Dental Erosion Industry - A BMJ journal · Dental Erosion in Industry H. J. TEN BRUGGENCATE Fromthe Turner Dental School, University ofManchester Five hundred and fifty-five acid

Brit. J. industr. Med., i968, 25, 249.

Dental Erosion in IndustryH. J. TEN BRUGGEN CATE

From the Turner Dental School, University of Manchester

Five hundred and fifty-five acid workers were examined between March I962 and October I964.One hundred and seventy-six (3I-7%) were affected by industrial dental erosion at the first examinations.In 33 cases (6-o%) the dentine was affected. During the period of the survey, 66 (20o4%) of 324 workersexamined more than once showed evidence that erosion was progressing. The prevalence and incidenceof erosion were highest among battery formation workers, lower among picklers, and least among otherprocesses covered by the survey. The age of workers did not appear to influence their susceptibility toerosion. The habit of working with the lips slightly parted had little effect. Erosion superimposed upon

attrition predisposed to more severe loss of tooth structure than either operating alone. Little inconvenienceor functional disability was suffered by acid workers due to erosion. Twenty-seven (23 7%) of 114 erosionswere considered to be disfiguring. Regular dental treatment was sought less by acid workers than bycontrols, and the oral hygiene of the latter was superior. There was no evidence to show any differencebetween caries experience among acid workers and controls. Calculus and periodontal disease were more

prevalent among acid workers than among controls, but it was not possible to attribute this to the workingenvironment. Black staining in iron picklers was considered to be due to the working environment. Theuse of closed acid containers or lip extraction on open acid vats prevented significant atmospheric con-

tamination and diminished the prevalence of erosion. The use of wall fans and detergent foaming agentswas helpful.

In I960 the Industrial Diseases Sub-committeeof the Industrial Injuries Advisory Council con-sidered the question whether dental erosion, due toacids used in industry, should be prescribed underthe National Insurance (Industrial Injuries) Act1946. Owing to the inadequacy of evidenceconcerning the prevalence of dental erosion, theCommittee was unable to reach a conclusion.

In March I959 the British Dental Associationpresented a Memorandum to the Council whichconcluded: 'that industrial dental erosion was ahazard which existed, and that in the majority ofcases severe dental damage, resulting in disfigure-ment, occurred.' The need for further researchinto the pattern and causes of dental erosion inindustry was pointed out. Oral evidence was heardfrom the Association of Industrial Medical Officers.

In the last 20 years, published reports of industrialdental erosion have been limited to observations onthe effects of nitric and sulphuric acids at a RoyalOrdnance Factory (Lynch and Bell, 1947), tartaricacid (Elsbury, Browne, and Boyes, I95i) and

sulphuric acid as used in the manufacture of lead-acid electric storage batteries (Malcolm and Paul,196I; Paul, I962).The work of Malcolm and Paul is of most interest

as it covers a group of 84 workers who had naturalteeth. The group was employed under modernconditions. Oral evidence of these observations wasgiven to the Industrial Diseases Sub-committee.

In i960, information on industrial dental erosionwas confined to isolated studies, often carried outon workers employed under abnormal conditionsby modern standards. In view of the lack of dataon the prevalence of the condition in modernindustrial environments, it was recommended thata field survey be undertaken to provide the Com-mittee with this evidence.The objectives of the survey were to determine:

(i) the prevalence of industrial dental erosion, withparticular reference to certain industrial processes;(2) the severity of the condition in those affected;(3) the rapidity of onset and advance; and (4) theextent of dental treatment sought and the degree ofinconvenience, disfigurement or functional dis-ability suffered by those affected.

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H. J. ten Bruggen Cate

Duration of Survey

The work of Malcolm and Paul (I96I) andPaul (I962) agreed with older reports in so far aserosion might become retarded or even static, onclinical examination, once a certain level relative tothe position of the lips had been reached. Mostreports have indicated that industrial erosionaffected incisors and occasionally canine teeth;premolar and molar teeth were never affected. Onlythe labial surfaces which did not normally makecontact with the lips were involved, and surfacesprotected by the lips and cheeks were not attacked.Thus it appeared that severe erosion which had

developed under poor working environments,perhaps many years ago, could have becomeretarded or even static as the lip line was reachedor as industrial conditions improved. It was clearthat a single examination of workers, relatingseverity of erosion to duration of employment withacids, would give a picture of the prevalence oferosion which was not representative of modemworking conditions. If it may be assumed thatindustrial environments in this country haveimproved, it might be that erosion now takes longerto develop or indeed may not occur at all.

It was therefore essential to observe a group ofworkers who were representative of modemindustrial conditions over a span of time. Thisperiod had to be sufficiently long to determinewhich cases were static and which were progressingwhatever the degree of erosion at the outset. Whilea long-term survey would give the most preciseinformation, it also depended on workers andconditions remaining unchanged. This seemedunlikely, and early answers to the questions posedwere required. It was therefore decided to examineworkers four times at intervals of eight months,thus allowing a period of two years' observation.

Method

It was decided to conduct the survey in three distinctmajor industrial areas. These were Manchester,Glasgow, and Wolverhampton. H.M. Factory Inspector-ate in these areas prepared lists of firms that itconsidered suitable for the survey. An attempt wasmade to include a range of industrial processes anda variety of firms, some using modem equipment andsome older works. By this means it was hoped toachieve as true a cross section of industry as possible.In some cases the Inspectorate tended to put forwardthose firms which were known to be likely to co-operate;the effect of this bias on the results of the survey cannotbe assessed.The Inspectorate informed all firms that had been

selected, and, following this preliminary notice of the

survey, the managements were approached by theauthor, through the firm's medical officers wherepossible, by means of an explanatory letter requestingco-operation.Twenty-four firms were approached in the Manchester

area, including three in Liverpool; io firms wereapproached in Glasgow and 39 in the Wolverhamptonarea, including one in Birmingham. Seventy per centof Manchester firms, all Glasgow firms, and 80% ofWolverhampton firms replied to the explanatory letter.A small number of firms which replied no longeroperated acid processes. These and firms which hadnot replied were discarded. Of the remainder, 96%hagreed to take part in the survey. The three firms inLiverpool and the single firm in Birmingham wereincluded because the Inspectorate felt that the processesoperated might be of particular interest.The number of factories visited in each area and the

total number of workers exposed to acids, includingedentulous workers, are shown in Table I.

TABLE IDISTRIBUTION OF FIRMS AND EXPOSED WORKERS

AMONG THE AREAS

Area No. of Firms No. of Workers

Manchester 17 2I2Glasgow 8 io8Wolverhampton 23 463

Total 48 783

Control Workers All control workers came fromacid-free departments of the firms participating in thesurvey. No worker was accepted as a control if he hadat any time worked with acid in any previous employ-ment. Considerable difficulty was experienced inobtaining sufficient workers to act as controls.Managements were inclined to make available

as controls workers from the younger, unskilledapprentice section of the labour force. Skilled workers,making up the older age groups, could not easily bespared without loss of production, as many of theprocesses required integrated team work. Rarely werewhole departments of men available to act as controls.Controls were taken from the same socio-economicgroups as exposed workers. Office staff, though oftenavailable, were avoided. The age difference betweenthe exposed group and the control group was noted(Fig. i). Although the latter was a satisfactory controlwhen factors where age plays no part were considered,its validity when age was known to be a factor influencingthe experience of disease, for example periodontaldisease, was doubtful.

