Restorative Dentistry

Diagnosis, therapy, and prevention of thecracked tooth syndrome

Werner Geurtsen, DDS, Dr Med Dent, PhDi/Thomas Schwarze, DDS, Dr Med Dent,Huesamettin Günay, DDS, Dr Med Dent,

Many morpholcgic, physical, and iatrcgenic factors, such as deep grooves, pronounced intraorai tempera-ture fluctuation, poor cavity preparation design, and wrong selection of restorative materials, may predis-pose posterior teeth to an incomplete fracture. The resulting cracked tooth syndrome is frequently associ-ated with bizarre symptoms that may complicate diagnosis and can persist for many years, Epidemiologiedata reveal that splits or fractures are the third most common cause of tooth ioss in industrialized coun-tries, primarily affecting maxillary molars and premolars and mandibular molars. This finding indicates thatthe cracked tooth syndrome is of high clinical impcrtance. Thus, at-risk teeth should be reinforced early, forinstance by castings with cusp coverage or by internai splinting with adhesive ceramic restorations,(Quintessence int 2003:34:409-417)

Key words: cracked tooth, diagnosis, etioicgy, prevention, therapy

Many innovative restorative techniques and mate-rials have been introduced into operative den-tistry during the past two decades, such as ultraconser-vative cavity preparation, modern dentin adhesives,hybrid-type resin composites, ceramic inserts, and in-lays. In addition, adhesive techniques, like the acid-etch technique and dentin bonding have been consid-erably improved. Altogether, it may be concluded thatthe spectrum of modern restorative therapy has beensignificantly extended.

On the other hand, however, these modern tech-niques require much more time to be done comparedto amalgam restorations, etc. Another problem thatalso arises is the increasing number of very large cavi-ties in posterior teeth that are adhesively restoredusing hybrid-type resin composites or compomers. But

'Professor and Director, Division ot Operative Dentistry, Department oíRestorative Dentistry. School of Dentistry, University of Washington,Seattle, Washington.

^Senior Lecturer, Department of Conservative Dentistry and Perio-dontology, Medical University Hannover, Hannover. Germany,

^Associate Protessor, Depaftrrent of Conservative Dentistry andPeriodontology, Medical University Hannover. Hannover, Germany.

Reprint requests: Dr Werner Geurtsen, Departmsnl ot RestorativeDentistry, Sohool of Oentistry, University ot Washington. Box 3574S6,Seattle, Washington 98195-7456. E-mail: wgert@j.washinglon.edij

it must be considered that these restorations oftencannot resist physiologic loads.''^ Thus, those over-loaded teeth frequently split.

Initially, the resulting cracks are incomplete and in-visible in most cases, which may make diagnosis verydifficuh. Sooner or later, however, the vast majority ofthese unidentified "grcenstick fractures" progress to-ward a complete crack, which could severely compli-cate a new restoration or even require the extractionof the tooth.

CLINICAL MANIFESTATION

The cracked tooth syndrome is defined as the incom-plete fracture of the natural crown of a premolar ormolar tooth.' Gibbs'* in 1954 was the first author to de-scribe an incomplete fracture in the dental literature,using the term cuspal fracture odontalgia. In 1957,Ritchey et aP reported various cases of incompletefracture with subsequent pulpitis. Finally, Cameron^created the common term cracked tooth syndrome in1964, Occasionally, greenstick fracture or split toothsyndrome are synonymously used by several authors.'^

Incomplete tooth cracks generally run in amesiodistal direction (Figs 1, 2c, and 3a).̂ Rarely hori-zontal, horizontal-vertical, or orovestibular cracksbave been observed (Figs 4 and 5), Incomplete cracks

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Fig 1 (ieft) Caries-free, unrestored maxiliary first premoiar aflerinitiai expiorative cavity preparation. A mesiodistai crack is cleariyvisibie. The patient reported the typicai reiief pain atter biting enhard cr tough substances.

Fig 2a (below) Nonvital mandibular second molar with localizeddeep periodcntal breakdown at the distal aspect indicating a spiitroot syndrome. The tooth was restored with a mesio-occiusai castgold iniay.

