endodontics,Marquette University School of Dentistry, .Milwaukee, Wisconsin, USA, * Department ofEndodontics, Baylor College of Dentistry, Dallas, Te.\as, USA and Private Practice in Jacksonville,Florida, USA

Summary, While the awarcncs,s of vertical toothtraclures, whether incomplete or complete, isincrea,sing, sufficient attention has not been paid tothe manner in which the dentist may contributeto the occurrence of these fractures. This paperfocuses on tbe most likely areas in wbicb tbepractitioner can eitber misdiagnose tbe presenceot a fractured tootb or wbere dental procedurescontribute to fracture of tbe tootb structure. Fortbis type of fracture tbe authors propose tbe term'odontiatrogenic tootb fracture'.

IntroductionThe diagnostic dilemmas that dental prac-titioners face with incompletely fracturedteeth were reviewed at length by C ameron(1%4), Me identified these teeth, withtheir bizarre symptoms, as exhibiting the'cracked-tooth syndrome'; the term is widelyused today, Luebke (1984) defined anincompletely fractured tooth as one with ademonstrable fracture line but with no visibleseparation of segments along the plane ofthefracture. He further classified a complete toothfracture as one in which there was a visibleseparation of the fractured segments whichcould easily be wedged apart. Other authorshave used various terms to describe essentiallythe same phenomenon seen in the crackedtooth: greenstick fracture ofthe tooth (Sutton19()2), split-root syndrome (Silvestri 1976),and vertical root fracture (Lommel et al.1978, Meister et al. 1980, Luebke 1984),These fractures can be further categorized as acrown fracture (fracture limited to the crownportion ofthe tooth) or a root fracture (verticalroot fracture). The latter often involves boththe crown and the root (complete toothfracture).

Correspondence: Dr J, Gutmann, Department ofEndodontics, Baylor C.ollege of Dentistry, 3302Gaston .Avenue, Dallas, Texas 75246, USA,

Early reports concerning fractured teethtended to emphasize factors or variableswhich the practitioner could not alter,which Maxwell & Braly (1977) later referredto as predisposing factors. These includemasticatory accidents (Cameron 1964, 1976,Wiebusch'l972, Rosen 1982), tight cusp-fossa relationships or steep intercuspation(Sutton 1962, Cameron 1964, 1976, Bender& Freedland 1983), bruxism and thermalcycling (Cameron 1964, Luebke 1984), Othercontributing factors, identified as precipatingfactors by Maxwell & Braly (1977), were due,in large part, to operator errors,

Ritchey et at. (1957) and Cameron (1964)found that a large number of incompletelyfractured teeth were restored with soft goldinlays. Also, large two, three, and four surfaceamalgam restorations were commonly foundin many fractured teeth (Cameron 1976,Maxweli & Braly 1977, Gher^ra/, 1987), Highspeed instrumentation and the increased useof rotary instruments resulting in excessiveremoval of tooth structure have been postu-lated as weakening the tooth and predisposingto fracture (Cameron 1964, Rosen 1982,Bender & Freedland 1983). Reinforcing pinshave also been known to cause microcracks,leading to possible fractures in teeth (Silvestri1976, Meister et al. 1980, Pitts et al. 1983),Intraradicular posts, when incorrectly used,may also damage the root or crown ofthe tooth(Maxwell & Braly 1977, Re et al. 1982, Pitts &Natkin 1983, Luebke 1984), Forces generatedduring the insertion of restorations such ascrow ns, onlays, or posts may also lead to toothfractures. Finally, hydrostatic pressures whichcan develop during cementation, especially ofposts, have been identified as contributing tovertical root fractures (Maxwell & Braly 1977,Wechsler et al. 1978, Luebke 1984).

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Odontiatrogenic tooth fracture 65

Recently, attention has been directedtoward endodontic procedures as major con-tributors to fractured teeth. Excessive forcesused during lateral and vertical condensationof gutta-percha have been cited as a cause ofvertical root fracture (Sinai & Katz 1978,Meister et al. 1980, Luebke 1984, Maxwell etal. 1986). Bender & Freedland (1983) pro-posed that placing of silver cones could alsodamage the root. Excessive removal of bothcoronal and radicular tooth structure duringaccess and canal preparation have been cited asfactors which will weaken the crown, root, orboth (Cameron 1964, Johnson et al. 1976,Maxwell & Braly 1977, Bender & Freedland1983). Lastly, failure to place a veneer or post-retained crown on every endodonticaliytreated tooth has been a long-held, empiricalbelief that predisposes to the fracture of theseteeth.

