Long-term retention of lithium disilicate crowns with a current bioactive cement.

OBJECTIVE: To determine if a recent bioactive cement provides acceptable lithium disilicate crown retention after long-term aging with monthly thermocycling. MATERIALS AND METHODS: Extracted molars prepared with flat occlusal, 20° taper, ~4 mm axial. Prepared teeth assigned to two groups for equal mean surface areas per group. Lithium disilicate crowns fabricated with occlusal bar to facilitate removal. Crowns etched with 9.5%HF and cleaned. Cements were Ceramir Crown & Bridge QuikCap (CM) and Ketac Cem Maxicap (KC). Before cementation, specimens stored in 37°C water. Crowns cemented with 196 N force, placed in 37°C, 100% humidity oven for setting. Specimens thermocycled (5-55°C) 5000 cycles monthly for 6 months; otherwise stored in phosphate buffered saline solution. Crowns removed axially at 0.5 mm/min. Removal forces recorded and stresses calculated using areas. Independent t-test (α = 0.05). RESULTS: Levene test not significant (P = 0.649). CM removal stresses and forces (P < 0.001) were higher (1.93 MPa, 261.4 N) compared to KC (1.06 MPa, 139.4 N). CM cement found principally on crown intaglio, KC found with most cement on prepared tooth. Chi-square significant (P < 0.001). CONCLUSIONS: Following long-term aging with monthly thermocycling, lithium disilicate crowns were best retained by CM cement, however both cements are capable of retaining lithium disilicate crowns with preparations of ideal taper and length. CLINICAL SIGNIFICANCE: Results serve as a basis for bioactive cement selection for retaining lithium disilicate crowns. Without optimal axial length, taper of preparation or retentive features, Ceramir Crown and Bridge QuikCap offers a bioactive cement with improved long-term retention when compared to Ketac Cem Maxicap for lithium disilicate crowns.

Long-term retention of zirconia crowns cemented with current automixed cements.

STATEMENT OF PROBLEM: Automixing and dispensing cements is a straightforward approach with consistent dosing. Previous studies have demonstrated clinically significant differences in crown retention between power-liquid and paste-paste forms of the same cement, as the composition between the 2 differs. A self-adhesive modified-resin (SAMR) and a resin-modified glass ionomer (RMGI) cement, originally offered as a powder-liquid, are now in common use as paste-paste automixed cements. With the increased use of zirconia restorations, the long-term retention of zirconia crowns for these 2 automixed cements should be evaluated. PURPOSE: The purpose of this in vitro study was to determine whether zirconia crowns cemented with 2 automixed cements provided clinically acceptable retention after 6 months of aging with monthly thermocycling. MATERIAL AND METHODS: Extracted molars were mounted in resin and prepared with a flat occlusal surface, 20-degree taper, approximately 4-mm axial length, and with the axio-occlusal line angle slightly rounded. Prepared teeth were equally distributed into 3 cementation groups (n=12) to achieve nearly equal mean preparation surface areas for each group. Zirconia crowns (IPS ZirCAD LT) were fabricated with an added occlusal bar to facilitate removal of the cemented crowns. Cement space was set at 45 µm axially and 55 µm occlusally. After sintering and before delivery, the intaglio surfaces were airborne-particle abraded with 50-µm alumina at 275-kPa pressure for 3 seconds and then steam cleaned. Cements were the original powder-liquid RelyX Luting (RMGI; RXL) as the control, paste-paste, automixed systems RelyX Luting Plus Automix (RMGI; RXLA), and RelyX Unicem 2 Automix (SAMR; RXUA). Crowns were cemented under 196 N force, placed in an oven at 37 °C and 100% humidity during setting and then thermocycled (5 °C-55 °C) for 5000 cycles monthly for 6 months. The crowns were removed axially with a universal testing machine at 0.5 mm/min. Removal forces were recorded and dislodgement stress calculated by using the surface area of each preparation. One-way ANOVA was used for dislodgement stress and force. Chi-square test was used for cement location after testing (α=.05). RESULTS: RXLA demonstrated considerably lower crown retention (1.3 MPa) and differed significantly (P<.001) from RXUA (3.1 MPa) and RXL (3.1 MPa). Modes of failure showed most of the cement remaining only in the crown intaglio for RXLA for all specimens, whereas half of the crowns for RXL and RXUA demonstrated cement adhesion to both dentin and the intaglio surface, indicating cohesive failure of the cement at separation. As the Levene test was significant, the Games-Howell test was used for mean differences. The χ2 analysis was significant. CONCLUSIONS: After long-term aging with monthly thermocycling, high-strength zirconia crowns were strongly retained by 2 (RXL, RXUA) of the 3 cements. Crown retention for RelyX Luting Plus Automix was less than half in comparison and with cement found only on the intaglio surface after separation.

Simplified cementation of lithium disilicate crowns: Retention with various adhesive resin cement combinations.

