Composite resin short-post technique for primary anterior teeth
Peter L. Judd, DDS, MSc David J. Kenny, DDS, PhD Douglas H. Johnston, DDS, MSc Rebecca Yacobi, MSc, DDS
A technique using a “m ushroom shaped” com posite resin short p o st constructed inside the pulp-treated root canal pro vides su ffic ie n t re te n tio n to b u ild a composite resin crown on the reinforced superstructure o f the rem aining crown dentin. T h is tech n iq u e was tested fo r 1 year in 92 teeth; they showed no failures o f retention o f the short post. Recurrent caries an d severe b r u x is m —fa cto rs beyond operator co n tro l—posed som e problems that were readily resolved.
arly carious destruction of m ax illary an terio r p rim ary teeth is com m on in both nursing bottle m outh and decay caused by snacking. In the p a st, these teeth were often extracted; however, many parents now request th at they be restored. Polycar bonate crowns have been commonly used as the anterior stainless steel crown1 and its open-faced m odification2 are esthetically poor in appearance. However, the reliab ility and d u rab ility of the p o ly carb o n ate crow n have been less th a n satisfactory because of excessive wear, poor fit, and esthetic appearance. Many clinicians have used composite resin posts reinforced w ith different types of metallic pins,3 ortho d o n tic tu b in g ,4 or wire5 to rebuild decayed prim ary tooth structure. Others have restored less involved primary anterior teeth w ith full-crown composite
resin restorations.3’6’7 T h e com posite resin short post and crown was developed for the restoration of severely decayed primary anterior teeth. Its development began in 1981 and the technique was first reported in 1986.8 T h is p a p e r describes the clin ical technique of the composite resin shortpost an d crown restoration studied for 1 year.
Methods and materials F or this prospective study, the inves tig ato rs used consecutive selection of subjects. All maxillary anterior primary teeth treated w ith p u lp e cto m ies9 and composite resin short-post and crown
Fig 1 ■ Short-post preparation with no. 6 round bur in place. T h e short post is b u ilt u p with light-cured resin in two steps, first to the cervical m arg in and th en to produce a supragingival post. Finally, a com posite full-coverage crown is built on the post.
resto ratio n s d u rin g a 3-m onth period were included in the study. Ninety-two teeth were treated by one of three clinicians involved in the study. Carious p ulp exposure and the necessity for pulp therapy were the entrance criteria for the study sample. G ross carious lesions were rem oved using a no. 8 carbide steel bur. Manual rotation and withdrawal of two Hedstrom endodontic files (usually no. 20), were used to rem ove the p u lp . T h e canals were cleaned with water lavage and air dried; no canal shaping was performed. T he teeth were subsequently obturated w ith n o n fo rtifie d zinc oxid e-eu g en o l paste (ZOE 2200, L. D. Caulk Co) with a rotary paste filler. Once the paste had set, a no. 6 round bur was used to remove the excess canal sealant and to create an inverted “m ush room u n d ercut” in the dentin (Fig 1). T he undercut was 3 to 4 mm apical to the g in g iv a l m arg in of the to o th . In p re p a ra tio n for the u ndercut, the bur was alig n ed p a ra lle l to the lo n g axis of the ro o t to p rev en t la te ra l ro o t perforation. T he m axim um lateral exten sion of the bur was limited by the shank of the bur as it contacted the dentinal w all. T h erefo re, the u n d e rc u t was a function of the radius of the no. 6 round b ur (Fig 1). In prim ary teeth that had n o t yet achieved full root closure, the th in d e n tin a l w alls d icta te d th a t the undercut be minimal. Crown preparation was required when JADA, Vol. 120, May 1990 ■ 553
supragingival crown structure remained after caries removal. A tapered diamond bur was used to reduce the mesial, distal, and labial axial surfaces at a 15 to 20° taper to create a beveled enamel margin. This provided room for an adequate bulk of com posite resin for strength of the re sto ra tio n , a d esirab le m a rg in , and optim al esthetic appearance. A rounded shoulder preparation was used in teeth with m inim al supragingival crown struc tu re w h en the m a rg in te rm in a te d on dentin or if the use of a beveled m argin w o u ld lead to loss of any re m a in in g enamel at the cementoenamel junction. The tooth was cleaned, etched, rinsed with water, and air dried. A light-cured bonding agent (Prisma Universal Bond, L. D. C au lk Co) was bru sh ed on the etched surface and th in n ed by a com pressed air blast. Light-cured composite resin (Prisma-Fil, L. D. Caulk Co) was injected w ith a resin gun (Caulk) into the can al ch am b er. T h e nozzle was removed as resin filled the chamber of the canal to form the sh o rt post. T he resin was com pressed in to the p o st preparation with a ball burnisher before p o ly m e riz a tio n . T h e resin sh o rt post (F ig 1) was lig h t cured in two steps: first the resin in the post preparation, follow ed by the resin th a t formed the su p e rstru c tu re of th e p o st. T h e n the crown was b u ilt u p freehand or w ith celluloid strip crowns (Pedo-form Strip Crowns, Unitek/3M ). T he strip crowns were trimmed (to the cingulum ) to create an arched in te rp ro x im a l m arg in to
Fig 2 ■ P hotographs of the teeth before (top) and after (bottom) com pletion of the composite crowns.
