Special Report

Graphic assessment of interincisal point movements during chewing ofhard and soft foodsSrdjan D. Postic* / Milos V. Teodosijevic** / Mirjana S. Krstic***

Interincisai point movetrtents in 35 healthy, dentate subjects were investigated with anelectrognathie apparatus. The main focus of the study was to find the average values ofdetermined point graphic assesst?wnt in fronted and sagittal planes during chewing ofhard and soft foods. However, as this was insufficient to obtain information on areaswhere ocdu.sal contacts were reached, border movement envelopes were also recorded toobtain indirect information in connection to the previous task. The results showed thatthe graphic assessment form of mandihular movements was dependent on the consisten-cy of the food that was chewed. (Quintessence Int 1991:22:623-630.)

Introduction

Graphic assessment of determined point movementson the mandible is frequently used to comprehendspecific characteristics of the chewing mechanism—one of the particularly individual and vital functionsof the stomatognathic system.

Several authors' '" have noticed that the graphic as-sessment form of mandibular movements is modifiedduring the mastication of different kinds of (bod: thisclearly indicates the connection between the chewingpattern and the consistency of the food.

Some authors^ * have indicated that it may be betterto study habitual chewing, which we accepted as thestarting point in this study. The present investigationis based on the assumption that the analysis of habit-ual chewing is possibly the most appropriate way tofind out the role of certain stomatognathic structures,such as muscles, in everyday chewing, in addition, thestudy of habitual chewing eliminates the infiuence ofcortical control on the chewing automation and the

Assistant Professor, Departmenl of Prosthodontics, Universilyof Belgrade, School of Dentistry, Dr Subotica 8, 11 ÜÜO Bel-grade, Yugoslavia.Colonel, Yugoslavian Army. Head, Departmenl of Gnathol-ogy, Cmotravaska 17, l i 000 Belgrade, Yugoslavia.Professor, Department of Prosthodontics, School of Dentistry,University of Beigrade.

redistribution of muscular activity that is probablygenerated during deliberate or unilateral chewing.Similar conclusions have been presented in the worksof Stohler" and Mongini,'- who recorded bioelectricalmuscular activity parallel to movement recording ofthe interincisal point.

The electrognathic apparatus, whose function isbased on the principle of recording the magnetic fiuxchanges, has proved to be useful for this kind of re-search, because it enables monitoring of the deter-mined point on the mandible in the planes selec-ted.^--'

This study attempts to determine the areas in whichthe movements of chewing hard and soft food takeplace.

Method and materiais

The subjects of this investigation were 35 undergrad-uate and postgraduate students from the School ofDentistry, University of Belgrade. The sample includ-ed 17 women and 18 men aged 20 to 28 years; themean age was 24 years 5 months. All subjects selectedhad a full complement of teeth (irrespective of thethird molars); an Angle Class i occlusion confirmedclinically and with lateral cephalometric radiographs(the mean point A-nasion-point B angle was 2.7 de-grees); no signs of stomatognathic system dysfunctionrecorded in the medical history and in clinical exam-

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Fig 1 Sirognathograph sensors in position. Fig 2 Magnet attached to the teeth.

ination; no clinically detectable pathologic findings;and no history of orthodontic treatment.

The subjects chewed two test substances: peanuts(about 4 g) and equally sized pieces of soft, whitebread (a roll).

Mandibniar movements were recorded by a Sirog-nathograph (Siemens Dental Div) (Fig 1). Informa-tion obtained from the changes in the magnetic fieldwere tratismitted through the analogue computer toan x-y recorder (575 OEM Recorder, Esterline Angus).

Each subject was comfortably seated in a dentalchair and asked to maintain the same head positionwhile performing border and habitual chewing move-ments.

The magnet was attached to the interincisal area byautopolymerizing resin (S, Palavit, G. Kuhzer & Co)and fixed by temporary cement (Temp-bond, Kerr/Sybron Corp). Tbe magnet was placed parallel to theFrankfort plane and free from interference of the op-posing teeth during functional mandibular movements(Fig 2). To define the impact of the teeth contacts inthe initial and terminal phases of the chewing cycle,the subjects were asked to move tbeir mandible fromcentric occlusion to maximal right and maximal leftpositions, and to glide the teeth over each other in thenormal manner. They were also asked to perform glid-ing movement from centric occlusion to maximal pro-truded position and then from centric occlusion toretruded contact position.

