Sex- and Age-relatedDifferences in Primary and

Secondary Dentin Formation

U. Zilberman, P. Smith

Laboratory of Bioanthropology and aDNA, Faculty of Dental Medicine,The Hebrew University-Hadassah, School of Dental Medicine, POB12272, Jerusalem 91 120, Israel; pat@cc.huji.ac.il

Adv Dent Res 15:42-45, August, 2001

Abstract — Clinical studies carried out on dentinthickness in adults, as well as experimental studies carriedout on ovariectomized animals, indicate that odontoblastactivity, like that of osteoblastic cells, differs in the twosexes. To examine the evidence for differences inodontoblast activity before puberty, we have measureddentin thickness and other crown dimensions from bite-wing radiographs of the lower first molars in 240 childrenaged 4-16 years. The radiographs were obtained frompedodontic clinics throughout Israel. Only teeth withoutcaries or fillings were used, and the study population hadminimal attrition. The results showed that dentinthickness, measured on the roof of the pulp chamber, wassignificantly greater in boys than in girls at all ages, andthat the differences increased during puberty. Thedifferences remained highly significant even whenstandardized for crown size. They demonstrate thatdimorphism in dentin thickness is present even in theearliest stages of odontogenesis and increase with puberty.

IntroductionBBBBBBJ. hree types of dentin have been identified in

human teeth: primary dentin, which formsrapidly, in association with enamel or cementumapposition, during tooth formation; secondary

dentin, which results from the continued but relativelyslow apposition of dentin in later life and may beassociated with a reduction in the number of functioningodontoblasts (Franquin et ah, 1998); and tertiary, irregular,dentin, laid down as a localized response to trauma (TenCate, 1998). Sex differences have been reported in thevolume of the dentin-pulp complex and enamel (Stroud etah, 1994; Zilberman and Smith, 1994; Alvesalo, 1997: Harrisand Hicks, 1998; Zilberman et al., 2000), and sex hormonesappear to affect odontoblast function in later life. Estrogenreceptor antigens have been identified in the pre-dentinal-odontoblast layer and pulpal blood vessels of extractedhuman wisdom teeth of both sexes (Hietala et al., 1998),while ovariectomized rats show enhanced dentin formationas well as enhanced periosteal bone formation (Hietala andLarmas, 1992; Svanberg et al, 1994).

This study examines the hypothesis that dimorphism inodontoblast activity occurs even before puberty, and isexpressed in differences in dentin thickness. The study wascarried out on bitewing radiographs of lower firstpermanent molars. In this tooth, crown formation iscompleted at age 3-4 years, and root formation is completedat age 8-9 years (Moorrees et al., 1963). The sample wasdivided into three age groups designed to provideinformation on primary dentin thickness, the combinedthickness of primary and secondary dentin laid downbefore puberty, and the amount of dentin laid down inadolescence.

Materials & MethodsBitewing radiographs of caries-free teeth withoutrestorations from 247 girls and 271 boys, aged 4 to 16 yearsand treated at different pedodontic clinics in Israel, wereexamined. The radiographs were taken as part of treatmentprotocol and were submitted to the authors with noidentification other than age and sex some years aftertreatment had been completed. Under these conditions, theHelsinki committee decided to waive the requirement forinformed consent. Exact age was known for 160 of the boysand 153 girls. Only radiographs with good superimpositionof cusp tips and no overlapping of mesial and distalborders of adjacent teeth were measured. In suchradiographs, rotation and distortion of the image seen onthe radiograph have been previously shown to be less than5 degrees (Zilberman et al., 1992). Age and sex of thechildren were obtained from their dental charts. Enamelheight (EH), dentin height (DH), and pulp height (PH) weremeasured as shown in the Fig. All measurements wereexpressed as a ratio of mesio-distal crown width (CW), tominimize the effects of external tooth size and possibleerrors due to magnification. To ensure unbiasedmeasurements, we coded all radiographs so that age andsex were unknown at the time of measurement. The sameexaminer performed all measurements using a digitalcaliper on a light table. The differences found betweenmeasurements of the same tooth after 10 days ranged from2-5% and averaged 3.2%. CW showed the least variationand EH the most.

