Ferrule Effect - SAGE Journals

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Ferrule Effect

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Review

Ferrule Effect: A Meta-analysis J.A. Skupien1, M.S. Luz1, and T. Pereira-Cenci1

Abstract: The aim of this study was to systematically review the literature for laboratory and clinical studies to evaluate the effect of ferrule in restored endodontically treated teeth. The search was conducted in 2 databases (PubMed, Scopus) with no publication year/language limits. From 1,872 potentially eligible studies, 124 studies were selected for full-text analysis, and 37 were included for review, with 32 of those considered in the meta-analysis and 5 considered in the survival analysis. Two reviewers independently selected the studies, extracted the data, and assessed the risk of bias. For laboratory studies, a meta-analysis was performed for the comparison of the fracture resistance of teeth with and without ferrule, and 3 subgroup analyses were conducted for ferrule height, post type, and type of tooth. For clinical studies, the Kaplan-Meier method was used to determine the survival of restorations, with log-rank test used to identify differences between groups (α = 5%). Teeth without ferrule had a lower fracture resistance ( P < 0.00001), and the higher the height of ferrule, the greater the fracture resistance was, irrespective of the type of post ( P < .000001). Teeth with ferrule had higher clinical longevity ( P = 0.002); however, the presence of a ferrule was related to higher survival only for premolars ( P = 0.05). In conclusion, the presence of a ferrule is

responsible for an improvement in the fracture resistance of the restoration in laboratory studies. Yet, other clinical factors besides the ferrule may be associated with survival in molars and anterior teeth and need to be further investigated. Knowledge Transfer Statement: The results of this study can be used by clinicians when deciding which approach to use when planning the restoration of endodontically treated teeth with and without ferrule. Ferrule may lead to higher tooth/restoration survival, while tooth location may influence therapeutic decisions. Keywords: systematic review, survival, fracture resistance, endodontically treated teeth, ceramics, clinical trials Introduction Restoration of endodontically treated teeth may be challenging in clinical practice (Skupien et al. 2013), as the remaining dental structure is often fragile because of the access opening for the pulp chamber and endodontic treatment, marginal ridge loss, and caries (Juloski et al. 2012). Therefore, placing a post in the root canal is required for retention of the restoration (Skupien et al. 2013). In addition, the traditional approach is still to place a crown after endodontic treatment and post cementation (Sarkis-

Onofre, Jacinto, et al. 2014), although direct restorations may be indicated in certain cases (Grandini et al. 2005). Remaining coronal dental structure is considered fundamental for treatment prognosis (Ferrari et al. 2012), with the ferrule effect considered one of the crucial factors influencing the clinical outcome of endodontically treated teeth. A circumferential dentin collar of 1.5 to 2 mm in height is reported to be directly associated with a higher fracture resistance and, as a consequence, a longer survival, but the latter remains to be proven (Mancebo et al. 2010; Watanabe et al. 2012; Samran et al. 2013). This collar is more important to prevent fracture than the placement of an intraradicular post (Al-Wahadni and Gutteridge 2002; Juloski et al. 2012; Ferrari et al. 2012; Juloski et al. 2014). In clinical practice, the ferrule effect is usually uncertain and mostly limited by coronal destruction with low residual remaining dental structure (Skupien et al. 2013). Thus, in many situations, a ferrule may not be present or may be partially present, decreasing post dislodgement resistance and enhancing the risk of fracture (Juloski et al. 2012). Although the presence of a ferrule is related to fracture resistance in vitro and survival in clinical studies, this conclusion is based on the assumption that these groups are comparable in all other aspects. However, other factors may influence the prognosis of the restoration, with a

DOI: 10.1177/2380084416636606. 1Graduate Program in Dentistry, Federal University of Pelotas, Brazil. Corresponding author: T. Pereira-Cenci, Graduate Program in Dentistry, Federal University of Pelotas, Brazil, R Gonçalves Chaves 457, Pelotas, RS, 96015-560, Brazil. Email: [email protected] A supplemental appendix to this article is published electronically only at http://jdrctr.sagepub.com/supplemental. © International & American Associations for Dental Research 2016

