The impact of three desensitizing materials on the shear strength between composite resin and dentin: an in-vitro study

Abstract

Background

The study investigated the effect of three commercially available desensitizers on the shear bond strength (SBS) of two bulk fill composites and a conventional composite resin to dentin.

Methods and methods

The study utilized 144 freshly extracted, caries free maxillary premolar teeth. The dentin surfaces of all the teeth were exposed and etched with 37% phosphoric acid for 15 s, rinsed with water and dried. Three main groups were made consisting of 48 teeth in each group, Group 1, 2, and 3. Each main group (Groups 1, 2, and 3) had 4 subgroups consisting of 12 teeth each depending upon the desensitizer used (Subgroup A-No desensitizer or control, Subgroup B-Gluma Dentin desensitizer, Subgroup C-Shield force Plus desensitizer, and Subgroup D-Telio CS desensitizer). As per the manufacturer’s instructions, the different dentin desensitizers were applied in all the test subgroups. With the help of a silicon mold, Group 1 received Bulk fill packable composite resin, Group 2 received Bulk fill flowable composite resin, and Group 3 received Conventional / Incremental composite resin to complete the sample preparation and shear bond test was performed. The parametric two-way Analysis of Variance (ANOVA) test with interaction design was applied and Tukey’s multiple Posthoc procedures were carried out for pairwise comparisons. A 95% confidence range was used to determine statistical significance for p ≤ 0.05.

Results

Highest SBS was seen in Shield force Plus desensitizer groups (16.47 Megapascals (MPa)) and Telio desensitizer groups showed the least SBS values (14.07 MPa). Bulk fill packable composite groups showed highest SBS (15.90 MPa) while Bulk fill flowable composite groups had least SBS values (14.75 MPa).

Conclusions

Since these three desensitizers can both strengthen the bond between composite resins and dentin, and reduce dentin hypersensitivity following composite restorations as per the earliar studies, clinicians should consider using them before placing composite restorations.

Clinical trial number

Not applicable.

Introduction

Resin-based composite restorations have progressively replaced amalgam as the preferred restorative material over the past few decades [1, 2]. These materials are favored for both anterior and posterior direct restorations due to their superior aesthetic and mechanical properties [3]. Good mechanical and biological characteristics of composite restorations result in a low yearly failure rate (1.1%) [4—6]. However, the application of composites is highly technique-sensitive. It necessitates complete polymerization and the use of incremental layering to minimize polymerization shrinkage, thorough curing, and sufficient curing time [3, 7]. Layering composites in increments no thicker than 2 mm enhances light penetration and polymerization efficiency while reducing stress from polymerization shrinkage [8–10]. However, this method is thought to be time-consuming and improper application of the layering technique can result in insufficient polymerization, leading to poorly cured material and air entrapment between the successive composite layers [8, 11]. This compromises the restoration’s strength and failure to achieve an optimal seal [12].

In addition to polymerization shrinkage, post-operative sensitivity related to composite resin also continues to be an important issue [13]. Since the tooth and the composite are physically bonded, this may create an opening for microleakage and allow particles or other materials to penetrate into the nerve endings through fractures. Patients who have complained of being sensitive to certain things that are hot, cold, or sweet have been linked to this finding. In other words, acute pain is one way to characterize the post-operative sensitivity related to composite restorations. The cavity design, bonding technique, and supplementary materials like micro leakage-preventing liners, all have a role in the composite restoration’s performance [14].

Lowering dentin permeability to decrease tubular fluid motions or using neurally active medicines to lessen intradental nerve excitability, are two possible therapeutic approaches for hypersensitive teeth. Desensitizing agents can be used as protective coatings for the management of these teeth as they obstruct or close the dentinal tubules, lowering the dentin’s permeability [15]. They may contain triclosan, fluoride, glutaraldehyde and benzalkonium chloride. It has been demonstrated that the liners also enhance bonding and lessen post-operative sensitivity in composite materials [16, 17]. Recent investigations have also confirmed that glutaraldehyde-based desensitizers not only occlude dentinal tubules but also stabilize the adhesive interface, enhancing long-term bond durability [18]. Also, newer clinical and in vitro evidence highlights the importance of evaluating newer desensitizing and bonding strategies under thermomechanical stress to simulate intraoral aging [19, 20].

