Wear patterns of composite restorative resins in vivo; observations by scanning electron microscopy

In this study, the wear pattern of seven commercial composite resins, one experimental composite and one dental amalgam were investigated. These materials were separately inserted in a separation preparation cavity of the patient's mouth. After clinical service for 3, 9 and 12 months the specimens were taken out and observed by scanning electron microscopy (SEM). It was found that the softer resin matrix wore away first while the inorganic filler particles showed no signs of abrasive wear, whereafter filler particles were loosened once there was no support of the resin matrix around them.     

A study of surfaces developed on composite resins in vivo during 4.5 years; observations by SEM

In this study seven commercial composite resins, one experimental composite and one dental amalgam were investigated. These materials were inserted into the cavities of denture molar teeth in different patients. After clinical service for 3, 9, 12, 24 and 54 months the specimens were removed and observed by scanning electron microscopy. The wear patterns of the filling materials and their changes with continuing clinical service for 4.5 years suggest that the abrasive mechanism of conventional composite resin is as follows. The softer resin matrix is worn away and inorganic filler particles are exposed, thereafter they loosen and fall off. As this process proceeds the composite resin is worn away. This process continues with time. In the case of microfilled composite, the organic fillers and resin matrix are worn away at the same rate. After long-term clinical service some cracks could be seen on the wear surface between the organic filler agglomerates and the resin matrix.     

An abrasion test for composite resins

An abrasive wear test for composite resins was proposed. A slurry of glass pearls and abrasive particles were used. The abrasive effect was examined for different particle sizes. Particle sizes were found which gave the same order of wear as found clinically for an amalgam, a composite resin, and unfilled resin.     

The In Vivo Wear Resistance of 12 Composite Resins

PURPOSE: The in vivo wear resistance of 12 composite resins were compared with an amalgam control using the Latin Square experimental design. Sixteen edentulous patients wearing specially designed complete dentures formed the experimental population. MATERIALS AND METHODS: The Michigan Computer Graphics Measurement System was used to digitize the surface of the control and composite resin samples before and after 3-month test periods to obtain wear data. The 12 composite resins selected for this investigation based on their published composite classification types were seven fine particle composites, three blends, and two microfilled composite resins. The Latin Square experimental design was found to be valid with the factor of material being statistically different at the 5% level of significance. Wear was computed as volume loss (mm3/mm2), and all of the composites studied had more wear than the amalgam control (P = .001). RESULTS: After 3 months, the mean (error) of wear of the amalgam was 0.028 (0.006). Means (error) of wear for the 12 composites were ranked from most to least wear by mean wear volume loss. CONCLUSION: The absence of any relationship between mean wear volume loss and the volume percentage filler was confirmed by the correlation coefficient r = -0.158.     

Surface textures of composite resins after combined wear test simulating both occlusal wear and brushing wear

The purpose of this study was to investigate the relation between the texture of worn surfaces of composite resins and the maximum wear depth. Three types of composite resins were investigated: a hybrid composite resin consisting of irregular-shaped inorganic filler particles (APX); a composite resin which contained small, irregular-shaped, inorganic filler particles and large organic composite filler particles (SRE); and another which contained spherical inorganic filler particles and large organic composite filler (SDX). Surface profile measurement and elemental analysis were carried out on the worn surfaces of these three composite resins using an electron probe microanalyzer (EPMA). For the composite resin which exhibited the largest maximum wear depth, its surface texture was slightly rough with fine pores and grooves. For the composite resin with lowest maximum wear depth, it had a smooth worn surface due to the large organic composite filler being abraded during the combined wear test.     

Wear patterns and rates of posterior composite resins

The use of composite resins as posterior restorative materials has been growing at a rapid rate. In spite of major improvements in both physical and mechanical characteristics secondary caries and resistance to wear are still major concerns. This paper deals with the wear rate and patterns of wear of posterior composite resins. Results of long term clinical studies show that a major difference exists between composites containing submicron or supramicron sized filler particles. In general, the wear rates of the larger filler particles composite resins decrease with time. On the other hand, the microfilled posterior composite resins appear to exhibit a linear rate of wear. The wear patterns of the two different types of posterior composite resins are also dissimilar. Composite resins containing filler particles larger than 1 micron tend to undergo a generalized loss of material. The microfilled composite resins also lose material generally but to a lesser degree. Furthermore, the submicron filled posterior composite resins tend to exhibit localized wear, particularly in centric holding areas. Such a change does not, as a rule, occur with composite resins containing larger filler particles. Finally, the microfilled composite resins tend to develop continuous marginal fractures at tooth restoration interfaces.     

