Simulation of dental microwear: Characteristic traces by opal phytoliths give clues to ancient human dietary behavior

Simulation of Dental Microwear: Characteristic Tracesby Opal Phytoliths Give Clues to Ancient Human DietaryBehaviorIrene Luise Gugel,1 Gisela Grupe,1,2* and Karl-Heinz Kunzelmann3

1Institut fur Anthropologie und Humangenetik, 80333 Munchen, Germany2Anthropologische Staatssammlung, 80333 Munchen, Germany3Poliklinik fur Zahnerhaltung und Parodontologie, 80336 Munchen, Germany

KEY WORDS paleodiet; microwear; phytoliths; abrasion

ABSTRACT In order to further evaluate the process ofmicrowear formation on human dental enamel, microwearwas experimentally produced by a chewing simulation withan Academic Center for Dentistry Amsterdam (ACTA) de-vice. For this simulation, several cereal species were pro-cessed according to historical milling techniques, the exper-imental results of which were compared with those obtainedfrom cereals processed after modern techniques, and alsowith natural microwear on early medieval human molars.Comparison of simulated microwear pits with natural mi-crowear pits showed that the simulation led to traces which

matched those found on the historical teeth in terms of bothsize and shape. Experimentally produced microwear pitswere especially characteristic for the cereal species used inthe simulations, and both pit morphology and enamel losswere a function of cereal phytolith content. Despite the highvariability of phytolith size and shape, certain types arecharacteristic for certain cereals, which in turn are capableof producing cereal-specific microwear. This experimentalapproach is likely to further define ancient human dietarybehavior, including food processing. Am J Phys Anthropol114:124–138, 2001. © 2001 Wiley-Liss, Inc.

The reconstruction of paleodiet is of major concernin physical anthropology because human populationgrowth is linked to food supply, and different sub-sistence strategies have different environmentalconsequences for the humans employing them. Tra-ditional nutritional strategies will change whenevernew food items are discovered or new food process-ing methods are developed. This holds even for sta-ple crops like cereals, the domestication of which ledto major dietary changes. Food processing like cook-ing, baking, or roasting will render the food betterdigestible as compared to the raw product, but willalso induce, for example, a loss of vitamins. Theplanting of crops as monocultures or varietal mix-tures, and local climatic and soil conditions thatfavored particular crops, are of interest because an-cient subsistence strategies underwrite ancient life-styles and the well-being of individuals. While thedevelopment of food production from Neolithic timesonward is fairly well known from archaeologicalmacrofinds and artifacts (Prossinger and Willms,1998), each human population made its own adjust-ment to living in its circumscribed environment.Though it is known that some subsistence strategiesaffect skeletal and dental homeostasis and develop-ment, the use of human skeletal remains to inferdetails of past dietary behavior is still in its infancy.

Dental microwear analysis may fill this gap. Boththe quality and quantity of scratches and pits pro-duced on dental enamel by abrasive particles in food

have been used to denote the feeding behavior ofmodern and extinct species, as well as historic pop-ulations (e.g., Bullington, 1991; Gordon, 1988;Grine, 1986; Harmon and Rose, 1988; Hojo, 1989;Molleson and Jones, 1991; Puech, 1992; Teaford andLytle, 1996; Teaford and Runestad, 1992; Teafordand Walker, 1984; Walker et al., 1978). According toTeaford (1988), abrasion, which yields pits andscratches (Gordon, 1982), is indicative of tooth-food-tooth contact and occurs all over the occlusal sur-face. Striations are formed by attrition, if there areabrasives caught between the teeth and abrasionprocesses (Gordon, 1982). Microwear features likedensity, relation of pits to scratches, linearity, orfeature size can be related to dietary behavior orother types of tooth use (Ungar and Spencer, 1999).Despite the high variety of microwear featurescaused by sand (e.g., milling debris) and dust, cer-tain abrasive food particles leave distinct damage.While all normal, functional teeth show a higher orlesser degree of wear, differences in the intensity ofsuch wear should be the consequence of type and

Grant sponsor: Deutsche Forschungsgemeinschaft.

*Correspondence to: Prof. Dr. Gisela Grupe, Institut fur Anthropologieund Humangenetik, Richard-Wagner-Str. 10/I, 80333 Munchen, Ger-many. E-mail: [email protected]

Received 16 February 1999; Accepted 22 September 2000.

AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 114:124–138 (2001)

© 2001 WILEY-LISS, INC.

quantity of abrasive material in the diet (Molnar etal., 1983).

In temperate climates, the most abrasive particlesin human food are opal phytoliths in cereals (forother types of abrasive particles, see Ungar et al.,1995). The role of opal phytoliths in the productionof microwear on primate teeth has already beendemonstrated by Lucas and Teaford (1995). Compa-rable in terms of hardness, but far inferior in termsof quantity in the human daily diet, are stone cellswhich occur, e.g., in pears (Kuster, personal commu-nication). Phytoliths consist largely of silicium,which is taken up by the plant with the groundwater and stored as opal phytoliths (SiO2 * n H2O)in the stem, leaves, and also blossoms. In addition,calcium-oxalate phytoliths are abundant in manyplants. Monocotyledone plants of temperate cli-mates, including various cereal species, producehigh quantities of opal phytoliths which are highlyvariable in size and shape. Certain types of thesesilica bodies and their combination, however, arerather species-specific (Kaplan et al., 1992) (Fig.1a,b). Variations in size are also known to occur in

the course of the domestication process. For thesereasons, and also because of their resistance to de-composition, investigation of opal phytoliths amongarchaeological plant remains (Piperno, 1988), andalso on dental enamel of archaeological skeletons(Lalueza Fox et al., 1996b; Lalueza Fox and Perez-Perez, 1994), is a valuable tool for the reconstructionof both paleoenvironments and paleodiet.