All control workers were found to be free fromindustrial dental erosion. Controls were examined onlyonce, and it must be admitted that over the two-yearperiod in which exposed employees were observed, somedeterioration in the dental condition of the controls

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Dental Erosion in Industry

a

Manchester (158)

50-

0

Glasgow (60)

Wolverhampto

IS 253n15 25 35

Age (years)

200-

150'

100

5(

4)

-0

TABLE IIDISTRIBUTION OF CONTROL FiRMs AND WoRKERs

AMONG THE AREAS

Area No. of Firms No. of Workers

Manchester I 67Glasgow I 38Wolverhampton 5 I88

TotalI 7 293Total | 7 293

)n (337) Edentulous Workers Thirty-eight per cent ofworkers exposed to acid examined at the first visit to allfirms were edentulous. Although some of these workerswere able to describe the conditions of their teeth priorto extraction, and it was clear from some of thesedescriptions that the teeth had been eroded, it was notpossible to conclude that erosion had been the reasonfor the extractions. No control edentulous group was

i 45 5 65 found to be possible. The evidence of the edentulousworkers was not reliable, and edentulous workers were

excluded from the results of the survey.

Wastage ofWorkers It was found that a number of1 acid (555) workers examined once or more were not available at

follow-up visits to their firms. This wastage was dueto normal labour turnover, redundancy, take-overs offirms resulting in closures, and transfer of workers tonon-acid processes. New workers were included in thesurvey at the second, third, and fourth visits to factoriesand, although these employees did not have the durationof exposure to acid of the workers lost by wastage whomthey replaced, they did help to provide information aboutthe early stages of erosion.The distribution of all workers having natural anterior

teeth seen throughout the survey is shown in Table III.

I50-

100*

50

Control (293)

Is 25Age (years)

35 45 55 65

FIG. i. Number of acid workers and controls in five agedivisions.

could not be ruled out. However, since at the time ofeamnination 67% of the controls had been in theiremployment more than two years, and some had lengthsof service of up to 35 years, it was thought most unlikelythat any erosion could develop in the group during thesurvey period. The distribution of control firms andworkers is shown in Table II. No edentulous controlswere examined.

TABLE IIIDISTRIBUTION OF ALL WORKERS HAVING NATURAL

ANTERIOR TEETH AMONG THE AREAS

Area No. of Workers

Manchester .. .. ..I58Glasgow .. .. .. .. 6oWolverhampton .. .. .. 337

Total . .. . ..555

Examination of Workers At the first examinationof each worker a history was taken with personal partic-ulars and details of employment. Observations were

made on the degree of erosion, and an assessment was

made of the caries experience and periodontal conditionof the anterior teeth. At the first and subsequent visitsa colour transparency was made, using Kodachrome II

daylight film, with standardized lighting provided by

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H. J. ten Bruggen Cateannular flash equipment. At all follow-up visits thedegree of erosion was assessed from clinical examination,and changes in conditions of employment were noted.Transparencies were used to show advancing erosionswithin particular grades of erosion. The grade oferosion was based on clinical observation alone.Examination of workers began in March I962 and

was completed in October I964. Table IV shows theproportion of workers examined once, twice, threetimes, and four times over the survey period.

TABLE IVPROPORTION OF ACID WORKERS ExAMINED AT

I, 2, 3, and 4 VISITS TO FIRMS

Time of No. of % ofNo. of Observation Workers TotalVisits (months) Examined Workers

I 231 4I 62 8 95 17.I3 i6 55 II*84 24 I64 29*5

Acid Processes Covered by Survey The acidprocesses on which exposed workers were engaged areshown in Table V. It should be noted that a number ofmen fell into more than one process category; forexample, a man might work as a pickler and as a plater.Some firms were engaged on more than one processinvolving acids.

The Clinical Picture in IndustrialDental Erosion

Industrial erosion first affected the surfaces ofthe teeth most exposed to the atmosphere. Thesewere the incisal one-third to one-half of the labialsurfaces of the incisor teeth. The canine teeth

were rarely affected and then generally only on thelabial surfaces nearest the midline. No erosion oftheposterior teeth was seen during this survey.The first sign of industrial erosion has been

described as an etching of the inciso-labial surfaces;the appearance has been likened to ground glass.This was seen as an early sign in a number ofworkers, though not in every case that becameaffected.As the condition progressed, loss of labial incisal

enamel was observed. The enamel surface acquireda smoother, polished, rounded appearance thougha few cases still retained the etched surface. Asthe enamel was eroded, an anterior open bitesometimes developed.When the process had advanced to involvement

of dentine, the dentine became stained but was notmore rapidly eroded than enamel. The mostsevere cases showed erosion to the level of secondarydentine, but pulpal exposure was not observed.The labial surface was always worst affected so

that in severe cases all labial enamel was missingand the dentine was extensively involved. Thelabial surfaces sloped away obliquely towards thelingual. The protective influence of the lips andcheeks has been stressed by Malcolm and Paul(I96I). In mildly affected teeth the etched or erodedsurfaces corresponded to the opening between thelips when slightly parted. The shape of the spacebetween the upper and lower teeth, when erosionhad caused anterior open bite, similarly reflectedthe position of the lips. The pattern of erosion wassometimes modified when attrition of the teeth wasevident.

Pain was very rarely reported and, when present,was described as a hypersensitivity to cold,especially when brushing. Of all 555 workers ex-amined, five reported pain for which erosion was

TABLE VAcm PROCESSES ON WHICH EXPOSED WORKERS WERE EMPLOYED: NUMBER OF FIRMS ANt ACIDS USED

Process Acids No. of Firms No. of Workers

Plating Chromic, nitric, sulphuric, hydrofluoric, phosphoric 9 114Galvanizing Hydrochloric, sulphuric 17 II4Other acid pickling Hydrochloric, nitric, sulphuric, hydrofluoric 13 231Battery manufacture Sulphuric 3 90Sanitary cleanser manufacture Acid sodium sulphate I 25Munitions manufacture Nitric, sulphuric I I2Sulphuric acid and Sulfan manufacture Sulphuric I I ISoft drinks manufacture Citric I 5Process engraving Nitric I 4Crystal glassworks Hydrofluoric I 2Dyestuffs container cleaning Hydrochloric I 7Enamel manufacture Sulphuric, hydrochloric I I

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considered to be the cause. In each case therewere either rapidly advancing or extensive erosions.However, most progressing and severe erosionswere painless.

Erosion lesions had rounded margins. This was

a consistent sign and may be regarded as. diagnosticof industrial erosion from airborne acids, whensevere loss of structure is confined to the anteriorteeth. With loss of tooth structure from mechanicalwear, as seen in attrition and abrasion, sharplydefined margins are evident. Teeth which have beenfractured also show sharp margins. Erosions causedby dietary constituents, for example citrus fruits,affect all the teeth rather than the labio-incisalsurfaces affected by airborne acid. The loss ofstructure seen in dental caries occurs in thestagnation areas between the teeth, near thegingival margin and in fissures, and is characterizedby softening and cavitation. In contrast, industrialerosion lesions occur on exposed surfaces and are

hard and convex without cavitation.