Status report on microfilled composite restorative resin. Council on Dental Materials, Instruments, and Equipment

Microfilled resins generally have physical properties inferior to those of conventional composites. A lower in organic filler content or higher polymer/filled ratio results in a lower modulus of elasticity, greater thermal dimensional change, less resistance to indentation and abrasion, and greater water sorption. The ability to finish and to maintain a smooth surface texture is a major advantage, although it has not been proved clinically that microfilled resin restorations result in less plaque adherence nor do they enhance soft tissue response. Early clinical trials, after two to three years in vivo, indicate a greater wear resistance for these materials than for conventional composites. At this time, current evidence suggests that a decrease in filler particles size to less than 1 micrometer and a lower filler loading of the resin matrix permit the clinical development and maintenance of a smooth surface texture on restoration surfaces. There is no published evidence that the decrease in many of the physical properties leads to early signs of clinical deterioration and failure. In vivo studies extended for longer periods are necessary to make a knowledgeable judgment on the true clinical value of these composites. A classification system for composite restorative resins is being prepared by the Council on Dental Materials, Instruments, and Equipment. It will be published in a future issue of The Journal.     

Characterization of the inorganic fraction of resin composites

The purposes of this study were to determine the weight fraction of filler in thirty-nine resin-based materials including flowable and packable composites, and to examine the morphology of the filler particles. The percentages of inorganic fillers by weight were determined by Thermogravimetric Analysis and by ashing in air technique at 900 degrees C. The size and shape of the filler particles were examined using scanning electron microscopy (SEM) after dissolution of the organic matrix. The weight fraction of inorganic fillers ranged between 41.6 and 84.6%. Wide variations were found among materials of the same category. Values found in the present study were sometimes different from those given by the manufacturers. The SEM photomicrographs showed various shapes, and sizes of inorganic fillers. Compared with universal hybrid restorative materials, flowable composites have lower filler loading and packable resin composites did not show higher values as claimed by some manufacturers. Various factors may explain the observed discrepancies between the manufacturer's data and our results. The silane treatment as well as the incorporation of organic material as part of the fillers of the composite could be responsible for those differences.     

Effect of filler content and size on properties of composites

Two series of dental composites, along with the unfilled resin matrix, were examined to determine the effects of filler level and size on selected properties. Both series were prepared by incorporating a silanated barium borosilicate filler into a visible-light-activated polyphenylene polymethacrylate resin matrix. One series had a filler particle size of 2 microns, with filler levels of 20, 40, 45, 50, and 53% (vol). The second series contained a 15-microns filler in amounts of 20, 40, 50, 60, and 65% (vol). Tests conducted included: depth of cure as evaluated by hardness, water sorption, compressive strength, stress-strain behavior under slow compression, toothbrush abrasion, and wear by hydroxyapatite. Analysis of the data indicated that increased filler levels resulted in increased hardness, compressive strength and stiffness, and decreased water sorption. Also, there was a slight trend toward improved depth of cure. Incorporation of the 2-microns filler decreased the abrasion resistance of the resins to toothbrushing as compared with the unfilled resin, while addition of the 15-microns filler improved resistance. All filled resins exhibited a significant improvement in resistance to wear by hydroxyapatite as compared with the unfilled resin. There was a trend for increased wear with increased filler level. The particle size of the filler appeared to have a moderate influence on the properties. When compared with 15-microns filled resins of the same filler levels, the 2-micron filled series appeared to have inferior properties in terms of depth of cure, compressive strength, water sorption, and resistance to toothbrush abrasion. Properties which were less affected by particle size were hardness, stiffness, and wear resistance to hydroxyapatite.     

Surface failure of commercial and experimental restorative resins.