Following Rose and Ungar (1998), who claimedthat one of the important research directions forfuture microwear analyses is to “unravel microwearformation processes,” it was the aim of this study toevaluate whether abrasion by opal phytoliths leavescharacteristic damage on the dental enamel which issufficiently distinct to answer questions about thetype of cereal consumed, and about ancient foodprocessing. To achieve this, dental microwear wascaused by several cereal species which had beenground according to historical milling techniques.This simulated microwear was compared with orig-inal microwear on molars of archaeological humanskeletons. In addition, valuable results in terms ofdifferential abrasiveness of various cereal specieswere obtained.

The study thus consists of two parts: an experi-mental portion (the simulation of microwear) and arestricted comparison of abrasion patterns on asmall sample of medieval teeth with the patternsarising from the simulation.

MATERIALS AND METHODS

The simulation studyChoice of cereals. Microwear was simulated withcereal species which were grown as staple crops inearly medieval Southern Bavaria (Kuster, 1995):spelt (Triticum spelta), wheat (Triticum aestivum),barley (Hordeum vulgare), rye (Secale cereale), andoats (Avena sativa), respectively. Wheat was in-cluded in this study as a representative of the threecommon Triticum species (wheat, emmer, andeinkorn) of medieval times. Foxtail millet (Setariaitalica), which was discovered at a few sites only inlater medieval periods, served as control since milletwith bracts (i.e., husks enclosing the flower and seedof a grass spikelet) (processed in an ordinary house-hold mill) is routinely used as reference material fora device normally used by dentistry to abrade restor-ative materials in vitro similar to in vivo conditions(Academic Center for Dentistry Amsterdam (ACTA)device; De Gee et al., 1986, and see below).

Preparation of cereals. All species with the ex-ception of millet were processed according to medi-eval milling techniques in a historical mill, rebuilt inthe Frankisches Freilandmuseum Bad Windsheim.Spelt (Triticum spelta) went through a special his-torical “Gerbgang” before being ground to removebracts that are anatomically fused to the seed. In themedieval Gerbgang, process bracts are removed me-chanically by the millstone. Specifically, the stone islifted for a few millimeters and then lowered to the

Fig. 1. a: Isolated phytolith from Setaria italica. Long andslender form with structured surface. b: Isolated phytolith fromTriticum spelta. Papilla of type IIa1 according to Kaplan et al.(1992).

MICROWEAR SIMULATION 125

scattered seeds underneath, thus producing a con-trolled pressure to crack away the bracts. To checkthe efficiency of the Gerbgang, spelt which had beenprocessed according to modern milling techniqueswas purchased from a modern bioshop and includedin the investigation. Ample evidence exists thatflour prepared according to medieval milling tech-niques is never free of bract residues, sand, and dustfrom the millstones, as is modern flour such as theone prepared from the spelt control from a modernbioshop.

Quantification of silica content. To quantify sil-ica deposits in the grain tissues, a combined methodof chemical oxidation (Rovner, 1971), followed by dryashing (Twiss et al., 1969, modified according toPearsall, 1989), was applied (Runge, personal com-munication). The sediment left after double oxida-tion consisted mainly of silica particles which weredetermined gravimetrically and analyzed by scan-ning electron microscope (SEM).

Enamel specimens. For every simulation experi-ment, 10 enamel specimens were prepared fromfreshly extracted, impacted permanent humanteeth, i.e., teeth which had never taken part in thechewing process, the enamel surfaces of which werefree of microwear. This experimental study consti-tutes the major part of our investigation.

The ACTA device. Experimental microwear wasproduced by inserting human dental enamel of une-rupted, impacted permanent teeth into an ACTAfacility (De Gee et al., 1986). Within the ACTA de-vice, the abrasive medium consisting of natural foodcontaining abrasive particles (Baker et al., 1959;Leek, 1972; Walker et al., 1978) is moved betweentwo antagonistic wheels (Fig. 2). During the experi-ment, the wheels were completely covered by theslurry (in a covered beaker), which was continuouslystirred by a wingscrew attached to the samplewheel. The wheels (sample and antagonist) withdifferent diameters rotate against each other with

different velocities. The velocity of the antagonisticwheel is 15% slower than that of the sample wheel,which rotates at 1 Hz constantly. The sliding motionsimulates the lateral sliding of antagonistic teeth inthe jaws during the crushing phase of the chewingcycle, and causes a slurry of food between the sur-faces (Pallav et al., 1993). To simulate physiologicalbiting forces (Eichner, 1963; DeLong and Douglas,1983) which are necessary for the original purpose ofthe ACTA device (test of abrasion on filling materi-al), the antagonistic wheel works with a constantload of 15 N. This method permits the simultaneousinvestigation of enamel loss and specific microwearfeatures produced by the food mush on the sample.

The sample wheel. The sample wheel, consistingof 20 specimen chambers, was pre-prepared withdental filling material and stored for 48 hr in Ringersolution (pH 6.7) until complete polymerization hadtaken place (Fig. 3), and then the composite materialwas polished. Ten chambers without enamel insertswere used as an internal reference for abrasion. Thecomposite basis for the enamel insert (HeliomolarRo, Vivadent) contains inorganic filling materialswith particle sizes around 40 nm, thus being 50–400times smaller than the smallest abrasive particles tobe expected (.10 mm for phytoliths, 2–63 mm forsandstone particles from the mill stone). Therefore,any composite particles which had become abraded,and thus included into the food mush during thechewing simulation, would produce unspecific mi-crowear at best, but would never produce wear thatcould be confused for specific microwear features.

Enamel inserts to the sample wheel. Surgicallyextracted human molars which had not yet takenpart in the mastication process were kept in Ringersolution with addition of NaN3 until the preparationof enamel samples (Fig. 4). For this, the molars werecut along the fossa centralis to the cervix. An addi-tional cut was from the buccal or lingual along theedge of the cervix to the intersection. Ten enamelsegments sized 3.5 mm (occlusal-cervical) 3 5.5 mm(mesial-distal) 3 2.0 mm (enamel-dentin) with theirnatural, untouched buccal and lingual surfaces werethus prepared for each sample wheel and fixed intothe composite material with Twinlock cement (Kul-

Fig. 2. ACTA device with sample wheel (S) and antagonisticwheel (A), and enamel specimens prepared in sample wheel.

