| Abstract|| |
Background: Laboratory reports show that fiber-reinforced composites have improved fracture resistance over traditional composites. However, limitations in the biomechanics of tests to evaluate the fracture resistance of fiber-reinforced composites need to be considered for accurate clinical applications. Aim: To assess the fracture resistance of particulate filler composites, glass fiber-reinforced composites, and polyethylene-fiber reinforced composites by analyzing the different fracture types and failure patterns. Materials and Methods: A standardized incisal (Group I) and mesioincisal fractures (Group II) were prepared on human maxillary central incisors. The test samples were further subdivided according to the restorative material used; particulate filler composites (Filtek Z 250), glass fiber-reinforced composites (fibre splint), and polyethylene-reinforced composites (Ribbond). The type of fractures was evaluated under the stereomicroscope and the failure patterns were analyzed using the graphical output from Universal Testing Machine. Statistical Analysis: The Chi-square test of association was used to test the association between fiber-reinforced composites and fracture resistance of tooth restoration complex. Results: No statistical association was observed between fiber-reinforced composites to the type of fractures in both incisal (P = 0.29) and mesioincisal restoration (P = 0.27). A significant association was observed between the fiber-reinforced composites to the failure patterns in both the incisal (P = 0.005) and mesioincisal restoration (P = 0.007). Conclusion: The glass and polyethylene fiber-reinforced composites showed improved fracture resistance properties than the traditional particulate filler composites in both incisal and mesioincisal restorations.
Keywords: Catastrophic failures, fibre reinforced composites, statistical failures, tooth fractures, traumatic dental injuries
|How to cite this article:|
Patnana AK, Vanga NR, Vabbalareddy R, Chandrabhatla SK. Evaluating the fracture resistance of fiber reinforced composite restorations - An in vitro analysis. Indian J Dent Res 2020;31:138-44
|How to cite this URL:|
Patnana AK, Vanga NR, Vabbalareddy R, Chandrabhatla SK. Evaluating the fracture resistance of fiber reinforced composite restorations - An in vitro analysis. Indian J Dent Res [serial online] 2020 [cited 2021 May 11];31:138-44. Available from: https://www.ijdr.in/text.asp?2020/31/1/138/281814
| Introduction|| |
Crown fractures in maxillary anterior teeth were the most common form of traumatic dental injuries (TDI) in children and young adolescents. The TDI leave a significant impact on masticatory functions, quality of life in children, and also an indirect effect on the parental well being., Among all the TDI, uncomplicated crown fractures affecting enamel and dentin are most common followed by the complicated crown fractures involving the pulp. The rehabilitation of the fractured anterior tooth was quite challenging as it needs to consider many parameters for successful restoration. In such a process of attaining a successful restoration, stainless steel crowns, orthodontic bands, resin held by pins, and porcelain crowns were developed., However, each method had its own limitations either related to esthetics or mechanical strength. Although reattachment techniques show better aesthetic outcomes, failure to withstand the re-trauma conditions need to be considered. In order to bear high impact forces during re-trauma conditions, ideal restorative material should have improved fracture resistance properties. Thus, to improve the fracture resistance properties of tooth restoration complex, different bonding systems were developed. But, the fracture resistance values did not reach (even) up to 50–60% of the intact incisors.,
In the quest of improving fracture resistance properties in anterior restorations, incorporation of fibers into the traditional restorative composites were proposed. Although various fibers such as carbon fibers, kelvar fibers, vectran fibers were suggested, glass fibers and polyethylene fibers display high aesthetic and fracture resistance properties.,In vitro studies have revealed that glass and polyethylene fibers improve the impact strength, modulus of elasticity, flexural strength, and reduced microleakage of composite restorative materials significantly.,, However, the limitations in the biomechanics of standard shear tests to evaluate the fracture resistance of the fiber-reinforced composites need to be considered. Thus, the existing results regarding the fracture resistance of fiber-reinforced composites need to be re-evaluated by analyzing different fracture types and failure patterns for better interpretation of results. Hence, the primary objective was to assess the fracture resistance of particulate filler composites, glass fiber-reinforced composites, and polyethylene fiber-reinforced composite restorations by analyzing the fracture types and failure patterns in tooth restoration complex. The null hypothesis states that there would not be any significant difference between fracture resistance of particulate filler composites, glass fiber-reinforced composites, and polyethylene fiber-reinforced composite restorations.
| Materials and Methods|| |
Thein vitro study was carried out in the Department of Pedodontics and Preventive Dentistry of a dental college hospital. Forty-two human permanent maxillary central incisors extracted because of periodontal reasons were collected from Department of Oral and Maxillofacial Surgery. Teeth with any visible fractures or crack lines, carious teeth, attrited teeth were excluded from the study. Surface debridement was done with hand scalers and custom-made strip crown preparation was done for all the samples to achieve original tooth morphology after restoration.