STATEMENT OF PROBLEM: A composite resin cement and matching self-etch adhesive was developed to simplify the dependable retention of lithium disilicate crowns. The efficacy of this new system is unknown. PURPOSE: The purpose of this in vitro study was to determine whether lithium disilicate crowns cemented with a new composite resin and adhesive system and 2 other popular systems provide clinically acceptable crown retention after long-term aging with monthly thermocycling. MATERIAL AND METHODS: Extracted human molars were prepared with a flat occlusal surface, 20-degree convergence, and 4 mm axial length. The axio-occlusal line angle was slightly rounded. The preparation surface area was determined by optical scanning and the analysis of the standard tessellation language (STL) files. The specimens were distributed into 3 cement groups (n=12) to obtain equal mean surface areas. Lithium disilicate crowns (IPS e.max Press) were fabricated for each preparation, etched with 9.5% hydrofluoric acid for 15 seconds, and cleaned. Cement systems were RelyX Ultimate with Scotch Bond Universal (3M Dental Products); Monobond S, Multilink Automix with Multilink Primer A and B (Ivoclar Vivadent AG); and NX3 Nexus with OptiBond XTR (Kerr Corp). Each adhesive provided self-etching of the dentin. Before cementation, the prepared specimens were stored in 35°C water. A force of 196 N was used to cement the crowns, and the specimens were polymerized in a 35°C oven at 100% humidity. After 24 hours of storage at 100% humidity, the cemented crowns were thermocycled (5°C to 55°C) for 5000 cycles each month for 6 months. The crowns were removed axially at 0.5 mm/min. The removal force was recorded and the dislodgement stress calculated using the preparation surface area. The type of cement failure was recorded, and the data were analyzed by 1-way ANOVA and the chi-square test (α=.05) after the equality of variances had been assessed with the Levene test. RESULTS: The Levene test was nonsignificant (P=.936). The ANOVA revealed the mean removal stresses, and forces did not differ for RelyX Ultimate with Scotchbond Universal (3.9 MPa; 522 N) and Multilink Automix with Multilink Primer (3.7 MPa; 511 N); both differed significantly (P=.022) from the mean for NX3 Nexus with OptiBond XTR (2.9 MPa; 387 N). For all 3 cements, the modes of failure showed cement principally on the crown intaglio, and the chi-square analysis was nonsignificant (P=.601). CONCLUSIONS: IPS e.max Press (lithium disilicate) crowns were well retained (2.9-3.9 MPa; 387-522 N) by the 3 cement-adhesive combinations after 6 months of aging with monthly thermocycling. These results can serve as a basis for cement selection for this type of crown because the values significantly exceeded those for zinc phosphate. Cements using their matched dentin bonding agent as the ceramic primer were as successful as cements with a separate silane coupling agent.

Clinical trial investigating success rates for polyether and vinyl polysiloxane impressions made with full-arch and dual-arch plastic trays.

STATEMENT OF PROBLEM: Success rates for making fixed prosthodontic impressions based on material and tray selection are not known. PURPOSE: The purpose of this clinical study was to compare first impression success rates for 2 types of impression material and 2 impression tray systems. MATERIAL AND METHODS: Dual-viscosity impressions were made with a vinyl polysiloxane (VPS) (Aquasil Ultra Monophase/Aquasil Ultra XLV) and a polyether (PE) (Impregum Penta Soft HB/Impregum Garant Soft LB) impression material. The first impression made was evaluated for success or failure using developed criteria. Fifty senior dental students participated. The type of impression material alternated for each new patient. A full-arch perforated plastic (President Tray) or a plastic dual-arch impression tray (Tri-Bite) was used based on clinical guidelines. Impression success rates were compared using logistic regression, fitted using the method of generalized estimating equations (alpha=.05). RESULTS: One hundred ninety-one impressions were evaluated, and the overall success rate was 61% for VPS and 54% for PE (P=.39). Additional regression analyses, adjusted for potential confounders, did not indicate a difference between the 2 systems (P=.35). There was little difference in success rates between the 2 materials when a full-arch tray was used (50% versus 49% success, P=.89), whereas a larger difference was apparent with the use of dual-arch trays (70% success with VPS versus 58% success with PE, P=.21). The most common critical defect was located on the preparation finish line (94%), and the most common operator error was inadequate gingival displacement (15%). CONCLUSIONS: There was little difference in success rates between VPS and PE when full-arch impression trays were used, but there was greater success when using VPS with dual-arch trays. For single teeth, the trend favored VPS, but when more than one prepared tooth per impression was involved, the success rate was higher for PE.

Retention of metal-ceramic crowns with contemporary dental cements.

