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RESEARCH AND EDUCATION
Effects of different cusp coverage restorations on the fracture resistance of endodontically treated maxillary premolars Tugba Serin Kalay, DDS, PhD,a Tahsin Yildirim, DDS, PhD,b and Mustafa Ulker, DDS, PhD c
Endodon Endodontica tically lly treated treated teeth teeth ABSTRACT (ETTs) are believed to be weak Statement of problem. Cusp coverage restorations for the restoration of endodontically treated and and bri brittle ttle beca becau use of the the teeth represent a more conservative approach in terms of function and esthetics. However, limited exten extensiv sivee loss loss of coron coronal al and scienti�c data are available regarding the optimum reduction design and thicknesses. radicular radicular tooth structure. structure.1-3 This Purpose. The purpose of this in vitro study was to evaluate the fracture resistance and fracture Purpose. decreas decreases es fractur fracturee resistanc resistancee patterns patterns of cusp coverage restorations restorations with different different cusp reduction reduction designs and reduction reduction thickand incre increase asess cusp cusp de�ection nesses nesses on endodonti endodontically cally treated treated maxillary maxillary premolars premolars (ETMPs) with mesio-occ mesio-occluso luso-dista -distall (MOD) under under functio functional nal forces. forces. Endcavities. odont odontic ic access access cavit cavitie iess comcomMaterial and methods. methods. One hundred sixty-�ve extracted intact human maxillary premolars were bined with mesio-occluso-dis mesio-occluso-distal tal divided into 11 groups: G1-10 (test groups) and G11 (intact group). In the test groups, all of the (MOD (MOD)) cavi cavity ty prep prepar arat atio ions ns teeth were restored with composite resin after canal treatments with MOD cavities. However, the dram dramati atical cally ly incre increas asee cusp cuspal al cusps of the G1-9 teeth were reduced with combinations of different thicknesses (1.5, 2.5, and 3.5 mm) and designs (beveled, horizontal, and anatomic). The specimens were subjected to 105 de�ection and le and lead ad to increased increased cycles of 50 N mechanical loading. Next, the specimens were subjected to a compressive load at tooth fragility.4,5 a crossh crosshead ead speed speed of 0.5 mm/min mm/min until until fractu fracture. re. The fractu fractured red specim specimens ens were were analyze analyzed d to Clinical Clinical surveys surveys show that dete determ rmin ine e the the fract fractur ure e patt patter ern. n. TwoTwo-wa wayy ANOV ANOVA A foll follow owed ed by the Fish Fisher er leas leastt sign signii�cant ETTs with ideal coronal restodifference (LSD) test was used to analyze the interaction between groups. rations are crucial for long-term Results. The Results. The fracture resistance values increased with increases in the cusp reductions. The fracture clinic success. The majority of resistance values of the G6 (2.5 mm, anatomic) and G9 (3.5 mm, anatomic) groups were signi �cantly ETTs ETTs are are lost lost becau because se of corona coronall greater than that of the MOD group. However, the G6, G8 (3.5 mm, horizontal), and G9 groups were restora restoration tion failures in the longcomparable with G11. The highest restorable fracture rates were observed in G6 and G9. term.6 An ideal coronal restoConclusions. Cusp Conclusions. Cusp reduction design and thickness in�uenced uenced the fracture resistance and fracture fracture ration preserves the root canal patterns ns of cusp cusp covera coverage ge restor restoratio ations ns of ETMPs ETMPs with with MOD cavities. cavities. The teeth teeth restor restored ed with with system, supports the remaining patter anatomic cusp reduction designs with reduction thicknesses of at least 2.5 mm exhibited greater tooth tooth structur structuree , and restores fracture resistance and more frequent restorable fractures. (J Prosthet Dent 2016; -:---) tooth function.7 Restor Restorati ations ons of ETTs ETTs with with adhesive techniques may conserve more more tooth structure adhesive cusp coverage restorations increase the fracture and provide suf �cient fracture strength.8-11 However, the resista resistance nce of endodo endodonti nticall callyy treated treated poster posterior ior teeth teeth direct direct composite composite resin restoration restoration of extensive extensive cavities compared with direct MOD composite resin restorations. cannot establish tooth strength , and a and a reliable alternative An early study reported that cusp reductions should be 12-14 for restoration may be needed. at least 1.5 mm to reduce the stress stress values on the cusp 15-22 25 R ecently ecently , several in vitro studies and clinical recoverage adhesive restorations, and later studies related 14,23,24 ports have found that in the protection of cavities, to cusp cusp cove covera rage ge rest restor orat atio ions ns appl applie ied d 1.5 1.5 to 3.5 mm a
Research Assistant, Department of Restorative Dentistry, Faculty of Dentistry, Karadeniz Technical University, Trabzon, Turkey. Professor, Department of Restorative Dentistry, Faculty of Dentistry, Karadeniz Technical University, Trabzon, Turkey. c Associate Professor, Department of Restorative Dentistry, Faculty of Dentistry, Selcuk University, Konya, Turkey.
