10.59987/ads/2016.1-2.4-10
Aim. To determine and compare the fracture resistance of endodontically treated teeth restored with a bulk fill flowable material (SDR) and a traditional resin composite. Methods. Thirty maxillary and 30 mandibular first molars were selected based on similar dimensions. After cleaning, shaping and filling of the root canals and adhesive procedures, specimens were assigned to 3 subgroups for each tooth type (n=10): Group A: control group, including intact teeth; Group B: access cavities were restored with a traditional resin composite (EsthetX; Dentsply-Italy, Rome, Italy); Group C: access cavities were restored with a bulk fill flowable composite (SDR; Dentsply-Italy), except 1.5 mm layer of the occlusal surface that was restored with the same resin composite as Group B. The specimens were subjected to compressive force in a material static-testing machine until fracture occurred, the maximum fracture load of the specimens was measured (N) and the type of fracture was recorded as favorable or unfavorable. Data were statistically analyzed with one-way analysis of variance (ANOVA) and Bonferroni tests (P&lt;0.05). Results. No statistically significant differences were found among groups (P&lt;0.05). Fracture resistance of endodontically treated teeth restored with a traditional resin composite and with a bulk fill flowable composite (SDR) was similar in both maxillary and mandibular molars and showed no significant decrease in fracture resistance compared to intact specimens. Conclusions. No significant difference was observed in the mechanical fracture resistance of endodontically treated molars restored with traditional resin composite restorations compared to bulk fill flowable composite restorations.
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Annali di stomatologia
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Fracture resistance of endodontically treated teeth restored with a bulkfill flowable material and a resin composite
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Original Article
2022-08-11
2022-08-11
2016-06-01
2023-12-04
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G. Gambarini
2016
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Endodontics Unit, Department of Oral and Maxillo- Facial Sciences, “Sapienza” University of Rome, Italy
1971-1441
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Fracture resistance of endodontically treated teeth restored with a bulkfill flowable material and a resin composite
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                                                                                                Original article



Fracture resistance of endodontically treated teeth
restored with a bulkfill flowable material and a resin
composite

Almira Isufi, DDS, PhD1                                 was recorded as favorable or unfavorable. Data
Gianluca Plotino, DDS, PhD1                             were statistically analyzed with one-way analysis
Nicola Maria Grande, DDS, PhD2                          of variance (ANOVA) and Bonferroni tests
Pietro Ioppolo3                                         (P<0.05).
Luca Testarelli, DDS, PhD1                              Results. No statistically significant differences
Rossella Bedini3                                        were found among groups (P<0.05). Fracture re-
Dina Al-Sudani, DDS4                                    sistance of endodontically treated teeth restored
Gianluca Gambarini, MD, DDS1                            with a traditional resin composite and with a bulk
                                                        fill flowable composite (SDR) was similar in both
                                                        maxillary and mandibular molars and showed no
1 Endodontics Unit, Department of Oral and Maxillo-     significant decrease in fracture resistance com-
Facial Sciences, “Sapienza” University of Rome, Italy   pared to intact specimens.
2 Department of Endodontics, Catholic University of     Conclusions. No significant difference was ob-
Sacred Heart, Rome, Italy                               served in the mechanical fracture resistance of
3 Istituto Superiore di Sanità, Technology and Health   endodontically treated molars restored with tradi-
Department, Rome, Italy                                 tional resin composite restorations compared to
4 Department of Restorative Dental Sciences, College    bulk fill flowable composite restorations.
of Dentistry, King Saud University, Riyadh, Saudi
Arabia                                                  Key words: fracture resistance, endodontic treat-
                                                        ment, bulk fill flowable composite, resin compos-
                                                        ite.
Corresponding author:
Almira Isufi
Endodontics Unit, Department of Oral and Maxillo-       Introduction
Facial Sciences, “Sapienza” University of Rome
Via Caserta 6                                           The functional and aesthetic rehabilitation of en-
00161 Rome, Italy                                       dodontically treated teeth has been the subject of dif-
E-mail: almiraisufi@yahoo.it                            ferent studies (1). The restoration should not only
                                                        provide function, aesthetic and marginal sealing, but
                                                        also protect the remaining tooth structure (2, 3). Dif-
Summary                                                 ferent studies have shown that the preparation of en-
                                                        dodontic access cavities reduces the strength of the
Aim. To determine and compare the fracture re-          teeth, because of deep and extended cavity prepara-
sistance of endodontically treated teeth restored       tions which critically reduce the amount of dentin (4-
with a bulk fill flowable material (SDR) and a tradi-   8) and increase cuspal deflection during function (9).
tional resin composite.                                 The importance of conserving the bulk of dentin was
Methods. Thirty maxillary and 30 mandibular first       demonstrated in maintaining the structural integrity
molars were selected based on similar dimen-            and in the prognosis of endodontically restored teeth
sions. After cleaning, shaping and filling of the       (10-13), as the fracture resistance and stress distribu-
root canals and adhesive procedures, specimens          tion of endodontically treated teeth is directly affected
were assigned to 3 subgroups for each tooth type        by the amount of residual coronal dentin (4, 14-18).
(n=10): Group A: control group, including intact        In posterior preparations, especially when the cervi-
teeth; Group B: access cavities were restored           cal margin is located in dentin, the polymerization
with a traditional resin composite (EsthetX;            shrinkage effects can be significant, producing mar-
Dentsply-Italy, Rome, Italy); Group C: access cav-      ginal defects and gaps despite careful application
ities were restored with a bulk fill flowable com-      (19). Several techniques and a variety of restorative
posite (SDR; Dentsply-Italy), except 1.5 mm layer       materials, which would minimize the stresses gener-
of the occlusal surface that was restored with the      ated on the interface of the restoration by modifying
same resin composite as Group B. The speci-             some physical and mechanical properties have been
mens were subjected to compressive force in a           proposed to reduce the effects of polymerization
material static-testing machine until fracture oc-      shrinkage (20-22). Furthermore, inadequate polymer-
curred, the maximum fracture load of the speci-         ization throughout the restoration may compromise its
mens was measured (N) and the type of fracture          physical properties and increase elution of monomer

