International Endodontic Journal (\9i6) 19, 194-197

A method of measuring the volume of human dental pulpcavities

K, B, ¥ KNABXJIKY:) \ Department of Oral Surgery, The Dental School, University ofNewcastle upon Tyne, Framlington Place, Newcastle upon Tyne

Summary, A method of measuring the volume ofthe human dental pulp cavity is described.

The crown of an extracted tooth is divided fromits root. .After cleaning the pulp cavity, it is filledwith an elastomer, and the fractured tooth surfacesrepositioned before the elastomer sets.

The tooth is corroded in acid to release theelastomer which is then weighed, and its volumecalculated.

The method has been applied to representativesof each human tooth type, and mean values aregiven.

IntroductionA knowledge of the dimensions of the humandental ptilp cavity is of importance to theclinician practising endodontics and otherprocedures in conservative dentistry, tostudents of oral anatomy and to researchworkers measuring temperature changes indental tissues. The size, shape and ana-tomical variations of the pulp cavity havebeen extensively described in the literature;however, the volume has not been previouslyreported.

In 1925, Hess presented a comprehensivehistorical background in his book andreviewed the work of previous authors,among which were Carabelli's (1844) descrip-tion of root canal variations, Preiswerk's(1908) metal corrosion preparations whichshowed the complicated pattern of the canalsfor the first time, the celluloid moulds of thepulp cavity prepared by Fischer (1908), themolten metal injection technique of Adloff(1913) and the Indian ink preparation ofMoral (1914). Hess (1925) himself investi-gated the shape of root canals of permanent

Correspondence: Mr Kersi B. Fanibunda, Depart-ment of Oral Surgery, The Dental School, Univer-sity of Newcastle upon Tyne, Framlington Place,Newcastle upon Tyne, NE2 4BW, UK,

teeth by reproducing them in vulcanizedrubber. Davis et al. (1972) studied the mor-phology of endodontieally prepared rootcanals, using an injectible silicone impressionmaterial. Barker et ,al. (1973) cut a channelthrough to the pulp chamber, injected aradio-opaque elastomer into the cavity andtook radiographs from various aspects. Theyalso reproduced translucent replicas of teethin clear resin, in which the pulp cavities wereinjected with red resin. Fisher et al. (1975)also gained entrance into the pulp chambervia an access cavity, prepared a dyed repro-duction of the pulp space in resin and pos-itioned it within a transparent tinted outertooth structure, Robertson et al. (1980) des-cribed a method which made the tooth trans-parent and then, via an access cavity, injectedIndia ink into the pulp chamber to outline theroot canals,

A major criticism of the techniques pre-viously reported is that part of the pulpal wallwas destroyed by grinding the teeth, or bycutting an access channel into the pulpchamber. The object of this paper is to describea method which preserved the integrity of thepulpal walls and at the same time producedan accurate replica, so that not only could thevolume of the pulp cavity be measured, but alsoits anatomical variations could be appreciated.

Materials and methodsTen teeth of each human tooth type werechosen, making a total of 160 teeth. The cri-teria for selection were that they should befreshly extracted, non-carious, fully formedpermanent teeth without undue attrition.

A ringed groove was sawn around thecrown, using a rotating disc, just coronal tothe amelo-cemental junction, without expos-

194

Measuring human dental pulp cavities 195

ing the pulp chamber. The root was thenheld firmly in a vice and the crown broken offwith a pair of pliers. A fracture of the toothproduced in this manner ensured that whenthe two pieces were realigned, an accurateapposition of the jagged crown and rootsurface took place, without any lateralmovement.

The two pieces were then immersed in asolution of 20 volumes hydrogen peroxide forapproximately 7-10 days, to facilitate removalof the pulp; when instruments were used insome cases to remove the pulpal residue, carewas taken not to scratch the pulpal walls. Thecrown and root were next thoroughly irri-gated with copious quantities of saline toremove all traces of hydrogen peroxide andthen dried.

An empty disposable injection syringebarrel with its needle end sawn off, or a trans-parent plastic cylinder of a diameter slightlylarger than an average molar tooth wasselected. The apical half of the fracturedtooth was partially inserted in one end andsealed with plasticine so that its fracturedsurface was visible externally; a vacuumpump was connected to the opposite end ofthe cylinder (Fig. 1).

A mix of Silastic E RTV mould-makingrubber^ was subjected to a vacuum of apressure of less than 20 mm of mercury toeliminate trapped air. It was then introducedinto the pulp chamber of the apical half of theroot piece and by means of the vacuum pro-vided from the opposite end of the cylinder,the mix was drawn through the root canal andapical foramen (Fig. 1). The vacuum wasmaintained until all the air from the pulpcavity was systematically removed and theSilastic extruded from the apical foramen. Insome instances when narrow pulp canals werepresent, this procedure took as long as 20-25minutes. The shallow roof of the pulpchamber in the crown portion of the dividedtooth was next filled with the mix and thecrown vibrated to exclude air bubbles.