b
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MATERIAL AND METHODS
Clinical Implications Adhesive cusp coverage MOD restorations are a more conservative treatment than traditional crowns for endodontically treated maxillary premolar teeth. Teeth prepared with anatomic cusp reduction designs and thicknesses of at least 2.5 mm exhibited greater fracture resistance and more frequent restorable fractures.
cuspal reductions with a single type of reduction design17-19 or applied different reduction designs with a single reduction thickness.15,20,26 However, limited scienti�c data are available regarding the optimum reduction thickness and the effects of different cusp reduction designs on the tooth-restoration complex. Additionally, cusp fractures are among the major reasons for the extractions of ETTs.27 Unrestorable subgingival or vertical cusp fractures are observed more commonly in ETTs with extensive intracoronal restorations.28 These fractures cannot be restored, and the majority of these situations result in the extraction of the tooth.29,30 Studies have reported that many factors in�uence the locations and directions of root fractures, speci�cally, the remaining tooth structure, the cavit y design, and the restorative procedures. 3,13,31-34 The purpose of this study was to determine the in�uences of various cusp reduction designs and thicknesses on the in vitro fracture resistances of ETMPs with MOD cavities to identify the optimum reduction thickness and design and to evaluate whether these various cavity designs affect the restorable fracture rate. The null hypothesis tested was that the reduction thickness and design would have no in�uence on the fracture resistance and fracture pattern of the cusp coverage restoration of endodontically treated maxillary premolars with MOD cavities.
This study protocol was approved by the Ethical Research Committee (2014.144) of the Karadeniz Technical University. Caries-free human maxillary premolars with two roots and two canals (extracted for orthodontic reasons) were used. Teeth with cracks, fractures, or defects and internal-external resorption were excluded from the study. The mesiodistal and buccolingual tooth sizes were measured with digital calipers, and teeth with similar dimensions were selected. The selected teeth were assigned to 11 groups of 15 teeth each ( Table 1 ) and were stored in 0.2% sodium azide solution. Before the preparations, an impression of each tooth was made with a heavy-body silicone impression material (Optosil; Heraeus Kulzer GmbH) for use as an anatomic guide to obtain an original form while the restoration was applied. Endodontic and restorative procedures were performed in groups 1 to 10, and all procedures were performed by 1 researcher (T.S.K.). MOD cavities were prepared without proximal steps at the cemento-enamel junction (CEJ) and with an occlusal isthmus width of one-half of the buccolingual distance. The buccal and lingual walls of the occlusal isthmus were prepared parallel to each other. The cavity dimensions were measured with digital calipers. For the endodontic cavity preparations, diamond rotary cutting instruments (Dentsply Maillefer) were used in a high-speed handpiece under copious air water cooling. After extirpating the pulp, size 15 K �les (Dentsply Maillefer) were inserted until their tips could be seen at the apical foramen. The working lengths were determined by subtracting 1 mm from this length. The endodontic treatments were performed using NiTi rotary instruments (ProTaper; Dentsply Maillefer). Standardized canal enlargements were performed with an engine-driven rotary NiTi system up to F3 for the apical preparation using a crown-down technique. Rotary instruments were used with a torque-limited engine (X-Smart; Dentsply Maillefer).
