An investigation of pH changes of various cementsZeynepYeçil Duymuç, DDS, PhD^

Objective: in this study, the time-related pH changes that occur in cements having différent structureswere observed. Method and materiais: Eight cements consisting of four permanent and (our temporarycements were used. The materials were prepared according to manufacturers' instructions. The materiaiswere used in 0.100 ± 0.02-g increments, with the purpose ol standardizing the effect of massive differ-ences. The 80 total specimens, including 10 from each cement type, were prepared, and the pH value ofthe distilled water was measured at 3,10, 30, 60, and 120 minutes, and then again 24 hours iater.Resuits: Analysis of variance showed the reiation between the kind of cement and its pH change duringthe course of the study was statistically significant. Conclusion: Though temporary cements indicatedneutral pH from the beginning of the study, the acidity of the other cements changed with time ahd tookvalues approximate to neutral pH within 24 hours. (Quintessence Int 2004;35:753-757)

Key words: cement, pH change, time

CLINiCAL RELEVANCE: One of the important factors toconsider in the selection of cements is the irritant effectthey can have on the pulp. This feature is closely relatedtc the pH values cements show while hardening.

Suitabilitji of the biologic features of dental cementswidely used for various dental purposes is as im-

portant as their mechanical,'-^ physical, and chemicalfeatures. Also, the fact that these materials don't leadto an irritant effect in pulp is a desired result."

Whether pulp is negatively affected depends on thenumber of cycles of the equipment used in tooth cut-ting, on the kind of the equipment, on the pressure ap-plied, on the exothermic heat produced, and on thehydroxide (OH) ion, namely the pH value, releasedduring cement hardening.^

'Professor, Departrrent of Prosthodontics, Schooi ot Dentistry. Atatüri<

University. Erzufum, Turkey.

Reprint requests: Dr Zeynep Yeçil Duymu§, Atatürk Üniversitesi, Di?Hekimiigi Fakültesi, Protetik DijTedauisi Anabilirr Dali, Erzurum, Türkiye.E-mail:zyesilz®hotmaii.com

Not only the acidic features cf cements but also thelikelihood that these features may lead to some dam-age in the pulp, have been investigated by many re-searchers.̂ '̂ -»* Acidic features of the cements resultfrom the fact that the used liquids are highly acidic.'^Measurement studies of cement pH values have beeninvestigated using various methods."''"'*" The purposeof this study was to observe tbe time-related changesthat occur in pH values of cements having differentstructures.

METHOD AND MATERIALS

In this study, eight cements, four permanent (Adhesor[Spofa Dental]; Durelon [ESPE]; Meron [Voco];Harvardid [Rihter & Hofmann Harvard Dental]) andfour temporary (Tempbond [KerrJ; Sinogol [POBD];Provilat [POB]; Scutabond nF [ESPE-3M]), were used(Table 1) and prepared according to manufacturer in-structions. The materials were used in 0.100 ± 0.02-gincrements with the purpose of standardizing the ef-fect of massive differences. The 80 total specimens, 10from each cement type, were prepared in 10 mL dis-tilled water at ÍT^C (pH 7). Before the glass electrode

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TABLE 1 Cementation materials used in the study

Cement

TemporaryZinc oxide eugenolWithout eugenolWithout eugenolZinc oxide eugenoi

PermanentZinc phosphateCernokosteieokáPolycarboxyiateGiass ionomerSilico phosphate

Product

TempbondSinogoiProvilat

Manufacturer

KerrPD DentaiPro medica

ScutabondnF 3M ESPE

Adhesor

Dure ionMeronHarvardid

S pota Dental

ESPE Í S K ^ ^

vocoRichter & HoffmanniHarvard Dental

TABLE 2

Source ofvariation

CementsTimeInteraction(cements xError

Analysis of variance

df

75

35time)

96• p < . o o i .dl = degrees of freedom.

Sum olsquares

130.6475,648

21,721

0.019

Meansquares

17.2351.1270.621

0,000

F

.00085768.09 J3168.99

TABLE 3 Mean pH value*

Product

TempbondProvilatSinogoiScutabond nFhiarvardidMeronAdhesorDu re Ion

•N = 10.

3 min

7.617.5B7.957.945.645.094.055.50

10 min

7.517.437.927.915.675.114.185.65

15 min

7.327.337.827.585.805.274.285.82

30 min

7.217.207.657.446.015.614.466.32

60 min

7.137.197.557,406.085.794.596.45

120 min

7.107.147.437.386.345.894 986,54

24 h

7.017.107.407.336.546.606.927.00

(electrode order No. 104023311) was used, it was cali-brated with the startdard-pH solutions. After startingthe mixing process, pH values of the distilled waterwere tneasured at 3, 10, 30, 60, and 120 minutes atidthen 24 hours later. pH measurements were madewith a digital pH meter (Model 701, Orion Research)by plunging the glass electrode into the distilled waterin which there was a cement specimen. The time-re-lated pH changes and their highest values were thendetermined. The connections between pH changesand time were figured, and the highest pH values weredetermined.