554 ■ JADA, Vol. 120, May 1990
Fig 3 ■ R adiographs of pre- and postoper ative conditions. Note the extensive caries approxim ating the p ri m ary p u lp s and the root-treated teeth with m u sh ro o m -sh a p e d short-post restorations and composite crowns.
accom m odate the in terd en ta l p ap illa. T he strip crown was filled with composite resin and placed on the tooth. The crown form was placed over the short post with a slightly excessive labial proclination to ensure adequate bulk of resin on the labial surface. The resin was light cured while finger pressure was applied to the incisal surface of the crown form. The final resin crown length approx imated that of the adjoining natural teeth, b u t the resin crow n was contoured so that it did n o t receive occlusal forces. In situ a tio n s in w hich the a d jo in in g natural teeth did not have intact crowns, com posite resin crowns were b u ilt up w ith a crown length approximately threequarters that of a natural tooth to reduce leverage forces. A fine tapered finishing diamond, placed subgingivally at approx imately 30° to the root surface, was used to create a finished margin. The tapered margin was not overfinished to prevent loss of integrity from overheating the com posite resin. T h e su p ra g in g iv a l structure was then contoured to proper anatom ical form (Fig 2) and finished. O cclusal interferences in norm al and p arafunctional m andibular movements were removed and postoperative radio graphs were taken as a final step (Fig 3). P a tie n ts were recalled at 6 and 12 m onths and the crow ns were assessed for fractures, loss of marginal integrity, m obility, and caries at the com posite resin-tooth margin.
Results This sample of 92 consecutively restored teeth showed no failures from dislodgement of the composite short post in the first year. F our teeth in two p a tie n ts showed recurrent caries at the composite resin-tooth cervical m argin. Poor oral hygiene and lack of diet control were identified as the cause, despite rigorous preventive instructions and counseling. Three of these teeth were repaired with com posite resin b u t the fo u rth tooth had to be extracted as it was not restorable. Three crowns showed incisal fractures of m inim al severity produced by normal masticatory function. These teeth were easily rebuilt w ith a resin add-on tech n iq u e . F o u r crow ns d isp lay ed severe a ttritio n in the same p atien t (a severe bruxer). T he composite add-on technique allow ed for easy reconstruction of the ab raded crow n. Seven of these eig h t crowns remain in function.
Discussion The composite resin short post described in this study had a 100% success rate for retention of the composite resin crown re sto ra tio n . F o u r sh o rt-p o st re tain ed crowns in two patients loosened because of recurrent caries at the gingival margin. In both cases, loosening resulted from lack of parent compliance in alteration of the diet or improvement of oral hygiene (this source of failure is beyond operator
control). The one tooth that was extracted exemplified the importance of the dentin undercut that locks the resin short post into the canal and, in turn, the crown onto the post. Teeth with carious destruc tio n of the cervical m a rg in of the re sto ra tio n may have a crow n th a t wobbles because of lost support, but still holds onto the root at the undercut. If the carious destruction is minim al, then caries removal and a local repair at the cervical m argin w ill restore the tooth to normal function. However, if the caries has destroyed the dentinal rim that locks the post into place, the tooth w ill not be restorable. Another prospective study is c u rre n tly u n d er way to assess the effectiveness of glass ionom er cem ent as a short post in com bination w ith a composite resin crown. It is hoped that fluoride release from the glass ionomer w ill in h ib it re c u rre n t caries a t the gingival margin. T he m ushroom -shaped resin post is the key to retention of the restoration. T h e sh o rt p o st m ust have a d efin ite m ushroom shape w ith a full undercut 360° around the canal chamber to ensure re te n tio n of the crow n. If th is is n o t achieved, the resto ratio n risks failu re from dislodgement of the crown. Details of the weaknesses of this restoration were established d u rin g the earlier stu d y .8 Grosso10 reported in 1987 a “new tech nique” resin crown and post, in which he indicated the post was of a tapered design that had “been used successfully for 4 years w ith excellen t re s u lts .” U nfortunately, no data were presented on the n u m b er of teeth treated, the percentage of failures, or the reason for their failures. Kenny and others8 reported in 1986 that in the development of the “ m ushroom core technique,” a design similar to that promoted by Grosso6 had been used. However, this design proved unreliable and led to crown dislodgement as a result of the less retentive straight post. Consequently, the straight short