Table 1. Fracture loads (N) Group (G) (n=15)
MOD Cavity Char acteristics
Fracture Loads (N) Mean ±SD
Minimum
Maximum
G1
1.5-mm beveled reduction
870.34 ±139.09 b
602.53
1184.07
b
G2
1.5-mm horizontal reduction
885.52 ±209.75
524.81
1228.47
G3
1.5-mm anatomic reduction
906.97 ±199.86 b
423.41
1187.40
851.30 ±173.13
b
555.65
1087.62
b
449.49
1264.50
751.49
1498.21
694.00
1343.64
599.47
1621.36
792.79
1570.81
434.64
1009.33
938.64
2194.17
G4
2.5-mm beveled reduction
G5
2.5-mm horizontal reduction
837.24 ±207.76
G6
2.5-mm anatomic reduction
1110.37 ±235.05 a
G7
3.5-mm beveled reduction
G8
3.5-mm horizontal reduction
961.82 ±216.88
b
1039.10 ±262.25a,b a
G9
3.5-mm anatomic reduction
1085.28 ±214.75
G10
No reduction
777.17 ±188.79 b
G11
Intact teeth
1640.80 ±455.76
a
Different superscript letters represent signi �cantly differences identi �ed by 1-way ANOVA with post hoc Tamhane tests ( P< .05).
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Five percent sodium hypochlorite was used for irrigation during the endodontic preparation. The canals were dried with paper points (Dentsply Maillefer), and all roots were obturated with ProTaper F3 gutta percha (Dentsply Maillefer) and endodontic sealer (AH Plus; Dentsply Maillefer). The coronal part of the gutta percha material was removed 2 mm apically to the CEJ, and glass-ionomer cement (Ketac Molar Easymix; 3M ESPE) was then inserted into this area as a coronal restoration. Teeth in the G11 group were left intact as the control group. After the endodontic treatments, teeth in the G10 group were only prepared with MOD cavities. In the reduction groups (G1-9), after the endodontic treatments and MOD cavity preparations, both cusps of the teeth were reduced with combinations of different thicknesses (1.5, 2.5, and 3.5 mm) and designs (beveled, horizontal, and anatomic) ( T able 1 ). In the horizontal reduction design, the cusp reduction was prepared parallel to the occlusal plane without bevels. In the beveled reduction design, after the reduction of the cusps parallel to the occlusal plane, bevel preparations were performed in an opposite angle to the natural cusp ridge. In the anatomic reduction design, the cusp reduction was prepared parallel to the natural cusp ridge. The reduction thicknesses were evaluated at the reference point (cusp tip) with digital calipers ( Fig. 1 A). The prepared surfaces were selectively etched (enamel for 30 seconds, dentin for 15 seconds) with 37% phosphoric acid (Scotchbond Etchant; 3M ESPE), rinsed for 20 seconds with an air/water spray, and gently airdried. A single-component bonding agent (Adper Single Bond 2; 3M ESPE) was applied to the tooth surface with a microbrush and then air-dried for 5 seconds; then, the surface was exposed to a light-emitting diode (LED)polymerization unit (Elipar S10; 3M ESPE). The teeth were placed into the impression guides previously made for each tooth, such that the cavities could not be over�lled at the margins and the reduced cusps could be restored to their original forms. Subsequently, the cavities were �lled with a posterior composite resin (P60; 3M ESPE). The composite resin was placed using the oblique incremental technique, and each increment was polymerized for 20 seconds. After the restorations were �nished, the teeth were polished with rubber cups and points (Idento�ex; Kerr Corp). Water-based liquid latex (Rubber-Sep; Kerr Corp) was applied to the roots to simulate the periodontal ligament,35 and the roots of the teeth were then embedded in acrylic resin up to 3 mm below the CEJ using cylindrical blocks. All of the specimens were submitted to 105 cycles of the application of 50-N loading forces at a frequency of 0.5 Hz in a mastication simulation machine36,37 (Vega Chewing Simulator; Nova Tic). The mechanical loading was applied to the center of the occlusal surface Serin Kalay et al
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Anatomic A
B
3 mm
Horizontal
A=2B
Beveled
A
I II
III
B Figure 1. A, Cusp reduction designs and cavity dimensions. B, Fracture patterns after fracture resistance tests.