The purpose of this paper will be to discussoperator contribution as a possible sourceof tooth fracture for which the authorssuggest the term odontiatrogenic tooth fracture.Just as the Greek term iatrogenic refers toharm or injury caused by the physician(laxpos), odontiatrogenic refers to the adversesequelae caused by the dentist (oSovxaipos).Possible ways to avoid practitioner contri-bution to this clinical malady will besuggested. In pursuit of this discussion, theaetiological factors will be grouped into threeareas of clinical practice: diagnosis and treat-ment planning, endodontic procedures, andrestorative procedures.

Diagnosis and treatment planningEarly diagnosis and/or detection of toothfracture is essential for successful treatment.Undetected, the fracture may lead to pulpaldegeneration (Walton et al. 1984), periodontalproblems (Hiatt 1973), and the eventual loss ofthe tooth in some cases. Only a brief review ofsome of the key elements in diagnosis anddetection will be discussed. The practitionershould be cognizant ofthe signs and symptomsof tooth fracture during treatment planningand should take measures to avoid eithermissing or contributing to this mishap.

In 1964, Cameron identified the mostimportant factor in the diagnosis of a crackedtooth as an awareness ofthe problem. Several

Fig. 1. One per cent methylene blue was used todisclose multiple craze lines in the pulpal roof of amandibular molar. A major fracture line is visibleacross the distal marginal ridge (arrow).

authors have since supported this (Maxwell &Braly 1977, Rosen 1982, Gher et al. 1987)and reports have served to elucidate thisproblem (Hiatt 1973, Meister et al. 1980,Pitts & Natkin 1983, Maxwell et al. 1986, Gheret al. 1987). However, the clinical detectionof these fractures can be difficult, especiallyin the initial stages, and radiographs are oflittle value (Matusow 1987). In addition, thepatient's symptoms may mimic many otherpossible diagnoses, such as temporomandi-bular joint syndrome, sinus problems, vagueheadaches, and ear pain, thereby misleadingthe practitioner.

Although detection is difficult, there areseveral techniques and clinical aids that mayhelp in identifying fractured teeth. While it isunlikely that the fracture line may always beseen, careful visual examination ofthe tooth ina dry field is essential. Occasionally it is poss-ible to 'highlight' a fracture by staining thetooth with 1 per cent methylene blue, iodine,or disclosing agent (Fig. 1). A sharp explorercan sometimes localize or catch the fracture

66 J. L. Schweitzer, J. I.. Gutmann S" R. Q. Bliss

Fig. 2. Fracture lines are visible down the mesial and buccal surfaces of maxillary molar (case courtesv of DrDavid Parkins).

line. If wedging a probe tip between the frac-tured segments or biting on a wood stick re-produces the patient's complaint, a diagnosisof cracked tooth may be considered. Often,removal ofthe restoration, if present, will re-veal the craek or fracture. Particular attentionshould be paid to the mesial or distal marginalridges (Fig. 2), as these are considered a weakarea ofthe tooth and so susceptible to fracture(Hiatt 1973). Transillumination is also usefulfor detecting fracture lines that are not readilyapparent (Cameron 1964, Luebke 1984) (F'ig.3).

In the advanced stages ofa vertical fracture,periodontal probing ofthe involved tooth givesa characteristic picture. Unlike a periodontalpocket which is wide and does not restrictmovement ofa probe as it is moved cireumfer-entially, the osseous defect caused by thevertical fracture is narrow and does not allowlateral movement of a probe (Pitts & Natkin1983, Luebke 1984), and has been likened toa narrow subgingival dehiscenee (Gerstein1987, personal communication).

