Influence of dowel type on push-out bond strength to regional root canal dentin.

PURPOSE: To compare the laboratory bond strengths of three different types of fiber-reinforced composite dowel systems in three different locations of prepared root canal dentin. METHODS: 60 human extracted intact upper central incisors were selected. The coronal aspect of each tooth was removed, and the remaining root received endodontic therapy. The roots were divided into three experimental groups (n = 20). Roots were restored with one of the following dowel systems according to the manufacturers' instructions: carbon fiber (C-Posts), quartz (Aestheti-Plus), glass fiber (FibreKor). A single bond adhesive (OptiBond Solo Plus) was applied to the walls of the dowel spaces, excess carefully removed with paper points, and then light cured for 10 seconds. A dual-polymerizing resin luting agent (Variolink II) was mixed and then placed in the dowel spaces using a lentulo spiral instrument. The roots were placed in light-protected cylinders; then the light source was placed directly on the flat cervical tooth surfaces and the cement was polymerized. Specimens were stored in light-proof boxes for 24 hours. Each root was cut horizontally, and three 1 mm-thick root segments (one apical, one middle, and one cervical) were prepared. Using a push-out test, the bond strength between dowel and dentin was measured using a universal testing machine. The data were analyzed with 2-way analysis of variance and Tukey's Honestly Significant Difference (HSD) test (alpha = 0.05). RESULTS: Dowel type and regional root canal dentin resulted in significant differences for push-out bond strength (P < 0.001). Glass fiber dowels (FibreKor) had significantly higher mean bond strength values (SD) for all dowel space regions: coronal (13.6 [1.5] MPa), middle (10.8 [1.8] MPa), and apical (8.9 [1.1] MPa). The carbon fiber dowels (C-Posts) had significantly lower bond strength values in all dowel space regions: coronal [8.6 (1.1) MPa], middle (4.7 [1.0] MPa), and apical (4.1 [1.1] MPa). Quartz dowels (Aestheti-Plus) had intermediate bond strength values: coronal (10.9 [1.1] MPa), middle (9.6 [1.1] MPa), and apical (7.7 [1.1] MPa). Also, there were differences in bond strength between regional root canal dentin, with a reduction in values from the coronal to middle and apical thirds for all experimental groups (P < 0.001).

Influence of tooth preparation burs on the roughness and bond strength of adhesives to human dentin surfaces.

PURPOSE: To characterize the surface roughness of human dentin prepared with different rotary instruments and its influence on the micro-tensile bond strength (microTBS) of self-etch adhesives. METHODS: Dentin surfaces were created from mid-coronal sound dentin in extracted, human third molars. The teeth were ground with high-speed diamond, tungsten carbide finishing, and cross-cut carbide rotary instruments. Morphological changes obtained were investigated with a surface texture analyzer. Two additional specimens from each group were treated and prepared for scanning electron microscopy. Resin composite (Z 100) was bonded to the surfaces using Optibond FL (control), Adper Prompt L-Pop (strong), Clearfil SE Bond (mild), or Clearfil S3 Bond (ultra-mild). Rectangular micro-specimens were prepared using the slow-speed diamond saw and tested in tensile to determine the microTBS. The data were analyzed with one-way analysis of variance and Tukey's HSD test (alpha= 0.05). RESULTS: Surface preparation resulted in significant differences for surface topography and micro-tensile bond strength (P< 0.001). The cross-cut carbide burs had significantly higher mean roughness readings (SD) for all parameters: Ra [8.6 (1.9) microm], Rq [10.9 (2.2) microm], and Ry [41.1 (2.1) microm], except for the mean Rz [12.1 (3.1) microm] value, which was recorded for diamonds. The other roughness parameters for the diamond rotary instruments were intermediate. Dentin surfaces completed with tungsten carbide finishing burs produced a smoother surface Ra [1.2 (0.5) microm)] Rq ([1.6 (0.6) microm], Ry [6.4 (2.6) microm)] and Rz [1.9 (0.6) microm)]. The etch-and-rinse adhesive (OptiBond FL) yielded high micro-tensile values (58.1-68.3 MPa), irrespective of the rotary instruments used. The micro-tensile bond strength values were comparable for self-etch adhesives (Adper Prompt L-Pop, Clearfil SE Bond, Clearfil S3 Bond) irrespective of the burs used. The microTBS values were significantly higher with tungsten carbide finishing burs and smooth dentin surfaces.