The subjects were instructed to hold their teeth incentric occlusion a few seconds before chewing, andalso after swallowing the food. After that, the sensoryarray was attached and adjusted to the subject's head.The volunteers performed mandibuiar border move-

ments first and then tbe chewing movements. The testsof chewing bard and soft foods were conducted sep-arately. Dislocation of tbe sensing device was cbeckedby inspection. A masticatory sequence included allactions from the intake of food to swallowing.

For tbe analysis and presentation of the data ob-tained, projections of interincisal point movement infrontal (Figs 3 and 4) and sagittal planes (Figs 5 and6) have been selected. Because the magnification se-lected on the x-y plotter was 2:1, all measured valueswere divided hy 2 before the statistical analysis to getexact values.

Approaching determination of the envelope of bor-der movements, projections of interincisal point spa-tial shifting were analyzed at four different levels, ex-cept for maximal left and maximal right points infrontal pattern, as well as for retruded contact positionand the completion of terminal hinge movement onsagittal projection, which are analyzed separately onthe graphic assessment. To determine the envelopes ofthe chewing sequences, chewing patterns of all thesubjects were analyzed at different low levels, exceptfor the points where occlusal contacts were reached,which were analyzed independently of those levels(Fig 7).

Results

Border movement envelopes

Movement projections of the left and right jaw open-ings are shown in Figs 8 and 9, Statistically significantdifference existed at the first level in favor of the leftmovement (Table 1). The x values were greaicr on the

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Fig 3 Tracing obtained in the frontal plane while the sub-ject was eating peanuts: (1) mastication of hard lood; (L)left side; (ñ) right side.

Fig 4 (right) Tracing obtained in the frontal plane whilethe subject was eating a roll: (2) mastication of soft food;(arrows) direction of interincisal point movements.

Fig 5 Tracing obtained in the sagittal plane while the sub-ject was eating peanuts: (1) mastication of hard food; (ar-rows) direction of interincisal point movements.

Fig 6 (above rigfit) Tracing obtained in the sagittal planewhile the subject was eating a roll: (2) mastication of softfood; (arrows) direction of interincisal point movements.

Fig 7 A method of analyzing an envelope of chewing se-quences.

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Figs 8 to 11 Green represents the mean envelope of border movemenis; yellow represents the mean envelope ol _ ;eatory sequences; borizontai yellow and green lines represent tbe reliability interval of x values for p = ,95 (x ¿ >< ><< X -I- 2 x), and vertical biue and purpie lines represent the reliability interval of y values for P = .95 (y ' 2 y < y _ y

Fig 8 Superimposition of mean envelope ot hard loodchewing sequences onto the mean envelope ot bordermovements in tbe frontal plane (in mm), (CO) Centric oc-clusion.

Fig 9 Superimposition ot mean envelope ot soft foodchewing sequences onto the mean enveiope of bordermovements in the frontal plane (in mm), (CO) Centric oc-ciusion.

Fig ID Superimposition of mean envelope ot hard foodchewing sequences onto the mean envelope of bordermovements In the sagittal plane (in mm). (CO) Centric oc-clusion; (RCP) retruded contact position.

Fig 11 Superimposition of mean envelope of soft toodchewing seqtjenees onto the mean envelope of bordermovements in the sagittai plane (in mm), (CO) Centric oc-ciusion; (RCP) retruded contact position.

Table 1 Test of equality of means (/ test) for bordermovements (mm)

Level X Left-right

2.477*1.3590.5341,061

Level = level of max iMom and i bular separation in mm.• P < .05.

left side up to half of the mandibular opening tnove-ment and became higher later during the jaw openingto the right side, but these differences were not statis-tically significant.

The envelope of border movements in the sagittalplane is presented in Figs 10 and 11

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Envelopes oj ehewing sequences

In the frontal plane, the y values on the left side weresignificantly greater during the chewing of soft food.Horizontal distances x were almost the same, butsomewhat greater at the beginning of the chewingcycle for soft food. From level 6, these values wereshghtly higher during chewing of hard food. Thesedifferences were not statistically significant, except atlevel 3 (Tahle 2).