BACKGROUND: New types of crown and bridge cement are in use by practitioners, and independent studies are needed to assess their effectiveness. The authors conducted a study in three parts (study A, study B, and study C) and to determine how well these new cements retain metal-ceramic crowns. METHODS: The authors prepared teeth with a 20-degree taper and a 4-millimeter length. They cast high-noble metal-ceramic copings, then fitted and cemented them with a force of 196 newtons. The types of cements they used were zinc phosphate, resin-modified glass ionomer, conventional resin and self-adhesive modified resin. They thermally cycled the cemented copings, then removed them. They recorded the removal force and calculated the stress of dislodgment by using the surface area of each preparation. They used a single-factor analysis of variance to analyze the data (alpha = .05). RESULTS: The mean stresses necessary to remove crowns, in megapascals, were 8.0 for RelyX Luting (3M ESPE, St. Paul, Minn.), 7.3 for RelyX Unicem (3M ESPE), 5.7 for Panavia F (Kuraray America, New York) and 4.0 for Fuji Plus (GC America, Alsip, Ill.) in study A; 8.1 for RelyX Luting, 2.6 for RelyX Luting Plus (3M ESPE) and 2.8 for Fuji CEM (GC America) in study B; and 4.9 for Maxcem (Kerr, Orange, Calif.), 4.0 for BisCem (Bisco, Schaumburg, Ill.), 3.7 for RelyX Unicem Clicker (3M ESPE), 2.9 for iCEM (Heraeus Kulzer, Armonk, N.Y.) and 2.3 for Fleck's Zinc Cement (Keystone Industries, Cherry Hill, N.J.) in study C. CONCLUSIONS: Powder-liquid versions of new cements were significantly more retentive than were paste-paste versions of the same cements. The mean value of crown removal stress for the new self-adhesive modified-resin cements varied appreciably among the four cements tested. All cements retained castings as well as or better than did zinc phosphate cement. CLINICAL IMPLICATIONS: Powder-liquid versions of cements, although less convenient to mix, may be a better clinical choice when crown retention is an issue. All cements tested will retain castings adequately on ideal preparations because the corresponding removal stresses are comparable with or higher than those associated with zinc phosphate. Powder-liquid resin-modified glass ionomer cement, selected self-adhesive modified-resin cements and conventional resin cements provide additional retention when desired.

Accuracy of a reformulated fast-set vinyl polysiloxane impression material using dual-arch trays.

STATEMENT OF PROBLEM: A common technique used for making crown impressions involves use of a vinyl polysiloxane impression material in combination with a dual-arch tray. A leading dental manufacturer has reformulated its vinyl polysiloxane (VPS) impression line, but the accuracy of the new material has not been verified. PURPOSE: The purpose of this study was to assess the accuracy of reformulated VPS impression materials using the single-step dual-arch impression technique. MATERIAL AND METHODS: Dual-arch impressions were made on a typodont containing a master stainless steel standard crown preparation die, from which gypsum working dies were formed, recovered, and measured. The impression materials evaluated were Imprint 3 Penta Putty with Quick Step Regular Body (IP-0); Imprint 3 Penta Quick Step Heavy Body with Quick Step Light Body (IP-1); Aquasil Ultra Rigid Fast Set with LV Fast Set (AQ-1); and Aquasil Ultra Heavy Fast Set with XLV Fast Set (AQ-2) (n=10). All impressions were disinfected with CaviCide spray for 10 minutes prior to pouring with type IV gypsum. Buccolingual (BL), mesiodistal (MD), and occlusogingival (OG) dimensions were measured and compared to the master die using an optical measuring microscope. Linear dimensional change was also assessed for IP-0 and AQ-1 at 1 and 24 hours based on ANSI/ADA Specification No. 19. Single-factor ANOVA with Dunnett's T3 multiple comparisons was used to compare BL, MD, and OG changes, with hypothesis testing at alpha=.05. A repeated-measures ANOVA was used to compare linear dimensional changes. RESULTS: There were statistical differences among the 4 impression systems for 3 of 4 dimensions of the master die. IP-0 working dies were significantly larger in MD and OG-L dimensions but significantly smaller in the BL dimension. IP-1 working dies were significantly smaller in the BL dimension compared to the master die. With the exception of IP-0, differences detected were small and clinically insignificant. No significant differences were observed for linear dimensional change. CONCLUSIONS: The single-step dual-arch impression technique produced working dies that were smaller in 3 of the 4 dimensions measured and may require additional die relief to achieve appropriate fit of cast restorations. Overall accuracy was acceptable for all impression groups with the exception of IP-0.

Assessment of preference of mixing techniques and duration of mixing and tray loading for two viscosities of vinyl polysiloxane material.

