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At least 343 records · Page 19Linked to original sources
PubMed1997

Effects of preparation designs and adhesive systems on retention of class II amalgam restorations.

PURPOSE: This study evaluated the effects of three preparation designs and the influence of an adhesive system in Class II amalgam restorations when a load was applied directly to the marginal ridge. MATERIAL AND METHODS: Seventy-two sound caries-free maxillary molars were divided into 6 groups of 12 teeth. In groups 1 and 4, the preparation had an extension through the occlusal groove, whereas the other four groups used a proximal slot (box-only) preparation. Groups 2 and 5 had facial and lingual retention grooves that extended from the gingival floor to the occlusal surface, and groups 3 and 6 had slots without grooves. Teeth in groups 1, 2, and 3 were restored with amalgam and groups 4, 5, and 6 were restored with resin bonded amalgam. The marginal ridges of the restorations were loaded at an angle of 13.5 degrees to the long axis of the tooth in an Instron testing machine until failure. RESULTS: Analysis of mean failure loads indicated that proximal slot preparations with retention grooves or occlusal extensions were statistically equivalent but significantly greater than proximal slots without grooves. The addition of an adhesive system improved fracture values for all three types of preparations. CONCLUSIONS: When proximal caries was diagnosed and no occlusal caries was evident, a proximal slot amalgam restoration combined with retention grooves and an adhesive system was the appropriate choice.

Analysis of Variance↗
PubMed1997

A review of esthetic alternatives for the restoration of anterior teeth.

PURPOSE: This article describes different options for the esthetic treatment of anterior teeth, starting with minimally invasive procedures, such as facial surface bleaching and bonding with composites. METHODS: The importance of metal ceramic restorations, porcelain shoulder techniques, and metal free ceramics are also emphasized. The options are carefully demonstrated to identify advantages and limitations of each technique.

Composite Resins↗
PubMed1997

Influence of dentinal adhesives and a prefabricated post on fracture resistance of silver amalgam cores.

PURPOSE: Failures of silver amalgam cores for endodontically treated teeth have been attributed to the use of posts. The use of adhesive agents has been reported to improve the strength of silver amalgam restorations. The purpose of this study was to test the effects of two adhesive agents on the fracture resistance of silver amalgam cores with and without a post. MATERIAL AND METHODS: Sixty mandibular molars were restored with the use of silver amalgam, with or without one of the adhesive agents and/or a tapered prefabricated post. A universal testing machine, with a constant load rate of 0.5 mm/minute, was used to determine the force in kilograms at failure. RESULTS: The use of either adhesive agent with silver amalgam significantly increased the force at failure, and neither adhesive agent was significantly better than the other. Silver amalgam with a post and without an adhesive agent had the least resistance to fracture. CONCLUSIONS: The results indicated that endodontically treated mandibular molars restored with silver amalgam are more resistant to fracture when an adhesive agent is used.

Analysis of Variance↗
PubMed1997

Effect of combinations of surface treatments and bonding agents on the bond strength of repaired composites.

STATEMENT OF PROBLEM: Enhancement of bond strength between new and old composite usually requires increasing the surface roughness to promote mechanical interlocking and coating of old composite with unfilled resin bonding agents to advance surface wetting and chemical bonding. PURPOSE: The purpose of this study was to evaluate the effect of combinations of surface treatments and bonding agents on the shear bond strength between new and old composite. MATERIAL AND METHODS: Six surface treatments, two bonding agents, and an untreated control comprised 18 different subgroups. RESULTS: The use of unfilled resin, alone or combined with silane, was the most effective procedure to enhance the shear bond strength of the repaired composite specimens, irrespective of the surface pretreatment processes. Silanation and unfilled resin slightly but not significantly improved the repair strength compared with unfilled resin alone. CONCLUSIONS: Different combinations of surface treatments and bonding agents affect shear bond strength differently. The highest shear bond strength values were achieved by grinding the surface with green Carborundum stone or sandblasting, whereas the lowest values were obtained with hydrofluoric acid as the surface treatment agent.

Analysis of Variance↗
PubMed1999

Effect of fluorosis on shear bond strength of glass ionomer-based restorative materials to dentin.

