Randomized Clinical Trial for Evaluation of Efficacy of a Tissue-displacing Impression System in Comparison with Conventionally Used Gingival Displacement Materials in Young Adult Population
Corresponding Author: Rajlakshmi Banerjee, Department of Prosthodontics, VSPM’s Dental College & Research Centre, Nagpur, Maharashtra, India, Phone: +91 9890324934, e-mail: email@example.com
Received on: 06 July 2023; Accepted on: 04 September 2023; Published on: 29 September 2023
Purpose: The purpose of the study was to comparatively evaluate these new gingival displacement materials for their efficacy when compared with the conventional chemomechanical gingival displacement method.
Materials and methods: This randomized control trial was carried out on 25 individuals according to the inclusion and exclusion criteria for gingival displacement using a retraction cord impregnated with aluminum chloride, ExpaSyl, and NoCord vinyl polysiloxane (VPS) impression system using Latin block design to evaluate the gingival displacement produced by three different tissue displacing materials on a right central incisor. Impressions were poured into the die stone. Casts were retrieved, and sections were made using a die cutter. Each slice thus obtained was evaluated under an optical microscope and transferred to the image analyzer to measure the amount of gingival retraction. The recorded values were statistically evaluated using the one-way analysis of variance (ANOVA) test, followed by the Tukey post hoc test for multiple comparisons.
Results: The amount of mean gingival displacement produced by retraction cord impregnated with astringent solution was 1.42 ± 0.32 µm, by ExpaSyl retraction paste was 1.40 ± 0.11 µm, and that by NoCord VPS impression was 0.62 ± 0.12 µm when subjected to one-way ANOVA which showed highly statistically significant difference (p = 0.001 )among all the three groups with respect to gingival displacement. NoCord Impression system produced optimum tissue displacement as compared to the other two techniques.
Conclusion: The retraction cord produced the maximum tissue displacement, followed by ExpaSyl, and the least displacement was caused by NoCord, although all displacement methods compared produced the optimum displacement required for impression making.
How to cite this article: Gajbhiye V, Banerjee R, Tekale R, et al. Randomized Clinical Trial for Evaluation of Efficacy of a Tissue-displacing Impression System in Comparison with Conventionally Used Gingival Displacement Materials in Young Adult Population. Int J Prosthodont Restor Dent 2023;13(3):163–169.
Source of support: Nil
Conflict of interest: None
Keywords: Gingival displacement, Gingival sulcus, Impression, Impression making, Subgingival finish line
Any prosthesis for a successful restoration should have proper marginal fit to avoid tissue trauma and gingival recession.1 To obtain an accurate impression to fabricate a prosthesis, it is important to displace the gingiva temporarily, especially when the finish line is at or below the gingival margin.2 Gingival displacement or retraction can be defined as the displacement of the gingiva away at the finish line to allow the placement of impression material into the gingival sulcus to obtain an accurate impression.3 This displacement should be a minimum of 0.2 mm so that the impression at the finish line doesn’t tear while being taken out.4 The gingival displacement can be achieved through mechanical, chemomechanical and surgical methods.5 The mechanical method using a retraction cord has been used commonly for a long time, which causes gingival displacement by physically displacing the gingiva far away from the finish line. The chemical method uses retraction cords soaked with hemostatic agents or astringents, which also help in managing the seepage of fluid and blood in the gingival sulcus.6
Retraction cords have commonly been used for gingival displacement.7 However, it can be difficult, technique-sensitive, painful for patients, and when done inappropriately, can lead to a gingival recession in due course of time.8 Preimpregnated cords soaked in an astringent can control the sulcular bleeding and improve gingival displacement. The vasoconstrictors like epinephrine and sympathomimetic amines and astringents like aluminum sulfate compounds can be used for the chemomechanical method.8
Cordless techniques have been introduced recently with several advantages of being time-saving and comfortable for the patient while being minimally invasive.8 NoCord by Centrix, United States of America is a newly introduced polyvinyl impression material to produce gingival displacement along with making accurate impressions.9
ExpaSyl was introduced as a retraction paste system, which is also a cordless retraction technique. However, there has not been a comparison between ExpaSyl and NoCord for clinical efficacy before.10 Therefore, a clinical comparison of the efficacy of the NoCord vinyl polysiloxane (VPS) Impression system with Retraction Cord and ExpaSyl for gingival displacement was decided.
