J. Pertodonmt Ra. 13: 563-572, 1978

The natural history of periodontaldisease in man

Tooth mortality rates before 40 years of age

HARALD LOE, AGE ANERUD, HANS BOYSEN AND MARTYN SMITH

School of Dental Medicine, University of Connecticut, Farmington, Connecticut, U.S.A.

The material presented in. this report was derived from a longitudinal study of the devel-opment and progress of periodontal disease and resultant tooth loss. The first populationgroup was established in Oslo, Norway in 1969 and consisted of 565 male, non-dentalstudents and academicians between 17 and 30-1- years. A second group was established inSri Lanka in 1970 and consisted of 480 male tea laborers between 15 and 30+ years. Bothpopulations were examined 4 times and the time span between the first and fourth exam-inations was in Oslo 6 years and 3 months, in Sri Lanka 7 years and 6 months. Eachparticipant was scored for various disease parameters and the number of permanent teeth(third molars excluded) was recorded at each examination. The results show that in theserandomly sampled groups no one was edentulous. The 17 year old Norwegian had 27.4teeth present out of 28 possible and no major loss of teeth occurred during the twentiesand thirties. As the participants approached 40 years of age, the mean number of teethpresent was 27.1 and the mean mortality rate was 0.01 teeth per year. The Sri Lankan 15year old had 27 teeth present and the 40 year old had 25.6 teeth. The mean mortalityrate ranged between 0.1 and 0.3 teeth per year. Teeth with deep periodontal lesions startedto exfoliate in Sri Lankans as they approached 40 years of age,

(Accepted for publication April 13, 1978}

in the same individuals over a lifetime orIntroduction ^^^-^^^ ^^^^^ portions of man's life are

it is generally accepted that the number of non-existent.teeth decreases with age and that caries and This paper, which reports on tooth mor-periodontal disease are the main causes of tality during the first forty years of life, istooth loss, although the relative impact of based on material from a longitudinal in-these two disease entities may vary in dif- vestigation, the purpose of which was toferent population groups and geographic describe the natural development and pro-areas. Most of our knowledge of tooth gress of periodontal disease in man and themortality stems from cross-sectional studies resultant tooth loss. The two populationof populations of different age and socio- groups involved in tbe study were chosen ineconomic circumstances, and longitudinal anticipation of big differences in the rate ofstudies in which tooth loss can be assessed periodontal destruction and in loss of teeth

564 L D E , A N E R U D , B O Y S E N A N D S M I T H

due to periodontal disease. Published re- clinically fair. The workers had never beenports on baseline data (Loe, Anerud, Boysen exposed to any programs or incidents rela-& Smith 1978a) and on the rate of perio- tive to prevention or treatment of dentaldontal destruction (Loe. Anerud, Boysen & diseases. Toothbmshing was unknown. BetelSmith 1978b) have substantiated this notion. chewing was common.

The Norwegian group was first examinedin 1969. Subsequent examinations took

Materials and Methods p,^^^ -^ j ^ ^ ^ ^ -,9^3 ^^^ .^ ^^^5 ^^^ ^^.The first group was established in Oslo, Lankan group was examined initially inNorway in 1969 and consisted of 565 1970, in 1971, 1973 and in 1977. The timehealthy male students and academicians be- span between the first and fourth exam-tween 17 and 30-|- years of age. The older inations was, in Oslo 6 years and 3 months,age groups were drawn at random from the and in Sri Lanka 7 years and 6 months.census filed with the Central Bureau of Sta- At each appointment the participants an-tistics and the younger age groups were re- swered questions regarding personal dentalcruited from three high schools in Oslo se- eare and habits. Clinical examinations in-lected by the City Board of Education. The eluded inspection of the orai cavity at largeprincipal reason for doing the study in Oslo as well as measurements and scoring of in-was that this city has had a dentai program dices relative to the periodontal status (Loeoffering systematic preventative, restorative, et al. 1978a). All examinations throughoutendodontic, orthodontic and surgical thera- the study were performed by the same twopy on an annual recall basis for ali children examiners who were both well-trained andand adolescents (3-16 years) and a docu- experienced periodontists. The number ofmented attendance record of 90 per cent teeth present, excluding third molars, wasfor the last 40 years. It is also a matter of recorded by the same investigator at all ex-record that the remaining 10 per cent make aminations. All scores were dictated to theuse of the personal dental services provided ehairside assistant who recorded the scoresby the private practitioners in the area. In on a special scoring chart. The examinationsaddition, the City of Oslo offers a reim- of the Norwegians took place at a facilitybursement pian for expenses incurred for provided by the Oslo University Faculty ofdental services between 18 and 21 years of Dentistry equipped with modern dentalage and the University, through its health chairs, scialitic lamps, compressed air andservices, provides a dental program for saiiva ejectors. The plantation groups in Sristudents. It is, therefore, fair to state that Lanka were examined in an outdoor facilitythe chosen population represents a group of comprising portabie dental chairs and sup-individuals that has had maximum exposure porting equipment, but no compressed airto conventional dentai care throughout its or saiiva ejectors. No preventive or thera-iife. peutic measures were undertaken during the