Fig. 3. Preparation of sample wheel of ACTA device: longitu-dinal section through sample wheel.

126 I.L. GUGEL ET AL.

zer, Inc.). As pretests to this study showed that,when the enamel surface was parallel to the antag-onistic wheel, only parallel scratches were producedfrom the slurry, the device was modified to simulatethe position of a cusp during the chewing process.The “occlusal” part of the enamel insert was lifted upto 850 mm maximum above the polished level of thesample wheel, while the cervical part was left at thepolished surface (Fig. 2). The corresponding enamelaspects did not show significant signs of fatigue in-dicative of a possible rise of pressure above physio-logical biting forces.

Experimental process. For every cereal speciestested, 10 enamel segments served for the simula-tion. From the ACTA device, two enamel specimenseach after 50,000, 100,000, and 150,000, and fourafter 200,000 “chewing” cycles, respectively, wereremoved, and the slurry was changed. This proce-dure simulates the physiological mastication pro-cess, where subsequent chewing produces a turn-over of microwear features (Teaford and Lytle, 1996,Teaford and Oyen, 1989). While specific microwearwas detectable on the enamel specimens quite earlyafter 50,000 cycles only, measurement of the enamelloss required 200,000 cycles, representing 1 year ofchewing (Bates et al., 1975). The slurry consisted offour portions with 150 g cereal each, processed ac-cording to modern or historical milling techniquesand 220 ml Ringer solution (pH 8.0) with 200 mMTRIS and 1 g NaN3 (to prevent microbiological con-tamination). After 5,000–50,000 cycles, the slurrywas homogenous in all cereal species tested. Thechange of pH depending on the grade of acidity ofthe respective cereal, and the viscosity of the slurryof wheat and spelt, which varies by the gluten pro-duction (Belitz and Grosch, 1992), were monitored.

For details concerning pretests, calibration, andstandardization of the simulation protocol, refer toGugel (1998).

Measurement of enamel loss. The height of ma-terial abraded from the four enamel specimens usedin each simulation experiment was measured by twoindependent methods, after the specimens had beenremoved from the ACTA device. First, enamel losswas directly measured by use of a perthometer (de-vice for profilometric scanning; PRK/S3P, FeinprufPerthen, Hannover, Germany). Secondly, enamelloss was determined indirectly with a laser sensor(Laserscan 3D Pro, Willytec, Munchen, Germany).This laser sensor uses the triangulation principle forthe determination of height data. A laser diodeemits a light line to the surface of the object, fromwhich the light is reflected to a CCD-cameramounted with a triangulation angle of 30° comparedto the laser diode. The laser scanner has an adjust-able lateral resolution. In our experiment, a lateralgrating of 25 mm in both the x- and y-directions wasused and could not be changed due to technicalrestrictions. The vertical resolution (z-coordinate) isbetter than 5 mm (Mehl et al., 1997). Independentfrom the methodology, the low number of specimensdoes not permit a valid statistical analysis. There-fore, analysis of possible cereal-related enamel lossremains on the descriptive level.

Replication for three-dimensional (3D) laserscanning. The optical properties of the translu-cent teeth necessitate a replication of the tooth toobtain a diffuse reflecting surface. 3D laser scanningwas the only method applied in our investigation tocasts of the enamel specimens; all other methodswere carried out on the original specimens. Replicaswere made by use of a combination of high and lowviscosity polyether material (Permadyne Grant/Per-madyne Penta, Espe, Seefeld, Germany). The repli-cas served as negatives for plaster casts (Fuji RockWhite, GC International, Leuven, Belgium), whichwere scanned.

Measuring process. One 3D laser scan was takenbefore the experiment (baseline data) and after200,000 cycles of simulation. The substance loss dueto wear simulation was determined according toKunzelmann (1997). The 3D data sets for baselineand follow-up were superimposed numerically witha least-squares matching algorithm (Kunzelmann,1997, Mehl et al., 1997) without reference points.After the parameters of translation and rotationwere determined, a “difference image” was calcu-lated by digital subtraction of the superimposed 3Ddata sets of loss, whereby both total wear volumeand maximal height loss (linear measurement) wereavailable. For the present evaluation, the mediancrown height loss (linear measurement), which cor-responds to the total wear volume normalized to theworn area (Kunzelmann, 1997), was used for com-parison.

Morphological inspection by SEM. The originalspecimens, archaeological teeth, and enamel after

Fig. 4. Preparation of enamel segments for simulation pro-cess.


all simulation experiments were examined by scan-ning electron microscopy. The specimens were inves-tigated in the secondary mode at 200 (overview) and500 times magnification (for measurement) with aLeitz AMR 1200 scanning electron microscope, op-erating at an accelerator voltage of 15–25 keV. Atleast eight areas (sized 0.04–0.2 mm2) of every ex-perimental enamel and two areas (sized 0.04 mm2)of each of the three facets inspected in archaeologi-cal teeth (see below) were digitized by video signalsand saved in a picturestoring card (Image-slave forWindows, MEECO Holidays, Australia). The sur-faces to be examined were oriented as perpendicu-larly as possible to the electron beam. To optimizethe three-dimensional description of the features,the samples were tilted, whereby the degree of tiltwas recorded and the data ascertained were calcu-lated and corrected by compensating raster com-pression (Lange and Blodorn, 1981). This procedurewas checked by analyzing a copper mesh at all an-gles of tilt. The orientation of the simulated masti-catory motion which was determined by the rotationof the surface of the wheels against each other wasused to define the major and minor axis of eachmicrowear feature. The major axis of the microwearfeature was defined by the sliding motion (from theocclusal to the cervical part of the inserted enamelsegment), and the minor axis by lateral extension ofthe microwear feature.