The study aimed to compare the clinical efficacy of tissue displacement achieved with retraction cord, ExpaSyl, and NoCord. The secondary objective was to evaluate whether the NoCord impression system could produce optimum tissue displacement. The null hypothesis established for the study was that the NoCord impression system is not efficient in producing optimum tissue displacement for impression-making when compared with the other techniques of tissue displacement.
MATERIALS AND METHODS
The randomized clinical trial was designed and carried out in the Department of Prosthodontics. The approval of the Institutional Ethics Committee of the institution was obtained (IEC/VSPMDCRC/13/2019 dated 18 October 2019) to compare the gingival displacement obtained using 3 different tissue displacing materials on the unprepared right central incisor.11 The Consolidated Standards of Reporting Trials (CONSORT) checklist was followed to ensure systematic reporting of the randomized clinical trial.12
Sample Size Determination
Taking reference from the study by Raghav et al.,13 the mean gingival displacement recorded for astringent-impregnated retraction cord and ExpaSyl paste were 0.5156 ± 0.087 and 0.4568 ± 0.145, respectively. Accordingly, the estimated effect size was 0.489 ± 0.5. For the proposed study, an effect size of 0.90 was acceptable, which resulted in a sample size of 20 per group that can provide the desired effect with 95% confidence and 80% power. The formulation used for estimating the sample size was:
where z1 − α/2 and z1− β are the critical values for a 95% confidence interval and 80% power, while s is the pooled standard deviation of the groups, and ε represents the tolerable difference between the groups. The difference and pooled standard deviation lead to effect size.
Sample Selection and Randomization
The study participants were selected randomly from the departmental outpatient from 20th October 2019 to 20 December 2019 in each group subject to the fulfilment of inclusion and exclusion criteria. Randomization was done according to Latin block design to have a computer-assisted standardized randomized allocation. The design was a crossover double-blinded trial design. Every individual was subjected to all three experimental groups. Patients and the analyzing personnel were blinded about the nature of the intervention at any given appointment. The gingival displacement was the primary outcome measured, and the gingival health following the gingival displacement was the secondary outcome. The participants were randomly assigned to the experimental groups and were analyzed for the primary outcome, as shown in Figure 1.
Inclusion and Exclusion Criteria
According to the inclusion criteria, 25 individuals with thick gingival biotype in the age-group of 20 and 25 years with healthy gingiva and periodontal health were recruited for the study.14-16 Individuals with thin gingival biotypes, crowding, rotation, diastema, restored anterior teeth, anterior malocclusion, systemic diseases, and pregnant and lactating women were excluded from the study.11 Each participant was informed about the objective and procedure of the study, and consent was obtained.
Custom Tray Fabrication
Maxillary irreversible hydrocolloid impressions were obtained with (Zelgan, Dentsply, Mumbai, India) for all the participants. Three sets of custom trays were fabricated using cold cure acrylic resin tray material (DPI, Mumbai, India) with a spacer of 2 mm thickness and tissue stops for correct orientation of the tray during impressions. These custom trays were then used to make impressions after 24 hours.10
Baseline impressions with no gingival displacement were made for the control group. Round bur was used to make perforations within the custom tray. The impressions were made with additional silicone (Aquasil, Dentsply, North Carolina, United States of America) with a putty wash technique after the spacer was removed from the custom tray. Once the material was set, the impression was removed from the patient’s mouth. The impressions were disinfected with a glutaraldehyde solution.