STATEMENT OF PROBLEM: Several studies have investigated the adhesion of glass ionomer-based restorative materials to nonfluorotic teeth, but there appears to be no information on the bond strength of these restorative materials to dentin in fluorotic teeth. PURPOSE: This study investigated the effect of dental fluorosis on the bond strength of Ketac-fil conventional glass ionomer cement, Vitremer resin-modified glass ionomer cement, and Dyract polyacid modified resin to dentin. MATERIAL AND METHODS: Ninety posterior teeth were classified according to the severity of fluorosis, by using the Thylstrup and Fejerskov index, TFI. The teeth were divided into 3 equal groups (TFI = 0,TFI = 1-3, TFI = 4+) of 30 teeth, which were again divided into 3 equal subgroups for testing each of the3 restorative materials. Occlusal surfaces of mounted teeth were ground flat to expose dentin. Cylindrical specimens (4 mm diameter and 4 mm high) of the restorative materials were bonded to the middle of the cleaned exposed dentin surfaces, according to the manufacturers' instructions. After storing the specimens in 100% humidity at 37 degrees C for 24 hours, shear bond strengths of the restorative materials were measured with an Instron testing machine at crosshead speed of 0.5 mm/min. RESULTS: Two-way analysis of variance and Tukey-B test revealed that Dyract had significantly higher shear bond strength to dentin than Ketac-fil or Vitremer cements, regardless of severity of fluorosis (P <.05). Furthermore, there was an inverse relationship between shear bond strength and the severity of fluorosis for each of the restorative materials. Cohesive mode of failure was most prevalent in nonfluorotic teeth (TFI = 0), especially with Ketac-fil cement, whereas Dyract cement had the greatest propensity for adhesive failure. CONCLUSION: Fluorosis reduces the shear bond strength of glass ionomer-based restorative materials to dentin.

Adhesiveness↗
PubMed1999

Rationalization of incisor shape: experimental-numerical analysis.

STATEMENT OF PROBLEM: Moving from the posterior segment in the anterior direction within the dental arch, the process of "incisivization" takes place. The occlusal table is gradually replaced by an incisal edge that has the function of cutting. PURPOSE: This study considers these genetically controlled changes by using strain gauge measurements and finite element analyses to rationalize the clinical and biologic advantages of incisal form. A direct clinical link in the common esthetic procedure of anterior veneering is expected. MATERIAL AND METHODS: Six maxillary incisors were mounted in a positioning device and equipped with 2 strain gauges bonded to the palatal surface: gauge 1 (G1) in the concavity and gauge 2 (G2) on the cingulum. A 50 N load was applied on the palatal side of the incisal edge, perpendicular to the long axis of the tooth. Displacement of the load tip and the palatal strain were recorded after successively removing one third, two thirds, and the total thickness of the facial enamel. The same experiment was reproduced with the finite element method (FEM). Four additional experimental designs were tested with the FEM by simulating the progressive thinning and elimination of palatal enamel and a thickened palatal lobe. Surface tangential stresses and local strain in the area corresponding to gauges 1 and 2 were calculated from the postprocessing files. RESULTS: The FEM was validated by experimental results considering both displacement of the load tip ( approximately 120 +/- 30 microm) and tangential surface strain at G1/G2. Recorded strains were always higher in the concavity when compared with the cingulum; high tensile strains were recorded at G1 after the total removal of the facial enamel. The entire facial surface was submitted to compressive forces. Subsequent compressive stresses were higher ( approximately 150 MPa) when facial enamel was thin or when the palatal enamel was removed. However, their absolute value never reached the elevated and potentially harmful tensile stresses measured in the palatal concavity, especially in the absence of facial enamel (272 MPa). Multiple experimental cracks were generated in the remaining palatal enamel as a consequence of stress redistribution. However, smooth and convex surfaces with local enamel bulk such as the cingulum, the marginal ridges, and the facial cervical third of the anatomic crown showed the lowest stress level. The optimal configuration with regard to the stress pattern was given by the modified natural tooth that exhibited thick palatal enamel and a mostly convex palatal surface. CONCLUSIONS: Palatal concavity that provides the incisor with its sharp incisal edge and cutting ability proved to be an area of stress concentration. This shortcoming can be compensated by specific areas that feature thick enamel such as the cingulum and the marginal ridges. When enamel is worn or removed from the facial surface, its replacement should be carried out by using materials with properties similar to enamel to restore the original biomechanical behavior of the tooth.

Compliance↗
PubMed2004

An interdisciplinary approach for restoring function and esthetics in a patient with amelogenesis imperfecta and malocclusion: a clinical report.

