RESEARCH AND EDUCATION
Effect of ferrule location on the fracture resistance of crowned mandibular premolars: An in vitro study Abdulaziz Samran, DDS, MSc, DMD,a Mahmoud Al-Afandi, DDS, MSc,b Jad-Alkareem Kadour, DDS, MSc, PhD,c and Matthias Kern, DMD, PhDd
The fracture resistance of ABSTRACT endodontically treated teeth is Statement of problem. How the location of a ferrule affects the fracture resistance of endodontically affected by the amount of subtreated mandibular premolars is unclear. stance loss,1,2 presence of a Purpose. The purpose of this study was to compare the effect of ferrule location on the fracture ferrule,3 location of the tooth in resistance of endodontically treated mandibular premolars. the dental arch,4 and the mateMaterial and methods. Seventy-two extracted human mandibular premolars were selected and rial and design of the post and divided into 6 test groups (n=12) according to ferrule location: control group, GHT; endodontically 5 core. The coronal substance treated teeth without endodontic posts and crowns, GCF; teeth with a 2 mm circumferential ferrule, loss of endodontically treated GBF; teeth with a 2 mm buccal ferrule; GLF, teeth with a 2 mm lingual ferrule; GBLF, teeth with a 2 teeth will increase their suscepmm buccal and lingual ferrule; and teeth without ferrule, GWF. After glass ﬁber posts were tibility to fracture. Therefore, the cemented with a self-adhesive resin cement and foundation restorations were placed, NiCr crowns longevity of the teeth depends were luted to each prepared tooth. All specimens were quasistatically loaded at 30 degrees in a universal testing machine until fractured. Data were then analyzed with 1-way ANOVA, followed on the amount of coronal tooth by multiple comparisons using the Tukey honestly signiﬁcant difference test (a=.05). structure and the capability of the restorative materials to Results. Mean ±SD failure loads for groups ranged from 791.1 ±177.5 N to 1086.1 ±181.1 N. Onereplace the substance lost.6 The way ANOVA revealed a statistically significant difference between the groups (P.05). However, no statistically signiﬁcant differences were observed among groups (P>.05), except between GHT use of resin cement resulted in (control group) and groups GBLF and GWF (P=.025, P=.022). increased tensile bond strength between ﬁber posts and root Conclusions. Within the limitations of this study, the location of the ferrule had no signiﬁcant effect on the fracture resistance of endodontically treated mandibular premolars. (J Prosthet Dent canal dentin and improved the 2015;-:---) fracture resistance of endodon7,8 tically treated teeth. increase in resistance to fracture or dislodgment gained Different post types are available and can be divided with intracoronal reinforcement when cast post and cores into cast post and cores, computer-aided design and or prefabricated or threaded posts were used. computer-aided manufacturing (CAD/CAM) post and Fiber posts are fabricated from resin materials and cores, and prefabricated post systems. A retrospective ﬁller components, including glass ﬁber.10 They have a study by Sorensen and Martinoff,9 which analyzed the similar modulus of elasticity to dentin and can distribute intracoronal reinforcement and coronal coverage of the load forces evenly along the root.11 However, several endodontically treated teeth, revealed no signiﬁcant
a Visiting Assistant Professor, Department of Prosthodontics, Propaedeutics and Dental Materials, School of Dentistry, Christian-Albrechts University at Kiel, Germany; Department of Fixed Prosthodontics, Faculty of Dentistry, University of Aleppo, Aleppo, Syria. Department of Fixed Prosthodontics, School of Dentistry, Ibb University, Yemen. b Lecturer, Department of Fixed Prosthodontics, Faculty of Dentistry, University of Aleppo, Syria; Department of Restorative Dental Sciences, Al-Farabi Dental College, Riyadh, Saudi Arabia. c Assistant Professor, Department of Fixed Prosthodontics, School of Dentistry, Aleppo University, Syria. d Professor and Chairman, Department of Prosthodontics, Propaedeutics and Dental Materials, School of Dentistry, Christian-Albrechts University at Kiel, Germany.