Pretests showed that enamel inserts which areintegrated on the level of the filling materials in thesample wheel show parallel scratches along the slid-ing motion on their surfaces. This kind of experi-mental design would not distinguish microwear fea-tures caused by different foodstuffs. Therefore, amodified design was developed, in which the occlusalaspects of the enamel inserts which meet the slurryfirst during rotation of the wheel surfaces againsteach other were lifted above the polished level of thesample wheel. This modified ACTA device now per-mitted simulation of the crushing and shearing com-ponents of the physiological mastication process. Onthe corresponding enamel aspects, pits accumulatedin the simulation, i.e., after contact with the slurry.As the ACTA device does not permit an elastic avoid-ance comparable to physiological masticatory condi-tions, scratches could not be simulated beyond theartificial appearance mentioned. Digital imageswere taken, and the features (pits) were finally mea-sured manually, and the measurement data werecalculated and also described morphologically. Thefollowing data were recorded: 1) mean featurelength (major axis), 2) mean feature width (minoraxis), and 3) feature shape (length/width ratio).

Since the simulation experiment revealed a rela-tionship between cereal species tested and pit mor-phology produced (see Results), the focus of thisstudy was on pit size and morphology. Pit morphol-ogy in relation to distinct food types has not yet beendescribed extensively in the available literature. Fora definition of microwear features, we followed the

suggestions by Grine (1986), Grine and Kay (1988),and Gordon (1988): linear features (“scratches”) arecharacterized by a length to width ratio .4:1, whilepunctual features (“pits”) have a variable length towidth ratio up to 4:1.

Microwear detectable on a sample of medievalteeth and comparison of medieval microwear

with that produced by ACTA simulation

For comparison, six pairs of matched sets of upperand lower second molars of human skeletons fromthe early medieval burial site (5th–8th century AD)at Wenigumstadt in Bavaria (Cipriano-Bechtle etal., 1996) were inspected. The pairs of second molarswere selected according to the following criteria: thedentition of the selected skeletal individual had tobe as complete as possible with at least one opposingsecond molar in the jaws; the teeth should showinitial abrasion only without dentin exposed on theocclusal surface; the jaws should show a normalocclusion pattern according to Angle class I (Schu-macher et al., 1990); and no dental anomalies shouldoccur. Microwear was investigated on three specificfacets on these molars (Kay, 1977; Gordon, 1982):facets 5 and 6 which occlude with their counterpartson the metaconid and the entoconid during thechewing phase I, and facet 9, which moves across itscomplementary facet on the hypoconid during phaseII in the chewing cycle. It was expected that a ma-jority of traces should be located on these facets,which were then analyzed together.

Examination of medieval teeth andstatistical comparisons

For the search of comparable features on archae-ological teeth, the total surface areas of the threeselected facets (5, 6, and 9) were inspected. All pitsin these areas were monitored and scanned follow-ing a lingual-buccal orientation. The lingual-buccalorientation was maintained by the aid of photo-graphs taken from the specimen prior to the SEManalyses and at higher magnification by the aid oflingual-buccal-oriented scratches. Digital imageswere taken and analyzed in the same way as theexperimentally produced microwear.

On account of the skewed distribution of the majorand minor axis of all recorded microwear pits (sim-ulated and on early-medieval molars), the data weretransformed to follow a log-normal distribution (chi-square test). The simultaneous investigation of morethan two groups showed that the variances in thesamples were not equal (equality is a prerequisitefor the ANOVA test). We therefore applied a Welchtest (which requires normal-distribution) to ascer-tain significant differences between mean mi-crowear values. Comparisons were made betweenpits produced by simulation and those on medievalteeth, as well as pit sizes produced by different ce-real slurries. The level of significance selected was0.01.


EDX analysis and high-resolution SEM

All deposits in pits and scratches in the areasinspected were analyzed by EDX (energy-dispersedX-ray device coupled to an DSM 960A, Zeiss) andanalytic software (Link Diagnostics, Oxford) (Fig. 5)to differentiate between phytoliths and other depos-its on the enamel surface.

A selection of specimens with experimentally pro-duced microwear was kindly analyzed for us by theBotanical Institute, Munchen, by high-resolutionSEM (Hitachi S-4100) at a magnification of 700–2,000 times to verify the structural characteristics ofthe lesions.

RESULTSSimulated abrasion and microwear

Abrasiveness of different cereals. The abrasive-ness of the various cereal species according to theprofilometric analysis is listed together with the sil-ica content of the respective cereals and the pH of

the mush after 200,000 cycles in the ACTA deviceeach, in Table 1. While increasing content of silicadeposits leads to an increase of enamel loss, as in-dicated by millet (median abrasion loss, 39.9 6 7.8mm) and the bioshop spelt (median abrasion loss,8.3 6 3.1 mm) as representatives of highest andlowest silica content, respectively, this relationshipis probably not a linear one. It is noteworthy that inthe course of the simulation cycles, pH of the cerealmush was not stable but rather tended to decrease.Since the effects of acids on enamel are sufficientlyknown, it cannot be excluded that the loss of enamelsubstance during the simulation cycles is also afunction of pH. It is conspicuous that spelt and mil-let, both test substances with the highest content ofsilica deposits (0.20% and 1.46% ash residue per dryweight), end up with a pH around 4.0 after 200,000simulation cycles, whereas the pH for all other ce-reals is much less acidic, with values of 6.0 andabove. Microscopic damage of the enamel should

Fig. 5. a: Opal phytolith (type IIa2 according toKaplan et al., 1992) impacted into the dental enamelof an early medieval human upper second molar. b:Clear signal of silicium of phytolith in a by an EDXspectrum. c: No silicium signal on enamel surround-ing the phytolith in a.


become worse in an acidified environment (e.g.,Davis and Winter, 1980), so both phytolith contentand pH are likely to be responsible for the resultsobtained by our experiment.

It is noteworthy, however, that bioshop spelt con-tains much less silica deposit (,0.01%) than speltprocessed according to historical milling techniques(0.20%), indicating that modern spelt underwent avery careful and efficient cleaning process. As a re-sult, bioshop spelt caused the least abrasion loss,despite producing a low pH of 4.1 only during thesimulation process. This example demonstrates theimportance of silica bodies in the abrasion process,despite some additional effect produced by the acidicenvironment, and the assumed contamination of gritthrough the milling process.

