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| 2010-22 |
| 22-1 |
ISSN (Print) 1013-9052
EISSN 1658-3558
P.O. Box 52500,
Riyadh 11563,
Kingdom of Saudi Arabia
| Tel. |
966-1-467-7328 |
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933-1-467-7308 / 966-1-467-7534 |
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saudidj@ksu.edu.sa |
| 2008-21-01-15-22-full |
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Digital assessment of the radiographic features of dental
OBJECTIVE: The aim of this study was to radiographically assess the different types of post made by undergraduate dental students. MATERIALS AND METHODS: Study sample were collected in 2007 from the existing dental records of 272 patients who received treatment with different types of post and crowns between September 2004 and May 2007. The treatment was performed according to the classical prosthodontic guidelines. All radiographs were scanned and measurements were made using special computer software (ImageToolR). RESULTS: Radiographs of 150 teeth with posts were evaluated: 119 teeth with cast post and core, and 31 teeth with prefabricated post. The remaining apical gutta percha (RAGP) was acceptable in 142 teeth (94.7%). Teeth with no gap between tip of the post and gutta-percha (GP) was 81 teeth (54%), 60 teeth (40%) with gap less than 2 mm and 9 teeth (6%) with a gap more than 2 mm. The long axis of the post coincided with the long axis of the root in 125 teeth (83.3%). Post length to crown length ratio was 1:1 or more in 107 teeth (71.3%) while in 43 teeth (28.7%), the ratio was less than one. Fifty-two teeth (34.7%) showed unacceptable width while 92 teeth (65.3%) showed acceptable width in the coronal third. In the middle third, 26 teeth (17.3%) showed unacceptable width and 124 teeth (82.7%) showed acceptable width. In the apical third, 12 teeth (8%) had unacceptable post width while 138 teeth had acceptable post width. CONCLUSION: This study showed that the radiographic features of the cases made by the undergraduate dental students were mostly satisfactory.
Almost 25% of prosthodontically restored teeth are non-vital and endodontically treated before prosthodontic restoration.1 Since the endodontic treatment of teeth results in loss of structural strength, crowning of such teeth is considered an integral component of the endodontic therapy.2 However, the location of an endodontically treated tooth seems to determine the risk of fracture. Therefore, adhesive-retained composite-resin or full coverage crown restorations are recommended. Goodacre and Spolnik3 concluded that crowns should generally be used on endodontically treated posterior teeth but not necessary on relatively sound anterior teeth.
There is some controversy about the necessity of post placement before prosthetic restoration.4 Some authors5,6 consider the placement of a post before prosthetic rehabilitation as obligatory while others7 believe that post space preparation may further weaken the abutment tooth. Therefore, post placement should be considered only when the retention for the core material is inadequate and does not fulfill the objective of strengthening the endodontically treated tooth.8,9 The criteria followed in preparing the post space in the literature indicate the post length in long-rooted teeth to be as close as possible to three-fourth of the root length for better retention and stress distribution. Sorensen and Martinoff10 found a marked increase in the clinical success rate when the post was equal to or greater than the crown length. However, not many teeth have posts that are equal in length to the crown because of limited root length and the need to retain 4 to 5 mm of apical gutta-percha (GP). Kvist et al.11 found that after the preparation of post space, roots with residual apical GP of < 3 mm are associated with a higher incidence of periapical radiolucency compared to roots with longer residual root canal filling. Standlee et al.12 studied the stress distribution from endodontic posts and found that stress concentration decreased with increased post length. According to Weine,13 short posts can increase the possibility of root fracture. Post diameter should be controlled to preserve root structure so that perforations are less likely to occur and root fracture resistance is enhanced. Trabert et al.14 found that increasing post diameter decreases the tooth resistance to fracture. Post diameter should not exceed one third of the root diameter at any location. Krupp et al.15 found that post length is more important for retention than post diameter. Post long axis should coincide with the long axis of the root.16 Ideally the post should be in contact with the remaining GP. In a study by Moshonov et al.,17 there was an increase in the disease rate and unfavorable outcomes when the distance between the post and the remaining root canal filling