Tanta Dental Journal

: 2018  |  Volume : 15  |  Issue : 2  |  Page : 82--90

Evaluation of fracture resistance of premolars restored with packable composite resin using different types of adhesive systems

Hasan Q Issa1, Hussein Y El Sayed2, Magda E Shalby2,  
1 Ministry of Health, Baghdad, Iraq
2 Department of Operative Dentistry, Faculty of Dentistry, Tanta University, Tanta, Egypt

Correspondence Address:
Hasan Q Issa
Ministry of Health, Baghdad


Purpose The aim of this study was to evaluate the fracture resistance of human extracted premolars restored with packable composite resin by using three types of adhesive systems: two-step etch-and-rinse system, two-step self-etch primer adhesive system, and one-step self-etch adhesive system. Materials and methods Fifty sound maxillary second premolars were selected. Forty specimens received class II mesio-occluso-distal cavities with a 2 ± 0.2 mm pulpal depth, 1.5 ± 0.2 mm gingival width, 2 ± 0.2 mm axial height, and parallel proximal walls with 3 ± 0.2 mm buccolingual width. All samples were divided into five groups (10 each): group I: positive control group (intact teeth), group II: negative control group (prepared unrestored), groups III, IV, and V: prepared and restored with Filtek Z350 XT packable composite resin by using three types of adhesive systems; Adper Single Bond, Clearfil liner Bond F, Single Bond Universal Adhesives respectively. After thermocycling, Specimens were subjected to compressive axial loading, and were tested individually in a universal testing machine. Peak loads at fracture were recorded. Statistical analysis was performed using SPSS, version 20.0. Results All groups were significantly higher than prepared but unrestored teeth with no significant difference was recorded between the three types of adhesives. Conclusion Restoring with packable composite using adhesive system had improved the fracture resistance of teeth subjected to class II mesio-occluso-distal preparations. Using the adhesive systems, insignificantly affect fracture resistance of premolars.

How to cite this article:
Issa HQ, El Sayed HY, Shalby ME. Evaluation of fracture resistance of premolars restored with packable composite resin using different types of adhesive systems.Tanta Dent J 2018;15:82-90

How to cite this URL:
Issa HQ, El Sayed HY, Shalby ME. Evaluation of fracture resistance of premolars restored with packable composite resin using different types of adhesive systems. Tanta Dent J [serial online] 2018 [cited 2018 Jul 18 ];15:82-90
Available from: http://www.tmj.eg.net/text.asp?2018/15/2/82/235135

Full Text


The fracture of teeth is a common dental problem. Tooth loss from fracture ranks third behind periodontal disease and caries [1]. Many factors such as tooth anatomy contribute to cusp fracture; however, cavity preparation procedures seem to be the major cause of most cuspal fractures. Posterior teeth, particularly premolars, have an anatomic shape that makes them more likely to fracture the cusps under occlusal load, whereas sound teeth are rarely fracture under normal masticatory function. Several studies have emphasized the importance of maintaining dental structure to preserve the strength of remaining tooth. Generally, the wider the involvement by caries or cavity preparation, the weaker the tooth [2],[3].

It has been shown that large intracoronal mesio-occluso-distal (MOD) preparation in premolar teeth reduces cusp stiffness to one-third of the level of sound teeth due to the loss of marginal ridges and microfractures caused by applied occlusal forces. Extending cavity dimensions, the remaining tooth structure weakens and occlusal forces will cause more deformation in the cusps [4]. In contrast, studies have shown that the weakening effect of preparation can be alleviated with the use of adhesive materials. The adhesive nature of composite has the ability to bind the cusps and decrease flexion, which is the main cause of fractures in teeth restored with amalgam. Furthermore, composite has a lower elastic modulus than amalgam, therefore, more load is absorbed within the composite. Composite may transmit lesser load to the underlying tooth structure, for this reason, and with an increase in esthetic demand and the development of adhesive techniques, resin composite has, for many, become the material of choice for posterior tooth restoration [5],[6],[7].

