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Additive manufacturing for tissue engineering applications offers the possibility to design scaffolds characterized by a fine and detailed microarchitecture. Several fabrication technologies are currently available which allow to prepare tailored structures with a large selection of materials for restoring and healing tissues. However, 3D printed scaffolds are generally collected by assembling repetitive geometrical units or reproducing specific patterns in the layering direction, leading to a highly ordered architecture that does not mimic the morphology of the natural extracellular matrix (ECM), one of the main goals to be reached for an effective therapeutic approach. It is usually stated in the tissue engineering field that a scaffold has to be considered a temporary ECM, resembling all the peculiar features as close as possible and, in this regard, an ordered microstructure cannot be usually observed within biological tissues and organs. With the aim to overcame this limitation and offer a potential approach for bone tissue applications, the present study proposes a design methodology to fabricate 3D printed scaffolds characterized by a random microarchitecture which can be repeatedly reproduced thanks to the intrinsic controllable process of additive manufacturing. In this framework, four different models in polylactic acid were fabricated by means of fused deposition modelling, including a three-dimensional random distribution of spherical pores of 400, 500, and 600 µm for the first three cases, and a randomly varied distribution in the range 400-600 µm for the fourth case. A detailed assessment by means of microcomputed tomography and mechanical evaluation was then carried out in order to fully analyse the resulting scaffolds, providing both morphological and quantitative data.

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INTRODUCTION: The purpose of this study was to compare in vitro the fracture strength of root-filled and restored teeth with traditional endodontic cavity (TEC), conservative endodontic cavity (CEC), or ultraconservative "ninja" endodontic cavity (NEC) access. METHODS: Extracted human intact maxillary and mandibular premolars and molars were selected and assigned to control (intact teeth), TEC, CEC, or NEC groups (n = 10/group/type). Teeth in the TEC group were prepared following the principles of traditional endodontic cavities. Minimal CECs and NECs were plotted on cone-beam computed tomographic images. Then, teeth were endodontically treated and restored. The 160 specimens were then loaded to fracture in a mechanical material testing machine (LR30 K; Lloyd Instruments Ltd, Fareham, UK). The maximum load at fracture and fracture pattern (restorable or unrestorable) were recorded. Fracture loads were compared statistically, and the data were examined with analysis of variance and the Student-Newman-Keuls test for multiple comparisons. RESULTS: The mean load at fracture for TEC was significantly lower than the one for the CEC, NEC, and control groups for all types of teeth (P < .05), whereas no difference was observed among CEC, NEC, and intact teeth (P > .05). Unrestorable fractures were significantly more frequent in the TEC, CEC, and NEC groups than in the control group in each tooth type (P < .05). CONCLUSIONS: Teeth with TEC access showed lower fracture strength than the ones prepared with CEC or NEC. Ultraconservative "ninja" endodontic cavity access did not increase the fracture strength of teeth compared with the ones prepared with CEC. Intact teeth showed more restorable fractures than all the prepared ones.

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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<0.05). RESULTS: No statistically significant differences were found among groups (P<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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PURPOSE: The clinical success and longevity of endosseous implants, after their prosthetic finalization, mainly depends on mechanical factors. Excessive mechanical stress has been shown to cause initial bone loss around implants in the presence of a rigid implant-prosthetic connection. The implant abutments are manufactured with high elastic modulus materials such as titanium, steel, precious alloys, or esthetic ceramics. These materials do not absorb any type of shock from the chewing loads or ensure protection of the bone-implant interface, especially when the esthetic restorative material is ceramic rather than composite resin. MATERIALS AND METHODS: The mechanical resistance to cyclical load was evaluated in a tooth-colored fiber-reinforced abutment prototype (TCFRA) and compared to that of a similarly shaped titanium abutment (TA). Eight TCFRAs and eight TAs were adhesively cemented on as many titanium implants. The swinging the two types of abutments showed during the application of sinusoidal load was also analyzed. RESULTS: In the TA group, fracture and deformation occurred in 12.5% of samples, while debonding occurred in 62.5%. In the TCFRA group, only debonding was present, in 37.5% of samples. In comparison to the TAs, the TCFRAs exhibited greater swinging during the application of sinusoidal load. In the TA group extrusion prevailed, whereas in the TCFRA group intrusion was more frequent. CONCLUSION: TCFRA demonstrated a greater elasticity than did TAs to the flexural load, absorbing part of the transversal load applied on the fixture during the chewing function and thus reducing the stress on the bone-implant interface.