In some instances, a diagnostic surgical pro-cedure is indicated to confirm the presence ofavertical root fracture. However, the fracture, ifincomplete in a buccolinguai direction, maynot be located without both buccal and lingualtissue reflections. Periodontal probing, priorto flap design, will usually indicate the antici-pated location of the fracture and serve as aguide for the surgical intervention. Surgical

exploration should only be used when all otherdiagnostic means cannot confirm the presenceand location ofthe fracture (Fig. 4). Certainly,in many cases, surgical exploration is indicatedbefore tooth extraction.

The above techniques, when used in combi-nation, can become effective in finding crackedor fractured teeth. But unless the practitioneris aware that cracked or fractured teeth arecommon, their presence may go unnoticed.

Generally, radiographs will not show frac-tures unless there is actual separation of theroot (Fig. 5). The fracture line will not be seenunless the central beam is parallel to the frac-ture line or is within a few degrees of it(Andreasen 1986) and the radiograph is ofgood quality and contrast (Stewart 1988).Rosen (1982) identified radiographs as usefulin discerning some ofthe other possible causesfor the patient seeking dental treatment, andwhose signs and symptoms may indicate acracked or fractured tooth. These include rootperforations, internal or external resorption,and endodontic failures. Radiographs mayalso give some suggestive or presumptive evi-dence ofa fracture. Since many fractured teetheventually develop periodontal defects, thesedefects have been radiographically describedas an area of radiolucency step-lilie in shape,having an angular rather than roundedappearance at its most apical level (Pitts &Natkin 1983). An indistinct radiolucent 'halo'or 'balloon' along the root wall or length may

Odontiatrogenic tooth fracture 67

Fig. 3. Transillumination from thebuccal surface of a maxillary premolar:normal room light (top left), reducedroom light (bottom left; note light doesnot pass through vertical fracture pres-ent), and a proximal radiograph (right)showing fracture line (arrows). Casecourtesy of Dr John Ross.

indicate a possible vertical root fracture (Fig.6). A radiolucent line adjacent to the root canalfilling material may indicate that there is aspace between the root canal wall and the fill-ing material possibly created by a fracture(Fig. 6). This space, however, must be differ-entiated from a spreader or plugger void.When radiopaque filling material is expressedthrough the fracture, it may appear on a radio-graph as an intensely radiopaque line withinthe obturated canal (Pitts & Natkin 1983).

While the diagnosis of fractured teeth isfurther complicated by bizarre symptoms, anaccurate assessment is still possible when allthe facts are considered. Although the classicalsymptom of a fractured tooth is pain duringmastication, usually upon release (Cameron,1964, Silvestri 1976, Pitts & Natkin 1983),even this may not always be true. Patients havereported pain ranging from none to severe,

with or without thermal or percussion sensi-tivity. Often, patients may be referred toseveral dental practitioners or physicians in anattempt to identify the source of their pain. Ahistory of repeated occlusal adjustments withonly temporary relief, may signal the presenceof a fracture. Occasionally the patient mayreport having heard a crack during root canalobturation. A history of a masticatory acci-dent, such as biting on a bone, is not anuncommon recollection by patients with acracked tooth. Cameron (1964) eloquentlystated that 'many of those (patients) withcracked teeth delighted in exerting maximumpressure on foods whether needing it or not.They took pleasure in biting hard'.

Some clinical features, previously men-tioned, may aid in diagnosis and treatmentplanning. Some of these are bruxism, occlusaldisharmonies, large intracoronal restorations.

68 7-1' Schweitzer, J. L. Gutmann £5" R. Q. Bliss

Fig. 4. A radiograph ofthe maxillary lateral incisor with an open apex and periradicular rarefaction (left); a hintof a radiolucent line can be seen in coronal half of root. Soft tissue reflection (right) reveals a hony defect andvertical fracture (arrows).

Fig. 5. .\ radiograph ofthe mandibular molar showing a radiolucent fracture line and separation ofthe rootsegments.

and aged patients. According to several stud-ies, mandibular first and second molars are themost frequently fractured teeth (Cameron1964, Hiatt 1973, Maxwell & Braly 1977, Gheret al. 1987), due to the increased number andextent of restorations, the presence of perio-dontal disease, their proximity to the fulcrum

ofthe jaw, and the increased presence of rootcanal fillings.