The Classification of Industrial DentalErosion

Malcolm and Paul (I96i) observed that any

estimation of the degree of erosion must besubjective, since the original dimensions of theteeth are not known. Nevertheless they divided thedegrees of erosion into etching of the enamel surfaceand three groups of erosion, based on an estimateof tooth loss deduced from an assumed size oftooth crown. In their group i, this loss did notexceed one fifth (2 mm.) of the incisal enamel; ingroup 2 there was loss of one-fifth to one-half of thetooth crown; and in group 3 there was loss of morethan half of the tooth crown.

It was considered that this classification was

unsatisfactory because it is difficult to estimate lossby subtracting the remaining tooth substance fromassumed dimensions for the original crown.

Secondly, the transition from group i to group 2

could not easily be defined. Therefore a broadclassification based on the tissues involved was

adopted as follows:Definition of grades of erosion (Fig. 2)Etching (Et)

This consisted of a dull, ground-glass appear-ance of the enamel surface without loss ofcontour (Plates i and 2)

Grade i erosion (G.ii)Loss of enamel only (Plates 3 and 4)

Grade 2 erosion (G.2)Loss of enamel with involvement of dentine(Plates 5 and 6)

DentinettDental pulp

ETCHING Enamel

GRADE 2

:~I secondaryI dentinc

253

GRADE I

,. f

GRADE 3

I,,'I

FIG. 2. The classification of erosion.

Grade 3 erosion (G.3)Loss of enamel and dentine with exposure ofsecondary dentine (Plates 7, 8, and 9)

Grade 4 erosion (G.4)Loss of enamel and dentine resulting in pulpalexposure

Results

Prevalence of Erosion The degree of erosionwas noted at the first examination of each workerand, where several grades were apparent in differentteeth in the same mouth, the case was graded bythe erosion seen in the most severely affected tooth.The prevalence of erosion, found at the firstexamination of all workers, is shown for the groupsof exposed and control workers in Table VI.No case of grade 4 erosion was observed, although

Lynch and Bell (i947) and Malcolm and Paul (I96I)each reported such a case. It was likely that painwould lead to early treatment of grade 4 erosion, inmost cases by extraction. The chances of such a

case being encountered, at one of four examinationsor less in two years, were slight.

Battery Formation Process The battery form-ation process has been described in detail byMalcolm and Paul (I96I). Battery formation andcharging workers were the subject of theirinvestigation. Two large and one small firm,engaged in the manufacture of lead-acid electricstorage batteries by a similar process, were includedin the present survey.Lead plates were placed vertically in tanks and

connected up to make an electrical circuit by means

of lead bars, which were tacked on to the plates




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H. . ten Bruggen Cate

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COLOUR PLATE I. Etching of inciso-labial surfaces of central incisors: battery formation worker after 7 years' service.

COLOUR PLATE 2. Etching of inciso-labial surfaces of central incisors: galvanizing worker after ii months' service.

COLOUR PLATE 3. Polished, rounded appearance of grade I erosion: acid dipper with 9 years' service in a Royal Ordnancefactory.

COLOUR PLATE 4. Same case as in 3: lateral view.

COLOUR PLATE 5. Grade 2 erosion with staining of dentine: battery formation worker after 8 years' service.

COLOUR PLATE 6. Same case as in plate 5: lateral view.

COLOUR PLATE 7. Grade 3 erosion and anterior open bite: galvanizing pickler with IO years' service.

COLOUR PLATE 8. Same case as in 7: occlusal view showing involvement of secondary dentine.

COLOUR PLATE 9. Grade 3 erosion, black staining, and anterior open bite: galvanizing pickler after IO years' service.

COLOUR PLATE IO. Grade 3 erosion: battery formation worker with I9 years' service. There was a marked overbite and attritionon the palatal surfaces of the upper central incisors.

COLOUR PLATE II. Same case as in Io: closed position showing overbite.

COLOUR PLATE I2. Black stain pattern: worker engaged on 'wheeling out' pickled work. This case had 3 months' service, hadan open lip habit, and did not clean the teeth.

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TABLE VIPREVALENCE OF INDUSTRIAL EROSION AMONG GROUPS AT FIRST EXAMINATION

Grade Manchester Glasgow Wolverhampton Total Control

Negative io6 67.I% 3I 517% 242 7I.8% 379 68-3% 293 100%Et 2I 13.3% io I6.7% 50 14-8% 8I I4.6%G.I 20 I2.7% io I6.7% 32 9 5% 62 II-2% _G.2 9 5 7% 4 6 7% 10 3 0% 23 4-I%G.3 2 I.3% 5 8 3% 3 0-9% Io i8% -

The number of workers affected by each grade is shown, and also expressed as a percentage of the workers in that group.

with a blow torch. The tanks were filled withdilute sulphuric acid, the specific gravity varyingbetween I O2 and i-i5. A current was then passedwhich charged or 'formed' the plates. This causedsmall bubbles of hydrogen to be given off. Thebubbles rise rapidly to the acid surface and burst,causing a fine acid mist. This mist is capable ofcausing severe dental erosion.

It was noticeable that men working in thecharging departments and some inspection workersshowed less erosion than formation workers. Thereis less acid in the atmosphere of charging depart-ments as the completed batteries have lids, whereasthe tanks in the formation process are open.Malcolm and Paul estimated that the atmosphericsulphuric acid load in their charging departmentwas of the order of one-quarter to one-fifth that inthe formation department. There are also depart-ments concerned with 'dry charging' of plates; thisprocedure involves the removal of acid from theplates by washing, dipping in paraffin, and drying.The prevalence of erosion at the first examination

of all workers in formation departments is shown inTable VII. Charging and inspection workers arealso shown. Some of these workers had beenemployed for only short periods and showedprogressive erosion at subsequent examinations.Almost 20% of formation workers showed grade

2 or grade 3 erosion in the combined figures of the

TABLE VIIPREVALENCE OF EROSION AT FIRST EXAMINATIONAMONG 70 BATTERY FORMATION WORKERS AND

I6 CHARGING AND INSPECTION WORKERS

No. of WorkersGrade ,

Formation Charging/InspectionNegative 28 IIEt I8 2G.I II 3G.2 10G.3 3

two larger firms. The smaller firm did not operatea night shift and the work was so arranged that theforming took place at night in the absence of theworkers. No erosion was observed in this firm, butit should be added that no worker had beenemployed for longer than I4 months.

Galvanizing Hot dip galvanizing consists ofcoating clean iron surfaces with zinc in order toprotect the surface from rusting. The acid used toclean the iron was usually hydrochloric thoughsulphuric was occasionally employed.Depending upon the type of work being treated,

the metal was pickled in hydrochloric acid whichvaried in strength from commercial concentratedacid (28 Twaddell') diluted i :i with water todilutions of I: 3 acid to water. Hydrochloric acidwas generally used at room temperature, so thatfume was worse in summer. Sulphuric acid wasgenerally used at 6o0C. at concentrations of up toio%. Hydrochloric acid is volatile and may be lostto the atmosphere by fuming, even when the surfaceof the acid is still. Sulphuric acid is not volatile tothis extent and is only lost to the atmosphere whenthe acid surface is disturbed as, for example, withthe bubbling that takes place in battery formation.The above higher temperature of sulphuric aciddoes not greatly predispose to fuming; however,raising the temperature of hydrochloric and nitricacid increases fuming considerably.