This clinical report describes an interdisciplinary approach for the coordinated treatment of a patient diagnosed with amelogenesis imperfecta and malocclusion. The patient's functional and esthetic expectations were successfully met with interdisciplinary treatments, including orthodontics, porcelain laminate veneers, metal-ceramic fixed partial dentures, and direct composite restorations.

Adult↗
PubMed1994

Effect of restorative procedures on the strength of endodontically treated molars.

Endodontically treated molar teeth are considered susceptible to fracture because of loss of tooth bulk. This study evaluated the significance of retaining intact marginal ridges and selective cusp coverage in preserving tooth stiffness during restoration. Strain gauges were bonded to four cusps of 36 intact extracted human lower molars. Teeth were loaded mesially and distally in a closed-loop servohydraulic system to measure stiffness. Endodontic access was followed by mesio-occlusal or mesio-occluso-distal preparation. Teeth were restored with either amalgam (no overlay), amalgam overlay, or gold overlay with partial or complete cusp coverage. Relative stiffness was calculated for all test conditions. Preserving a marginal ridge in molars did not fully conserve the strength of adjacent cusps; selective cusp coverage reinforced only the capped cusps; full occlusal coverage with gold or amalgam strengthened all cusps, but gold did so more consistently. It is more important to cover cusps than to preserve tooth structure (including a marginal ridge) in endodontically treated molar teeth.

Analysis of Variance↗
PubMed1992

Strength of roots before and after endodontic treatment and restoration.

The resistance to fracture of mandibular premolar roots before and after endodontic and restorative procedures was tested. Seven treatment groups were evaluated. A Universal testing machine was used to apply vertical and lateral (45-degree) forces. Overall, the untreated roots showed the highest resistance to fracture. Factors of importance to prevent fracture were found to be (a) the amount of remaining tooth structure; (b) strength of post and core; and (c) bonding between core material and dentin. These factors suggest that a composite core following the use of EDTA to remove the smear layer may be a successful treatment when sufficient tooth structure remains.

Bicuspid↗
PubMed1991

Resistance to fracture of endodontically treated premolars restored with glass ionomer cement or acid etch composite resin.

MOD cavity preparations in 64 endodontically treated premolars were restored using four different methods. Copper rings were filled with commercial hard-setting cement and the teeth were placed into the cement up to the level of the cementoenamel junction. The teeth were grouped according to restorative method, mounted in an Instrom T.T. machine, and the buccal walls subjected to a slowly increasing compressive force until fracture occurred. The force of fracture of the walls of each tooth was recorded and the results in the various groups compared. All teeth fractured in a similar manner irrespective of the restorative method used. The resistance to fracture of the teeth was the same when they were restored with glass ionomer cement as a base over which an amalgam or composite resin was placed or with acid-etched resin. When the entire cavities were filled with glass ionomer cement the resistance to fracture of the teeth decreased significantly compared with the acid etch resin technique.

Acid Etching, Dental↗
PubMed2001

Bonding of restorative and veneering composite resin to some polymeric composites.

OBJECTIVES: The aim of the study was to determine bond strengths between different fiber-reinforced composites (FRC) and visible light-curing composites (VCR). METHODS: A total of 180 specimens comprising eight types of FRC substrates and four types of VCR substrates were fabricated and divided in 36 different groups. Substrate surfaces were ground with 1200-grit silicon carbide paper before adding a repair composite (RC). The shear bond strength was determined for specimens without the use of an intermediate resin (IMR), for specimens with the IMR and for specimens with the IMR and thermocycling. Surface roughness of the substrate was measured with a profilometer before adding RC on the substrate. RESULTS: The univariate analyses of variance (ANOVA) revealed significant differences (p<0.001) related to the type of the substrate, the IMR and the thermocycling. The highest shear bond strength for FRC substrates was achieved with StickNet/Z-100 combination and for VCR substrates with Sinfony/Sinfony combination. Surface roughness (R(a)) varied from 0.10 microm of Targis VCR to 0.50 microm for Vectris Pontic FRC. SIGNIFICANCE: Surface roughness seemed not to influence shear bond strengths of RC to FRC and VCR substrates. High shear bond strengths were related to specific materials and IMRs used. In some cases materials performed better without the use of the accessory IMR.

Analysis of Variance↗
PubMed2001

Mode of failure in the dentin-adhesive resin-resin composite bonded joint as determined by strength-based (muTBS) and fracture-based (CNSB) mechanical testing.