is greater than 2 mm. They concluded that the larger the gap, the higher the disease rate in the periapical area. GP extension considered acceptable up to one millimeter short from the radiographic apex.18 Goodacre et al.19 in 2003 reported the most common complications of posts and cores are post loosening (5%), root fracture (3%), caries (2%) and periodontal disease (2%). The preparation of an endodontically treated tooth to receive any type of post is made following certain guidelines. The close adherence to those guidelines affects the quality of post design and prognosis. For example, one of the guidelines is to leave 3-5 mm of apical GP or more to maintain the apical seal. If less than 3 mm of GP is left, apical seal is violated and periapical pathosis may develop.11 The width of the post should not be more than one third of the root. If the post becomes wider than one third of the root, this will weaken the root and it may fracture.14 On the other hand, thin post is more prone to fracture. The length of the crown to the length of the post ratio should be one or less. If the crown is longer than the post, more stresses are concentrated on the root and the post and/or the root may fracture.12,13 This explains the importance of following certain guidelines when preparing an endodontically treated tooth to receive a post for improving the retention. The design of the post will directly affect the longevity of the restoration and /or prognosis of the tooth. The students are trained to follow those guidelines when preparing an endodontically treated tooth for a post. The aim of this study was to evaluate radiographically different types of post made by undergraduate dental students. The length of the post, remaining apical GP (RAGP), width of the post, and post/crown ratio were evaluated radiographically according to certain guidelines. The present study might give a feedback retrospectively about the quality of students work and how close they follow such guidelines.
Study sample were collected in 2007 from existing dental records of 272 patients received treatment with different types of posts between September 2004 and May 2007. Posts were made by 4th and 5th year dental students at College of Dentistry, King Saud University. A total of 150 acceptable periapical radiographs of 150 posts were included in this study. Radiographs with dimensional errors were excluded. The parallel radiographic technique was used with E-speed films (Kodak®, Ektaspeed, Eastman Kodak Co., Rochester, NY, USA). The posts included were prefabricated post (ParaPost® XP™, Coltene Whaledent, Langenau, Germany) and cast post and cores using either direct or indirect technique. The treatment was performed according to the classical prosthodontic guidelines.32025
Some of these guidelines can be summarized according to the following (Fig. 1):• Minimum of 3-5 mm of apical GP should be left to maintain the apical seal. • The post length/crown length ratio should be 1:1 or more. • Post diameter should be made according to the endodontic instrumentation but not exceeding one third of the root width. • No gap between the tip of the post and the apical GP. • Long axis of post coincides with the long axis of the root. All PA radiographs were scanned by (Epson Perfection 4870 Photo Scanner, Epson®, Long Beach, USA) to be digitalized with the original size of the radiograph maintained. Special software (ImageTool®, University of Texas Health Science Center in San Antonio, USA) was used to make the measurements. The software made the measurements by calculating the number of pixels that exists in one millimeter which was already calibrated. The calculations were made by one examiner. The previously mentioned criteria were evaluated as acceptable and not acceptable as shown in Table 1. The other criteria were evaluated and measured such as the extension of the apical GP and any evidence of perforation. Post length was measured from the apical end of the crown to the apical end of the post. The width of the post was measured in three different areas (i.e. coronal, middle, apical) in relation to the root. The long axis of the postwas determined by drawing a line in the center of the post vertically and another line passing through the center of the root2 (Fig. 2). The angle between the two lines was measured to evaluate the degree of deviation of the post. RAGP measured from its coronal end (not the apical end of the post) to the radiographic root tip according to the following:15,20 • If it is extended up to 1 mm short of the radiographic tip of the root, it is considered acceptable. • Shorter than 1mm from tip, it is considered under-extended. • Extended beyond the tip, it is considered over-extended. All the measurements were made by one examiner. Intra-examiner test was done with less than 5% difference. Statistical analysis was made using SPSS 13 software.