After the work had been cleaned by pickling inthe acid bath, it was washed and dried and thenpassed over to the molten zinc bath to be dipped.Considerable fume arose from the zinc bath, asammonium salts were added to act as a flux, but it isunlikely that this had any eroding effect on the teeth.The prevalence of erosion at the first examinations

of all men working in galvanizing shops is shown in

'Twaddell is a hydrometer scale used in the United

Kingdom (Specific Gravity = I + 200 )Standard temperature of scale is 6o0F.

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Table VIII. Workers employed on stages of theprocess other than pickling, for example, zincdipping or wheeling work out, will be referred to as'non-picklers'.

TABLE VIIIPREVALENCE OF EROSION AMONG 72 PICKLERS AND35 NON-PICKLERS AT FIRST EXAMINATIONS, IN

GALVANIZING SHOPS

Picklers Non-picklersGrade

No. of % of No. of % ofWorkers Total Workers Total

Negative 31 431I 28 8o-oEt I8 25-0 3 8-6G.I I6 22 2 3 8-6G.2 3 4-2 I 2-9G.3 4 5-6

It was observed that 20% of non-picklers wereaffected by erosion, compared with 57% of thepicklers. The latter were more affected in all grades,including etching, and it is considered that thehigher prevalence is due to more direct contactwith acid. Of all galvanizing workers, 7 5% wereaffected by grade 2 or grade 3 erosion, comparedwith 20% among battery formation workers.

Other Pickling Treatments This was a group ofprocesses which involved the etching or cleaning ofmetal surfaces prior to a variety of treatments.Sulphuric and hydrochloric acids were generallyused, though nitric and hydrofluoric acids wereemployed for stripping or descaling purposes. Thiswas a widely scattered group, and the degree ofexposure to acids of workers varied considerablyamong processes. The only common factor amongthe workers was that they were picklers, not in thegalvanizing process. The group was designated'non-galvanizing picklers', and the prevalence oferosion among the workers is shown in Table IX.

TABLE IXPREVALENCE OF EROSION AMONG I32 NON-GALVANIZING

PICKLERS

Grade No. of Workers % of Total

Negative 94 7I *2Et 20 15.2G.I I6 12-IG.2 I o-8G.3 o-8

On comparison with Table VIII it appears thatgalvanizing picklers suffered more erosion than thenon-galvanizing picklers. However, the lengths ofservice of a number of the latter group were short.For example, whereas only four out of 30 galvan-izing picklers had less than one year's service inWolverhampton, the figure for non-galvanizingpicklers in that district was 52 out of I02. It isclear that Tables VIII and IX are not strictlycomparable. The influence of length of service onthe prevalence of erosion will be discussed underthe section on rate of erosion.

Plating This category covered workers inchrome and nickel plating, cadmium plating, andspecialized zinc plating. Metal surfaces weregenerally acid etched prior to plating. The platingsolutions themselves were acidified; for example,in chrome plating, chromic acid with one part ofconcentrated sulphuric acid added per hundredparts of chromic acid was used.Both hydrochloric and sulphuric acids were used

for etching. The range of concentrations for theformer acid was 3 2%-50% commercial con-centrated acid, and for sulphuric acid 5.2%-65%.For normal chrome plating of steels the chromicacid concentration varied between 250 and 500 g.per litre with several firms using 450 g. per litre.Specialized solutions were used to etch and platealloys.

TABLE XPREVALENCE OF EROSION AMONG 76 PLATING WORKERS:

PREVALENCE AMONG 34 CHROME PLATERS SHOWNSEPARATELY

All Platers Chrome PlatersGrade

No. of % of No. of % ofWorkers Total Workers Total

Negative 65 85-5 30 88-2Et 7 9-2 2 5.9G.i 4 5.3 2 5-9G.2 - - -

G.3 -

The prevalence of erosion among all platingworkers is shown in Table X. Chrome platersincluded in this total are also shown separately, asthey make up almost half the total.

It was noted that the prevalence among platerswas low compared with all classes of picklers. Thestandard of fume extraction in shops using chromicacid was high, because of the risks peculiar to

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chromic acid. Some firms operated fully automaticprocesses, so that employees were exposed to acidonly when replenishment of a tank was required orin the event of the occasional breakdown.

It will be understood that the terms plater andpickler have been handed down in industry andthey are used to cover men engaged on variousprocesses, which involve greatly differing degreesof exposure to acid. It is useless to try to definea standard pickler, and broad groups are inevitable.

Other Processes Each remaining process wasobserved at one factory only. The prevalence oferosion among workers is shown in Table XI.

TABLE XIPREVALENCE OF EROSION AMONG REMAINING WORKERS

No. of WorkersProcess

Total -ve Et G.I G.2 G.3

Munitions manufacture 12 7 I I I 2Sulphuric acid and Sulfan

manufacture II I - - - -Sanitary cleansermanufacture 25 19 3 2 -

Soft drinks manufacture 5 4 I - - -Process engraving 4 4 - - - -Crystal glassworks 2 2 - - - -Enamel manufacture I I - - - -Dyestuffs container cleaning 7 I 3 3 -

The Rapidity of Onset and Advanceof Erosion

Association between Length of Service andDegree of Erosion Attention has already beendrawn to the errors of correlating the length ofservice in acid environments with the degree oferosion seen at a single examination. It wasnecessary to examine workers on at least twooccasions, in order to establish whether erosionwas static or advancing, or whether the conditionoccurred at all under modem industrial environ-ments.

Nevertheless, there did appear to be a relation-ship between erosion experience and length ofservice, as found at a single examination. This isshown in Figure 3. Workers were divided into Iolengths of service divisions', and the percentage of

100

4,

0304c

L"I

91-

0 5Length of service (years)

FIG. 3. The relationship between degree of erosion, at firstexamination of 555 acid workers, and length of service.

workers in each division who were free of erosionor showed etching, or grade I, 2, or 3 erosion wasdetermined. The proportion of negative casesreduced as the length of service increased. Etchingincreased to a peak in the 2-5 years service divisionand then fell off, while grade i cases appearedfrom four to six months and the proportion ofworkers affected by this grade increased steadily.Grade 2 cases first appeared in the 2-5 years servicedivision and the proportion increased steadily,while the earliest grade 3 cases occurred in the6-io years division. It should be noted that thenumber of grade 3 cases seen was small, and it wasalso found that the relationship did not hold goodin workers with more than 20 years' service. Itseems likely that this was due to the increasingproportion of static erosions.

Proportion of Cases Observed to beAdvancing Erosions During the two-year periodof the survey, of the 379 workers unaffected at theirfirst examinations (Table VI), 32 advanced to showetching and five of these progressed further tograde i. A further seven workers advanced tograde I, etching being unobserved. Thus 12workers in all progressed from negative to grade i.Of the 8I cases exhibiting etching at the first

examinations, seven advanced to grade i. Noworkers were observed to advance into the moresevere grades 2 and 3, but progressing erosion wasdetected in a number of cases within the limits ofthe grades in which these cases were classified attheir first examinations. Thus progressing erosion,but without grade advancement, occurred in eightcases of etching, seven cases of grade i, four casesof grade 2, and in a single case of grade 3.

'Length of service divisions were: 0-3 months, 4-6months, 7-I2 months, 13-24 months, 2-5 years, 6-io years,11-20 years, 21-30 years, 31-40 years, more than 40 years.

