The effect of one-step vs. two-step impression techniques on long-term accuracy and dimensional stability when the finish line is within the gingival sulcular area.

PURPOSE: To evaluate the effect of two putty-wash impression techniques on the long-term accuracy and dimensional stability of poly(vinyl siloxane) (PVS) in the gingival sulcus area. MATERIALS AND METHODS: Impressions were taken from a master cast to simulate molar crown preparation. A space around the abutment served as the gingival sulcus. Fifteen impressions using the one- and two-step impression techniques were taken using Express Regular, Express Fast, and President impression materials with custom trays. Using a Toolmaker's microscope, the long (LD) and short distances (SD) of the abutment and the planar distance between two parallel lines (PL) at the circumference of the cast were taken at 0.5, 2, 24, 48, 72, 96, 120, and 144 hours after mixing. ANOVA was performed, with the discrepancy between the distances of the impressions and the master cast as the dependent variable. RESULTS: The differences when different materials and impression techniques were used were significant (p < 0.001) for LD, SD, and PL, as was the interaction between the material, time, and technique (p < 0.001). SD discrepancies were higher than those of LD for all materials and times. The two-step impression technique was more accurate, with smaller discrepancies than the one-step impression technique. For all materials, the PL discrepancy was deemed acceptable (less than 0.5%) for all tested times. President had higher discrepancies than the other materials. CONCLUSIONS: When using the two-step putty-wash impression technique, pouring of the impressions may be postponed up to 30 hours; however, when using the one-step impression technique, pouring should be performed within 2 hours.

Dimensional stability of polyvinyl siloxane impression material reproducing the sulcular area.

The dimensional stability of a thin intra sulcular impression material reproducing the preparation finish line was evaluated. Impressions were taken of a stainless-steel master model of a simulated abutment with a 'gingival sulcus' using Express regular, Express fast and Aquasil. The putty-wash two-step technique was applied with spacer thicknesses of 0.5, 1 and 1.5 mm. Mid mesiodistal and bucco-lingual measurements were taken directly from the sulcular impression material after 0.5, 2, 24, 48 and 72 h via a Toolmaker's microscope. The discrepancies between the measurements of the impression material and the master model were calculated. The discrepancies changed significantly over time (p<0.001). The use of a 0.5 mm spacer resulted in a negative deviation from the model (2-46 µm), minimally after 2 h. The use of 1 and 1.5 mm spacers showed a positive deviation from the model (21-52 µm) and both are equally recommended. Investment can be postponed until 72 h.

Radiographic features of vertically fractured endodontically treated mesial roots of mandibular molars.

OBJECTIVE: The purpose of this study was to evaluate the most frequent radiographic appearance of bony lesions around endodontically treated vertically fractured mesial roots of mandibular molars. STUDY DESIGN: For the study, 49 extracted mesial roots with vertical fractures (study group) were evaluated and compared to 52 extracted roots without fractures (control). RESULTS: The "halo" (36.7%) and "periodontal" (28.6%) type radiolucencies were the most typical appearances of periradicular areas around the mesial roots of mandibular molars with vertical root fractures. By itself, bifurcation radiolucency was statistically insignificant (6.1%), however in conjunction with other areas of radiolucency, it was significant (63.3%, P < .0378). No radiolucency (38.5%) and periapical radiolucency (32.7%) were predominant features in the control (nonfractured roots). Amalgam dowel in the coronal part (1-2 mm) of the root was found in 67.3% of the vertically fractured roots (P < .0006). Defined but not corticated (57.2%) or diffuse (32.6%) borders were typical for vertically fractured mesial roots. CONCLUSIONS: The use of significant variables, such as "periodontal" and "halo" bony radiolucencies, bifurcation involvement, and the presence of amalgam dowel, has prediction sensitivity of 77.6% (VRF group) and specificity of 82.7% (nonfractured roots).

Abutment positioning in a cantilevered shortened dental arch: a clinical report and static analysis.

This article describes the extension of a shortened dental arch with a cantilever fixed partial denture in a patient who refused to be treated with an implant-supported and retained prosthesis. Orthodontic movement of the distal abutment to enlarge the interabutment span was performed before the final restoration. The mechanical advantage of the enlarged span in a cantilever fixed partial denture is analyzed, discussed, and demonstrated by 2-dimensional static analysis.

Effect of a fluoride varnish on the margin leakage and retention of luted provisional crowns.

STATEMENT OF PROBLEM: Provisional crowns cemented with provisional luting agents are susceptible to washout, margin leakage, and secondary caries when placed for a prolonged period. PURPOSE: This study was conducted to determine the effect of combining a varnish containing 2.26% NaF with 2 provisional luting agents on the margin leakage and retention of provisional crowns. MATERIAL AND METHODS: Acrylic resin provisional crowns were fabricated for 8 shoulder-prepared molars. The eight provisional (N=24) crowns were luted individually with Temp-Bond (TB), Freegenol (FG), or Duraphat (DU). Specimens were thermocycled 500 times (5 degrees and 60 degrees C) with a 1-minute dwell time, stored in 100% relative humidity at 37 degrees C for 6 days, and then immersed in a 0.5% Gentian violet solution for 24 hours. Seven days after cementation, a removal test of the crowns (shear retention test) was conducted with a universal testing machine at a crosshead speed of 5 mm/min. Retention was determined as the maximum recorded force needed for crown dislodgment. DU varnish was applied to the inner surface of the dislodged crowns with no removal of the cement layer TB, FG (N=16). The crowns were relined with a 0.5-mm layer of acrylic resin and luted with a combination of luting agent and DU (TB, FG) N=16. No luting agent (NC) served as the control (N=8). Results were analyzed with the Wilcoxon matched-pairs signed-ranks test. Leakage at the margins was assessed with a 4-level dye penetration scale, and statistical differences were identified with a chi(2) test. All hypothesis testing was conducted at the 95% level of confidence. RESULTS: The mean 7-day retention forces were as follows: 44.5 N (Temp-Bond), 51.6 N (Freegenol), and 35.9 N (Duraphat). There were no significant differences among these values. Duraphat combined with Freegenol decreased the retention of provisional crowns, but Duraphat combined with Temp-Bond increased the retention of provisional crowns by 69-145%. Duraphat alone and in combination with both provisional luting agents significantly reduced margin leakage (P<.05). The least margin leakage was evident when the provisional crowns were luted with Duraphat alone. CONCLUSION: With regard to retention and margin leakage, the results of this study suggest that Duraphat varnish can be successfully used as provisional luting agent for single provisional crowns.