RESULTS

Analysis of variance was used for statistical evaluation.Mean and standard deviations were calculated, and amultiply comparison (least significant difference [LDS])test was conducted. The results are presented in Table 2.

The cement type and pH change seen during thecourse of time was found to be statistically significant(P < .001). The distribution of obtained pH values arepresented in Table 3,

The results of the multiply comparison LSD test,which was made to reveal the differences between thegroups, helped determine that the cements and the

changes occurring during the course of time were dif-ferent from each other (see Table 3).

pH values were obtained for tbe permanent ce-ments used, and it was determined that tbe cementhaving the most acidic pH was zinc phosphate.However, the most neutral cement was polycarboxy-late cement, and it was noted tbat tbe liquids didn'thave neutral pH in contrast to the claims of many pro-ducers of zinc. It was observed tbat the permanent ce-ments resulted in a high pH during the first 10 min-utes, after which the pH became close to neutral 24hours later (Fig 1}, Regarding the temporary cements,a neutral pH resulted from the beginning (Fig 2),

DISCUSSION

In general, evaluation of the obtained results indicatedthat the different cement types show difterent pH val-ues. The differences depend mostly on the structure ofthe liquid and powder that constitute tbe cement, onthe features of the liquid, and on the reactions tbat de-velop after the powder and liquid are mixed. Tbestrong and weak acids tbat cement liquids contain af-fect pH values.

The cements used in tbe study, in general, were di-vided into two groups according to tbe structure of the

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D.

6 -

4-

2-

• Harvard idCl Meron

3 10

—i' ."-

15

•: Adhesor• Du re Ion

30 60

Time (min)

120 24 h

Fig 1 pH variances thai permanent cements shewed during thecourse of time.

• Tempbond o Sinogolci Provilat • Scutabond nF

3 10 15 30 60 120 24 h

Time (min)

Fig 2 pH variances that temporary cements showed during (hecourse of time.

powder they contain: those containing zinc oxide struc-ture; and fluor-releasing alumina silicates.'*''̂

The most common cements used in provisionallyfixed prostheses are those containing zinc-oxideeugenol (ZOE). They are easy to remove from the pre-pared tooth and are low in cost, and ZOE also hasbeen proven to have sedative effects on dentin hyper-sensitivity and to have antibacterial properties.^"'̂ ' It isfor this reason that eugenol-free products, which oftencontain a calcium-hydroxide base or other biocompat-ible substances, were introduced some time ago inorder to reduce bacterial propagation in provisionalcrowns. Zinc-oxide eugenol cements have a sedativeeffect on pulp. There should be cementation, espe-cially of the sensitive tooth, with ZOE cements for aperiod of time.̂ -̂̂ *

Zinc-polycarboxylate cement is reported to be su-perior to zinc-phosphate cement in many respects,such as its negligible injury to the pulp and its adhe-sion to the tooth structure, as well as to the casting al-loys.̂ '̂ ^ Its liquid, an aqueous solution of polyacrylicacid, is viscous, and the powder and liquid cannot bereadily mixed to have a satisfactory consistency.''

The pH of water-settable, zinc-polycarboxylate ce-ment is still higher, almost neutral. This result suggeststhat pulpal injury caused by this cement is equal to orless than that of regular zinc-polycarboxylate cement.»

Tbe principal advantages of zinc-phosphate ce-ments are their good manipulative characteristics andtheir relatively high compressive strength when usedconsistently to give a low fíhn thickness to cementa-tion. Their acidity leads to pulpal irritation and to thenecessity of an insulating lining in deep cavities.̂ ^

Many researchers have stated that the heat andacidity that occur during the hardening of phosphatecements affect pulp negatively while polycarboxylatecements have lower pH values.^-'o Perhaps the

strongest clinical merit of this cement lies in its re-ported biocompatibility with the dental pulp, whichcould be due to a rapid rise in pH after mixing and/orlack of tubular penetration from the large and poorly-dissociated polyacrylic-acid molecule.'^

The initial low pH of glass-ionomer cement waspreviously reported and implicated as a cause ofpostcementation sensitivity,' though subsequent stud-ies have disputed this implication.̂ .̂as puipal injuryand postcementation hypersensitivity are most proba-bly multifactorial, caused by irritation from cavitypreparation, thin cement mix in conjunction with ex-cessive hydraulic force, and microleakage.^*'"

Smith and Dorin Ruse* reported that the degree ofpulpal reaction depends on the continuity of the pHvalue and the quality of acid, and that the hardeningreactions of cements change between 4 and 14 min-utes. They have asserted that the pH value of phos-phate cements is 4 after the first hour and between 6and 7 after 24 hours.

In this study, permanent cements resulted in highpH values during the first 10 minutes and near neutralpH values 24 hours later.