The y value was considerably greater on the rightside in favor of soft food. The horizontal distance xwas consistently greater during chewing of soft food,but these differences were statistically significant onlyat levels 2, 3, and 4,

In the sagittal plane, y values of front border en-velopes of masticatory sequences were significantlygreater during the chewing of soft food. The x valueswere significantly different at levels 5, 6, and 7,

At the posterior envelope of masticatory sequences,both X and y values were higher, but for x values thisdifference was statistically significant at levels 8 and9, and for y values it was statistically significatit at alllevels.

Areas of oeelusal contact

Frontal projection of areas where occlusal contactswere reached are shown, together with teeth glidinglengths, in Figs 12 and 13. The projections of areas inthe sagittal plane where teeth contacts were estab-lished, as well as the teeth gliding length, are shownin Figs 14 and 15,

Statistical analysis of values for areas of occlusalcontact is shown in Tables 3 and 4,

Discussion

The mandible approaches centric occlusion positionin the terminal phase of closing. During this move-ment, the occlusal contacts on the working side areusually established,'-''^•'^•"•'' Because the subjects in thepresent study used more or less both sides during thechewing of hard and soft foods, the contacts on boththe left and right sides were recorded. In this way, theresults of this study confirmed earher reports that, inhumans, habitual chewing is usually bilateral,"'^

The frontal projection analysis of areas in whichocclusal contacts occur during chewing of hard foodrevealed that the y values were somewhat higher onthe right side. Thus, this area is situated lower on the

Table 2 Test of equality of means (( test) for chewingof hard and soft foods (mm)

LevelX

123456789

10

y

Level ='P <

*'P <'"P <

Left-left

0,2941.8282.266*1.6371,5091.6300,8680,1690,8840,2263.889***

Right-right

1,2862,618**2.446*2.164*1.6981.4740,9181,1080,3510,4003,434**

level of masillomandibnlar,05,,01.,001,

Forward-forward

0,4620,0500.2051,2843.657***5.774***7.888***1.4581,7321,7193,052**

Backward-backward

0.1860.3790,0000,3050.4430,7121,3132,554***2.049*1.6743.312**

separation in inm.

graphic assessment than is the same area on the leftside, which means that the first teeth contacts oc-curred on the right side. This result is in accordancewith the statement that "a general preference for right-sided chewing exists, often expressed in the first chew-ing cycle,"" Values of x coordinates on the left sidewere somewhat higher than the same values on theright side.

During chewing of soft food, the areas of occlusalcontact had, in fact, identical coordinates on the leftand right sides.

Frontal projection of the average glide lengths was1,2 mm during chewing of hard food and ahout 1 mmduring chewing of soft food, which approaches thevalues measured by Hildebrand,^^ Gibbs and Lun-deen,' and Pröschel et al,̂

The average glide length in sagittal projection wasabout 1 mm in front during chewing of hard food andabout 0,8 during chewing of soft food. Because thevalues in sagittal projection were lower than those inthe front, teeth contacts recorded in front of the axisz were mostly attributed to laterotrusive movementand not to the contact of the incisal edges of man-dibular incisors with lingual surfaces of maxillaryteeth, as might be concluded from the graphic assess-ment at first sight.

The longesf contact glide occurred during chewingof hard food, confirming observations of Neill and

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Fig 12 Magnified segment of Fig 8. White crosses repre-sent areas of occlusal contact. (CO) Centric occlusion.

Fig 13 Magnified segment of Fig 9. White crosses repre-sent areas of occlusal contact. (CO) Centric occlusion.

Livrr 9 'JWBWlfiffBBÜ^

-• + 3 2 l ( ^

1 1 1 1 N ^...JüJiiJiiiluüiiiiiliiiiüiiiuiiuii'ilinLui

RCP/^

/y U i

I3.d,-i.H3

,¡.Jl i 3 4 5lUlüliüllUlllUllllllllllltlIllllilliltlIlllllllUlUi:

Fig 14 Magnified segment of Fig 10. White cross repre-sents area of occlusal contact. (00) Centric occlusion;(RCP) retruded contact posilion.