According to a research by Sayed, M.E., published in 2021, Gluma desensitizer, Shield force Plus, and Telio CS desensitizer can be used for sensitivity reduction after tooth preparation [21]. A study by Dewan, H., using the same desensitizing agents, concluded that the post-treatment sensitivity was decreased by a single use of any of these substances prior to the placement of Class I composite restorations [14]. Given the varying perspectives in existing literature regarding the SBS of different composite materials [22, 23], this study aims to compare the bond strength of two bulk fill composites (from a single manufacturer) to dental tissues, relative to conventional composites after the use of three readily available desensitizers: Telio CS (Ivoclar Vivadent, Schaan, Liechtenstein), Shield force Plus (Tokuyama Dental America Inc., San Diego, CA, USA), and Gluma (Heraeus Kulzer, Hanau, Germany).

Materials and methods

Ethical statement and sample size selection

This study was conducted in accordance with the principles of the Declaration of Helsinki. The study protocol and the use of extracted human teeth were approved by the Institutional Review board (IRB) of College of Dentistry, Jazan University (Ref. No. CODJU-23081).

The application utilized for determining the sample size was G*Power (version 3.1.9.7), and it made the assumption that there would be a comparison between 12 groups. 144 tooth specimens in total were made. A 0.05 alpha, 80% power, and 0.80 effect size was achieved with a minimum sample size of 48 (at least 12 in each subgroup). The materials used and their compositions are stated in Table 1.

Table 1.

The materials used (type of desensitizer or composite), their composition, and mechanisms of action

Group	Material Trade Name	Manufacturer	Composition	Mechanism of Action
A	No desensitizer used (Control Group)	-	-	-
B	Gluma Dentin Desensitizer	Heraeus Kulzer, Hanau, Germany	5% glutaraldehyde, 35% 2-hydroxyethyl methacrylate (HEMA)	The tubular size is reduced when glutaraldehyde and the dentinal protein component combine to form a clogging mass.
C	Shield force Plus Desensitizer	Tokuyama Dental America Inc., San Diego, CA, USA	10–30% phosphoric acid monomer, 10–30% 2-hydroxyethyl methacrylate (HEMA),10–30% bisphenol A dis (2-hydroxy propoxy) dimethacrylate, 30–60% propan-2-ol, 5–10% triethylene glycol dimethacrylate, 5–10% water.	The initial coating layer is created by a direct reaction between the adhesive monomer and the tooth’s calcium component. The curing process creates another durable layer.
D	Telio CS Desensitizer	IvoclarVivadent, Schaan, Liechtenstein	55% water, 35% polyethylene glycol dimethacrylate, 50% glutaraldehyde, < 0.01% maleic acid.	Glutaraldehyde and polyethylene glycol dimethacrylate (PEG-DMA) provide excellent material choices to help seal the dentinal tubules.
1	Tetric N-Ceram Bulk Fill Composite	IvoclarVivadent, Schaan, Liechtenstein	Dimethacrylates (19–21% weight), fillers like barium glass, prepolymer, ytterbium trifluoride and mixed oxide, Additives, catalysts, stabilizers and pigments (< 1.0% weight), inorganic fillers (75–77% weight or 53–55% volume). The inorganic fillers particle size is between 0.04 and 3 μm.	Makes it possible to restore posterior teeth with a single layer up to four millimeters thick, which greatly boosts efficiency. A particularly conditioned shrinkage stress reliever reduces shrinkage and shrinkage stress during polymerization.
2	Tetric N Flow Bulk Fill Composite	IvoclarVivadent, Schaan, Liechtenstein	Monomer matrix: 28% dimethacrylates and monomethacrylates Fillers: 71%-barium glass, ytterbium trifluoride, and copolymers Additives, initiators, stabilizers, and pigments (< 1.0 wt%)	It needs brief light exposure durations and may be light-cured in huge increments of up to four millimeters. Ivocerin, a proprietary light activator, is in charge of making sure the filling cures completely.
3	Teric N Ceram Composite	Ivoclar Vivadent clinical AG Schaan/Liechtenstein	Dimethacrylates (19–20 wt%), fillers (80–81 wt%). Additives, initiators, stabilizers, and pigments (< 1 wt%), inorganic fillers (55–57 vol%). inorganic fillers has particle size of 40–3000 nm.	A moldable, all-purpose composite for anterior and posterior restorations.

Groups and subgroups

144 human maxillary premolars that were freshly removed for orthodontic purposes and devoid of cavities, anatomical deformities, etc. were chosen. The teeth were carefully cleaned and kept in distilled water. As soon as the specimens were extracted, they were processed. The diamond discs (SS White, Lakewood, New Jersey, USA) were used to split the crowns’ occlusal surfaces, revealing the surface of the dentin. The exposed occlusal dentin surface of each tooth was then oriented upwards and incorporated using self-cure acrylic resin (Quick resin, Ivoclar, Schaan, Liechtenstein) into a rectangular metal mold measuring 1 cm x 4 cm. The acrylic resin-filled metal molds were then placed in distilled water to release the exothermic heat generated during polymerization. Wet silicon carbide paper (600, 800, and 1200 grit) was used to polish the dentin surfaces in order to create a uniform surface for bonding and treatment [3]. The teeth were divided into three major groups (Groups 1, 2, 3) (n = 48). Each major group was divided into four subgroups (Subgroups A, B, C, D) (n = 12) according to the type of desensitizer to be used. The tested null hypothesis was that the use of desensitizing agents on tooth surfaces prepared for composite restorations does not affect their shear bond strength.