Demmel'^ has investigated chemical and thermaleffects of cements and determined that zinc phosphatehas more acidity than polycarboxylate cement.

Klötzer et al" determined that the pH of zinc-phos-phate cement is between 6 and 6.5, hut the pH ofpolycarboxylate cements is between 6.5 and 7. Theyhave also stated that polycarboxylate cements are neu-tralized more quickly than zinc-phosphate cement.

Staehle and Ziegler'" measured the pH values duringa 5-hour time period of cements having an acidic fea-ture and determined the pH values of zinc phosphatesto be 4,0 to 5,4, polycarboxylates to be 5.0 to 6.0, andglass ionomers to be approximately 4.2 to 4.4. Staehleand Ziegler'f have stated that the presence in cements

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of the unbound OH group during the hardening processis characteristic and that diffusion in dentin is slowerhecause polyacryhc-acid molecules are bigger thanphosphoric acid, and zinc-phosphate cement, accord-ingly, shows the highest pH increase. At the same time,Staehle and Ziegler'" have measured the amount of OHion transmitted by the dentin of the aforementionedmaterials in another study and determined that the pHof zinc phosphate is 6,0 to 6,3 and 6,4 to 6,8 for poly-carboxylate and glass ionomer cements, respectively.

In their study to investigate the pH changes occur-ring during cement hardening, Charlton et al" deter-mined that two of three ionomer cements are similarbut that one shows a pH value different from the others,

Bcn-Amar et aP' have measured the pH changes ofresin-modified, glass ionomer (RMGI) and glass-ionomer liners at various intervals of time and foundthat there is a graded rise on the pH surface of all lin-ers tested.

Smith and Dorin Ruse^ have stated that pH valuesof cements in the first 10 minutes are between 3.4 and4.5, pH values of zinc-phosphate cements are 6.5, 6,2for polycarboxylate cements 24 hours later, and the ce-ment whose value is 2,0 would form a pulpal answer.

Acids cause OH ions to diffuse into the pulp faymaking hydrodynamic influence on the dentin-pulpcompDnent,̂ Some researchers have stated that thereis some OH diffusion on dentin in phosphate cementsbecause organic acids diffuse more quickly thanacrylic acids but that dentin diffusion is less in car-boxylatc and glass-ionomer cements,"'^ Mortimer andTranter^ have stated that acrylic acid is less acidic thanphosphoric acid. On one hand, Klötzer et aP' haveobserved that cementation pain is seen in phosphatecements having a high pH value, while conversely, hehas observed that polycarboxylate cement causes lesspain (6.6%) and realized that this situation resultsfrom the fact that polycarfaoxylate cements have a verylow pH value.

Staehle and Ziegler'" and Klötzer et a l" havepointed out that acidity in cements or their beingacidic is not the only one criterion for pulpal irritation.

More recently, glass-ionomer cements (GICs) havebecome popular because of the fact that they offer fa-vorable adhesion to dental tissues and materials, fluo-ride release, and biocompatibility.'^ " Glass-poiyalken-oate cements have a cariostatic effect,''' the ability tobond to tooth structure, and are relatively bland to thepulp. No local or systemic adverse effects of glass-polyalkenoate cements have been reported. They havebeen claimed to be of iow pulpal toxicity in clinicaluse,'' yet pulp sensitivity foliowing their use in crowncementation has been reported,^^ Hydraulic pressurecreated by cementation has been postulated as a possi-ble cause of the sensitivity,"

It has been determined that the pH values obtainedfrom cements used for permanent cementation corre-spond with the findings of the above-mentioned re-searchers, and that the cement having the most acidicpH is zinc-phosphate cement, but the most neutral ce-ment is polycarboxylate cement. On the other hand, ithas been seen that the liquids don't have a neutral pHvalue in contrast to the claim of many producers of zincphosphate that their liquid is neutral, for neutral phos-phoric acid has not yet been developed. It has been de-termined that this cement, which was acidic at the be-ginning, showed a neutral pH 24 hours later because ofits structure. It has been thought that in the first fewhours, some damage to the pulp would occur due to theacid attack on it. The pH of glass ionomer has beenfound to be more acidic than expected,̂

In this study, temporary cements showed a neutralpH from the beginning. This is in agreement withPhillips et al^" who stated that temporary cementsshow a neutral structure and exhibit superiority overother types of cements with respect to biologic fea-tures because of their nonirritating pulp effects.

CONCLUSION

The acidity of cements in this study changed depend-ing on the time, and took values approximate to theneutral pH, while temporary cements exhibited neu-tral pH from the beginning. It was considered thatwhen cements with acidic features were used, the pHof the liquid in dentin tubules might change because ofthe permeability feature of the tooth's hard tissues. Itwas concluded that it is suitable, advisable, and prefer-able to use temporary cements before permanent ce-mentation, especially in sensitive teeth, because oftheir relieving pulpal effects.

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