Root Fusion in Molars: Incidence and Sex LinkageIra Franklin Ross, and Patricia A. Evanchik

The study was done to determine the incidence and distribution of root fusion in 1340maxillary and mandibular molars in 170 patients. A second objective was to determine whetherroot fusion of molars is sex-linked. A substantial percentage, 29% of all molars, had fusedroots. Root fusion was found more frequently in maxillary than mandibular molars, 35% to24%, and it occurred in many patients, rather than being limited to a few. Root fusion wasmost common in third molars, followed by second molars, in both jaws. It occurred in almostequal numbers in corresponding molars of opposite sides, approaching bilateral symmetry.The proportion of molars with root fusion was approximately 5% greater in females than inmales, and about 13% more females had molar root fusion than males.

Several recent studies have dealt with furcal involve-ment (f.i.) of molars.1"9 One of these studies, our firstreport, described retention of maxillary molars with f.i.for 5 to 25 years, with all roots intact.6 A second studydealt with the diagnosis and incidence of f.i. amongmaxillary and mandibular molars. That study was lim-ited to patients who had at least three maxillary andthree mandibular molars and had received periodontaltherapy at least 1 year before the study began.7

After starting a new series of studies to investigateadditional aspects of f.i., we found that many patientshad molars with fused roots. Inasmuch as molars withfused roots cannot develop f.i., it became obvious thatour first priority should be to determine how manymolars were capable of developing f.i. Therefore a studywas done to determine the incidence and distribution ofmolars with fused and nonfused roots in the maxilla andmandible. In addition, data were compiled to determinewhether there was a relation between the sex of individ-uals and root fusion of their molars.

METHOD OF INVESTIGATION

Subjects of the study were the first 170 patients, withat least one maxillary and one mandibular molar, ex-

amined in the office of a periodontist (I.F.R.). Of thattotal, 99 (58%) were females and 71 (42%) males. Theirages ranged from 23 to 73, with 94% (106 patients) over

34 and 49% (83 patients) over 54. All patients had chronicdestructive periodontal disease. Some had been seen fordiagnosis only, some were receiving periodontal therapy,and the remainder were receiving periodontal mainte-nance therapy, having had active periodontal therapy atan earlier time.

The determination as to whether molar roots werefused was based on radiographie examination: 14 peri-apical and four bitewing radiographs. All patients and

radiographs were examined by the same periodontist(I.F.R.).

The following criteria were used to differentiate be-tween molars with fused roots and those with nonfusedroots. Any molar that had one root or whose roots werefused apical to the usual furcal position was considereda molar with fused roots (Figs. 1, 2). This includedmolars with fusion of one-third or less of the roots andmolars with fusion of entire root surfaces. A tooth wasconsidered fused regardless of location of the fusion.Fusion could occur in the apical one-third, middle one-third, or cervical one-third of the roots or in any com-bination of two or more of these areas. In some cases,molars had roots fused only in the apical one-third andhad a normal furcation with alveolar bone and otherperiodontal structures present. These teeth were includedin the category of fused teeth to avoid misunderstandingand inconsistency.

RESULTSA total of 1340 molars in 170 patients were studied,

including 657 (49%) maxillary molars and 683 (51%)mandibular molars (Table 1). The average number ofmaxillary molars per patient was 3.9 while the averagenumber of mandibular molars per patient was 4.0.

Incidence of Root Fusion of MolarsRoot fusion of molars was far more common than had

been expected. Of all molars in the study, 29% (395 of1340) had fused roots (Table 1). The average number ofmolars with fused roots was 2.3 per patient, compared to5.6 molars with nonfused roots per patient, a ratio ofapproximately 1 (fused):2.4(nonfused).Incidence of Root Fusion of Maxillary andMandibular Molars

Roots of maxillary molars were fused more frequently663

664 Ross, EvanchikJ. Periodontol.

November, 1981

Figure 1. Maxillary second molar with a conicalfused root. This type ofroot predisposes to mobility of the tooth because it provides poor anchor-age. Adjacent first molar has a nonfused root.

Figure 2. Mandibular second molar with afused root. Note wellformedmesial and distal canals in one root.

Table 1Number ofMolars with Fused or Nonfused Roots

Maxillary Mandibular TotalFused 233 (35%) 162 (24%) 395 (29%)Nonfused 424 (65%) 521 (76%) 945 (71%)Total 657 100% 683 100% 1340 100%

than those of mandibular molars; with 35% of all max-

illary molars displaying root fusion, compared to 24% ofmandibular molars (Table 1).