The study design, groups and subgroups are shown in Fig. 1.

Fig. 1.

The study design and the main groups and subgroups

Bonding procedure

A moist, glossy surface was left behind after the superficial dentin was etched for 15 s using 37% phosphoric acid (Meta Etchant, Meta Biomed co. Ltd, Chungcheongbuk-do, Korea), washed with water for another 20 s, and then blot-dried with a wet cotton pellet. All groups (except subgroup A, which is the control group) received a single application of the dental desensitizing agent prior to the placement of composite resin, according to the guidelines provided by the manufacturer. Subgroup A in each main group (Group 1, 2, 3) served as the 24-hour control group, in which specimens were tested for SBS after 24 h of storage in distilled water at 37 °C, without thermocycling.

Subgroup A: Control group

This group did not receive any application of desensitizing agent.

Subgroup B: Gluma dentin desensitizer group

An applicator brush was used to apply Gluma desensitizer to the prepared tooth surface, and it was left to dry for 30 to 60 s. After thoroughly cleaning the dentin surface with an air stream and sprinkling it with water, it was vacuumed.

Subgroup C: Shield force Plus desensitizer group

An applicator brush was used to apply Shield force desensitizer, which was then kept on for 10 s. Using a light-blocking plate, the dispensed desensitizer was shielded from outside light. The desensitizer surface was continually exposed to weak air flow for five seconds, and then strong air flow for an additional five seconds. For 10 s, light curing (Woodpecker LED H Curing Light, Guilin Woodpecker Medical Instrument Co., Ltd., China) was applied to the surface (intensity > 300 m W/cm2), while the light-curing tip was kept within 2 mm of the surface.

Subgroup D: Telio CS desensitizer group

Using an applicator brush, a small coating of Telio CS desensitizer was applied, and it was left on for 10 s. An air syringe was used to spread the surplus into a thin coating.

Composite application and sample completion

Tetric N-bond Universal (Ivoclar Vivadent, Tech Gate Vienna, Austria) was used as bonding agent in all the samples. A single coat of adhesive was applied on the treated surfaces of all the samples with a microbrush for 20 s to facilitate penetration into the dentin. The samples were then air dried for 10 s. A mild air pressure from the air syringe was used to blow the solvent and remove any remaining water. The adhesive was then light cured for 10 s using the light cure unit.

Group 1: Bulk fill packable composite group

A silicon putty mold (4 mm in height and 4 mm in diameter) was placed on the dentin surface in each group (Fig. 2A). A teflon-coated tool was used to apply and condense the condensable composite Tetric N-Ceram Bulk Fill (Ivoclar Vivadent, Schaan, Liechtenstein) in a single 4-mm layer (maximum thickness) inside the mold. After that, the mold was exposed to light for 40 s for curing [7]. To achieve a uniform superficial surface, a mylar strip was applied over the composite in the mold before light curing. The putty mold was removed after composite application and curing. The completed samples (Fig. 2B) were kept in distilled water [3].

Fig. 2.

A The 4 mm diameter and 4 mm height silicon mold. B Completed samples

Group 2: Bulk fill flowable composite group

Inside the prior mold, a single 4-mm layer of the bulk fill flowable composite Tetric N Flow Bulk Fill (Ivoclar Vivadent, Schaan, Liechtenstein) was applied, and light-cured for 40 s [7]. The samples were completed as mentioned in Group 1.

Group 3: Conventional nanohybrid (incremental) composite group

Tetric N Ceram (Ivoclar Vivadent, Schaan, Liechtenstein), a traditional nanohybrid composite, was applied, compacted in two 2 mm increments within the same mold, and light-cured for 40 s [7]. The samples were completed as mentioned in Group 1.

Thermocycling and shear bond strength testing

The specimens were mounted on polyvinyl chloride (PVC) rings with help of acrylic resin (Fig. 3). They were then heated in a thermocycling device (Model 1100, SD Mechatronik, Bayern, Germany) from 5 to 55 degrees Celsius for 3000 cycles with a 30-second dwell time (Fig. 4) (except for the control group). The specimens were then positioned among the jigs of the Instron Corp., Canton, Massachusetts, USA model 3345 universal testing apparatus. At the dentin-composite contact, a knife edge shearing chisel was engaged, and the force was exerted perpendicular to the long axis of the specimen (Fig. 5). The force to debond the composite was measured in Newtons (N), and the apparatus was run at a cross-head speed of 1 mm/min. The shear bond strength (MPa) was calculated by dividing the maximum stress in Newtons by the bonded contact’s cross-sectional area.