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lack of the ferrule effect (Skupien et al. 2013). The lack of resistance to support the fracture or post/core fracture may be connected and may result in tooth loss. Therefore, the aim of this study was to 1) evaluate the ferrule effect in endodontically treated teeth in laboratory and clinical studies with a meta-analysis and survival analysis; 2) test the influence of variables for type of tooth, post, and remaining dental height on fracture resistance (in vitro) and survival (in clinical studies); and 3) verify if in vitro results are comparable with the clinical outcomes. The hypothesis tested was that the ferrule effect would be associated with higher fracture resistance (in vitro) and clinical survival in endodontically treated teeth, irrespective of other factors. Materials and Methods Data Sources

This systematic review was reported according to the PRISMA statement (Preferred Reporting Items for Systematic Reviews and Meta-analyses; Liberati et al. 2009). Two electronic databases (MEDLINE via PubMed and Scopus) were searched to identify manuscripts that could be included in the review. The following search strategies were performed: 1) computer search of databases, 2) review of reference lists of all included articles, and 3) contact with authors and experts about the issue. No publication year or language limit was used, and the last search was performed June 2015. The search strategy was as follows: ((endodontically treated OR nonvital OR pulpless) AND (teeth OR tooth)) AND (post OR core OR ferrule OR cusp OR 2 mm OR height OR surface OR remaining OR cej OR fracture OR survival). References of all included articles were manually searched for further relevant studies that could fulfill the inclusion criteria, which were in vitro and clinical studies that evaluated the effect of a ferrule in restored endodontically treated teeth. For the in vitro studies, data on fracture resistance were considered (in human and bovine teeth) through use of any type of post, cement, or crown material. For the 32

clinical studies, data were extracted from studies in which the teeth received a single crown and that compared the presence of a ferrule with a control group without a ferrule. The outcome fracture resistance, in MPa, was required for inclusion. Papers were excluded that did not provide such data, even after an e-mail request to authors (at least twice), or due to the impossibility of converting data to MPa. Search Steps: Screening and Selection

Step 1: Titles and abstracts were reviewed by 2 authors (M.S.L. and T.P.C.) and selected for further review if they met the inclusion criteria (1,872 potential eligible articles). Step 2: Abstracts were independently reviewed by 2 authors (M.S.L. and T.P.C.) and selected per their consensus according to the same inclusion criteria used in step 1. If consensus was not reached, the abstract was set aside for further evaluation. Step 3: Full-text articles of abstracts selected in step 2 were retrieved and reviewed by 1 author (M.S.L.). Inclusion was based on the consensus between 2 investigators (M.S.L. and T.P.C.). Disagreements were discussed with a third author (J.A.S.). The reference lists of all articles selected in step 3 were reviewed, and the full texts of potentially interesting studies were examined. Data Extraction

A protocol for data extraction was defined and evaluated by 2 authors (M.S.L. and T.P.C.) and divided into in vitro and clinical studies. In vitro studies were excluded if they did not present a comparison between ferrule heights (or presence/absence of ferrule), they presented direct restorations, or strength was applied on the post. Clinical studies were excluded if they did not present data on ferrule height or if they restored with direct restorations. Data were extracted from full-text articles by 1 author (M.S.L.) and reviewed by a second (T.P.C.) using a standardized outline. The

extraction of fracture resistance (in vitro) and survival (clinical studies) data was conducted. To simplify the identification of variables found in the papers, similar information was categorized into groups. Authors were contacted via e-mail if data were missing or more information was needed for studies that did not report the precise fracture resistance values and showed the results in a graph or figure. In the selected studies, only the data of interest were extracted to be analyzed in the meta-analyses. For example, if a study presented direct and indirect restorations, only the indirect restoration data were collected. To determine pooled estimates, each study contributed with the interested estimate. Assessment of Risk of Bias