4                                                                          Annali di Stomatologia 2016;VII (1-2): 4-10
     Fracture resistance of endodontically treated teeth restored with a bulkfill flow able material and a resin composite


     (23-26) and may lead to undesirable effects, such as                  dures and were restored with a resin composite
     gap formation, marginal leakage, recurrent caries. It                 (EsthetX; Dentsply-Italy, Rome, Italy);
     may also negatively affect pulp tissue and may lead              • Group C, which included 10 maxillary and 10
     to premature failure of the restoration (27, 28).                     mandibular molars, which were subjected to en-
     Several manufacturers have recently developed and                     dodontic access cavity and endodontic proce-
     introduced new types of resin composites, so-called                   dures and were restored with a bulk fill flowable
     “bulk ﬁll” materials, which can be applied to the cavity              composite (SDR; Dentsply-Italy), except 1.5 mm
     and light cured to a maximal increment thickness of 4                 layer of the occlusal surface that was restored
     mm (29-32) with enhanced curing, shrinkage and                        with the same resin composite as Group B.
     physical properties (33). Bulk fill flowable resin com-          The access cavity was prepared using water-cooled
     posites are used in association with conventional                round-ended cylindrical diamond burs and non-end-
     composites for aesthetic restorations in posterior               cutting diamond burs mounted on a high-speed hand
     teeth, having lower polymerization stress, better flow           piece with different diameters. Root canals were ne-
     with easy placement, an excellent adaptation to the              gotiated with size 10 K-type files (Flexofile; Dentsply
     cavity walls and low modulus of elasticity, which can            Maillefer, Ballaigues, Switzerland) to the major apical
     reduce the stress generated on the cavity walls (34).            foramen and canals instrumented to length with NiTi
     The purpose of this in vitro study was to compare the            rotary instruments (Mtwo; Sweden & Martina, Padova,
     fracture resistance of endodontically treated upper              Italy) up to the #25 tip size and 0.06 taper file. During
     and lower molars restored with direct traditional and            the endodontic treatment 5.25% sodium hypochlorite
     bulk fill flowable resin composite restorations. The             (Niclor 5, Ogna, Muggiò Milan, Italy) for irrigation was
     null hypothesis tested was that there was a difference           intermittently deposited using Pro Rinse side-vented
     in the fracture resistance and the mode of failure be-           30-G needles (Dentsply Tulsa Dental Specialties, Tul-
     tween endodontically treated maxillary and mandibu-              sa, OK). The canals were dried with paper points and
     lar molars restored with traditional and bulk fill flow-         filled with gutta-percha (single-cone #25/0.06 taper)
     able resin composite.                                            and a resin-based endodontic sealer (AH-Plus,
                                                                      Dentsply Maillefer, Ballaigues, Switzerland). After the
                                                                      cleaning, shaping and filling procedures, post-opera-
     Materials and methods                                            tive radiographs were taken in the two perpendicular
                                                                      dimensions (MD and BL) to evaluate the endodontic
     Sixty intact recently extracted human maxillary and              treatment. Then, the enamel and dentin of the access
     mandibular molars with completely formed apices                  cavity were etched with 37% phosphoric acid for 30
     were used in this in vitro study. The exclusion criteria         and 15 seconds respectively, rinsed for 30 seconds