Bender & Freedland (1983) classified anadditional type of fracture, the pathologicalfracture, which may occur subsequent toperiodontal disease and weakened osseousradicular support. Nyman & Lindhe (1979)

Odontiatrogenic tooth fracture 69

Fig. 6. A radiograph of the mandibuiar caninewhich shows diffuse longitudinal bone loss alongthe distal aspect of the root. Also discernible is aradiolucent line adjacent to the distal margin ofthegutta-percha filling (arrows).

found that the potential for fracture of perio-dontally involved teeth was increased if endo-dontic treatment had been performed. Thisrisk was further increased if the tooth was laterrestored extensively. Reinhardt et al. (1983),studying dentine stresses in reconstructedteeth with decreased bone support, concludedthat after 4—6 mm of supporting bone had beenlost, the potential for root fracture would begreater than if the tooth had normal support oreven a 2 mm loss of bone height. Subsequently,if a large post was inserted into an endodonti-cally treated tooth which had 40 per cent boneloss, and served as an abutment, the strainmight lead to vertical root fracture. Fracturesmay be prevented as early as the planning stageof treatment. Identification of predisposingfactors for fractured teeth during the oralexamination should lead to adjustments in thetreatment plan. Instead of large three and foursurface amalgam restorations being the finalrestorations in patients with tightly interdigi-tating cusps and fossae, crowns may be more

appropriate. When teeth are planned toreceive root canal therapy and factors existwhich predispose to fractures, banding of thetooth prior to treatment should be considered(Fig. 7). In many endodontically treated cases,restorations should include well-placed coresand crowns without posts. Extensive restora-tive work may need to be reconsidered in thepatient who has suffered severe periodontaldisease, especially if the teeth have been endo-dontically treated.

Endodontic proceduresDuring endodontic treatment, the practitionermay either cause tooth fracture, most oftena vertical root fracture, or contribute to itseventual development. The most commonlycited cause is the use of excessive force duringlateral condensation of gutta-percha (Maxwell& Braly 1977, Sinai & Katz 1978, Meister et al.1980, Bender & Freedland 1983, Pitts et al.1983, Gher et al. 1987, Holcomb et al. 1987).Excessive removal of tooth structure duringaccess to the root canal system is also con-sidered to contribute to crown fracture(Cameron 1976, Bender & Freedland 1983,Maxwell et al. 1986). Although the use ofsilver cones for obturation has decreased.Bender & Freedland (1983) discussed them asa factor in some fractures, especially when alarge cone had been wedged in a root whichwas narrow apically. The effect of failing torestore teeth adequately after endodontictreatment has also been known to result infractures and sometimes loss of teeth.

Meister et al. (1980) attributed 84 per centof all vertical fractures to excessive condensa-tion forces. Harvey et al. (1981) found that agroup of eight endodontists exerted between1-3 kg of force during lateral condensation.Pitts et at. (1983) demonstrated that 7.2 kg offorce could cause vertical fractures, from thisstudy it was conjectured that 5 kg of force wasreasonable to achieve obturation withoutdamaging the tooth. However, recent findingsby Holcomb et al. (1987) showed that spreaderloads of 1.5 kg produced fractures and that 13per cent of the sample (54 teeth) fractured atloads of 3.5 kg or less. Therefore, it was rec-ommended that condensing instrumentsshould not be wedged against the root canalwalls.

70 J. L. Schweitzer. J. L. Cutmann (^ R. Q. Bliss

l"ig. 7. A mandibular molar with a crown fracture banded for endodontic treatment; note the mesial and distalfracture lines.

During cndodontic acccs.s preparation,canal cleaning and shaping, and preparation ofthe canal space to receive a post, excessiveamounts of tooth structure may be removedintentionally or unintentionally. Some authors(Bender & Freedland 1983) attributed frac-tures to the recent introduction of techniquesthat advocate the use of rotary instrumentswithin the root canal. Instruments such asPeeso reamers and Gates Glidden burs cut in astraight line, resulting in the removal of sig-nificant amounts of dentine, especially innaturally thin areas of roots (Abou-Rass ct al.19<S2). Care and caution must be exercisedwhen using these instruments; this also appliesto sonic and ultrasonic instruments. Preser-vation of not only coronal, but also radiculartooth structure is needed for successful treat-ment ofthe tooth.

