Comparative Evaluation of Flexural Strength and Surface Microhardness of Temporary Dental Disocclusion Materials with and Without Thermocycling - An in Vitro Study

International Journal of Dental Science and Innovative Research (IJDSIR) IJDSIR : Dental Publication Service Available Online at:www.ijdsir.com Volume – 8, Issue – 5, September – 2025, Page No. : 249 - 259 Corresponding Author: Katte Sheethal Chandana, ijdsir, Volume – 8 Issue - 5, Page No. : 249 - 259 Page249 ISSN: 2581-5989 PubMed - National Library of Medicine - ID: 101738774 Comparative Evaluation of Flexural Strength and Surface Microhardness of Temporary Dental Disocclusion Materials with and Without Thermocycling - An in Vitro Study 1Katte Sheethal Chandana, Postgraduate Student, Government Dental College and Hospital, Afzalgunj, Hyderabad 2Chandulal Jadav, HOD, Government Dental College and Hospital, Afzalgunj, Hyderabad 3Venkata Ramana Irukulla, Associate Professor, Government Dental College and Hospital, Afzalgunj, Hyderabad 4Srinivasulu Enagganti, Associate Professor, Government Dental College and Hospital, Afzalgunj, Hyderabad 5Brahmasri Amulya Sharma, Associate Professor, Government Dental College and Hospital, Afzalgunj, Hyderabad 6Tamizhselvan G, Postgraduate Student, Government Dental College and Hospital, Afzalgunj, Hyderabad Corresponding Author: Katte Sheethal Chandana, Postgraduate Student, Government Dental College and Hospital, Afzalgunj, Hyderabad. Citation of this Article: Katte Sheethal Chandana, Chandulal Jadav, Venkata Ramana Irukulla, Srinivasulu Enagganti, Brahmasri Amulya Sharma, Tamizhselvan G, “Comparative Evaluation of Flexural Strength and Surface Microhardness of Temporary Dental Disocclusion Materials with and Without Thermocycling - An in Vitro Study”, IJDSIRSeptember – 2025, Volume – 8, Issue – 5, P. No. 249 – 259. Copyright: © 2025, Katte Sheethal Chandana, et al. This is an open access journal and article distributed under the terms of the creative common’s attribution non-commercial License. Which allows others to remix, tweak, and build upon the work non-commercially, as long as appropriate credit is given, and the new creations are licensed under the identical terms. Type of Publication: Original Research Article Conflicts of Interest: Nil Introduction In Orthodontics, there are several indications for bite opening. Fixed appliances, though small, can interfere with occlusion and function, potentially causing tooth abrasion or bracket debonding. To prevent occlusal interferences from damaging mandibular brackets, temporary dental disocclusion is often necessary. This facilitates tooth movement that may otherwise be restricted by deep bites, telescopic bites, buccal nonocclusions, or crossbites.1 Orthodontic bite raisers are specially designed surfaces placed anteriorly or posteriorly to create a contact plane that prevents full jaw closure.2 While removable bite plates require patient compliance and laboratory fabrication, many orthodontists now prefer directly bonded materials like composite resins and glass ionomers due to their ease of use and improved bonding techniques. These bonded attachments are actually commonly known as “bite turbos.”3 A wide range of composite materials is available for both direct and indirect bonding, valued for their favorable physical and mechanical properties. These composites typically consist of an organic polymatrix, inorganic fillers, and a silane coupling agent. Their mechanical behavior is closely tied to composition and also microstructure. Nanofilled composites, which contain Katte Sheethal Chandana, et al. International Journal of Dental Science and Innovative Research (IJDSIR) ©2025 IJDSIR, All Rights Reserved Page250 Page250 Page250 Page250 Page250 Page250 Page250 Page250 Page250 Page250 Page250 Page250 Page250 Page250 Page250 Page250 Page250 Page250 Page250 uniformly dispersed nanosized particles, offer better protection to the matrix due to reduced inter particle spacing. As a result, they exhibit enhanced wear resistance and microhardness.4 