Wear model simulating clinical abrasion on composite filling materials

Awareness of possible complications associated with direct composite restorations: A multinational survey among dentists from 13 countries with meta-analysis

OBJECTIVES

Resin-based composites (RBCs) evolved into favoured materials for teeth restorations, marking a significant change in dental practice. Despite many advantages, RBCs exhibit various limitations in their physical and chemical properties. Therefore, we assessed the dentists' awareness of possible complications after direct composite restorations and their opinions about this material.

METHODS

The online questionnaire was created in English in May 2023. A 16-item survey was dedicated to general dentists and specialists. The first section included four questions related to demographic characteristics. The second section comprised twelve questions and focused on awareness of potential side effects of composite restorations, the most crucial advantages and disadvantages of composite resins, and the frequency of experienced clinical complications after the application of composite materials.

RESULTS

A total of 1830 dentists from 13 countries took part in the survey. Dentists most often declared awareness of low adhesion to the dentine (77.5 %) and, most rarely, solubility in oral fluids (42.6 %). Aesthetics was identified as the main advantage of composite fillings (79 %), followed by the possibility of repair (59 %) and adhesion to enamel (57 %). Polymerisation shrinkage was a major disadvantage for most countries (70 % overall). Analysing the declared potential clinical complications for all countries, statistically significant findings were obtained for marginal discolouration (OR=2.982, 95 % CI: 1.321-6.730, p-value=0.009) and borderline significance for secondary caries (OR=1.814, 95 % CI: 0.964-3.415, p-value=0.065).

CONCLUSIONS

Dentists value aesthetics and repairability but are aware of shrinkage and experience discolouration. The issue of toxicity and solubility seems to be the least known to dentists.

CLINICAL SIGNIFICANCE

Dentists should use RBCs with critical caution due to possible side effects. Despite the undoubted aesthetics of direct composite restorations, it is necessary to remember potential clinical complications such as marginal discolouration or secondary caries.

A comparative evaluation of mechanical wear of adhesives used for bonded retainers that underwent brushing for 1 hour under 36 mm of linear action, using computer-aided 3D scan-an in vitro study

OBJECTIVES

The aim of the present study was to comparatively evaluate the mechanical wear of adhesives used in bonded retainers.

MATERIALS AND METHODS

Eighty mandibular acrylic teeth were included in the study that were divided into 4 different groups based upon the composite used. Each acrylic tooth was bonded with a retainer wire and composite of their respective group (Heliosit, Restofill, Tetric-N-flow, and Filtek Z350 XT). These bonded acrylic teeth were subjected to 3D scan in order to evaluate the volume and surface area of the composite. The 3D scans were recorded using MEDIT 3D scanner. After evaluating, the samples were subjected to brushing with the aid of a custom-made brushing simulator using a toothbrush with soft bristles and toothpaste slurry. The samples were subjected to 1 hr of brushing. These samples were again subjected to 3D scans to evaluate (post-test volume and surface area) and underwent statistical analysis.

RESULTS

The results showed the Heliosit group exhibited the highest mean volume (1.76 mm3) and surface area (4.81 mm2) difference between the pre-test and post-test values whereas the least mean volume difference (1.10 mm3) and surface area difference (3.21 mm2) were seen in the Tetric-N-flow group.

CONCLUSION

All the four composites underwent change in the mean surface area and volume after being subjected to brushing, suggesting that the composites routinely used for bonding fixed bonded lingual retainers are subjected to changes due to abrasion. The Heliosit group, which showed least filler loading among the 4 composites, exhibited least resistance to wear, whereas the Tetric-N-flow group which had highest filler loading among the composites exhibited highest resistance to wear.

CLINICAL RELEVANCE

The most crucial phase during orthodontic treatment is the retention phase. This phase is responsible for the long-term results of the treatment. The retainers that are placed in the oral cavity are subjected to changes due to oral environment, chemical changes, and mechanical changes. These changes have a direct effect on the retainers, which tend to alter their properties. Thus, the effects of these changes are to be studied thoroughly.

Toothbrush Abrasion of Restorations Fabricated with Flowable Resin Composites with Different Viscosities In Vitro

The purpose of this study was to examine toothbrush-induced abrasion of resin composite restorations fabricated with flowable resin composites of different viscosities in vitro. In this study, six types of flowable resin composites with different flowability (Beautifil Flow F02, F02; Beautifil Flow F10, F10; Beautifil Flow Plus F00, P00; Beautifil Flow Plus F03, P03; Beautifil Flow Plus X F00, X00; and Beautifil Flow Plus X F03, X03) were used. For the toothbrush abrasion test, the standard cavity (4 mm in diameter and 2 mm in depth) formed on the ceramic block was filled with each flowable resin composite (n = 10) and brushed for up to 40,000 strokes in a suspension containing commercial toothpaste under the conditions of 500 g load, 60 strokes/min, and 30 mm stroke distance. After every 10,000 strokes, the brushed surface of the specimen was impressed with a silicone rubber material. The amount of toothbrush-induced abrasion observed on each impression of the specimen was measured using a wide-area 3D measurement device (n = 10). The viscosity was determined using a cone-and-plate rotational measurement system. Because of the effect of different shear rates on viscosity and clinical use, the values 1.0 and 2.0 s⁻¹ were adopted as data (n = 6). In this study, the results of the toothbrush abrasion test demonstrated no significant differences in the amount of toothbrush-induced abrasion among flowable resin composites used (p > 0.05). No significant correlation was reported between toothbrush-induced abrasion and viscosities of flowable resin composites.