in contact with both cusp ridges with a stainless steel antagonist with a rounded end that was 6 mm in diameter.38 The specimens were maintained in a humid environment throughout the mastication simulation. After the arti�cial aging procedures, the specimens were subjected to a compressive load at a crosshead speed of 0.5 mm/min in a universal testing machine (Instron 3382; Instron Corp). The compressive load was applied parallel to the long axis of the tooth with a 6-mm-diameter stainless steel antagonist placed in the center of the tooth with contacts only on the buccal and lingual cusps. The force required for fracture was recorded in newtons. The fractured specimens were analyzed to determine the fracture patterns according to the location of the fracture as follows ( Fig. 1B): type I, coronal fractures involving small amounts of enamel/composite resin (restorable); type II, THE JOURNAL OF PROSTHETIC DENTISTRY
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Table 2. Distribution of fracture patterns for each group Fracture Pattern % - (n) Restorable Group (G)
Type I
Type II
Nonrestorable Type III
G1 (1.5-mm beveled)
6.7 (1)
6.6 (4)
66.7 (10)
G2 (1.5-mm horizontal)
0
6.7 (4)
73.3 (11)
G3 (1.5-mm anatomic)
6.7 (1)
20.0 (3)
73.3 (11)
G4 (2.5-mm beveled)
6.7 (1)
33.3 (5)
60.0 (9)
G5 (2.5-mm horizontal)
0
20.0 (3)
80.0 (12)
G6 (2.5-mm anatomic)
20.0 (3)
26.7 (4)
53.3 (8)
G7 (3.5-mm beveled)
0
33.3 (5)
66.7 (10)
G8 (3.5-mm horizontal)
0
33.3 (5)
66.7 (10)
G9 (3.5-mm anatomic)
26.7 (4)
26.6 (4)
46.7 (7)
0
13.3 (2)
86.7 (13)
60.0 (9)
26.7 (4)
13.3 (2)
G10 MOD) G11 (Intact teeth)
coronal cusp fractures involving the dentin at a maximum of 1 mm below the CEJ (restorable); type III, vertical root/coronal fractures greater than 1 mm below than CEJ (nonrestorable) ( Table 2 ). A power analysis revealed a power of 93.02% for this study. The statistical analyses were performed with the Shapiro-Wilk test for normal distributions and 1-way analysis of variance (ANOVA) followed by the Tamhane tests. Two-way ANOVA followed by the Fisher least signi�cant difference (LSD) test was used to analyze the interaction between the cusp reduction thicknesses and the designs of the reduction groups ( a=.05 for all tests). RESULTS
The data exhibited normal distributions according to the Shapiro-Wilk tests. Regarding the control and reduction groups, the 1-way ANOVA revealed signi �cant differences ( P < .001) among all groups. A Tamhane test revealed differences between the reduction groups and the control group ( Table 1 ). All of the reduction groups exhibited higher fracture resistances than the MOD group. Signi�cantly higher fracture resistance values were observed in 2 reduction groups (2.5-mm anatomic and 3.5-mm anatomic) compared with the MOD group. Additionally, similar fracture resistance values were observed in the G6 (2.5-mm anatomic), G8 (3.5-mm horizontal), and G9 (3.5-mm anatomic) group relative to the intact tooth group. The 2-way ANOVA followed by the Fisher LSD tests indicated differences in terms of the interaction between reduction thickness and reduction design. Different designs were compared, and the results are graphically displayed in the box plots in Fig. 2. No signi�cant differences between any of the reduction designs were observed at the 1.5-mm and 3.5-mm reduction thicknesses. Regarding the 2.5-mm thickness, the anatomic reduction design exhibited a signi�cantly THE JOURNAL OF PROSTHETIC DENTISTRY
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higher fracture resistance compared with the horizontal and beveled groups. The thicknesses of the 1.5-, 2.5-, and 3.5-mm reductions were compared ( Fig. 3 ). No signi�cant differences among the reduction thicknesses were observed with the beveled reduction design. Regarding the horizontal design, the 3.5-mm thickness exhibited a signi�cantly higher fracture resistance than the 1.5- and 2.5-mm thicknesses. Regarding the anatomic design, the 2.5- and 3.5-mm thickness groups exhibited signi�cantly higher fracture resistances than the 1.5-mm thickness group. The intact teeth predominantly fractured with restorable patterns; conversely, the teeth in the MOD group fractured with nonrestorable patterns. In the reduction groups (G1-9), the highest restorable fracture rates were observed in the 2.5-mm and 3.5-mm anatomic reduction groups; furthermore, 80% of the fractures in the anatomic reduction design group exhibited type I patterns ( Table 2 ). DISCUSSION