A second group was established in Sri examinations.Lanka in 1970 and consisted of 480 maie The data from each examination weretea iaborers between 15 and 30-1- years of computerized and updated on an ongoingage. The participants were all tamils and basis and are being subjected to detaileddescendants of groups who 2-3 generations analysis. Each population was divided intoago emigrated from Southern India. They two-year age cohorts to facilitate the analy-were healthy and well-built by local stan- sis. A certain number of individuals drop-dards and their nutritional condition was ped out and eould not be followed up.

T H E N A T U R A L H I S T O R Y O F P E R I O D O N T A L D I S E A S E 565

Table 1Cumulative number of observations in each

age category for all participants and for thosewho appeared in all four surveys

(in parenthesis)

Age

15-1617-1819 2021-2223-2425-2627-2829-3031-3233-3435-3637+

1969-1975

and academicians

81127150216232232174147753314

(21)(34)(60)(97)

(102)(111)(98)(70)(44)(22)( 9)

1970-1977

tea laborers

7712716219620319917014585571919

(34)(58)(72)(95)(96)

(104)(91)(85)(59)(38)(18)(16)

However, in both populations the Ioss tofollow-up individijals appeared to be inde-pendent of age (Loe et al. 1978a). In theanalysis, the most interesting groups werethose who were present in all surveys(IAS). Analyses were also perfortned on allvalid observation groups (AVO). The IASgroup was compared to the total AVOgroup to determine if those lost to follow-up were significantly different from thosethat remained in the study. Tbe cumulativetooth mortality rate was calculated on thebasis of all individuals who appeared atboth the first and fourth surveys. When in-significant changes in the estimates of theparameters occurred over time, the birthcohorts were collapsed into age cohorts togive a picture of eaeh population over 25

years (Table ]). For further details on thedesign of the study and the baseline data,see Loe et al. 1978a.

Results

The 565 Norwegians who participated inthe first examination in 1969 showed a totalof 441 missing teeth, excluding third molars(Table 2). None of the participants wereedentulous. The average number of leethstanding per person was 27.22 (range 26.9-27.5) (Table 3) or an average of 0.78 mis-sing teeth per person. There were more mis-sing bicuspids than all other teeth put to-gether (Table 2). In 1969 the 17 year oldsaveraged 27.4 teeth present and the 30-1-year olds had 27.2, indicating that in thispopulation there had been no significanttooth loss in 15 years of adult life (Table3). It is also seen that those who were 17,19, 21 etc. in 1969 and appeared at some(Table 3) or all reexaminations (Table 4)continued to have the same number of teethpresent and that no major loss of teeth hadoccurred between 30 and 40 years in thispopulation. The 245 participants of all agegroups who participated in the first (1969)and the last (1975) examinations had lost atotal of 27 teeth (17 molars and 10 bicus-pids. Table 5), averaging 0.11 tooth per in-dividual over the six year period (Table 6).Actually, the vast majority of the partici-pants (229 out of 245) had lost no teeth atall, and only 16 individuals accounted forthe 27 teeth lost (Table 7).

Thirty-one of the students who were 17

Table 2Number and types of teeth missing in both study populations at baseline in 1969 and 1970

Populatio

NorwegiaiSri Lankai

ns

n students aind a'cademician

individuals

s 565480

Numberteeth lost

441415

MolMax

5959

Mand

86212

BiciMax

15B39

ispidsMand

51

Max

2728

Mand

1326

566 L O E . A N E R U D . B O Y S E N A N D S M I T H

Table 3Average number of teeth present in Norwegian students and aoademicians that participated in

ali vaiid observation groups. 1969-1975Yearsof age

1969

1970

1971

1973

1975

Cross-nctionaMeans

17 18

27,41

\

27.4181

19 20

26.90

27,45

\

27-17127

21 22

27,28

26.91

27.33

\

27.17150

23 24

27,50

27.43

27.09

27.42

27.63216

25 26

27.29

27.58

27.20

26.60

27,16232

27 28

27-13

27.35

27-61

27,32

27,37232

29 30

26.95

27,13

27.28

27.59

27.27174

31 32

27,17

27.18

26,89

27,52

27.29147

33 34

\

26.83

27.19

26.78

26.9375

35 36

\

27.42

27.22

27.3233

37 38

\

26.86

26.8614

Average number of teeth present in Norwegian students and academicians that participated inall four surveys. 1969-1975

