Influence of Salvadora persica (miswak) extract on physical and antimicrobial properties of glass ionomer cement.

AIM: To investigate physical and antimicrobial properties of Glass Ionomer Cement (GIC) combined with Salvadora Persica Extract (SPE). METHODS: SPE was added to GIC (Fuji IX) in concentrations of 1%, 2% and 4% w/w. The compressive strength and diametral tensile strength were measured at 1 h, 24 h and 7 days. The antimicrobial effect was tested in agar dilution assay in blood agar plates with Candida albicans, Streptococcus mutans, Streptococcus sanguis, Streptococcus mitis, Streptococcus salivarius and Actinomyces naeslundii as test organisms. GIC containing 5% chlorhexidine served as positive control. RESULTS: Significant differences were found for the compressive strength and diametral tensile strength as a result of adding SPE to GIC (p<0.05). GIC with 2 or 4 % SPE was significantly weaker than the GIC control, while GIC with 1% SPE was not different from the control. The mean values for the 4% SPE-containing specimens and the GIC control group ranged from 108.7MPa to 141.1MPa for CS and from 8.2MPa to 12.5MPa for DTS. The 1% SPE-containing specimens were not different in physical properties compared to the control GIC specimens; the 2% SPE-containing specimens were statistically slightly less strong (p<0.05), but within an acceptable range. As compared with pure GIC the antimicrobial properties of the SPE-containing specimens were increased significantly (p<0.01). It has been found up to a 2-fold increased inhibition compared to the GIC with increasing concentrations of SPE. For most microorganisms tested the SPE group inhibited less than Chlorhexidine, but significantly better than pure GIC (p<0.01). CONCLUSION: SPE could be a promising natural material as an additive to GICs. Further studies should include in vivo tests and other antimicrobial and physical properties of this combination.

Contraction stress in dentin adhesives bonded to dentin.

Adhesives cured under constrained conditions develop contraction stresses. We hypothesized that, with dentin as a bonding substrate, the stress would reach a maximum, followed by a continuous decline. Stress development was determined with a tensilometer for two total-etch systems and two systems with self-etching primers. The adhesives were placed in a thin layer between a glass plate and a flat dentin surface pretreated with phosphoric acid or self-etching primer. After an initial maximum shortly after light-curing, the stress decreased dramatically for the total-etch systems (70%) and, to a lesser extent, for the adhesives with self-etching primers (30%). The greater stress decrease for the total-etch systems was ascribed to water and/or solvents released into the adhesives from the fully opened dentinal tubules by the pulling/sucking action of the contraction stress. This happened less with the adhesives with self-etching primers, where the tubules remained mainly closed.

The influence of accelerating the setting rate by ultrasound or heat on the bond strength of glass ionomers used as orthodontic bracket cements.

Conventional glass ionomer cements (GICs) may be a viable option for bracket bonding when the major disadvantages of these materials, such as the slow setting reaction and the weak initial bond strength, are solved. The aim of this in vitro study was to investigate the influence of ultrasound and heat application on the setting reaction of GICs, and to determine the tensile force to debond the brackets from the enamel. A conventional fast-setting GIC, Fuji IX Fast, and two resin-modified glass ionomer cements (RMGICs), Fuji Ortho LC and Fuji Plus, were investigated. Three modes of curing were performed (n = 10): (1) according to the manufacturer's prescription, (2) with 60 seconds application of heat, or (3) with 60 seconds application of ultrasound. The tensile force required to debond the brackets was determined as the tension 15 minutes after the start of the bonding procedure. The mode of failure was scored according to the Adhesive Remnant Index (ARI) to establish the relative amount of cement remnants on the enamel surface. Curing with heat and ultrasound shortened the setting reaction and significantly (P < 0.05) increased the bond strength to enamel. The ARI scores showed an increase for all materials after heat and ultrasound compared with the standard curing method, most notably after heat application.

The influence of specimen attachment and dimension on microtensile strength.

The higher microtensile bond strength values found for specimens with a smaller cross-sectional area are often explained by the lower occurrence of internal defects and surface flaws. We hypothesized that this aberrant behavior is mainly caused by the lateral way of attachment of the specimens to the testing device, which makes the strength dependent on the thickness. This study showed that composite bars of 1x1x10, 1x2x10, and 1x3x10mm attached at their 1-mm-wide side (situation A) fractured at loads of the same magnitude, as a result of which the microtensile strength ( micro TS), calculated as F/A (force at fracture/cross-sectional area), significantly increased for specimens with decreasing thickness. Attachment at the 1-, 2-, or 3-mm-wide side (situation B) resulted in equal micro TS values (P > 0.05). Finite element analysis showed different stress patterns for situation A, but comparable patterns for situation B. Both situations showed the same maximum stress at fracture.

