ABSTRACT
Introduction:
This in vitro study evaluated fracture resistance in pulpectomized second primary molars restored with nanohybrid composite resin, comparing reinforcements using vertical and cross-pattern glass fibers.
Materials and Methods:
Sixty teeth were divided into four groups: intact teeth, composite-only restorations, and composite with cross or vertical fiber reinforcement.
Results:
Vertical fiber-reinforced restorations achieved the highest fracture resistance (893.5 N ± 53.2), significantly outperforming composite-only and cross-pattern reinforcement.
Conclusions:
Vertical fiber orientation provided superior stress distribution, making it an effective, esthetic alternative to traditional restorative techniques for pulpectomized primary molars.
KEYWORDS: Fracture resistance, nanohybrid composite resin, pulpectomy
INTRODUCTION
Primary molars serve as vital components in maintaining occlusion, chewing efficiency, and space for permanent teeth eruption. However, when subjected to pulpectomy—a common treatment for pulp pathology—these teeth become structurally compromised, increasing their vulnerability to fractures.[1]
Traditional restorative options, such as stainless steel crowns (SSCs), are widely used for their durability.[2] However, SSCs necessitate extensive preparation, resulting in substantial loss of healthy tooth structure, and lack of esthetic appeal. Modern dentistry emphasizes conservative and visually acceptable materials, prompting the exploration of alternatives like composite resins.[3]
Nanohybrid composite resins, known for their improved compressive strength and wear resistance, are increasingly favored for restoring pulpectomized teeth.[4] However, composite-only restorations often lack the mechanical resilience required to withstand occlusal forces.[5]
Incorporating glass fibers into composite resins has shown promise in enhancing fracture resistance.[6] Fiber-reinforced composites (FRCs) create a monobloc structure that distributes stress more effectively. The orientation of fibers significantly influences performance; vertical fibers align with occlusal forces to optimize resistance, whereas cross-pattern fibers provide moderate multidirectional reinforcement.[7]
This study evaluates the fracture resistance of pulpectomized second primary molars restored with nanohybrid composite resin with and without glass fiber reinforcement, aiming to determine the most effective reinforcement technique for long-term restorative success.
MATERIALS AND METHODS
This in vitro study analyzed 60 extracted second primary molars. Teeth were selected based on specific inclusion criteria, including intact roots, no prior restorations, and caries limited to the cementoenamel junction (CEJ). Exclusion criteria included developmental anomalies, advanced root resorption, or previous restorative treatment. The selected teeth were divided into four groups of 15 samples each. Group 1 consisted of intact teeth with no preparation, serving as the control. Group 2 involved restoration using nanohybrid composite resin without reinforcement. Group 3 included composite restorations reinforced with glass fibers arranged in a cross-pattern, while Group 4 utilized vertically oriented glass fiber reinforcement within the composite.
All specimens were embedded in cold-cure acrylic resin blocks, simulating periodontal ligaments with silicone paste. Pulpectomy was performed on Groups 2 through 4 using K-files, followed by irrigation with 3% sodium hypochlorite and obturation with zinc oxide eugenol. Restorations were applied according to group protocols. Group 2 restorations included light-cured glass ionomer lining and incremental nanohybrid composite resin placement. For Group 3, cross-pattern glass fibers were embedded within flowable composite before completing the restoration. In Group 4, vertically oriented fibers were inserted into the canal space and extended coronally during the restoration process.
Following a 24-h immersion in distilled water, the specimens were subjected to compressive testing using a Universal Testing Machine. Force was applied perpendicular to the occlusal surface at a crosshead speed of 0.5 mm per minute until fracture occurred. Fracture resistance was recorded in newton (N). Data analysis was conducted using one-way analysis of variance (ANOVA) to determine significant differences between groups, followed by post hoc testing with a significance level set at P < 0.05.
RESULTS
Fracture resistance differed significantly among the groups. Group 4 exhibited the highest resistance (893.5 N ± 53.2), closely approaching the strength of intact teeth (Group 1, 857.2 N ± 42.8). Group 3 (701.8 N ± 32.4) showed moderate improvement, while Group 2 (672.4 N ± 38.7) demonstrated the lowest resistance.
Fractures in Group 4 were predominantly restorable, occurring above the CEJ. Group 2 displayed catastrophic fractures, often extending below the CEJ, rendering these teeth non-restorable [Table 1].
Table 1.