Simulated microwear. As a result of the designof the ACTA experiment, the “cervical” parts of theabraded areas of enamel segments with only hori-zontal slip contact with the slurry showed paralleland uniform scratches (Fig. 6a,b) and nearly no pits.Traces of abrasion on the “occlusal” part of theenamel samples, which had both horizontal and ver-tical slip contact, were dominated by pits with avariety of morphological characteristics (Fig. 6a,b).This finding holds for every cereal species tested.The spatial distribution of scratches and pits is anexperimental artifact and not comparable to mi-crowear produced in vivo; therefore, the calculation,for example, of scratch to pit ratios on the experi-mental enamel segments would have been meaning-less. Figures 6 and 8 demonstrate that scratches (ifpresent at all) are very long, parallel, and in linewith the unidirectional “chewing direction.” Thisfinding is different from any observable physiologi-cal produced microwear, and may reflect the ACTAartifact mentioned above. The accumulation of pitsin the areas with both horizontal and vertical slipcontact, on the other hand, reflects microscopic dam-age of the enamel by phytoliths which had hit theenamel surface at varying angles.

Fig. 6. a: Overview of simulated microwear by Avena sativa,mainly caused by horizontal slip contact, but also by vertical slipcontact at the occlusal aspect. Enamel surface is dominated byscratches. Orientation: cervical (left) occlusal (right); arrow indicatessliding motion. b: Overview of simulated microwear by Triticumaestivum, caused by both horizontal and vertical slip contact. Sev-eral pits (arrowheads) are on “occlusal” part of specimen. Orienta-tion: cervical (left) occlusal (right); arrow indicates sliding motion.

TABLE 1. Median enamel abrasion after 200,000 cycles of chewing simulation with ACTA device, in relationto silica content and pH of food mush for all cereals tested1

Spelt (b) Spelt (m) Rye (m) Wheat (m) Barley (m) Oats (m) Millet (h)

% ash residue per dryweight2

,0.01 0.20 0.01 n.d.3 0.18 0.03 1.46

Median abrasion loss(mm) 6 1 sd4

28.3 (3.1) 230.2 (5.5) 217.3 (6.3) 222.2 (9.7) 228.0 (16.9) 227.9 (13.1) 239.9 (7.8)

Maximum abrasion loss(mm) 6 1 sd4

226.6 (9.2) 277.7 (14.8) 238.6 (14.5) 257.8 (10.4) 278.7 (34.6) 294.6 (43.5) 2101.3 (45.6)

pH of cereal mush atbeginning of experiment

7.9 6.1 8.5 8.1 8.0 7.3 8.4

pH of cereal mush after200,000 cycles

4.1 4.6 6.2 6.6 6.2 6.0 4.0

1 200,000 cycles equivalent to one year of mastication (Bates et al., 1975). b, bioshop, ground in mill with korund-ceramics; m, groundin historical mill; h, ground in modern household mill.2 After both wet and dry ashing, consisting mainly of silica. Data were kindly provided by PD Dr. F. Runge, Institute of PhysicalGeography, University of Paderborn.3 Not detected, but usually similar to rye and oat; Runge pers. comm.4 Standard deviation in parentheses.


We further focused on pits, the features whichcould be analyzed both in terms of size (metricalanalysis) and shape (morphological analysis), to re-veal a relationship between cereal species tested.Only such pits were described which were clearlyidentifiable, more or less isolated and not obscuredby overlying scratches. Since the number of analyz-able pits was a random artifact by the ACTA device,no reliable pit density analysis was possible. Themajority of all pits were unspecific in terms of di-mensions and morphology; therefore, we will notexclude that this unspecifity may as well be partlyartificial because of the ACTA design. About 25% ofall distinguishable pits, however, had characteristicfeatures (see below). The length to width ratio for allpits analyzed was in the range between 0.4:1–3:1.We have not differentiated pits from enamels fromdifferent simulation cycles because of the physiolog-ical turnover during the mastication process. Also,since after each set of cycles the slurry was renewed,the experimental parameters responsible for mi-crowear did not change.

Firstly, the dimensions of the major (x) and minor(y) axis of a total of 191 pits produced by the variouscereals were compared. The distribution of majorand minor axis dimensions for the different cereals(Fig. 7, Table 2) showed a clear relationship betweenthe major and minor axis dimensions, but also aconsiderable overlap.

Secondly, a close morphological inspection of thepits revealed some very characteristic features interms of shape, in contrast to size. Out of the 191pits, 135 were without any recognizable distinct fea-tures, as all were circular or oval by shape, withvariable size and depth. However, 56 pits were dis-tinct both in terms of morphology and of cereal spe-cies (Table 3, Figs. 8a–g). High-resolution SEM im-ages (at different magnifications to show the totalextension of each pit) support the specific morphol-ogy and submorphology of enamel lesions (Fig. 9a,b).These pits could have been produced by phytolithswhich had hit the enamel surface, producing a lesionon the enamel which may be very close to a mirrorimage of the particle itself (Fig. 10b). Despite the

fact that cereal phytoliths can be classified into dis-crete categories (see Kaplan et al., 1992), each phy-tolith type maintains a certain variability in termsof morphology. With regard to the morphology of pitsproduced by cereal-specific phytoliths, another vari-able is added by the different angles with which theparticles hit the enamel surface. As a result, pitcategories cannot be defined in an absolutely dis-crete way, since a certain amount of overlap willalways remain. However, the morphological appear-ance of more than a fourth of all pits analyzed jus-tifies the hope that a clear relation of pits to cerealspecies tested will be found through further investi-gation.

Medieval microwear and a comparison withsimulated microwear

Microwear on medieval molars. All archaeolog-ical teeth investigated in this study showed a ratherhigh abundance of scratches running both in bucco-lingual and mesio-distal directions. Such a high fre-quency of scratches is commonly interpreted as anindication of a coarse diet dominated by cereals(Puech, 1992; Lalueza Fox et al., 1996a). A total of226 pits was inspected, 77 on molar facets from theupper jaw, and 149 on molar facets from the lowerjaw. While the size of the pits matched those pro-duced in the simulation experiment (Table 2), theirshapes were highly variable. Circular and ovalshaped pits were most common (n 5 197), some-times with a lateral nick (n 5 29). But triangular,trichomoid, and diamond-shaped pits also occurred,often with special subcharacteristics like lateral orcentral notches, or central holes.

