Optimal post length and diameter and microleakage of ...

Post and core• The primary purposeof a post is to retain acore that can be usedto retain the defeniteprosthesisWooden dental prostesisof the Tokugawa era(1603-1867)

Do posts reinforceendodontically treated teeth?

• Lovdahl and Nicholls (1977)• Guzy and Nicholls (1979)• Trope et al (1985)

What are the most commontypes of post and core failures?• Dislodgement and loosening• Root fracture• Caries and apical lesions

Factors affecting the retention• Post length• Post diameter• Post design• Luting agents• Luting method• Canal shape• Preparation of the canal space and tooth• Location in the dental arch

• Various guidelines have been recommendedregarding post length– The post should be equal of the crown– The post should be 1/3 the length of the crown– The post should be ½, 2/3, or 4/5– The post should end halfway betwen the crestal boneand the root apex– The post should be as long as possible withoutdisturbing the apical seal

Post length• Studies have reported that the length of the posthas a significant effect on its retention and inmost instances, the more deeply the post isplaced, the more retentive it becomes (Standleeet al 1978)• Leary et al (1987) found that posts with length ofat least 3-quarters of the length of the rootoffered the greatest rigidity and least rootdeflection when compared with posts that werehalf the root length

Post length• From laboratory studies,it is apparent that a lengthguideline ideally wouldbe three fourths of theroot length, but thisdimension is notachievable withoutcompromising the apicalseal on many teeth

Post diameter• Increasing the diameter of the post does notprovide a significant increase in the retentionof the post (Standlee et al 1978, Sorensen et al1984, Hunter et al 1989)• However it can increase the stiffness of thepost at the expense of the remaining dentinand the fracture resistance of the root (Tropeet al, Mattison et al 1982, Trabert et al 1978)

Post diameter• Goodacre et al suggested that postdiameters should not exceed one third of theroot diameter at any location• Studies also indicate that the diameter at thetip should usually be 1 mm or less(Goodacre et al, Abou-Rass et al 1982)

Camp et al (1983)determined that when4 mm of gutta perchawas retained only 1 of89 specimens showedleakage, whereas 32 of89 specimens leakedwhen 2 mm of guttapercha was retained

Madison, Zakarison(1984) and Neagley(1969) found noleakage at 4 mm

Zmener (1980)found that in rootcanals sealed withlateralcondensationtechnique, leakagewas reduced whenmore than 4 mm ofgutta-percharemained in theapical portion

• Portell et al (1982) determined that most of thespecimens with only 3 mm of apical gutta perchahad some leakage• Mattison et al (1984) found significantdifferences between 3, 5, and 7 mm of guttapercha, and they concluded that at least 5 mm ofgutta percha is necessary for an adequate apicalseal

Post space preparation andleakage• During the mechanical preparation of the postspace it is possible that the root filling may betwisted or vibrated, with disruption of the seal• It now seems that the advantages of leaving theapical portion of the root filling undisturbed isoutweighed by the fact that much of the canalsystem is vulnerable to contamination from aninadequate seal coronally

• Provided a minimum of 5 mm of sound apicalroot filling is left in situ, studies have shown thatremoval of laterally condensed gutta percha doesnot affect the apical seal, irrespective of whetherthe post space is prepared immediately afterobturation or is delayed (Zmener 1980, Neagley1969, Bourgeois et al 1981)

• The success of endodontic therapy iscommonly thought of in terms of an adequateapical seal• However, the coronal seal achieved by therestoration may be considered as importantfor the ultimate success of endodontictreatment (Marshall et al, Swanson et al,Torabinejad et al, Magura et al. Khayat et al,Ray et al, Tronstad et al)

Strinberg, in 1956,considered that the mostcommon cause of failurewas leakage of tissuefluids apically aroundinadequate root fillingsIngle in 1965 found thatof 104 failed cases, 66were associated with apoor apical seal

Importance of coronal leakage infailure of root canal treatment• Obturated root canals can be recontaminatedby micro-organisms in a number of ways:– Delay in placing a coronal restoration. Temporarymaterials will dissolve slowly after in time in thepresence of saliva and the seal may break down. Atemporary restoration of inadequate thickness willeventually leak