Orthodontic composites like Orthobite and Orthocem also offer additional advantages such as pigmentation and fluorescence, which facilitate easy identification and removal of bite turbos after treatment without causing iatrogenic damage.5 In the oral environment, materials undergo cyclic stress due to exposure to hot and cold foods and beverages such as tea, coffee, juices, and carbonated drinks. These conditions can alter the properties of materials used intraorally. Although bite raisers are temporary, their mechanical performance—particularly flexural strength and surface microhardness—is critical. These parameters should be key considerations for clinicians selecting adhesives for bite-raising applications.6 Therefore, the purpose of the study is to compare and evaluate the effect of temperature variation on flexural strength and surface microhardness of five different materials used for making a temporary dental disocclusion. Material and Methodology Sample preparation This in-vitro study was done in the Department of Orthodontics and Dentofacial Orthopaedics in Government Dental College and Hospital, Afzalgunj, Hyderabad. The materials and equipment utilized in the study included a variety of dental composites and specialized instruments. Vitrebond, Transbond Plus color change adhesive, Filtek Supreme, Orthobite (a blue-colored resin composite), and Orthocem (a UV resin composite) were used as restorative and adhesive materials. Distilled water served as the immersion medium for sample storage, simulating intraoral conditions. Samples were prepared on standard glass slides measuring 75 mm × 50 mm × 1 mm and then secured using a bipartite metallic matrix. A Teflon-coated composite instrument was employed for manipulation of the composites, while a polyester strip was used to achieve a smooth surface finish. To simulate the oral environment, the specimens were immersed in distilled water and incubated at 37°C. Light polymerization was performed using an LED curing unit (Woodpecker). Dimensional accuracy and measurements were obtained using a digital vernier caliper (Model - TH-M61). Mechanical testing involved the use of a Universal Testing Machine (INSTRON, Model-1185) to evaluate bond strength, and a Microhardness Testing Machine (CMV-1000) to assess surface hardness of the materials. Additionally, a Thermocycling Machine (CME, Pvt. Ltd.) was used to subject the samples to thermal stresses, thereby mimicking temperature variations encountered in the oral cavity. Inclusion Criteria  Samples of five different materials with measurements 25mm×2mm×2mm.  Materials compatible with the planned testing methodologies. eg: Flexural strength.  Resins that are manufactured in compliance with international standard ISO: 4049. Exclusion Criteria  Materials beyond expiry date. Methodology A total of 100 samples were prepared and divided into five groups (20 specimens each) according to ISO 4049:1988 standards, using a bipartite metallic matrix (25 mm × 2 mm × 2 mm) supported on a glass plate. Specimen Preparation  Vitrebond: Mixed in a 1.4:1.0 powder-to-liquid ratio and placed into the matrix using a disposable syringe. Katte Sheethal Chandana, et al. International Journal of Dental Science and Innovative Research (IJDSIR) ©2025 IJDSIR, All Rights Reserved Page251 Page251 Page251 Page251 Page251 Page251 Page251 Page251 Page251 Page251 Page251 Page251 Page251 Page251 Page251 Page251 Page251 Page251 Page251 A polyester strip and glass slide (75 mm × 50 mm × 1 mm, 1 kg) were placed on top to standardize the sample.  