The risk-of-bias evaluation for the in vitro studies was conducted according to the description of the following parameters for the quality assessment (Montagner et al. 2014; Sarkis-Onofre, Skupien, et al. 2014): type of post (metal or not), post design (diameter, length), periodontal ligament simulation, force application (considering occlusal contacts in vivo), description of sample size calculation, and blinding of evaluators. If the authors reported a parameter, the paper had a Y (yes or low risk) on that specific parameter; if it was not possible to find the information, the paper received an N (no or high risk). Papers that reported 1 to 3 items were classified as being a high risk of bias; 4 or 5 items, medium risk; and 6 or 7 items, low risk (Appendix). The risk-of-bias analysis was conducted in the selected clinical and in vitro studies according to the Cochrane Collaboration tool, via Review Manager 5.3 (Nordic Cochrane Centre, Cochrane Collaboration, Copenhagen, Denmark; Appendix). Data Analyses In Vitro

All possible comparisons of fracture resistance of groups with or without ferrule were part of the meta-analysis and subgroup analyses. The estimated effect of pooled data was obtained by the comparison of means and was represented by the weights between

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different means (P < 0.05 was considered statistically significant). Statistical heterogeneity of the treatment effect among studies was assessed with the Cochran’s Q test, with a threshold P value of 0.1, and the inconsistency I 2 test, in which values >50% were considered indicative of high heterogeneity (Higgins and Green 2009). One meta-analysis of all of the pooled data and 3 subgroup analyses were performed through the random-effect model. In consideration that the analyses of ferrule height, type of post, and tooth location comparison could present a high heterogeneity, subgroup analyses based on the different heights were carried out to explore that influence on the results. The following analyses were carried out: 1) 3-mm ferrule vs. no ferrule, 2-mm ferrule vs. no ferrule, and 1-mm ferrule vs. no ferrule; 2) with or without a ferrule in metal or nonmetal posts; and 3) with or without a ferrule in anterior or posterior teeth (molars and premolars were analyzed separately). All analyses were conducted using Review Manager 5.3. Clinical Studies

Data were divided into 2 categories: success of the restoration and survival of the tooth. If no failure was reported, both the tooth and the restoration were considered to have successfully survived. If a restoration had failed but the failure was considered eligible for repair, the success of restoration stopped, but the tooth survived. If a failure was reported as leading to extraction (or extraction itself), teeth and restorations were both considered failures. In all cases, data were divided according to the available author’s information. The longevity of restorations and teeth was analyzed with Kaplan-Meier statistics and log-rank tests for differences between groups (P < 0.05). Statistical analyses were performed with SPSS 22 (SPSS Inc., Chicago, IL, USA). Results Thirty-two in vitro and 5 prospective clinical studies were considered for statistical analysis (Appendix). For the included 32 in vitro studies, 6 used

bovine teeth; 10, human posterior teeth; and 16, anterior human teeth. Studies performed various cycling techniques, with 5 performing mechanical cycling, 3 performing thermocycling, 9 storing the specimens in distilled water for 7 d, 3 storing the specimens in distilled water for 30 d, and 12 not reporting if there was any cycling method. Clinical studies presented follow-up periods ranging from 21 to 204 mo. Only 1 study reported using a cast metal post, while the other studies had both prefabricated metal and fiber posts, with 1 also using a fiber post with zirconia. The risk-of-bias analysis was performed according to previously published literature (Sarkis-Onofre, Skupien, et al. 2014), and the in vitro studies were considered as presenting a medium risk of bias. For the clinical studies, most studies were considered as presenting an unclear risk of bias (Appendix). Meta-analysis

Statistically significant differences were found, with the ferrule group presenting a higher fracture resistance versus the groups without a ferrule (–213.92; 95% confidence interval [95% CI]: –247.09 to –180.75; Fig. 1). For the subgroup analysis, teeth with ferrule showed a higher fracture resistance when compared with teeth without ferrule for metal posts (–245.01; 95% CI: –299.13 to –190.88) and nonmetal posts (–185.97; 95% CI: –225.35 to –146.59), while no statistically significant difference was found among types of posts (P = 0.08; Fig. 2). When ferrule heights were considered, there was increased fracture resistance for heights of 1 mm (–125.21; 95% CI: –167.57 to –82.85), 2 mm (–218.34; 95% CI: –259.09 to –177.60), and 3 mm (–310.52; 95% CI: –431.68 to –189.36), with the highest ferrule height showing the highest fracture resistance (P = 0.0008; Fig. 3). For the comparison of anterior versus posterior teeth, the presence of a ferrule increased fracture resistance for both tooth groups—anterior (–229.05; 95% CI: –285.74 to –172.36) and posterior (–182.21; 95% CI: –232.94 to –131.49)—without statistically significant differences between tooth groups (P = 0.23; Fig. 4).