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TABLE XIIDISTRIBUTION AND PROPORTION OF WORKERS SHOWING PROGRESSING EROSION

Extent of Progress of Erosion Observed Manchester Glasgow Wolverhampton Total

Negative to etching .. .. .. .. 6 2 I9 27Negative to grade I .. .. .. .. 4 I 7 I2Etching to grade I .. .. .. .. - 7 7Progress within etching grade .. .. .. 2 - 6 8Progressing erosion within G.I .. .. .. - 6 7Progressing erosion within G.2 .. .. I - 3 4Progressing erosion within G.3 .. ..- I

No. of workers showing progressing erosion .4.4 3 49 66No. of workers examined more than once .. 83 32 209 324Proportion showing progressing erosion .. | 168% 98% 234% 204%

The distribution and proportion of workersshowing progressing erosion are shown inTable XII.

Occupations of Workers showing Progress-ing Erosion The occupations of the 66 workersshowing progressing erosions are shown in TableXIII. The proportion of workers showing activeerosion who were examined more than once isindicated.

It was noted that 5o% of battery formationworkers, examined more than once, showed activeerosion. The figure for galvanizing picklers was

24-5% and for non-galvanizing picklers 22-3%.All other occupations taken together showed 7.3%of employees affected by active erosion.These results supported the prevalence figures,

in that the battery formation process is the mostlikely to produce dental erosion. Furthermore,

these results are based on cases actually observedto advance under modem industrial environmentalconditions. Thus the incidence of erosion is highestamong battery formation workers, lower amonggalvanizing and other picklers, and lowest amongworkers on other processes. Analysis of the otherprocesses was of no value, as there were but IO cases

showing active erosion in total, and these were

widely scattered.

Earliest Cases of Erosion Five cases ofetching developed within three months' exposure,and a further IO cases within six months. Theearliest case was in a battery formation workerafter five weeks' service.

Eight cases of grade i erosion occurred withini8 months' exposure. Of these the earliest was

within six months and two further cases withinnine months.

.E XIII

OCCUPATIONS IN FOUR CATEGORIES OF 66 WORKERS SHOWING ACTIVE EROSION, AND THE PROPORTION OF WORKERS,SHOWING ACTIVE EROSION, IN THE OCCUPATIONS

Occupations (no. of workers)

Extent of Progress of Erosion BatteryFormation Galvanizing Non-galvanizing OtherWorkers Picklers Picklers Processes

Negative to etching .. .. .. 5 5 12 5Negative to G.i .. .. 5 I 4 2Etching to G.I .. .. .. 3 I 2 IProgress within etching grade .. 3 I 2 2Progressing erosion within G. I .. .. 4 2 I -

Progressing erosion within G.2.. .. .. 4 - -

Progressing erosion within G.3 .. .. I - -

No. of workers showing progressing erosion.. 24 II 2I 10No. of workers examined more than once .. 48 45 94 I37Proportion showing progressing erosion .. 50% 245% 22-3% 7 3%

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The earliest cases ofgrade 2 erosion were observedin two workers who had two-and-a-half years'service and in two further workers who each hadfive years' service.

Grade 3 erosion was encountered in only IOcases, and the earliest observed was in a workerwho had six years' service.

The Value of a Prospective Survey

It is interesting to compare Table VI withTable XII. Table VI shows the prevalence oferosion, based on a single examination, or cross-sectional survey. The prevalence of erosion wassimilar in Manchester and Wolverhampton workers,though the small number of grade 2 and grade 3cases must be stressed. However, the Tableindicates a higher prevalence in Glasgow, althoughthe sample of workers was smaller.

It was noted from Fig. 4 that the Glasgow grouphad greater lengths of service in acid environmentsthan the Manchester and Wolverhampton groups.It was possible that some of the severe erosions seenin Glasgow were long-established cases, perhapscaused by less satisfactory working environmentsthan are found today; indeed these cases may havebeen clinically static.

Table XII is based on several examinations ofworkers, i.e., a prospective survey reflecting presentindustrial working conditions. It can be seen thatthe Glasgow group shows the lowest proportion ofadvancing cases, even though the cross-sectional

10

0

a

Gla ssgow

Length of service (years)

assessment by Table VI shows the highestprevalence.During the survey the author spoke to many

workers who considered that working environmentshad been greatly improved while they had beenemployed by their firms. Erosion may be muchreduced or even eliminated by the installation ofefficient exhaust systems, redesign of equipmentso that acid is remote from workers, or the improve-ment of raw materials, for example the quality ofsteel from modem rolling mills, so that weaker acidcan be used for treatments.Although a relationship has been shown between

length of service and degree of erosion in a cross-sectional survey, a prospective assessment gives amore reliable picture of erosion under modemconditions.

The Influence of Age on Erosion

It has been shown that the permeability of enameldecreases with age, particularly in the third decade(Atkinson, I947). This may have some influenceon erosion. To test this, the first three age groups(Fig. i) were compared. Clearly, workers in theolder age groups would tend to show more erosionthan younger workers because the latter cannothave such long lengths of service. Therefore it wasnecessary to study the degree of erosion in eachlength of service division of every age group. Therewas no evidence to suggest that erosion affects oneage group more or less than another (ten BruggenCate, I966).

loo, b

'Total acid

50 , .,

1 A

0110 20 30 40

Length of service (years)

FIG. 4. The number of workers in each length of service category. This is also expressed as a proportion of thegroup total.

2

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The Role of Attrition

Attrition is a mechanical wearing down of theocclusal, incisal, and proximal surfaces of the teethduring masticatory movements, resulting in polishedfacets having sharp margins. Severe attrition mayoccur from the habit, known as Bruxism, of grind-ing the teeth during sleep.

Attrition was noted in 7I cases (I2-8%) of acidworkers and in 22 cases (7-5%) of control workers.Table XIV shows the degree of erosion in the7I attrited acid workers and indicates the proportionthey represented of all workers in their erosiongrades. The Table is based on the first examinationof each worker.

TABLE XIVNUMBER AND PROPORTION OF WORKERS SHOWING

ATTRITION IN EACH GRADE OF EROSION

Degree of Erosion

Negative Et IG.i G.2 G.3I ~I

Total no. of workers 379 8i 62 23 10No. of workers showing

attrition 32 4 I4 I4 7Proportion as % show-

ing attrition 8-5 4-9 22-7 60-9 70-0

It was noted that the prevalence of attritionincreased strikingly among workers suffering themore severe grades of erosion. Furthermore, it wasfound that nine cases (I3-6%) of the 66 workerswho showed advancing erosion during the surveyexhibited attrition.There is reason to believe that workers having

attrition, or a marked overbite (both may occur

through the loss of posterior teeth), develop erosion,particularly of the lower incisors, to a more severedegree than workers without these occlusalcharacteristics (Plates io and ii).

In some workers with grade 3 erosion, an anterioropen bite had developed, so that there was a spacecorresponding to the opening between the lips,between the upper and lower anterior teeth. Inthese cases the eroded teeth could not be broughtinto contact, and attrition could not play a part inthe loss of tooth substance (Plates 7 and 9).The enamel of acid-eroded teeth is abnormally

fragile at the surface, judging by extracted teeththat have been kept moist, sectioned, and polishedfor histological examination. The author has theimpression that acid-eroded enamel is more easilyattrited than normal enamel; attrition and erosion

operating together may cause more rapid loss oftooth structure than either operating alone.The cases showing severe loss of tooth structure

in the presence of a marked overbite resembled the'chisel' type erosions described by Malcolm andPaul (i96i).