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PURPOSE: So far, definitive implant abutments have been performed with high elastic modulus materials, which prevented any type of shock absorption of the chewing loads and as a consequence, the protection of the bone-fixture interface. This is particularly the case when the esthetic restorative material chosen is ceramic rather than composite resin. The adoption of an anisotropic abutment, characterized by an elastic deformability, could allow decreasing the impulse of chewing forces transmitted to the crestal bone. MATERIALS AND METHODS: According to research protocol, the mechanical resistance to cyclical load was evaluated in a tooth-colored fiber-reinforced abutment (TCFRA) prototype and compared to that of a titanium abutment (TA), thus eight TCFRAs and eight TAs were adhesively cemented on as many titanium implants. The swinging that the two types of abutments showed during the application of sinusoidal load was also analyzed. RESULTS: In the TA group, both fracture and deformation occurred in 12.5% of samples while debonding 62.5%. In the TCFRA group, only debonding was present in 37.5% of samples. In comparison to the TAs, the TCFRAs exhibited a greater swinging during the application of sinusoidal load. In the TA group, the extrusion prevailed, whereas in the TCFRA group, the intrusion was more frequent. CONCLUSION: The greater elasticity of TCFRA to the flexural load allows absorbing part of the transversal load applied on the fixture during the chewing function, thus reducing the stress on the bone-implant interface.

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OBJECTIVES: To evaluate whether custom modification resulting in an anatomically shaped post and whether the span/diameter ratio (L/D) would affect the mechanical properties of fiber-reinforced composite posts. METHODS: Preformed glass-fiber posts (Group 1) and modified glass-fiber posts (Group 2) and glass-fiber rods (Groups 3 and 4) (n=20) were loaded to failure in a three-point bending test to determine the maximum load (N), flexural strength (MPa) and flexural modulus (GPa). The span distance tested for Group 3 was 10.0mm, while for Group 4 was 22.0mm. Data were subjected to different statistical analysis with significance levels of P<0.05. RESULTS: The maximum load recorded for Groups 1 and 2 was 72.5+/-5.9N and 73.4+/-6.4N respectively, while for Groups 3 and 4 was 215.3+/-7N and 156.6+/-3.6N respectively. The flexural strength for Groups 1 and 2 was 914.6+/-53.1MPa and 1069.2+/-115.6MPa, while for Groups 3 and 4 was 685.4+/-22.2MPa and 899.6+/-46.1MPa. The flexural modulus recorded for Groups 1 and 2 was 32.6+/-3.2GPa and 33.4+/-2.2GPa respectively, while for Groups 3 and 4 was 13.7+/-0.3GPa and 34.4+/-0.3GPa respectively. CONCLUSIONS: The flexural properties of an anatomically custom modified fiber post were not affected by the modification procedure and the span-diameter ratio is an important parameter for the interpretation of flexural strength and flexural modulus values.

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The aims of this study were to compare Resilon (Resilon Research LLC, Madison, CT) in conjunction with either a bonding (Epiphany; Pentron Clinical Technologies, Wallingford, CT) or a nonbonding endodontic sealer (Pulp Canal Sealer; Kerr Corporation, Orange, CA) to EndoRez (Ultradent Products Inc, South Jordan, UT) and gutta-percha with regards to the physical properties and flexural stress in standardized dentin cylinders and the flexural stress of Resilon and gutta-percha. The external surface of 50 maxillary central incisors was reduced by means of mechanical milling to obtain dentin cylinders with an external diameter of 3 mm and minimum length of 12 mm. Root canals were prepared to obtain a standardized cylindrical preparation of 1.3 mm in diameter at the center of the root. The cylinders were randomly divided into five groups (n = 10): group 1: obturation with gutta-percha and Pulp Canal Sealer; group 2: obturation with Resilon, Epiphany primer, and Epiphany; group 3: obturation with Resilon and Pulp Canal Sealer; group 4: obturation with EndoRez methacrylate-based endodontic sealer; and group 5: dentin cylinders were not obturated. Ten gutta-percha (group 6) and Resilon (group 7) pellets for the Obtura gun were also tested. A three-point bending test was used to measure the maximum load values of specimens from groups 1 to 5 and the flexural strength and flexural modulus values for specimens from groups 6 and 7. Statistical analysis was performed to determine significance differences (p < 0.05). An analysis of variance test showed no significant difference among groups 1 to 5 (p = 0.697; F = 0.60). An independent sample t test showed statistically significant differences between groups 6 and 7 in flexural strength (p = 0.000) and flexural modulus (p = 0.000). Within the limits of this study, it may be concluded that the currently available endodontic-filling materials and their recommended adhesive procedures are not able to influence the mechanical properties of root canal dentin and that the flexural properties of Resilon and gutta-percha are too low to reinforce roots.

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