STATEMENT OF PROBLEM: Information regarding operators' preferences for different impression mixing techniques and duration of mixing and tray loading is limited. PURPOSE: The purpose of this study was to assess operators' preferences, and the duration of mixing and tray loading using different mixing techniques. MATERIAL AND METHODS: Thirty dentists, 30 dental assistants, and 30 inexperienced dental students evaluated mixing heavy-body vinyl polysiloxane material (VPS) using electronic mixing compared to automixing, and extra-heavy-body material using electronic mixing compared to hand mixing. Participants rated their level of preference using a scale from 0 to 10 for ease of mixing, control of loading, quality of mixing, level of cleanliness, and overall rating. The duration of mixing and tray loading was also measured. Mean values were compared within participant groups using the paired t test (alpha=.05) and between groups using 1-way analysis of variance (ANOVA) (alpha=.05). Holm's procedure was used to adjust the level of significance for the multiple comparisons. RESULTS: The paired t test showed that mean values of level of preference for electronic mixing were significantly higher (P<.001 to .033) than those for automixing or hand mixing. The mean values of duration of mixing and tray loading with electronic mixing were significantly higher (P<.001 to .002) than those with automixing or hand mixing, except for students using heavy-body materials (P=.31). One-way ANOVA showed that there were no significant differences between the 3 participant groups in preference and duration of mixing and tray loading, both of heavy-body and extra-heavy-body VPS impression materials. CONCLUSIONS: All participant groups preferred electronic mixing to automixing or hand mixing. Electronic mixing was significantly slower for all groups except for students using heavy-body materials. There was no significant difference between the 3 participant groups in the preference or duration of mixing and tray loading for the mixing techniques tested.

Accuracy of newly formulated fast-setting elastomeric impression materials.

STATEMENT OF PROBLEM: Elastomeric impression materials have been reformulated to achieve a faster set. The accuracy of fast-setting elastomeric impression materials should be confirmed, particularly with respect to disinfection. PURPOSE: The purpose of this study was to assess the accuracy of 2 types of fast-setting impression materials when disinfected with acid glutaraldehyde. MATERIAL AND METHODS: Impressions of the mandibular arch of a modified dentoform master model were made, from which gypsum working casts and dies were formed. Measurements of the master model and working casts included anteroposterior (AP) and cross-arch (CA) dimensions. A stainless steel circular crown preparation incorporated within the master model was measured in buccolingual (BL), mesiodistal (MD), and occlusogingival (OG) dimensions and compared to measurements from recovered gypsum dies. The impression materials examined were a fast-set vinyl polysiloxane (VPS-FS, Aquasil Ultra Fast Set), a fast-set polyether (PE-FS, Impregum Penta Soft Quick Step), and a regular-setting polyether as a control (PE, Impregum Penta). Disinfection involved immersion in 3.5% acid glutaraldehyde (Banicide Advanced) for 20 minutes, and nondisinfected impressions served as a control. Linear measurements were made with a measuring microscope. Statistical analysis utilized a 2-way and single-factor analysis of variance with pair-wise comparison of mean values when appropriate. Hypothesis testing was conducted at alpha = .05 RESULTS: No differences were shown between the disinfected and nondisinfected conditions for all locations. However, there were statistical differences among the 3 materials for AP, CA, MD, and OG dimensions. AP and CA dimensions of all working casts were larger than the master model. Impressions produced oval-shaped working dies for all impression materials. PE and PE-FS working dies were larger in all dimensions compared to the stainless steel preparation, whereas VPS-FS-generated working dies were reduced in OG and MD dimensions. Differences detected were small and may not be of clinical significance. CONCLUSIONS: Impression material accuracy was unaffected by immersion disinfection. The working casts and dies were similar for PE and PE-FS. VPS-FS generated gypsum dies that were smaller in 2 of the 3 dimensions measured and may require additional die relief. Overall accuracy was acceptable for all 3 impression materials.

A three-year clinical evaluation of two-bottle versus one-bottle dentin adhesives.

BACKGROUND: The authors conducted an in vivo investigation to compare the clinical performance of two commercial one-bottle adhesives and a two-bottle adhesive for restoration of noncarious cervical lesions (NCCLs). METHOD: The patient pool consisted of 57 patients and 171 teeth (three teeth per patient), with one NCCL per tooth. Each patient received three resin-based composite restorations, each with a different adhesive: one tooth with a two-bottle, water-based adhesive as the control; another tooth with a one-bottle, ethanol-based adhesive; and a third tooth with a one-bottle, solvent-free adhesive. The authors assessed restorations in terms of retention, marginal integrity, margin discoloration and air sensitivity at baseline, six months, one year, two years and three years after initial placement. RESULTS: The retention rates at 36 months were 88 percent for the first adhesive, 81 percent for the second adhesive and 90 percent for the third adhesive. No statistically significant differences in retention rates could be shown, with 86 percent of restorations retained overall. Measures of marginal integrity, marginal discoloration and sensitivity also had no statistically significant differences between the three adhesives (P > .05). CONCLUSIONS: All three adhesives performed with acceptable outcomes after a 36-month period, with small differences between the one- and two-bottle systems and between the various solvents. Retention rate was moderately high and air sensitivity was markedly reduced; however, superficial marginal discoloration and marginal degradation was notable. Certain lesion, tooth and patient characteristics may predispose restorations to retention failure. CLINICAL IMPLICATIONS: The type of solvent may not be a major factor in retention of Class V restorations in NCCLs. Both single-bottle adhesives and conventional two-bottle adhesives performed acceptably.

The effect of a resin-based sealer on crown retention for three types of cement.