The test samples were divided into two groups as Group I: Restorations in the incisal fractures; Group II: Restorations in the mesioincisal fractures. A standardized incisal and mesioincisal fracture were generated using the diamond disks under water coolant [Figure 1]a and [Figure 2]a). A circumferential chamfer preparation was done on the fractured tooth 2 mm below the fracture line. In both, the experimental group's test samples were further divided into three subgroups, each group containing seven teeth according to the restorative material used. The division of groups and subgroups were shown in [Table 1].
|Figure 1: Incisal fracture preparation in test samples. (a) Incisal fracture preparation; (b) Palatal cavity prepared for fiber placement; (c) Position of fibers in palatal cavity|
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|Figure 2: Palatal fracture preparation in test samples. (a) Mesioincisal fracture preparation; (b) Palatal cavity prepared for fiber placement; (c) Position of fibers in palatal cavity|
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|Table 1: The division of groups and subgroups according to the restorative material used in the present study|
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In Group IA and IIA, surfaces of the fractured site on tooth structure were etched for 20 seconds using 37% of orthophosphoric acid gel (Meta Etchant, Meta Biomed Co. Ltd.). The gel was rinsed with water thoroughly and air dried gently. The dentin bonding agent (3M Single bond 2) was applied and polymerization was done using light curing unit (Elipar 2500 3M ESPE, Germany) for 20 seconds, which was according to the manufacturer's instructions. Particulate filler composite (Filtek Z 250 XT, 3M ESPE) was placed and polymerized incrementally using the light curing unit. Original tooth anatomy was restored using the templates prepared earlier specific to each sample.
Following the sample preparations in Groups IB, IC, IIB, and IIC, an additional cavity with dimensions of 0.5 mm depth, 4 mm mesiodistal width and 4 mm cervicoincisal height was prepared in order to accommodate the fiber bundles on the palatal side [Figure 1]b and [Figure 2]b)., Acid etching (Meta Etchant, Meta Biomed Co. Ltd.) was done on the fracture site and palatal cavity. After thorough cleaning of the etchant, bonding agent (3M Single bond 2) was applied and polymerized using light curing unit (Elipar 2500 3M ESPE, Germany). A required length of both glass fibres (Fibre splint, Polydentia SA, Switzerland) and polyethylene fibers (Ribbond, Ribbond INC, Seattle, Washington, USA) were taken such that the fiber extending 2 mm below the fracture line of test samples [Figure 1]c and [Figure 2]c). The fiber bundle was coated with the bonding agent and excess was cleared with gentle air blow. A layer of nano-hybrid composite (Filtek Z 250, 3M ESPE, St Paul, MN, USA) was placed in the palatal cavity, as this thin layer act as a glue, which in turn holds the fibrous bundle during the placement. Then, the fibrous bundle was carried over the palatal cavity and positioned such that the fiber extending 2 mm below the fracture line and polymerized (Elipar 2500 3M ESPE, Germany). Another layer of particulate filler composite was added on the fibrous bundle and original tooth anatomy was achieved using the custom-made templates. Followed by the restorations, all test samples were stored in distilled water at room temperature for 24 hours before sample testing.
The test samples were anchored in the acrylic blocks up to the cementoenamel junction using auto polymerized acrylic resin (DPI-RR cold cure acrylic repair material, Mumbai) with long axis of the tooth perpendicular to the base of the acrylic blocks. The acrylic blocks with test samples were snuggly fitted in the custom-made inclined metal base to provide 90° angulation to the horizontal plane of the Universal Testing Machine (UTM, Capacity 250 KN, and Instron make). A compressive fatigue load was applied with custom-made pointer tip with a crosshead diameter of 1 mm, at a constant speed of 1 mm/minute. The load application was given perpendicular to the labial surface at the junction of the tooth and the restoration complex. During the testing procedure, a reading of applied load was observed both graphically and numerically. A sudden drop in the load value of the graph was considered as peak fracture load in Newton for the particular specimen. The fractured specimens were then evaluated by the second examiner using Stereomicroscope (Olympus, Shinjuku, Tokyo, Japan) at 2X magnifications to evaluate the site and type of fracture. The actual type of fracture was recorded according to the following criteria:
- Cohesive fractures:
Completely within the restoration (CR), [Figure 3]a
|Figure 3: Different types of fractures observed in the test samples. (a) Cohesive fracture completely within the restoration (CR); (b) Cohesive fracture completely within the tooth structure (CT); (c) Adhesive fractures at the interface of restoration and tooth structure (a); (d) Mixed fractures (m)|
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Completely within the tooth structure (CT), [Figure 3]b
- Adhesive fractures:
Fracture at the interface of restoration and tooth structure (A), [Figure 3]c
- Mixed fractures:
Partial cohesive fracture in restoration along with partial adhesive fracture (M), [Figure 3]d.