     for tested teeth were the presence of caries, previous           with a water/air spray, and gently air-dried to avoid
     restoration and visible fracture lines or cracks. After a        desiccation. A light-polymerizing primer-bond adhe-
     debridement with hand scaling instruments and                    sive (XP Bond, Dentsply International, York, USA)
     cleansing with rubber cup and pomice, the teeth were             was applied, gently air-thinned and exposed to LED
     stored in individually numbered containers with 0.1%             polymerization for 40 seconds. In group B access cav-
     thymol solution at 4° C until used. Thirty maxillary             ities were restored with direct resin composite (Es-
     first molars with three separate roots and 30                    thetX; Dentsply-Italy, Rome, Italy) with material incre-
     mandibular first molars with two separate roots were             ments of maximum 2 mm. The specimens in Group C
     selected based on similar anatomical crown height,               were restored with a bulk fill flowable composite with
     measured from the occlusal surface to the cemento-               maximal increment thickness of 4 mm (SDR;
     enamel junction on the four sides of the teeth, and              Dentsply-Italy), except for 1.5 mm layer of the occlusal
     bucco-lingual (BL), mesio-distal (MD) dimensions at              surface that was restored with the same resin com-
     the occlusal surface. Tooth measurements were tak-               posite as Group B (Fig. 1).
     en with a digital caliper. Preliminary radiographs were          All the specimens were marked 2 mm below the ce-
     taken in two perpendicular directions (MD and BL) to             mento-enamel junction and were covered with approx-
     determine root canal anatomy and measure the                     imately 0.25 mm-thick wax. The specimens were em-
     length and degree of canal curvature using the                   bedded in autopolymerizing acrylic resin (SR Ivolen;
     Schneider method (35). Specimens were subse-                     IvoclarVivadent, Schaan, Lichtenstein) in metallic cylin-
     quently assigned to 3 groups (n=10) for each tooth               drical molds in position with their long axis parallel to that
     type creating homogenous groups considering the                  of the cylindrical molds. To simulate the periodontal
     average of teeth dimensions in order to minimize the             ligament, at the first signs of the beginning of polymer-
     influence of size and shape variations on the results:           ization, the teeth were removed from the resin blocks
     • Group A, the negative control group, which includ-             and the wax was cleaned from the root surfaces. A
          ed 10 maxillary and 10 mandibular molars that               standardized silicone layer was created using a light-
          were left intact for fracture testing, without any          body silicone-based impression material (Aquasil ultra
          cavity preparation or root canal treatment;                 light bodies, Dentsply International, York, USA) which
     • Group B, which included 10 maxillary and 10                    was injected into the polymerizing resin bases. The
          mandibular molars, which were subjected to en-              teeth with now wax-free root surfaces were inserted in-
          dodontic access cavity and endodontic proce-                to the resin bases immediately after the silicone injec-

     Annali di Stomatologia 2016;VII (1-2): 4-10                                                                                  5
Copyright © 2016 CIC Edizioni Internazionali Unauthorized reproduction of this article is prohibited.
     A. Isufi et al.




     Figure 1. Representative images of enamel and dentin of access cavity etched with 37% phosphoric acid (A), application of
     a light-polymerizing primer-bond adhesive (B), application of a bulk fill flowable composite with maximal increment thickness
     of 4 mm (C) , and final restoration of 1.5 mm layer of the occlusal surface restored a traditional resin composite (D).