Impression-making Following Gingival Displacement
A Latin block design was followed for gingival displacement and impression-making, as presented in Table 1. The baseline impression was made on day 1, following which, on days 2, 17, and 32, impressions were made after displacement with any one of three displacement agents according to Latin block design; a computer-assisted standardized randomized allocation was used for the technique.10
|Subject||Day 1||Day 2||Day 12||Day 22|
A, Aquasil; C, control; N, NoCord; R, retraction cord
Gingival Displacement Using Retraction Cord and Impression
The working area was maintained dry with cotton rolls on the right central incisor. According to the measured depth of the gingival sulcus, the size of the retraction cord was selected. A knitted retraction cord (Primecord, Primedent, India) soaked in 25% aluminum chloride by hemostat clear (Medicept, Medicept Dental India Pvt Ltd, Mumbai, India) was gently placed on the labial gingival sulcus of the tooth with the assistance of gingival cord packer (GDC, Mumbai, India) (Fig. 2). The cord was taken out after 10 minutes, and the impressions were made.13 A gap of 7 days was kept between the three postdisplacement impressions of the same individual following the Latin block design to avoid tissue fatigue, as presented in Table 1.10,14
ExpaSyl Displacement and Impression
After reconfirming the gingival index to be zero in the right central incisor,16 ExpaSyl displacement paste (Acteon Pharma, Merignac, France) was injected slowly into the sulcus (Fig. 3). After 2 minutes, ExpaSyl paste was washed away from the sulcus to impressions were made.
NoCord VPS Impression System
For NoCord impression (Centrix INC, Shelton, United States of America), a second set of trays for each patient was used to make an impression following the manufacturer’s instructions. The tray impression was made following the manufacturer’s instructions (Fig. 4). The intraoral tips provided with the material were used for injecting a light body into the gingival crevice and were picked up with the tray impression.
Pouring of Impression and Sample Preparation
Die stone (Ultrarock, Kalabhai and Karson Pvt ltd, Mumbai, India) was used to pour all impressions and the casts were retrieved without causing any damage. The mesiodistal width of the right central incisor was measured using a Vernier calliper, and the center was marked on the cast. The cast was stabilized on the platform of the die cutter, and a cut was made on the marked line in the buccolingual direction.
Measuring Gingival Displacement
The amount of gingival displacement was measured under an optical microscope (Olympus, Mumbai, India) at a magnification of ×100, using the image Analysis Software (Metal Power Image Analyzer Version 126.96.36.199, Bengaluru, India). The distance between the crest of the gingival margin to the corresponding mid-labial surface of the tooth in a straight line was measured. A total of 25 such readings were obtained for each group (Fig. 5).
Statistical Package for the Social Sciences (SPSS) was used to perform the statistical analysis (IBM Corp. Released 2013. IBM SPSS Statistics for Windows, Version 22.0. Armonk, New York: IBM Corp.). The results were statistically evaluated using the one-way analysis of variance (ANOVA), followed by the Tukey post hoc test for multiple comparisons. Any significant differences between two or more independent groups were analyzed using one-way ANOVA. The pair-wise comparison between preoperative (pre-op) and postoperative (post-op) gingival displacement among the control and the experimental groups was done using a paired t-test. The p-values at or below 0.05 were considered significant for the study.
The descriptive statistics have been presented in Table 2. The mean gingival displacement produced by retraction cord was 1.42 µm with a standard deviation of 0.32 µm, that by ExpaSyl retraction paste was 1.40 µm with a standard deviation of 0.11 µm, and that by NoCord VPS impression was 0.62 µm with a standard deviation of 0.12 µm. A statistically significant difference was noted among all three groups when subjected to one-way ANOVA (p = 0.001) (Table 3).
|The method used for gingival retraction||Mean (µm)||Standard deviation||95% confidence interval|
|Retraction cord impregnated with astringent solution||142.36||32.97||126.92||157.79|
|ExpaSyl retraction paste||140.47||11.03||135.31||145.63|
|NoCord VPS impression system||62.34||12.75||56.37||68.31|
|Retraction methods||Sum of squares||Degree of freedom (df)||Mean square||F||p-value|
*indicates p < 0.05 as statistically significant
A post hoc test was used to perform multiple comparisons. It was observed that the amount of gingival displacement produced was greater with retraction cord impregnated with astringent solution as compared to ExpaSyl retraction paste, although no statistically significant difference was observed (p = 0.95). This difference was highly statistically significant between the retraction cord impregnated with an astringent solution and the NoCord VPS impression system (p = 0.001). Similar results were obtained when the gingival displacement was compared between the ExpaSyl retraction paste and NoCord VPS impression system (p = 0.001). So, it was seen that the retraction cord impregnated with an astringent solution produced maximum gingival displacement followed by ExpaSyl retraction paste and NoCord VPS impression system (Table 4). A mean gingival displacement of >0.2 mm was recorded with all three gingival displacement techniques, which is the optimum amount of retraction required for impression-making.