Failure pattern after peak load application was explained under three categories as described by Craig and Courtney in 1975 such as catastrophic/instantaneous failures, statistical failures, and stepwise failures. Instantaneous failure occurs after a load causes a strain concentration in a narrow region sufficient to break the composite restorative material [Figure 4]a. When a strain concentration was distributed to a wide region in the restorative material, it requires a further load to promote the fracture at tooth restoration complex, thus leading to stepwise (more bending type) or statistical failure (series of small intense fractures, which recover before complete failure and require more load to progress the failure pattern [Figure 4]b. Applying to the present study, instantaneous fractures result in complete dislodgement of the tooth fragment from the restored tooth structure [Figure 5]a. In statistical failure patterns, even after applying the peak fracture load, the restored fragment could not be separated from the tooth structure. [Figure 5]b.
|Figure 4: Graphical representation of failure patterns in the test samples by Universal Testing Machine. (a) Catastrophic failure pattern observed in particulate filler composite restorations of mesioincisal fractures; (b) Statistical failure pattern observed in polyethylene fiber-reinforced composite restorations of mesioincisal fractures|
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|Figure 5: Differentiation of catastrophic and statistical failure patterns in test samples. (a) Catastrophic failure pattern; (b) Statistical failure pattern|
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The results were analyzed using the Chi-square test of association, evaluating the association between different experimental restorative materials and observed types of fracture and failure patterns. The P value of 0.05 was considered as statistically significant. The statistical analysis was performed using the SPSS software (16.0 version).
| Results|| |
The fracture type distribution for incisal (Group I) and mesioincisal restorations (Group II) are shown in [Table 2]. In incisal fracture restorations, Group IA showed more of cohesive fractures within the restoration (57%), Group IB showed more of mixed fractures (43%), and Group IC showed more of cohesive fractures within the tooth (28%), which are not observed in other experimental groups. In mesioincisal fracture restorations, Group IIA showed more of mixed fractures (57%), Group IIB also showed more of mixed fractures (43%), and Group IC showed a maximum of cohesive fractures within the tooth, (43%) which are virtually absent in other experimental groups. The Chi-square test of association showed no association between the experimental restorative materials to the type of fracture in Group I (P = 0.29) and Group II (P = 0.27).
|Table 2: Distribution and analysis of fracture types in Incisal restorations and Mesio-incisal restorations groups|
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The failure pattern distribution for incisal (Group I) and mesioincisal restorations (Group II) are shown in [Table 3]. Group IA showed a maximum of catastrophic failure (85%), Group IB showed more of statistical failures (57%), and Group IC showed only statistical failures (100%) in all the test samples. Group IIA showed more of catastrophic failure (63%), Group IIB showed more of statistical failures (85%), and Group IIC showed only statistical failures (100%) in the test samples. The Chi-square test of association showed a significant association between the experimental restorative materials to the failure patterns in Group I (P = 0.005) and Group II (P = 0.007).
|Table 3: Distribution and analysis of failure patterns in Incisal and Mesio-incisal restoration groups|
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| Discussion|| |
The presentin vitro study was done to evaluate the fracture type and failure patterns in different fiber-reinforced composite restorative materials used for incisal and mesioincisal restorations. In the present study, particulate filler composites in incisal restorations showed that the cohesive fractures within the restoration are more common than other types of fractures. The present study results regarding particulate filler composites were contrary to the results of Badakar et al. and Garoushi et al., where they observed that adhesive fractures between tooth and restoration were more common than cohesive fractures within the restoration., The contrary results with Badakar et al. and Garoushi et al. could be attributed to the methodological variations to the present study., A chamfer preparation of 2 mm extending below the fracture line was prepared for all samples in the present study, whereas no such preparation was done by Badakar et al. and Garoushi et al., The present study results regarding particulate filler composites are in accordance with Xuet al., Eid et al., and Gandhi et al., where they observed that chamfer preparation on the fractured tooth surfaces allows a bulk of composite material to be present at the restoration/tooth interface and thereby preventing the adhesive fractures between tooth and restoration interface.,, Analysis of particulate filler composite restorations in mesioincisal fractures showed more of mixed fractures rather than cohesive fractures. The reduced area of chamfer preparation in mesioincisal fractures reduces the surface area for bonding in mesioincisal restorations when compared with incisal fractures which lead to the mixed type of fractures.