Yearsof age

1969

1970

1971

1973

1975

Cross-sectionalMeans

17 1B

27.38

21

\

\

27.38

21

19 20

26.92

13

27.38

21

\

\

27,20

34

21 22

27.50

26

27-00

13

27,24

21

\

\

60

23 24

27,68

37

27.54

26

26,85

13

27.24

21

97

25 26

26.46

26

27.68

37

27.50

26

26.92

13

102

27 28

26.00

22

27,46

26

27,62

37

27.58

26

111

29 30

27.23

13

26.77

22

27.35

26

27.68

37

98

31 32

26.78

9

27-38

13

26.64

22

27.38

26

27.07

70

33 34

\

\

26.78

9

27.38

13

26.64

22

26,89

44

35 36

\

\

26.78

9

27.31

13

27.09

22

37 38

\

\

27.11

9

27.11

9

The number and types of teeth lost in Norway during 1969-1975 and in Sri Lanka during 1970-1977 for those participating in the first and fourth survey

Populations

Norwegian students sSri Lankan tea labore

ind academiciansrs

Numberindividuals

245228

Numberteeth lost

27169

Molars

17121

1016 32

T H E N A T U R A L H I S T O R Y O F P E R I O D O N T A L D I S E A S E 567

Table 6Number of teeth lost and tooth mortaiity rates

by birth cohorts for 245 Norwegian studentsand academicians. 1969-1975

Birth- Number o. ",""'1'" ' Six y.a,;.,H;..;^...,I., ' " ^ ' t6in ,..,1;.... ._

Table 7Frequency distribution of teeth lost in 245

Norwegian students and academicians in sixyears. 1969-1975

teeth lost individuals

1934-39T94O

194619481950

years old in 1969 (born in 1952) and re-ported back six years later had lost a totalof 3 teeth or an average of 0.09 tooth perperson over the six year period and 20 whowere 19 years old in 1969 (born in 1950)had lost no teeth in the six years (Table 6).None of the teeth lost between the age of

17 to 37-i- were extracted or lost due toperiodontal disease.

The 480 Sri Lankan tea laborers showeda total ot" 415 missing teeth at the first ex-amination in 1970 (Table 2). The averagenumber of teeth present (Table 8) per indi-vidual was 27.05 (range 27.7-25.8) or anaverage of 0.95 missing teeth per person.There were considerably more missing mo-lars, especially mandibular molars, thanother types of teelh (Table 2). The 15 year

Average number of teeth present in Sri Lankan tea laborers that participated in all validobservation groups. 1970-1977

Yeanof ge

1970

1971

1973

1977

Cron.tectionsMeans

14 15

27.00

40

16 17

27.70

47

27.65

34

27.50

77.5

18 19

27.67

69

27,47

40

29

27.54

127

20 21

27.34

62

27.43

63

3d

27.44

162.5

22 23

27.16

77

27.22

54

54

26.63

19

27.14

196.5

24

26

26.97

65

51

26.91

22

27.00

203.5

25

54

26 27

27.31

61

26.55

5T

26.74

68

26.88

33

26.80

199.5

2B

25

27.06

52

26.09

43

27.00

27

26.72

170.5

29

81

36

30 31

26.71

34

26.78

32

26.70

46

26.66

32

26.38

145

32

26.39

31

24.44

27

25.93

27

25.62

85

33 34

26.11

27

26.60

30

26.37

57

35 36

24.63

19

24.63

19

37 38

25.63

19

26.63

19

L O E , A N E R U D , B O Y S E N A N D S M I T H

Average number of teeth present in Sri Lankan tea laborers that partioipated in ail four surveys.1970-1977

Yeanof age

1970

1971

1973

1977

Cross-sect ionaMeant

14 15

27-00

17

16 17

27.78

27.47

17

34.5

18

18

27

27-50

18

27.24

17

58

19

75

28

20 21

27-33

27.50

26

27.44

18

72

24

22 23

27.14

27.25

24

27.29

28

26.65

17

95

28

24

26

27.00

28

27.12

24

27.22

18

96 5

25

60

25

26 27

27.18

26.52

25

26.86

28

26 71

28

104.5

22

28 29

26.00

27,00

22

26.08

25

27.08

24

91

18

30 31

26.87

25.89

18

26.91

22

26.68

28

85

16

32

26.81

16

25.56

18

26.08

25

59

33 34

26.50

16

27.09

22

38

35 36

24.89

18

18

37 38

26.12

16

16

olds had an average of 27.0 teetb and the30+ year olds had 26.7 (Table 8).