Survival Analysis

A meta-analysis was not possible for clinical studies because of heterogeneity of the data. Thus, longevity was evaluated, and teeth with ferrules presented higher longevity when compared with teeth without ferrules, for both tooth survival (P = 0.002) and restoration survival (P < 0.0001; Fig. 5). Regarding tooth location, premolars with ferrules showed higher survival (P = 0.05), while molars and anterior teeth did not present statistically significant differences for their survival with or without a ferrule (P > 0.05). Discussion The present study was the first to systematically review the literature and evaluate the ferrule effect in endodontically treated teeth that received a post and crown in laboratorial and clinical studies. This study compared in vitro results with clinical outcomes. Comparisons among studies should take into account the risk of bias. Although most in vitro studies presented low risk of bias for most evaluated criteria, the assumption that these groups are comparable in all other aspects to clinical practice may not be valid but may directly influence future research. In terms of clinical studies, a low quality of report impaired a better risk-of-bias analysis, and deficiencies in the reporting of trials can affect different spheres of knowledge and society because the methodological aspects and research findings are used to base decisions made by clinicians and provide future research questions (Montenegro et al. 2002; SarkisOnofre et al. 2015). Among the factors that could influence our comparison are tooth location (anterior or posterior), type of post (metallic or not), restorative material (full metal, metal ceramic, or metalfree crown), and luting material (selfadhesive, regular, glass ionomer cement, or zinc phosphate). However, the present study did not consider the various types of restorations and luting materials. Indirect and direct restorations act in distinct ways, present singular mechanical behavior, and should be taken into 33

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Figure 1. Meta-analysis (with or without ferrule).

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Figure 2. Meta-analysis considering post type (metal or nonmetal).

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Figure 3. Meta-analysis considering ferrule height (1, 2, or 3 mm).

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Figure 4. Meta-analysis considering tooth location (anterior or posterior).

account in future studies. It is important to highlight that in this study, no separation for type of post cemented with different luting materials was considered, as several subgroups would be created, making the meta-analysis impossible. Still, although the latter is important, it was not the aim of this systematic review; thus, the luting materials could influence outcomes, but that issue remains to be

tested. The remaining tooth structure can directly influence tooth survival. Some in vitro studies may consider varying ferrule heights, with comparisons among partial ferrules (buccal, lingual, mesial, complete, incomplete) to make a direct comparison with clinical practice. The amount of remaining tooth root structure is also variable in clinical practice—the so-called ferrule width (Jotkowitz and

Samet 2010)—but was not considered in most of the included studies. There is consistency among the studies that coronal dentinal structure, in many situations, may not be able to stand occlusal forces applied to the tooth (Eraslan et al. 2009). The ferrule effect was always beneficial, irrespective of the subgroup analysis in all in vitro studies. Additionally, the higher the ferrule, the 37

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Figure 5. Kaplan-Meier analysis, in months: survival (A; log-rank test, P = 0.002) and success (B; log-rank test, P < 0.0001); (C) anterior teeth (P = 0.329), (D) premolars (P = 0.05), and (E) molars (P = 0.559).