In the present study, the fracture resistances of ETMPs restored with various cusp coverage restorations were evaluated. Many factors may in�uence in vitro results; thus, in vitro experiments should represent the intraoral environment. Simulations of periodontal ligaments can in�uence not onl y the fracture load values but also the fracture patterns.35 For these reasons, the roots of the teeth were covered with latex liners. Changes in the mechanical properties of a restoration under masticatory load and fatigue failures after a period of clinical use are important. A masticatory simulator was used to simulate the clinical conditions that occur during mastication with the intention of mimicking at least 1 year of in vivo clinical use. Restorations are thought to undergo 1 000 000 active stress cycles in 20 years.37 In the present study, 105 cycles of mechanical loading were applied at a frequency of 0.5 Hz, which is close to the masticatory cycle in vivo.36 Maxillary premolars were used in this study because their anatomy is susceptible to cusp de�ection and fracture under occlusal loads.9 The removal of tooth structure for endodontic and restorative procedures increases cuspal de�ection and susceptibility to fracture and also affects the restoration type. Cusp coverage becomes necessary when the width of the cavity isthmus is greater than two thirds of the intercuspal distance or one half of the buccolingual distance.21 In our study, the width of the MOD cavity isthmus was prepared to be one half of the buccolingual distance. Restorations of ETTs with adhesive methods support the remaining tooth structure, prevent additional tissue loss and exhibit more homogeneous distributions Serin Kalay et al
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Anatomic
3.5 d e l e 2.5 v e B 1.5
P = .546
5 . Horizontal 3
P = .108 P = .313
Beveled
Anatomic p u 5 . Horizontal o 2 r G Beveled
P = .00 P = .854
Anatomic
P = .01
P = .779
5 . 1 Horizontal
P = .843
P = .632
Beveled
500
750
1000
1250
1500
1750
Load (00)
p u o r G
P = .150 P = .803
l 3.5 a t n o 2.5 z i r o H 1.5
P = .223
P = .009 P = .528
c 3.5 i m o t 2.5 a n A 1.5
P = .046
P = .743 P = .021 P = .009
500
750
1000
1250
1500
1750
Load (00)
Figure 2. Box plots of load to fracture test (N). Comparison of reduction groups with identical reduction thicknesses and different reduction designs.
Figure 3. Box plots of the load to fracture test (N). Comparison of reduction groups with identical reduction designs and different reduction thicknesses.
of occlusal forces.8,14,20,22 The use of bonded cuspal coverage restorations, such as onlays, overlays, and endocrowns, for the restoration of ETTs with large structural losses represents a more conservative approach in terms of function and esthetics.14,17,18 Although earlier studies reported that bonded cusp coverage restorations improve fracture resistance,14,15,18-20,23-26 the literature remains unclear regarding which cusp reduction thicknesses and designs are optimal for weakened ETTs. In the present study, 3 different cusp reduction designs (anatomic, horizontal, and beveled) were applied at 3 different thicknesses (1.5, 2.5, and 3.5 mm) to obtain the optimum reduction thickness and design within the limitations of the study. The results of the present study support the existence of differences in the resistance to fracture and the mode of failure between cusp coverage restorations of ETMPs with MOD cavities according to various reduction thicknesses and designs. Cusp reduction was found to increase the fracture resistances of ETMP restorations with extensive MOD cavities compared with restoration without cusp coverage. The 2.5-mm anatomic and 3.5mm anatomic groups exhibited signi�cantly increased ETMP fracture resistances compared with the MOD group. The results from the 2.5-mm anatomic, 3.5-mm horizontal, and 3.5-mm anatomic groups were statistically similar to those of the intact teeth, and these �ndings agree with those of other studies.18,26 Moreover, some studies have reported that cusp coverage restorations improve fracture resistance compared with MOD restorations, but the fracture resistances of such restorations remain sig ni�cantly below those of intact teeth.9 Magne et al17 evaluated the in�uences of overlay thickness (1.5, 2.5, and 3.5 mm) on the in vitro fatigue resistances and failure modes of endodontically treated
premolars. These authors used only a single type of reduction design and reported that thick composite resin overlays increased the fatigue resistances of endodontically treated premolars compared with thin overlays. Mondelli et al18 investigated the in�uences of 2-mm overlay thicknesses in a single type of reduction design on the fracture resistances and fracture modes of endodontically treated premolars with MOD cavities and found that the cusp coverage resulted in fracture resistances similar to those of sound teeth. The present study con�rmed these results, � nding that cusp reduction increased fracture resistance. Studies related to cusp coverage restorations of extensive MOD cavities ha ve applied different cusp reduction designs. Krifka et al20 evaluated cusp coverage methods with a horizontal reduction design of