The influence of resin composite and bonded amalgam restorations on dentine permeability in Class II cavities in vitro.

OBJECTIVES: This study was conducted to measure and compare dentine permeability reduction in Class II preparations, after restoration with resin composite or bonded amalgam, using either a multi-step or one-bottle dental adhesive system. METHODS: An in vitro fluid transport model was used to measure initial dentine permeability in Class II cavities with an intact smear layer in crown segments from extracted human premolars. One week and 3 months after restoration with resin composite or bonded amalgam, using either multi-step or one-bottle dental adhesive system, the measurements were repeated and the reduction in permeability was calculated as a percentage of the initial values. The data were analyzed statistically using a one-way ANOVA and Least Significant Difference tests. RESULTS: After 1 week the resin composite with one-bottle dental adhesive system provided the highest reduction in dentine permeability, whereas after 3 months the bonded amalgam caused the highest reduction. At both time intervals the resin composite with multi-step adhesive system provided the lowest reduction. (P=0.036 at 1 week, P=0.016 at 3 months). After 3-months storage in water a significant increase in dentine permeability reduction was found in the bonded amalgam group only (P=0.017). The reduction in dentine permeability provided by resin composite with one-bottle dental adhesive system and bonded amalgam in Class II cavities was similar at both time intervals. (P=0.182 at 1 week, P=0.750 at 3 months). SIGNIFICANCE: The results of this study indicated that on the basis of reducing dentine permeability in vitro, resin composite restorations with the investigated one-bottle adhesive system was superior to its multi-step equivalent and bonded amalgam can also be preferred in Class II restorations.

Fracture strength of different core build-up designs.

PURPOSE: To investigate the resistance to fracture of three crown and core combinations, made with different core build-up systems on human teeth, using a standardized test method. MATERIALS AND METHODS: The anatomic crowns were removed from six groups (n = 8) of endodontically treated, human premolars in conformity with a brass master dye, using the Celay duplicating device. Three of these groups were provided with a core build-up with-out an endodontic post (Ti-Core, Photo-Core and Ketac-Molar); two other groups were provided with a core build-up with an endodontic post (a cast post and core, and a composite with a silica post), and one group was not provided with a core. All groups were then prepared in conformity with a master dye. This preparation ended in axial dentin, 2 mm apical from the core build-up. Thus in the sixth group (premolars without a core build-up), this preparation only affected the 2 mm axial dentin (ferrule), which resulted in a small retention area (2 mm axial dentine) for the crown. Finally, a standard crown was cemented and 24 hrs afterwards loaded until fracture in an Instron testing machine at an angle of 45 degrees. For comparison with the standardized procedures, a seventh group (Photo-core without post) was prepared manually, with dimensions similar to the standardized groups. RESULTS: Within the standardized test set-up no significant difference in strength between the 6 groups could be demonstrated. Only in the case of the hand-made Photo-Core and the cast core was the fracture load significantly different (P= 0.01). In addition, this hand-made group displayed a larger standard deviation than the standardized groups. Taking into consideration the fact that the maximum bite force in the bicuspid region is about 580 N, these tests showed that within the limitations of the standardized test set-up, where the samples had no history of fatiguing, a core build-up without a post is an alternative for the conventional cast core. In this study, the fabrication of the standardized samples proved to be accurate, fast and economical. This method also enables the evaluation of the performance of core and crown design combinations in relationship to the amount of remaining tooth structure by using different master dies and, moreover, to reduce the high standard deviation in this kind of research.

Visco-elastic parameters of dental restorative materials during setting.

Contraction stresses generated in restoratives during setting are among the major problems in adhesive dentistry, since they often result in loss of adhesion from the cavity walls or in post-operative pain. The rate of stress development and the ultimate magnitude of the stress, which determine the seriousness of these problems, depend on the relatively unknown visco-elastic behavior of the restoratives during setting. The aim of this study was to determine the visco-elastic parameters during setting, to aid our understanding of the process of contraction stress development. A dynamic mechanical method was used in which the materials were subjected to periodic strain cycles in a universal testing machine during the first 60 min of setting. The visco-elastic parameters (viscosity eta and Young's modulus E) were calculated by analysis of the experimental stress-strain data with a simple mechanical model according to Maxwell. Two restorative materials from different classes were investigated: a two-paste resin composite and a conventional glass-ionomer cement. A comparison of the results showed significant differences in the development of viscosity and stiffness in the early stage of setting. The resultant relaxation time (eta/E) of the glass ionomer remained at a low level during the first 15 min, whereas that of the resin composite increased markedly. This is of clinical importance, since it implies that, during the early setting stage, glass ionomers are better capable of reducing the contraction stresses than resin composites, thus increasing the likelihood that the bond with the cavity walls will form and survive during setting.