The Influence of Lip Posture

Many workers with normal lip postures and withteeth that were considered to be in a normalrelationship to the lips (i.e., not prominent) werefound to work with their lips apart. It was likelythat acid workers breathed through their mouths,when the acid level in the atmosphere became sohigh that nose breathing became unpleasant.Workers were questioned about this matter, andan examination of the lips in the rest position wasalso made. An attempt was made to divide theworkers into those having open lip habits and thosewith closed lip postures. The degree of erosion wascompared between the two groups, and it was foundthat the habit of working with the lips slightlyparted did not greatly influence the likelihood oferosion developing. It is pointed out that very fewmen had prominent teeth with short upper lips;the latter may predispose to erosion.The number and proportion of open lip habits

among exposed, eroded, and control workers areshown in Table XV.

TABLE XVNUMBER AND PROPORTION OF OPEN LiP POSTURESAMONG ExPoSED, ERODED, AND CONTROL WORKERS

Acid WorkersLip Posture All Acid Showing Control

Workers Erosion WorkersNo. % No. % No. %

Open 107 19*5 51I 24-0 99 33 8Closed 441 8i.5 I62 76-o I94 66-2

Seven Indian Wolverhampton workers could not beassessed because of language difficulties.

Comparison of Environments ProducingActive Erosion with Those having No Effect

Although all workers were not equally affectedby any one environment, it was reasonable topostulate that erosion became more prevalent as theatmospheric acid load increased. An attempt wasmade to test this by comparing the workingenvironments of two groups of men.

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The first group having active erosion was madeup of the 66 workers showing active erosion duringthe survey period and any other workers showingerosion with not more than two years' service, evenif examined only once. It was assumed for thepurpose of this comparison that the latter had activeerosion. Confirmed static erosions were ignored.By this means an 'active erosion' group of io6workers was collected.The group of men used for comparison with the

active group consisted of those workers who hadbeen examined at least twice and showed no

progression and of whom none had less than twoyears' service. Thus it could not reasonably beargued that as a group they had less exposure thanthe active group and might have developed erosionafter longer exposure. This unaffected group

numbered i i6 workers.These groups were considered to be representative

of industrial conditions as found between I960 andI964.

Exhaust and ventilation methods were dividedinto the categories of lip extraction, consisting ofan exhaust system drawing fume into an opening

around the lip of the acid vat and preventing escapeinto the atmosphere; roof or wall fans, whichoperated to remove air containing acid fume fromthe atmosphere of the work place; and naturalventilation. The latter depended upon the sidesof the building containing the acid being open;natural ventilation relied upon weather conditions.Some of the common combinations of acid

concentrations and related exhaust methods seenduring the survey are shown in Table XVI. Itcan be seen that in general the complexity andefficiency of exhaust and ventilation systems arerelated to the concentration and temperature ofthe acid. Thus, if there was heavy emission of fume,lip extraction was usually employed; if little fumewas given off, roof fans or natural ventilation wereregarded as adequate by most managements.The influence of single factors on the number of

active erosions and unaffected cases is shown inthe upper half of Table XVII. The influence ofmore than one factor is shown in the lower half.The number of part-time workers and those

employed near acid, though not directly involved,is indicated by each total.

TABLE XVIRELATION BETWEEN CONCENTRATION OF ACID AND PREVENTIVE MEASURES, TO LOWER THE ATMOSPHERIC ACID LEVEL

Dilutions Temperature ('C.) Preventive Measures

Sulphuric Acid Commercial conc. (95%)Pure .. R.T. Completely enclosed65%0 R.T. No fan, but remote from menI8% . R.T. Wall fans and Zeromist'15% 6o Lip extractionI2%0 8o Lip extraction8-12 . .. .. 65 Lip extraction7% .. .. .. .. 65 Lip extraction10% .. 65 Wall fans2-5% .. .. .. .. .. .. 6o Wall fansIo% .. .. .. .. .. R.T. Roof fans3-5% .. .. .. .. .. .. R.T. No fans, but Zeromist

Hydrochloric Acid Commercial 28 Tw. (28 Twaddell is approx. 28%)28 Tw. undiluted .. .. .. .. .. R.T. Lip extraction and ZeromistAcid: water = I: I .. .. .. .. .. R.T. Lip extraction and lids

I: 15 .. .. .. .. R.T. Lip extractionI: 2 .. .. .. .. R.T. Lip extraction or wall fansI:3 .. .. .. .. R.T. Wall fans1:3 .. .. .. .. R.T. Open air, no fansI: 4 .. .. R.T. No fans, often roof ventilationI:5.. R.T. No fans or ventilation

Nitric Acid Commercial conc. (70%)22% .. .. .. .. .. .. .. R.T. Enclosing exhaust hoodIO% .. .. .. .. .. .. ..6o Lip extraction

R.T. room temperature.

'Zeromist is a product used to reduce loss from liquid surfaces due to evaporation, fuming, and spraying (see text).

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TABLE XVIIEFFECT OF ISOLATED FACTORS ON THE PREVALENCE OF EROSION IN Two GROUPS OF WORKERS

Active Erosion Teeth UnaffectedEnvironmental Common Factor ._l_l_I

Total Near Part Total Near PartAcid Time Acid Time

Hydrochloric acid .. .. .. .. .. 44 7 53 I9Sulphuricacid.. 52 2 I 57 9 2Nitric acid .. .. .. .. .. .. 3- 29 -

Chromic acid .. .. .. .. .. .. 4 - 21 3 -

Hot acid (over 6o'C.) I5 I 3 27 3 3Cold acid .. .. .. .. .. .. 9I 8 - 89 25 I

Lip extraction .. .. .. .. .. .. 23 5 I 69 i6 IRoof or wall fans .. .. . . .. 6o 4 I 52 I2 2No fans .. .. .. .. .. .. 37 3 2 25 3 2Natural ventilation .. .. .. .. .. - 69 23 3No natural ventilation.. .. .. .. .. 29 2 3 47 5 IMasks.. .. .. .. .. .. .. 10 - IO -

More than one common factorPickling cold hydrochloric acid .. .. .. 28 - - 20 -

Pickling hot sulphuric acid .. .. .. I I - - i8 - -

Cold hydrochloric acid with lip extraction .. 9 - 32 - -

Hot sulphuric acid with lip extraction .. I0 - - 14 - -

Lip extraction, fans, natural ventilation .. 7 - - _ 8 - -

No fans and no ventilation .. .. .. .. 2 - - 6 - -

It was observed that hydrochloric acid andsulphuric acid accounted for far more erosion casesthan nitric or chromic acids. Moreover, the propor-

tion of workers showing active erosion is higheramong those working with the former two acidsthan among those employed on work using thelatter acids. This was to be expected from resultson prevalence and rate of erosion; battery formationworkers (sulphuric) and picklers (hydrochloricand sulphuric) showed more erosion than platers.Chromic acid was seen to have been used in onlyfour instances of active erosion, and records showedthat these workers were also exposed to sulphuricand nitric acids. It has already been pointed outthat chrome plating production lines were oftenfully automatic and fume was particularly efficientlyextracted.The Table indicates that hot acid produced less

erosions than cold acids, group for group. This wasbecause battery formation and pickling withhydrochloric acid are carried out cold, and exhaustfacilities needed to be more effective with hot acidsas there was likely to be more fume.