better the results. This corroborates finite element analysis studies showing that the presence of a ferrule decreases dentinal stress for both metallic (Eraslan et al. 2009) and nonmetallic posts (Watanabe et al. 2012). This meta-analysis showed no difference when metallic and nonmetallic posts were compared, although metallic posts are expected to present a different behavior, as nonmetallic posts present an elastic modulus more similar to that of dentin, resulting in a better stress distribution (Silva et al. 2009). A possible reason this occurred is that other factors, as previously mentioned, are responsible for fracture resistance, with ferrule and type of post (Naumann et al. 2012). The presence of ferrule has been extensively tested in vitro (Aykent et al. 2006; Pereira et al. 2006; Meng et al. 2007; Gomez-Polo et al. 2010; Bassir et al. 2013; Evangelinaki et al. 2013). Our results corroborate the findings that the presence of a ferrule will increase fracture resistance, irrespective of the restorative technique and tooth location. Moreover, 38

the amount of coronal dental structure was also related to a better outcome. Thus, although other factors, such as ferrule width and number of remaining walls, were not evaluated, they will probably lead to a more stable restoration, increasing the restoration longevity. Few clinical studies have assessed the ferrule effect. Among the included studies, it was possible to note that the presence of a ferrule was related to a lower failure rate, which is directly related to the in vitro results of our analysis. Yet, a difference was found when clinical and laboratorial results were compared—namely, tooth location influenced tooth survival. For anterior teeth and molars, the presence of a ferrule was not related to higher survival, while it could be clearly observed that premolar survival is directly influenced by the presence of ferrule. This may be linked to a more invasive treatment in premolars (with the placement of a crown), as they survived more often than the molars and anterior teeth (Baba et al. 2009; SarkisOnofre, Jacinto, et al. 2014). Crown placement will result in a more aggressive

treatment but may also be beneficial, acting as a reinforcement with the loss of marginal ridges and pulp chamber openings (Willershausen et al. 2005; Baba et al. 2009). Irrespective of the presence of ferrule, tooth location is an important factor to be considered. Molars and anterior teeth showed an increased rate of survival. Anterior teeth have fewer occlusal requirements, and the molars will support more intense occlusal demands due to their anatomy. Premolars can also participate in occlusal movements, receiving both axial and oblique forces (Meng et al. 2007). Premolars will perform differently, while it is reasonable to say that premolars will fail more than molars and anterior teeth, as previously discussed. It is also reasonable to suggest that other factors are associated with ferrule height for a better performance of the restoration, such as root and ferrule width, occlusal pattern, type of post, and luting agent. These factors should be considered and specially reported in future clinical studies. Although the presence of a ferrule is responsible for an improvement in the

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fracture resistance of teeth in laboratory studies, other clinical factors may be associated with the survival of molars and anterior teeth and need to be further investigated. Author Contributions J.A. Skupien, contributed to conception, design, and data analysis, drafted and critically revised the manuscript; M.S. Luz, contributed to conception and design, drafted the manuscript; T. PereiraCenci, contributed to conception, design, and data analysis, critically revised the manuscript. All authors gave final approval and agree to be accountable for all aspects of the work. Acknowledgments The authors received no financial support and declare no potential conflicts of interest with respect to the authorship and/or publication of this article. References Al-Wahadni A, Gutteridge DL. 2002. An in vitro investigation into the effects of retained coronal dentine on the strength of a tooth restored with a cemented post and partial core restoration. Int Endod J. 35(11):913–918. Aykent F, Kalkan M, Yucel MT, Ozyesil AG. 2006. Effect of dentin bonding and ferrule preparation on the fracture strength of crowned teeth restored with dowels and amalgam cores. J Prosthet Dent. 95(4):297–301. Baba NZ, Goodacre CJ, Daher T. 2009. Restoration of endodontically treated teeth: the seven keys to success. Gen Dent. 57(6):596–603. Bassir MM, Labibzadeh A, Mollaverdi F. 2013. The effect of amount of lost tooth structure and restorative technique on fracture resistance of endodontically treated premolars. J Conserv Dent. 16(5):413–417. Eraslan O, Aykent F, Yücel MT, Akman S. 2009. The finite element analysis of the effect of ferrule height on stress distribution at post-and-core-restored all-ceramic anterior crowns. Clin Oral Investig. 13(2):223–227. Evangelinaki E, Tortopidis D, Kontonasaki E, Fragou T, Gogos C, Koidis P. 2013. Effect of a crown ferrule on the fracture strength of endodontically treated canines restored with

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