While endodontic procedures may contrib-ute to the fractures of teeth, Matusow (1987) isofthe view that many of fractures are presentprior to endodontic diagnosis and treatment,and are often overlooked as aetiological factorsin pulpal demise and patient discomfort. Thiscould be especially true where rubber damclamp pressure, pre-endodontic banding, orcrowns temporarily mask pre-existing hairlinefractures. Although evidence for this is em-pirical, the possibility ofa fracture in posteriorteeth requiring endodontic treatment shouldalwavs be considered.

Restorative proceduresAn increase in dentine brittleness has beenpostulated by many as a contributing factor tothe increased susceptibility to fracture ofpulpless teeth. Heifer et al. (1972) found a 9per cent moisture loss in the calcified tissues ofpulpless dog's teeth compared with vital teeth.Carter et al. (1983), using a punch shear test,found that dentine from endodonticallytreated molars was weaker and more brittlethan vital dentine. However, Lewinstein &Grajower (1981), testing the Vicker's hardnessof dentine, found that endodontic treatmentdid not significantly affect the hardness of den-tine. They indicated that the mechanicalproperties of teeth may change after root canaltreatment and that microcracks may developas a result of canal preparation and water loss.

While the view that endodontically treatedteeth are more brittle is controversial, it isknown that the architecture of the tooth hasbeen altered, sometimes significantly (Tid-marsh 1976). Therefore, it is advisable that themajority of posterior teeth and some anteriorteeth should receive a restoration which willprotect the tooth during function. It has beenrecommended that all teeth should have fullcuspal coverage (Johnson et al. 1976, Rosen1982, Goerig & Mueninghoff 1983). However,excessive removal of enamel and dentine maylead to fractures by weakening the remainingtooth structure. With the advent of stronger

Odontiatrogenic tooth fracture 71

Fig. 8. Presence of a crown fracture (arrow) under a gold inlay; the patient had experienced severe pulpitis.

amalgam alloys and resin bonded to acidetched enamel, an increasing number of stud-ies have identified these newer materials andtechniques as alternatives to crowns for multi-lated tooth (Brown et al. 1979, Nayyar et al.1980, Oliviera et al. 1987). Re et al. (1982)concluded that there was no statistical differ-ence in the fracture strength of teeth withthree surface alloys and unrestored teeth.When large alloys did fracture, the resultantfracture left the tooth unrestorable in a ma-jority of cases. On the other hand, Gher et al.(1987) found that multisurface amalgam resto-rations were the most common restoration infractured teeth. Comparing both amalgamrestorations and acid-etched posterior compo-site resins on endodonticaliy treated teeth,Oliviera et al. (1987) showed that the compo-site enhanced the resistance to fracture. Whiledefinitive guide-lines for the effective use of allmaterials in the restoration of endodonticaliytreated teeth are unknown, it is commonlybelieved by all investigators that the greatestfactor influencing the strength of endodonti-caliy treated teeth is the amount of remainingtooth structure, and that all reasonable effortsshould be expended to preserve it.

Often, large three and four surface amalgamrestorations are made possible by the use ofpins, although pins do not strengthen the res-toration. If too many pins are used, or ifimproperly placed, they can cause crazing andmicrocracks in the tooth, thus contributing tofracture (Cameron 1976, Johnson et al. 1976,

Mazwell & Braly 1977, Rosen 1982). How-ever, pin-retained amalgam restorations havebeen recommended for incompletely frac-tured teeth to bind the segments and provideinternal stabilization (Clark & Caughman1984). Recently Stewart (1988) demonstratedthe use of reinforced glass ionomer cements tobind tooth segments together in the presenceof vertical fractures.

Cameron (1964, 1976) and Ritchey et al.(1957) noted that many cracked or fracturedteeth had inlays, particularly those made ofsoft gold. This restoration, by design, can actas a wedge during function thereby forcing thetooth apart (Fig. 8). The effect may be exacer-bated if the patient has occlusal disharmonieswhich are thought to predispose to fractures.