When root fusion was present, it was far more commonfor an individual to have a mixture of fused and nonfusedroots than to have all roots of all molars fused. Only fivepatients had the roots of all maxillary and mandibularmolars fused. Six had all maxillary molars with fusedroots, but among the opposing mandibular molars therewere some with fused and some with nonfused roots.

Only three patients had all mandibular molars with fusedroots opposed by maxillary molars, some with fused andsome with nonfused roots.

Distribution of Maxillary and Mandibular Molars WithFused and Nonfused Roots

It had been expected that the great majority of patientswould have maxillary and mandibular molars with non-

fused roots, and this assumption proved to be correct.However, we were surprised to learn that so many pa-tients had one or more molars with fused roots. Rootfusion was so common that 70% of the patients had oneor more maxillary molars with fused roots and 54% hadone or more mandibular molars with fused roots (Table2). At the same time, 93.5% of the patients had one ormore maxillary molars with nonfused roots and 95% hadone or more mandibular molars with nonfused roots(Table 3).

Fusion of Roots of Specific Molars

Of all maxillary molars, root fusion occurred mostfrequently in third molars, followed by second molars.Fusion occurred in only 7.7% of the roots of maxillaryfirst molars (23 of 299 maxillary first molars) (Table 4A).Likewise, among all mandibular molars, root fusionoccurred most frequently in third molars followed bysecond molars. Fusion occurred in only 3.3% of mandib-ular first molars (9 of 273 mandibular first molars) (Table4B). In evaluating these results it should be recognized

Table 2Distribution ofPatients According to Number ofMolars with FusedRoots per Arch

No. of patientsNo. of molars-Maxillary molars Mandibular molars

None 51(30%) 78 (46%)1 43 (25% 42 (25%)2 49 (29%) 34 (20%)3 16 (9.5%) 12 (7%)4 11 (6.5%) 4 (2%)

170 100% 170 100%

Table 3Distribution ofPatients According to Number ofMolars with NonfusedRoots per Arch

No. of PatientsNo. of molars-Maxillary molars Mandibular molars

None 11(6.5%) 8(5%)1 24(14%) 19(11%)2 56 (33%) 28 (16%)3 34 (20%) 37 (22%)4 39 (23%) 59 (35%)5 6 (3.5%) 15 (9%)6 0 (0%) 4 (2%)

170 100% 170 100%

Volume 52Number 11 Root Fusion in Molars 665

that there were many fewer third molars (9.3% maxillarythird molars and 15.4% mandibular third molars) thanfirst or second molars in this study, which was carriedout in a predominantly middle and older age population(Table 4).

Symmetry of Root Fusion in MolarsRoot fusion occurred in an almost bilateral symmet-

rical pattern in both maxillary and mandibular molars(Tables 5A and B). Fusion occurred in the roots of 50%of the maxillary right second molars and 55.8% in themaxillary left second molars. In addition, fusion occurredin 35% of the roots of the mandibular right second molarsand 29% of the mandibular left second molars.

Relation Between the Sex of Individuals and Fusionor Nonfusion of Their Molar Roots

Two evaluations were made in this section of thestudy: the number of molars with fused or nonfusedroots in males and females, and the number of males andfemales with fused and/or nonfused molar roots. Thelatter evaluation, number of patients, was done to deter-mine whether fusion was an isolated occurrence orwhether it was present in many individuals of one or

both sexes.A comparison of the data for all molars, molars with

fused roots and those with nonfused roots is containedin Tables 6 and 7. Among the totals of 580 molars inmales and 760 molars in females, root fusion was ap-

Table 4Number and Percent ofMolars With Root Fusion or NonfusionA. Maxillary Molars

Total FusedTooth

No. Percent No. Percent

Nonfused

No. Percent3rd Molars2nd Molars1st MolarsTotals

61297299657

9.345.245.5

100

5315723

233

86.952.9

7.7140276424

13.147.192.3

B. Mandibular MolarsTotal Fused

ToothNo. Percent No. Percent

Nonfused

No. Percent

3rd Molars2nd Molars1st MolarsTotals

105305273683

15.444.739.9

100

5598

9

162

52.432.1

3.3

50207264521

47.667.996.7

Table 5Root Fusion and Nonfusion of Specific MolarsA. Maxillary Molars

Tooth TotalFused

No. Percent

Nonfused

No. Percent

Right 3rd molarRight 2nd molarRight 1st molarLeft 1st molarLeft 2nd molarLeft 3rd molarTotals