A single-pass test was used to study the surface failure of commercial and experimental restorative resins and composites. The surface failure observed for unfilled diacrylate resins was more severe than that seen for an unfilled acrylic resin. Addition of nonsilanated filler to the diacrylate resins increased the resistance to penetration but did not dramatically change the mode of surface failure. The surface failure of the commercial composite resins, which contain silanated filler, was ductile in mode and the resistance to penetration of the diamond slider was the highest of the materials studied. The wear of restorative resins and composites is determined, therefore, by resistance to penetration as well as mode of deformation during sliding.     

Physical and mechanical properties of anterior and posterior composite restorative materials

The physical and mechanical properties of two photo-cured anterior filling materials and a photo-cured posterior filling material have been compared with those of a conventional-cure resin composite. The properties of these materials were found to be dependent on their matrix resin compositions, filler contents, and filler particle sizes. One material with a low (50%) inorganic filler content of small particle size (0.04 micron) was found to have a lower mechanical strength with significantly higher water sorption and solubility characteristics than more heavily filled materials. A new hybrid photo-cured anterior composite with a smaller filler particle size was found to have comparable sorption and solubility behavior but a tensile strength superior to that of a conventional-cure composite. The superior properties of the new photo-cured systems are thought to result from their hybrid composite structures and the smaller filler particle sizes.     

Influence of filler loading on the two-body wear of a dental composite

The purpose of the study was to explore the fundamental wear behaviour of a dental composite with different filler loadings under two-body wear conditions. The parent resin and filler components were mixed according to different weight ratios to produce experimental composites with filler loadings ranging from 20 to 87.5% by weight. A two-body wear test was conducted on the experimental composites using a wear-testing machine. The machine was designed to simulate the impact of the direct cyclic masticatory loading that occurs in the occlusal contact area in vivo. The results showed that there was little increase in the rate of wear with filler loadings below 60 wt%, but a sharp increase between 80 and 87.5 wt% in filler loading. Wide striations and bulk loss of material were apparent on the wear surfaces at higher filler loadings. Coefficients of friction increased with filler loading and followed the increase in rate of wear loss closely. It was concluded that, under two-body wear conditions, addition of high levels of filler particles into the resin matrix could reduce the wear resistance of dental composites. This finding may help when designing future dental composites for use in particular clinical settings.     

In vitro contact wear of dental composites.

OBJECTIVE: The aim of this study is to determine the in vitro two-body contact wear mechanisms of three medium filled composites and compare these with a highly filled composite previously investigated. MATERIALS AND METHODS: Three commercial dental composites with filler mass fraction loading of 75-76% were evaluated. Two of the composites contained Ba-B-Al-silicate glass fillers and fumed silica with different particle sizes and distributions. One of these composites contained a fairly uniform distribution of filler particles ranging in size from 1 to 5 microm, whereas the particle size distribution in the second composite was bimodal consisting of small (less than 1 microm) and large (about 10 microm) particles. The third composite contained Ba-Al-silicate glass and silica with a filler particle size of approximately 1 microm. The composite disks were tested for wear against harder alumina counterfaces. Wear tests were conducted in distilled water using a pin-on-disk tribometer under conditions that represented typical oral conditions (sliding speed of 2.5 mm/s and contact loads ranging from 1 to 20 N). The wear tracks were analyzed by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy to elucidate the wear mechanisms. The chemical composition of the water solution collected after the tests was determined using an inductively coupled plasma-mass spectrometer (ICP-MS) to detect possible chemical changes, e.g. dissolution of trace elements due to submersion or wear. The wear results were compared with those reported in an earlier study on a highly filled composite containing predominately alumino-silicate glass fillers and alumina at a filler loading of 92%. RESULTS: The differences in two-body wear rates between the three medium filled composites were not statistically significant (p<0.05) indicating that the variations in filler particle size and slight differences in chemical composition of the glass fillers do not affect the in vitro wear rates of these composites. Wear rates of these medium filled composites, however, were significantly lower than the highly filled composite (p<0.05). SEM, FTIR and ICP-MS analyses suggested that wear in the medium filled composites occurs by a complex set of processes involving tribochemical reactions between filler particles and water, formation of surface films containing a mixture of filler fragments and reaction products, and film delamination, as well as dissolution of the reaction products. SIGNIFICANCE: This study reveals that subtle changes in the filler particle size and small differences in filler composition do not significantly affect the two-body wear behavior of medium filled composites. However, the chemistry of filler particles plays an important role in altering the wear performance of composites when significant changes are made in the chemical composition of the fillers and when the filler loading is increased.     