However, polymerization shrinkage is a critical limitation of dental composites. During the setting reaction in the pregel phase, the material is able to flow and stresses can be distributed more evenly. Conversely, the postgel polymerization results in stresses in the structure of the tooth and also in the tooth-material bonding interfaces [8]. These stresses may be transferred through bonding to the tooth structure, which may lead to the deformation of the tooth walls, cuspal deflection and/or enamel cracks. The magnitude of the contraction stress is affected by the configuration of the cavity, the volume of the applied material, and the filling technique [9],[10].

Development in bonding agents has moved from multistep bonding process (etching, washing, drying, primer, adhesive) to simplification, that is, self-etch and single bottle system. Ideal bonding agent should have adequate bond strength and should bond to enamel and dentin. Various dentin bonding agents were developed to improve the quality of adhesives and composite restorations [11],[12]. The bonding effectiveness of self-etch adhesives to dentin has been well documented. However, their performance on enamel bonding is questionable. In etch-and-rinse adhesive systems, the bonding of resin to enamel surfaces is a durable and reliable clinical procedure with the use of phosphoric acid etching. The high hydrophilic nature of acidic monomers in one-step self-etch adhesives might compromise enamel bond strength and there are conflicting results about the bonding effectiveness of one-step and two-step self-etch adhesives to enamel [13],[14],[15]. It has been stated that remaining tooth structure restored with adhesive technology presents higher fracture resistance [6]. However, the hypothesis that directs cusp coverage is still necessary even when adhesive procedures are used in large cavities must be confirmed [3].

A new type of single-step self-etch adhesive that is categorized as 'universal' or 'multimode' has been recently introduced for patient care. Universal adhesives are 'universal' in two main ways. First, they can be used on a wide range of substrates such as enamel, dentin, silica-based glass ceramics, zirconia ceramics, and metal alloys, without individual pretreatment [16],[17]. In particular, they may be helpful for repair of resin composite restorations that involve different adherent substrates in the same region [18]. Second, they are recommended by dental manufacturers for use both with and without acid pretreatment of tooth surfaces [19].

Packable composites (sometimes also called condensable composites), have been introduced to the market with high expectations as an alternative to amalgam. They are characterized by a high-filler load and a filler distribution that gives them a different consistency compared with hybrid composites. Packable composites are claimed for use in stress bearing posterior restorations with improved handling properties, as an application technique similar to the manipulation of amalgam can be used for the placement. Easier establishment of physiological interproximal contacts in class II restorations, the use of metal matrix bands and wooden wedges, and possible bulk curing of the restorations are advantageous. These clinical advantages of packable composite resins captured the interest of clinicians. On the basis of the perceived high-filler load, these materials were expected to exhibit superior physical and mechanical properties besides the improvements in handling [5],[20].

Previous investigations found that fracture resistance of weakened teeth restored with packable resin composite have been similar of sound teeth, whereas other studies shows that protection by cusps coverage may be needed to recover the fracture resistance in similar values of sound teeth. This probably occurred because the cavity size used is different from one study to the other [3]. So the current research presented to evaluate fracture resistance of premolars with standardized MOD cavity size restored by packable composite restoration by using different types of adhesive systems.

 Materials and Methods


Materials that have been used in this study illustrated in [Table 1] including the following:{Table 1}

Two-step etch-and-rinse adhesive system (Adper Single Bond)Two-step self-etch primer adhesive system (Clearfil Liner Bond F)One-step self-etch adhesive system (Single Bond Universal Adhesive)Packable composite restoration (Filtek Z350 XT Universal 'shade A3').


Collection of teeth

Fifty sound maxillary second premolars, extracted for orthodontic purposes, with no carious lesions, restorations, abrasions or cracks were selected for this study, obtained from donors (15–25 years of age) from the maxillofacial clinic, at the Faculty of Dentistry, University of Tanta. Any calculus deposits and soft tissue were removed from the selected teeth using a hand scaler. The teeth were cleaned with pumice and water and stored in 0.5% chloramine-T solution at 5°C for 3 months.

Approval for this project was obtained from Faculty of Dentistry, Tanta University Research Ethics Committee. The purpose of this study was explained to the patients and informed consents were taken from these patients to use their teeth for research, according to the guidelines on human research published by the Research Ethics Committee at Faculty of Dentistry, Tanta University.