The type of fracture analysis in glass fiber-reinforced composites showed more of mixed fractures for both the experimental groups in the present study. However, the percentage of adhesive fractures increased in the glass fiber-reinforced composite group when compared with particulate filler composites. These findings are contrary to the results of Garoushi et al., where they observed that glass fiber-reinforced composites showed cohesive fractures within the tooth structure rather than at the adhesive fractures. The contrary results with Garoushi et al. can be explained by the variation in the type of glass fibers (Fibre splint, Polydentia SA, Switzerland) used and direction of load application (perpendicular to the labial surface) in the present study.
The polyethylene fiber-reinforced composites showed a maximum of cohesive fractures within the tooth structure for both incisal and mesioincisal restorations, which infers that the polyethylene fibers (Ribbond, Ribbond INC, Seattle, Washington, USA) result in increased fracture resistance of tooth and restoration complex in the present study. These findings are in accordance with the Potiket al., where they observed that increasing the stiffness of tooth restoration complex results in cohesive fractures within the tooth structure. Thus, the evidence of cohesive fractures within the tooth structure infers that the polyethylene fibers improve the fracture resistance of tooth restoration complex. Furthermore, the percentage of cohesive fractures within the tooth structure increased in the mesioincisal restoration group when compared with incisal restorations in the present study. The present findings can be explained according to the Gogutaet al., where they observed that reinforcing ability of the fibers will improve by increasing the area of fibers in the dentures. Accordingly, in the present study, the area of fiber reinforcement in mesioincisal restorations is more than the area of fiber reinforcement in incisal restorations which in turn increases the percentage of cohesive fractures in mesioincisal restorations. However, the experimental groups do not differ significantly in the type of fracture type analysis and infer that there is no association between the type of restorative material used to the type of fracture observed.
The failure pattern analysis in the particulate filler composite restorations showed more of catastrophic failures than other failure patterns for both incisal and mesioincisal restorations in the present study. These findings infer that the particulate filler composites lead to the complete dislodgement of the restorative fragment from the tooth surface when loading forces were applied. The present study results are in accordance with Ellakwa et al., where they observed that catastrophic failures are more common in particulate filler composites. The glass fiber-reinforced composite restorations in the incisal and mesioincisal groups showed more statistical failures in the present study. The results infer that glass fibers in the present study (Fibre splint, Polydentia SA, Switzerland) not only aid in reinforcing the tooth restoration complex but also aids in retaining the restorative fragment in re-trauma conditions.
The incisal and mesioincisal restorations of polyethylene fiber-reinforced composites showed statistical failures for all the test samples in the present study. These findings infer that even after peak failure load application, restorative fragments were not completely detached from the tooth surface and thus enhancing the fracture resistance of the tooth restoration complex. Similar findings were observed by Dyer et al., where they observed that the fiber reinforcement minimizes the instantaneous or catastrophic failures and also aids in retaining the fractured restored segment. The failure pattern analysis showed a significant difference between the experimental restorative materials in both incisal and mesioincisal restorative groups, which reject the null hypothesis and infers that there is an association between the type of restorative material used and the fracture resistance of the tooth restoration complex.
| Limitations|| |
Although every effort was taken to mimic the clinical conditions, thermocycling and the influence of dynamic/cyclic loading was not investigated in the presentin vitro study. Hence, it must be noted that the direct application of the present study results may vary with the clinical conditions. Therefore, the authors recommend further studies considering the impact of thermocycling, and dynamic load on fracture strength on fiber-reinforced composite restorations.
| Conclusion|| |
The type of fracture analysis in the presentin vitro study observed no association between fiber-reinforced composites to the fracture resistance of the tooth restoration complex. However, the failure pattern analysis revealed that the fiber-reinforced composites efficiently increase the fracture resistance of the tooth restoration complex.
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Conflicts of interest
There are no conflicts of interest.
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Arun Kumar Patnana
Department of Dentistry, All India Institute of Medical Sciences, Jodhpur, Rajasthan - 342 005
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
[Table 1], [Table 2], [Table 3]