the cusps. Mondelli et al18 and Magne et al17 evaluated cusp coverage restorations with reductions parallel to the cusp incline. Dejak et al15 evaluated different onlay designs with horizontal, beveled, and rounded shoulder preparation designs and reported that onlays with rounded shoulder margins exhibited favorable stress distributions between the restorations and the tissues. In the present study, the fracture resistances of the restored premolars with various cusp reduction designs were different. The anatomic cusp reduction design signi�cantly strengthened the teeth. When the results of the cusp fracture patterns were assessed, the greatest proportion of restorable fractures among the reduction groups was also observed in the anatomic reduction groups. This �nding is most likely due to the axial direction of the cusp reduction design, which would lead to a favorable distribution of occlusal forces and transfer to the tooth structure when a compressive load is applied. Additionally, this �nding might be attributable to the
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improved resistance to fracture associated with beveled margins. Beveled margins have been reported to enhance the properties of restored teeth compared with nonbeveled cavities.10,11,32 The importance of the loading area and the cusp inclination34,38 and location of the remaining tooth structure3,33 has previously been reported in in vitro studies. With overlay restorations, favorable cusp inclinations, occlusal contacts and favorable remaining tooth structure locations with adequate cusp reduction preparations can be provided. These �ndings suggest that both cusp reduction design and thickness in�uence the fracture resistances of ETMP restorations. Cusp reductions with all of the thicknesses and designs used in this study improved the fracture resistances compared with the MOD cavity design. However, according to the statistical results and fracture patterns observed in this in vitro study, anatomic reduction designs with at least 2.5-mm-thick reductions are a safe option because such treatments limit the risk of nonrestorable cusp fractures of cusp coverage restorations of ETMPs with extensive MOD cavities. CONCLUSIONS
Adhesive cusp coverage restorations increased the fracture resistances of ETMPs with MOD cavities to a level comparable with that of intact teeth. The cusp reduction designs and thicknesses in�uenced the fracture resistances and fracture patterns. Increases in cusp reduction thickness increased the mean fracture resistance values. The teeth restored with anatomic cusp reduction designs and reduction thicknesses of least 2.5 mm exhibited greater fracture resistances and greater proportions of restorable fractures than the teeth subjected to horizontal and beveled reduction designs. REFERENCES 1. Soares PV, Santos-Filho PC, Queiroz EC, Araujo TC, Campos RE, Araujo CA, et al. Fracture resistance and stress distribution in endodontically treated maxillary premolars restored with composite resin. J Prosthodont 2008;17: 114-9. 2. Scotti N, Coero Borga FA, Alovisi M, Rota R, Pasqualini D, Berutti E. Is fracture resistance of endodontically treated mandibular molars restored with indirect onlay composite restorations in �uenced by � bre post insertion? J Dent 2012;40:814-20. 3. Ibrahim AM, Richards LC, Berekally TL. Effect of remaining tooth structure on the fracture resistance of endodontically-treated maxillary premolars: an in vitro study. J Prosthet Dent 2016;115:290-5. 4. Gonzalez-Lopez S, Vilchez Diaz MA, de Haro-Gasquet F, Ceballos L, de Haro-Munoz C. Cuspal � exure of teeth with composite restorations subjected to occlusal loading. J Adhes Dent 2007;9:11-5. 5. Gonzalez-Lopez S, De Haro-Gasquet F, Vilchez-Diaz MA, Ceballos L, Bravo M. In�uence of cavity type and size of composite restorations on cuspal �exure. Med Oral Patol Oral Cir Bucal 2006;11:536-40. 6. Gillen BM, Looney SW, Gu LS, Loushine BA, Weller RN, Loushine RJ, et al. Impact of the quality of coronal restoration versus the quality of root canal �llings on success of root canal treatment: a systematic review and metaanalysis. J Endod 2011;37:895-902. 7. Ree M, Schwartz RS. The endo-restorative interface: current concepts. Dent Clin North 2010;54:345-74. 8. Mannocci F, Bertelli E, Sherriff M, Watson TF, Pitt Ford TR. Three-year clinical comparison of survival of endodontically treated teeth restored with
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Corresponding author:
Dr Tugba Serin Kalay Faculty of Dentistry, Karadeniz Technical University 61080, Trabzon TURKEY Email:
[email protected] Acknowledgments
The authors thank Dr Tamer Tuzuner for support while preparing this study. Copyright © 2016 by the Editorial Council for The Journal of Prosthetic Dentistry.
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