THE JOURNAL OF PROSTHETIC DENTISTRY
Clinical Implications This in vitro study revealed that the location of the ferrule had no significant inﬂuence on the fracture resistance of endodontically treated mandibular premolars.
published clinical studies have shown higher failure rates with glass fiber posts than with zirconia ceramic posts.12-14 Another important consideration when restoring endodontically treated teeth is the ferrule design. A ferrule has been deﬁned as a metal band that encircles the external dimension of the residual tooth.15 The presence of a ferrule can signiﬁcantly increase the fracture resistance of endodontically treated teeth by reinforcing the tooth at its external surface.16 The pattern of stress distribution by the ferrule design under load is of great importance in ensuring an optimal design for the deﬁnitive prosthesis. Several studies have indicated the importance of remaining coronal structure and a circumferential ferrule design with a dentin collar of at least 2 mm in height.3,17-27 Samran et al21 reported that to get the advantages of ferrule effect, it should have a minimum height of 1.5 to 2 mm. Mangold and Kern1 revealed the effect of posts on the fracture strength of endodontically treated teeth with different wall numbers, but they did not evaluate the inﬂuence of ferrule location. Samran et al21 reported that increasing the number of residual walls and the ferrule height increased the fracture strength of endodontically treated teeth, but they also did not evaluate the effect of the ferrule location on the fracture strength. No other publications could be found that evaluated the effect of the ferrule location on the fracture resistance of crowned premolars. Therefore, the purpose of the present study was to evaluate the effect of ferrule location on the fracture strength of endodontically treated premolars. The null hypothesis was that the ferrule location would not inﬂuence their fracture strength. MATERIAL AND METHODS Seventy-two human mandibular premolars, which were extracted for periodontal or orthodontics reasons, were collected and soaked in 5% formol/saline solution at room temperature. The absence of cracks was conﬁrmed under magnification. Dental plaque, calculus, and periodontal tissues were removed with a hand scaler. The teeth were stored at room temperature during the study. Teeth with similar dimensions were selected and assigned to 6 groups of 12 specimens each. Root length, measured from the apex to the labial middle point of the cement-enamel junction (CEJ), together with labiolingual THE JOURNAL OF PROSTHETIC DENTISTRY
and mesiodistal dimensions at the level of the cervical margin, were recorded with the aid of a digital caliper (Links Brand; Harbin Metering Instrument Works). Access cavities were made as small as possible with a continuous water-cooled high-speed handpiece and round diamond rotary instrument (Dia-Tessin; Vanetti SA). Working length was established to be 1 mm short of the apex. The canals were prepared with a rotary system (X-Smart; Dentsply Maillefer). Instrumentation was according to the manufacturer’s guidelines. Sodium hypochlorite (3%) was used to irrigate the canals throughout instrumentation. The root canals were dried with air jets and absorbing paper points (Spident; Meta Biomed Co Ltd). All root canals were obturated in a standard way with resin sealer (AH Plus sealer; Dentsply DeTrey) and lateral condensation of gutta percha points (Spident; Meta Biomed Co Ltd) to the working length. Subsequently, the access cavities and apexes were sealed with interim restorations (Coltosol; Coltène/Whaledent Inc). The roots were stored in distilled water at room temperature for at least 72 hours. After removing the gutta percha from the canal with Gates-Glidden rotary instruments, the cavities were sealed again with interim restorations. The root of each tooth was embedded into an autopolymerizing acrylic resin (Idofast Unipol; Unidesa-Odi) up to a level 2 mm below the CEJ and with its long axis vertical by using a custom-made surveyor. The roots were notched to avoid dislodgement from the acrylic resin blocks. To simulate the periodontal ligament, the roots were immersed into melted wax to a depth of 2 mm below the CEJ and were then embedded in acrylic resin blocks. The roots were removed from the resin blocks when the primary signs of polymerization were noticed. The wax spacer was replaced by a silicone-based impression material (Light body; Speedex; Coltène/Whaledent Inc) injected into the acrylic resin. The tooth was then reinserted into the resin block, and the excess impression material was removed with a surgical blade. The crowns were prepared with a 0.8 mm wide shoulder ﬁnishing line 1 mm above the CEJ faciolingually and 2 mm mesiodistally with diamond rotary instruments with a 3degree taper (Dia Tessin; Vanetti SA) under continuous air-water coolant. To obtain a standardized 6-degree convergence angle, a high-speed handpiece was attached to a custom-made parallelometer. Rotary instruments were changed after 4 preparations. All 72 teeth were assigned to 6 groups as follows: GHT, control group of healthy root ﬁlled tooth specimens without endodontic posts and crowns; GCF, teeth with a 2 mm circumferential ferrule; GBF, teeth with a 2 mm buccal ferrule; GLF, teeth with a 2 mm lingual ferrule; GBLF, teeth with a 2 mm buccal and lingual ferrule; and GWF, teeth without ferrule (Fig. 1). All ferrules were 2 mm in height and 1 mm in thickness. Post spaces were prepared (for all Samran et al
Figure 1. Dimensions of preparation (mm).
