Self Disinfecting (Anti-Viral)Alginate Impression Material-

Safety First!

Mangala P. Patel

(NA Nallamuthu & M Braden)

• To develop a self disinfecting (anti-viral) dental alginate impressionmaterial

Aim

Why Disinfect?

• The handling of contaminated dental impressionspresents a particular hazard to dental personnel →one of the routes of transmission of infectiousmicro-organisms from patients (McNeill et al, 1992).

• Micro-organisms could be transferred to gypsumcasts from contaminated dental impressions(source of cross-contamination) (Rowe and Forrest1978; Leung & Schonfeld, 1983).

British Dental Association, 2003

• Updated advice: recommend the decontaminationof all impressions under running tap water untilvisibly clean, prior to chemical disinfection,according to the manufacturer’s recommendations

• Encourage immersion disinfection rather thanspraying techniques

• Disinfection should take place immediately afterthe removal of the impression from the patient’smouth

Survey

• Carried out in UK dental schools

• All questionnaires received a response: 83%(25) of the departments used chemicaldisinfecting procedures: 17% (5) onlyrinsed them in water

• British dental schools 45% - no disinfection

• Under-developed countries rarely usedisinfection

Alginates

• Principle elastic impression material inunder-developed countries

• Viral diseases are widespread

• Problem of imbibition (also cost)

• Self-disinfecting material – does not requirethe Dentist to disinfect

How To Kill A Virus!

• Retroscreen – Prof J Oxford

• Change the pH of its environment

• Rely completely on host cells for survival

• Function at physiological pH (7.2-7.4)

• If the pH is lowered (~2-3), a virus particlecan be inactivated within a matter of secs -out of its’ survival range (Dimmock & Primrose,

1994).

Which Virus?

• Herpes Simplex Virus (HSV-1)• A potential hazard to

dental practice- cross-infection

• Considerably moreinfective than HIV(Marsh & Martin, 1999)

• Affects mainly the upperbody (e.g. mouth and eyes)

Structure of HSV-1virion particle(Grünewald et al, 2003)

Herpes Simplex Virus (HSV-1)

• Common cold sore, eyeinfections, vesicles in &around oral cavity,encephalitis (rare-v serious)

• The herpetic whitlow- frequent dentists complaint

before the use of gloves(Marsh & Martin, 1999; Rowe et al, 1982)

(Grist et al, 1998)

1) Effect of pH on the log reduction of the virus• Formulate a set of experimental alginates with

a range of pH values• Evaluate the antiviral action of the experimental

alginates against HSV-1 - a virucidal assay

2)The effect of formulation changes on physicalproperties: eg: dimensional stability, hardness,(elastic moduli), setting, tear strength.Modifications must not compromise properties

Objectives

• Development of a low pH alginate impressionmaterial - antiviral

• Recommended formulations for dental alginatesfrom manufacturers eg ISP Alginates and FMCBiopolymer, included magnesium oxide (MgO)

• Most Dental Materials textbooks omit thisingredient (eg Anusavice, 1996; McCabe, 1998)

• Not mentioned in an early definitive paper on thecomposition of alginates (Buchan & Peggie, 1966)

Further

Methods

• Experimental alginate formulations were preparedab initio, (ISP Alginates and FMC Biopolymer):

sodium alginate (Manugel DJX/ISP) -14%

calcium sulphate hemihydrate – 9%

potassium fluorotitanate (K2TiF6) – 3%

tetrasodium pyrophosphate – 0.84%

diatomaceous earth - 63.16%

magnesium oxide 0 – 10% variants

Methods Contd.

• Alginate powder – 10g mixed with 23mlwater

• Proprietary alginates as controls:Neocolloid (Zhermack – sodium alginate),Palgat Plus (3M ESPE – sodium alginate),Blueprint Cremix (Dentsply DeTrey -potassium alginate)

Virology

• Experimental alginates varying in pH &MgO content

• Evaluate the antiviral action of theexperimental alginates against HSV-1, bymeans of a virucidal assay, by RetroscreenVirology Ltd, QMUL.

Contents of eachwell transferred to96-well plate andincubated withVero cells

Alginate samplemixed anddispensed into a6-well plate

Centrifuge tubeinserted into wellto create knownsurface area

Tube removed whenalginate sets andvirus suspensionadded to wells

Alginate and virusincubated for 5,30, 60 or 240minutes

Neutralisingmedia added towells to terminatereaction

Virus infectivity of Verocell line determined by CPEobservations

Schematic representation of the virucidal test system

Virology Contd.

• Dimethyl sulfoxide (DMSO) (1.5%) wasused as a positive control substance

• A Vero cell line was cultivated according tothe Retroscreen Virology Ltd standardoperating procedure (SOP). All of theexperiments were done in duplicate.

Other Methods Contd.