OBJECTIVE: To determine the failure mode between dentin-adhesive resin-resin composite bonded joint produced with a chevron-notch short-bar (CNSB) and microtensile test methods. METHODS: Forty teeth were randomly selected for microtensile and forty for CNSB specimen fabrication and stored in 0.5% chloramine T at 37 degrees C until respective static load to failure testing at 30 and 180days. Failure modes were categorized by SEM and tested with Fisher's exact test. Within respective mechanical testing methods the probability of failure curve distributions being significantly different were analyzed by the Wald chi-square statistic. RESULTS: The characteristic fracture toughness at 30- and 180-day storage was 0.82 and 0.87MPam(1/2), while the Weibull Modulus (m) for the failure distributions, was 4.60 and 4.56, respectively. No significant difference was demonstrated in the failure distributions between these groups (p=0.45). The characteristic tensile strength (muTBS(o)) at 30- and 180-day storage was 52.53 and 14.71MPa with an m of 3.04 and 1.56, respectively. Failure distributions for muTBS groups were significantly different (p<0.001). K(IvM) failure modes, regardless of storage time, were within the adhesive joint with 30-day debonds primarily through the top region of the hybrid layer (THL) and after 180-days involving the bottom of the hybrid layer (BHL). The 30-day muTBS group demonstrated a propensity to debond in dentin or resin composite substrates but after 180-days storage debonds again involved the BHL. SIGNIFICANCE: The weak links in the dentin-adhesive resin-resin composite bonded joint may be the interphase regions between the THL and the adhesive resin and the BHL and dentin.

Adhesiveness↗
PubMed2001

Polymerization contraction stress in light-cured packable composite resins.

OBJECTIVE: Determination of the polymerization contraction stress of packable composites (ALERT, Surefil, Solitaire, Solitaire 2) and a packable ORMOCER material (Definite) in comparison with a conventional hybrid composite (Tetric Ceram). METHODS: Contraction force generated by the test materials (10 replications each) was measured by polymerizing the composites filled in a plastic tray between two aluminum attachments mounted in a Stress-Strain-Analyzer testing machine (specimen size: 4x4x2 mm, C-factor=0.33). Contraction force was recorded for 300s under a standard exposure condition (40s, 800mW/cm(2)). Maximum contraction stress (MPa), force rate (N/s), relative force rate (%/s) of each material were statistically analyzed by ANOVA (alpha=0.05) and post-hoc Tukey's test. RESULTS: Maximum contraction stresses of the packable materials were 4.60 +/- 0.32MPa (ALERT), 4.16 +/- 0.18MPa (Definite), 3.36 +/- 0.08MPa (Solitaire 2), 3.33 +/- 0.23MPa (Solitaire) and 3.13 +/- 0.18MPa (Surefil), which were significantly higher than that of Tetric Ceram (2.51 +/- 0.14MPa). Tetric Ceram exhibited the significantly lowest force rate. Force/time curves were S-shaped. Solitaire especially showed a longer pre-gelation phase before contraction force was recorded. SIGNIFICANCE: High contraction stress and rapid contraction force development can lead to failure of bond to tooth structure. This study suggested that, packable composite resins are less capable of reducing the contraction stress during the early setting stage, thus not superior in maintaining the bond with cavity walls to conventional hybrid composite Tetric Ceram.

Analysis of Variance↗
PubMed2001

Suitability of a shear punch test for dental restorative materials.

OBJECTIVE: The aim of the study was to evaluate the suitability of a shear punch test for determining the mechanical properties of dental restorative materials. The method was evaluated by measuring and comparing the shear punch strength of seven different restorative materials, that is amalgam, composite resin, compomer, composite containing pre-reacted glass ionomer filler, resin modified glass ionomer, glass ionomer and polycarboxylate cement. METHOD: The effects of specimen restraining conditions, specimen thickness and test speed on the shear punch strength were evaluated using polycarboxylate cement and two different equipment set-ups. Using the preferred testing regime as determined in the preliminary experiments, the shear punch strength of seven different materials were measured and compared. Twenty disc specimens, 0.5mm thick and 10mm diameter, were prepared for each material, restrained within the test equipment and tested at a speed of 1.0mm/min. RESULTS: The shear punch strength increased as the torque used for restraining a specimen was increased. There was no difference in shear punch strength for specimens of different thickness. The greatest shear punch strength was obtained at the test speed of 1.0mm/min. The shear punch strength values decreased in the order composite>composite containing pre-reacted glass ionomer filler>amalgam>compomer>resin-modified glass ionomer>glass ionomer>polycarboxylate. A difference in the shear punch strength for seven different kinds of restorative materials clearly emerged. Specimen fracture occurred by circumferential cracking for the shear-punch test. However, for some glass ionomer and amalgam specimens radial cracking was also observed. SIGNIFICANCE: This study suggests that the simple test described is suitable for standardization purposes.

