Restorative Dentistry

A comparison of the retention of tooth-colored postsAlison J. E. Qualirough, BChD, MSc, PhD, FDS, MRD {RCS EdjVNicholas P. Chandler, BDS,DavidG. Purton,

Objective: The aim of this in vitro sludy was to compare the retention ot five different esthGtic post sys-tems of similar dimensions in extracted teeth using titanium posts as controls. Method and materials:Sixty recentiy extracted single-rooted, cari9s-lree teeth were sectioned horizontaliy and mounted in acrylicresin. The samples were randomly allocated into six groups of 10 for post preparation. Post space prepara-tion was carried out according to the individual manutaoturer's instructions. Ail posts were bended usingPanavia F. A 4-mm hollow, metal sleeve was iuted over the tree end of each post prior to mounting in auniversal testing machine, and the torces required to dislodge the posts using a cross-head speed of 5mm/min were reoorded. Results: It was found that the parailei-sided Lightposts were significantly more re-tentive than all of the other posts. Parapost Fibrewhite posts were more retentive than tapered Lightpostsand Snowposts. There was no significant difference between the retention of stainiess steel Paraposts andany of the other groups. Conclusions: Serrated paral I el-sided stainless steel posts were no more reten-tive than either parallel-sided or tapered tooth-cclored posts in this study. When ail groups were consid-ered, post dimension appeared to influence retention, with paraliei-sided posts being more retentive thantapered posts. (Quintessence Int 2003;34:199-201)

Key words: biomaterials, post retention, retention-testing, tooth-oolored posts

CUNICAL RELEVANCE: Tooth-oolored posts have Ihepotential to replace metal posts in many clinical situa-tions. Due to the nature of the bonding mechanism, theshape of the tootfi-colored post may be less significant toits retention than it is for metal posts.

Root canal posts are commonly used to retain pros-thetic cores for restoration of endodonticaliy

treated teeth. Conventionally, metal posts have beenused.' Although successful in many cases, there are sig-nificant disadvantages, including the less than optimalesthetics. Failure of restorations retained by metal posts

'Senior E_ecluier, Unit o! Operative Dentistry and Endodontotogy, Universit/

Dental Hospital of Manchester, Manchester, United Kingdorr.

^Senior Lecturer, Department of Oral Rehabilitation, University ot Otago,

School ol Oenlistry, Dunedin, New Zealand.

Reprint requests: Dr Alison J. E. Qualtrougn, Unit ot Operative Dentistryand Endodontology, University Dental Hospital oí Manctiesler, HigtierCambridge Street, Manchester M15 6FH, United Kingdom. E-mail;alison.qualtroughQman,ac.uk

can result in post fracture or bending, loss of retention,core fracture, or root fracture. Corrosion bas also beenproposed as a cause of failure.̂ Manufacturers havetherefore introduced systems that are esthetic, areclaimed to be biocompatible, do not stress the tooth,and are strong, retentive, corrosion resistant, and com-patible with otber materials.

Tootb-colored posts vary in respect to several fac-tors including cbemical and physical properties andpost shape. Ceramic posts and fiber-reinforced postswith an epoxy or bis-GMA resin matrix are available.Ceramic posts are rigid and strong, but should a postfail, its removal can be difficult. Tbe properties offiber-reinforced materials are dependent on the natureof fhe matrix and fibers and on fbe interface strengthand geometry of reinforcement.^ The addition of fibersto a polymer matrix can result in significant improve-ment in tbe mechanical properties of strength, fracturetoughness, stiffness, and fatigue resistance.-* While notesthetic, carbon fiber posts have fhe potential to re-place stainless steel and otber posts in many clinicalsituations due fo their inherent rigidity, allowingsmaiier sizes fo be used for equivalent strength.^Although data are limited, preformed, nonmetal posts

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• Qualtrough et ai

TABLE 1 Forces required to dislodge posts(Newtons)

Group

1 Pa ra post T Hani um2 Lightpost (tapered)3 Lightpost (pa ral i el-sided)4 Parapost Fibre white5 Snow post6 Dentatus Luscent