3115214915014530

657

267612118127

233

83.950.0

8.07.4

55.890.0

576

13713964

3424

16.150.092.092.644.210.0

B. Mandibular Molars

Tooth TotalFused

No. Percent

Nonfused

No. PercentLeft 3rd molarLeft 2nd molarLeft 1st molarRight 1st molarRight 2nd molarRight 3rd molarTotals

5015413314015155

683

2645

54

5329

162

52.029.0

3.82.9

35.052.7

241091281369826

521

48.071.096.297.165.047.3

666 Ross, Evanchik J. Periodontol.November, 1981

Table 6Number of Molars With Fused or Nonfused Roots in Males and Females

Molars (Males) Molars (Females)No. Percent No. Percent

Difference

Maxillary fused 84 14.5 149 19.6 +5.1% (female)Mandibular fused 53 9.1 109 14.4 +5.3% (female)Maxillary nonfused 201 34.7 223 29.3 +5.4% (male)Mandibular nonfused 242 41.7 279 36.7 +5.0% (male)Totals 580 100 760 100

Table 7Number ofMale and Female Patients With Fused or Nonfused Molar RootsTotal Males = 71, Total Females = 99

Males Females

No. Percent No. PercentDifference

Maxillary fused 42 59.2 77 77.8 +18.6% (female)Mandibular fused 35 49.3 57 57.6 +8.3% (female)Maxillary nonfused 68 95.8 91 92.0 +3.8% (male)Mandibular nonfused 69 97.2 93 94.0 +3.2% (male)Totals 214 318

proximately 5% more common in the molars of femalesthan males (Table 6).

Root fusion of molars also occurred in more individualfemales than males, with 18.6% more females havingmaxillary molars with fused roots and 8.3% more femaleshaving mandibular molars with fused roots. Figures forthe molars with nonfused roots show that 3.8% more

males had nonfused maxillary molar roots and 3.2%more males had nonfused mandibular molar roots (Table7).

DISCUSSIONThe number, length, shape, and spread of molar roots

affect their anchorage in the maxilla and mandible to a

significant degree10,11 and are important factors in deter-mining prognosis of a tooth. One important aspect ofroot morphology is root fusion. Fused roots are fre-quently shorter than nonfused roots and therefore con-

tribute to an unfavorable crown-root ratio. As a result,molars with fused roots are more likely to become mobilewhen they are subjected to heavy occlusal forces.

This study indicates that fusion of molar roots isrelatively common. Therefore, because root fusion can

affect anchorage and stability of a tooth, it may be a

significant factor in the outcome of treatment and thelength of functional survival of many molars.

Several intriguing questions arise from this study. Aremolars with fused roots more susceptible to periodontalpocket formation than molars with nonfused roots? Aremolars with fused roots less likely to survive than molarswith nonfused roots? Is molar root formation influencedby the sex of the individual? Are women more susceptible

to loss of molars than men? If so, is root fusion of molarsa significant reason for this? How does survival rate ofmolars with fused roots compare with survival rate ofmolars with furcal involvement?

All patients in this study were of European ancestry,and 94% (160) were over 34 years of age. Some patientshad had molars extracted earlier in their lives. A sam-

pling of younger individuals might include a larger num-

ber of molars, particularly third molars, and this sam-

pling might provide data different from those presentedhere. In addition, data from other ethnic groups mightdiffer from these findings.

Another important consideration is that all molarswith fused roots were grouped in this study withoutregard to the degree or location of the fusion. Futurestudies may show that different degrees or location offusion have different effects on anchorage and/or sur-vival of molars.

ACKNOWLEDGMENTThe authors gratefully acknowledge the contribution of Dr. Robert

H. Thompson Jr. who assisted in the preparation of the article.

REFERENCES1. Hamp, S. E., Nyman, S., and Lindhe, J.: Periodontal treatment

of multirooted teeth. Results after 5 years. J Clin Periodont 2: 126,1975.

2. Klavan, .: Clinical observations following root amputation inmaxillary molar teeth. J Periodontol 46: 1, 1975.

3. Gerstein, . .: The role of vital root resection in periodontics.J Periodontol 48: 478, 1977.

4. Gutman, J. L.: Prevalence, location and patency of accessorycanals in the furcation region of permanent molars. J Periodontol 49:21, 1978.