Fig. 3.

Representative image of the completed specimens mounted on the PVC rings with help of acrylic resin

Fig. 4.

Thermocycling from 5 to 55 degrees Celsius for 3000 cycles with a 30-second dwell time

Fig. 5.

Shear bond testing being carried out using Instron testing apparatus

Failure mode

Following testing, the mode of failure was identified by examining each debonded surface under a stereomicroscope at a 25x magnification (Fig. 6). The failure mode was categorized as follows:

Fig. 6.

The mode of failure. Examples of (A) Adhesive failure, (B) Cohesive failure, and (C) Mixed failure

A) Adhesive failure: failure at the adhesive-dentine or adhesive-composite contact,B) Cohesive failure: A breakdown in the composite or dentine, and C) A combination of (a) and (b) known as mixed failure.

Statistical analysis

Utilizing computer software called the Statistical Package for Social Sciences (SPSS) (version 16.0) (SPSS Inc., Chicago, IL, USA), the values were statistically examined. The standard deviation and mean were used to express the data. Normality of the SBS scores in three main groups (1, 2, 3) and four subgroups (A, B, C, D) was tested by the Shapiro-Wilk test (Table 2). Since the SBS scores in the three main groups (1, 2, 3) and the four subgroups (A, B, C, D) followed normal distribution, therefore, the parametric two-way ANOVA test with interaction design was applied and Tukey’s multiple Posthoc procedures were carried out for pairwise comparisons. A 95% confidence range was used to determine statistical significance for p ≤ 0.05. A chi-square test (χ²) was performed to determine whether the observed distribution of failure modes differed significantly from an equal distribution.

Table 2.

Normality of the SBS scores [MPa] using Shapiro-Wilk test [Groups: types of composite resin (1, 2, 3); subgroups: types of desensitizer (A, B, C, D)]

Group	Subgroup	Shapiro-Wilk	Degrees of Freedom	p-value
Group 1	Subgroup A	0.9740	11	0.9200
	Subgroup B	0.8630	11	0.0630
	Subgroup C	0.9470	11	0.6060
	Subgroup D	0.9050	11	0.2100
Group 2	Subgroup A	0.9700	11	0.8890
	Subgroup B	0.9600	11	0.7650
	Subgroup C	0.9540	11	0.6980
	Subgroup D	0.9120	11	0.2590
Group 3	Subgroup A	0.9150	11	0.2770
	Subgroup B	0.9870	11	0.9940
	Subgroup C	0.9680	11	0.8660
	Subgroup D	0.9670	11	0.8530

Results

The summary of SBS scores in three main groups (composites) and four subgroups (desensitizers) is presented in the Table 3, showing that the bulk fill packable composite group with Shield force desensitizer application had the highest SBS (17.66 MPa) and the bulk fill flowable composite group with Telio desensitizer application exhibited the lowest SBS (13.59 MPa).

Table 3.

Summary of the mean shear bond strength scores [Mpa] in the three groups and four subgroups [Groups: types of composite resin (1, 2, 3); subgroups: types of desensitizer (A, B, C, D)]

Factor	Level of factor	N	Mean	SD	SE	95% CI for mean
						Lower	Upper
Group	Group 1	48	15.90	2.02	0.30	15.29	16.51
	Group 2	48	14.75	1.86	0.28	14.18	15.32
	Group 3	48	15.35	2.03	0.31	14.74	15.97
Subgroup	Subgroup A	36	15.02	2.07	0.36	14.28	15.75
	Subgroup B	36	15.78	1.78	0.31	15.15	16.41
	Subgroup C	36	16.47	1.83	0.32	15.82	17.11
	Subgroup D	36	14.07	1.58	0.27	13.51	14.63
Group with Subgroup	Group 1 with subgroup A	12	15.16	1.10	0.33	14.42	15.90
	Group 1 with subgroup B	12	16.43	2.03	0.61	15.07	17.79
	Group 1 with subgroup C	12	17.66	1.57	0.47	16.60	18.71
	Group 1 with subgroup D	12	14.35	1.66	0.50	13.24	15.46
	Group 2 with subgroup A	12	15.73	2.67	0.81	13.93	17.53
	Group 2 with subgroup B	12	14.90	1.38	0.42	13.97	15.83
	Group 2 with subgroup C	12	14.77	1.19	0.36	13.98	15.57
	Group 2 with subgroup D	12	13.59	1.37	0.41	12.67	14.52
	Group 3 with subgroup A	12	14.15	2.00	0.60	12.81	15.50
	Group 3 with subgroup B	12	16.02	1.64	0.49	14.92	17.12
	Group 3 with subgroup C	12	16.97	1.35	0.41	16.06	17.88
	Group 3 with subgroup D	12	14.28	1.71	0.52	13.12	15.43