Light-curing units, polymerization, and clinical implications.

A comprehensive review of the techniques of light initiation of dental composites with special attention to polymerization efficacy and shrinkage stress control is presented. Optimal setting of an average-sized composite restoration requires a certain quantity of light energy. The amount of energy depends on the characteristics of the light source used and the time of irradiation. Swift conversion with high-energy lamps is proportionally accompanied by rapid hardening and could negatively affect the marginal integrity of the adhesive restoration. However, preliminary stress measurements did not show an increase in the rate of stress development. Full conversion in the deeper areas of the restoration may not be possible if defects occur in one or more of the various lamp components. Prolonging the irradiation time could reduce this risk. A regular check on the energy output of the light source is recommended. Although the high-energy light sources with their extremely short irradiation times should be used in a more critical way than the conventional light sources, they save a considerable amount of time and facilitate bond application, leading to better restorations where isolation control need not be optimal.

Effect of tubule orientation in the cavity wall on the seal of dental filling materials: an in vitro study.

Dentinal tubules are oriented perpendicularly to the root canal walls but parallel to the lateral walls of class I occlusal preparation. It was hypothesized that the contact surface area of the material may depend on the tubule orientation in the cavity wall to which the material is applied, and that the difference in contact surface may affect the seal provided by the filling material. Standard central lumens, 2.6 mm in diameter and 3 mm high, were machined in human crown or root specimens. After removal of the smear layer with a conditioner, the specimens in each experimental group, consisting of 20 crown and 20 root specimens, were filled with amalgam, Fuji II glass ionomer (with or without varnish), or gutta-percha with Ketac-Endo root canal sealer. A modified fluid transport model was used to test the leakage along the fillings. Selected specimens were then split longitudinally and observed in a scanning electron microscope. The micrographs showed that all the test materials were pressed into the dentinal tubules. The contact surface of the material was calculated to be at least 45% larger in root specimens than in crown specimens, depending on the depth of the tubular penetration of the test material. The leakage results showed that all the test materials leaked less in root specimens than in crown specimens (P = 0.0000 for amalgam, P = 0.0374 for Fuji II with varnish, P = 0.0088 for Fuji II without varnish, P = 0.002 for gutta-percha with sealer). It was concluded that the tubule orientation in the cavity wall may influence the seal provided by certain dental filling materials.

Structural integrity of resin-modified glass ionomers as affected by the delay or omission of light activation.

Since light activation of resin-modified glass ionomers as a means of polymerizing the HEMA is usually done shortly after mixing occurs, the acid-base reaction will proceed mainly within a formed HEMA-polymer matrix. Delaying or omitting light activation may alter the structure and consequently its integrity. The aim of this study was to investigate the effect on the structural integrity of Fuji II LC, Photac-Fil, and Vitremer by delaying or omitting light initiation as compared with the integrity when light activation is performed 2 min after mixing occurs. We evaluated integrity by three-body wear experiments, conducted 8 hrs after sample preparation, to establish the integrity in the early phase of hardening, as well as after 1 wk and after 4 mos, to follow the materials throughout the process of maturation. When light activation was delayed for 1 hr, the structural integrity of Fuji II LC and Photac-Fil improved significantly in the early stages of hardening. In the case of Vitremer, an hour's delay of light activation significantly decreased integrity, which declined further when light activation was omitted. Fuji II LC was not affected by the omission of light activation, while Photac-Fil was markedly weakened. After 4 mos of aging, most of the samples of each product which had been cured by the different methods attained equal integrity, with the exception of the non-light-activated Vitremer samples, which remained weaker. We concluded that the structural integrity of resin-modified glass-ionomer cements benefits from a chemical integration of the polyalkenoate and poly-HEMA networks, as in Vitremer. Improvement in the structural integrity in the early phase for cements with a mechanical entanglement of the matrices, as in Fuji II LC and Photac-Fil, requires an acid-base reaction, a considerable portion of which may take place before activation of the HEMA polymerization.

Polymerization contraction stress in thin resin composite layers as a function of layer thickness.