Relationship of margin design for fiber-reinforced composite crowns to compressive fracture resistance.

PURPOSE: Fiber-reinforced composite restorations provide excellent esthetics; however, little is known regarding the influence of margin design on marginal fit and fracture resistance for this type of crown. This study evaluated the effect of variations in tooth-preparation design on the marginal fit and compressive fracture resistance of fiber-reinforced composite crowns. MATERIALS AND METHODS: Three metal dies with a total convergence of 5° and different margin designs (0.5-mm light chamfer, 1.0-mm deep chamfer, and 1.0-mm shoulder) were prepared. Sixty standardized crowns (FibreKor) were made on duplicated base metal alloy dies (n = 20 for each margin design). Marginal fit was stereoscopically evaluated by measuring the distances between each of the four pairs of indentations on the crowns and on the dies. The specimens were then subjected to a compressive fracture-loading test using a universal testing machine. The data were analyzed with one-way analysis of variance (ANOVA) followed by Ryan-Einot-Gabriel-Welsch multiple-range test (α = 0.05). RESULTS: Analysis of marginal fit and fracture resistance disclosed a statistically significant difference for tooth-preparation design (p < 0.001). The marginal adaptation of preparations with the 0.5-mm light chamfer (66.2 µm) and 1.0-mm deep chamfer (69.7 µm) was significantly better than preparations with a shoulder finish line (92.8 µm) (p < 0.001). The fracture strength of the preparations with the 0.5-mm light chamfer (15.8 MPa) and 1.0-mm deep chamfer (15.1 MPa) was significantly greater than those of the preparations with the 1.0-mm shoulder (13.7 MPa) (p < 0.001). CONCLUSIONS: Marginal fit of fiber-reinforced crowns was adversely affected by tooth-preparation design. The marginal gaps were greater for the shoulder margin specimens than in the light or deep chamfer margin specimens; however, the fracture strength of the chamfer margin specimens was greater than that of the shoulder margin specimens.

Reinforcement of thin-walled root canal structures for placement of esthetic dowels: a clinical report.

Thin-walled root canals always present a challenge to dentists to select a restorative treatment that does not further weaken the thin tooth structure. The prognosis of dowel and core restorations can be unpredictable. This clinical report describes the treatment of a patient with extensive caries extending into the root canal of an endodontically treated maxillary central incisor. The use of a flowable composite resin in combination with a quartz fiber reinforced post is described, resulting in the rehabilitation of a structurally compromised root canal with satisfactory esthetic and functional outcomes.

Influence of irrigant, dowel type, and root-reinforcing material on fracture resistance of thin-walled endodontically treated teeth.

PURPOSE: Unresolved controversy exists concerning the optimum restorative material to reinforce the thin-walled roots of endodontically treated teeth to improve their fracture resistance under occlusal load. This study evaluated the effectiveness of irrigant, dowel type, and root-reinforcing material on the fracture resistance of thin-walled endodontically treated teeth. MATERIALS AND METHODS: The root canals of 140 maxillary central incisors were enlarged and equally divided into seven groups according to the canal irrigant: no irrigant (control), 5% hydrogen peroxide, 5% sodium hypochlorite, a combination of 5% hydrogen peroxide and sodium hypochlorite, 15% ethylenediaminotetraacetic acid (EDTA), 10% lactic acid, or 20% lactic acid. Within each group, root canals were lined with composite resin (PermaFlo) or glass ionomer cement (Fuji II LC). A light-transmitting plastic dowel (Luminex) was used to create space for a quartz fiber-reinforced dowel (Aestheti Post) or a titanium alloy dowel (ParaPost XH) and to cure the restorative materials. Following dowel cementation and restoration of the roots with composite core, the teeth were submitted to fracture resistance testing, and data were analyzed with 3-way ANOVA followed by Ryan-Einot-Gabriel-Welsch Multiple Range Test (α= 0.05). RESULTS: Fracture resistance values were significantly different among irrigants, restorative materials, and their interaction (p < 0.001); however, the dowel type was not significantly different (p= 0.51). CONCLUSIONS: Thin-walled roots that had the smear layer removed with lactic acid and that were then lined with composite resin had a higher fracture resistance.

Resin composite polyethylene fiber reinforcement: effect on fracture resistance of weakened marginal ridges.