STATEMENT OF PROBLEM: In an effort to control postoperative sensitivity, dentin sealers are being applied following crown preparation with little knowledge of how crown retention might be affected. A previous study demonstrated no adverse effect when using a glutaraldehyde-based sealer, and existing studies have shown conflicting results for resin-based products. PURPOSE: This study determined if a resin sealer applied to prepared dentin affected retention of cemented castings when using 3 common types of luting agents. MATERIAL AND METHODS: Extracted human molars (n=55) were prepared with a flat occlusal, 20-degree taper, and 4-mm axial length. The axial surface area of each preparation was determined and specimens were distributed equally among groups (n=11). A 2-step, single-bottle adhesive system (One Step) was used to seal dentin following tooth preparation. Sealer was not used on the control specimens except for the modified-resin cement (Resinomer) specimens that required use of adhesive with cementation. Using ceramometal high noble alloy (Olympia), a casting was produced for each specimen and cemented with a seating force of 20 Kg using either zinc phosphate (Fleck's), glass ionomer (Ketac-Cem) or modified-resin cement (Resinomer) with the single-bottle adhesive. Castings were thermal cycled at 5 degrees C and 55 degrees C for 2500 cycles; then removed along the path of insertion using a universal testing machine at 0.5 mm/min. A single-factor ANOVA was used with alpha=.05. The nature of failure was also recorded and the data analyzed with a chi-square test. RESULTS: Mean dislodgment stresses for unsealed and sealed conditions were 3.7 +/- 1.0 and 2.2 +/- 0.8 MPa for zinc phosphate; 2.7 +/- 1.2 and 4.2 +/- 0.9 MPa for glass ionomer, respectively (P<.001). Retentive stress of castings cemented with modified-resin cement was 6.4 +/- 1.7 MPa. With resin sealer in combination with zinc phosphate, cement resided totally on castings in 82% of the situations and was on both surfaces without sealer. The tooth failed before casting dislodgment in 9 of 11 specimens cemented with modified-resin cement. CONCLUSIONS: Resin sealer decreased casting retentive stress by 42% when used with zinc phosphate. However, sealer use resulted in 55% increased retention when used with glass ionomer. The modified-resin cement produced the highest mean dislodgment stress, nearly always exceeding the strength of the tooth.

One-year clinical evaluation of an ethanol-based and a solvent-free dentin adhesive.

PURPOSE: To analyze the clinical performance of adhesives with various solvents for restoration of non-carious cervical lesions. METHODS: The patient pool consisted of a total of 57 patients and 171 teeth (3 teeth per patient), with one non-carious cervical lesion per tooth. For each patient, one tooth was restored with a water-based, two-bottle adhesive (Scotchbond Multi-Purpose - SM), and another tooth with an ethanol-based, one-bottle adhesive (Single Bond - SB), and the other tooth with a solvent-free, one-bottle adhesive (One Coat Bond - OCB), all with resin-based composites (Silux Plus or Synergy). Restorations were assessed by retention, marginal integrity, margin discoloration and air sensitivity, according to modified USPHS criteria. The evaluations were performed at baseline, 6 months and 12 months after initial placement. RESULTS: The retention rates at 12 months were 98% for the SM adhesive, 91% for the SB adhesive, and 93% for the OCB adhesive. The differences in retention rates were not statistically significant, with 94% restorations retained overall. Measures of marginal integrity, marginal discoloration and sensitivity also had no statistically significant differences between the three adhesives. Overall, for the restorations still retained after 12 months, 80% had non/slightly detectable margins, 80% had no marginal discoloration and 90% had none/mild sensitivity. All three adhesives performed comparably with excellent outcomes after a 12-month period, with no significant differences between the water-based, ethanol-based and solvent-free adhesives, nor between the one-and two-bottle systems. Retention rate was high, air sensitivity was markedly reduced, and marginal integrity was good. Although superficial marginal discoloration was notable, no deep staining was evident. Certain lesion, tooth and patient characteristics may predispose restorations to retention failure.

The effect of surface moisture on detail reproduction of elastomeric impressions.