OBJECTIVES: In the present study, the effect of layer thickness on the curing stress in thin resin composite layers was investigated. Since the value of the contraction stress is dependent on the compliance of the measuring equipment (especially for thin films), a method to determine the compliance of the test apparatus was tested. METHODS: A chemically initiated resin composite (Clearfil F2, Kuraray) was inserted between two sandblasted and silane-coated stainless steel discs in a tensilometer. The curing contraction of the cylindrical samples was continuously counteracted by feedback displacement of the tensilometer crosshead, and the curing stress development was registered. After 20 min, the samples were loaded in tension until fracture. The curing stress was determined for layer thicknesses of 50, 100, 200, 300, 400, 500, 600, 700 microns, 1.4 mm and 2.7 mm. The compliance of the apparatus was calculated with the aid of a non-linear regression analysis, using an equation derived from Hooke's Law as the model. RESULTS: None of the samples fractured due to contraction stress prior to tensile loading. The contraction stress after 20 min decreased from 23.3 +/- 5.3 MPa for the 50 microns layer to 5.5 +/- 0.6 MPa for the 2.7 mm layer. The compliance on the apparatus was 0.029 mm/MPa. SIGNIFICANCE: A measuring method was developed which was found to be suitable for the determination of axial polymerization contraction stress in this films of chemically initiated resin composites. The method makes it possible to estimate the stress levels that occur in resin composite films in the clinical situation.

Leakage of AH26 and Ketac-Endo used with injected warm gutta-percha.

Condensing warm gutta-percha (GP) can greatly reduce the distance between the GP and the root canal walls (RCW). Different sealers with different film thicknesses may seal such close fits differently. With the use of a fluid transport model, leakage of AH26 and Ketac-Endo used with injected warm GP to fill root canals was measured. The distance between the condensed GP and RCW and the film thickness of the two sealers was determined as well. After condensation, the distance between GP and RCW was mostly less than 25 microns. AH26, with a film thickness of 39 microns, leaked more than Ketac-Endo (p < 0.05) of which the film thickness was 22 microns. It seems that film thickness of sealer is an influencing factor on the sealing ability of a root canal filling when condensation of thermoplasticized GP is performed.

Fracture resistance of endodontically-treated premolars adhesively restored.

PURPOSE: To investigate the cusp fracture resistance of endodontically treated teeth, adhesively restored with various materials. MATERIALS AND METHODS: MOD preparations and endodontic treatment was carried out on extracted sound maxillary premolars. The cavities were restored with the amalgam Valiant in combination with Superbond or Panavia bonding, the resin composites Z100, Herculite XRV or Clearfil RP with their respective bonding systems, Z100 in combination with the glass ionomers Ketac Fil, Fuji II and Vitremer, and Tetric in combination with Compoglass. Fracture resistance was measured by axial loading in an Instron testing machine. RESULTS: One of the restorative methods, resin composites in combination with dentin bonding systems in beveled MOD preparations rendered the tooth a cusp fracture resistance which did not differ significantly from that of sound natural teeth. Two other restorative methods, bonded amalgam and a sandwich of glass ionomer cement/resin composite in beveled preparations were significantly weaker in resisting cusp fracture than sound natural teeth, but still significantly stronger than the unrestored tooth with a MOD preparation. It was statistically apparent that several adhesive restorative systems could satisfactorily be used to restore teeth after endodontic therapy.

The effect of curing light variations on bulk curing and wall-to-wall quality of two types and various shades of resin composites.

OBJECTIVES: This study evaluated the influence of light intensity and irradiation time variations on the curing efficacy of two types and various shades of resin composites and the effect of reduced light intensity on the preservation of wall-to-wall continuity. MATERIALS AND METHODS: Three microfilled composites (in three different shades) and one hybrid composite were used in this study. Polymerization shrinkage, and the hardness and adaptation of adhesive restorations in dentin cavities were determined at light intensities of 175 and 700 mW/cm2 and irradiation times of 10 and 60 s. Data were compared using in a general linear model analysis. RESULTS: Shrinkage measurements were the indication of conversion and conversion rate. Reduced intensity slowed down the rate of polymerization but did not reduce the conversion as long as an irradiation time of 60 s was employed. High-energy irradiation caused increased separation of the composite from the tooth structure. On the basis of obtaining optimal conversion and adaption, it was demonstrated that the irradiation time to be more effective than irradiation energy. SIGNIFICANCE: Light-cured composites require an understanding of their structure, pigmentation and irradiation parameters to obtain optimal performance. High intensity light-curing does not necessarily lead to optimal quality.

Sealing ability of eight resin bonding systems in a Class II restoration after mechanical fatiguing.