Detection of phytoliths. It is noteworthy that ev-ery archaeological enamel specimen exhibited atleast one phytolith which stuck into the enamel.These phytoliths must have been tightly fixed intothe surface, since they withstood the cleaning of theskeletons by brushing under running water shortlyafter excavation a few years ago. While some ofthese phytoliths were connected with scratches, end-ing in a depression (Fig. 10a), others were sur-rounded by pits of comparable size and shape (Fig.10b). Identification of these particles as phytolithswas supported by EDX analyses (Fig. 5). Figure 5ashows a phytolith type IIa2 (Kaplan et al., 1992) onthe enamel surface of the second molar (17) of amedieval individual. Figure 5b,c shows the results ofthe EDX analyses of this phytolith, with a clearsignal for silicium (Fig. 5b) and no signal for siliciumon the enamel surrounding the phytolith (Fig. 5c).

While some of these phytoliths could not be iden-tified, most probably due to in vivo or postmortemdamage, some could clearly be identified as mem-bers of one of the distinct phytolith classes (Fig. 5a).It is clear that at this stage of the investigation, themorphological inspection of a few selected matchedsets of upper and lower second molars from archae-ological skeletons cannot reveal all pit types identi-

Fig. 7. Distribution of major and minor axes (logarithmicscale) of pits produced by different cereals in the course of thesimulation. Total distributions show a considerable overlap. b,bioshop spelt; m, historical mill.


fied in the course of the simulation process. Whilethe microwear on the archaeological teeth had beenproduced by a mixed diet, only a single cereal specieswas tested in the course of the experimental setting.Therefore, a recovery of all simulated pit types onthese archaeological specimens cannot be expected.Also, it would be far too early to relate detailed pitmorphology of archaeological microwear to the ex-perimental features. However, the comparison ofsimulated and medieval microwear led to very prom-ising results, even at this stage of the investigation.

Comparison of simulated and medieval mi-crowear. A very important result is that overallpit dimensions on dental enamel after the simula-tion experiment and on archaeological teeth werethe same (Table 2, Fig. 11a,b), which highly sup-ports the validity of the simulation protocol. Figure11 does not differentiate between cereal species.

Furthermore, a pairwise statistical comparison(Welch test) reveals some significant differences in pitdimensions, both between pits produced by the variouscereal species in the course of the simulation despitethe overlap of the dot plots, and between simulatedand original pits (Table 4): the mean major and minoraxis dimensions of pits produced by spelt purchasedfrom a bioshop are highly significantly smaller thanof all other cereals and found on medieval molars,with the exception of oats (major axis). Pits producedby rye are highly significantly larger than those pro-duced by millet, oats, and both spelt fractions interms of the major axis, and from medieval molars.Pits produced by millet are highly significantlysmaller than those produced by rye and wheat, andhighly significantly larger than those produced bybioshop spelt in terms of the major axis. The minoraxes of pits produced by rye were significantly largerand by spelt significantly smaller than millet, andby rye significantly larger and by spelt significantlysmaller than those found on medieval molars. All

differences noted above are at the 0.01 level of sig-nificance. All other differences were insignificant.

DISCUSSION

The major result of the simulation experimentwas the production of microwear pits of differentsizes and shapes on human dental enamel by vari-ous cereal species. The correlation of structuralcharacteristics of pits with specific cereal species islikely to introduce a novel aspect into dental mi-crowear analysis. Comparison with archaeologicalhuman molars supported the validity of the simula-tion protocol and led to the possible exclusion ofcertain cereal species as producers of archaeologicalmicrowear. The number of archaeological teeth in-vestigated is by far too low for a valid statisticalcomparison of simulated and archaeological fea-tures. The archaeological sample served as an im-portant control of whether experimentally producedpits fall into the range of real microwear, or appearcompletely artificial. The latter was obviously notthe case. However, tooth wear is a very complexphenomenon, and differential impacts of factors likeabundance of abrasive particles, their size andshape, and pH have to be sorted out carefully. Forinstance, damage or complete removal of dental mi-crowear by acidic treatment was demonstrated byKing et al. (1999). Other factors like cereal fat con-tent, or gluten production, which will influence theviscosity of the food mush, may also be consideredbut will have similar consequences for microwearboth in a simulated and in an original setting.

Less important for the reconstruction of paleodiet,but highly interesting for modern dentistry, is theexceptional state of bioshop spelt, which was lowestin silica content and led to the least abrasion vol-ume. Compared to spelt which had been subjected toa historical milling technique, modern cleaning pro-cedures will remove the majority of silica bodies, and

TABLE 2. Statistical parameters of pits on early-medieval molars and human enamel from ACTA-simulation1

Spelt (b) Rye (m) Wheat (m) Barley (m) Millet (h) Spelt (m) Oats (m)

Early-medieval

molars (total)

n 12 18 29 34 33 41 23 226Major axis (mm)

Mean 6 sd 21.8 (6.4) 60.9 (25.9) 54.5 (35.4) 47.4 (33.5) 31.5 (13.2) 39.6 (24.0) 33.5 (21.8) 40.5 (27.2)Median 20.5 73.1 49.8 37.0 31.5 32.1 25.4 33.1

ln (major axis),mean 6 sd

3.044 (0.298) 3.972 (0.537) 3.784 (0.686) 3.638 (0.672) 3.363 (0.433) 3.512 (0.579) 3.355 (0.546) 3.493 (0.654)

Minor axis (mm)Mean 6 sd1 28.1 (9.3) 40.4 (25.6) 43.6 (33.7) 37.8 (38.4) 28.3 (11.8) 26.1 (11.1) 28.0 (15.7) 36.2 (23.5)Median 26.9 37.3 32.8 26.3 26.1 27.6 24.6 30.1

ln (minor axis),mean 6 sd

3.282 (0.353) 3.567 (0.671) 3.508 (0.750) 3.349 (0.690) 3.263 (0.408) 3.167 (0.456) 3.214 (0.478) 3.376 (0.679)