STATEMENT OF PROBLEM: Monophase and dual-viscosity impression techniques are available with little knowledge of which one might render better quality under wet and dry surface conditions. PURPOSE: The purpose of this study was to determine whether type of material, viscosity selection, and presence of moisture affect detail reproduction of elastomeric impressions. MATERIALS AND METHODS: Single-viscosity systems were polyether (Impregum Penta) and vinyl polysiloxanes (President MonoBody, Extrude MPV, and Aquasil). Dual-viscosity systems included polyether (Impregum Penta/Permadyne Garant) and vinyl polysiloxanes (Dimension Penta H/Dimension Garant L, Extrude Extra/Extrude Wash, and Aquasil/Aquasil LV). Impressions were made of a surface analyzer calibration standard possessing a uniform "saw-tooth" pattern with a mean roughness (Ra) of 2.87 mum, which was one fourth of the peak-to-valley height. Each of the 8 impression groups was subjected to dry (control) and wet conditions. The wet condition consisted of 3 mL of distilled water applied to the surface of the standard but allowed to escape during the procedure. Eighty impressions were made, 5 for each test group. After setting, the surface of each impression was scanned at 5 locations using a Surfanalyzer 4000. A 3-factor ANOVA and Student-Newman-Kuels test were used to analyze the data (alpha=.05). RESULTS: There were significant differences between polyether and vinyl polysiloxane materials, dual and monophase techniques, and the 2 surface conditions (P<.05). Cross-product interactions were not significant, allowing comparison of mean values for each factor. The mean Ra for single viscosity was 2.21 mum versus 1.67 mum for dual viscosity; polyether was 2.12 mum versus 1.89 mum for addition silicone; and under dry conditions, the mean was 2.04 mum versus 1.86 mum for wet conditions. CONCLUSION: Single-viscosity systems reproduced the standard saw-tooth pattern better than the dual-viscosity systems, as did polyether impression materials compared to addition silicones. Moisture led to a lower Ra or less detail compared to dry conditions.

A clinical study comparing the three-dimensional accuracy of a working die generated from two dual-arch trays and a complete-arch custom tray.

STATEMENT OF PROBLEM: Dual-arch trays are often used by the dentists to make crown impressions of opposing quadrants simultaneously. Metal and plastic trays are available, but little is known about the accuracy of the impressions and resultant working dies. PURPOSE: The purpose of this study was to conduct a clinical trial to compare the accuracy of gypsum working dies made from impressions with metal dual-arch, plastic dual-arch, and complete-arch custom trays. MATERIAL AND METHODS: Eight patients requiring a posterior single tooth implant restoration were selected on the basis of inclusion and exclusion criteria. A customized abutment was measured in 3 dimensions (buccolingual, mesiodistal, and occlusogingival) by use of a measuring microscope. Three polyvinyl siloxane impressions were made of the abutment with a complete-arch custom tray, a plastic, and a metal dual-arch tray. Each impression was poured with type IV improved dental die stone. The diameter (buccolingual and mesiodistal), from gingivoaxial to gingivoaxial point angle, and height (occlusogingival), gingivoaxial to occlusoaxial point angle of the abutment standard was determined by measuring each dimension several times to obtain a mean. These 3 mean values served as the controls and were compared with the same measurements of the gypsum dies generated by the 3 different impression techniques. The patient was asked to rank the 3 impressions in order of overall comfort. A multivariate repeated measures single factor ANOVA was used in the statistical analysis (alpha=.05). When main effects were significant, a pairwise comparison of mean values was conducted with Bonferonni adjustment for multiple comparisons. RESULTS: There were no significant differences in die accuracy among the 3 trays for the mesiodistal (3.507 mm) and occlusogingival (3.584 mm) dimensions of the implant abutment. Dies were smaller than the standard for these 2 dimensions and larger in the buccolingual dimension. There was a significant difference in accuracy between the metal and plastic dual-arch trays. The dies produced from the metal dual-arch tray were 20 microm larger than the abutment standard compared with 3 microm larger for the plastic tray. The occlusogingival dimension of the working dies was 30 to 40 microm shorter than the implant abutment. Seven of the 8 patients ranked the plastic dual-arch impression as the most comfortable and the complete-arch custom tray as the least comfortable. CONCLUSIONS: Within the limitations of this study, the dimensions of working dies from a custom tray impression did not differ significantly from those created with dual arch trays. However, working dies from a plastic dual-arch tray were more accurate buccolingually than those from metal dual-arch trays.

The effect of tray selection, viscosity of impression material, and sequence of pour on the accuracy of dies made from dual-arch impressions.