Figure 2. Different ferrule locations. Table 1. Materials used for restorative procedures
groups except GHT) with a low-speed corresponding drill provided by the post manufacturer to achieve a post space length of 10 mm for all teeth to eliminate variables caused by difference in post length. The access opening of each canal was expanded faciolingually to 3 mm in width and 2 mm in depth to obtain standard coronal openings for all specimens. Glass ﬁber posts (White Post DC; FGM) were airborne-particle abraded with 50 mm alumina particles (Aluminum Oxide Abrasive; Heraeus Kulzer) for 5 seconds at 0.25 MPa and cleaned ultrasonically in 96% isopropanol for 3 minutes. The post spaces were then rinsed with a 3% sodium hypochlorite solution, irrigated with 70% ethanol, and dried with absorbent paper points. The walls of the post space were etched with 37% phosphoric acid (Meta Etchant; Meta Biomed Co Ltd) for 15 seconds, rinsed with water spray, and air dried. The posts were coated with freshly mixed self-adhesive resin cement (RelyX Unicem; 3M ESPE) applied with disposable microbrushes. Each post was seated with finger pressure for 10 seconds. Excess resin cement was spread to cover the occlusal part of the post. Light-polymerizing composite resin cores (Filtek Z250 XT; 3M ESPE) were built up according to the manufacturer’s instructions. Finally, the cores were prepared to the required dimensions (Fig. 2). All procedures were performed by the same operator (M.A.). A 1-stage impression was made for each prepared tooth with a silicone impression material (Speedex; Coltène/Whaledent Inc). Type IV dental stone (Fujirock EP; GC Europe) was poured into the impressions. To obtain similar crown dimensions in all specimens, a stylized reference crown with a 30-degree angulation of the buccal cusp slope to the long axis of the tooth was fabricated in wax. Then, the crowns were replicated on the other dies by inserting heated liquid wax into a silicone mold (Deguform; Degudent). The crown wax patterns were measured with a wax caliper to make sure that all patterns had the same dimensions.21 Then the wax Samran et al
Material Diamond rotary instruments (Dia-Tessin)
Company Vanetti SA
Batch No. 1312I
Glass ﬁber posts
White post DC, FGM
Self-adhesive resin cement
RelyX Unicem, 3M ESPE
Filtek Z250 XT, 3M ESPE
Glass ionomer cement
Silicone impression material
Speedex, Coltène/ Whaledent AG
Putty D84891, Light D87416
models were invested and cast in NiCr alloy free of beryllium (Kera NH; Eisenbacher Dentalwaren) according to the instructions of the manufacturer. The cast crowns were airborne-particle abraded with 150-mm alumina particles (Aluminum Oxide Abrasive; Heraeus Kulzer) at 0.25 MPa pressure and cleaned ultrasonically in 96% isopropanol. The tooth surfaces were cleaned with a rotary brush and pumice, rinsed with water, and dried before deﬁnitive cementation. Cast crowns were cemented with glass ionomer cement (Meron; Voco), which was mixed according to the manufacturer’s instructions. Each crown was held in position for 7 minutes under a 29 N force with a custom-made device. The materials used are listed in Table 1. All specimens were quasistatically tested with a universal testing machine (Instron Corp) until fracture. The crosshead speed was 1 mm/min at an angle of 30 degrees to the long axis of the tooth. Compressive load was applied onto a prepared notch on the lingual surface (in the middle of the lingual slope of the buccal cusp). The failure load was recorded when the force-versus-time graph showed a sudden dip. Specimens were visually inspected to determine the type, location, and direction of failure. Data were explored for normality with the AndersonDarling test, which showed that data were normally distributed. Among the 6 groups, fracture load data were THE JOURNAL OF PROSTHETIC DENTISTRY
Table 2. Fracture load (N)
Table 3. ANOVA table for analysis of failure loads
GHT (control group)
GCF (circumferential 2 mm ferrule)
GBF (buccal 2 mm ferrule)
GLF (lingual 2 mm ferrule)
GBLF (buccal and lingual 2 mm ferrule)
GWF (without ferrule)
Sum of Squares
GBLF 11x 1x
GWF 10x 2x
Fracture Mode (%)
Statistically different means (P.05) are indicated by different superscript letters.