|(I) Group||(J) Group||Mean difference (I-J)||Standard error||p-value|
*p ≤ 0.001 highly significant using the post hoc Tukey test
Table 5 depicts a pair-wise comparison of mean values of gingival displacement with standard deviation between the control and the experimental groups. The paired t-test was used to find out whether the difference in width produced was in the range of clinical significance. It was inferred that the effect produced with all three agents gave highly statistically significant (p = 0.001) results in terms of gingival displacement (Table 6). The null hypothesis was negated as the NoCord impression system was found to be as efficient as the conventional retraction methods used for tissue displacement.
|Pair-wise comparison||N||Mean||Standard deviation|
|Pair 1||Control (pre-op)||20||27.35||2.86|
|Retraction cord (post-op)||20||142.36||32.97|
|Pair 2||Control (pre-op)||20||27.35||2.86|
|Pair 3||Control (pre-op)||20||27.35||2.86|
|Pair-wise comparison||Mean||Standard deviation||Standard error||t||df||p-value|
|Pair 1||Control—Retraction cord||−115.00||32.5||7.3||−15.7||19||0.001*|
*indicates p < 0.05 as statistically significant
For the fabrication of fixed prostheses, the accuracy of the cast plays a pivotal role, especially with regard to the accurate reproduction of the cervical margin. In clinical situations where both functional and esthetic demands require the cervical margins to be placed subgingivally, it is critical to obtain an accurate impression.15 An impression with incomplete details will lead to a prosthesis with faulty margins, which may result in marginal leakage and secondary caries in the underlying tooth structure. Thus, adequate temporary displacement of the gingiva is obligatory for an esthetical and functionally successful prosthesis.15 Polyvinyl siloxane (PVS) materials like Magic Foam Cord have been evaluated as a way of cordless gingival retraction.14 Magic foam claims to be self-expanding, causing expansion of the gingival sulcus using specially designed caps.14,15 NoCord by Centrix, United States of America, is another latest PVS-based impression material which also produces gingival displacement. Another material in the segment of cordless retraction systems is ExpaSyl, which was introduced long back and shown to be clinically effective. However, the efficacy of NoCord is yet to be evaluated and compared with contemporary systems like retraction cord and ExpaSyl. Therefore, the present study was deemed necessary.
To avoid tissue fatigue, the sequencing of the technique was done using a Latin block design.10,15 Although 7–15 days have been advocated as the minimum time needed to recover the gingival tissues, if traumatized, Latin block design also gives an equal chance for each technique to express its effects independently.10 The sequence of displacement with retraction cord, ExpaSyl, and NoCord VPS impression system was changed for each subject and according to the Latin block design to eliminate the bias.