Influences of composition on brush wear of composite resins. Influences of particle size and content of filler

The influences of the composition on abrasion resistance of composite resins were examined using various experimental composite resins which had various matrix resin, filler size and content. The abrasion test was conducted by the experimental toothbrush abrasion testing machine developed in our laboratory. Three series of heat-curing composite resins were tested. One series was made from a Bis-MPEPP or UDMA monomer, and a silica filler with an average particle size of 0.04, 1.9, 3.8, 4.3, 7.5, 13.8 and 14.1 microns. The filler content of this series was constant at 45 wt%. The second series contained a silica filler of 4.3 microns in a content ranging from 35 to 75 wt%. The third series contained a microfiller (0.04 microns) and macrofiller (4.3 microns) in total content of 45 wt%. In this series, the microfiller was gradually replaced by 5, 15, 25 and 45 wt% of the macrofiller. The results obtained for these three series indicated that the abrasion resistance of composite resins was controlled by the inorganic filler, mainly filler size and content. The abrasion loss did not vary with the difference of matrix resin. When the particle size of the filler was below about 5 microns, the abrasion resistance decreased markedly with the decrease in filler size. The composite resin which contained a 0.04 or 1.9 micron filler was less resistant to toothbrush wear than the unfilled matrix resin. However, the microfiller also contributed to abrasion resistance when used in combination with the macrofiller, although abrasion resistance decreased with the increase in the microfiller concentration. The increase of filler content clearly improved the abrasion resistance when used the macrofiller. The analysis of these results and SEM observations of the brushed surfaces of samples suggested that the toothbrush abrasion was three-body abrasion caused by the abrasive in the toothpaste, and affected by the difference in the particle size between abrasive and filler, and between the abrasive size and the interparticle distance of the filler.     

Effects of occlusal and brushing cycles on wear of composite resins in combined wear test

The effects of occlusal cycles and brushing cycles on wear of composite resins were investigated using a combined wear test, which carried out occlusal and toothbrush wear tests alternately. Worn volume and maximum worn depth were measured to evaluate wear under four combinations of two different cycles (occlusal cycles: 50 and 150 cycles; brushing cycles: 20 and 50 cycles). With composite resin APX, which consisted of relatively large and irregular-shaped filler particles, its worn volume and worn depth significantly increased with the number of occlusal cycles. With composite resin Z100, which consisted of relatively small and irregular-shaped filler particles, its wear values significantly increased with both brushing and occlusal cycles. With composite resin SRE, which consisted of small, irregular-shaped, inorganic filler particles and large organic filler particles, its worn volume significantly increased with the occlusal cycle when under a lower brushing cycle. With composite resin SDX, which consisted of spherical inorganic filler particles and large organic filler particles, its wear was not influenced by increases in both brushing and occlusal cycles.     

Development of metal-resin composite restorative material. Part 3. Flexural properties and condensability of metal-resin composite using Ag-Sn irregular particles

Powder-liquid type metal-resin composites, using Ag-Sn irregular particles as the filler, 4-META as coupling agent and UDMA + TEGDMA as resin matrix, were experimentally prepared under 9 different conditions (three different particle sizes and three different filler contents). The flexural strength and flexural modulus were measured. Three different irregular particle size MRCs without redox-initiator at 94% filler content, as well as amalgam, conventional hybrid composite and Ag-Sn spherical particle MRC were evaluated for condensability. The flexural strength of the Ag-Sn irregular particle MRC was significantly influenced by both the filler particle size and filler contents (p < 0.01). It increased when either the filler content increased or the particles size decreased. The highest flexural strength (97.6 MPa) was obtained from the condition of particles size < 20 microns and 94% filler content. The flexural modulus was significantly influenced by filler content and it increased with increasing filler content. The condensability of the Ag-Sn irregular particle MRC was lower than that of amalgam but much higher than presently available conventional composites and spherical particle MRC.     