PURPOSE: To investigate the in vitro effect of polyethylene woven fiber reinforcement of resin composite on the fracture resistance of weakened marginal ridges in molar teeth. METHODS: 50 sound extracted human mandibular molars were used. Specimens were divided into five groups (n = 10). Group 1: served as a control for comparison; Group 2: Class I cavity preparation with resin composite (Prodigy); Group 3: Class I cavity preparation with polyethylene ribbon fiber (Ribbond) and resin composite. Group 4: Class II cavity preparation with resin composite restoration; Group 5: Class II cavity preparation with polyethylene woven fiber and resin composite. Specimens were stored in 100% humidity at 37 degrees C for 7 days. Compressive loading of the teeth was performed with a universal testing machine at a cross-head speed of 0.5 mm/minute until failure. The data were analyzed with 1-way ANOVA followed by the Ryan-Einot-Gabriel-Welsch Multiple Range Test (alpha = 0.05). RESULTS: Reinforcement with polyethylene fiber resulted in significant differences for fracture resistance (P < 0.001). Mean fracture resistance (SD) was [1737.4 (84.8) N] for control group. Among the experimental groups, the highest mean fracture resistance (SD) [1543.8 (71.1) N] was associated with Class I cavity preparation with polyethylene fiber and resin composite. The lowest mean fracture resistance (SD) [869.2 (91.7) N] was recorded for Class II cavity preparation with conventional resin composite.

Morphological characteristics of the interface between resin composite and glass-ionomer cement to thin-walled roots: a microscopic investigation.

PURPOSE: To identify how different treatments of the root dentin surface affect the microscopic appearance of the resin composite/glass-ionomer cement-to-dentin interface. METHODS: The root canals of 70 extracted human single-rooted teeth were enlarged to reduce dentin wall thicknesses to 0.5 mm. The roots were randomly divided into seven test groups (n=10) according to the canal irrigant used: no irrigant (control), 5% hydrogen peroxide, 5% sodium hypochlorite, a combination of 5% hydrogen peroxide and sodium hypochlorite, 15% ethylenediaminetetraacetic acid (EDTA), 10% lactic acid, or 20% lactic acid. To simulate thin-walled roots, within each group, crowns were sectioned and the entire surface of each root canal space was enlarged with Profile instrument. Half of treated root canals (n=5) were filled with resin composite (PermaFlo) and the other half were filled with glass-ionomer cement (Fuji II LC). A light-transmitting plastic post (Luminex) was used to create space for a fiber-reinforced post and to ensure polymerization of the restorative material. Specimens were critical-point dried and freeze fractured for scanning electron microscope analysis. Three sites along the root were evaluated (cervical, middle, and apical). RESULTS: Scanning electron micrographs showed no differences in the morphology of the resin tags at the cervical, middle or apical levels with any of the irrigants or the restorative materials used. Also, no difference in surface topography was found within individual groups. A resin-dentin interdiffusion zone and resin tags developed after application of resin composite with lactic acid solutions and EDTA but not with the glass-ionomer cement.

Effect of lactic acid irrigant on shear bond strength of Epiphany adhesive sealer to human dentin surface.

OBJECTIVE: To examine the effects of varied dilutions of lactic acid as a root canal irrigant and compare the shear bond strength of Epiphany adhesive sealer to human dentin surface with other solutions deemed to be suitable root canal irrigants. STUDY DESIGN: The occlusal surfaces of 60 extracted molar teeth were ground wet and treated with one of the following irrigants: 1) no irrigant (control); 1) 5% hydrogen peroxide; 3) 5% sodium hypochlorite; 4) 15% ethylenediaminetetraacetic acid (EDTA); 5) 10% lactic acid; or 6) 20% lactic acid. An additional specimen for each group was critical-point dried and freeze-fractured to evaluate the dentin surfaces after treatment by scanning electron microscopy. Specimens were treated with Epiphany primer, hollow steel tubes were placed on the dentin surfaces, and resin sealer (Epiphany) was applied to dentin inside the tubes. Specimens were stored in 100% humidity, then loaded to failure in a universal testing machine in the shear mode with a cross speed of 0.05 mm/min. RESULTS: Dentin surface treatment resulted in significant differences for surface topography and shear bond strength of Epiphany sealer (P < .001). Lactic acid and EDTA significantly improved epiphany- dentin bond strengths when compared with other irrigants (P < .001). The highest mean (SD) bond strength was 1.95 (0.47) MPa for dentin surfaces treated with 20% lactic acid. The lowest mean bond strength [0.41 (0.29) MPa] was associated with untreated dentin surfaces. Scanning electron micrographs showed that the surface of the control specimens had a smear layer that contained smear plug material. Similarly, hydrogen peroxide and sodium hypochlorite produced surfaces with a smear layer. Lactic acid solutions and EDTA, however, removed the dentinal smear layer but left remnants of smear plugs in the dentinal tubules. CONCLUSION: Lactic acid irrigant performed similarly to 15% EDTA and demonstrated higher bond strength of Epiphany sealer to dentin surface.