Fig 2b Radiograph o! Ill Fig 2c Occlusai view afler removai of the casting. The wide cav-ity significantly reduced the tracture resistance of the tooth. Thespiit extended to ihe root as weil as lo the puip with subsequentnecrosis.

are either limited to the crown or may also include theroot. CombineiJ fractures are called split root syn-drome {Figs 2 and 6 to 8),'" Initial cracks are usuallylimited to the coronal area of the crown without inclu-sion of the pulp (Figs 1 and 3a},"

EPIDEMIOLOGY

Most incompletely fractured teeth areHowever, the share of caries-tree and nonrestored teethis amazingly high (see Fig 1). Their percentage varies be-tween 13% and 35%.'''' In particular, mandibular molars

are affected (Table 1; Figs 2, 5, and 9), It is hypothesizedthat the maxillary molars are more resistant to partialcracks than mandibular molars due to their stabilizingocclusal oblique ridge. In addition, loading of mandibu-lar molars during mastication is higher than in maxillarymolars. Further, a potential "wedging effect" of theprominent mesiopalatal cusp of maxillary molars maypredispose the mandibular molars for incompletecracks.'' This was confirmed by a recent clinical study"in which the maxiliary molars and premolars andmandibular molars were much more frequently affectedby a cracked tooth syndrome than mandibular premo-lars (Table 1),

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Fig 4 Maxillary right first molar after removal of an extendedmesio-occlusopalatal gold inlay. The tooth reveals a horizontalsplit running in a mesiopalatal direction. Such a wide cavity gen-erally requires a splinting ol the tooth either by cusp coveragewiih a casting or by internal adhesive reinforcement by means ota ceramic restoration. The patieni suffered from a sharp and brietpain when eating hard or tough foods.

Fig 3a (left) This maxillary second premolar was originally re-stored with a cast ooolusodistal gold inlay. A split runs on the cav-ity floor in a mesiodistal direction. The pulp was not involved.

Fig 3b (below) Reinforcement of (he premolar using a partialcrown with cusp coverage and oircumlereniial reinlorcement.

Fig 5 Mandibular first molar of a 30-year-old témale patient suf-fering from bulimia with frequent vomiting. The gastric acideroded the enamel almost completely. The acidogenic loss ofenamel in combination with the occlusal amalgam restoration sig-nificantly reduced the fracture resistance of this molar A verticalsplit is clearly visible on the lingual aspect.

Various aiitfiors investigated a potential connec-tion between a patient's age and tfie prevalence ofincompletely fractured teeth. Contradictory datawere reported: Cameron* determined that predomi-nantly persons older than 50 years suffer from acracked tooth syndrome, whereas Hiatt» and Talimand Gohil'* reported the maximum number of splitteeth to be in patients between the ages of 40 and 49.On the contrary, Fitzpatriek'^ observed that incom-plete fractures primarily occurred in people betweenthe ages of 30 and 39, Tbese findings indicate thatmore and more younger patients are affected by acracked tooth syndrome.^

Additionally, Cameron'^ and Fitzpatrick'^ reportedthat female patients more frequently had incompletefractures. On the contrary. Dewberry'' found littledifference in sex distribution, with slightly morecracks occurring in male patients (52.3%). Recently,it was reported that 20% of tiie participants inthe Florida Dental Care Study who were examinedduring a 2-year period sustained a tooth fracture(Fig 2).'«

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Fig 6 Extracted rnaxillary molar revealing afiplit rooi syndrome

Fig 7a (top ieft) Cünicai view of a maxiiiaryfiisl premolar with a pronounced buccal ab-scess.

Fig 7b (top right) Radiologicaily, the pre-molar reveals signs ot an initiai circumferen-tiai periodontai breakdown which is rndioa-tive o( a spiit root syndrome.

Fig 7c (bottom ieft) First premoiar after ex-traction reveaiing a split root, very likely dueto an overzealous laterai condensation ofthe gutta peroha root oanai fiiiings.