Transbond Plus, Filtek Supreme, Orthobite, Orthocem: Inserted using a Teflon-coated spatula, followed by the same polyester strip and glass slide procedure. Light curing (400 mW/cm²) was performed in four 6 mm increments. Post-curing, sample dimensions were confirmed using a digital vernier caliper (TH-M61, accuracy 0.01 mm).All specimens were stored in distilled water at 37°C for 24 hours. Half of each group then underwent 1150 thermocycles (5°C–55°C, 30 seconds immersion, 10 seconds interval), simulating 4 months of intraoral conditions. After thermocycling, all samples were again stored at 37°C in distilled water for 24 hours prior to testing. Figure 1: Prepared Sample Specimens of Five Different Groups Figure 2: Three Point Bending Test For Flexural Strength Figure 3: Knoop Hardness Testing Procedure Flexural Strength Test Conducted on a Universal Testing Machine (INSTRON Model-1185) with a 20 mm span, applying 5 kN load at 0.5 mm/min until fracture. Surface Microhardness Test Performed using a CMV-1000 Microhardness tester with a Knoop diamond indenter, 25 g load, and 10-second dwell time. Three indentations per specimen were made, spaced 100 µm apart. The Knoop microhardness results were obtained automatically by calculating the following formula: KHN = C .c/d2 KHN = Knoop hardness value, C (constant) = 14,230, c = load, d = length of the longest diagonal of the impression. The resulting number of Knoop hardness was determined for each specimen by averaging the values obtained from the three impressions. Katte Sheethal Chandana, et al. International Journal of Dental Science and Innovative Research (IJDSIR) ©2025 IJDSIR, All Rights Reserved Page252 Page252 Page252 Page252 Page252 Page252 Page252 Page252 Page252 Page252 Page252 Page252 Page252 Page252 Page252 Page252 Page252 Page252 Page252 Results All the materials except Vitrebond showed significant difference in both flexural strength and surface microhardness tests after thermocyling. (Table 1 & 2 and Graphs 1 & 2) Table 1: Post-hoc comparison of Mean Flexural Strength Scores between Groups Using One-Way ANOVA Sum of Squares df Mean Square F p-value Vitrebond Between Groups 0.625 1 0.625 0.253 0.62 Within Groups 19.759 8 2.470 Total 20.384 9 Transbond Plus Between Groups 1644.550 1 1644.550 1906.658 0.001* Within Groups 6.900 8 0.863 Total 1651.450 9 Filtek Supreme Between Groups 2033.476 1 2033.476 1333.991 0.001* Within Groups 12.195 8 1.524 Total 2045.671 9 Orthobite Between Groups 3906.948 1 3906.948 2098.310 0.001* Within Groups 14.896 8 1.862 Total 3921.843 9 Orthocem Between Groups 4535.622 1 4535.622 2192.870 0.001* Within Groups 16.547 8 2.068 Total 4552.169 9 *p<0.05 is considered as statistically significant Table 2: Post-hoc comparison of Mean Microhardness Scores between Groups Using One-Way ANOVA ANOVA Sum of Squares df Mean Square F p-value Vitrebond Between Groups 0.225 1 0.225 0.500 0.50 Within Groups 3.602 8 0.450 Total 3.827 9 Transbond Plus Between Groups 150.622 1 150.622 109.419 0.001* Within Groups 11.012 8 1.377 Total 161.634 9 Filtek Supreme Between Groups 149.150 1 149.150 92.264 0.001* Within Groups 12.933 8 1.617 Total 162.083 9 Orthobite Between Groups 26.179 1 26.179 5.061 0.05* Within Groups 41.381 8 5.173 Katte Sheethal Chandana, et al. International Journal of Dental Science and Innovative Research (IJDSIR) ©2025 IJDSIR, All Rights Reserved Page253 Page253 Page253 Page253 Page253 Page253 Page253 Page253 Page253 Page253 Page253 Page253 Page253 Page253 Page253 Page253 Page253 Page253 Page253 Total 67.560 9 Orthocem Between Groups 32.400 1 32.400 27.576 0.001* Within Groups 9.400 8 1.175 Total 41.800 9 *p<0.05 is considered as statistically significant Graph 1: sample distribution of five groups with and without thermocycling Graph 2: Comparison of mean flexural strength scores of study groups based on thermal cycling According to the results of the analysis of variance, the material’s flexural strength varied significantly. The variation is dependent on the factors such as material type and temperature effect. Greater the F-ratio, greater is the significance, Hence all the groups except vitrebond showed greater F statistic indicating the level of significance between the groups. According to the tukeys post hoc comparision test, there was no discernible difference in mean resistance between the cycling and non-cycling groups for vitrebond (table 3 & 4). Katte Sheethal Chandana, et al. International Journal of Dental Science and Innovative Research (IJDSIR) ©2025 IJDSIR, All Rights Reserved