Analysis of Variance↗
PubMed2002

Effect of adhesive layer properties on stress distribution in composite restorations--a 3D finite element analysis.

OBJECTIVES: Teeth, adhesively restored with resin-based materials, were modeled by 3D-finite elements analysis that showed a premature failure during polymerization shrinkage and occlusal loading. METHODS: Simulation of Class II MOD composite restorations with a resin bonding system revealed a complex biomechanical behavior arising from the simultaneous effects of polymerization shrinkage, composite stiffness and adhesive interface strain. Due to a polymerization contraction, shrinkage stress increases with the rigidity of the composites utilised in the restoration, while the cusp movements under occlusal loading are inversely proportional to the rigidity of the composites. The adhesive layer's strain also plays a relevant role in the attenuation of the polymerization and occlusal loading stresses. RESULTS: The choice of an appropriately compliant adhesive layer, able to partially absorb the composite deformation, limits the intensity of the stress transmitted to the remaining natural tooth tissues. For adhesives and composites of different rigidities, FEM analysis allows the determination of the optimal adhesive layer thickness leading to maximum stress release while preserving the interface integrity. Application of a thin layer of a more flexible adhesive (lower elastic modulus) leads to the same stress relief as thick layers of less flexible adhesive (higher elastic modulus).

Composite Resins↗
PubMed2003

Modeling of the viscoelastic behavior of dental light-activated resin composites during curing.

OBJECTIVE: Three models consisting of springs and dashpots were investigated to describe the viscoelastic behavior of a commercial light-activated restorative composite during curing. METHODS: Stress-strain data on Z100 were recorded by means of a dynamic test method performed on a universal testing machine. The model was tested by matching its response to experimental data and the material parameters, E (Young's modulus) and eta (viscosity), associated with the model were calculated. RESULTS: The universal testing machine generated reliable stress-strain data on the fast curing, light-activated resin composite during curing. The high polymerization rate of Z100 had a negative effect on the viscous flow capability of the material. A predictive model of the viscoelastic behavior of Z100 during curing was carried out, using the Maxwell model for the initial 3 min in the curing process and the Kelvin model for the remainder of the process. SIGNIFICANCE: Dental researchers analyzing shrinkage stress problems by mathematical modeling can obtain a good quantitative estimate of the shrinkage stress development of Z100 before the restoration is actually made.

Composite Resins↗
PubMed2003

Effect of storage time on microtensile strength of polyacid-modified resin composites.

OBJECTIVE: The purpose of this study was to determine the cohesive microtensile strength of four polyacid-modified resin composites (PAMRC: Dyract, Dyract AP, Freedom and F2000) after 24h and 6 months of storage in water using the microtensile technique. METHODS: Blocks measuring 1.5 cm x 1.5 cm x 1.0 cm were constructed incrementally for each material using a silicone matrix. The blocks were stored in distilled water at 37 degrees C for 24 h and were then serially sectioned in both x and y directions to obtain several beams measuring 1.0 cm x 1.0 mm x 1.0 mm. Each beam was gently trimmed from two sides with ultra-fine diamond burs to reduce the cross-sectional area to a 'neck' of approximately 0.4mm(2) located in the middle of their length. The beams (18-22 per material) were randomly divided and tested in tension either after 24 h or after 6 months of storage in water at 37 degrees C in a Vitrodyne testing machine at 0.6 mm/min. RESULTS: Mean microtensile strengths (MPa) at 24 h were: 48.7+/-13.8 for Dyract AP; 36.5+/-14.1 for Dyract; 38.2+/-14.5 for Freedom and 48.6+/-7.2 for F2000. There was no statistically significant difference among the materials (p>0.05). At 6 months, only Dyract AP showed significant increase in microtensile strength (p<0.05) while the other materials showed no differences in microtensile strength with time (p>0.05). SIGNIFICANCE: The results indicate that storage in water for 6 months caused no reduction of the microtensile strength of PAMRC materials.

Analysis of Variance↗