Temporary tissue retraction before taking impression. A multi-center randomized controlled clinical trial comparing the use of retraction cord, aluminum chloride paste (Expasyl®) and combination of aluminum chloride paste and retraction cord
When making a tooth-supported fixed prosthesis, an impeccable impression is required. Therefore, the gingival tissue around an abutment tooth needs to be temporarily retracted to enable the impression material to flow around the preparation margin. For years, the method of choice has been placing a cotton retraction cord into the gingival sulcus to make space for the impression material. In 2000, a new material, aluminium chloride paste (Expasyl®), was introduced, which was supposed to play the same role as the retraction cord. Until now, this paste has not been fully studied and has never been compared to the classic method. The aim of this randomized controlled clinical trial (RCT) is to evaluate the influence of three different methods for temporary tissue retraction before impression taking on the gingiva. Additionally, patients' perception of the intervention and technicians' evaluation of the impression material and easiness of the preparation of the master cast will be evaluated using a Visual Analogue Scale. Sixty-seven individuals in need of a tooth-supported reconstruction were included in the study and randomized into three equally large groups. In the first group (T1)only Expasyl® aluminum chloride paste was used to retract the gingiva. In the second group (T2)a retraction cord was inserted proximally and orally and Expasyl® was used as a second layer of retraction. In the third group (C) two retraction cords were used to retract the gingival tissue (the traditional double cord technique). This multi-center study took place at the Faculty of Odontology, University of Iceland, and in four private practices in Iceland. Clinical measurements were made at baseline and 30±10 days after cementation. To evaluate the gingival position, four study casts were taken at different stages: #1 just before impression taking, #2 before cementing the reconstruction, #3 immediately after cementation, and #4 was taken 30±10 days after cementation. Standardized photographs of the study casts were taken, the photographs were overlapped and magnified using a graphics editing software, and changes in the gingival position were measured. In addition, patients' perception of the treatment and the technicians' evaluation of the impression material and the easiness of making the master cast were recorded. The baseline evaluation did not reveal any significant difference between the three groups regarding soft tissue conditions, tooth position, and tooth mobility. In the period between impression-taking and cementation, a minor (0.058 mm and 0.013 mm) gain in gingival height was reported for groups T1 and T2. However, a minor gingival recession (0.049 mm) was reported for group C. The results showed that 21% of abutment teeth gained >0.1 mm gingival height, 58% had stable gingival height (0 ± 0.10 mm), 21% showed minor gingival recessions (0.1-0.5 mm), and no abutment teeth showed moderate or substantial gingival recessions (>0.5 mm). The lowest incidence (8%) of minor gingival recession was seen in T1. The respective figures in T2 were 23% and 32% in C. The difference in gingival position between the three groups reached statistical significance (p=0.015). Evaluating the changes in gingival position during the first 30 days after cementation revealed that 19% of the abutment teeth gained gingival height, 51% showed stable gingival position and 29% experienced gingival recession. During this time period, the highest incidence (40%) of gingival recession was reported in T2. The respective figures were 22% for T1 and 26% for C. Fifteen subjects, or 24%, experienced some discomfort or pain after the procedure. The mean VAS score was 27 and the median was 22 (range 3-62). The difference between the groups was not significant and only 8% needed medication to cope with the discomfort. Evaluating the easiness of preparing the master cast the technicians reported the easiest preparation process for group C. The difference between the groups was statistically significant (p=0.003). The mean number of impressions needed to get a sufficient impression was lowest (1.1) for group C, compared with 1.4 and 1.3 for groups T1 and T2, respectively. The probability of sufficient first impression was also highest (86%) in C. For two subjects with deep sub-gingival preparation margins, it was not possible to get a sufficient impression utilizing Expasyl® and a different approach had to be used. Conclusion Comparing aluminium chloride paste (Expasyl®) with the traditional double cord technique in a randomized, controlled clinical trial indicated that minor gingival recessions (<0.5 mm) are more likely to occur when conventional cotton cords are used to temporarily retract the gingival tissue before impression is taken. Utilizing the double cord technique, the dental technicians graded it easier to prepare the master cast, compared with impressions taken using the aluminium chloride paste for gingival retraction.
Tannlæknisfræði, Tannsmíði, Tannhold, Tanngervi
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