Importance of coronal leakage infailure of root canal treatment– Fracture of the coronal restoration and /or thetooth– Preparation of post space when the remainingapical section of the root filling is of inadequatedensity and / or length

Coronal leakage…• The concept that one cause of failure of rootcanal treatment may be the result of coronalleakage is not a new one• Marshall & Massler, in 1961, carried out aleakage study using a radioactive tracer andshowed that coronal leakage occurred despitethe presence of a coronal dressing

Allison et al, in1979 made briefreference to thepossibility that apoor coronal sealmight contribute toclinical failure

Swanson & Madison,in 1987, did an in vitrostudy where theyshowed that after only3 days exposure toartificial saliva therewas extensive coronalleakage of a tracer dyethrough aparentlysound root filling

Madison & Wilcox,in 1988, confirmedthat exposure of rootcanals to the oralenvironment allowedcoronal leakage totake place, in somecases along the wholelength of the rootcanals

Torabinejad et al, in 1990,found that 50% of singlerootedteeth, root filledusing lateral condensationof gutta percha and a sealercement, were contaminatedwith bacteria along thewhole length of the rootafter 19 days or 42 days,depending upon thecontaminating organism

Khayat et al, in 1993, haveshown that root canalsobturated with gutta perchaand Roth’s sealer, usingeither lateral condensationor vertical condensationwere contaminated apicallywith bacteria from salivaexposed to the coronal partof the root canal only. Allcanals were contaminatedwithin 30 days of exposure

MicroleakageActual bacterial penetration throughobturating materials may not be necessaryto cause treatment failure. Moreimportant may be leakage of bacterial byproductsBacterial metabolites, toxins anddegradation products are much smallerthan bacteria and could penetrate fasterHovland & Dumsha, in 1985, showed thatmost leakage occurs between the rootcanal sealer and the wall of the root canal

Prokaryptic cells(bacteria) are thesmallest of theunicellularorganisms. Theyare, for the mostpart,approximately 1 to1.5 µm wide and 2to 6 µm longEscherichia coli is approximately1 µm in diameter

Bacterial mechanism of tissuedamage and bacterial productsBacterial factors forcolonization and growthBacterial factors forinvasion and tissue damage

Bacterial factors for invasionand tissue damageDirectIndirectCytotoxicproductsEnzymesInflammatoryresponseTissue damage

Enzymes• Collagenase• Trypsin-like protease• Gelatinase• Aminopeptidase• Phospholipase A• Alkaline phosphotase• Acid phosphotase• hyaluronidase

Toxic factors• Bone resorbing factors– Lipoteichoic acid– Lipopolysaccharide– Capsule• Cytotoxins– Butyric and propionicacids– Indole– Amines– Ammonia– Volitile sulphurcompounds

Microleakage ofendodonticallytreated teethrestored withpostsBachicha et al. 1998

Purpose• To measure by fluid filtration the microleakageof a stainless-steel post system and a carbonfiberpost system cemented with zinc phosphateand glass ionomer as nondentin-bondingcements, and Panavia-21 and C& B Metabondas dentin-bonding cements

Microleakage ….• Leakage of endodontic obturation materials hasbeen measured by:– Dyes (Swanson et al, Madison et al)– Radioactive isotopes (Marshall et al)– Bacteria (Mortensen et al, Goldman et al, Torabinejadet al)

Fluid filtration system• Was developed by Derksen et al. 1986 tomeasure quantitatively microleakage aroundcoronal restorations

The movement of the airbubble in themicropipette toward theapical end of the root perunit time provided ameans of measuringmicroleakage as fluidmoved from inside theroot toward the externalsurface

ControlExperimental

µl/min0,40,350,30,250,20,150,10,050SS PostCF PostZn Phos Glass Ion Panavia-21 C & B MetaMicroleakage

0,40,350,30,25Zn PhosGlass IonPanavia-21C & B Metaµl/min0,20,150,10,050SS PostCF PostMicroleakage

ConclusionBased on the observations of the present study,using the accelerating leakage pressures, itseems that the dentin-bonding cements haveless microleakage than the traditional,nondentin-bonding cements