Fig 15 Magnified segment of Fig 11. White cross repre-sents area of occlusal contact. (00) Centric occlusion;(RCP) retruded contact position.

Table 3 Test of equality of means (r test) for areasof occlusal contact (mm)

Table 4 Test of equahty of means (t test) for areasof occlusal contact (mm)

Hardfood

RightLeft

Soft food

Right

X y

0.059 0.607

Left

X

0.264

y

0.057

Hardfood

ForwardBackward

Soft food

Forward

X y

1.082 0.344

Backward

X y

L711 0.000

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However, in the present study, we recordedthe projected gliding lengths, and not the real lengths,which are probably longer.

Mandibular chewing movernents are modified in ac-cordance with the forces that will be used for crushingfood and softening the bolus. It seems reasonable tbatfor hard food a stronger force is needed, so that theclosing movements are directed more vertically in re-lation to the position in which crushing of food willtake place. Soft food requires weaker chewing forces,which results in a mandibular approach to centralocclusion from a more lateral direction.

Food consistency determined the envelope of chew-ing movements. During occlusal phases, soft food waschewed with a smaller number of movements resultingin smaller teeth gliding projections than those duringchewing of hard food. In all other parts of the graphicassessment in both frontal and sagittal planes (exceptfor levels 1, 2, and 3 in tbe sagittal plane), the averagemovement values were lower during chewing of softfood. In our opinion, tbe difference was the result notonly of the food consistency, but also of the differencein bolus size.

Envelopes of movement in the frontal plane were,especiaily during chewing of soft food, slightly locatedto the left in the lower part. This finding was, accord-ing to our interpretation and also to the interpretafionof the subjects, the result of the way the bolus is movedfrom the right to the left side and vice versa.

The direction of mandibular movement was clock-wise in the majority of single chewing cycles, whenthe right side was working, and counterclockwisewhen the left side was working.

The projection of interincisal point movement in thesagittal plane during the jaw opening can be located

ante nor- or posterior" to the closingmovement. In tbe present study, both possibilities wererecorded. All opening and closing movements wereanterior to the terminal hinge border, indicating thatchewing movements of hard and soft foods did nothave the characteristics of the hinge-rotary move-ments. Retruded contact position did not prove to bethe funcfional position during chewing and swallow-ing of the food.

Conclusion

Projections of interincisal point movements in the se-lected planes during habitual chewing can be success-fully used for the assessment of chewing hehavior.Food consistency affects envelopes of chewing se-

quences us well as teeth gliding length; this indirectlyindicates the possibility that stomatognatbic muscleshave various roles in performing concrete mandibularmovements.

We think that the combination of graphic assess-ment of tbe determined point movements on mandibleand electromyography could offer more precise an-swers to questions concerning stomatognathic func-tions.

References

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2. Miîuno K: A study of the masticatory stroke at a near part ofintercuäpal position, Aichi-Gakuin Daigaku Shigakki Shi 1980;17:259-283.

3. Gibbs CH, Lundeen HC: Advances in Occlusion. Boston, WrightPSG Inc, 1982, pp 2-32.

4. I>win A: Eleetrognattiographics. Chicago, Quintessence PublCo, 1985.

5. Pröschel P, Hofmann M, Ott R: Zur Orthofunktion des Kau-organs. Dtsch Zuhnärztt Z 1985;40:186-19t.

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8. Neill DJ, Howell PGT: A study of mastication in dentate in-dividuals. Int J Prosthodont 1988;l:93-98

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It. Stobler CS: A comparative electromyograpbic and kinesiograph-ic study of deliberate and habitual mastication in man. ArchOrat Biol 1986;31:659-678.

12. Mongini F, Tempi a-Valen ta G, Benvegnu G: Computer basedassessment of habitual mastication. J Prosthet Dent 1986;55:638-649.

13. Jankelson B, Swain CS, Crane PF, el al: Kinesiometric instru-mentation: a new technology. J Am Dent Assoc 1975; 90:834-840.

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19, Mai-iiyamii T, Kuwabura T, Nakamaura Y, et al: A new man-dibular movement recording and analysing system composed ofsirognathograph and a personal computer, and its clinical sp-plicatioti, / Osaka Utiiv Dent Sch I9B4;24:97-111,

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