The RAGP was acceptable (3 mm and more) in 142 teeth (94.7%) and not acceptable (less than 3 mm) in 8 teeth (5.3%). Table 2 showed the RAGP in relation to the type of post used. All teeth with unacceptable RAGP were treated with cast post and cores. Teeth with no gap between tip of the post and GP were 81 teeth (54%), 60 teeth (40%) with gap less than 2mm and 9 teeth (6%) with a gap more than 2mm. The distribution of teeth between cast post and core, and prefabricated post was shown in Table 3. In 125 teeth (83.3%), the long axis of the post coincided with the long axis of the root while 25 teeth (16.7%) did not. The mean angle of deviation was 5.310. Figure 3 showed the long axis discrepancy of the two types of post in relation to the root long axis. Two posterior teeth restored with prefabricated post showed radiographic evidence of perforation. Post length to crown length ratio was 1:1 or more in 107 teeth (71.3%) while in 43 teeth (28.7%), the ratio was less than one (Fig. 4). Table 4 summarized the width of both types of post in the coronal, middle and apical part of the post. Forty-two of the treated teeth (28%) had periapical radiolucency, while 108 teeth (72%) had no apical radiolucency. The RAGP was considered to have acceptable extension in relation to the radiographic tip of the root in 86 teeth (57.3%), 16 teeth (10.7%) were overextended and 48 teeth (32%) were underextended.
According to Moshonov et al.17 teeth with a gap between post and RAGP of more than 2 mm usually associated with unfavorable clinical outcomes. In that study, 20% of the cases had a gap more than 2 mm compared to only 6% of cases with such finding in the present study. Depending on Moshonov's conclusion, fewer teeth were expected to have less unfavorable clinical outcomes in this study. Grieve and Radford23 found that 40% of the cases they examined showed a defect (ranging from 1 to 7 mm) between the end of the post and root filling. In another study,26 they found 22% of the cases with space between the end of the post and root filling. The long axis of the post was deviated from the long axis of the root with mean angle of deviation of 5.310 in 16.7% of the teeth. This is slightly less than the finding of Grieve and Radford23 (20%). Two cases of posterior teeth with radiographic evidence of lateral perforation were both treated by prefabricated posts. The post length to crown length ratio was 1:1 or more in 71.3% of the cases. This confirmed the findings of Al-Hamad et al.22 where only 58% of the cases examined showed acceptable post to crown length ratio. Lewis and Smith24 reported that acceptable post length was achieved in only 18% of the cases. In Grieve and Radford study,23 only one third of the cases showed post length equal to the crown length. Absolute guidelines for optimal post length are difficult to define. Ideally the post should be as long as possible without jeopardizing the apical seal or strength and integrity of the remaining root structure.27 Maintaining an apical seal of 5 mm is considered satisfactory.25 It is generally accepted that the length of the post into the root canal should normally be at least 10 mm or equal to the length of the natural crown as measured from the gingival margin of the preparation.22,26 In case of short roots and long clinical crowns, an apical seal of 3 mm is considered acceptable.23 Generally, 3-5 mm is needed to maintain the integrity of the apical seal.27 Nevertheless, post length ranging from 8 to 12 mm, depending on the length of the root, is generally considered satisfactory.28 A long post will not only ensure optimal alveolar bone support but will also promote stress distribution and retention.29 On the other hand, excessively long post that enters the narrow apical part of the root may weaken it30 and disturb the apical seal.31
In this study, 42 teeth (28%) showed periapical pathosis which was considered relatively high. This result was comparable to Al-Hamad et al. study,22 where 34% of the cases had periapical pathosis. Since the endodontic history was not available for some of the cases, it is difficult to draw conclusions from the radiographic evidence of periapical radiolucent area alone. It is possible some of the cases had recent root canal treatment with incomplete periapical healing.27 Poor impression technique or poor laboratory work may have accounted for the cases that had a space between the end of the post and the root filling. In some cases, the post space may have been prepared adequately in regard to length but the preparation was not optimally utilized to extend the post fully into the prepared canal. The use of clinically proven impression material and technique may help to reduce these problems. Perhaps the use of either preformed or burnout style posts rather than simply taking impressions of the post canals would reduce the problem of inadequate post fit.27,28 Radiographs still show dimensional distortion.34 Vertical distortion occurs equally in the crown and root of the radiograph, and since crown-to-root ratio is not dependent on absolute values, the effect of vertical distortion on the ratio was minimal.35 Limitations of this study included the small sample size and the evaluated radiographs taken by different technicians. Also, since majority of the teeth were treated by cast post and core compared to prefabricated post, valid comparison cannot be made between the two post types.
     
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