It was also observed that when lip extraction was

operating the ratio of the number of workers show-ing active erosion to the number unaffected was

lower than when wall fans were used. In turn, theratio was lower in the presence of wall fans than intheir absence. Also, the presence of natural ventil-ation appeared to show a lower ratio than the'no fans' category. The odd finding that no naturalventilation showed less erosion than naturalventilation is explained by the fact that lipextraction or wall fans, or both, were operating inthe absence of natural ventilation.When more than one factor was compared, as

in the lower half of Table XVII, the sample ofworkers in each category decreased markedly. Thisproduced some bizarre results; for example, inpickling, hot sulphuric or cold hydrochloric acid isgenerally used, and it appeared that hydrochloricacid produced more erosion. However, when lipextraction was used with these acids (not only forpickling) the position was reversed and sulphuricacid appeared to produce more erosion. This cannotbe explained by the appearance of the batteryformation figures in the total for sulphuric acid(other than pickling) as lip extraction was not usedin formation tanks.Assuming that lip extraction systems result in

a lower atmospheric acid load than the use of wallfans and that the use of the latter keeps the load to

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reasonable proportions more effectively than naturalventilation, the ratio of active erosion to unaffectedcases for the three systems supports the postulate:i.e., erosion becomes more prevalent as the acidlevel in the atmosphere increases.

Otherwise the value of Table XVII is limited; itmay merely be concluded that few workers areemployed under conditions likely to produce rapid,severe erosion, and that extraction exhaust arrange-ments are usually geared to the magnitude of theacid hazard. The desirability of lip extractionsystems is clear.Mention should be made of surface tension

reducing agents in their application for the purposeof reducing acid mist. The product Zeromist isespecially designed for the purpose of reducingloss of liquids by evaporation, fuming, and spraying.Teepol is a detergent product having a similareffect but it is not specifically designed for thisindustrial application. Both products operate byforming a foam on the surface of the liquid, in thiscase acid, the foam trapping bubbles rising to thesurface causing spray and also preventing fumingand evaporation.The advantage of this system over exhaust

systems is that there is less loss of acid, whichwould otherwise require constant replenishment,exhaust equipment is not so quickly corroded, andthere is less pollution of the outside atmosphere.The medical officers of the two large battery

manufacturing firms considered that the workingenvironment of the formation departments hadgreatly improved with the introduction of theseproducts.

The Extent of Dental Treatment Soughtby Workers

Throughout the survey there was no evidence oftreatment to restore function or appearance toacid-eroded natural teeth. Thirty-three (6%) of555 workers showed erosion involving dentine(Table VI). Three workers having grade 3 erosionwere provided with full dentures in the surveyperiod.The restoration of grade 2 or grade 3 eroded

teeth requires the preparation of the teeth and theconstruction of faced inlays or jacket crowns.Conservative treatment of extreme cases involvesdevitalizing the teeth, root canal therapy, and thepreparation of post retained crowns. These pro-cedures are time-consuming and require precisionif the end result is to be of lasting service to thepatient.

It is certain that a number of workers were notinterested in this level of dental treatment; equally,

some were unaware that it was possible. To gaininformation on the dental awareness of workers,all were asked whether they attended a dentalsurgeon regularly, or if they consulted a dentalsurgeon solely for the relief of pain, when necessary.For this purpose an annual check-up was con-sidered as regular attendance.

It was found that 5 -I% of acid workers attendedregularly for treatment compared with 23-9% of thecontrol workers. The control group consisted ofyounger workers and these, particularly theapprentices, had a more enlightened attitude todental health. Nevertheless, there was still amarked difference between acid workers and controlsin the older age groups. Tooth brushing was alsomore regular among controls than among acid work-ers, though the disparity was less than that seen inthe figures for regular dental treatment.

The Degree of Inconvenience, Disfigurementor Functional Disability suffered by Acid

Workers

Inconvenience and disfigurement are subjectiveand cannot be measured by standards that applyto all workers. It is difficult to obtain informationwithout posing leading questions.

It was noticeable that some workers with obviouserosion were quite unconcerned about the appear-ance of the teeth, while others, with no erosion buthaving large, untreated carious lesions, expressedconcern and in some cases held their work respon-sible for their dental condition.

Inconvenience It has been mentioned thatin five cases acid workers reported hypersensitivityof the teeth to cold, and erosion was considered bythe author to be the cause. It was pointed out thatno evidence was observed of conservative proceduresto restore function or appearance to eroded teethand that the proportion of acid workers underregular dental care was 5I%. Therefore it maybe concluded that acid workers suffered littleinconvenience from toothache or from restorativetreatment, over and above normal requirements,that could be attributed to their workingenvironment.

Disfigurement Because of the wide variationin the attitude of workers to dental health andappearance, an attempt was made to measuredisfigurement by the author's personal assessment.This is necessarily subjective and it is possible thatsome cases classed as disfigurement would not beregarded as such by the workers concerned andvice versa.

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All workers showing grades I, 2 or 3 wereconsidered. The most recent photograph of theteeth in each case was examined and any teethshowing obvious loss of contour from erosion werecounted disfigured. For this purpose staining,attrition, poor oral hygiene or missing teeth wereignored.The number of workers showing disfigurement

according to this assessment is shown in TableXVIII. It was observed that of the 33 workers

TABLE XVIIINUMBER AND PROPORTION OF WORKERS SHOWINGDISFIGUREMENT IN EACH GRADE OF EROSION

Grade of Erosion

G.i G.2 G.3No. of workers showing disfigurement 2 I5 10No. considered .. .. .. 8i 23 IOProportion showing disfigurement (%) 2-5 65-2 IOO

having erosion to dentine, 25 were disfigured. Theremaining eight cases were early grade 2, or caseswith only the lower incisors affected and havinga pronounced overbite. The two workers disfiguredby grade i erosion were seen to have the entirelabial surface of the enamel of upper and lowerincisors affected. This was very rarely seen. Thus23 -7% of the erosions were classed as disfiguring.

Functional Disability Industrial erosion mayproduce functional disability because it sometimescauses the condition of anterior open bite. In thissituation the individual has a space in the verticaldimension, between the upper and lower incisorteeth when the posterior teeth are meeting. Thisspace is oval, corresponding to the lip opening(Plates 7 and 9). The anterior teeth cannot bebrought together and it is difficult to incise certainfoods, for example beef sandwiches.

Anterior open bite was produced by erosion inthree grade 2 and four grade 3 cases. It was difficultto determine the degree of functional disabilitysuffered by these seven workers, but the author hasthe impression that they overcame their difficultiesby using the canine teeth, and that little disabilitywas caused.

Dental Caries, Periodontal Disease, andStaining of the Teeth in Acid Workers

Dental Caries Acids are thought to play a

major part in the destruction of tooth substance seen

in dental caries. It is widely believed that at pHvalues below a critical level, depending partlyupon the concentration of calcium and phosphateions in the saliva, solution of the mineral salts ofthe enamel takes place. The critical level of pHvaries between 5-5 and 6 5, depending upon thesaliva (Jenkins, I966).

