Surface properties of dental nanocomposites after finishing with rigid rotary instruments.

This study evaluated the surface characteristics of three nanoparticle resin composites (Z350, Heritage 7 Nanohybrid, and Ice) using profilometry and scanning electronic microscopy (SEM) after subjecting them to sequential finishing procedures using rigid rotary instruments. Fifteen 8 mm × 8 mm × 2 mm specimens were fabricated for each tested composite and subjected to one of the following finishing regimens: finishing with green stones followed by white stones, finishing with 45-µm diamond followed by 15-µm diamond, finishing with a 12-fluted carbide followed by a 20-fluted carbide. After finishing, the surfaces were subjected to profilometric testing. Eight parallel tracings were used to scan the finished surface of each specimen. For each recorded profile, the average roughness (Ra) and extreme value descriptor (Rmax) were recorded. On completion of the profilometric testing, two specimens from each group were randomly selected for qualitative assessment by SEM. Profilometric data was analyzed using a one-way analysis of variance and post hoc Scheffe tests. The results demonstrated that the three control groups of the tested nanocomposites behaved as a coherent group with respect to surface roughness. With the exception of the nanohybrid Heritage 7 finished with the carbide instruments, all composites showed an increase in surface roughness. The Z350 and Ice finished with the carbide finishing instruments showed no statistically significant increase in Ra, but both of these composites showed significantly rougher surfaces when finished with diamonds compared with controls. The nanohybrids Ice and Heritage 7 demonstrated significantly higher roughness in terms of Rmax when finished with stones. The SEM correlated well with roughness measurements. The conclusion may be drawn that diamonds and stones produce unacceptable surfaces in terms of roughness on the tested nanocomposites whereas finishing carbides produce acceptable surfaces.

Surface Properties of Dental Nanocomposites After Finishing With Rigid Rotary Instruments

This study evaluated the surface characteristics of three nanoparticle resin composites (Z350, Heritage 7 Nanohybrid, and Ice) using profilometry and scanning electronic microscopy (SEM) after subjecting them to sequential finishing procedures using rigid rotary instruments. Fifteen 8 mm·8mm·2mmspecimens were fabricated for each tested composite and subjected to one of the following finishing regimens: finishing with green stones followed by white stones, finishing with 45-lm diamond followed by 15-lm diamond, finishing with a 12-fluted carbide followed by a 20-fluted carbide. After finishing, the surfaces were subjected to profilometric testing. Eight parallel tracings were used to scan the finished surface of each specimen. For each recorded profile, the average roughness (Ra ) and extreme value descriptor (Rmax ) were recorded. On completion of the profilometric testing, two specimens from each group were randomly selected for qualitative assessment by SEM. Profilometric data was analyzed using aone-way analysis of variance and post hoc Scheffe tests. The results demonstrated that the three control groups of the tested nanocomposites behaved as a coherent group with respect to surface roughness. With the exception of the nanohybrid Heritage 7 finished with the carbide instruments, all composites showed an increase in surface roughness. The Z350 and Ice finished with the carbide finishing instruments showed no statistically significant increase in Ra , but both of these composites showed significantly rougher surfaces when finished with diamonds compared with controls. The nanohybrids Ice and Heritage 7 demonstrated significantly higher roughness in terms of Rmax when finished with stones. The SEM correlated well with roughness measurements. The conclusion may be drawn that diamonds and stones produce unacceptable surfaces in terms of roughness on the tested nanocomposites whereas finishing carbides produce acceptable surfaces.

Effect of reduced exposure times on the microhardness of nanocomposites polymerized by QTH and second-generation LED curing lights.