The cross-sectional means for the cumu-lative observations of the different agegroups showed that there was a decrease inthe number of teeth per individual fromthe age of 15 (27.5) to 30+ (25.6) of ap-

proximately 2 teeth (Tables 8). When onlythose who participated in ali four surveyswere considered (Table 9), It is seen that asimilar decrease has taken place.

An examination of the 228 individualswho participated in the first and last exam-inations (Table 5) showed that they had losta total of 169 teeth (121 molars, 16 bicus-

Number of teeth and tooth mortality rates bybirth cohorts for 228 Sri Lankan tea laborers.

1970-1977

Bir th-year

Nuind

mbEivid

irofuals

Nur

in se'

nbe SGvemorta

n yeahty rate

19421944

1.321.05

Frequency distribution of teeth lost in 228 SriLankan tea laborers in seven years. 1970-1977

Number ot .,^^ , ,. , Number ofteeth lost (169 teeth) individuals

1950' 1952

1954

T H E N A T U R A L H I S T O R Y O F P E R i O D O N T A L D I S E A S E

pids, 32 anteriors) averaging 0.72 over theseven years (Table 10). As can be seen fromTable 11, 77 individuals accounted for theloss of these 169 teeth and 151 had !ostnone.

Out of the 196 individuals who partici-pated in all surveys 7 showed 10 teeth v/Uhloss of attachment equal to or greater than10 mm in 1970. In the course of the subse-quent seven years, 6 of these teeth werelost. This gives a mortality rate of 0.6 ascompared with over 5,000 teeth which werescored with less than 10 mm and out ofwhich 141 teeth were lost over the s&meperiod, or a mortality rate oi 0.03. This willbe explored further in subsequent reports.

Discussion

AH eross-seetional studies of tooth mortahtydemonstrate that with increasing age thereis a decrease in rhe number of leelh preseni(Brekhus 1929, Klein 1943, Belting, Massler& Schour 1953, Krogh 1958, Sandier &Stahl 1960, Johnson, Kelly & Van KirkI9f>5. KoUchke 1%5, Bay & Oati A%7.Ltindquist 1967, Sheiham, hiobdeU & Cowell1969, Johansen 1970, Grey et a). 1970,Jackson & Murray 1972, Axelson et al.1975, Edmuttds &. Crahb 1975). 0T^ thebasis of these reports it appears that ingeneral the 20 year old western patient haslost between 3 and 5 teeth; 30 year oldshave on an average lost between 5 and 7teeth, and at 40 years of age the averagepatient has lost approximately 10 teeth. It isalso apparent from this literature that atapproximately 40 years of age some S to 1 flper cent of the teetb have been losf due toperiodontal disease. At or before 30 yearsless ihan 1 per cent of moat western popula-tions are edentulous (Johnson et al. 1^65,Grey et al. 1970, Axelson et al. J975, Roder1975). However, after this age, althoughvarying greatly for specific populations, thefrequency of edentulousness increases sig-

nificantly. and at 40 years of age generallyranges between 10 and 30 per cent.

In the present study populations, both ofwhich were chosen at random, no one par-ticipant in Norway nor in Sri JLanfca w^ asedentulous at the first examination in 1969^70 and none were seen 6-7 years later.

At the baseline scoring in 1969, the 17year old Norwegian student had an averageof 27.4 of possible 28 teeth present (thirdmolars eJtcluded) and the 30+ year oldshad 27.2, indicating that virtually no toothloss had occurred between 17 and 30 +years of age.

The speciat design of the present studypermitted the comparing of the initiaJ cross-sectional data of groups of different ageswith individual reaching the same agelevels in the course of the study. Such ananalysis along with a study of those whoreported for ail four surveys or of those ofeach age group who parlicipated in tbe fiisiand last survey, demonstrated that the num-ber of teeth present in individuals of thesame age at different time periods was es-?.eviViaUy th^ same. This shows that in Nor-wegian students and academicians below 40years of age, the frequency of tooth ex-traction has been consistently low duringttie last 30 years. (Vs a matter of fact, toothmortality in this population is much lowerthan in any other age-comparable group re-

Another feature of this particular pop-ulation is that more teeth had been ex-tracted before 17 years of age than between17 and 40 years. 3udged by the type ofteeth missing in the 17 year olds at the1969 examinations, there Js reason to be-lieve that the majority of the teeth were ex-tracted oTi orthodotitic indications (bicus-pids and incisors). This conclusion is con-firmed by recent reports from the manage-ment of the Oslo City School Denial Pro-gram (Engh 1978) that from 1971 through1977 the ratio of tooth extractions on or-

570 L O E . A N E R U D , B O Y S E N A N D S M I T H

thodontic indications to number of teethextracted for other reasons ranged between4:1 and 7:1.

