PRACTICE I N B R I E F The timing of post placement following root canal treatment is critical to maintain an apical seal to the root filling and provide a coronal seal to the root canal system. Appropriate gutta-percha removal and post space preparation is important to prevent unnecessary weakening of the root dentine, damage to the periodontium and post perforation. 2 Within the limitations of root length, curvature and maintaining 4–5 mm of apical gutta- percha for an apical seal, post length is critical to retention of post-retained crowns. Preservation of coronal tooth tissue is important in order that a ferrule can be created, reducing the risk of root fracture. Tooth preparation for post-retained restorations D. N. J. Ricketts,1 C. M. E. Tait,2 and A. J. Higgins3 Failure of root canal treatment and/or post crowns can be avoided in many cases if appropriate tooth preparation is carried out. This paper discusses the rationale for the timing of post placement following root canal treatment and appropriate methods for removal of gutta-percha prior to post space preparation. The basic principles of post space preparation are described, which should reduce the risk of weakening the root unnecessarily, causing damage to the periodontium and post perforation. INTRODUCTION epidemiological studies paints a bleaker picture, RESTORATION OF THE Teeth that have received post-retained restora- with only a 61–77% success rate. An explana- ENDODONTICALLY TREATED tions can fail for a variety of reasons including tion for the difference may lie in the fact that the TOOTH loss of retention, vertical root fracture, root perfo- former root treatments were carried out under 1. Restoration of the root- ration and failure of the root canal filling. Many carefully controlled environments in either spe- filled tooth: of these failures can be avoided with a thorough cialist practice or dental schools. Today, the suc- pre-operative assessment pre-operative assessment and appropriate tooth cess rate amongst General Dental Practitioners 2. Tooth preparation for preparation. The pre-operative assessment of a may be better, as the majority of the studies post-retained restorations tooth that has previously been root filled by reviewed predate 1990 and since then knowl- 3. Post and core systems, another dentist, or by the same dentist some years edge and techniques for root canal preparation refinements to tooth ago, has been discussed in the first of these publi- have improved. In addition, in some studies the preparation and cations. However, dentists are frequently faced observation period was low, varying from as lit- cementation with the dilemma of how long to wait, following tle as six months to ten years.2 Clearly six 4. Weakened anterior roots root canal treatment, before a definitive restora- months is inadequate follow-up and the Euro- - intraradicular tion is placed. In some cases this will be a post and pean Society of Endodontology suggest radi- rehabilitation indirect restoration which has a relatively high ographic assessment after one year and if com- financial cost to the patient. Retrievability is a plete healing has not occurred, follow-up for 1*Senior Lecturer/Hon Consultant in concern if the endodontic treatment is unsuccess- four years. Only then is an asymptomatic root Restorative Dentistry, Dundee Dental ful. As such, many dentists want to establish the canal treated tooth with a persistent periradicu- Hospital and School, Park Place, Dundee, success of the endodontic treatment first. But is lar radiolucency condemned a failure.3 DD1 4HR. 2Lecturer in Endodontics, Dundee Dental this approach logical and appropriate? Four years is obviously an unacceptable time Hospital and School, Park Place, Dundee, to wait before placing a definitive restoration DD1 4HR. / Specialist Private Practice, WHEN SHOULD THE DEFINITIVE RESTORATION and cross-sectional studies have shown that the Edinburgh, 3Vocational Trainee, Falkirk, Scotland BE PLACED? technical quality of the finally obturated root *Correspondence to: David Ricketts, The success rate of endodontics canal is strongly correlated with the success of Dundee Dental Hospital and School, Park Carefully controlled clinical studies have evalu- the root filling.4,5 Short or over-extended root Place, Dundee, DD1 4HR. ated the success rate of conventional endodontic fillings or those with an incomplete apical seal Refereed Paper treatment based upon radiographic evaluation. have been found to be associated with higher doi: 10.1038/sj.bdj.4812249 These have shown that between 83% and 94% of failure, as have re-treatment cases.5–9 Whilst © British Dental Journal 2005; 198: treatments are successful.1 However, data from these factors can be evaluated, resolution of an 463–471 BRITISH DENTAL JOURNAL VOLUME 198 NO. 8 APRIL 23 2005 463 PRACTICE important than the apical seal of the root canal filling.24,25 A restoration with a poor coronal seal (Fig. 1) will potentially allow saliva, bacte- ria and endotoxins access to