This study investigated the effectiveness of polymerization of various curing regimes on five nanocomposite restorative materials­Z350, Grandio, Clearfil Majesty Esthetic, Ice and Tetric EvoCeram­by utilizing microhardness measurements. Five (n=5) disc-shaped specimens of each material were subjected to one of three curing regimes: curing with a halogen light for 20 seconds, curing with an LED light for 20 seconds and curing with an LED light for 10 seconds. Immediately following curing, hardness measurements were made with a Vickers indenter at five different locations on both the top and bottom surfaces of each disc. The mean for each surface was calculated. Data were analyzed using a one-way ANOVA and post-hoc Tukey HSD (α=0.05). The results demonstrated that among the Z350 composite samples, top and bottom microhardness values showed no statistical differences when cured with the halogen 20 second or LED 20 second regimes (p>0.05). Comparison of the top and bottom values of discs cured with the LED 10 second regime demonstrated significant differences (p<0.0001). Grandio samples cured with the halogen 20 second regime showed no statistical differences between top and bottom microhardness values (p>0.05); however, the bottom values of Grandio discs cured with the LED 20 second and 10 second regimes were significantly lower when compared with top surface values (p=0.001 and p<0.0001, respectively). Clearfil Majesty Esthetic, Ice and Tetric Evo Ceram samples cured with the halogen 20 second regime produced significantly lower bottom microhardness values, while both LED regimes produced top and bottom surfaces that were statistically comparable. The conclusion may be drawn that LED 10 second curing regimes were insufficient to cure Z350 and Grandio, while they were adequate for curing Clearfil Majesty Esthetic, Ice and Tetric EvoCeram.

Effect of Reduced Exposure Times on the Microhardness of Nanocomposites Polymerized by QTH and Second-generation LED Curing Lights

This study investigated the effectiveness of polymerization of various curing regimes on five nanocomposite restorative materials­Z350, Grandio, Clearfil Majesty Esthetic, Ice and Tetric EvoCeram­by utilizingmicrohardnessmeasurements. Five (n=5) disc-shaped specimens of each material were subjected to one of three curing regimes: curing with a halogen light for 20 seconds, curing with an LED light for 20 seconds and curing with an LED light for 10 seconds. Immediately following curing, hardness measurements were made with a Vickers indenter at five different locations on both the top and bottom surfaces of each disc. The mean for each surface was calculated. Data were analyzed using a one-way ANOVA and post-hoc Tukey HSD (α=0.05). The results demonstrated that among the Z350 composite samples, top and bottom microhardness values showed no statistical differences when cured with the halogen 20 second or LED 20 second regimes (p>0.05). Comparison of the top and bottom values of discs cured with the LED 10 second regime demonstrated significant differences (p<0.0001). Grandio samples cured with the halogen 20 second regime showed no statistical differences between top and bottom microhardness values (p>0.05); however, the bottom values of Grandio discs cured with the LED 20 second and 10 second regimes were significantly lowerwhen comparedwith top surface values (p=0.001 and p<0.0001, respectively). Clearfil Majesty Esthetic, Ice and Tetric EvoCeram samples cured with the halogen 20 second regime produced significantly lower bottom microhardness values, while both LED regimes produced top and bottom surfaces that were statistically comparable. The conclusion may be drawn that LED 10 second curing regimes were insufficient to cure Z350 and Grandio, while they were adequate for curing Clearfil Majesty Esthetic, Ice and Tetric EvoCeram.

The effect of thermocycling on the fracture toughness and hardness of core buildup materials.

STATEMENT OF PROBLEM: Thermocycling has been shown to cause surface degradation of many dental materials, but its effect on the fracture toughness and hardness of direct core buildup materials is unknown. PURPOSE: This study was designed to determine the effect of thermocycling on the fracture toughness and hardness of 5 core buildup materials. MATERIAL AND METHODS: Fifteen specimens were prepared from each of the following materials: Fluorocore, VariGlass VLC, Valiant PhD, Vitremer, and Chelon-Silver. American Standard for Testing Materials guidelines for single-edge notch, bar-shaped specimens were used. Ten specimens of each material were thermocycled for 2000 cycles; the other 5 specimens were not thermocycled. All specimens were subjected to 3-point bending in a universal testing machine. The load at fracture was recorded, and the fracture toughness (K(IC)) was calculated. Barcol hardness values were also determined. Data were analyzed with 1-way analysis of variance and compared with the Tukey multiple range test (P<.05). Pearson's correlation coefficient was also calculated to measure the association between fracture toughness and hardness. RESULTS: Fluorocore had the highest thermocycled mean K(IC) and Valiant PhD the highest non-thermocycled K(IC). Chelon-Silver demonstrated the lowest mean K(IC) both before and after thermocycling. One-way analysis of variance demonstrated significant differences between conditions, and the Tukey test showed significant differences (P<.05) between materials for both conditions. Most specimens also showed significant hardness differences between conditions. Pearson's correlation coefficient indicated only a mild-to-moderate correlation between hardness and fracture toughness. CONCLUSION: Within the limitations of this study, the thermocycling process negatively affected the fracture toughness and hardness of the core buildup materials tested.