Specimen preparation

To simulate periodontium, root surfaces were dipped into melted wax to a depth of 2 mm below the cementoenamel junction to produce a 0.2–0.3 mm layer, and then mounted in polyvinyl plastic cylinders with self-cure acrylic resin 2 mm below the cementoenamel junction. Each tooth was removed from the acrylic, and the wax spacer was removed from the root and acrylic surfaces. Polyether impression material (Silibest impression elastomer putty material; BMS Dental) was placed into the residual space, and teeth were reinserted into the cylinders. Thus, the periodontal ligament was simulated to some extent [Figure 1] [20].{Figure 1}

Ten specimens remained intact (unprepared) to serve as positive control group. Forty specimens received an operator prepared class II MOD cavities with a 2 ± 0.2 mm pulpal depth, 1.5 ± 0.2 mm gingival width, 2 ± 0.2 mm axial height, parallel proximal walls with 3 ± 0.2 mm buccolingual width. For better harmony among the cavities, a single periodontal probe was used as a guide (Hu Friedy, Chicago, Illinois, USA) and no bevel was performed except for the axiopulpal line-angles. Each tooth was prepared by using a no. 56 carbide fissure bur (Straight plane carbide fissure bur; Dentsply) in a high-speed hand-piece with water spray. Each bur was used to cut four teeth and discarded [Figure 2] [20].{Figure 2}

Grouping of specimens

The teeth were randomly divided into five groups (from I to V) with 10 specimens for each (n = 10) as follows:

Group I: were unprepared, remained intact as positive control groupGroup II: were prepared but remain unrestored as negative control groupGroup III: were prepared and restored using Adper Single Bond AdhesiveGroup IV: were prepared and restored using Clearfil liner Bond F AdhesiveGroup V: were prepared and restored using Single Bond Universal Adhesive.

One type of composite resin was used to restore cavities in groups III, IV, and V.

Restorative procedure

All adhesives and composite resin were applied according to the manufacturer's instructions as shown in [Table 1].

Compressive loading test

All specimens were subjected to compressive axial loading by cross-head speed (0.5 mm/min) with a maximum load cell of 2000 N, and were tested individually in a universal testing machine. A 4-mm diameter steel sphere was applied occlusaly on the buccal and lingual cusps of the tested restored and control specimens. The ball contacted the inclined planes of the facial and palatal cups beyond the margins of the restorations [Figure 1]. Peak load to fracture values were recorded in Newton (N) for each specimen and the mean was calculated for each group [21],[22].

Fracture pattern

All fractured teeth were examined; different types of failure patterns were seen in the experimental groups. They were classified according to the following categories:

Mode I: adhesive fracture at the interface between the tooth and the restorationMode II: cohesive fracture of the tooth structureMode III: cohesive failure of the restorative materialMode IV: complete fracture of the specimens involving the two cusps and the restorative material [23].

Statistical analysis

One-way analysis of variance test of significance used for comparing variables affecting mean values, followed by Tukey's test to detect significance between groups as effect of adhesive system. Student's t-test was performed to detect significance between positive and negative control groups. Statistical analysis was performed using statistical package for the social sciences software for Windows, version 20.0 (SPSS Inc., Chicago, Illinois, USA). P values less than or equal to 0.05 are considered to be statistically significant in all tests.


Fracture resistance

The mean loads (in Newton) necessary to induce fracture for all experimental groups are presented in [Table 2] and [Table 3], and graphically drawn in [Figure 3].{Table 2}{Table 3}{Figure 3}

By using analysis of variance and Tukey's tests, it was found that, the mean value of fracture resistance load of group I (intact teeth) recorded the higher significant fracture resistance (1042.67 ± 171.79 N) than the other experimental groups (P ≤ 0.05). Although group II (prepared, unrestored teeth) recorded the lowest significant fracture resistance (334.86 ± 169.57 N) (P ≤ 0.05).

Meanwhile, the mean values (in Newton) of fracture resistance of cavities restored with Filtek Z350 XT with different adhesive systems; Adper Single Bond, Clearfil Liner Bond F, and Single Bond Universal Adhesive recorded 645.66 ± 95.45, 737.34 ± 179.49, and 631.72 ± 268.60 N, respectively, and according to Tukey's test the differences were statistically nonsignificant at P value more than 0.05 (P = 0.430).