Comparison of the mean SBS scores in the three main groups (1, 2, 3) and the four subgroups (A, B, C, D) using Two-way ANOVA test is shown in Table 4 (Fig. 7). In the analysis, several sources of variation were examined, including the main effects of the groups (1, 2, 3) and the subgroups (A, B, C, D) as well as the 2-way interaction effect between the three groups and the four subgroups on the SBS.

Table 4.

Comparison of the mean SBS [Mpa] using Two-way ANOVA test [Groups: types of composite resin (1, 2, 3); subgroups: types of desensitizer (A, B, C, D)]

Sources of variation	Sum of squares	Degrees of freedom	Mean sum of squares	F-value	p-value
Main effects
Groups	29.0914	2	14.5457	5.0799	0.0076*
Subgroup	104.7824	3	34.9275	12.1980	0.0001*
2-way interaction effects
GroupxSub group	52.3526	6	8.7254	3.0473	0.0083*
Error	343.6046	120	2.8634
Total	529.8310	131

*statistically significant

Fig. 7.

Graph showing the comparison of the mean SBS scores [MPa] [Groups: Types of Composite Resin (1, 2, 3); Subgroups: Types of Desensitizer (A, B, C, D)]

The analysis of the impact of the groups (1, 2, 3) on the SBS demonstrated a statistically significant effect. The F-value was 5.0799, with a corresponding p-value of 0.0076. As the calculated F-value exceeds the critical F-value of 3.0700 (with 2 and 120 degrees of freedom), it confirms that the types of the composite significantly influence the SBS.

The analysis of the impact of the subgroups (A, B, C, D) on the SBS demonstrated a statistically significant effect. The F-value was 12.1980, with a corresponding p-value of 0.0001. As the calculated F-value exceeds the critical F-value of 2.6800 (with 3 and 120 degrees of freedom), it confirms that the types of the desensitizer significantly influence the SBS.

In other words, the mean SBS scores significantly differ in three main groups and the four subgroups. The null hypothesis stating that the use of desensitizing agents to coat the tooth surface prepared for composite restoration did not influence their SBS was, thus, rejected.

The interaction effect of the groups (1, 2, 3) and subgroups (A, B, C, D) on the SBS was found to be statistically significant. The F-value was 3.0473, with a corresponding p-value of 0.0083. Since the calculated F-value exceeds the critical F-value of 2.1200 (with 6 and 120 degrees of freedom), this indicates a significant interaction effect between the groups (1, 2, 3) and the subgroups (A, B, C, D) on the SBS. In other words, composites combined with different types of desensitizers have different SBS.

Pairwise comparison of the mean SBS scores in the three main groups (1, 2, 3) was done using Tukey’s multiple Posthoc procedures and the results are presented in Table 5. Table 5 shows a significant difference between Group 1 and Group 2 in their mean SBS at 5% level of significance. It means that, the mean shear bond strength is significantly higher in Group 1 and minimum in Group 2 and Group 3. Fig. 8 depicts the comparison of the mean SBS scores in the three main groups.

Table 5.

Pairwise comparison in the three groups using tukey’s multiple posthoc procedures

Group	Group 1	Group 2	Group 3
Mean	15.90	14.75	15.35
SD	2.02	1.86	2.03
Group 1	-	p = 0.0053*	p = 0.2898
Group 2	p = 0.0053*	-	p = 0.2189
Group 3	p = 0.2898	p = 0.2189	-

*statistically significant

Fig. 8.

Graph showing the comparison of the mean SBS scores [MPa] in the three groups

Pairwise comparison of the mean SBS scores in the in the four subgroups (A, B, C, D) was also done using Tukey’s multiple Posthoc procedures and the results are presented in Table 6. Table 6 shows a significant difference between subgroup A and subgroup C, subgroup B and subgroup D, subgroup C and subgroup D in their mean SBS scores at 5% level of significance. It means that, the mean SBS is significantly higher in subgroup C and minimum in subgroup D followed by subgroup A and subgroup B. Fig. 9 depicts the comparison of the mean SBS scores in the four subgroups.

Table 6.