Two-tailed Student's t test was carried out for the totalsample. Individuals of known age were then divided intothree age groups (4-7, 8-11, and 12-16 years) and analyzedby two-tailed Student's t test and analysis of variance. In allgroups, enamel formation and thus enamel apposition andcrown formation were complete. Dentin thickness in thethree groups, however, represents the total dentin formedunder different conditions. In the first group, all dentinpresent is primary dentin, since the roots are not yet fullyformed. In the second group, there is some secondarydentin, while in the third group, dentin thicknessrepresents the total amount of dentin formed both inchildhood and during puberty.

ResultsTable 1 shows the mean values for tooth components inboys and girls. For the entire sample, DH, PW, and CWwere significantly larger in boys than in girls.. However,when tooth components were calculated as a ratio of CW,only DH/CW showed statistically significant differences(Table 1). EH/CW and EW/CW were significantly larger ingirls. For the 160 boys and 153 girls for whom the exact agewas known, mean age was similar: 9 years for boyscompared with 9.1 years for girls. In all age groups, DH was

Key Words

Dentin, teeth, dimorphism, odontogenesis, odontoblasts.

Presented at the International Meeting on Signaling Mechanisms inDentin Development, Regeneration, and Repair: from Bench toClinic, held at Thessaloniki, Greece, November 10-11, 2000

42

TABLE 1 — Mean Values for Tooth Components in Mandibular First Permanent Molars (in mm)

EH

DH

PH

EW

PW

CW

EH/CW

DH/CW

PH/CW

EW/CW

PW/CW

Age

MeanNo.SD

MeanNo.SD

MeanNo.SD

MeanNo.SD

MeanNo,SD

MeanNo.SD

MeanNo.SD

MeanNo.SD

MeanNo.SD

MeanNo.SD

MeanNo.SD

MeanNo.SD

TotalBoys

1.742470.33

3.582470.51

1.852400.57

1.422460.22

4.612450.49

11.782470.57

0.1472470.03

0.32470.04

0.1572400.05

0.122460.02

0.392450.03

9.011612.5

Girls

1.752710.32

3.21**2710.45

1.862680.57

1.442710.21

4.48**2710.45

11.43*2710.6

0.153*2710.03

0.28**2710.04

0.1632680.05

0.13**2710.02

0.392710.03

9.111532.2

Boys

1.76540.38

3.46540.53

2.05510.56

1.48540.23

4.76520.57

11.78540.54

0.15540.03

0.29540.04

0.17510.05

0.13540.01

0.4520.04

6.56541.03

: 8 yrsGirls

1.65410.31

3.13**410.41

2.3*400.51

1.46410.18

4.53*410.54

11.28**410.57

0.15410.03

0.28410.04

0.2**400.05

0.13410.02

0.4410.04

6.67410.78

Boys

1.68800.3

3.6800.48

1.87770.57

1.46800.2

4.63800.45

11.78800.57

0.14800.02

0.31800.04

0.16770.05

0.12800.02

0.39800.03

9.24800.94

11 yrsGirls

1.72820.4

3.21**820.47

1.92810.49

1.47820.21

4.63820.42

11.39**820.59

0.15820.03

0.28**820.04

0.17810.05

0.13820.02

0.39820.03

9.04820.83

Boys

1.71260.5

4.0260.37

1.47260.47

1.46260.28

4.39260.46

11.63260.73

0.15260.04

0.35260.03

0.13260.04

0.126260.02

0.38260.02

13.35261.5

16 yrsGirls

1.99**300.3

3.4**300.47

1.47300.4

1.66**300.23

4.51300.48

11.61300.71

0.17**300.02

0.29**300.04

0.13300.04

0.143**300.02

0.39300.03

12.62301.3

Note: EH = Enamel Height; EW = Enamel Width; DH = Dentin Height; PW = Pulp Width; PH = Pulp Height; CW = Crown Width.* P value < 0.05.

** Pvalue<0.0 l .

significantly greater in boys. PH was significantly greater ingirls in the youngest age group, and EH and EW weresignificantly larger in girls than in boys in the two oldestage groups. With tooth components standardized fordifferences in crown width (Table 1), the ratio DH/CW wassignificantly greater in boys than in girls of similar age andincreased more rapidly with age in boys than in girls.PH/CW ratios, however, were similar in both sexes, whileEH/CW and EW/CW ratios tended to be greater in girls.