Multi-scale analysis of the influence of filler shapes on the mechanical performance of resin composites using high resolution nano-CT images

OBJECTIVE

The aim of this study was to investigate the criteria for predicting the fracture initiation of resin composites (RCs) at the micro-scale and assess the influence of filler shapes on the flexural properties of RCs by combining nano-CT imaging and in silico multi-scale analysis.

METHODS

Experimental RCs composed of irregular-shaped (IS) silica filler (31.2 vol%/50.0 wt%) and Bis-GMA/TEGDMA were prepared. The RC specimens were scanned by a nano-CT with 500-nm resolution, and 10 micro-scale models (100 × 100 × 100 μm) were randomly extracted from a scanned region. In silico micro-scale models containing sphere-shaped (SS) fillers with the same volume content as the experimental RC were designed. Each RC model's elastic modulus and Poisson's ratio at the macro-scale were calculated using homogenization analysis. The flexural strength of the RC models were predicted by finite element analysis using the elastic moduli and Poisson's ratio values.

RESULTS

Significantly greater elastic modulus values were obtained in the X, Y, and Z directions for RC models containing IS fillers than SS fillers. Similarly, smaller Poisson's ratio values were observed in the Y and Z directions for RC model containing IS fillers than SS fillers (p < 0.05). The flexural strength of RC model containing IS fillers was significantly greater than the RC model containing SS fillers (p < 0.05).

SIGNIFICANCE

The in silico multi-scale analysis established in this study demonstrated that RC model containing irregular-shaped fillers had greater flexural strength than RC model loaded with SS fillers, suggesting that the mechanical strength of the RC can be improved by optimizing the shape of the silica fillers.

The Effect of Finishing and Polishing Sequences on The Surface Roughness of Three Different Nanocomposites and Composite/Enamel and Composite/Cementum Interfaces

The purpose of this study was to investigate the effect of final surface treatment and dental composite type on the roughness of the composite surface, composite/enamel interface, and composite/cementum interface, as well as on the polishing time. Class V cavities prepared in extracted teeth (n = 126) were restored using one of the three nanohybrid composites with different filler sizes. The specimens were randomly assigned to three different finishing and polishing sequences. The roughness (Ra) of the investigated surfaces was measured using the contact profilometer. The time required to achieve visible gloss was documented. The data were analyzed using ANOVA with Tukey's post hoc test (p < 0.05). There was no significant influence of the composite type on the restoration surface roughness (p = 0.088), while the polishing method had a significant impact (p < 0.001). The Ra of the composites ranged between 0.08 µm and 0.29 µm, with the lowest values (0.09 µm ± 0.05 µm) found in the aluminum oxide disc group (p < 0.001). The time to achieve a visible composite gloss was influenced by the polishing method, composite type, and interactions between these factors (p < 0.001). The interface roughness was significantly greater than that of the composite surface (p < 0.001), and depended on the composite type and polishing system employed.

Recent advances in understanding the fatigue and wear behavior of dental composites and ceramics

Dental composite and ceramic restorative materials are designed to closely mimic the aesthetics and function of natural tooth tissue, and their longevity in the oral environment depends to a large degree on their fatigue and wear properties. The purpose of this review is to highlight some recent advances in our understanding of fatigue and wear mechanisms, and how they contribute to restoration failures in the complex oral environment. Overall, fatigue and wear processes are found to be closely related, with wear of dental ceramic occlusal surfaces providing initiation sites for fatigue failures, and subsurface fatigue crack propagation driving key wear mechanisms for composites, ceramics, and enamel. Furthermore, both fatigue and wear of composite restorations may be important in enabling secondary caries formation, which is the leading cause of composite restoration failures. Overall, developing a mechanistic description of fatigue, wear, and secondary caries formation, along with understanding the interconnectivity of all three processes, are together seen as essential keys to successfully using in vitro studies to predict in vivo outcomes and develop improved dental restorative materials.

Effect of filler size and filler loading on wear of experimental flowable resin composites

The relationship between wear resistance and filler size or filler loading was clarified for the universal resin composite; however, their relationship in flowable resin composites has not been clarified.

Effect of short LED lamp exposure on wear resistance, residual monomer and degree of conversion for Filtek Z250 and Tetric EvoCeram composites

OBJECTIVES

The latest LED dental curing devices claim sufficient curing of restorative materials with short curing times. This study evaluates mechanical and chemical properties as a function of curing time of two commercial composite filling materials cured with three different LED lamps.

METHODS

The composites were Filtek Z250 (3M ESPE) and Tetric EvoCeram (Ivoclar Vivadent) and the LED curing devices were bluephase 16i (Ivoclar Vivadent), L.E.Demetron II (Kerr) and Mini L.E.D. (Satelec). Control samples were cured with a QTH-lamp (VCL 400, Kerr). The wear resistance after simulated tooth brushing, degree of conversion, curing depth, and amounts of residual monomers were measured after different curing times.

RESULTS

The results of this study show that short curing time with high-intensity LEDs may influence the bulk properties of the materials, resulting in lower curing depth and increased residual monomer content. The measured surface properties of the materials, degree of conversion and wear resistance, were not affected by short curing times to the same extent.

SIGNIFICANCE

This study demonstrates that reduced exposure time with high intensity LEDs can result in composite restorations with inferior curing depth and increased leaching of monomers. Dentists are recommended to use sufficient curing times even with high intensity LEDs to ensure adequate curing and minimize the risk of monomer leaching.