Pairwise comparison in the in the four subgroups using tukey’s multiple posthoc procedures

Subgroup	Subgroup A	Subgroup B	Subgroup C	Subgroup D
Mean	15.02	15.78	16.47	14.07
SD	2.07	1.78	1.83	1.58
Subgroup A	-	p = 0.2577	p = 0.0039*	p = 0.1132
Subgroup B	p = 0.2577	-	p = 0.3615	p = 0.0005*
Subgroup C	p = 0.0039*	p = 0.3615	-	p = 0.0001*
Subgroup D	p = 0.1132	p = 0.0005*	p = 0.0001*	-

*statistically significant

Fig. 9.

Graph showing the comparison of the mean SBS scores [MPa] in the four subgroups

Table 7 shows the comparison of the interactions of the mean SBS scores in the three main groups (1, 2, 3) and the four subgroups (A, B, C, D) using Tukey’s multiple Posthoc procedures.

Table 7.

Comparison of the interactions in the three main groups and the four subgroups using tukey’s multiple posthoc procedures

Interactions	Group 1 with sub group A	Group 1 with sub group B	Group 1 with sub group C	Group 1 with sub group D	Group 2 with sub group A	Group 2 with sub group B	Group 2 with sub group C	Group 2 with sub group D	Group 3 with sub group A	Group 3 with sub group B	Group 3 with sub group C	Group 3 with sub group D
Mean	15.16	16.43	17.66	14.35	15.73	14.90	14.77	13.59	14.15	16.02	16.97	14.28
SD	1.10	2.03	1.57	1.66	2.67	1.38	1.19	1.37	2.00	1.64	1.35	1.71
Group 1 with subgroup A	-
Group 1 with subgroup B	p = 0.837 9	-
Group 1 with subgroup C	p = 0.034 9	p = 0.864 1	-
Group 1 with subgroup D	p = 0.993 1	p = 0.161 9	p = 0.000 8	-
Group 2 with subgroup A	p = 0.999 7	p = 0.998 1	p = 0.254 3	p = 0.750 1	-
Group 2 with subgroup B	p = 1.000 0	p = 0.614 2	p = 0.011 3*	p = 0.999 8	p = 0.991 9	-
Group 2 with subgroup C	p = 1.000 0	p = 0.486 1	p = 0.006 1*	p = 1.000 0	p = 0.974 1	p = 1.000 0	-
Group 2 with subgroup D	p = 0.572 2	p = 0.007 7*	p = 0.000 1*	p = 0.996 2	p = 0.133 9	p = 0.806 5	p = 0.892 9	-
Group 3 with subgroup A	p = 0.962 3	p = 0.082 5	p = 0.000 3*	p = 1.000 0	p = 0.564 8	p = 0.996 5	p = 0.999 4	p = 0.999 8	-
Group 3 with subgroup B	p = 0.989 0	p = 1.000 0	p = 0.504 3	p = 0.474 0	p = 1.000 0	p = 0.924 2	p = 0.851 9	p = 0.046 2*	p = 0.300 3	-
Group 3 with subgroup C	p = 0.347 1	p = 0.999 8	p = 0.998 4	p = 0.020 6*	p = 0.856 6	p = 0.168 2	p = 0.109 0	p = 0.000 6*	p = 0.008 5*	p = 0.975 5	-
Group 3 with subgroup D	p = 0.985 6	p = 0.126 2	p = 0.000 6*	p = 1.000 0	p = 0.681 7	p = 0.999 3	p = 0.999 9	p = 0.998 5	p = 1.000 0	p = 0.402 9	p = 0.014 7*	-

*statistically significant

Mode of failure

Amongst the samples, the majority (90 sample, 62.5%) had mixed failures, 25% (36 samples) had cohesive failures, and 12.5% ( 18 samples) had adhesive failures (Fig. 10). Table 8 shows the distribution and statistical analysis of failure modes among tested samples.

Fig. 10.

Percentages of failures: Mixed failures − 62.5%, Cohesive failures-25%, and Adhesive failures-12.5%

Table 8.

Distribution and statistical analysis of failure modes among tested samples

Failure mode	Frequency (n)	Percentage (%)	Expected frequency	(Observed frequency–Expected frequency)²/Expected frequency
Mixed	90	62.5	48	36.75
Cohesive	36	25.0	48	3.00
Adhesive	18	12.5	48	18.75
Total / χ²	144	100.0	—	58.5

The analysis revealed a statistically significant difference among the failure types (χ² = 58.5, degrees of freedom = 2, p < 0.001), indicating that mixed failures occurred at a significantly higher frequency than cohesive or adhesive failures.