One-way analysis of variance, carried out with age andsex as dependent variables and CW as co-variant, showed thatsex was the main factor contributing to differences in dentinthickness (36.9%), followed by age (27%), with CWcontributing only 5% to total variance (Table 2). The combinedeffect of age and sex was only 47%, since the pattern ofincrease in dentin thickness differed in boys and girls

DiscussionDimorphism in the dentin-pulp complex of the mandibularfirst permanent molar studied here is then expressed in

relatively thinner enamel relative to crown size and fasterapposition of dentin. The quantity of primary andsecondary dentin formed in boys, at least on the roof of thepulp chamber, is greater than in girls, even beforeadolescence. These differences are statistically significant atage 7. Given the young age and lack of attrition in thesample examined, it is highly unlikely that functionaldifferences influenced dentin thickness. Moreover, asshown in Table 2, crown size contributed only some 5% tothe variance in dentin thickness, while sex contributed 39%and age 26%. The fact that this was a cross-sectional studycarried out on individuals with different growth trajectoriesmay account for some of the unexplained variance in DH.

Studies carried out on the teeth of individuals of unknownsex have shown that more dentin is deposited on the floor ofthe pulp chamber of multi-rooted teeth than on the roof orwalls (Philippas, 1961; Mjor, 1986). Philippas (1961) interpretedthis as due to the reduced growth potential of coronalodontoblasts. Our study did not directly measure the thicknessof dentin deposited on the floor of the pulp chamber.However, while in boys all of the reduction in pulp height

Adv Dent Res 1 5:42-45, August, 2001 Sex and Age Differences in Dentin Formation 43

Fig. — Cross-section of molar showing measurements taken. Measurementswere taken as follows: Enamel height (EH), dentin height (DH), and pulpheight (PH) were measured parallel to the long axis of the tooth, onemillimeter mesial to the central fossa on the same line. Pulp width (PW) wasmeasured perpendicular to the long axis of the tooth on the widest part ofthe tooth. Enamel width (EW) and maximal crown width (CW) were measuredon the widest mesio-distal length of the tooth on a line perpendicular to thelong axis of the tooth.

observed can be attributed to the increased dentin thickness onthe roof of the chamber, this does not apply to the girls. Themean difference in pulp height between boys in the youngestand oldest age groups was 0.58 mm, and this can be explainedby increased dentin thickness in the oldest group. The meandifference in pulp height between the youngest and oldest girlswas 0.83 mm. The reduction in pulp chamber height in thegirls was much greater than can be accounted for by theincreased dentin height. In girls, therefore, there may havebeen additional dentin deposited on the floorof the pulp chamber. This raises the issue ofpossible sex differences in the location as wellas the quantity of secondary dentin formed.This dimorphism may be related to thedifferent developmental pathway of coronaland radicular odontoblasts. The formerdifferentiate earlier, show a more rapid rate ofprimary dentin formation, and follow asinusoidal path. The radicular odontoblastsdifferentiate later, in a different milieu(Hertwig's epithelial sheath and cement-oblasts), and follow a straighter, more parallelpath (Ten Cate, 1998).

Most of the previous studies of age-relatedchanges in the dentin thickness of human teethhave been carried out on older adults, with fewif any juveniles included. Most used samplesfrom individuals of unknown sex and focusedon anterior teeth (Gustafson, 1950; Philippas,

1961; Philippas and Applebaum, 1966; Woods et al, 1990;Solheim, 1992; Drusini et al, 1997). In those studies in whichsamples of known sex were examined, significant dimorphicdifferences were found in the rate of dentin formation in adults(Woods et al, 1990; Solheim, 1992). Another study carried out byDrusini et al. (1977) showed a similar pattern of dimorphicdifferences. However, they concluded that these differences wereunimportant for age estimation. Woods et al. (1990) examinedlower molars of known sex, age, and population group. Theyconcluded that all factors influenced the amount of secondarydentin laid down, and that in females the rate of dentinformation appeared to increase suddenly in the fourth decade.However, they did not directly examine dentin thickness butmeasured changes in the dimensions of the pulp cavity. Theresults presented here show that the sex differences in dentinthickness present in adults are already present in infancy andaccelerate during puberty. They support the hypothesis ofdimorphism in odontoblast activity throughout life.