Statistical analysis of the fracture resistance of group 1 to 4
| Descriptive Statistics | ||||||
|---|---|---|---|---|---|---|
|
| ||||||
| Group | n | Mean | Sth. Deviation | Sth. Error | 95% CI | |
|
| ||||||
| Lower Bound | Upper Bound | |||||
| Group 1 | 15 | 836.58 | 41.97393 | 10.83762 | 813.3404 | 859.8292 |
| Group 2 | 15 | 666.62 | 36.74371 | 9.48719 | 646.2715 | 686.9675 |
| Group 3 | 15 | 702.19 | 25.45399 | 6.57219 | 688.0968 | 716.2887 |
| Group 4 | 15 | 866.60 | 47.6196 | 12.29533 | 840.2314 | 892.9731 |
| Total | 60 | 768.00 | 93.87221 | 12.11885 | 743.7501 | 792.2496 |
Statistical analysis confirmed significant differences between Group 4 and all other groups (P < 0.05). Group 3 also outperformed Group 2 but did not match the resistance of Group 4, highlighting the effectiveness of vertical fiber reinforcement [Tables 2 and 3].
Table 2.
Intragroup and intergroup comparison
| ANOVA | |||||
|---|---|---|---|---|---|
|
| |||||
| Fracture resistance | Sum of Squares | df | Mean Square | F | Sig. |
| Between Groups | 435523.311 | 3 | 145174.4 | 96.342 | 0.00 |
| Within Groups | 84384.199 | 56 | 1506.861 | ||
| Total | 519907.51 | 59 | |||
Table 3.
Multiple comparisons between groups
| Fracture resistance in newton Tukey HSD | ||||||
|---|---|---|---|---|---|---|
|
| ||||||
| (I) Group | (J) Group | Mean Difference (I-J) | Sth. Error | Sig. | 95% CI | |
|
| ||||||
| Lower Bound | Upper Bound | |||||
| Control | Composite-Only | 169.96530* | 14.17444 | 0.00 | 132.433 | 207.4976 |
| Composite with glass fiber in cross-pattern | 134.39209* | 14.17444 | 0.00 | 96.8598 | 171.9244 | |
| Composite with glass fiber in vertical direction | -30.0175 | 14.17444 | 0.16 | -67.5498 | 7.5149 | |
| Composite-Only | Control | -169.96530* | 14.17444 | 0.00 | -207.498 | -132.433 |
| Composite with glass fiber in cross-pattern | -35.5732 | 14.17444 | 0.07 | -73.1055 | 1.9591 | |
| Composite with glass | -199.98277* | 14.17444 | 0.00 | -237.515 | -162.45 | |
| fiber in vertical direction | ||||||
| Composite with glass fiber in cross-pattern | Control | -134.39209* | 14.17444 | 0.00 | -171.924 | -96.8598 |
| Composite-Only | 35.57321 | 14.17444 | 0.07 | -1.9591 | 73.1055 | |
| Composite with glass fiber in vertical direction | -164.40956* | 14.17444 | 0.00 | -201.942 | -126.877 | |
| Composite with glass fiber in vertical direction | Control | 30.01747 | 14.17444 | 0.16 | -7.5149 | 67.5498 |
| Composite-Only | 199.98277* | 14.17444 | 0.00 | 162.4504 | 237.5151 | |
| Composite with glass fiber in cross-pattern | 164.40956* | 14.17444 | 0.00 | 126.8772 | 201.9419 | |
DISCUSSION
This study underscores the importance of fiber reinforcement in restoring pulpectomized primary molars. Composite-only restorations, while esthetically pleasing, lack sufficient fracture resistance, as demonstrated by Group 2’s low resistance and catastrophic fracture patterns.
Vertical fiber reinforcement (Group 4) emerged as the most effective technique, significantly enhancing fracture resistance and closely mimicking the strength of intact teeth. Vertical fibers align with occlusal forces, optimizing stress distribution and reducing the likelihood of catastrophic failures. These findings align with existing research highlighting the superior mechanical performance of vertically oriented fibers.[8]
Cross-pattern reinforcement (Group 3) provided moderate improvement but was less effective than vertical reinforcement. The multidirectional arrangement may not align optimally with the occlusal forces acting on molars, limiting its ability to prevent fractures effectively.[9]
Clinically, vertical fiber reinforcement offers an esthetic and minimally invasive alternative to SSCs. By preserving tooth structure and providing robust mechanical support, this technique aligns with the goals of contemporary pediatric dentistry.[10] However, this study’s in vitro nature limits its application to clinical settings, as factors such as mastication forces, thermal fluctuations, and saliva exposure were not replicated.
Future research should include in vivo studies to validate these findings, exploring variations in fiber materials and orientations to further optimize restorative outcomes.
CONCLUSION
Vertical glass fiber reinforcement significantly enhances the fracture resistance of pulpectomized second primary molars, providing a reliable and esthetic alternative to traditional restorations. This technique demonstrates promising potential for improving the longevity and functionality of compromised primary teeth. Further clinical trials are warranted to confirm these results in real-world scenarios.
Conflicts of interest
There are no conflicts of interest.
Funding Statement
Nil.
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