Major(mm)/minor(mm) axisMean 6 sd 0.8 (0.2) 1.6 (0.6) 1.4 (0.5) 1.5 (0.6) 1.2 (0.4) 1.5 (0.7) 1.2 (0.3) 1.2 (0.4)Median 0.8 1.4 1.3 1.2 1.2 1.3 1.1 1.2

1 Standard deviations in parentheses. b, bioshop, ground in mill with korund-ceramics; m, ground in historical mill; h, ground inmodern household mill.


at the same time the majority of abrasive particles.With regard to the simulation, bioshop spelt was ofgreat value because of its low abrasivity despite adrop in pH to 4.1, which constitutes a considerablyacidified microenvironment for the enamel speci-men. The difference in abrasivity between bioshopspelt and spelt processed in a historical mill (about22 mm) is therefore in fact largely the result of theabundance of abrasive particles.

The question about the nature of these abrasiveparticles remains. While the detection of phytolithstrapped in the enamel surface is proof for their abra-sive potential, quartz and other silica particles fromthe milling debris should seriously be taken intoaccount. It is highly unlikely that these particleswill produce characteristic cereal-specific pits (Table3), since phytoliths are characterized by certainforms and shapes, while sand and dust particlesshould show a continuous variability in both fea-

tures. Therefore, these particles are most probablyresponsible for an unspecific background microwear.During the quantitative analysis of silica content inthe cereal species, no milling debris were detectablewithin detection limits. Light-microscopic inspectionof the purified silica bodies led to the identification ofvery few and isolated sand particles. However, thisdoes not imply that sand and dust impurities arenegligible, since the abrasive potential of sand isabout 10 times higher than the abrasive potential ofopal phytoliths (Newesely, 1985). Thus, an impurityof 1 mg sand per 100 g cereals will theoretically besufficient to produce a similar wear and abrasion ascereals with 0.01% silica content. A similar simula-tion experiment with controlled admixtures of sandparticles is likely to solve this problem and is thesubject of ongoing investigations.

While opal phytoliths are doubtlessly a majorcause of abrasion and at the same time responsible

Fig. 8. Characteristic pits on dental enamel, produced by various cereal species in the course of the simulation. Arrow: occlusal3cervical. Arrowheads indicate specific features. All images were originally taken at the same magnification (3500), except of barley andmillet (3200). a: Spelt from a bioshop: isolated, shallow pits with a small, central depression. b: Spelt processed according to historicalmilling techniques: several shallow pits, deep scratches. c: Rye: isolated, oval pits with a deep, central cleft. d: Wheat: flat pits ofirregular shape. e: Oats: deep oval pits with a central, longitudinal cleft. f: Barley: big oval pits with several central depressions. Lowmagnification was chosen because of the absolute pit size. g: Millet: round pits, deep scratches. Low magnification was chosen todemonstrate the dominating abundance of scratches. (e, f, and g page 134.)


for the generation of rather specific microwear pits,the diagnostic potential of pits in terms of whichcereals had been consumed in which condition stillneeds to be worked out. Although some significantdifferences in major and minor axis dimensions werefound after the simulation, these differences werelargely due to the variability of pit sizes produced by

different cereals. Especially for the lower dimen-sions, pit size distributions showed a complete over-lap (Fig. 7). Independent from size, distinct morpho-logical features remain for potential differentialdiagnoses. The low diagnostic potential of pit sizes islargely due to the fact that distinct microwear tracescan be completely obscured by subsequent chewing

Fig. 8. Legend page 133.

TABLE 3. Distribution and morphological description of characteristic pits, produced by different cereal species1

Cerealspecies

Number ofpits described

Number ofcharacteristic pits

Morphological description ofcharacteristic features

Spelt (b) 12 2 Pits with a small, central depressionSpelt (m) 42 8 Expanded flat oval pits, some with pointed ending, frequently

ending in a continuing scratchRye (m) 18 7 Oval pits with a deep central cleftOats (m) 23 19 1) deep oval pits, some with a central longitudinal cleft,

some with circular central depression2) nests of oval pits, either flat and big, or deep with a

central star-shaped cleftWheat (m) 29 9 Expanded flat pit of irregular shapeBarley (m) 34 8 Big oval pits with one or several central depressionsMillet (h) 33 3 Flat pits of variable size with several small depressions

1 b, bioshop, ground in mill with korund-ceramics; m, ground in historical mill; h, ground in modern household mill.


cycles, particularly if the rates of abrasion are veryhigh. In vivo studies by Teaford and Oyen (1989)and Teaford and Lytle (1996) came to the conclusionthat microwear may have a complete turnoverwithin days, hours, or only minutes under certainconditions, which holds especially for scratches. Tea-ford (1988, 1991) also provided evidence that pitdimensions are not significant discriminators be-

tween different diets or archaeological sites, but hewas able to find different degrees of variation in theaverage pit width. In other words, the simulated pitsdescribed in our study were produced under con-trolled conditions by a single cereal species only.Clearly, such a situation does not hold for in vivoconditions when people live on mixed diets. Accord-ingly, pit size will not serve as a valid diagnosticfeature that can discriminate between different ce-reals in the diet that caused the feature. However,we cannot exclude that a gradual change of pit sizescould be diagnostic for a gradual change, e.g., incereal processing and food preparing methods. Onthe other hand, inspection of pit morphology is muchmore promising in this regard. Certain pit shapeswere clearly restricted to individual cereal species(Table 3). This is largely due to cereal bracts whichare known for their incorporation of large quantities

Fig. 9. Arrow: occlusal 3 cervical. a: High-resolution SEMimage (3700) of a typical pit produced by spelt, processed accord-ing to historical milling technique (by Prof. Wanner, BotanicalInstitute, University of Munchen). b: High-resolution SEM image(32,000) of a typical pit produced by rye, with a deep dentral cleft(arrowheads) (by Prof. Wanner, Botanical Institute, University ofMunchen).