Corrosion behavior of as-received and previously cast type III gold alloy.

PURPOSE: The rationale for using gold alloys is based largely upon their alleged ability to resist corrosion, but little information is available to determine the corrosion behavior of recast alloys. This study characterized the elemental composition of as-received and recast type III gold alloy and examined the in vitro corrosion behavior in two media using a potentiodynamic polarization technique. MATERIALS AND METHODS: Seventy-eight disk-shaped specimens were prepared from a type III gold alloy under three casting protocols according to the proportion of as-received and recast gold alloy (n = 26). (1) Group as received (100% as-received metal), (2) group 50% to 50% (50% wt. new metal, 50% wt. once recast metal), and (3) group recast (100% once recast metal). The surface structures of 20 specimens from each group were examined under scanning electron microscopy, and their elemental compositions were determined using X-ray energy-dispersive spectroscopy. Further, the potentiodynamic cyclic polarization between -1000 and +1000 mV (SCE) were performed for six specimens from each casting protocol in 0.09% NaCl solution (n = 3) and Fusayama artificial saliva (n = 3) at 37 degrees C. Zero-current potential and corrosion current density were determined. The data were analyzed with 1-way ANOVA and the Ryan-Einot-Gabriel-Welsch multiple-range test t (alpha= 0.05). RESULTS: Elemental composition was significantly different among the casting groups (p < 0.001). The mean weight percentage values were 72.4 to 75.7% Au, 4.5 to 7.0% Pd, 10.7 to 11.1% Ag, 7.8 to 8.4% Cu, and 1.0 to 1.4% Zn. The mean values for Zero-current potential and corrosion current density for all casting protocols were not significant (p > 0.05); however, the difference between the electrolytes was significant (p < 0.001). Fusayama artificial saliva seemed to offer the most corrosive environment. CONCLUSIONS: Type III gold alloy in any casting protocol retained passivity under electrochemical conditions similar to the oral environment. Moreover, high-gold type III alloys from reputable manufacturers and recasting protocol tested should produce acceptable corrosion-resistant castings.

Influence of tooth preparation taper and cement type on recementation strength of complete metal crowns.

STATEMENT OF PROBLEM: Clinical studies have shown that lack of retention is one of the major causes of fixed dental prosthesis failure. PURPOSE: The purpose of this study was to determine the relationship between the convergence angle of a complete metal crown tooth preparation and the recementation strength for restorations cemented with conventional and adhesive cements. MATERIAL AND METHODS: One hundred twenty artificial crowns were cast for standardized complete metal crown tooth preparations accomplished with the use of a milling machine on extracted human teeth. Three different tapers, 5, 12, and 25 degrees, were used (n=40). The crowns in each group were subdivided into 4 subgroups (n=10) according to the luting cement: zinc phosphate cement (Fleck's), glass ionomer cement (Ketac-Cem), and adhesive resin cements (Panavia 21 and C&B-Metabond). Retention was evaluated by measuring the tensile force required to dislodge the crowns from the tooth preparations in a universal testing machine. Subsequently, the tooth preparations were scraped clean and polished with prophylaxis paste, and the intaglio surfaces of the artificial crowns were ultrasonically cleaned and airborne-particle abraded with 50-mum aluminum oxide powder prior to recementation. The data were analyzed with 3-way repeated-measures ANOVA and Tukey's HSD test (alpha=.05). RESULTS: Analysis of measurements disclosed a significant difference for taper and luting cement (P<.001); however, their interaction was not significant. Also, there was a statistically significant difference between the retention of the first cementation and the second cementation (P<.001). However, the interaction was not significant with taper or cement. Regardless of the taper used, Panavia 21 cement exhibited the highest mean initial retention, but the difference was not significantly different from the recementation retentive strength. CONCLUSIONS: Tooth preparation taper and type of luting cement had a direct effect on the recementation strength of complete metal crowns.