Discussion

One of the most used materials for aesthetic restoration is composite. Although earlier literature proposed that composite resin materials might compromise pulpal health due to their synthetic composition [24, 25], more recent clinical evidence suggests that postoperative symptoms are largely related to operative factors rather than to the intrinsic properties of the composite material itself. Clinical studies have shown that postoperative sensitivity following resin restorations is influenced by variables such as the adhesive protocol, cavity preparation technique, and the effectiveness of sealing dentin rather than direct pulpal toxicity of the restorative material [14, 21]. The application of glutaraldehyde-based desensitizer like Gluma Desensitizer prior to the bonding procedure might significantly reduce postoperative sensitivity according to various studies [14, 26, 27] or might not significantly reduce postoperative sensitivity, neither spontaneous nor stimuli-induced, in posterior composite restorations according to other studies [28–31]. Research investigating the effect of these dentin desensitizers on bond strength of different bonding agents has also shown various results. Some research discovered that desensitizing agents had no effect on bonding capacity [32], while other studies found that desensitizer-treated teeth had a reduced bond strength than untreated teeth [33] and still other studies observed that treated teeth had a stronger bond strength than untreated teeth [34].

The use of ozone and bioactive materials in desensitizer formulations has been recently reported to improve tubule occlusion and interfacial stability [35, 36]. Recent evidence demonstrates that universal adhesives’ bond strengths to dentin continue to improve under optimized application protocols [37]. Double-layer application techniques have been shown to increase micro-tensile bond strength of universal adhesives [38]. Investigations into substrate contamination (e.g., root-canal sealer–affected dentin) emphasise the importance of cleaning protocols prior to bonding to maintain bond integrity [39]. Moreover, minimal etching protocols (short dentin etch) with universal adhesives favourably affect both bond strength and marginal adaptation [40]. Finally, the durability of bond strength for modern bioactive restorative materials even in Silver diamine fluoride treated demineralised dentin has been demonstrated [41].

According to a 2021 research by Sayed, M.E [14]. , the Gluma, Shield force Plus, and Telio CS desensitizers successfully reduced sensitivity after composite restorations. The same desensitizers were used in the current investigation to assess their impact on the composite resin’s ability to form a strong connection with the prepared tooth. The present results are consistent with recent reports demonstrating comparable or enhanced shear bond strength when modern desensitizers are used with universal adhesives [42, 43].

Gluma desensitizer and Shield force Plus groups had higher bond strength values than Telio CS. This discrepancy may result from variations in their constituents or modes of action, their resistance to dissolution, and the varying degrees of solubility of precipitate formation in the dentinal tubules. These are resin-based desensitizers containing Hydroxyethyl methacrylate (HEMA), which provide better permeation of resin monomers into the tubules because of increased dentin wetting [44]. Various studies supported the current findings of higher bond strength values with Gluma, Sheildforce Plus and Telio CS desensitizers compared to the control group [45–47]. HEMA (in the desensitizers) and phosphoric acid in the bonding agent undergo a condensation reaction, thereby strengthening the binding [16]. In case of Gluma, the tubular size is reduced when glutaraldehyde and the dentinal protein component combine to form a clogging mass.

Shield force Plus is based on 3D- SR (3-Dimensional Self-Reinforcing) technology in which, the monomer component exhibits three-dimensional cross-linking reactions, permeates the tooth substrate, and forms multi-point contacts with apatite calcium. It creates a thin, homogeneous, hard covering on the tooth surface for better bonding ability to the dental substance. On application of Shield force Plus, the initial coating layer is created by a direct reaction between the adhesive monomer and the tooth’s calcium component. The curing process creates another durable layer. This can be the reason for the highest bond strength values seen in these groups [46, 48]. Glutaraldehyde and polyethylene glycol dimethacrylate (PEG-DMA) provide excellent material choices to help seal the dentinal tubules in case of Telio CS. However, lower dentin bond strength values may have resulted from the Telio group’s decreased dentin permeability, which inhibited the adhesive resin’s ability to penetrate dentin. According to earlier research, desensitizing substances can lower dentin permeability by 60% to 80% [49].

Tetric N-Bond, the adhesive used, contained phosphoric acid acrylate, HEMA, Bis-GMA, and urethane dimethacrylate. It provided reliable mechanical blockage and sealing of the dentin tubules. As a result, a consistent adhesive coating with unique formation of resin tags, successfully sealed the dentin.

Since the current research used standard cylindrical-shaped silicon molds to apply composite resins to the dentin surfaces, the curing light distance, bonding area, and composite resin thickness were all highly standardized. Compared to bulk-fill flowable composites (14.75 MPa) and regular/conventional nanohybrid composites layered progressively (15.35 MPa), the bulk-fill packable composite in this investigation exhibited greater mean bond strength values (15.90 MPa). This could be because of the variations in these materials’ mechanical, rheological, and filler loadings (60% by volume for bulk fill) [50]. Compared to conventional composites, the bulk fill composite used in this investigation has a greater depth of cure. This is because, in addition to the camphoroquinone/amine initiator system, a new initiator called Ivocerin has been added to these composites which increases the depth of penetration. This germanium-based photoinitiator outperforms traditional camphorquinone by enabling deeper photocuring and absorbing more light energy within the 400–450 nm range [12]. Higher depth of cure can be the reason of high bond strength values seen in this group [23, 51, 52].