The present study has also shown that therate of tooth loss among young and adultacademicians in Oslo, Norway is remark-ably low. During the first ten years of thepermanent dentition (6-17 years) the toothloss averaged 0.6 teeth per person. Duringthe next two decades the average loss wasless than 0.2 teeth per person. This is equalto a mortality rate of 0.01 teeth per year.The average Norwegian academician at 40years of age has lost less than one tooth,and no teeth were lost due to periodontaldisease (Loe et al. 1978b). Given the factthat from this age on most extractionsusually occur due to periodontal disease(Brekhus 1929, Metha et al. 1958, Kotzchke1965, Bay & Gad 1967) and that the longi-tudinal data have revealed a remarkahlyslow rate of progress of this disease (ap-proximately 0.09 mm mean loss of attach-ment per year) in this population (Loe et al.1978b), the likelihood exists that on theaverage, these individuals will advance intothe 5O's and 6O's with insignificant changesin the number of teeth present. As far ascan be seen from the literature (Klein 1943,Grey et al. 1970, Jackson 1966, Jackson &Murray 1972, Johansen 1970, Bjorn 1974,Hansen & Johansen 1976) these rates com-pare favorably with most studies and holdpromise for drastic improvements in thelongevity of the dentition.

The 15 year old Sri Lankan tea laborerhas approximately 27 teeth present and ex-hibits a tooth mortality situation which ismuch like that of the 17 year old Norwe-gian student. However, over the next 25years the mortality rate increases and leavesthe 40 year old tea laborer with an averageof 25.6 teeth. This reflects a significantlyhigher mortality rate than that found inNorwegian academicians over the sametime span, hut it is still relatively low com-

pared to other western population groups.The cause of this low tooth mortality rate

during the early part of life is without doubtthe almost total absence of dental caries inthis population. It is equally evident how-ever, that moderate and advanced peri-odontal disease is prevalent already beforetwenty years of age and that it progressesrapidly (approximately 0.3 mm loss of at-tachment per year, Loe et al. 1978b) to tbepoint where the teeth start to loosen andfall out. Jn other instances, the periodontaldestruction is so advanced already between20 and 30 years of age that, under normalcircumstances, the individual teeth wouldhave been extracted, hut due to the factthat these people have no access to dentalcare, such teeth will remain in place untilthey fall out or can be removed by the pa-tient himself. It is expected, therefore, thatduring the next decade an increasing num-ber of teeth will he lost due to periodontaldisease.

Extending the life span of the dentitioneither by prevention or by treatment of den-tal diseases is a major objective of dentalcare. The mean number of teeth presentper person is therefore, an important para-meter in the assessment of the longevity ofthe dentition of a particular populationgroup, and may reflect the effectiveness ofthe dental care services of a country orcommunity (Sheiham, Hobdell & Cowell1969). Although the complete answer lothis argument must await further analysis.the preliminary data suggest that the lowmortality rate of teeth in the Norwegiangroup is primarily due to systematic per-sonal dental care services from childhood,through adolescence and adult life. On theother hand, it is also apparent from thestudy of the Sri Lankan group that in apredominantly caries resistant and peri-odontal disease prone population up to 40years of age, the number of teeth present ortooth mortality rates as single characters-

T H E N A T U R A L H I S T O R Y O F P E R I O D O N T A L D I S E A S E 5 7 1

tics, reflect poorly the true quality of thedentition and are, therefore, less validparameters in the characterization of thesepeople's dentai health status.

AcknowledgmentThis study was supported by grants fromthe Danish Research Council, the RoyalDanish Foreign Ministry (DANIDA) andthe University of Connecticut ResearchFoundation. The authors would like to ex-press their gratitude to Professor S. B. Dis-sanayake, his colleagues, staff and studentsat the University of Sri Lanka in Paraden-iya, to the staff at the tea plantations andto the many others in Colombo and Kandy,without whose wholehearted support thisstudy could not have been undertaken andcontinued.

Thanks are also due to Oslo Universityand its Faculty of Dentistry for providingclinical facilities during the examinations,to the public school authorities in Oslo andthe university administration for their sup-port during all phases of this work.

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572 .. L O E , A N E R U D , B O Y S E N A N D S M I T H

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