Influence of dental rotary instruments on the roughness and wettability of human dentin surfaces.

STATEMENT OF PROBLEM: Although it is known that different dental rotary instrument types produce distinct surface roughness of the axial walls which may contribute to the clinical performance of a cast restoration, the ideal roughness that produces optimum wetting at the adhesive interface is unclear. PURPOSE: The purpose of this study was to characterize the surface roughness and its influence on wettability of teeth prepared for complete veneer crowns with different dental rotary instruments. MATERIAL AND METHODS: Sixty standardized tooth preparations for complete crowns were completed using a modified milling machine on extracted human teeth with diamond, tungsten carbide finishing, and cross-cut carbide rotary instruments of similar shape (n=20). Morphological changes obtained were investigated with a surface texture analyzer. Two additional specimens from each group were treated and prepared for scanning electron microscopy. The contact angle of a drop of distilled water on each of the prepared surfaces was used as the measure of wettability with a goniometer microscope. The data were analyzed with 1-way ANOVA and Tukey's Honestly Significant Difference (HSD) test (alpha=.05). RESULTS: Surface preparation resulted in significant differences for surface topography and wettability (P<.001). The carbide burs had significantly higher mean roughness readings (SD) for all parameters: Ra (8.6 (1.9) microm), Rq (10.9 (2.2) microm), and Ry (41.1 (2.1) microm), except for the mean Rz (12.1 (3.1) microm) value, which was recorded for diamonds. The other roughness parameters for the diamond rotary instruments were intermediate. Teeth completed with carbide finishing burs produced a smoother surface Ra (1.2 (0.5) microm), Rq (1.6 (0.6) microm), Ry (6.4 (2.6) microm), and Rz (1.9 (0.6) microm). The highest mean contact angle (SD), 81.5 (9.1) degrees, was associated with diamond rotary instruments, and the lowest (75.3 (5.9) degrees) was recorded for finishing burs. The contact angle for teeth prepared with tungsten carbide burs was intermediate: 76.1 (5.9) degrees. CONCLUSIONS: The selection of dental rotary instruments for tooth preparation significantly affects surface roughness and wettability of dentin, which may influence the retention of cast restorations.

Effects of tooth preparation burs and luting cement types on the marginal fit of extracoronal restorations.

PURPOSE: Although surface roughness of axial walls could contribute to precision of a cast restoration, it is unclear how the roughness of tooth preparation affects marginal fit of the restoration in clinical practice. The purpose of this study was to describe the morphologic features of dentin surfaces prepared by common rotary instruments of similar shapes and to determine their effects on the marginal fit for complete cast crowns. MATERIALS AND METHODS: Ninety crowns were cast for standardized complete crown tooth preparations. Diamond, tungsten carbide finishing, and crosscut carbide burs of similar shape were used (N = 30). The crowns in each group were subdivided into three groups (n = 10) for use with different luting cements: zinc phosphate cement (Fleck's), glass ionomer cement (Ketac-Cem), and adhesive resin cement (Panavia 21). Marginal fit was measured with a light microscope in a plane parallel to the tooth surface before and after cementation between four pairs of index indentations placed at equal distances around the circumference of each specimen. Difference among groups was tested for statistical significance with analysis of variance (ANOVA) followed by Ryan-Einot-Gabriel-Welsch Multiple Range Test (alpha= 0.05). RESULTS: Analysis of measurements disclosed a statistically significant difference for burs used to finish tooth preparations (p < 0.001); however, luting cement measurements were not significantly different (p= 0.152). Also, the interaction effect was not significantly different (p= 0.685). For zinc phosphate cement, the highest marginal discrepancy value (100 +/- 106 microm) was for tooth preparations refined with carbide burs, and the lowest discrepancy value (36 +/- 30 microm) was for tooth preparations refined with finishing burs. For glass ionomer cement, the highest marginal discrepancy value (61 +/- 47 microm) was for tooth preparations refined with carbide burs, and the lowest discrepancy value (33 +/- 40 microm) was for tooth preparations refined with finishing burs. For adhesive resin cement, the highest marginal discrepancy value (88 +/- 81 microm) was for tooth preparations refined with carbide burs, and the lowest discrepancy value (19 +/- 17 microm) was for tooth preparations refined with finishing burs. CONCLUSIONS: Marginal fit of complete cast crowns is influenced by tooth preparation surface characteristics, regardless of the type of luting agent used for cementation. Tooth preparations refined with finishing burs may favor the placement of restorations with the smallest marginal discrepancies, regardless of the type of cement used.