Fracture pattern

Different patterns of fracture were represented in the experimental groups. Fracture pattern was categorized as: Mode I: adhesive fracture at the interface between the tooth and the restoration. Mode II: cohesive fracture of the tooth structure. Mode III: cohesive failure of the restorative material. Mode IV: mixed fracture of the specimens involving the tooth structure and the restorative material [Figure 4].{Figure 4}

Group IV (Clearfil Liner Bond F; two-step self-etch primer adhesive with Filtek Z350 XT packable composite) recorded the least at mode I (adhesive fracture at the interface between the tooth and the restoration) 20%, whereas the remaining two groups (group III; Adper Single Bond with Filtek Z350 XT packable composite and group V; Single Bond Universal adhesives with Filtek Z350 XT packable composite) recorded 30%.

At the same time, group IV (Clearfil Liner Bond F adhesive Filtek Z350 XT packable composite) recorded the highest in mode II (cohesive fracture of the tooth structure) 40% followed by group III (Adper Single Bond with Filtek Z350 XT packable composite) which recorded 30% and group V (Single Bond Universal adhesives with Filtek Z350 XT packable composite) 20%.

Although for mode III (cohesive failure of the restorative material); group III (Adper Single Bond with Filtek Z350 XT packable composite) recorded lower cohesive restoration failure 10% compared with 20% of the two other restored groups; group IV (Clearfil Liner Bond F adhesive with Filtek Z350 XT packable composite) and group V (Single Bond Universal adhesives Filtek Z350 XT packable composite).

For mode IV (complete fracture of the specimens involving the two cusps and the restorative material), Clearfil Liner Bond F adhesive Filtek Z350 XT packable composite (group IV) recorded the least between the three restored groups which was 20% compared with 30% of the two other restored groups.

χ2-Test was used to compare the mode of failures of the tested groups and it was found that nonsignificant difference was recorded between all groups at P value equal to 0.955 (P > 0.05) as shown in [Table 4] and [Figure 5].{Table 4}{Figure 5}


Fracture is defined by the point when stress intensity reaches or exceeds a critical value prompting rupture. Although teeth are covered by enamel, which is a brittle tissue, it is under-layered by dentin, which has ductile behavior. In addition, the periodontal ligament can deform and accommodate the tooth in the alveolus, which alleviates stress in the cervical region of the tooth. In this experiment, a polyether impression material was used with acrylic resin to simulate a clinical fracture resistance test [21].

Masticatory forces on restored or unrestored teeth have a tendency to deflect the cusps under stress. Even though in-vitro studies are not an actual reproduction of a typical chewing stroke, in that they apply a continuously increasing force until the tooth fractures, they represent an important source of information on the structural integrity of the tooth. They also identify the weakest component, whether it is inherent properties of the restoration or the fatigue of the brittle tooth tissues at the adhesive interface. Clinically, masticatory forces are of a relatively consistent magnitude and applied over a longer period of time. They vary in speed of application and direction and contribute to a different pattern of fracture when it occurs [24].

In the posterior region, forces range from 8 to 880 N during normal mastication, but greater loads have been described in bruxism, and teeth in this region may be exposed to extremely high forces when accidentally biting on a hard object or in trauma [22],[25].

The natural and drastic consequence of dental weakness is cusp fracture, and the study of this pathology is relevant because it is considered a common occurrence in clinics [3]. However, experimental conditions in this study did not identically duplicate conditions in the mouth, since maxillary premolars are subjected to a mixture of shear and compressive forces [24].

Posterior teeth, particularly maxillary premolars, have an anatomic shape that makes them more likely to fracture under occlusal load. In addition, these teeth when treated with cavity preparation can be easily fractured because of the removal of tooth structure, mainly when the marginal ridge is thin or totally removed. This was the reason behind choosing the premolar teeth in the current study [3].

MOD cavities were prepared in specimens of this study because it has shown that large (MOD) preparation in premolar teeth reduces cusp stiffness to one-third of the level of sound teeth. Extending cavity dimensions, the remaining tooth structure weakens and occlusal forces will cause more deformation in the cusps [2].