Many teeth are severely mutilated, requiringsome type of post along with coronal buildup.Posts used either alone or in combination witha core, may cause root fractures (Maxwell &Braly 1977, Meister et al. 1980, Pitts &Natkin 1983, Luebke 1984), therefore, properpost preparation, design, and insertion areneeded to protect against such accidents(Abou-Rass 1985).

There are two basic prefabricated postdesigns, tapered and parallel, and there aretwo design modifications, threaded andgrooved. While a detailed analysis of posts isoutside the scope of this paper, factors whiehhave a bearing on odontiatrogenic tooth frac-tures will be addressed. The use of posts andcores in the restoration of endodonticaliy

72 J. L. Schmeitzer,f. L. Gutmunn £5" R. Q. Bliss

treated teeth has been reviewed by Stokes(1987).

Overenlargement of the root canal mayweaken the root through loss of dentine (Learyet al. 1987, Stokes 1987) and may result inperforation or fracture (Johnson et al. 1976,Abou-Rass et al. 1982). A knowledge of rootcanal morphology, along with diagnosticradiographs, will help to prevent overenlarge-ment ofthe canal or improper post selection.

The insertion of a tapered prefabricatedpost or a custom cast post and core exertsminimal stress on the root walls as the hydros-tatic pressure of cementation is usuallyrelieved due to the design of the post. Pref-erence is often given to the prefabricated postbecause it is easier to use and the tooth can berebuilt and prepared in one appointment(Abou-Rass 1985). The cast post and core,however, possesses superior adaptation to thecanal walls and distributes stresses generatedduring function more evenly throughout theroot structure and supporting bone. Both sys-tems are, however, minimally retentive andcan exert a wedging effect on the root duringfunction.

The parallcl-sidcd post has more retentionand distributes forces better than the taperedpost(Standleet7rt/. 1972, Johnson f/«/. 1976).During post space preparation, perforation orfracture ofthe root is possible due to the post'sconfiguration and the apical tapering of theroot. With a radiograph, it is simple to com-pare two dimcnsionally the post configurationwith that of the root; root concavities in thethird dimension must also be considered.During cementation it is advisable to vent thepost to alleviate the hydrostatic pressureswhich can produce high apical stresses andultimate fracture. The apically tapered, paral-lel-sided post was introduced to prevent apicalperforations in roots which are narrow andthin in their middle and apical portions. How-ever, ("ooney et al. (1986) found that this postdesign produced a wedging stress at its apicalextent which was not found with the parallel-sided post.

Threaded posts exhibit the most retentionand exert the least apical stress on the rootwhen used correctly (Standlee et al. 1972,1978). However, the tapping or threadingrequired to prepare the root for their insertion

can lead to stress. Because ofthe high reportedincidence of root fractures with these type ofposts (Sorensen & Martinoff 1984, Stewart1988), care should be exercised in their use.

ConclusionsWithin the past 25 years it has become clini-cally accepted that cracked or fractured teethare common. Early reports identified factorsover which the dental practitioner had no con-trol. However, in this paper the authors haveattempted to identify practitioner generatedcauses which may contribute to fracturedteeth.

With a sizeable array of clinical tests avail-able, the practitioner should be able to diag-nose the presence of fractured teeth. Patientscomplaining of bizarre symptoms should bethoroughly evaluated for the presence offractures prior to referral to a specialist. Inaddition, the ability to diagnose the presenceor possibility of a fractured tooth during treat-ment planning will enhance the interceptionand correction of those clinical features whichhave contributed to the fracture.

Because there is an increased awareness ofperiodontal disease by the general population,larger numbers of patients are retaining theirteeth longer. With longer retention, moreendodontic treatment will be initiated. Thiscould lead to an increase in the number ofpathological fractures seen in dental practice.It behoves the practitioner to identify thoseclinical situations which predispose to thefracture of teeth. It is also necessary to exercisegood clinical judgement during treatment toavoid contributing to the fracture of teeth.This will often necessitate modification ofendodontic or restorative techniques. Mostodontiatrogenic tooth fractures can he prevented.

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