Effect of filler system on the mechanical properties of light-cured composite resins. I. Effect of various types of silica fillers on the mechanical properties of the composite resins

To investigate the effect of silica fillers on the mechanical properties of visible light-cured composite resins, Bis-GMA-based composites with four types of silica fillers were prepared. The mechanical properties of the composites with splinter-shaped silica fillers increased with increasing the filler fraction. Although the spherical silica filler could be filled more with resin monomer than the splinter-shaped silica filler, the mechanical properties of spherical silica-filled composite were relatively lower than those of the composite with splinter-shaped silica fillers. The micro particle silica-filled composite showed no obvious increase in the mechanical properties in either the dry or wet conditions. SEM observations of the fractured resin surface revealed that fracture occurred through the resin matrix as well as the resin/filler interface and the mechanical properties of each composite resin were correlated with the nature of crack propagation.     

Wear model simulating clinical abrasion on composite filling materials

The aim of this study was to establish a wear model for testing composite filling materials with abrasion properties closer to a clinical situation. In addition, the model was used to evaluate the effect of filler volume and particle size on surface roughness and wear resistance. Each incisor tooth was prepared with nine identical standardized cavities with respect to depth, diameter, and angle. Generic composite of 3 different filler volumes and 3 different particle sizes held together with the same resin were randomly filled in respective cavities. A multidirectional wet-grinder with molar cusps as antagonist wore the surface of the incisors containing the composite fillings in a bath of human saliva at a constant temperature of 37°C. The present study suggests that the most wear resistant filling materials should consist of medium filling content (75%) and that particles size is not as critical as earlier reported.     

Effect of filler fraction on strength,viscosity and porosity of experimental compomer materials

OBJECTIVE: The primary goal is to develop a self-cured polyacid-modified resin composite with good mechanical and rheological properties. To achieve such a goal, the aim of this study is to determine how volume filler fraction (VFF) affects mechanical properties and viscosities of such materials containing different filler volumes. METHODS: A series of self-cured polyacid-modified composites made from polyacid modified resins and TEGDMA, mixed with filler particles, were evaluated regarding compressive strength (CS), diametral compressive strength (DCS) and viscosity. The maximum filler content, which could be incorporated into the materials, was calculated from CS tests as well as from viscosity measurements using Mooney's equation. Porosity contents were also determined in an attempt to explain different failure behaviours. RESULTS: The CS values peaked at 18.9 vol.% filler particles and declined afterwards for self-cured polyacid-modified resin composites cured in air. Using photopolymerisation and barium filler in the polyacid-modified resin composites resulted in the highest CS and DCS values. The viscosity increased continuously with increased VFF. VFF results determined experimentally and with Mooney's equation at shear rates of 0.01, 0.1, 1.0, and 10.0 s(-1) revealed that the maximal filler fraction values were 54.9+/-1.8, 55.9+/-1.3, 56.3+/-0.9, and 56.8+/-0.8 vol.%, respectively. The largest porosity content occurred at a VFF value of 53 vol.% CONCLUSIONS: We conclude that an increase in filler fraction of the investigated experimental polyacid-modified resin composite materials above a certain value (20-30 vol.%) does not result in improved mechanical properties.     

Mechanical properties of heat-treated composite resin restorative materials.

Clinical methods for heat treating composite resin restorations have been developed. In this investigation, the effect of heat treatments on the diametral tensile strength of composite resin was determined. The composite resin restorative materials were selected according to the manufacturers' suggested use for anterior or posterior teeth, filler particle composition, and light-cured or chemical polymerization. Samples were prepared according to American Dental Association specification No. 27, and heat treatments were accomplished with a Coltene DI 500 oven for curing at approximately 120 degrees C for 7 minutes. Heat treatment substantially increased the diametral tensile strength tested, with the exception of the anterior hybrid particle (p less than 0.05). Composite resins with fine-particle inorganic fillers were significantly stronger than hybrid and microfilled composite resins.