     tion (36). All the specimens were stored in buffered             man-Keuls test for multiple comparisons (Prism 5.0;
     saline plus 1.5% thymol at room temperature (24-28° C)           GraphPad Software, Inc, La Jolla, CA) with the sig-
     until the fracture testing procedure.                            nificance level established at 5% (P < .05).
     All the 60 specimens were mounted in a mechanical
     material testing machine (LR30K; Lloyd Instruments
     Ltd, Fareham, UK) equipped by a (5k ± 5) N load                  Results
     cell. The teeth were loaded at their central fossa at
     a 30° angle to the long axis of the tooth (Fig. 2). The          The mean of the bucco-lingual (BL) and mesio-distal
     continuous compressive force at a cross- head                    (MD) dimensions at the occlusal surface and the
     speed of 1.6 mm/s was applied with a 6 mm diame-                 anatomical crown height of the teeth tested are pre-
     ter ball-ended steel compressive head until visible              sented in Table 1. No significant difference was found
     or audible evidence of fracture was shown. The                   comparing all teeth dimensions in control and test
     force at fracture was measured in Newton (N) and                 groups (P > .05).
     type of fracture was recorded as “favorable” be-                 No statistically significant differences were found
     cause restorable, when the failures were above the               among groups (P<0.05). Fracture resistance of en-
     level of bone simulation (site of fracture above the             dodontically treated teeth restored with a traditional
     acrylic resin) and as “unfavorable” because non-re-              resin composite and with a bulk fill flowable compos-
     storable, when the failures were extending below                 ite (SDR) was similar in both maxillary (Group B:
     the level of bone simulation (site of fracture below             1072±525N; Group C: 1241±388N) and mandibular
     the acrylic resin). The data were verified with the              molars (Group B: 1332±318N; Group C: 1527±449N).
     Kolmogorov-Smirnov test for the normality of the                 Restored teeth showed no significant decrease in
     distribution and the Levene test for the homogeneity             fracture resistance compared to intact specimens
     of variances. Thus, they were statistically evaluated            similar in both maxillary (Group A: 1183±313N) and
     by the analysis of variance test and Student-New-                mandibular molars (Group A: 1620±170N) (Tab. 2).

     6                                                                                    Annali di Stomatologia 2016;VII (1-2): 4-10

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     Fracture resistance of endodontically treated teeth restored with a bulkfill flow able material and a resin composite




     Figure 2. Simulated occlusal loading using a 6-mm-diameter steel sphere placed on the central fossa with lingual orientation
     in& axio-occlusal
          &            line at 30° angle to the long axis of a mandibular molar tooth.




     Table 1. Mean and Standard Deviation of the Mesio-Distal (MD) and Buccal-Lingual (BL) dimensions and the anatomical
     crown height (measured at the four sides of the tooth) of the tested teeth in each group.


          Groups                       Control                         Bulk fill material (SDR)             Traditional resin composite

        Tooth Type            Occlusal             Anatomical          Occlusal           Anatomical             Occlusal     Anatomical
          (n=10)              Surface                Crown             Surface              Crown                Surface        Crown
                                                     Height                                 Height                              Height
                            MD         BL                             MD         BL                          MD        BL
                               a          a                     b           a         a                b         a
          Upper            9.9        9.7           5.4 (0.1)        10.0       10.1       5.6 (0.6)         9.9      10.1a       5.4 (0.4)b
          Molars           (0.6)      (0.7)                          (0.5)      (1.1)                        (0.5)    (0.9)
          Lower           10.7 a      10.3 a        5.7 (0.4)b      10.6a       10.1a      5.5 (0.4)b       10.4a     10.2a       5.6 (0.7)b
          Molars           (1.2)      (0.6)                         (0.8)       (0.7)                       (1.2)     (0.8)
     Similar upper letter case in the same row indicates no statistically significant differences (P > .05).




     Table 2. Load at fracture (mean ± standard deviation) and type of fracture, Favorable (F) or Unfavorable (U) for intact teeth
     (control, Group A), and teeth restored with traditional resin composite (Group B) or with bulk fill flowable material (SDR)
     (Group C) assessed after the static test using the Instron Universal Machine.

          Tooth Type                           Load at Fracture (N)                                        Type of Fracture
            (n=10)
                                                                                          F            U     F          U     F           U
                                   Group A             Group B          Group C               Group A            Group B      Group C

         Upper Molars          1172 (598)a          1001 (453)a        1313 (428)a        8a       2b            3b    7a     3b        7a
         Lower Molars          1572 (639)a          1375 (310)a        1484 (471)a        7a       3b            3b     7a    2b        8a
     Similar upper letter case in the same row indicates no statistically significant differences (P > .05).


     Annali di Stomatologia 2016;VII (1-2): 4-10                                                                                               7
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     A. Isufi et al.