Packable or condensable composite resins that possess inorganic filler particles of smaller size and greater volumetric concentration than previous materials have become popular posterior restorative materials. Filtek Z350 XT Universal composite restoration (3M ESPE, St Paul, Minnesota, USA) has been proven to be one of the superior materials with better flexural strength and lower wear rate during in-vivo and in-vitro studies among the packable composite resins in the market, and was selected as the restorative material in this stud [26],[27].

The adhesive materials tested in this study were chosen to represent two different categories of products currently available on the market for adhesion to dental tissues: total-etch and self-etch adhesives [21].

Adper Single Bond is an etch-and-rinse adhesive, to be used in combination with phosphoric acid. The acid-etch technique has revolutionized the practice of restorative dentistry. Enamel adhesion has been considered the 'golden standard'. The etchant is a strong acid that effectively etches the enamel, whereas on dentin substrate, it removes the smear layer, demineralizes the subsurface enamel and opening the tubules. Resin bonded to enamel protects the resin–dentin interface against degradation in vitro [28] and clinically [29],[30].

Clearfil Liner Bond F is a self-etching primer (two-step), which is The Brand-New SE, the fluoride releasing property in addition to the basic characteristic of CLEARFIL SE BOND. It is less aggressive acidic solutions which affect a mild demineralization of the dental tissues, and do not solubilize the smear layer with pH of ~2 [31],[32].

Another component contributing to the bonding effectiveness of Clearfil liner Bond F, might be the particle-filled adhesive resin that is typically applied in a relatively thick layer. It has been hypothesized before that a relatively thick adhesive layer may act as an intermediary stress reliever to compensate for the shrinkage stress imposed during polymerization of the composite to the resin-cavity wall/bottom bond which causes cusp deflection [33]. Finite element analysis also revealed that with increasing thickness or decreasing elastic modulus of the adhesive resin, the shrinkage stresses can be considerably decreased. Consequently, this elastic bonding concept may, to a large extent, explain the good resistance Clearfil liner Bond F have against polymerization shrinkage, when applied in a high C-factor cavity [34],[35],[36].

Single Bond Universal adhesive, which had been chosen in the current study as the one-step self-etch system has a pH within a range around 3 and this pH range partially demineralize dentine, leaving a substantial amount of hydroxyapatite crystals around the collagen fibrils. Also, Single Bond Universal contains 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) monomer as a functional monomer in its composition, and bonds chemically to dentine [37],[38].

So far, commonly used functional monomers in commercial self-etching adhesives are phosphate monomers, such as 10-MDP, 4-methacryloxyethyl trimellitic acid or and 2-methacryloxyethyl phenyl hydrogen phosphate. These monomers have been used as etching monomers in self-etching primers and in bonding agents to promote resin diffusion and adhesion. However, the chemical bonding potential of 10-MDP with hydroxyapatite was significantly the highest and the most hydrolytically stable [39],[40].

Factors such as cavity width, cavity depth, width of interproximal dentin, cross-head speed of the loading, diameter of the loading head, restorative materials, and sample preparation varied among studies, therefore, it is difficult to answer whether the direct composite resin will restore cuspal fracture resistance to its original value [1].

In the present in-vitro study, the strength of prepared unrestored premolar teeth (group II) was significantly lower than the intact teeth (group I) and all the remaining groups as well. This is similar to the previous findings which reported that the sound teeth presented higher resistance to fracture because of the rigidity and the integrity of the tooth structure and the isthmus width and pulpal depth of an MOD preparation are important factors for cuspal fracture resistance. They are inversely proportional to fracture resistance [41],[42].

Also, the teeth with MOD preparations are severely weakened due to the loss of reinforcing and cross-belting structures, such as marginal ridges and crossing ridges. These findings were agreed by several studies who reported that the increase of tooth structure removal after MOD cavity preparation will increase tooth weakness, and to the extent of our knowledge, no study had shown controversy [8],[43].