5. Hirschfeld, L., and Wasserman, B.: A long-term survey of toothloss in 600 treated periodontal patients. J Periodontol 49: 225, 1978.

Volume 52Number 11 Root Fusion in Molars 667

6. Ross, I. F., and Thompson, R. H. Jr.: A long term study of rootretention in the treatment of maxillary molars with furcation involve-ment. J Periodontol 49: 238, 1978.

7. Ross, I. F., and Thompson, R. H. Jr.: Furcation involvement inmaxillary and mandibular molars. J Periodontol 51: 450, 1980.

8. Bower, R. C: Furcation morphology relative to periodontaltreatment. Furcation entrance architecture. J Periodontol 50: 23, 1979.

9. Bower, R. C: Furcation morphology relative to periodontaltreatment. Furcation root surface anatomy. J Periodontol 50: 366, 1979.

10. Ross, I. F.: The functional environment and periodontal disease.NJ State Dent Soc Bull V32: 3, pp 12-18, Nov., 1960.

11. Ross, I. F.: The functional environment of the teeth. J Am DentAssoc 63: 61$, 1961.

Send reprint requests to: Dr. Ira Franklin Ross, Medical Arts Bldg,116 Millburn Ave, Millburn, NJ 07041.

AnnouncementsTHE AMERICAN ACADEMY OF ORAL MEDICINE

The American Academy of Oral Medicine announces its 35th Mid-Annual Meeting December 3-6, 1981 at Cherry Hill, NJ. The programincludes: Non-Steroidal Antiinflammatory Analgesics; Forensic Odon-tology; Occlusion; Orofacial Pain; Lichen Planus and Its MalignantTransformations; Immunologie and Inflammatory Mechanisms inPeriodontal Disease; Microbiology of Periodontal Disease; Nutritionand a Clinical Pathology Conference.

For further information contact: Mrs. Joyce Guithues, 829 Hana-moor Court, St. Louis, MO 63122.

PAPERS INVITED FOR THE SIXTH INTERNATIONALCONGRESS OF DENTISTRY FOR THE HANDICAPPED 1982

The Sixth Congress of the International Association of Dentistryfor the Handicapped will take place in Toronto, Canada at the HarbourCastle Hilton Hotel, from July 20-25, 1982. The general program willinclude Scientific Sessions in: Basic Science; Research; Growth andDevelopment; Clinical Dentistry and Psychology. The Congress alsofeatures audiovisual capability, posters, exhibits, abstracts and a fullsocial program.

Papers and other material related to Dentistry for the Handicapped(including Cleft Palate) should be submitted to: Programme Chairman,Sixth Congress I.A.D.H. Department of Paedodontics, Faculty ofDentistry, University of Toronto, 124 Edward St., Toronto, OntarioCANADA M5G 1G6.

INTERNATIONAL CONFERENCE ON PERIODONTALRESEARCH

The Fifth International Conference on Periodontal Research willbe held in Seattle, July 24 through 28, 1982. The conference will centeraround the methodologies for clinical assessment, microbiology, andthe role of host factors in the etiology, pathogenesis, diagnosis andmanagement of the periodontal diseases. Speakers will be selected bythe Organizing Committee on the basis of submitted abstracts.

The conference is sponsored by the Periodontal Research Group ofthe I.A.D.R. and is supported by the Procter and Gamble Company.The objective of the meeting is to bring together active researchers inthe field of periodontology for the purpose of discussing currentobservations and future directions. All reports and summary discus-sions will be published in the Journal of Periodontal Research. Attend-ance will be limited to approximately 125 participants and is open tomembers of the Periodontal Research Group of the I.A.D.R. andothers who have an active interest in periodontal research and who are

expected to contribute to the discussions. Participants other than invitedspeakers will be accepted on a first come, first serve basis.

Registration forms may be obtained from and returned to Dr. RoyC. Page, Director, Center for Research in Oral Biology, SM-42, Uni-versity of Washington, Seattle, WA 98195 U.S.A. before March 1,1982. Registration will be confirmed approximately April 15, 1982,and each participant will receive the detailed program and informationon accomodations and prepayment. Participants will have an oppor-tunity to attend the German Cycle of Richard Wagner's Ring of theNibelung during the meeting.