Xavier Lepe

Dimensional stability and detail reproduction of irreversible hydrocolloid and elastomeric impressions disinfected by immersion.

STATEMENT OF PROBLEM Because irreversible hydrocolloid impressions imbibe blood and saliva, immersion rather than spray disinfection may be more effective. Polyether has been shown to be dimensionally sensitive to immersion disinfection. PURPOSE The aim of this study was to determine whether irreversible hydrocolloid and polyether impressions could be disinfected by immersion without sacrificing accuracy and surface quality. MATERIAL AND METHODS Impressions were made of a master mandibular arch containing a crown preparation. Changes between the master and working casts were assessed. Irreversible hydrocolloids (Jeltrate; Palgaflex), a polyether (Impregum F), and an addition silicone (President) were used. Disinfectants were an iodophor (Biocide), a glyoxal glutaraldehyde (Impresept de), and a phenol glutaraldehyde (Sporicidin). The control was without disinfection. Casts were formed in Type IV gypsum. The roughness of working dies was also recorded and an analysis of variance was used for statistical evaluation. Results. Casts from disinfected irreversible hydrocolloid and elastomeric impressions maintained accuracy for anteroposterior and cross arch dimensions where differences from the master was less than 0.1%. Buccolingual and mesiodistal dimensions of working dies (disinfected and control) were 6 to 8 microm larger than the master for addition silicones and 11 to 16 pm for polyethers. The occlusogingival dimension of dies for control and disinfected polyether was 9 pm longer than the master compared with -3 microm for addition silicone. The range of mean surface roughness of working dies made from irreversible hydrocolloids was 1.4 to 1.7 microm and ranged from 0.5 to 0.7 microm for elastomeric impressions. Conclusion. Immersion disinfection of Jeltrate material with iodophor and Palgaflex material with glyoxal glutaraldehyde produced casts and dies as accurate as the control. Control and disinfected elastomeric impression produced dies as clinically accurate and smooth as the master. Disinfection of irreversible hydrocolloid impressions with the glyoxal and phenol glutaraldehyde produced a surface smoother than controls.

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.

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.

Surface characteristics of polyether and addition silicone impression materials after long-term disinfection

It has been demonstrated that short-term disinfection can affect the surface properties of impression materials. This study evaluated advancing contact angle, receding contact angle, inhibition and mass loss of a polyether impression materials, and two different viscosities of an addition silicone impression material after long-term immersion disinfection (18 hours). The brand names of the impression materials tested were Impregum F, Extrude Extra, and Extrude Wash, and all were tested by use of the Wilhelmy technique; first, for the nondisinfected state, which served as controls, and then after 1 and 18 hours of disinfection in a full-strength solution of acid glutaraldehyde. Weight changes before and after the disinfection process were also measured to detect weight loss and mass change over time. All materials exhibited some degree of inhibition. Polyether lost 0.4% mass in air, which indicated loss of a volatile component. Polyether and addition silicone were both relatively hydrophobic and could be disinfected with acid glutaraldehyde for up to 18 hours without affecting wettability.

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 Dunnetts 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.

Retention of provisional crowns fabricated from two materials with the use of four temporary cements.

STATEMENT OF PROBLEM Practitioners often choose resin materials and temporary cements with little understanding about their effect on provisional crown retention. PURPOSE This study evaluated the retention of provisional restorations made with 2 materials and cemented with 4 temporary cements. METHODS AND MATERIAL Recently extracted molars were prepared with a flat occlusal surface, 4-mm axial length and 20-degree angle of convergence. Specimens were distributed into equivalent groups. Provisional crowns were constructed for each preparation with polymethyl methacrylate (Temporary Bridge Resin) or bis-acrylic composite (Protemp Garant) and later cemented with Temp-Bond, Temp-Bond NE, Temrex, and an experimental calcium hydroxide temporary cement. A second group with Temrex was evaluated using half the recommended liquid. A cementing force of 2.5 kg for 5 minutes was used. After initial bench set followed by 24 hours in room temperature water, the crowns were removed with an Instron mechanical testing machine at 0.5 mm/min. A 2-factor ANOVA was used with alpha=.05 (n = 10). Mode of debonding was analyzed with a nonparametric chi-square test of association. RESULTS Mean dislodgment stresses ranged from 670 to 1072 kPa for polymethyl methacrylate crowns and 554 to 884 kPa for those made of composite. Differences were nearly significant for the type of provisional material (P =.061) and the cross-product interaction (P =.376) was not significant, whereas there were significant differences among the cements (P =.002) and the mode of debonding (P =.0034). CONCLUSIONS Excluding Temp-Bond to eliminate a cross-product interaction demonstrated that the polymethyl methacrylate crowns were 19.3% more retentive than the composite crowns (P =.015). There was no statistically significant difference among the 4 temporary cements when the manufacturers mixing instructions were followed (P =.186). However, the thicker consistency Temrex was more retentive than the recommended Temrex mix and Temp-Bond.