OBJECTIVE: The purpose of this in vitro study was to evaluate eight different adhesive systems to determine whether functional loading affects the marginal integrity of Class II restorations. METHODS: In 80 extracted upper human premolars, Class II cavities were prepared and restored with eight different commercially available adhesive resin restorative systems. The occlusal margins were located in enamel and the gingival margins in dentin. During immersion in a dye solution, half of the restored teeth were exposed to a load-cycling procedure, after which all the specimens were sectioned, and the extent of dye penetration was visually examined using a stereo microscope. The results were analyzed statistically using the Mann-Whitney U-test and Wilcoxons Rank test. RESULTS: Exposure of the restorations to load cycling significantly reduced the marginal integrity cervically. Perfect sealing was found practically at all occlusal margins. Significant differences (p < 0.05) were found in the cervical sealing quality of the various adhesive systems. SIGNIFICANCE: The results of this study show that functional loading damages the cervical marginal seal of adhesive Class II restorations. For many adhesive systems, the setting shrinkage stress alone was not able to damage the marginal integrity cervically. Therefore, mechanical fatiguing distinguishes the sealing quality of adhesive systems in a more expressive way. There is a substantial difference in sealing quality between the various resin restorative systems tested.

Light initiation of dental resins: dynamics of the polymerization.

Literature has shown that slowing down the curing rate of light-initiated resin composites by lowering the light intensity of the light source improved the integrity of the adhesive composite-cavity interface as a result of a more gradual contraction stress development. This study investigated how the curing rate could be controlled by varying the concentrations of the photoinitiator components in BisGMA-TEGDMA resin. Conversions and curing rates were evaluated by linear contraction experiments and Fourier transform infrared spectroscopy. Curing rates could be moderated significantly be reducing the concentrations of both photoinitiator and reducing agent without affecting the conversion, provided that the light exposure with a standard dental light curing unit lasts for 60 s.

[Mechanisms and theory of occlusal wear]. / Mechanismen en theorie van occlusale slijtage.

The various mechanisms which cause wear of occlusal surfaces of the teeth, erosion as caused by the food, direct contact wear, and surface fatigue are discussed from their theoretical bases. Special attention is paid to the implications for the oral environment. The ACTA wear machine, designed to simulate these mechanisms, as well as some of its results, are briefly discussed.

Early and long-term wear of conventional and resin-modified glass ionomers.

Various studies have shown that glass ionomers are susceptible to brittle fracture and acid conditions and that they undergo long-term changes in their mechanical properties. Little information is available on how brittleness, acid susceptibility, and long-term changes are reflected in the wear characteristics of glass ionomers. The purpose of this study was to evaluate long-term changes in conventional glass ionomers, metal-reinforced glass ionomers (including a cermet), and (light-curing) resinmodified glass ionomers by wear experiments simulating the wear process in occlusal contact-free areas. The wear tests were conducted periodically over a period of one year. In addition, wear was determined after one year at a pH of 5 or 6, for assessment of acid susceptibility, and at a condition as found in the occlusal contact areas. All materials showed high early-wear rates which decreased significantly during the one-year test period. This long-term process may be related to a slow progression of the acid-base reaction extending over several months. At each stage, the resinmodified glass ionomers wore significantly faster than the acid-base setting glass ionomers. Most of these materials were not affected at a pH of 6.0, while at a pH of 5.0 only the conventional and the metal-reinforced glass ionomers showed increased wear. Direct contacts with the antagonist led to a significant increase in wear in comparison with contact-free wear, probably as a result of sub-surface fatigue phenomena. In view of the unfavorable wear characteristics of the resin-modified glass ionomers and the high early wear of the conventional glass ionomers, including the metal-reinforced glass ionomers, it was concluded that none of these materials can yet be recommended for use in high-stress-bearing situations.

Influence of enzymes and plaque acids on in vitro wear of dental composites.

The purpose of this investigation was to test the effect of an enzymatic and an acidic medium on in vitro wear of dental resin composites and an amalgam. Wear was evaluated in two-body and three-body wear conditions. The third body was a food slurry either in water, an esterase solution or an acid solution at a composition and concentration as found in caries active plaque fluid. In the two-body tests the slurry was left out. Under three-body wear conditions neither the enzyme nor the acids showed any significant (P < 0.05) effect on wear. Enzyme inactivation from a large excess of food constituents in the slurry or the absence of an effect from surface diffusion rates of the acids resulted in the lack of an effect on wear. The two-body/acids wear rates were statistically (P < 0.05) lower than the two-body/water wear rates caused by increased lubrication from the acids between sliding surfaces. A significant (P < 0.05) increase in wear was found in the two-body/enzyme experiments, showing that the enzymatic activity can start directly at the outer surface of the composites.