Infection and exposure control in North American dental schools.

The results of a survey sent to all U.S. and Canadian dental schools clearly indicate that several substantial changes have occurred in infection control and exposure control in the past fifteen to twenty years. Predominant among these are that the responsibility for instrument preparation and sterilization in most schools has passed from the student to trained staff, the routine practice of universal precautions has eliminated the need to treat patients known to carry bloodborne diseases in a special area, and pre-admission and enrollment vaccination and health screening requirements have changed significantly. Other important changes result from the fact that the majority of U.S. schools responding to the survey are now, to a great extent, in compliance with the OSHA Bloodborne Pathogens Standard or equivalent requirements.

The qualitative effects of various types of hygiene instrumentation on commercially pure titanium and titanium alloy implant abutments: an in vitro and scanning electron microscope study.

STATEMENT OF PROBLEM: Implant survival depends on proper and timely oral hygiene maintenance, and a wide variety of oral prophylaxis procedures have been recommended and used on implant abutments. PURPOSE: This in vitro study compared the surface quality of both commercially pure titanium and titanium-alloy implant abutments, subjected to various hygiene methods and instruments with a standardized, clinically applicable scaling force. MATERIAL AND METHODS: Commercially pure titanium and titanium-alloy abutments were exposed to five oral hygiene methods; a gold-alloy-tipped scaler, a high-grade resin scaler, a graphite-reinforced scaler, an air-powder abrasive system, and a rubber cup with tin oxide slurry. A customized test device that simulated the scaling motion and allowed the application of a standard load at the tip of the scaler was used. Scanning electron photomicrographs (x200) of the pretreatment and treated surfaces were obtained and compared qualitatively. RESULTS AND CONCLUSIONS: No significant surface alteration was produced by the air abrasive system. All other hygiene methods either created significant surface alterations, left residual particles on the abutment surfaces, or both.

Fracture toughness and load relaxation of dentin bonding resin systems.

OBJECTIVES: The fracture toughness (KIC) and load relaxation of four dentin bonding resins were determined to characterize some of the mechanical properties of these materials after polymerization. METHODS: A total of 40 single-edge notch bar specimens were fabricated, 10 each of four commercially available brands, and subjected to three-point bending until fracture, as described in ASTM Standard E399-83 (1991a). The critical stress intensification factor, KIC, was derived for each specimen and compared by analysis of variance and Scheffé's multiple comparisons test (p < 0.01). To study the load relaxation characteristics, five rectangular specimens (without notches) of each brand were subjected to three-point loading until a predetermined limiting load value was reached. The test load was allowed to relax for 4 min, after which the specimen was unloaded to the zero load condition, and the load was allowed to build up on its own accord for 3 min. Load relaxation values were measured from the chart, and the mean percent load drop was calculated. The load relaxation data were compared using analysis of variance and Scheffé's multiple comparisons test (p < 0.05). RESULTS: The fracture toughness (KIC) values of the four adhesive resins studied in this investigation ranged from 0.37-0.94 MPa.m0.5 and were statistically different from each other (p < 0.001). The load relaxation values were found to be greatest within the first 0.5 min, with the total load relaxation of the four bonding agents ranging from 16%-30%. Two of the materials studied showed significantly different short-term load relaxation behavior than the other two resins (p < 0.05). SIGNIFICANCE: Bonding agents can be implicated as one of the factors that weaken the interface between the dentin and the composite restorative material. These materials are capable of a rapid short-term response, demonstrating significant load relaxation in the first 0.5 min after loading.

Rechargeability of fluoride releasing pit and fissure sealants and restorative resin composites.