Mean

127,53117,72304.11206,01

98,10147,15

Standard deviation

48.3642,5876,9199,9635.0232,77

have been sbown to have a fracture resistance wbicb,altbougb lower tban that of metal posts, is adequatefor clinical use,̂ This iower fracture resistance is seento be more favorable because if fracture occurs, it ismore likely to be at the post-eore interface or witbintbe post itself, witbout causing fracture of tbe root,̂ *Two otber factors that may affect tbe fracture strengthof the post and tooth are the surface treatment (eg,sandblasting) of the post and the presence of corrosiveproducts,'

Teeth restored with tooth-colored posts have beensbown to have superior esthetics compared with tradi-tional post-core crown systems. They have better Iigbttransmission and reflectance, providing a more naturaltranslucency,'" Tbis, combined with otber positivefindings for nonmetal post systems, bas led to in-creased patient acceptance of tbis type of restoration,Wben carbon-fiber or resin-reinforced post systemsare used witb a dentin-bonding resin cement, it hasbeen sbown that microleakage between the post andtooth tissue is less than when a nonbonding cement isused. Tbis is thought to be due to the insolubility oftbe resin and its adberence to the tooth tissue,"

Although the esthetics of the final restoration areimpotlant, the retention of the post remains a signifi-cant feature of the restoration. Retention depends onseveral factors, including the geometry of the post, thephysical nature of the post and bonding agents, theirsurface treatments, the nature of the bond between tbedentin and post, and tbe luting procedures.

METHOD AND MATERIALS

Sixty recently extracted, single-rooted teeth with nosurface defects or restorations in the roots and with nounfilled canai spaces were selected. The teeth werestored in saline at ZTC.

The teeth were sectioned horizontally, 1 mm coro-nal to the labial cementoenamei junction, and reten-tive grooves were cut onto the external aspect of theroot surfaces using a water-cooled diamond bur run-ning at bigb speed. Tbe roots were embedded in indi-vidual acrylic hlocks sbaped to fit into a retention de-vice. Mounted roots were randomly allocated into sixgroups of 10 for post concentration as follows:

Group 1: Paraposts {titanium, No, 6, 1,5 mm,Coltene Wbaledent); Group 2: Tapered Lightposts(No, 2, 1.8 mm, RTD); Group 3: Parallel-sidedLightposts (No, 2, 1,8 mm, RTD); Group 4: ParapostFibrewhite (No, 6, 1,5 mm, Coltene Whaledent);Group 5: Snowposts (1,6 mm, Carbotech); Group 6:Dentatus Luscent Anchor (Medium, 1,6 mm, DentatusUSA),Following coronal shaping witb sizes 2 and 3Gates Glidden burs, and irrigation using a 2% solutionof sodium hypochlorite, post space preparation wascarried out according to each manufacturer's instruc-tions. The post holes were then dried using paperpoints followed by oil-free air, ED Primer (Kuraray)was mixed according to tbe manufacturer's directiotisand applied to the post preparation using a bristlebrusb. After 60 seconds, tbe post hole was gently driedwith compressed air. Excess primer was removed witha paper point. All posts were wasbed in isopropyl al-cobol and dried prior to being coated witb freshlymixed Panavia F, Posts were inserted into the toothroots using finger pressure prior to activation with acuring light. The specimens were kept in a water bathfilled witb saline at 37"C prior to retention testing,

A 4-mm bollow, metal sleeve was luted over thecoronal part of each post prior to mounting in a uni-versal testing machine (Instron), The post was graspedin the vice of the testing machine, and a tensile forcewas applied at a cross-head speed of 5 mm/min, Auniversal coupling was placed in the assembly to en-sure tbat tension was applied axially along tbe postTbe force required to dislodge tbe posts was recordedand tbe data analyzed using ANOVA and Duncan'sNew Multiple Range Tests,

RESULTS

The mean values for retention of the six groups areshoviTi in Table 1, It was found tbat tbe parallel-sidedLightposts (Group 3) were significantly more retentivethan all ofthe other posts (P<,05), Parapost Fibrewhiteposts (Group 4) were more retentive than taperedLightposts (Group 2) and Snovt̂ DOSts (Group 5), Therewas no significant difference between tbe retention of ti-tanium Paraposts and any of the other groups.