STATEMENT OF PROBLEM: Dual-arch trays are often used to generate impressions of prepared teeth and of the opposing arch simultaneously. There is concern that accuracy of the casts generated with this technique can be affected by the type of tray, viscosity of the impression material, and sequence of pouring the cast. PURPOSE: This study compared the accuracy of working dies made from impressions with metal and plastic dual-arch trays, for 2 different viscosities of impression tray material and by altering which side of the impression was poured first. MATERIALS AND METHODS: Impressions were made of a typodont mandibular arch containing a circular stainless steel crown preparation (standard). There were 3 variables: type of dual-arch tray, impression material viscosity, and order of pour of the impressioned arches. A balanced design with independent samples was used (n=10). Two types of dual-arch trays, plastic (Triple Tray) and metal (COE Impression Tray), and 2 viscosities of addition silicone for the tray were used (Aquasil Rigid and Aquasil Monophase). Type IV gypsum (Fuji-Rock) with a ratio of 20 mL of distilled water to 100 g of powder was hand-mixed for 10 seconds then mixed under vacuum for 40 seconds and poured into the trays while being vibrated. One side of the dual-arch impression was poured with 35 g of stone and allowed to set for 1 hour before the other side was poured with 35 g of stone. The order of pour was randomized, and all casts were allowed to set for 24 hours at room temperature before removal. The dies were measured in 3 dimensions (buccolingual, mesiodistal, and occlusogingival) with a measuring microscope. The gypsum working dies were placed into a custom jig fabricated to permit measurement at a fixed, reproducible position under the microscope. Each dimension of the working dies was measured 3 times, and the mean was used for the sample value. The same 3 aspects of the stainless steel standard were measured multiple times, before and then at the conclusion of measuring all working dies, to arrive at the 3 standard values to which all working die means were compared. The means for the standard used in the statistical analysis were those taken at the conclusion of the study. The intraexaminer variation for measuring the standard was 0.001 mm. A 3-factor analysis of variance was used for the statistical analysis with hypothesis testing at alpha=.05. RESULTS: Statistically significant differences were found with viscosity selection for the buccolingual and occlusogingival dimensions of the working die. The rigid material produced working dies slightly taller (1 microm) than the standard, and those from the monophase material were 4 microm shorter. Regarding tray selection, metal trays were slightly more accurate in the mesiodistal dimension, and when monophase was used in a plastic tray, gypsum dies were nearly 30 microm smaller in the mesiodistal dimension (P<.05). Differences were not detected for sequence of pouring impressions. CONCLUSION: Within the limitations of this study, the monophase material, when compared with the rigid impression material, was most accurate for the occlusogingival and mesiodistal dimensions, although not as accurate in the buccolingual. This buccolingual difference (0.002 mm-0.006 mm) would be clinically inconsequential with the application of die spacer. The rigid impression material was also unaffected by tray selection for the mesiodistal, whereas monophase was affected. When a monophase impression material was used, plastic dual-arch trays yielded gypsum dies which were significantly smaller (0.029 mm) than the ones generated from the metal trays (0.006 mm). Thus rigid impression materials can be recommended for use in dual-arch trays; however, the magnitude of the differences would generally not be clinically significant because they could be compensated for with several coats of die spacer.

Temperature effects on the rheological properties of current polyether and polysiloxane impression materials during setting.

STATEMENT OF PROBLEM: Rheological tests of elastomeric impression materials during setting have been most often conducted at room temperature rather than at intraoral temperature. Because temperature may affect properties and the setting kinetics, clinically relevant inferences may not be accurate with studies conducted at room temperature. PURPOSE: The purpose of this study was to determine the viscoelastic properties of new low- and medium-viscosity elastomeric impression materials during setting at 33 degrees C and to evaluate the medium-viscosity materials at 3 additional temperatures. MATERIAL AND METHODS: The impression materials investigated at 33 degrees C were 2 polyvinylsiloxanes (PVS) (Aquasil Deca and Aquasil LV) and 5 polyethers (PE) (Impregum Penta, Impregum Penta Soft H, Impregum Penta Soft L, Impregum Garant Soft L, and Permadyne Garant L). Three impression materials (Aquasil Deca, Impregum Penta, and Impregum Penta Soft H) were also investigated at 25 degrees, 29 degrees, and 37 degrees C. Time-dependent oscillatory rheometry was carried out on these materials (n=3) with a rheometer with a 25-mm diameter parallel plate cell. The storage modulus (G') and the loss tangent (tandelta) were determined as functions of time over a period from 0 seconds to 900 seconds, commencing 40 seconds after mixing. Induction time (t(ind)) or initial setting time and tandelta, the relative liquidlike behavior, were also computed. A single-factor analysis of variance (ANOVA) was used for the properties determined at 33 degrees C and a 2-factor ANOVA was used for the temperature studies, with hypothesis testing at alpha=.05. RESULTS: The G'(t) curves for all materials displayed the expected sigmoidal shape with time, with the solid-like behavior rising slowly, then more rapidly, and again slowly to final set. The initial setting time (t(ind)) was found to be approximately 2.8 minutes for the PVS materials and for Impregum Penta and Impregum Penta Soft H, but was significantly longer for the remaining 3 PE low viscosity materials. The solid-like behavior (G') at final set or shear modulus differed among all materials, ranging from 1.0 MPa for Aquasil Decca, 1.69 for Impregum Penta Soft H, and 1.8 MPa for Impregum Penta. G' for low-viscosity materials ranged from 0.66 MPa for Aquasil LV and 0.79 MPa for Permadyne Garant L to 1.2 MPa for Impregum Penta Soft L. The loss tangent at 40 seconds tandelta (t(0)) varied among medium and low viscosity materials, ranging from liquid-like behavior of 4.3 for Permadyne Garant and less than unity or significant solid-like behavior for Impregum Penta. All materials showed tandelta values less than unity at their setting times. The temperature studies revealed significant changes in the kinetics of setting, with the setting time decreasing more than 3-fold between 25 degrees and 37 degrees C for the Aquasil Deca and the Impregum Penta Soft H and more than 2-fold for the Impregum Penta. At room temperature of 25 degrees C, the storage modulus for Impregum Penta Soft H and Aquasil Deca was 1.1% and 37.5% lower than Impregum Penta, respectively. CONCLUSION: The development of the viscoelastic rheological properties with time for 3 medium- and 4 low-viscosity impression materials at 33 degrees C showed significant differences in the setting time and the magnitude of the storage modulus. Compared with Impregum Penta, the new Impregum Penta Soft H was 6% less stiff when set, compared with 44% lower stiffness for the medium viscosity addition silicone. Temperature studies between 25 degrees C and 37 degrees C revealed strong temperature sensitivity of the kinetics of setting and evolution with time of their rheological properties.