Page254 Page254 Page254 Page254 Page254 Page254 Page254 Page254 Page254 Page254 Page254 Page254 Page254 Page254 Page254 Page254 Page254 Page254 Page254 Table 3: Comparison of Mean Flexural Strength Scores between Groups N Mean Std. Deviation Std. Error 95% Confidence Interval for Mean Minimum Maximum Lower Bound Upper Bound Vitrebond Without thermal cycling 5 12.7840 1.50334 .67231 10.9174 14.6506 10.34 14.05 With thermal cycling 5 12.2840 1.63697 .73208 10.2514 14.3166 10.35 14.43 Total 10 12.5340 1.50495 .47591 11.4574 13.6106 10.34 14.43 Trans Bond Plus Without thermal cycling 5 60.7840 .92916 .41553 59.6303 61.9377 59.85 62.12 With thermal cycling 5 35.1360 .92829 .41515 33.9834 36.2886 33.83 36.02 Total 10 47.9600 13.54601 4.28363 38.2698 57.6502 33.83 62.12 Filtek Supreme Without thermal cycling 5 64.5440 1.43036 .63968 62.7680 66.3200 62.88 66.45 With thermal cycling 5 36.0240 1.00139 .44783 34.7806 37.2674 34.67 37.01 Total 10 50.2840 15.07636 4.76756 39.4990 61.0690 34.67 66.45 Orthobite Without thermal cycling 5 85.0580 1.09623 .49025 83.6969 86.4191 83.28 86.14 With thermal cycling 5 45.5260 1.58814 .71024 43.5541 47.4979 43.99 47.86 Total 10 65.2920 20.87487 6.60121 50.3590 80.2250 43.99 86.14 Orthocem Without thermal cycling 5 88.7980 .63700 .28488 88.0071 89.5889 87.86 89.35 With thermal cycling 5 46.2040 1.93156 .86382 43.8056 48.6024 43.56 48.44 Total 10 67.5010 22.48992 7.11194 51.4127 83.5893 43.56 89.35 Table 4: Comparison of Mean Microhardness Scores between Groups N Mean Std. Deviation Std. Error 95% Confidence Interval for Mean Minimum Maximum Lower Bound Upper Bound Vitrebond Without thermal cycling 5 46.4120 .60027 .26845 45.6667 47.1573 45.8 47.33 Katte Sheethal Chandana, et al. International Journal of Dental Science and Innovative Research (IJDSIR) ©2025 IJDSIR, All Rights Reserved Page255 Page255 Page255 Page255 Page255 Page255 Page255 Page255 Page255 Page255 Page255 Page255 Page255 Page255 Page255 Page255 Page255 Page255 Page255 With thermal cycling 5 46.7120 .73503 .32872 45.7993 47.6247 45.4 47.34 Total 10 46.5620 .65212 .20622 46.0955 47.0285 45.4 47.34 Transbond Plus Without thermal cycling 5 65.1220 .62082 .27764 64.3511 65.8929 64.3 66.01 With thermal cycling 5 57.3600 1.53873 .68814 55.4494 59.2706 55.6 59.32 Total 10 61.2410 4.23785 1.34012 58.2094 64.2726 55.6 66.01 Filtek Supreme Without thermal cycling 5 66.4640 1.60265 .71673 64.4740 68.4540 64.8 69.01 With thermal cycling 5 58.7400 .81526 .36460 57.7277 59.7523 57.6 59.86 Total 10 62.6020 4.24373 1.34198 59.5662 65.6378 57.6 69.01 Orthobite Without thermal cycling 5 80.5940 2.31998 1.03753 77.7134 83.4746 77.1 82.45 With thermal cycling 5 77.3580 2.22775 .99628 74.5919 80.1241 74.5 79.68 Total 10 78.9760 2.73983 .86641 77.0160 80.9360 74.5 82.45 Orthocem Without thermal cycling 5 82.3580 1.32686 .59339 80.7105 84.0055 80.1 83.45 With thermal cycling 5 78.7580 .76767 .34331 77.8048 79.7112 77.8 79.88 Total 10 80.5580 2.15509 .68150 79.0163 82.0997 77.8 83.45 The cycling groups had significantly lower averages (P < 0.05) for the other materials. Orthodontic Composite resins, Orthocem and Orthobite materials had considerably greater resistance than Vitrebond in the thermal cycling groups (P < 0.05). Regarding the microhardness of the materials, (Table 2) the tukey test revealed that the groups that got cycling had considerably lower averages (p< 0.05), with the exception of Vitrebond. The average microhardness of the Orthocem was higher than that of the Orthobite in the groups without cycling, however the differences were not statistically significant (P > 0.05). The average microhardness was lower in Vitrebond. The mean microhardness of the Vitrebond was lower than that of the other cycling groups, whereas the mean microhardness of the Orthocem and Orthobite materials was significantly higher than the other materials (P< 0.05).The cycling groups had decreased means (P < 0.05) for microhardness and flexural strength, with the exception of GIC. The Vitrebond demonstrated reduced resistance to bending