Corrosion behavior of as-received and previously cast high noble alloy.

STATEMENT OF PROBLEM: The rationale for using high noble alloys is based largely upon their alleged ability to resist corrosion. However, combining previously cast metal with new alloy might have a detrimental effect on the corrosion behavior of a high noble alloy. PURPOSE: The purpose of this study was to characterize the elemental composition of an as-received and recast high noble alloy and to examine the in vitro corrosion behavior in 2 media, using a potentiodynamic polarization technique. MATERIAL AND METHODS: Disk-shaped specimens, 6 mm in diameter and 3 mm thick, were prepared from a high noble alloy (Ney-Oro-B2) under 3 casting protocols, according to the proportion of as-received and recast gold alloy (n=26); the groups included an as-received (100% as-received metal) group, 50% to 50% group (50 wt% new metal, 50 wt% once-recast metal), and recast group (100% once-recast metal). The surface structures of 20 specimens from each group were examined under scanning electron microscopy (SEM), the elemental compositions were determined using x-ray energy-dispersive spectroscopy at 3 sites on the specimen, and the data were averaged. Further, the potentiodynamic cyclic polarization between -1000 and +1000 mV (SCE, or saturated calomel electrode) was performed for 6 specimens from each casting protocol in 0.09% NaCl solution (n=3) and Fusayama artificial saliva (n=3) at 37 degrees C. Zero-current potential and corrosion current density were determined. The data were analyzed with 1-way and 2-way analysis of variance and the Ryan-Einot-Gabriel-Welsch multiple-range t test (alpha=.05). RESULTS: Elemental composition was significantly different among the casting groups (P<.001). The mean weight percentage values were 72.7% to 75.7% Au, 4.5 to 7.0% Pd, 10.7% to 11.1% Ag, 7.8% to 8.4% Cu, and 1.0% to 1.4% Zn. The mean values for zero-current potential (ZCP) and corrosion current density (I(CORR)) for all the casting protocols were not significant (P=.67 and P=.51, respectively). Moreover, the mean values were not significant for corrosion current density with the electrolyte effect (P=.45). Only zero-current potential had a significant electrolyte effect (P<.001). Furthermore, the interaction between casting protocols and electrolyte were not significant among all corrosion parameters. CONCLUSIONS: High noble alloy in all casting protocols evaluated retained passivity under electrochemical conditions similar to the oral environment.

Effect of the crown preparation margin and die type on the marginal accuracy of fiber-reinforced composite crowns.

AIM: The objective of this laboratory investigation was to determine the effect of different preparation designs (light chamfer, deep chamfer, and shoulder) and die-making materials (stone and epoxy) on the resulting margin misfit for fiber-reinforced composite crowns using a measuring microscope. METHODS AND MATERIALS: Sixty standardized FibreKor crowns were made on stone and epoxy resin dies (n=30 each) duplicated from three metal master dies representing complete crown tooth preparation with a total convergence of 5 degrees . For each die group, three of the tooth preparation designs were established in relation to the type of finish line (n=0 each) as follows: Group A (0.5-mm light chamfer finish line); Group B (1.0-mm deep chamfer finish line); and Group C (1.0-mm shoulder finish line). Marginal accuracy was evaluated by measuring the distances between each of four pairs of indentations on the crowns and on the dies with a Nikon measuring microscope. RESULTS: Analysis of seating measurements with parametric analysis of variance and Tukey's Studentized Range (HSD) disclosed a statistically significant difference for both tooth preparation design and die material (p< 0.001). However, the interaction effect was not significant (p=0.9073). The least marginal opening value was for FibreKor crowns made on epoxy resin dies with a light chamfer finish line (57 microm), but the difference was not statistically significantly different from crowns made on epoxy resin dies with a deep chamfer light chamfer finish line (61 microm). However, crowns made on epoxy resin dies with a shoulder finish line (81 microm) had significantly higher values (p< 0.05). FibreKor crowns made on stone dies with the shoulder finish line (95 microm) had statistically higher marginal opening values (p< 0.05). The least marginal opening value was for crowns made on stone dies with a light chamfer finish line (66 microm), but the difference was not statistically significantly different from crowns made on stone dies with a deep chamfer light chamfer finish line (70 microm). CONCLUSIONS: Significant differences were found among the die material used for the shoulder margin design. However, there was no significant difference between light chamfer and deep chamfer margin designs for both die materials.