Fig. 10. Arrow: baccal4 lingual. a: Phytolith, type not iden-tified, on the enamel surface of a medieval upper second molar(young adult female), at the end of a deep scratch. b: Phytolith,type not identified (arrow), on the enamel surface of a medievallower second molar (young adult female), surrounded by pits.


of silica bodies of characteristic shape (Kaplan et al.,1992; Miller Rosen, 1992; Ball et al., 1996).

The identification of at least one opal phytolith onevery archaeological tooth inspected was surprisingfor two reasons: first, the occurrence of opal phyto-liths on human dental enamel was previously de-scribed by two other investigations only (LaluezaFox and Perez-Perez, 1994; Lalueza Fox et al.,1996b), and there are again only two other reports ofopal phytoliths present in human dental calculus(Middleton, 1993; Holt, 1993). Normally, most ofthese particles should be lost in the course of themastication process. Second, the archaeological

skeletons investigated by us had been subject to acommon cleaning procedure right after excavation,and the phytoliths fixed into the enamel obviouslywithstood the brushing, although we cannot excludethat some of them were indeed lost and thus not allof them were still preserved on the enamel.

Intact phytoliths preserved on the enamel of ar-chaeological teeth may be of great value in terms ofthe exclusion of certain cereals for that particularfeature. Although it was not possible to subclassifyall preserved phytoliths into the IIa and IIb groups,or into the IIa1-3 or IIb1-2 subgroups according toKaplan et al. (1992), others were clearly undamagedand therefore identifiable. For instance, in fourcases phytoliths of the type IIb2 (taxonomy afterKaplan et al., 1992) were identified, which havebeen detected in rye and oats only, but not in othercereals like wheat, spelt, and barley, nor in emmernor einkorn, two important cereal species not yettested by us.

Characterstic pits produced by phytoliths can con-stitute a complete negative imprint of their causalagent in the ideal case (Fig. 10b), and should there-fore permit an exclusion principle in analogy to thediagnostic potential of preserved phytoliths them-selves. The majority of pits, however will be pro-duced by contact of phytoliths and other abrasiveparticles at different angles, which will leave lessspecific or unspecific microwear.

Several authors (e.g., Piperno, 1988; Pearsall,1989; Ball et al., 1996) have pointed out that adifferentiation of cereal species by opal phytolithswithin one genus (e.g., spelt, wheat, einkorn, andemmer) is possible only as long as the typologicalapproach is combined with a morphometric one, i.e.,a consistent consideration of both shape and size.Moreover, the same phytolith type may occur inmore than one cereal species (redundance), and sev-eral phytolith types may be found within the samespecies (multiplicity). Therefore, absence of a certainphytolith type is less a sufficient criterion for deter-mination of the species of cereals than its presence.Consequently, the detection of microwear pits whichreally reflect size and shape of the causing phytolithmust be a rare event. Also, the respective phytolithmust have hit the enamel surface both with theappropriate impact force and at an ideal impactangle. Our simulation experiment has shown that,though rarely, these ideal circumstances are met insome cases. Perhaps this problem may find a solu-tion in analogy to many other morphometric ap-proaches, where the diagnostic criterion is given bysize and shape analysis of a considerably high num-ber of features due to normal biological variability.At present, we are not yet capable of estimating theprobable proportion of characteristic pits among allpits produced.

CONCLUSIONS

Although the simulation experiment is only agross approximation to natural conditions because

Fig. 11. Comparison of pit sizes (major and minor axes in mm)produced by the simulation (a) and on medieval molars (b).


the food mushes consisted of only single cereal spe-cies each, these controlled conditions led to the de-tection of specific microwear pits related to the phy-tolith content in different types of cereals. While theanalysis of pit size and shape permits a clear differ-entiation between highly purified cereal flour andflour with a considerable proportion of silica bodiesleft, characteristic pit shapes suggest that pits maybe used to diagnose the specific cereals that wereconsumed. This diagnosis should be possible by theexclusion principle, but there is some hope that theconsumption of certain cereals could also be deter-mined. While phytoliths impacted on the enamel ofarchaeological human teeth and microscopic pits ob-servable on those teeth may be equally diagnostic ofdiet, archaeological dental microwear is a very com-plex phenomenon because of mixed cereal diets andcereal impurities (weeds). Also, the detailed influ-ence of mill debris in the flour must be further eval-uated. Our ongoing research thus focuses on a fur-ther refinement of the simulation process, and ascanning of prehistoric and historic human teeth ofpopulations from well-defined time horizons and en-vironmental settings. Besides the evaluation ofmore details concerning ancient subsistence behav-ior, valuable information about tooth wear related todietary behavior is expected, which is of equal im-portance for physical anthropology and modern den-tistry. Simulation experiments are therefore suit-able to unravel microwear formation processes.

ACKNOWLEDGMENTS

We are most indebted to Prof. Dr. H.-J. Kuster,Institute of Geobotany, University of Hannover, forhis advice and abundant information on phytoliths.Many thanks to P.D. Dr. F. Runge, Institute of Phys-ical Geography, University of Paderborn, for thedetermination of silica content in the test cereals.Prof. Dr. G. Wanner, Botanical Institute, University

of Munchen, provided access to the high-resolutionSEM. We thank Dipl. Stat. A. Grobmeyer, Instituteof Anthropology and Human Genetics, University ofMunchen, for his statistical advice. Many thanksalso go to three anonymous referees for their helpfulcomments.

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Wheat (m) 8.10p10201 5.59p10202 4.25p10201 1.03p10201 5.38p10202

Barley (m) 5.02p10202 6.18p10201 8.85p10202 5.45p10202

Millet (h) 1.04p10202 7.29p10201 5.96p10201

Spelt (m) 2.07p10202 7.32p10203

Oats (m) 9.18p10201

1 b, bioshop, ground in mill with korund-ceramics; m, ground in historical mill; h, ground in modern household mill; shaded areas,significant differences on a level of significance of 1%.


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Simulation of dental microwear: Characteristic traces by opal phytoliths give clues to ancient human dietary behavior