The subjects included in the study were assessed for the sound condition of the teeth.16 Thick gingival biotype has a broad zone of keratinized tissue which can better withstand forces and, therefore, was chosen as the inclusion criteria for the study. Whereas thin gingival biotype is more sensitive to trauma as a result of minimum keratinized tissue, resulting in severe recession when exposed to pressure.16-18
Retraction cords as a method for gingival displacement are the most commonly used. Weir and Williams19 and Runyan et al.20 demonstrated that cords impregnated with aluminum sulfate were more efficient for hemostasis than nonimpregnated cords. Hence, in this present study, a 10% aluminum chloride hemostatic agent was used in the cord technique. De Camargo et al.21 concluded that the cords impregnated with hemostatic solutions did not interfere with the polymerization and did not affect the accuracy of the impression materials. O’Mahony et al.22 suggested careful removal of any hemostatic medication used from the sulcus before recording the impression. Around 10% aluminum chloride was used with the Ultrapak cord, which is a knitted cord consisting of 100% cotton miniature loops with an interlocking long chain. Optimal tissue displacement occurs in 3–8 minutes of application of the retraction cord. Aluminum chloride is the most widely used astringent, which acts by vasoconstriction, protein precipitation, and by removing the fluid from tissues,10 when used in a concentration of 5–25% to minimize tissue damage.19
In this study, an ultrapak cord system was used to produce gingival displacement for the first experimental group. In the second group, ExpaSyl, which also uses 15% aluminum chloride in the matrix containing kaolin, was used for gingival displacement, which claims to reduce the flow of sulcular fluids similar to that of epinephrine-soaked cords.23-25 No adverse effects have been reported with the use of ExpaSyl for gingival displacement.26,27 The injectable matrix is hydrophilic and, therefore, can be easily flushed away from the gingival crevice, also providing advantages of being easy to use, painless and therefore more comfortable to the patient as well as being less time-consuming.28 NoCord VPS Impression system, marketed by Centrix, United States of America, is a newer material and does not have any clinical studies reported for its efficacy except one study, which was to compare its efficacy as an impression material by Gajbhiye et al.10 The material claims to record accurate impressions along with retracting the gingiva for a better marginal impression. Gingival tips of 0.5 mm in diameter are provided in the kit, along with a mega body cartridge wash impression cartridge to push the wash material into the sulcus. NoCord light body impression material also contains 15% alum (aluminum chloride) as the hemostatic. The mega body tray material of NoCord is a unique stiff material designed to push the wash material into the gingival crevice. The NoCord material produced the least amount of gingival displacement, which was statistically significantly lower than that obtained with retraction cord and ExpaSyl, which might be due to the light body, which is highly free-flowing pushed into the sulcus to provide displacement while taking care of least damage to the subgingival tissues.28
In the present study, maximum gingival displacement was obtained with an aluminum chloride-impregnated retraction cord (1.42 µm) which is in accordance with many previous studies.2,14,19,29 However, both the other cordless systems ExpaSyl (1.40 µm) and the PVS-based NoCord (0.62 µm) also produced an optimum displacement.30
In a recently published systematic review on gingival displacement, it was reported that the most common risks of bias were randomization and blinded outcome assessment.31 Therefore, in this study, utmost care was taken in randomization, and all procedures were done by a single operator to reduce the operator bias in complete adherence to the CONSORT guidelines.12,32
Within the scope of this study, it can be concluded that an optimum tissue displacement of 0.22 mm could be obtained with all three methods used in the study of retraction.12,16,19 The use of the paste system, as well as combined retraction and impression using NoCord, are clinically viable alternatives, providing the advantages of being quick and easy and thereby saving chair side time.
The limitation of this study is that, although all possible care was taken to minimize any potential trauma to the gingival tissues, any unintentional damage to the tissues in the long term could not be evaluated. The specific time of 7 days between the interventions was maintained, similar to the study by Thimmappa et al.,33 which reported gingival damage of negligible to none. Even though standardized procedures were followed for all aspects of the study, every patient’s tissue response may have differed, hence the response of the gingiva to the retraction material. In the present study, the vertical component of displacement with double cord techniques was not assessed as was done in other studies.34,35 Newer materials like polytetrafluoroethylene have also been tested recently for gingival displacement and ease of application as compared with retraction cord.36 The previous condition of gingiva and its effect on the gingival displacement was not in the purview of the present study, as reported by other studies.37,38 The result of this study needs to be confirmed in a variety of situations in different age-groups in a larger population.
From this study, it can be concluded that maximum displacement was produced by the retraction cord, followed by ExpaSyl and NoCord. The NoCord VPS impression system also produced an optimum level of gingival displacement when compared with the conventional methods. ExpaSyl and NoCord can save chairside time and produce gingival displacement without any patient discomfort.
Rahul Tekale https://orcid.org/0009-0008-8833-2603
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