Effect of surface treatment on roughness and bond strength of a heat-pressed ceramic.

STATEMENT OF PROBLEM: Bonding ceramic restorations to tooth structure relies on treatment of the ceramic intaglio surface, selection of a suitable resin luting agent, and appropriate treatment of prepared tooth structure. Various ceramic surface treatments have been advocated which produce different topographies and bond strengths, but little information is available to identify the interaction between the resulting surface topography and bond strength. PURPOSE: The purpose of this in vitro study was to evaluate the effect of surface treatments on surface roughness and bond strength to dentin and enamel of a commercially available heat-pressed dental ceramic (IPS Empress). MATERIAL AND METHODS: One hundred heat-pressed ceramic disks were fabricated according to the manufacturer's recommendations. Specimens were divided into 5 groups (n=20) and treated with 1 of the following: (1) etching with 9.5% hydrofluoric acid, (2) 50%, or (3) 60% orthophosphoric acid and airborne-particle abrasion with (4) 50-microm, or (5) 250-microm alumina for 10 seconds. Morphological changes obtained with the surface treatments were investigated with a surface texture analyzer on half of the treated specimens. Two additional specimens from each group were treated and prepared for scanning electron microscopy. The specimens were then used for a bond strength test. The treated specimens were silanated and luted with a composite resin luting agent (Nexus 2) to enamel (n=50) and dentin (n=50) surfaces with 10 specimens for each treatment group. The luted specimens were loaded to failure in a universal testing machine in the shear mode with a crosshead speed of 0.05 mm/min. The data were analyzed with 1-way ANOVA followed by the Ryan-Einot-Gabriel-Welsch Multiple Range Test (alpha=.05). RESULTS: Surface treatments resulted in significant differences for surface topography and shear bond strength (P<.001). Mean surface roughness (Ra) (SD) was (2.54 (0.21) microm) for ceramic surfaces treated with 50-microm aluminum powder. Treatment of ceramic specimens with 50% orthophosphoric acid appeared to result in a smoother surface (1.02 (0.38) microm). The highest mean bond strength (SD) to enamel (14.7 (0.6) MPa) and dentin (8.2 (1.5) MPa) was associated with hydrofluoric acid etching. The lowest mean bond strength (SD) to enamel (2.7 (0.8) MPa) and dentin (1.5 (0.1) MPa) was recorded for 50% phosphoric acid. CONCLUSIONS: Hydrofluoric acid treatment resulted in the generation of pores and grooves that produced the greatest bond strength between the ceramic and tooth dentin and enamel. Orthophosphoric acid treatment was the least effective surface treatment method evaluated. The results are applicable to only the all-ceramic/luting system evaluated.

Assessment of convergence angles of tooth preparations for complete crowns among dental students.

OBJECTIVES: Convergence angles for complete crown preparations have been recommended at 4-12 degrees . However, practitioners have difficulty meeting these recommendations. This study measured and compared the convergence angles of tooth preparations for complete crowns prepared at three Colleges of Dentistry: the University of Tanta, Egypt, King Abdulaziz University, Saudi Arabia, and The Ohio State University, Columbus, Ohio. METHODS: The convergence angles of 499 tooth preparations for complete crowns were evaluated. These comprised of a random sample of 262 teeth prepared by third-year dental students at the University of Tanta on extracted molars under normal preclinical conditions, 37 preparations on molar teeth on typodonts done by first-year dental students. The Ohio State University and 200 molar typodont complete crown preparations done by fourth-year dental students at King Abdulaziz University, Saudi Arabia. The bucco-lingual and mesio-distal convergence angles of each preparation were measured with a goniometer microscope. Mean convergence angles were calculated, and differences between groups were tested for statistical significance with analysis of variance (ANOVA) at 5% level of confidence. RESULTS: Convergence angle measurements were significantly different between the groups and the dimensions (P<0.001). The greatest convergence value (19.8+/-10.0) was for bucco-lingual measurements prepared by Egyptian dental students. The smallest convergence value (14.1+/-3.8) was for mesio-distal measurements prepared by Saudi dental students. CONCLUSIONS: This study emphasized the difference between what is taught at dental schools (what is theoretically possible) and the school results of actual practice. There was a considerable disparity between the convergent angles recorded in this study and the ideal configurations recommended in fixed prosthodontic textbooks and the dental literature.