Fig 7d (bottom right) Cross section in themiddle ot the root. The crack penetrates tineroot compiete I y

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Fig 6a Mandibular firsl premolar with gin-gival absoess ¡arrow} at the facial aspect

Fig 8b Radiographie view shows a severepeiiodontal breakdown due to a split rootsyndrome.

Fig 8c After extraction, a vertical spliL iSvisible extending to the apical atea oí theroot.

TABLE 1 Percentage of cracked teeth related to the various types ofposterior teetfi

Author N

Cameron' 50Cameron'^ 102Hiait" 100Taiim and Gohil" 40Dewberry'' 256Fit2patrick'= 242Vellmaaieial" 1141

MaxMolars

28

23.519

22,523,422,312,9

larv (%)Premolars

16

10

10

25

12,921,913.4

Mandibular (%)Molars

54

66.570

45

62.148,724.7

Premolars

2

—

1

7 5

1 67

5.3

Fig 9 Fracture of the distolmgLial ojsp of amandibular second molar, due to the ex-tended cavity preparation in oombinatlonwitin the lingual inclination ot the tooth.

ETIOLOGY

The most common cause for an incomplete fracture ismasticatory or accidental trauma,'-'^ For instance, un-intentional biting with physiologic masticatory force ona small and very hard object, such as a seed, may sud-denly generate an excessive load due to the very smallcontact area. As a consequence, the loaded tooth maysplit or fracture (see Fig 1),̂ °

A number of cofactors that decrease the stability ofa tooth may predispose it to a cracked tooth syn-drome, like a wide cavity preparation (Figs 2 to 4 and10),''-21 v̂ Tong cavity design (see Fig 9},22and nonre-

stored deep carious lesions,^^^ Further, endodonti-cally treated teeth show an increased rislc of fractures,predominately due to the unavoidable loss of hardtooth substance during preparation of the access cav-ity,̂ '' In addition, it must be considered that the highpressure applied during lateral condensation of guttapercha or the cementation of a tightly fitting post maycause incomplete vertical root cracks (Figs 7 andg) 35.2f. xhus^ it is not surprising that between 26''/o and72"/o of endodonticaily treated posterior teeth re-stored with mesio-occlusal, occlusodistal, or mesio-occlusodistal amalgam restorations cracked over a20-year-period,^'

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Fig 10 Fracture oí both buccal cusps ot a maxiilary iett tirstmolar with exposure of the puip space. The wide and deep cavitywitti subsequent amalgam restoration created susceplibiiity totracture

Various morpbologic cofactors are also associatedwith the emergence of a cracked tooth syndrome, likedeep occlusal grooves, pronounced vertical radiculargrooves, or a bifurcation. Thus, maxillary premolarsare significantly more susceptible to fracture thanmandibular premolars (see Fig 1), Additionally, an ex-tensive pulp space, a "steep cusp/deep groove" inler-relationship between the maxillary and mandibularpremolars, and the resulting wedging effect of theprominent facial cusps of tiiandibular premolars, con-tribute to the increased susceptibility to fracture ofmaxiiiary premolars (see Figs 1 and 3).'^-^^

The lingual inclination predisposes the oral cusps ofmandibular molars to cracks or fractures (see Fig 9),This hypothesis was confirmed by an epidemiologicstudy tbat found especially hngual cusps fractured inmandibular molars, with the first molar most likely tosuffer complete fracture of both lingual cusps.-^

Recently, various authors have speculated that pos-terior teeth with wide and deep cavity preparationscan be internally splinted using adhesive resin com-posite restorations. Experiments by the current au-thors, as well as studies from other scientists, resultedin very contradictory findings (Table 2),''^ Obviously,each cavity significantly reduces the fracture resis-tance. A subsequent filling increases stability again,very likely due to a better distribution of the loadingforces being effective on the restored tooth. But ifmust be considered that no restorative material, nei-ther amalgam nor conventional or polyacid-modifiedresin composites [compomers), can restore the origi-nal fracture resistance of an unrestored, caries-free