Bulk fill composites, which may be placed into the cavity in thicknesses of up to 4–6 mm, were introduced in order to address the afore-mentioned drawbacks [2]. These materials reduce the need for incremental layering and minimize contraction stress, thereby offering a quicker and more efficient restoration process [53–56].

The fracture samples were observed under microscope for failure mode analysis. Majority (62.5%) of the samples showed mixed failures whereas adhesive failure was seen in 12.5% of the samples. This statistical analysis suggested that the bonding interfaces demonstrated adequate mechanical integrity, resulting in a combination of cohesive and adhesive characteristics during debonding.

The findings of this study were consistent with those of a study by Miljkovic et al. that found that teeth treated with conventional composites primarily experienced mixed failures [57]. Equivalent observations were seen in an investigation by Noor et al., which showed that teeth repaired using total etch adhesives and nano hybrid composites primarily experienced mixed failures [58]. These mixed failures are due to variations in the bond strength values in different groups when the desensitizers were used.

Although the present study’s composite materials are the most widely used, dental professionals should also be aware of other recently developed advanced composite materials, such as self-etched and nano composites, as assessing their shear bond strength can improve the potential for composite restorations in the office.

Limitations of the study

It should be mentioned that the study had certain limitations. The shear test was used in this in vitro study along with a standard protocol for human teeth preparation, desensitizer application, and composite application. However, in-vivo conditions, where factors like saliva and other dislodgment forces from different food textures are present, the results may differ. The bonding and sealing properties of bonding agents to dentin merit more research due to the inherent constraints of an in vitro study. The amounts of other components such solvents, activators, inhibitors, cross-linking monomers, and functional monomers may vary in bonding agents. There are variations in the amounts of diluents, filler loads, and monomers. Moreover, the makeup and manner of action of desensitizing agents vary. The type and storage conditions of the tooth, the amount of demineralization, the surface to be tested, the different dentin micro morphologies of the removed teeth, and the testing circumstances are some of the variables that influence the bond strength of resin and dentin in in-vitro conditions [59]. Additionally, it is possible that some of the dentin-fluid protein was lost in these extracted premolars, which would have impacted how the desensitizers and protein interacted. The SBS might be impacted by each of these elements. Lastly, the specimens in this investigation were artificially aged using thermocycling, which replicated a clinical setting and standardized the temperature of each group. More longitudinal clinical-aging data could, however, produce more accurate results.

Conclusions

Dentin shear bond strength has been found to vary according on the bonding agent employed, despite the fact that using a dentin desensitizer prior to bonding agent application may lessen post-operative sensation. The study’s limitations allow for the following findings to be made:

1. Highest bond strength was seen in Shield force Plus desensitizer groups followed by Gluma desensitizer groups.

2. Telio CS desensitizer groups showed least bond strength values.

3. Bulk-fill packable composites showed highest bond strength while bulk-fill flowable composites had least bond strength values.

4. Since these three desensitizers can strengthen the bond between composite resins and dentin and reduce dentin hypersensitivity following composite restorations, practitioners should consider implementing their use in their clinics.

Abbreviations

MPa

Megapascal

PVC

Polyvinyl chloride

N

Newtons

ANOVA

Analysis of Variance

SPSS

Statistical Package for Social Sciences

SD

Standard Deviation

SE

Standard Error

CI

Confidence Interval

χ²

chi-square Test

3D- SR

3-Dimensional Self-Reinforcing

HEMA

Hydroxyethyl methacrylate

PEG-DMA

Polyethylene glycol dimethacrylate

Authors’ contributions

HC performed the formal analysis and contributed to writing. HD was a major contributor in writing the original draft. WN, RH, and AA performed the methodology and data curation. SA and MohA managed the resources. MA and NH reviewed and edited the manuscript. MS supervised the entire project. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data availability

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

This study was conducted in accordance with the principles of the Declaration of Helsinki. The study protocol and the use of extracted human teeth was approved by the Institutional Review Board of College of Dentistry, Jazan University (Ref. No. CODJU-23081).

Consent for publication

Not applicable (The Institutional Review Board determined that informed consent was not required, as the extracted teeth were anonymized and collected as part of routine dental procedures).

Competing interests

The authors declare no competing interests.