PURPOSE: To evaluate the effect of exposure of 1.23% acidulated phosphate fluoride gel on fluoride release from fluoride releasing pit and fissure sealants and restorative resin composites. MATERIALS AND METHODS: Specimens of four fluoride releasing pit and fissure sealants (Helioseal F, Ultraseal XT, Seal Rite-Low Viscosity and Seal Rite-Regular Viscosity) and two fluoride releasing restorative resin composites (Tetric and Heliomolar Radiopaque) were prepared using a Teflon mold. The specimens were divided into two groups. The experimental group was exposed to 1.23% acidulated phosphate fluoride gel and the control group was exposed to 1.23% acidulated phosphate gel without fluoride. The specimens were stored in deionized water and the fluoride concentration of the solution was measured every 24 hours. On day 7, the discs were exposed to the respective gel for 4 minutes and then rinsed in a continuous stream of deionized water for 30 seconds. The fluoride concentration was then measured for another 7 days. RESULTS: There was a significant increase after the fluoride gel treatment in the amount of fluoride released from all of the materials studied. When the cumulative amount of fluoride released was evaluated, Tetric, Heliomolar radiopaque, Helioseal F, and Ultraseal XT released significantly (P < 0.01) more fluoride than the respective control groups. There was no significant difference between groups from day 8 to day 14 for Seal Rite-Regular Viscosity and Seal Rite-Low Viscosity.

The fracture toughness of various core materials.

PURPOSE: This study determined the fracture toughness of four core buildup materials. MATERIALS AND METHODS: Single-edge notch, bar-shaped specimens conforming to the American Society for Testing Materials standard E-399 were fabricated for a high copper amalgam alloy, two composite resins, and a glass ionomer buildup material. The specimens were stored in air for 1 week and then tested in three-point bending mode with an Instron Universal Testing Machine (Instron Corporation, Canton, MA). RESULTS: Fracture toughness values obtained were as follows: Fluorocore (composite resin; Caulk, Milford, DE), 1.54 MN.m-1.5; Ti-Core (composite resin and titanium; Essential Dental Systems, New York, NY), 1.34 MN.m-1.5; Valiant Ph.D. (amalgam; Caulk), 1.29 MN.m-1.5; and Coreshade Glass Ionomer Base Cement (Shofu Inc, Kyota, Japan), 0.55 MN.m-1.5. CONCLUSIONS: Glass ionomer materials are probably unsuitable as core buildup materials because of their relatively low fracture toughness. Fluorocore, Ti-Core, and amalgam all had fracture toughness values significantly greater than the glass ionomer (P < .01).

Fracture toughness of high alumina core dental ceramics: the effect of water and artificial saliva.

The fracture toughnesses of two high alumina core ceramics were determined by using the single edge notched specimen method. Measurements were made in air, water, and artificial saliva. Fracture toughnesses of 1.89 and 1.75 MPa.m1/2 were obtained for Cerestore and Vitadur N samples, respectively, tested in air. Values obtained from Vitadur N samples that were tested in deionized water were significantly lower than those that were measured in air. Values for samples of both ceramics that were tested in artificial saliva were not significantly different from those that were tested in air. The fracture mode was a combination of intergranular and transgranular for Cerestore and predominantly transgranular for Vitadur N.

Composite microfiller content and its effect on fracture toughness and diametral tensile strength.

Previous studies have examined the relationship between total filler content in hybrid restorative composites and some of their mechanical properties. This investigation evaluated the effect of varying the amount of microfiller in an experimental hybrid composite on fracture toughness (single edge-notch technique) and diametral tensile strength. The microfiller content in the experimental hybrid composite was varied from 0-44 wt% for seven specimen groups, while the total filler content ranged from 77-84 wt%. It was found that 9 wt% microfiller loading produced the highest mean fracture toughness (1.33 MPa.m(1/2)) and 44 wt% loading produced the lowest mean value (0.80 MPa.m(1/2)). Only the 9 wt% microfiller content group differed significantly in fracture toughness from the other specimen groups. The diametral tensile strength displayed only small differences for the range of microfiller content studied with mean values ranging from 42.1-49.6 MPa. Additional research on the viscoelastic properties of these heavily filled hybrid composites may provide some insight into the differences for the fracture toughness and diametral tensile strength results.

Shear, torsional, and tensile bond strengths of ceramic brackets using three adhesive filler concentrations.