Lactic acid root canal irrigation for dowel and core treatment: a pilot study.

STATEMENT OF PROBLEM: Various solutions used to irrigate root canals and remove the smear layer prior to obturation of a root canal affect surface topography and may influence the sealing ability of endodontic therapy, retention of endodontic dowels, and restoration survival. PURPOSE: This study microscopically evaluated the effects of varying dilutions of lactic acid on the removal of the smear layer created by hand instrumentation in the coronal, middle, and apical thirds of root canals. Lactic acid solution was compared with other solutions deemed to be suitable root canal irrigants. MATERIAL AND METHODS: Thirty-five extracted human single-rooted teeth were manually shaped with files (K-flex) using the step-back technique. ISO size 50 files were used as master apical files. The teeth were equally divided into 7 test groups according to the canal irrigant used. While the teeth were cleaned and shaped, the root canals were irrigated with 3 mL of 1 of the following irrigants between each file size and as a final flush: no irrigant (control), 5% hydrogen peroxide, 5% sodium hypochlorite, a combination of 5% hydrogen peroxide and 5% sodium hypochlorite, 15% ethylenediaminotetraacetic acid (EDTA), 10% lactic acid, or 20% lactic acid. Specimens were critical-point dried and freeze-fractured for scanning electron microscope analysis at 3 sites (cervical, middle, and apical). RESULTS: Scanning electron micrographs showed no differences between the cervical, middle, and apical levels of the specimens tested with any of the irrigants used. Also, no difference was found within individual groups. The surface of the control specimens had a smear layer that contained smear plug material. Hydrogen peroxide and sodium hypochlorite used separately and in combination consistently produced surfaces with a smear layer. Lactic acid solutions and EDTA, however, removed the dentinal smear layer but left remnants of smear plugs in the dentinal tubules. CONCLUSIONS: Within the limitations of this study, differences related to the type of irrigant used were found in the characteristics of the pulpal dentin surface. Although lactic acid effectively cleaned and smoothed the dentin walls of root canals of endodontically prepared teeth, further study is needed before this procedure can be recommended for routine clinical use.

Compositional stability and marginal accuracy of complete cast crowns made with as-received and recast type III gold alloy.

STATEMENT OF PROBLEM: The effect of combining new and recast metal on the compositional stability of the alloy used and accuracy of the final restoration is not known. PURPOSE: This study characterized the elemental compositional stability of as-received and recast type III gold alloy. The effect of combining these alloys on the marginal accuracy of complete cast crowns also was evaluated. MATERIAL AND METHODS: Sixty standardized type III gold alloy complete crowns were made on epoxy resin dies duplicated from a metal master die with conventional laboratory techniques. Three casting protocols (n = 20 each) were established in relation to the proportion of as-received and recast gold alloys: Group A (100% as-received metal), Group B (50% wt new metal, 50% wt once recast metal), and Group C (100% once recast metal). An elemental analysis was performed at 3 sites along the cast crown (cervical, middle, and occlusal) with x-ray energy-dispersive spectroscopy. Marginal accuracy was measured with a microscope before and after cementation. Results were subjected to 1-way analysis of variance followed by the Ryan-Einot-Gabriel-Welsch multiple-range test at a 1% level of significance. RESULTS: Elemental composition was significantly different among the casting groups (P<.001). The mean weight percentage values were 72.4% to 75.7% Au, 4.5% to 7.0% Pd, 10.7% to 11.1% Ag, 7.8% to 8.4% Cu, and 1.0% to 1.4% Zn. Statistically but not clinically significant differences also were found for marginal accuracy. The marginal discrepancy was less than 25 microm for all casting conditions, with the lowest value recorded for Group A (7 microm), the highest for Group C (12 microm), and an intermediate value for Group B (9 microm) specimens. CONCLUSION: Recasting type III gold alloys may adversely affect the marginal accuracy of complete cast crowns. In this study, however, such effects were not clinically significant.