In addition, in the current study, restoration of cavities with Filtek Z350 XT composite restoration by using any type of the three adhesive systems (groups III, IV, and V; etch-and-rinse system, self-etch primer system, and self-etch adhesive system, respectively) had improved significantly the resistance to fracture of prepared teeth comparing to the unrestored specimens group (group II). It is proposed that this material increases the resistance of cusp deflection by joining the two cusps. These results of resin system of Filtek Z350 XT with different adhesive system may be due to the composition which consisting of three major components: TEGDMA, UDMA and BIS-EMA, where the majority of TEGDMA has been replaced with a blend of UDMA and BIS-EMA, contributing to the resistance of a tooth breaking that has been restored with this material [44].

It would be expected that, irrespective to the adhesive system used, all of the restored groups have higher resistance to fracture when compared with the prepared unrestored group because the 'emptiness' of the preparation was replaced by rigid restorative materials. In the restored teeth, the composite rigidity (elastic modulus) would restore the resistance to fracture as well as guide the mode of fracture that was evaluated [21]. These results agree with those of El Gezawi and Al Harbi [5], Hamouda and Shehata [24], and Zamboni et al. [44] who reported that prepared unrestored specimens recorded significantly the lowest mean values of fracture resistance load between all the experimental groups including intact teeth and restored specimens.

In addition, there was no significant difference between the mean values of fracture resistance of differently restored groups of specimens. These results agree with those of Coelho-de-Souza et al. [23] who compared etch-and-rinse system (Adper Single Bond) and two-step self-etch primer system (Clearfil SE Bond) both with Filtek Z250 Universal Restorative (microhybrid composite) composite restoration in butt joint preparation who reported that no significant difference was reported between these two groups. In contrast, these results disagree in that all restorative treatments were able to recover the fracture strength of nonrestored teeth to levels similar to those of sound teeth. In addition, the use of etch-and-rinse adhesive system (Adper Single Bond) with the bevel preparation produced a resistance higher than that observed for two-step self-etch system (Clearfil SE Bond), both with Filtek Z250 (3M ESPE) composite restoration.

Also, these results agree with Kikuti et al. [21] who reported that there was no significant difference in fracture resistance load of specimens in groups restored with two-step self-etch (Adper Single Bond 2), and one-step self-etch systems (Adper Easy One) both with Filtek P60 (packable composite) composite restoration. But these results disagree in that the etched and bonded composite (Adper Single Bond 2 with Filtek P60) restoration returned the tooth to fracture strength as high as the intact tooth.

Such variations in results could be due to differences in cavities configurations, testing methods, and the use of different adhesives and composite materials [8].

In the present study, fracture pattern analysis showed no significant difference between all of the groups. However, for adhesive failure, Clearfil Liner Bond F adhesive (group IV) recorded the least adhesive failure (mode I) 20%, whereas the remaining two groups (group III; Adper Single Bond and group V; Single Bond Universal adhesives) recorded 30%. These results agree with those of Coelho-de-Souza et al. [23] who reported that there was no significant difference in mode of fracture pattern between specimens in groups prepared with butt joint and restored with two types of adhesive system; etch-and-rinse system (Adper Single Bond) and two-step self-etch primer system (Clearfil SE Bond) both with Filtek Z250 Universal Restorative (microhybrid composite). But these results disagree when the same materials were used with bevel preparation, where group of etch-and-rinse system (Adper Single Bond) recorded zero specimens in adhesive fracture at the interface (mode I), whereas group of two-step self-etch primer system (Clearfil SE Bond) recorded in adhesive fracture at the interface (mode I) 50% of the specimens.

Regarding the type of fracture observed in all groups, palatal cusp fracture was more frequent than buccal fractures, in addition, recovery was 100% for intact teeth, 90% for all restored specimens, and 60% for prepared unrestored teeth. Although previous clinical studies have observed similar incidence of buccal and lingual cusp fracture in posterior teeth. The results of the present study agree with those of Mondelli et al. [45], and also concluded that 67% of the fractures in maxillary premolars occurred in the nonfunctional cusps.


The results showed that restoring premolar teeth with packable composite with adhesive systems had improved significantly the fracture resistance of teeth subjected to class II MOD preparations.There was no significant difference between the three different adhesive systems used in the present study either using etch-and-rinse type or self-etch adhesives.Meanwhile, group IV (Clearfil liner Bond F Adhesive with Filtek Z350 XT packable composite) show the highest insignificant fracture resistance load comparable to the other adhesives.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


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