Contemporary Restoration of Endodontically Treated Teeth. Nadim Z. Baba
in all types of teeth that received crowns than in those that did not. Studies of the physical properties of ETT have produced some differing results, but there are documented changes in some of the physical properties and characteristics of nonvital teeth that may make them more susceptible to fracture.
Outcomes Data for Posts
Laboratory data
A popular misconception is that posts strengthen ETT. However, research indicates otherwise. In fact, numerous studies have shown that, rather than strengthen teeth, posts and cores actually weaken extracted teeth (decrease their fracture resistance) or fail to increase their fracture resistance.51–56 Maxillary incisors without posts were found to resist higher loads than were other types of teeth with posts and crowns.57 Likewise, mandibular incisors with intact natural crowns exhibited greater resistance to transverse loads than ETT with either prefabricated posts or cast posts and cores.58 However, if a ferruled cast post and core was used, the likelihood of root fracture was reduced.58
A condition where a post and core may have a positive impact on a tooth was identified in a photoelastic stress analysis study.59 That research indicated that posts reduced dentin stress in situations where the root canal space was excessively enlarged and the dentin walls were thinned.59
Clinical data
Clinical data also fail to support the perception that posts enhance the survival of teeth. While one investigation demonstrated that teeth with and without posts had the same longevity outcome,60 another clinical study determined that teeth with posts exhibited significantly more apical periodontitis than teeth without posts.61 Results from the latter study indicated that the preparation and placement of a post can actually compromise the apical endodontic seal. The previously cited examination of 1.4 million teeth with initial endodontic treatment found no significant difference between the extracted teeth with posts and those without posts.20
Guidelines for use of a post
While there is no evidence to support the contention that posts promote tooth survival or strengthen the root of a tooth, there is evidence that posts actually can decrease the fracture resistance of ETT.51–56 Consequently, clinicians should recognize that the main purpose of a post is to retain a coronal core that cannot otherwise be placed in tooth structure by some other means.
Clinical Complications of Post and Core Restorations
A review of the literature for clinical post and core studies identified the two most common types of postoperative complications as post loosening and root fracture.62 Both of these negative outcomes were reported in more than 10 studies and were found to be the most common reasons for failure.
Root perforation is a serious complication but was not reported in this literature review.62 Therefore, a literature search was completed to identify clinical studies with data related to the incidence of clinical root perforation. In 1984, Sorensen and Martinoff19 reviewed the patient treatment records and radiographs of nine general dentists. Among 420 posts, only three perforations (0.7%) were noted.19 In another study, a review of radiographs for 327 ETT with posts, most of which were referred by general dentists for a variety of reasons, only 5 teeth (1.5%) with root perforations were identified.63 A third investigation involving a radiographic analysis of 3,178 ETT determined that 1.1% of the teeth had perforations of either the root walls or the floor of the pulp chamber.64
Additional studies published between 2005 and 2010 were identified in which the endodontic treatment was provided by predoctoral dental students.65–68 A review of 388 teeth with 620 treated root canals in an undergraduate dental clinic found perforations in 17 root canals (2.7%).65 A second study involved the assessment of endodontic treatment performed by predoctoral dental students in single-rooted teeth; examination of 100 radiographs of obturated root canals found no evidence of root perforations.66 A third investigation involving 550 teeth treated by predoctoral students reported the incidence of root perforation to be 7.0%.67 A 2010 retrospective study from a university clinic reported a total of 116 root perforations in 5,048 ETT in 2,002 patients for an incidence rate of 2.3%.68 Over a 26-year span, the incidence of root perforation by general dentists and predoctoral dental students ranged from 0% to 7%.68
The literature also has information about perforations as a reported complication in insurance claims, a reason for tooth extraction, and the basis for referral to an endodontist. In a review of 966 dental complications, claims submitted to the Swedish patient insurance program included 183 root perforations related to preparation for posts.69 The teeth identified as having the greatest number of perforations were the mandibular first molar followed by the maxillary first premolar.69 In another study of 119 teeth, iatrogenic perforations and thinning of the dentin to the location of the cementum (a process known as stripping) were responsible for 4.2% of the extractions.70 Of 2,000 patients referred to an endodontist, 1,688 patients required some type of treatment in 2,221 teeth. Perforations were identified in 119 teeth for an incidence of 5.4%,71 well within the range of 0% to 7% reported in other studies.
The aforementioned data on complications reveal why it is important to understand the factors responsible for post loosening, root fracture, and root perforation. Once identified, appropriate steps can be taken to minimize, if not totally avoid, such complications. As already mentioned, the main purpose of a post is to provide a core for a tooth when no other means is available for a coronal buildup; therefore, the following content relates only to clinical situations where a post is needed.
Post loosening
Influence of post form
The geometry, or form, of a post also has been identified as a factor that can contribute to post loosening.72, 73 Threaded posts generally are recognized as the most retentive type of post.72, 73 At the same time, threaded posts also are responsible for producing high stess,74 and tapered threaded posts are the worst stress producers.75, 76 In fact, comparative clinical studies have linked high stress from threaded posts to root fracture rates that are higher than those associated with cemented posts.77, 78 One meta-analysis of clinical studies reported survival rates of 81% for threaded posts and 91% for cemented posts.79 Based on these findings, and to avoid potential root fractures, use of threaded posts is not recommended.
Influence of post length
Optimizing the post length is an important and safer method of preventing post loosening than the use of threaded posts to increase retention.80 Posts that are three-quarters the root length were found to be 24% to 30% more retentive than those that were half the root length or equal in length to the crown height.81 However, with posts that are three-quarters the length of the root, there is an accompanying risk of compromise to the seal of the root canal filling material in teeth with average or shorter-than-average root lengths. What is more, extension of the post spaces to three-quarters the root length also reduces the amount of gutta-percha to less than that required to ensure the maintenance of an adequate seal. Therefore, post length should not be extended to the point that it requires the removal of so much apical gutta-percha that the apical seal is unknowingly compromised.
A number of laboratory studies have reviewed the amount of gutta-percha needed and its effects on the apical seal. It was determined that a large number of ETT specimens leak when there is only 2.0 mm of apical gutta-percha,82 and most specimens leaked when left with 3.0 mm of gutta-percha.83 In addition, a clinical study found significantly more posttreatment periapical radiolucencies in teeth with less than 3.0 mm of apical gutta-percha.84 However, in the presence of at least 4.0 mm of apical gutta-percha, studies show there is little leakage82, 85 or no leakage.86, 87
Based on these data, it appears that 4.0 mm should be considered the minimum amount of gutta-percha required for an adequate apical seal. However, because length determinations are frequently based on radiographic images and the angulations of radiographs vary clinically, it is proposed that 5.0 mm of gutta-percha be retained apically as measured