The fractured surfaces of the crown androot were next repositioned together accu-rately and maintained in position by means ofa spring clip for 72 hours in a warm place, to* Dow Corning Corporation, Midland, Michigan,USA.

Fig. 1. The apical half of the fractured tooth wassealed with plasticine at one end of the transparentcylinder and a vacuum pump connected to itsopposite end. The Silastie mix whieh was drawnthrough from its coronal side to the apical foramenis demonstrated.

allow the mix to set in the enclosed pulpspace. The tooth was then corroded in a sol-ution of 50 per cent hydrochloric acid for 24hours and the resultant Silastic replica wascarefully washed with water (Fig, 2).

If the crown and root fragments had beenaccurately aligned, a negligible excess ofSilastic was found at the junction. This wasflaked off carefully with a knife and the speci-men was then examined for air bubbles, Astereo-magnifier (x 30) was employed forboth these procedures. The specimen wasnext weighed and its mass was divided bythe density of the Silastic (1.12), thus givingthe volume of the pulp cavity according to the

mequation: v = —.

dEach Silastic replica was then cut into slices

196 K. B. Eanihunda

Table I. Mean volume (mm^) and standarddeviation (SD) of dental pulp cavities

Fig. 2. Silastic replicas of the pulp cavities of(left to right) mandibular canine, first premolarand second premolar. Markings aie shown inmillimetres.

at 1 mm intervals and examined under thestereomagnifier for the presence of air bubblesand if any were found, the specimen wasdiscarded; approximately 20 per cent of thereplicas were eliminated from the study forthis reason.

In order to eliminate any untoward effectof acid on the Silastic, three specimens of therubber material were weighed before andafter immersion in 50 per cent hydrochloricacid for 24 hours.

The minimal size of the pulp cavity wasappreciated by comparing it with the volumeof a drop of water. A 21G hypodermic needlewas attached to a 1 ml syringe filled with dis-tilled water and the plunger depressed withthe barrel held vertically, until a drop ofwater detached itself from the tip of theneedle. Ten drops of water thus obtainedwere weighed individually.

ResultsThe mean volumes of the pulp cavities of 10teeth oi each tooth type w ere calculated andthe results of the maxillary and mandibularteeth are shown in Table I.

Following immersion of the three speci-mens of Silastic in 50 per cent hydrochloricacid for the same length of time as in the

Tooth tvpe

Central incisorLateral incisorCanineFirst premolarSecond premolarFirst molarSecond molarThird molar

Maxillary

Mean

12.411.414.718,216.568,244,322,6

SD

3.34,64.85,14.2

21.429,7

Mandibular

Mean

6.17.1

14.214.914.952.5.̂ 2.931.1

SD

2.52.15.45.76.38.58.4

11.2

experiment, it was found that no significantloss of weight was detected.

The mean weight of one drop of water wasfound to be 12.2 mg with a standard deviationof 0,26 mg. The drop therefore had a volumeof 12.2 ^

DiscussionThe study illustrates a simple and inexpens-ive means of measuring the volume of dentalpulp cavities; by virtue of the selection cri-teria for the specimens, extremes of age wereexcluded. The measurement of pulpal volumehas hitherto been an unknown quantity andfactors such as heredity and secondary den-tine complicate its standardization. Thisvariation was reflected by the high standarddeviation (Table I) obtained in this sample often teeth of each tooth type.

To appreciate the small volume of the pulpcavity, the average volume of a drop of waterobtained under the conditions specified wassimilar to the average volume of the pulpcavity of an upper central incisor in thisseries. It was interesting to note that themaxillary first molar pulp cavity showed thelargest average volume followed by the man-dibular molar, while the lower central incisorpulp cavity showed the smallest volumemeasurement.

The method of fracturing the tooth nearthe amelo-cemental junction facilitated accessinto the cavity and at the same time preservedthe integrity of the inner pulpal surface.

When the apposition of the crown and rootpieces was accurate, a negligible excess ofSilastic appeared at its junction. Althoughthis excess was easily trimmed with a knife, itcould have been a possible source of error inmeasurement, Silastic was a very suitablematerial as far as reproduction of detail, avail-able working time and resistance to tear wereconcerned. The presence of trapped air in theset material was minimized by following themanufacturer's instructions rigidly and bydiscarding the mould if bubbles were foundiri .the slices after weighing.

In conclusion, an accurate replica of thepulp cavity provides the clinician and studentw ith an appreciation of the dimensions of acomplex root canal system. In addition, themethod described furnishes information onpulpal volume, a previously unreported aspect.

AcknowledgementsI wish to thank Mr W, G, Wright and MrE, Alderson, Newcastle upon Tyne DentalSchool for their technical assistance and MrM. Gross, Newcastle upon Tyne DentalSchool, for his advice on the water dropexperiment.

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Measuring human dental pulp cavities 197

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