AcknowledgmentsThe authors thank all those pedodontists who contributedradiographs for this study. This investigation was supported inpart by the Israel Science Foundation.

ReferencesAlvesalo L (1997). Sex chromosome and human growth. A

dental approach. Hum Genet 101:1-5.Drusini AG, Toso O, Ranzato C (1997). The coronal pulp cavity

index: a biomarker for age determination in human adults.Am J Phys Anthropol 103:353-363.

Franquin JC, Remusat M, Abou Hashiech I, Dejou J (1998).Immunocytochemical detection of apoptosis in humanodontoblasts. Lux] Oral Sci 106 (Suppl l):384-387.

Gustafson G (1950). Age determinations on teeth. / Am DentSoc 41:45-54.

Harris EF, Hicks JD (1998). A radiographic assessment ofenamel thickness in human maxillary incisors. Arch OralBiol 43:825-831.

Hietala EL, Larmas M (1992). The effect of ovariectomy ondentin formation and caries in adult rats. Ada OdontolScand 50:337-343.

Hietala EL, Larmas M, Salo T (1998). Localization ofestrogen-receptor-related antigen in human odontoblasts.JDent Res 67:1384-1387.

Mjor IA (1986). Age changes in the teeth. In: Geriatricdentistry: a textbook of oral gerontology. Holm-PedersenP, Loe H, editors. St. Louis: C.V. Mosby Co., pp. 94-101.

Moorrees CFA, Fanning EA, Hunt EE Jr (1963). Age variation

TABLE 2 — Analysis of Variance: Dentin Height by Age Groups and Sex withCrown Width (experimental sums of squares; covariates entered first)

CovariatesCrown width

Main effectsAge groupsSex

2-way interactionsAge groups and sex

ExplainedResidualTotal

Sum of Squares

8.8478.847

13.0675.7258.162

1.5031.503

23.41662.49985.915

DF

11

321

22

6306312

Mean Square

8.8478.847

4.3562.8638.162

0.7510.751

3.9030.2040.275

F

43.31443.315

21.32514.01639.960

3.6793.679

19.109

Sig. of F

0.0000.000

0.0000.0000.000

0.0260.026

0.000

Note: Multiple Classification Analysis results for dentin height by age group and sex, with crown width, show thatsex contributes 37%, age group 26%, and CW 5% to variance found.

44 Zilberman & Smith Adv Dent Res 1 5:42-45, August, 2001

of formation stages for ten permanent teeth. / Dent Res42:1490-1502.

Philippas GG (1961). Influence of occlusal wear and age onformation of dentin and size of pulp chamber. / Dent Res40:1186-1198.

Philippas GG, Applebaum E (1966). Age factor in secondarydentin formation. / Dent Res 45:778-789.

Solheim T (1992). Amount of secondary dentin as an indicatorof age. Scand ] Dent Res 100:193-199.

Stroud JL, Buschang PH, Goaz PW (1994). Sexual dimorphismin mesiodistal dentin and enamel thickness.Dentomaxillofac Radiol 23:169-171.

Svanberg M, Hietala EL, Knuuttila M (1994). The effect ofdietary xylitol on dentin formation in ovariectomized rats.Acta Odontol Scand 52:82-85.

Ten Cate AR (1998). Oral histology: developmental structureand function. 5th rev. ed. St. Louis: The C.V. Mosby Co.

Woods MA, Robinson QC, Harris EF (1990). Age progressivechanges in pulp widths and root lengths duringadulthood: a study of American blacks and whites.Gerodontology 9:41-50.

Zilberman U, Smith P (1994). Sex discrimination using toothcomponents measured from bite-wing radiographs(abstract). Am ] Phys Anthropol (Suppl 18):214.

Zilberman U, Skinner M, Smith P (1992). Tooth components ofmandibular deciduous molars of Homo sapiens sapiens andHomo sapiens neanderthalensis. Am J Phys Anthropol 87:255-262.

Zilberman U, Smith P, Alvesalo L (2000). Crown componentsof mandibular molar teeth in 45,X females (TurnerSyndrome). Arch Oral Biol 45:217-225.

Adv Dent Res 1 5:42-45, August, 2001 Sex and Age Differences in Dentin Formation 45