80% 60% 40% 20% 0%
Non-favorable Favorable Figure 4. Fracture mode of each group.
Figure 3. Fracture pattern and frequency of groups.
analyzed with 1-way analysis of variance (ANOVA) followed by multiple comparisons with the Tukey honestly signiﬁcant difference (HSD) test (a=.05). Fracture load data were analyzed with software (SPSS 18.0 for Windows; IBM). According to the signiﬁcance level (a=.05) and the sample size (n=12), the test of choice had adequate power to detect signiﬁcant differences which could justify clinical relevance. RESULTS The mean fracture loads of 6 groups and standard deviations are presented in Table 2. They ranged from 791.1 ±177.5 N to 1086.1 ±181.1 N. The highest mean fracture load was recorded for GHT, and the lowest one was recorded for GWF. One-way ANOVA (Table 3) revealed statistically significant differences among groups (P.05). However, further analysis with the Tukey HSD test (Table 2) indicated that differences between GHT and the test groups were only signiﬁcant for GBLF and GWF (P=.020, P=.018). The failure mode was determined by visual inspection (Fig. 3). There were 2 types of root fracture. Specimens that presented cervical third fracture were classiﬁed as favorable mode, whereas specimens that presented middle and apical third fracture were classiﬁed as catastrophic mode. All groups (except GHT) showed complete favorable fracture mode (Fig. 4). The mode of failure in GHT was typically an oblique root fracture at the THE JOURNAL OF PROSTHETIC DENTISTRY
middle of the root, extending from the lingual surface down to the buccal surface, whereas the majority of fracture modes in the other groups were horizontal or oblique fractures extending from the dentin-core junction down to the facial surface of the cervical third. DISCUSSION The present study investigated the inﬂuence of different ferrule locations on the fracture resistance of crowned mandibular premolars. The use of natural teeth is a reliable methodology in fracture testing and has also been used by many authors.1,21,22 The fracture strength of the roots is one of the most important factors when restoring endodontically treated teeth which have lost a considerable amount of their crown tissue. Various ferrule locations were investigated in this study to mimic the different clinical conditions in which various possibilities for the loss of dental tissue occur. A ferrule of 2 mm was chosen to achieve the full beneﬁts of the ferrule effect as suggested by Samran et al.21 Glass ﬁber posts were selected because of their low elastic modulus similar to dentin and because they can distribute the load forces evenly along the root.11 Furthermore, these types of post systems have the advantages of superior esthetics, ease of retrievability, and simple application technique, allowing the clinician to complete the procedure in the same visit. However using other types of post systems, such as zirconia ceramic posts or titanium posts, might have resulted in a different outcome. Samran et al
Mandibular premolar teeth were selected because they are easy to collect (extracted for orthodontic reasons) and have a single root. In addition, these teeth are highly susceptible to fracture that may require the placement of a crown restoration.4 However, testing other teeth in the dental arch, such as molar or anterior teeth, might have led to different results. A self-adhesive resin cement was selected because of its higher push-out bond strength compared to conventional dual-polymerizing resin cements.8 A custommade parallelometer was used to obtain standardized preparations for all specimens. After foundation buildup, the deﬁnitive preparation was ﬁnished with a low-speed handpiece with a ﬁne-grit diamond rotary instrument. This procedure resulted in a slight overestimation of the remaining coronal structure. However, because this was performed in the same manner in all groups, it was assumed that this would not affect the results considerably. Excluding the control group, all teeth were crowned before subjecting them to compressive load in order to mimic clinical conditions. Several studies have reported that a ferrule enhances fracture resistance;19,20 however, in many clinical situations, it is difﬁcult to prepare an ideal ferrule. This investigation compared the fracture strength of endodontically treated teeth with different ferrule locations that represented clinical situations. The authors identiﬁed no other studies that evaluated the effect of the ferrule location on the fracture resistance of crowned mandibular premolars. The hypothesis that the ferrule location would not affect the fracture strength of crowned mandibular premolars was accepted. The ferrule