Recently, it was obsetred that one out of two

tested modern, hybrid-type resin composites applied incombination with the appropriate dentin adhesive in-creased fracture resistance of human molars to vaiuesthat were not significantly different from unrestoredcontrols. It may be speculated that tbese effects weredue to improved mechanical properties of this particu-lar product and an increased interfacial stiffness be-tween tbe various components,'*" Tbis hypothesis,however, needs to be verified by further studies, in-cluding a number of other new resin cotTiposites, be-fore adhesive restorations with modern resin compos-ites can be generally recommended for internalsplinting of at-risk posterior teeth.

Finally, it should be pointed out that an acidogenicextensive loss of enamel and dentin, for instancecaused by bulimia or anorexia nervosa, may also in-crease the risk of a fracture (see Fig 5),

There is evidence in the dental literature that nu-merous iatrogenic parameters may contribute to frac-tures, such as rotating instruments during cavitypreparation,•" the wedging effect of poorly fittingmetal inlays, the over-zealous (mechanical) condensa-tion of amalgam,'-'̂ excessive lateral condensation ofgutta percha during root canal filling (see Figs 7 and8), and the injudicious application or placement offriction-lock or self-threading pins,̂ '̂'̂ ''̂

Additionally, cyclic thermal stress with a clinicallyrelevant temperature fluctuation of 5O''C''-' or over-loading due to an occlusal trauma, parafunction, ormalposition also increase susceptibility to frac-ture,''̂ ''-^^ Altogetber, it may be concluded that mostfractures are very likely caused by a combination oíseveral factors.

Symptoms

The symptoms of an incomplete fracture mainly de-pend on the depth and location of the crack. Patientsfrequently feel a brief and sharp pain when eafinghard or tough food. Many authors consider this phe-nomenon a primary symptom (see Figs 1 and 4), '̂̂ Ithas heen speculated that this short and sharp pain isgenerated by an alternating stretching and compress-ing of the odontoblastic processes located in thecrack,'^ But it is also hypothesized that this typicalpain is created by the stretching of the fractured toothsegments with subsequent irritation of tbe pulp or theperiodontal ligament,'' Nearly every patient also com-plains about an increased sensitivity to thermal or os-motic stimuli,''̂ •''s

Since many fractures are not diagnosed in time,these bizarre symptoms may continue for many years.Finally, many undiagnosed fractures enter the pulpchamber, causing pulpal inflammation and necrosis(see Figs 2 and 10),'"

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TABLE 2 Fracture resistance of adhesively restored teeth

Tooth type

Occiusaldimensionol cavity*

Reste rationtype

Fractureresistance

Wendt et al™Oliueira et aP'

Ausiello et aFSteeie and Johnson^Stampalia et a l "Gelb et aFReel and MitcheiF

Geurtsen et aRoznowski et

Bremer and Geurtsen'

Maxiliary premolars'Manillary andmandibular premoiars'Maxiilary premolars"Maxiliary premoiars'Maxiilary premolarsMaxiliary premolarsMaxiliary premolars

PremolarsPremclarsMoiarsMoiars

1.5 mm Com ± DA2.0 mm Com + DA

2.0 mm Com + DACom - DA

1,4 mm Com ± DA1,0 mm Com

One haif inter- Com + DAcuspai distance

2.0 mm Com ± DA2 0 mm DCi ± DA

ca2 0mm Com2 0 mm Com ± DA

DCIICIiCel

One half inter- ICelcuspai distance DCel

Com #1 + DACom #2 + DA

jöhesive. DCi = direct resin compositeimic inlay; DCel = duect ceramic iniay;''rois. — = fracture resistance signili-

Fractures extending to the root generally causeperiodontal inflammation. Thus, a locahzed perio-dontal breakdown adjacent to a restored and particu-larly unrestored tooth frequently indicates a fracture(see Figs 2, 7, and 8),