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• Quaitrough et ai

DISCUSSION

One of the primary requirements of a root canal postis that it is strongly retained in the root canal, as lossof retention is a documented cause of post failure.Studies have addressed retention of metal post sys-tems.'' High retention is known to be associated withparallel, serrated posts and low retention for tapered,smooth posts.'' Tooth-colored posts differ with respectto their physical, mechanical, and chemical properties.This experiment suggests that the physical features oftooth-colored posts are less significant than of metalposts due to an increased reliance on the bondingmechanism, thus permitting more conservative ta-pered preparations.

In this study, natural teeth were used and posts ofsimilar dimensions were selected. All posts weretreated in the same way, and the same bonding agentwas used In all cases to eliminate variabies. The resuitsof tbis study indicate tbat parallel-sided Lightpostswere significantly more retentive tban any of tbe otherpost systems, including titanium posts. ParapostFibrewhite posts also performed well. This may be ex-plained by the fact that tbese posts have the optimalconfiguration and are also bonded to tooth tissue.There is the potential for minimai microleakage. Metalposts were not foimd to he any more retentive thanany ofthe tooth-colored post systems.

CONCLUSION

1. Senated, parailel-sided titanium posts were no moreretentive than the tooth-colored posts investigated.

2. Post dimension may influence the retention oftooth-colored posts, vnth parallel-sided posts beingmore retentive than tapered posts.

3. Parallel-sided Lightposts were significantly more re-tentive than all of the other posts considered in thisstudy.

4. Parapost Fibrewhite posts were more retentive thantapered Lightposts and Snowposts.

REFERENCES

1. Restoration of the endodontically treated tooth. Iti;Rosenstiel SF, Land MF, Fujimoto J (eds]. ContetnporaryFixed Prosthodontics, ed 3. St Louis: Mosby, 2001:401-405.

2. Silness J, Gustavsen F, Hunsheth [. Distribution of corrosionproducts in teeth restored with metai crowns retained bystainless steel posts. Acta Odontoi Scand 1979;37:317-321.

3. Isaac DH. Engineering aspects of fibre-reinforced cotnpos-ites. In: Vallittu PK (ed). The First Symposium on FibreReinforced Plastics in Dentistry. Turku, Fitiland: Institute ofDentistry, 1997:1-21.

4. Drummond JL. In vitro evaluation of endodontic posts AmIDent2000;13:5B-8B.

5. Purton DG, Payne JA. Comparison of carbon fiber andstainless steel root canal posts. Quintessence Int 1996127:93-97.

6. Ferrari M, Vichi A, Mannocci F, Mason PN. Retrospectivestudy of the clinical petiormance of fiber posts. Am J Dent2000;13:9B-13B.

7. Martinez-insua A, da Silva L, Rilo B, Satana U. Comparisonof the fracture resistances of pulpless teeth restored with acast post and core or carbon-fiber post with a compositecore. J Prosthet Dent 1998;80:527-532.

8. Mannocci F, Ferrari M, Watson TF. Intermittent loading ofteeth restored using quartz fiber, carbon-quartz fiber andzirconium dioxide ceramic root canal posts. J Adhes Dent1999;1:153-158.

9. Mullay BH. Ahmed M. Periodontal signs and symptoms as-sociated with vertical root fracture. Dent Update 2000;27:356-360.

10. Koutayas SO, Kern M. All-ceramic posts and cores: Thestate of the art. Quintessence Int 1999;30:383-392.

11. Bachicha WS, DiFiore PM, Miller DA, Lautenschlager EP,Pashley DH. Microleakage of endodontically treated teethrestored with posts. J Endod 1998;24:703-708.

12. Purton DG, Chandler NP, Love RM. Rigidity and retentionofroot canal posts. BrDentJ 1998; 184:294-296.

13. Standlee JP, Caputo AA, Hanson EC. Retention of endodon-tic dowels: Effects of cement, dowel length, diameter anddesign. J Prosthet Dent 197S;39:401-4Ü5.

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