the root canal and Fig. 1. Periapical radiograph of possible penetration along its entire length tooth 47 showing a poor coronal leading to periradicular periodontitis.25–33 The seal distally to the crown and core endotoxins alone can predictably move potentially allowing bacteria and bacterial endotoxins access to the through an obturated root canal and so bacte- root filling and root canal system. ria around a defective coronal restoration, This could account for the could theoretically sustain a periradicular periradicular periodontitis inflammation.26 associated with the distal root. The 34 fractured instrument in one of the In reality, Ray and Trope (1995) have shown mesial root canals may additionally that in 1,010 endodontically treated teeth, exam- lead to a poor apical seal and ined radiographically, the quality of the coronal associated periradicular restoration is more important than the endodon- periodontitis. tic treatment for apical periodontal health. How- ever, in this study none of the coronal restora- apical lesion will occur even in the absence of a tions were post retained. This was addressed by root filling,10 provided all the infected root canal Fox and Gutteridge (1997)35 in a laboratory tissue is removed and ingress of bacteria is pre- study. They investigated cast post and cores vented by a coronal restoration which provides a cemented with zinc phosphate cement, pre- bacterial seal. Patients who present with a root formed stainless steel (Paraposts, Whaledent Inc. canal filling placed by another dentist therefore NY, USA) posts cemented with a resin luting pose a problem, as the dentist will be unsure if cement and composite core, and finally an alu- an aseptic technique was used to prepare and minium temporary post (Parapost) with a poly- irrigate the root canal; the use of rubber dam carbonate temporary crown (Directa) filled with and copious amounts of antibacterial irrigant, self-curing acrylic (Trim), cemented with a tem- such as sodium hypochlorite, being of para- porary luting cement. It was shown that there mount importance. was no significant difference in the coronal A final factor to be borne in mind when leakage around cast post and cores and the pre- determining the prognosis of a root canal filling formed stainless steel posts and composite cores. is whether there was a periradicular lesion pres- However, the temporary post crowns demon- ent prior to root treatment. The success rate can strated significantly more leakage than the per- fall from 96% where there was no pathology evi- manently cemented posts. The authors therefore dent to 86% where there was a periradicular suggest immediate restoration of the tooth with lesion.5 a pre-fabricated post and composite core, as the These features, such as the knowledge of an need for a temporary post crown is unnecessary. aseptic root canal preparation, obturation to If temporary post crowns are used, they should achieve an apical and coronal seal, and no evi- have a good marginal fit and only be left in dence of pre-operative periradicular pathology place for as short a time as possible. can be accompanied by a good prognosis and delaying post placement serves no purpose. Advantages of immediate post placement Following obturation of the root canal, immedi- Coronal versus apical seal ate preparation for post placement has a number Historically, endodontists have paid great of additional advantages. The operator has importance to the creation and maintenance of greater familiarity with the root canal morphol- an apical seal during obturation and post space ogy and its working length, and there is less risk preparation.11 The effect of preparation tech- of coronal tooth tissue fracturing, so losing the nique,12 irrigant,13 removal of the smear reference point from where the working length layer,14 how the root canal is dried,15 which was determined. This leads to the appropriate obturation technique is used16 and which sealer amount of gutta-percha removal and less risk of has been used17–22 have all been investigated post perforation. with regard to the integrity of the apical seal of Concerns that early preparation is likely to a root canal filling. Most of these laboratory disrupt the apical gutta-percha seal can be dis- studies have used dye penetration techniques pelled as the reverse is true.36,37 Fan et al to assess the apical seal, however, a recent (1999)36 found more apical leakage after delayed study of 116 teeth root canal treated in vivo and post preparation compared with immediate extracted at least six months later, has cast preparation and removal of laterally compacted doubts as to the clinical relevance of the apical gutta-percha with either AH26 or Pulp Canal seal.23 In this study all of the teeth demonstrat- sealer. In a similar dye leakage study, immediate ed dye leakage irrespective of whether the preparation of canals obturated with gutta- endodontic treatment was deemed to be suc- percha and a zinc oxide–eugenol based sealer cessful or not.