location had no signiﬁcant inﬂuence on the ﬁnal fracture strength (P>.05). The fracture strength of all specimens ranged from 791.1 ±177.5 N (GWF) to 1086.1 ±181.1 N (GHT), which compares well with previous in vitro studies.23,24 The lowest fracture strength values were found for GWF, whereas GHT had a significantly higher fracture resistance. These results might explain how the presence of a ferrule can enhance the fracture resistance of endodontically treated teeth.17,21,25 The presence of a ferrule appears to be a crucial factor in the prognosis of endodontically treated teeth. This result is in agreement with the ﬁndings of another study24 in which the anterior teeth were restored with quartz ﬁber posts and composite resin cores. On the other hand, these results are not consistent with the conclusions of other studies.23,26,27 This could be explained by the fact that glass ﬁber posts (used in this study) distributed the loading stresses over a greater surface area of the tooth structure similarly for all tested groups. These results may also be explained as the resin bonded ﬁber posts with resin cement cores formed a monoblock system which exerted a reinforcing effect by supporting the remaining structure regardless of Samran et al
the ferrule location. Although specimens in GBLF had buccal and lingual walls, they showed lower fracture resistance values. This may be attributed to the variables in human teeth that include tooth condition previous to the extraction, tooth age, pulp status at the time of extraction, and root anatomy. All groups (except GHT) showed complete favorable fracture mode. These ﬁndings agree with those of previous studies1,21 that stated that prefabricated ﬁber posts frequently showed more favorable failure modes. This could be attributed to the low rigidity of glass ﬁber posts. However, in light of recently published clinical studies showing higher failure rates with glass fiber posts than with zirconia ceramic posts, the validity of this concept might be questioned. 12-14 In light of the results of this study, the location of the ferrule seems not to be an important factor in terms of increasing the fracture strength of endodontically treated premolars. A limitation of this study may be that a single load to fracture test was incorporated. Dynamic loading, temperature effects, and oral environment effects were not included in the present study and might be considered as a shortcoming. To mimic the intraoral condition, further studies should be done with thermocycling and dynamic fatigue loading. Further investigations including other types of post systems (zirconia, or titanium posts) and other teeth in the dental arch (molars or anterior teeth) are recommended to complement the present study. CONCLUSIONS Within the limitations of this study, the location of the ferrule did not affect the fracture strength of endodontically treated teeth restored with glass ﬁber posts. REFERENCES 1. Mangold JT, Kern M. Inﬂuence of glass-ﬁber posts on the fracture resistance and failure pattern of endodontically treated premolars with varying substance loss: an in vitro study. J Prosthet Dent 2011;105:387-93. 2. Bitter K, Noetzel J, Stamm O, Vaudt J, Meyer-Lueckel H, Neumann K, et al. Randomized clinical trial comparing the effects of post placement on failure rate of postendodontic restorations: preliminary results of a mean period of 32 months. J Endod 2009;35:1477-82. 3. Stankiewicz NR, Wilson PR. The ferrule effect: a literature review. Int Endod J 2002;35:575-81. 4. Tamse A, Fuss Z, Lustig J, Kaplavi J. An evaluation of endodontically treated vertically fractured teeth. J Endodont 1999;25:506-8. 5. Sidoli GE, King PA, Setchell DJ. An in vitro evaluation of a carbon ﬁber-based post and core system. J Prosthet Dent 1997;78:5-9. 6. Fernandes AS, Dessai GS. Factors affecting the fracture resistance of postcore reconstructed teeth: a review. Int J Prosthodont 2001;14:355-63. 7. Buttel L, Krastl G, Lorch H, Naumann M, Zitzmann NU, Weiger R. Inﬂuence of post ﬁt and post length on fracture resistance. Int Endodont J 2009;42: 47-53. 8. Pereira JR, Valle AL, Ghizoni JS, So MV, Ramos MB, Lorenzoni FC. Evaluation of push-out bond strength of four luting agents and SEM observation of the dentine/ﬁbreglass bond interface. Int Endodontic J 2013;46:982-92. 9. Sorensen JA, Martinoff JT. Intracoronal reinforcement and coronal coverage: a study of endodontically treated teeth. J Prosthet Dent 1984;51:780-4. 10. Freedman GA. Esthetic post-and-core treatment. Dent Clin North Am 2001;45:103-16. 11. Akkayan B, Gulmez T. Resistance to fracture of endodontically treated teeth restored with different post systems. J Prosthet Dent 2002;87:431-7.