It was possible that the pH around the teeth ofacid workers was lowered by airborne acids and thatthese teeth might be particularly prone to attackby dental caries.The number of decayed, missing, and filled

incisor and canine teeth was recorded in eachworker. The premolar and molar teeth wereignored as it was impossible to diagnose inter-proximal caries in these teeth, under the conditionsin which workers were examined, at most firms.One hundred and thirty-seven acid workers

showing etching or erosion were compared withI95 controls. All workers in both groups had atleast two years' service. The groups were comparedby age divisions, and it was found that there wasno constant difference between acid workers andcontrols (ten Bruggen Cate, I966). It is concludedthat acid environments have no influence on cariesexperience.

Periodontal Disease Dental calculus isbelieved to be an important factor in the develop-ment of periodontal disease, and the compositionof calculus, though variable, always consists ofabout 8o% inorganic material containing calcium,magnesium, phosphate, and carbonate. As thisfraction would be soluble in acid, it was possiblethat periodontal disease might be less prevalentamong acid workers than among controls. It mustat once be stated that oral hygiene and regularscaling treatment will have a great influence, and ithas been shown that the control group was moreconscientious in these respects than the acidworkers.The same groups that were compared for caries

experience were assessed for the presence or absenceof calculus. The results did not indicate that lesscalculus is deposited around the teeth of workershaving etching or erosion: indeed they supportedthe reverse.The results were complicated by the high propor-

tion of coloured workers in Wolverhamptonengaged on acid work. These men had much morecalculus deposition than European workers.Furthermore, there was but a small proportion ofcoloured workers among the controls.

In order to make a more accurate comparison,only European workers out of the I37 acid workersshowing etching or erosion and the i95 controls

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were considered. It was found that acid workersstill showed more calculus deposition. Bearing inmind the unsatisfactory nature of the control group,because of the better oral hygiene, there seems tobe no evidence that calculus deposition increaseswith erosion, but it certainly does not decrease.A direct assessment of periodontal disease was

made at the first examinations of all workers. Noaccount was taken of change during the survey,because several workers improved their oral hygieneand periodontal condition following treatment,suggested by the author and carried out by localdental surgeons.The periodontal condition was graded according

to the degree of inflammation, stagnation, andpocketing around the teeth. Workers were classedas good, fair, poor, and bad.The results indicated that acid workers suffered

more periodontal disease than the controls(ten Bruggen Cate, I966). It was not possible toattribute this difference to the working environment,as differences in age and oral hygiene may have thesame effect.

Staining It was noticeable that many acidworkers, particularly picklers, complained of stain-ing of the teeth. The staining was seen on thesurfaces of the teeth that were not in contact withthe lips, i.e., the same exposed surfaces prone toerosion (Plate I2). When regular brushing wascarried out this stain was reduced or even confinedto the stagnation areas, in the crevices between theteeth, beyond easy reach of the tooth brush.Carious lesions were often deeply stained.

This deep black stain was confined to ironpicklers and workers near the pickle baths. It wasrarely observed in other acid workers. Brown orgreen staining was sometimes present and this wasparticularly noticeable when oral hygiene was poor.The latter staining may be improved and eveneliminated by normal brushing, but the author is ofthe opinion that the most rigorous brushing regimemust be carried out in order to keep the black stain,seen in picklers, to even reasonable proportions.This black staining can be temporarily removed bybrushing and prophylaxis carried out by a dentalsurgeon or hygienist, but it quickly returns in theinterproximal stagnation areas.

Postscript

On completion of the survey, the findings werecommunicated to the Industrial Diseases Sub-committee of the Industrial Injuries AdvisoryCouncil.

In the light of the data provided by the survey the

Sub-committee considered the question whethererosion of the teeth, due to airborne acids inindustry, should be prescribed under the NationalInsurance (Industrial Injuries) Act I965.The Chairman of the Industrial Injuries Advisory

Council forwarded the Report ofthe Sub-committeeto the Minister of Pensions and National Insuranceon July 30, I966. The Report is contained in apublication of the Ministry of Social Securityentitled "Erosion of the Teeth," and is availablefrom H.M.S.O. (Ref. Cmnd. 3114).The summary of the Report states:

'We recognize that a case for the prescription oftooth erosion can be made out. We feel, however,that the nature of the condition and the difficultiesinherent in prescription provide arguments whichcarry the greater weight. The condition is trivial.It only affects the front teeth. It causes no loss offaculty in most cases, and the cosmetic effect is verysmall. We have grave doubts whether the number ofspeculative claims could be kept to a tolerableminimum. The form of occupational cover presentsconsiderable difficulty, and we can see no completelysatisfactory way of dealing with the problem ofdiagnosis after the teeth have been extracted. Takingall these factors into account, we recommend thattooth erosion due to industrial acid should not beprescribed.'

There was a note of dissent by one member of theCouncil.

The author is indebted to the Ministry of NationalInsurance and Pensions for the grant that made thisproject possible, and to the late Professor H. G.Radden and also Professor J. L. Hardwick for help andguidance.The author wishes to thank H.M. Factory Inspector-

ate in Manchester, Glasgow, and Wolverhampton, andthe Medical Officers, management, and staff of thevarious firms taking part in the survey for their helpand kind co-operation.

Finally, thanks are due to the Department of MedicalIllustration of the Manchester Royal Infirmary for thefigures and illustrations and to the Trustees of the Well-come Trust for assistance with the production of thecolour plates.

REFERENCES

Atkinson, H. F. (I947). An investigation into the permeabilityof human enamel using osmotic methods. Brit. den?t.7., 83, 205-214-

British Dental Association (I959). Memorandum on theerosion of teeth, presented to the Industrial InjuriesAdvisory Council. Brit. dent. J., Io6, 239-242.

ten Bruggen Cate, H. J. (I965). Dental erosion in industry.Survey carried out for Industrial Diseases Sub-committee of I.I.A.C.

(i966). Thesis submitted for part two of degree ofM.D.S. to University of Manchester.

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266 H. J. ten Bruggen CateElsbury, W. B., Browne, R. C., and Boyes, J. (I95I). Erosion Malcolm, D., and Paul, E. (i96i). Erosion of the teeth due

of teeth due to tartaric acid dust. Brit. J. industr. to sulphuric acid in the battery industry. Ibid., I8,Med., 8, 179-I80. 63-69.

Jenkins, G. N. (I966). The Physiology of the Mouth, 3rd ed., Ministry of Social Security (i966). National InsurancePP. 57-59, 93 and 300. Blackwell Scientific Publica- (Industrial Injuries) Act, i965. Erosion of the teeth.tions, Oxford. Report by the Industrial Injuries Advisory Council.

Cmnd. 3II4. H.M.S.O., London.Lynch, J. B., and Bell, J. (I947). Dental erosion in workers Paul, E. (i962). Erosion of the teeth due to industrial

exposed to inorganic acid fumes. Ibid., 4, 84-86. sulphuric acid. Dental Mag. (Lond.), 79, 3, I37-143.



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Documents

Dental Erosion Industry - A BMJ journal · Dental Erosion in Industry H. J. TEN BRUGGENCATE Fromthe Turner Dental School, University ofManchester Five hundred and fifty-five acid