post was changed to the current m ush room design an d no fu rth e r failures caused by crown dislodgement secondary to loss of sh o rt-p o st re te n tio n have occurred. Long-term data from a retrospective study8 dem onstrated th at full-coverage composite resin crowns are color stable, w ithstand normal occlusal function, and last until the tooth is naturally exfoliated. T his 1-year prospective study indicates the restoration is both durable and has excellent esthetic qualities. T he seven crowns that chipped or were subject to severe bruxism were easily repaired in the chair and remain functional. It is im p o rta n t to rem ove occlusal interferences between the crown and the op posing prim ary anterior teeth. P ar ticular attention m ust be paid to m an dibular lateral incisor and canine inter ferences d u rin g p a ra fu n c tio n a l m a n d ib u la r m ovements. Previous data re vealed the necessity to make the resin crow n sh o rter th a n is an ato m ically accurate.8 In cases of severe anterior caries, the esthetic improvement is so dramatic that parents are not concerned that the teeth are slightly shorter than normal. C au tio n sh o u ld be exercised before placement of the restoration when severe b ru x ism is seen. P aren ts need to be advised of the possibility of crown wear and fractures caused by bruxism forces. T he 15 to 20° taper of the axial surfaces may seem excessive compared with adult crown preparations; however, there is m inim al retentive strength from the axial surfaces of the tooth. T he resin short post provides retention for the crown, but bulk on the labial surface is needed to provide strength to the resin crown an d to decrease “ show th ro u g h ” or transp aren cy of the u n d e rly in g tooth material. Conclusion
The design described for a composite
T E C H N IQ U E S
resin short-post and crown restoration provides a durable, color-stable resto ration w ith excellent esthetic qualities. U nder n o rm a l m asticato ry fu n c tio n , reasonable diet, and hygiene control, the restoration can be expected to last u n til n atu ral exfoliation of the tooth. P oor o ral hygiene an d a d iet th a t co n tin u e s to p ro m o te caries are the greatest threats to success of the shortpost restoration.
-------------------- JA D A -------------------Inform ation about the products m entioned in this article may be available from the authors. Neither the authors nor the American Dental Association has any commercial interest in any of the products mentioned in this article. Dr. Judd is staff paediatric dentist; Dr. Kenny is dentist-in-chief; Dr. Johnston is head, Division of Paediatric Dentistry; and Dr. Yacobi is staff paediatric dentist, department of dentistry, The H ospital for Sick Children, 555 University Ave, Toronto, Ontario M5G 1X8. Address requests for reprints to Dr. Judd. 1. Mink JR, Hall CJ. Crowns for anterior primary teeth. Dent Clin North Am 1973;17:85-92. 2. Hartman CR. The open-faced stainless steel crown: an esthetic technique. J Dent Child 1983;50:313. 3. Rifkin AJ. Composite post-crowns in anterior primary teeth. J Dent Assoc S Afr 1983;38:225-7. 4. Starkey P. The use of self-curing resin in the restoration of young fractured primary anterior teeth. J Dent Child 1967;34:15-29. 5. Kennedy DB. Paediatric operative dentistry. Bristol, England: John Wright and Sons, 1979:99102. 6. Grosso FC. Primary anterior strip crowns. J Pedodont 1987;11:182-6. 7. Kubo S, et al. Clinical evaluation of composite resin full crowns on primary anterior teeth. Shikwas Gakuho 1984;84:103-8. 8. Kenny DJ, et al. The composite resin shortpost: a review of 625 teeth. Ont Dent 1986;63:128. 9. Yacobi R, et al. C linical and radiographic evaluation of non-aldehyde pulp therapy in primary teeth [Abstract]. J Dent Res 1988:67 (Suppl):751. 10. Grosso FC. Primary anterior strip crowns: a new technique for severely decayed anterior primary teeth. J Pedodont 1987;1:375-84.
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