and microhardness across the noncycling groups (P < 0.05). Discussion In orthodontics, bite-opening materials such as composite, compomer, glass ionomer cement (GIC), and self-curing acrylic resin are widely used on occlusal or Katte Sheethal Chandana, et al. International Journal of Dental Science and Innovative Research (IJDSIR) ©2025 IJDSIR, All Rights Reserved Page256 Page256 Page256 Page256 Page256 Page256 Page256 Page256 Page256 Page256 Page256 Page256 Page256 Page256 Page256 Page256 Page256 Page256 Page256 lingual surfaces to increase the vertical dimension, protect brackets from premature contact, and manage malocclusions like deep bites, crossbites, telescopic bites, and buccal non-occlusions. Anterior and posterior bite turbos are commonly employed to address occlusal interferences, but many of these materials were not originally designed to endure occlusal forces, and their wear resistance remains underexplored.2 Anterior resin turbos are commonly bonded to the palatal surfaces of the upper central incisors in patients with horizontal growth patterns to manage deep bites. Bonding both central incisors helps evenly distribute occlusal forces, promotes forward mandibular closure, and minimizes the risk of posterior mandibular displacement.⁶ These turbos are typically maintained for 4–6 months, or approximately three months in cases involving anterior crossbites. However, in individuals with vertical growth patterns, their use requires caution due to the potential for unwanted posterior tooth extrusion. Close periodontal monitoring of the mandibular incisors is essential throughout the duration of turbo use.⁷ Posterior bite build-ups help achieve posterior disocclusion, allowing for immediate bracket placement. They facilitate arch leveling in deep bite cases by promoting maxillary incisor extrusion and molar intrusion, aiding in anterior open bite closure. These build-ups are temporary, easily adjustable chairside, and do not require appliance removal.8 According to Singh et al.,⁹ resin-based bite turbos provide several benefits over conventional acrylic appliances, including improved oral hygiene, reduced chairside time, lower profile, enhanced patient comfort, and less impact on speech. However, these turbos also have limitations, such as the risk of anterior occlusal trauma, potential loss of pulp vitality, posterior tooth intrusion leading to open bite, material wear, breakage, and debonding. Material selection for bite turbos should be informed by location, duration of application, and wear resistance. Softer materials adapt to occlusal changes and minimize wear on opposing dentition, but may need frequent repair. Conversely, harder materials provide durability but increase risk of enamel abrasion.5 Material wear is influenced by the hardness of filler particles, resistance to grinding, and oral conditions like humidity and temperature variation, all of which can accelerate material degradation. Therefore, materials must be chosen for their mechanical stability in intraoral environments.2 The study assessed five widely used bite-opening materials—Vitrebond, Transbond Plus, Filtek Supreme, Orthobite, and Orthocem—through three-point bending tests and Knoop hardness evaluations, both before and after thermocycling. Knoop hardness testing, which measures a material’s resistance to wear under controlled pressure, revealed significant differences. Composite resins showed greater surface hardness than resinmodified GICs (RMGIC), likely due to the presence of silica fillers enhancing wear resistance.10 Nanofilled composites demonstrated lower hardness compared to Orthobite and Orthocem, potentially due to impaired polymerization from light scattering by nanofillers and nanoclusters.10 Surface hardness varied based on composition, light-curing method, and filler distribution. These results align with Rosen et al. (2001)11, who found composites and compomers generally outperform RMGICs in surface hardness. Flexural strength—a key property for stress-bearing applications—was evaluated