THE JOURNAL OF PROSTHETIC DENTISTRY
12. Bateli M, Kern M, Wolkewitz M, Strub JR, Att W. A retrospective evaluation of teeth restored with zirconia ceramic posts: 10-year results. Clin Oral Investig 2014;18:1181-7. 13. Naumann M, Koelpin M, Beuer F, Meyer-Lueckel H. 10-year survival evaluation for glass-ﬁber-supported postendodontic restoration: a prospective observational clinical study. J Endod 2012;38:432-5. 14. Schmitter M, Hamadi K, Rammelsberg P. Survival of two post systems-ﬁveyear results of a randomized clinical trial. Quintessence Int 2011;42:843-50. 15. Cohen S, Burns RC. Pathways of the pulp. 10th ed. St Louis: Mosby; 2002. p. 781. 16. Isidor F, Brondum K, Ravnholt G. The inﬂuence of post length and crown ferrule length on the resistance to cyclic loading of bovine teeth with prefabricated titanium posts. Int J Prosthodont 1999;12:78-82. 17. Sorensen JA, Engelman MJ. Ferrule design and fracture resistance of endodontically treated teeth. J Prosthet Dent 1990;63:529-36. 18. Zhi-Yue L, Yu-Xing Z. Effects of post-core design and ferrule on fracture resistance of endodontically treated maxillary central incisors. J Prosthet Dent 2003;89:368-73. 19. Aykent F, Kalkan M, Yucel MT, Ozyesil AG. Effect of dentin bonding and ferrule preparation on the fracture strength of crowned teeth restored with dowels and amalgam cores. J Prosthet Dent 2006;95:297-301. 20. Ma PS, Nicholls JI, Junge T, Phillips KM. Load fatigue of teeth with different ferrule lengths, restored with ﬁber posts, composite resin cores, and allceramic crowns. J Prosthet Dent 2009;102:229-34. 21. Samran A, El Bahra S, Kern M. The inﬂuence of substance loss and ferrule height on the fracture resistance of endodontically treated premolars. An in vitro study. Dent Mater 2013;29:1280-6. 22. Sherfudhin H, Hobeich J, Carvalho CA, Aboushelib MN, Sadig W, Salameh Z. Effect of different ferrule designs on the fracture resistance and
THE JOURNAL OF PROSTHETIC DENTISTRY
25. 26. 27.
failure pattern of endodontically treated teeth restored with ﬁber posts and all-ceramic crowns. J Appl Oral Sci 2011;19:28-33. Ng CC, Dumbrigue HB, Al-Bayat MI, Griggs JA, Wakeﬁeld CW. Inﬂuence of remaining coronal tooth structure location on the fracture resistance of restored endodontically treated anterior teeth. J Prosthet Dent 2006;95:290-6. Dikbas I, Tanalp J, Ozel E, Koksal T, Ersoy M. Evaluation of the effect of different ferrule designs on the fracture resistance of endodontically treated maxillary central incisors incorporating ﬁber posts, composite cores and crown restorations. J Contemp Dent Pract 2007;8:62-9. Pereira JR, de Ornelas F, Conti PC, do Valle AL. Effect of a crown ferrule on the fracture resistance of endodontically treated teeth restored with prefabricated posts. J Prosthet Dent 2006;95:50-4. Arunpraditkul S, Saengsanon S, Pakviwat W. Fracture resistance of endodontically treated teeth: three walls versus four walls of remaining coronal tooth structure. J Prosthodont 2009;18:49-53. Pereira JR, Neto Tde M, Porto Vde C, Pegoraro LF, do Valle AL. Inﬂuence of the remaining coronal structure on the resistance of teeth with intraradicular retainer. Braz Dent J 2005;16:197-201.
Corresponding author: Dr Abdulaziz Samran Arnold-Heller Strasse 16 24105 Kiel GERMANY Email: [email protected]
Copyright © 2015 by the Editorial Council for The Journal of Prosthetic Dentistry.
Samran et al