Effect of mixing technique on surface characteristics of impression materials

STATEMENT OF PROBLEM Previous studies have shown a relationship between the disinfection process, wettability, and mass change of impression materials. Hand-mixed high viscosity impression materials usually result in a material with numerous voids, which contribute to surface roughness and affect the surface characteristics of the material. PURPOSE This study evaluated the effect of mixing technique on advancing contact angle, receding contact angle, imbibition, and mass loss of various high and low viscosity polyether and polyvinyl siloxane materials. The null hypothesis tested was no differences exist between the different mixing systems. MATERIAL AND METHODS The Wilhelmy technique was used for deriving wetting properties of the materials used (Impregum F and Penta, Permadyne Syringe, Garant and Penta, Dimension Penta and Garant L, Aquasil). Conditions included no disinfection (0 hours) and 1, 5, and 18 hours of immersion disinfection in a full-strength solution of 2% acid glutaraldehyde disinfectant (Banicide). Weight changes before and after disinfection were measured to detect weight loss or mass increase over time. Weight loss in air was also measured to detect mass loss. Data were analyzed with a one-way analysis of variance at alpha = 0.05. RESULTS All materials displayed some degree of imbibition of the disinfectant and experienced mass loss with polymerization, except the light viscosity polyvinyl that gained 0.18% at 5 hours. No significant differences were found in wettability among the polyether materials after 1 hour of disinfection. Less imbibition was observed for high viscosity mechanically mixed materials compared with the hand-mixed materials for both polyether and polyvinyl siloxane at 1-hour disinfection time. CONCLUSIONS Polyether materials were more wettable than polyvinyl. Imbibition of high viscosity polyether and polyvinyl materials after 1 and 18 hours of disinfection were affected by the mixing system used.

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.

Fracture strength of Type IV and Type V die stone as a function of time

STATEMENT OF PROBLEM During the removal of casts from the impression there is the risk of stone fracture. PURPOSE This study evaluated the fracture resistance of four die stone materials at different time intervals. MATERIAL AND METHODS Additional silicone impressions were made of a maxillary master cast. Two Type V, one Type IV die stones and one Type IV resin reinforced stone were tested. A total of 80 casts were prepared, separated, and tested on the Instron Universal Testing Machine at 1/2, 1, 12, and 24 hours to measure resistance to fracture. RESULTS Significant differences to fracture resistance of the different die stone materials were observed at all time intervals except at 24 hours. The data were analyzed with ANOVA at alpha = 0.005 and n = 5. CONCLUSION It is recommended to wait at least 12 to 24 hours when separating casts from impressions to avoid fracturing casts. Residual moisture content in a stone cast may contribute to fracture.

A method for true coordinate three-dimensional measurement of casts using a measuring microscope.

Exact 3-dimensional measurements are more useful for researchers and clinicians than are relative distance measurements. Through the use of a measuring microscope and a personal computer, the technique presented in this article provides meaningful and accurate (0.005 mm) 3-dimensional measurements of casts in true coordinates (x, y, z). By fabricating the master cast with reference landmarks, leveling the casts before measurement, removing the cast between repeat measures, and mathematically rotating the data points, this technique places all the landmarks in a standardized reference plane that allows for the comparison of dimensional changes between different casts.