Diagnosis

It may be difficult to diagnose a split tooth since thesymptoms associated with this syndrome are oftenbizarre and varying. Diagnosis is only simple whenthe crack is visible, for instance due to exogenicstaining from food or beverages. In most cases, how-ever, fractured teeth are restored with occlusal andproximal restorations. Thus, the most common mesi-odistal cracks are invisible (see Fig 2a), Furthermore,it must be considered that the majority of the initialclefts are so tiny that they cannot be seen with thenaked eye.""̂

Radiographie examination rarely improves the diag-nosis of a crack since it usually runs parallel to theplane of the film. But the radiologie findings of a local-ized periodontal breakdown in an otherwise perio-dontally healthy dentition may indicate a split tooth(see Figs 2, 7, and 8).̂ ^

Sharp pain on chewing of hard or tough food is veryimportant diagnostic evidence for a cracked tooth."t̂This type of pain predominantly is triggered as the pres-sure is released. In order to provoke this characteristicsharp and brief "relief pain and thus to verify a case ofcracked tooth syndrome, the patient should be asked tobite on a hard object, like an orange wood stick, andthen release the pressure quickly. Extensive restorationsshould be removed in order to determine the directionand extension of tbe crack. Various authors recom-mend staining the crack using méthylène blue. Staining,however, takes severa! days, and thus requires a tempo-rary restoration of the cavity. Alternatively, translUumi-nation is applied to visualize the crack.

The application of magnifying glasses (two-/four-fold)or an operating mieroscope is clinically more importantthan the two aforementioned time-consuming methods.Affected cusps can be determined by selective loadingfrom various aspects with an orange wood stick,'̂ '̂ ^

Therapy

Immediate therapy. The primary gual must be to splintand stabilize a cracked tooth immediately. This rein-forcement prevents a further extension or complete

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Fig 11a Right mandibular first molar after removal of an ex-tended amalgam lestoiation. Deep cavüy aieas were leveledusing calcium hydroxide and glass-ionomer cement.

Fig l i b Internal adhesive splinting of the molar by means of anadhesive ceramic onlay.

fracture of the tooth. Orthodontic steel bands are idealfor this purpose, whereas copper bands must be care-fully put into tiie necessary anatomic shape in order toavoid gingival or periodontai irritation. Diagnosis canbe verified directly after splinting since the diagnosticbite test wili no ionger provoiie the typical relief pain."

Some authors have suggested reducing or eiiminat-ing the occlusal contacts and thus avoiding an over-load of a spiit tooth. It must be considered, however,that the tooth may stiii be critically stressed by thefood bolus to such an extent that the risk of fracturepersists."''' This aiso applies for an internal temporarysplinting with adiiesive Class I or II resin compositefilling as previousiy mentioned (see Table 2).

Final therapy. Cast metal inlays with cusp coverageor partial crowns with circumferentiai externai splint-ing are applied when esthetics are of little significance(Fig 3). If esthetic appearance is of importance, adhe-sive ceramic restorations are the therapy of choice(see Table 2; Fig 11).''2

PREVENTION

Epidemiologic data clearly reveal that fewer teeth wiilbe extracted in the future due to caries or periodontaldiseases. However, epidemiologic findings alsodemonstrate that simultaneously more and more pa-tients will suffer from a split or fractured tooth.'̂ -^^There is evidence in the dental literature that fracturesare the third tnost common cause of tooth loss in in-dustrialized countries. "'̂ ^ Thus, it is of outstanding im-portance to avoid or eliminate risk factors, such asinjudicious wide and deep cavity preparations. Experi-mental studies indicate that the orovestibular dimen-sion of amalgam or resin composite restorationssiiould not exceed one fourth to one third of the inter-

ctispal distance. Cavity preparations wider than haif ofthis distance significantly increase the risk of splits oreraciis if the tooth is not sufticiently splinted by a rein-forcing casting or an adhesive ceramic restoration.'•''In addition, occlusal adjustment, ortbodontic treat-ment of malposed teetb, conservative cavity prepara-tion, and early restorative reinforcement of at-riskteetb are important measures for eliminating or mini-mizing the occurrence of the cracked tooth syndrome.

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