     60.8% of the failures in total were unfavorable (Group      teeth. These findings may be attributed to the elastic
     B 70%; Group C, 75%; control group, 25%). No sig-           buffer effect of using low viscosity flowable composite
     nificant differences were found in the mode of failure      and the characteristic low contraction stress and low
     of the differently restored teeth between Group B and       modulus of elasticity of SDR flow (44, 45). High flex-
     Group C, while intact teeth presented significantly         ural modulus can inhibit the ability of a material to re-
     more favorable fractures compared to restored speci-        sist deformation due to loading and promote the ac-
     mens (both Group B and Group C).                            cumulation of surface and bulk defects, which may
                                                                 lead to premature failure (46, 47). These findings are
                                                                 in agreement with those of Atiyah et al. (48), who re-
     Discussion                                                  ported increased fracture resistance of endodontically
                                                                 treated premolars restored with SDR.
     The null hypothesis investigated in the present study       In the present study 75% of the samples in the intact
     can be rejected, as the results obtained support that       control teeth presented favorable fracture type that
     there is no difference in the fracture resistance and in    was an important statistical difference with the re-
     the mode of failure between endodontically treated          stored groups. In fact, the majority of the teeth re-
     maxillary and mandibular molars restored with a bulk        stored with SDR (75%) and with a traditional resin
     fill flowable resin composite (SDR) or a traditional        composite (70%) reported unfavorable type of frac-
     resin composite.                                            ture. However, no significant differences were found
     Fracture susceptibility of root-filled teeth is affected    in the mode of failure between restored teeth. Fur-
     mostly by the amount of the remaining dentin (4, 37)        thermore, all failures of the restored teeth were cohe-
     and it is not related to its biomechanical properties af-   sive fractures, regardless of the type of restoration.
     ter endodontic treatment, such as hardness and              The low elastic modulus may explain the severity of
     toughness (38). Some studies have shown that the            fracture type presented in restored teeth groups and
     reduction of tooth structure results in weaker teeth        the occurrence of unfavorable fracture. These find-
     due to restorative procedures (6-8). However, accord-       ings are in agreement with previous reports that
     ing to Reeh et al. (4), endodontic procedures have          found an increased frequency and severity of cuspal
     only a small effect on the tooth, reducing the relative     fracture due to removal of cervical dentin (49).
     rigidity by 5%, which is contributed entirely by the ac-    The limitations of this study must be recognized. The
     cess opening. Restorative procedures and, particular-       experimental methods used for in vitro analyses do
     ly, the loss of marginal ridge integrity, were the great-   not accurately reflect intraoral conditions, in which fail-
     est contributors to loss of tooth resistance. The loss      ures occur primarily due to fatigue. Future research in
     of 1 marginal ridge resulted in a 46% loss in tooth         this area should use cyclic loading and other fatiguing
     rigidity, and a MOD preparation resulted in an aver-        simulation to more accurately reproduce the clinical
     age loss of 63% in relative cuspal rigidity.                environment. Additional clinical studies are necessary
     Several studies were conducted to determine the ide-        to determine the long-term prognosis of endodontical-
     al materials and techniques to restore endodontically       ly treated maxillary and mandibular molars restored
     treated teeth because their long-term prognosis de-         with bulk fill flowable resin composite.
     pends on the quality of the final restoration (39-42).      Within the limitations of this in vitro study, endodonti-
     Usually, to restore endodontically treated teeth sever-     cally treated upper and lower molars restored with
     al resin increments are required to fill the cavity         bulk fill flowable resin composite presented a resis-
     preparation because of the large volume of the              tance to fracture under simulated compressive force
     restoration. Thus, the clinician must compensate the        not significantly different than that of traditional resin
     polymerization shrinkage of traditional resin-based         composite restorations. Restored teeth showed no
     composite, by filling the cavities in several increments    significant decrease in fracture resistance compared
     (43). A new category of flowable resin-based com-           to intact specimens. Furthermore, no differences
     posites has been introduced as bulk fill base material      were found in the mode of failure of the differently re-
     that can be applied in 4 mm thick bulks instead of us-      stored teeth, while intact teeth presented statistically
     ing the incremental placement technique, without            more favorable fractures.
     negatively affecting the polymerization shrinkage,          Bulk fill flowable composites can be used to restore
     cavity adaptation or the degree of conversion (30).         endodontically treated posterior teeth using 4 mm
     The results of the present study show that there were       maximum increments and 1.5 mm occlusal traditional
     no significant differences in the static fracture resis-    layer because this does not reduce the mechanical
     tance of endodontically treated molars restored with        resistance of the restored teeth, while making the
     bulk fill flowable resin composite (SDR) and a tradi-       procedure easier, less stressful and with a reduced
     tional resin composite. Moreover, the mean fracture         chair side time.
     load for teeth restored with SDR was higher com-
     pared with the mean fracture load of specimens re-
     stored with traditional resin composites, without any       Acknowledgements
     statistical significance. Furthermore, the results of
     this study showed that there was no significant differ-     The Authors deny any conflicts of interest.
     ence between teeth restored with SDR and intact             The Authors affirm that we have no financial affiliation

     8                                                                              Annali di Stomatologia 2016;VII (1-2): 4-10

Copyright © 2016 CIC Edizioni Internazionali Unauthorized reproduction of this article is prohibited.
     Fracture resistance of endodontically treated teeth restored with a bulkfill flow able material and a resin composite


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