A crown venting technique for the cementation of implant-supported crowns.

With the increased use of implant systems for the replacement of single teeth, some dental practitioners are choosing to permanently cement the final restoration instead of using the screw-retention modality. Many of these restorations have subgingival margins; therefore, the cementation technique becomes a critical procedure because incomplete seating of the restoration or excess cement can be lodged in the gingival sulcus. The use of a cement escape way or venting technique for the cementation of an implant-supported restoration is described.

Wettability, imbibition, and mass change of disinfected low-viscosity impression materials.

STATEMENT OF PROBLEM: There is an ongoing effort by dental manufacturers to create impression materials with improved wetting properties. Disinfection solutions may alter the surface characteristics of these newer materials. PURPOSE: This study compared wettability, imbibition, and mass change of various recently introduced automixed low-viscosity addition silicone and polyether materials before and after immersion disinfection. MATERIAL AND METHODS: The Wilhelmy technique was used for deriving wetting properties of 5 addition silicone materials (Clinician's Choice Affinity, Clinician's Choice Superhydrophilic [experimental], Kerr's Take One, 3M's Imprint II, and Dentsply's Aquasil LV) and 2 polyether materials (ESPE's Permadyne Garant and Impregum Garant). Conditions included a control with no disinfection (0 hours), as well as (1/2) hour of immersion disinfection in a full-strength solution of 2% acid glutaraldehyde disinfectant (Banicide). Weight changes before and after disinfection and weight loss in air were measured over an 18-hour period to detect imbibition and mass change over time. The data were analyzed with a 1-way analysis of variance at alpha=0.05, with n = 3 for advancing (ACA) and receding (RCA) contact angles and n = 2 for imbibition and mass change. RESULTS: Statistical significant differences in wettability (P<.001) were found among nondisinfection control groups, as well as among (1/2)-hour disinfection groups. Polyethers were the most wettable materials overall. Impregum Garant polyether demonstrated significantly lower RCA for the control (48.4 degrees) and at (1/2) hour of disinfection (51.8 degrees). The 2 polyethers and Take One lost mass, whereas Aquasil LV gained mass in air; however, all materials exhibited some degree of imbibition during disinfection. CONCLUSION: Within the limitations of this study, the 2 polyether materials tested exhibited significantly lower ACA's and RCA's compared with the 5 addition silicones tested. Imbibition for the 2 polyether materials was significantly higher (P<.001). Polyether materials lost significantly more (0.6% to 0.8%) and Aquasil LV gained significantly more (0.6%) mass in air.

Characteristics of noncarious cervical lesions: a clinical investigation.

BACKGROUND: The purpose of the authors' in vivo investigation was to analyze the characteristics of noncarious cervical lesions, or NCCLs, in adult patients who had a high incidence of them. METHODS: The patient pool consisted of a total of 57 patients and 171 teeth (three teeth per patient), with one NCCL per tooth. The characteristics the authors evaluated were shape, dimensions, sensitivity, sclerosis and occlusion. RESULTS: In terms of lesion characteristics, 91 percent of the lesions had axial depths of 1 to 2 millimeters, 49 percent had occlusogingival widths of 1 to 2 mm, 74 percent had an angular shape of 45 to 135 degrees, 76 percent had mild or moderate sclerosis, and 73 percent had no or mild sensitivity. In terms of occlusion, 75 percent of teeth had an Angle Class I occlusion on the involved side, 60 percent had group function or mixed excursive guidance, 82 percent had wear facets, and 99 percent had Type 0 or I mobility. In terms of tooth location, 70 percent of NCCLs were on posterior teeth, 65 percent were on maxillary teeth, and 46 percent were on premolars. CONCLUSIONS: The evaluated NCCLs were found mainly to have small dimensions of depth and width (< 2 mm) and to be roughly right-angled in shape, and many had sclerosis and low sensitivity. A majority of the dentitions studied had Class I occlusion, with group function, prevalent wear facets, and little or no mobility. Cervical lesions were more common with posterior maxillary teeth and premolars, especially first premolars, which had the highest prevalence of lesions. Older patients were more likely to exhibit noncarious cervical lesions, but no great difference in incidence was found between men and women. Clinical Implications. A knowledge of the NCCL characteristics and etiologic covariables aids in proper case selection for treatment, aids in selection of appropriate treatment protocols and improves assessment of prognosis.