• pH measurements: Gelplas flat tip electrode withan Orion 720A pH meter – readings: immediatelyafter mixing, then every 30s seconds for 15minutes

• Setting time: Oscillating rheometer 5 repeatruns/sample

• Shore A hardness: ASTM 2240 (1986) - every 5mins after setting up to 30 mins

• Tear energy (Γ): ‘trouser’ test piece - Γ calculatedfrom force (F) necessary to propagate the tear at agiven speed from G =2F/h, (h = sample thickness)

RESULTS

Formulation pH % MgO

ExII F1 4.07 0

ExII F2 4.64 0.1

ExII F3 5.10 1.0

ExII F4 5.41 1.25

ExII F5 6.02 1.4

ExII F6 6.82 1.6

ExII F7 7.03 2.0

ExII 8.25 10.0

pH Values of Experimental AlginateImpression Materials – Virology Study

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

ExII

F1

ExII

F2

ExII

F3

ExII

F4

ExII

F5

ExII

F6

ExII

F7

ExII

Lo

gR

ed

uc

tio

n/-

log

10

TC

ID50

5min

30min

60min

240min

Log reduction/-log10 TCID50 of HSV-1 withexperimental alginate materials

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5min 30min 60min 240min

Time/minutes

Lo

gR

ed

uc

tio

n/-

log

10

TC

ID50

ExII F1

ExII F2

ExII F3

ExII F4

ExII F5

ExII F6

ExII F7

ExII

Log reduction/-log10 TCID50 of HSV-1 withexperimental alginates at each time point

equivalent to a factor of 100 to 10,000

Note!

• Best results were seen with materials ExIIF1 and ExII F2, both achieving a logreduction of 4.0 at 240 minutes

• These two materials had the lowest pH(4.07-4.64)

3.000

4.000

5.000

6.000

7.000

8.000

9.000

10.000

11.000

0 200 400 600 800

Time/seconds

pH

N

PP

BC

ExII

ExI

ExII F1

pH changes of Neocolloid, Palgat Plus,Blueprint Cremix and experimentalmaterials ExI, ExII and ExII F1 (n=3)

• ExII F1-no MgO

• Could pHbe MgOcontentdependent

Effect of varying MgO content on the pH ofExII (ISP-Alginate formulation)

3.000

4.000

5.000

6.000

7.000

8.000

9.000

10.000

0 200 400 600 800 1000

Time/seconds

pH

No MgO

0.10% Mgo

0.25% MgO

0.50% MgO

0.75% MgO

1.00% MgO

1.25% MgO

1.40% MgO

1.50% MgO

1.60% MgO

1.75% MgO

2.00% MgO

MgO inalginatepowders

↓directeffect onpH

Setting Times/Elastic Modulus/TearEnergy

Material Setting Tm

(secs)

Elastic Mod(MPa)

Tear En.

(J/m2)

Neocolloid 204 0.91 303 (90)

Palgat Plus 161 1.14 323 (80)

Blueprint C 101 0.76 -

Exp-MgO 240 1.59 403 (30)

ExpII-noMgO

362 0.91 321 (40)

Setting time increases

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

0 5 10 15 20

Time/minutes

Ha

rdn

es

s

N

PP

BC

ExI

ExII

ExII F1

Average hardness (Neocolloid, PalgatPlus, Blueprint Cremix and experimentalmaterials ExI, ExII, ExII F1 (n=3)

No MgO-hardnessdecreases

ExII F1 was very close to that of the Palgat Plus

Discussion

• Two experimental formulations can bedeemed as antiviral

• These two alginates had the lowest pHvalues (4.07 & 4.64)

• Maximum log reduction of HSV-1 achievedby these experimental alginates was 4.

• General European Standards stipulate logreductions of 4-5

• K2TiF6 + 2H2O → 2KF + TiO2 + 4HF

• MgO - insoluble in water, but hydrolyses toMg(OH)2, which is more soluble. It ispostulated that this then reacts with HF:

Mg(OH)2 +HF → MgF2 + H2O

• Giving the soluble MgF2 (0.66g/100cc),which ionises (Mg2+ and F-).

Discussion Contd.

• The resulting magnesium ions thencontribute to the cross-linking reaction.

• The setting time will be shorter as there isnow a second cross-linking agent as well ascalcium sulphate, forming bonds betweenthe alginate molecules

Discussion Contd.

Discussion Contd.

Confirmed by: i) hardness measurements - noMgO → softer product

ii) setting times - no MgOincreases setting time

iii) increasing the MgOcontent increases the pH

• Mg(OH)2 -HF reaction → shape of the pH plots:pH decreases as HF formed, then increases as acidis removed from the system via MgF2 formation

Discussion Contd.

3.000

4.000

5.000

6.000

7.000

8.000

9.000

10.000

11.000

0 200 400 600 800

Time/seconds

pH

N

PP

BC

ExII

ExI

ExII F1

Conclusions

• Lowering the pH of an alginate impressionmaterial to ~ 4 confers the material anti-viralagainst HSV-1

• No extra cost to the material

• Removing MgO from the alginate formulationresults in a lower degree of cross-linking andultimately a softer material

• MgO adds to the choices in formulation to givedesired properties for dental and otherbiomaterials applications

Where To Next?

• Grant to EPSRC looking at other viruses andbacteria

• Effects of detergents and other reagents (2,4dichlorbenzyl alcohol, Amylmetacresol)

• Assess the compatibility of experimental alginateswith dental casting materials

• Further tests on properties eg compressive strengthand reproduction of fine detail.

Thank You!