using the three-point bending method, considered the gold standard for its low variability. According to ISO 4049/2009, 80 MPa is the Katte Sheethal Chandana, et al. International Journal of Dental Science and Innovative Research (IJDSIR) ©2025 IJDSIR, All Rights Reserved Page257 Page257 Page257 Page257 Page257 Page257 Page257 Page257 Page257 Page257 Page257 Page257 Page257 Page257 Page257 Page257 Page257 Page257 Page257 minimum threshold for occlusal materials. Both Orthobite and Orthocem surpassed this benchmark (85.05 MPa and 88.79 MPa respectively), which is attributed to their high filler content, optimized resin viscosity, and effective curing characteristics. Thermocycling (1150 cycles to simulate four months of oral use) significantly reduced the flexural strength and surface hardness of all materials. While Orthobite and Orthocem performed best prior to thermocycling, all materials deteriorated post-thermocycling. Vitrebond showed the weakest performance both before and after, likely due to its low resin content and limited matrixfiller bonding.12 Nanofilled composites showed greater degradation under thermocycling, attributed to higher TEGDMA monomer release, water sorption at filler–matrix interfaces, and their large surface area. These changes result in matrix plasticization, filler detachment, and internal microfractures, weakening the material over time.6,10 The mechanical strength of composite resins depends on filler characteristics, monomer composition, and matrixfiller coupling. Despite standardized methods, inconsistencies in resin structure may lead to surface flaws. Compomers, which contain fluorosilicate glass within a methacrylate matrix, demonstrated intermediate performance—better than RMGICs but inferior to composites due to limited light penetration and polymerization.12 Among the tested materials, Vitrebond exhibited the least degradation post-thermocycling, likely due to HEMAinduced inhibition of the acid-base reaction, which prevents structural breakdown. However, its mechanical properties remained suboptimal. Orthocem, which contains fluorescent pigments, and Orthobite, pigmented blue, allow easy identification of residual adhesive without impacting performance—a feature supported by studies from Flaviana et al. (2020)13 and Rossato et al. (2020)14, Samadi et al. (2019)15 and Pereira et al. (2007)16 also confirmed post-thermocycling declines in bond strength and hardness due to water absorption and mismatch in thermal expansion. Overall, thermocycling significantly compromises composite resin performance, reinforcing the importance of selecting materials with high mechanical resilience for stress-bearing applications such as bite turbos. The study proves that Orthobite and Orthocem offer superior microhardness and flexural strength, making them suitable for long-term orthodontic use. Their performance, durability, and ease of identification make them preferable for managing occlusal discrepancies in clinical practice. Conclusion The primary objective of this study was to evaluate and compare the flexural strength and microhardness of five different dental disocclusion materials, both before and after exposure to thermocycling. The study aimed to assess how thermocycling, which simulates the thermal stresses encountered in the oral cavity due to fluctuating temperatures, impacts the mechanical properties of these materials. Upon analysis, it was observed that all the tested materials exhibited significant degradation in their properties following thermocycling. This finding indicates that repeated thermal cycling adversely affects the structural integrity of dental disocclusion materials. Among the five materials tested, Orthocem and Orthobite demonstrated the highest values of flexural strength, indicating superior resistance to bending and fracture under stress. In contrast, Vitrebond showed the lowest flexural strength, followed by Transbond Plus and Filtek Supreme, which also exhibited comparatively reduced performance. These results suggest that Orthocem and