The effect of changes in adhesive filler concentration on the shear, torsional, and tensile bond strength of a chemical, a mechanical, and a chemical/mechanical retained ceramic bracket was evaluated. Two hundred ten bovine teeth were bonded with one of three ceramic brackets using a 30%, 55%, or 80% filled adhesive. The brackets were debonded with a shear, torsional, or tensile force to test the bond strength and the site of bond failure. No significant difference was found in the shear, torsional, or tensile bond strength of each ceramic bracket type in relation to changes in the adhesive filler concentration. However, there was a trend toward increased bond strength with increasing filler concentration. Combining the data according to adhesive type revealed that the 80% filled adhesive displayed a significantly greater shear bond strength than the 30% or 55% filled adhesive and a greater torsional bond strength than the 30% filled adhesive. This supports the hypothesis of increased bond strength with increased adhesive filler concentration. The mechanically retained ceramic bracket showed greater shear bond strength and maximum shear bond strength in torsion than the chemical or chemical/mechanical retained ceramic bracket. The tensile bond strength of the mechanically retained ceramic bracket was similar to that of metal brackets reported in other studies, and the failure site was at the bracket-adhesive interface.

Infection control in North American dental schools.

A questionnaire concerning infection control issues was sent to all North American dental schools in 1987. The results were compared with a similar survey conducted by the same authors in 1982. The purposes of the survey were to identify changes that have occurred in dental school infection control policies in the past six to seven years, and to study strengths and weaknesses of current policies. The results of the survey indicate a much greater emphasis on instrument sterilization and the use of barriers during dental treatment than in 1982. Compliance with the policy is not always satisfactory, however. It also shows some inconsistency and confusion in areas dealing with hepatitis B and HIV carrier patients and dental school personnel. Several respondents included written infection control protocols with the questionnaire. Information gained from the survey and the enclosures were used to develop guidelines to help schools improve and update their infection control policies.

Accuracy of impression materials for complete-arch fixed partial dentures.

The accuracy of 12 impression materials of six different types were studied by using complete-arch FPD impressions. Sixty impressions were made of a Columbia dentoform maxillary model with complete cast crown abutment preparations on the canines and the second molars. A one-piece casting was constructed by connecting the four individual castings made for the four abutment teeth. The master prosthesis was seated on the stone casts produced from the impressions. The marginal adaptation on the four abutments was then evaluated with a travelling microscope. The individual marginal adaptation of the four castings on the abutments was also examined after sectioning the four joints. The following conclusions were drawn. 1. The polyethers produced the most accurate complete-arch replicas. The second most accurate were the vinyl polysiloxanes, followed by the polysulfides and the irreversible-reversible hydrocolloids. The least accurate were the reversible hydrocolloids and the irreversible hydrocolloids. 2. The polyether impression materials exhibited the most consistent accuracy for a master cast to fabricate a complete-arch FPD.

The fracture toughness of repaired composite.

The fracture toughness (K'IC) at the interface formed between a composite substrate and more recently placed composite has been measured to determine the strength of the repair. The substrate material was 24 h old at the time of the repair and the fracture toughness of the repair was measured 24 h later. Five composite products were selected for repair by using either that particular product or one of the others. Repairs were made to clean fractured surfaces, and these after contamination with artificial saliva. The fracture toughness factor of any repair was significantly less than that for the respective control. The effect of surface contamination proved highly significant and reduced the fracture toughness. An interaction existed between adherend (substrate) and adhesive (addition) materials. Compatibility between these for matrix and initiation chemistries did not appear to be significant.

Comparison of accuracy of multiunit one-piece castings.

An investigation was conducted to evaluate the accuracy of one-piece castings of FPDs consisting of three, four, and five units with a ceramometal alloy cast in a large circular ring. A three-piece aluminum mold with stainless steel dies simulating the various lengths of the FPDs was used. A total of 18 castings, six castings for each FPD, were fabricated. Marginal discrepancies of the castings on the dies and the length of the castings were compared before and after sectioning the castings at the connectors. The following conclusions were drawn from the study. Seating of the castings improved approximately 50% after sectioning, which indicates that the castings were distorted. The distortion was a three-dimensional phenomenon, with the greatest discrepancy on the mesiogingival surface of the anterior retainer and on the distolingual surface of the posterior retainer. The distortion was least for the three-unit FPDs and greatest for the five-unit FPDs. The lingual-facial diameter of the castings at the gingival axial line angle was significantly larger than the dies in most cases. The mesiodistal diameter of the castings at the gingival axial line angle was smaller than that of the dies but was only significant with the three-unit FPDs. Although the castings were slightly oversized or undersized, the primary reason the castings did not seat was warpage.