INTRODUCTION:

Prosthodontics, as a speciality of dentistry has evolved over several decades in terms of both the techniques and materials used for optimising treatment provided to patients. Owing to the growing elderly population, complete denture prosthesis has been in great demand.

Most practitioners agree that impression making is the primary step in complete denture fabrication, as it determines the success of the prosthesis. The materials and techniques used for impression making are the two main factors which govern the replicative accuracy of an impression.

The choice of impression material differs for primary and secondary impressions according to the objective of the two procedures. The primary impression is made for the purpose of diagnosis or for the construction of the tray. Thus, the material should have good dimensional stability, ease of manipulation and use, and good accuracy. Impression compound and irreversible hydrocolloids (Alginate) are currently the most commonly used materials for making the preliminary impression.

Secondary impressions record the finer details of the denture bearing area and muscular peripheral tissues in function. Zinc-Oxide eugenol impression paste and elastomeric impression materials like polyvinylsiloxane, polysulphide, etc. are used for their favourable properties like low viscosity and greater accuracy^[1].

A significant variation exists in the theories used for making the impression among practitioners. The clinical situation often governs whether the impression is made by mucostatic, mucocompressive/functional or by selective pressure method. Similarly, the decision to perform border moulding and the material used for the same varies according to the theory used for impression making and the clinical situation ^[2].

Several surveys have been conducted regarding the techniques and materials used for impression making. However, due to the changing trend and introduction of materials with better properties in the market, the opinion of practitioners regarding the same varies. The purpose of this study was to survey the dental practitioners of Saveetha Dental College, Chennai, regarding the same and analyse and compare the results obtained.

MATERIALS AND METHODS:

A questionnaire based on a recent survey ^[3] was prepared and distributed randomly to 50 practitioners of Saveetha Dental College, Chennai irrespective of their field of specialisation. The survey comprised of 11 questions regarding the impression procedures and choice of materials used for the same. Each respondent was allowed to choose only one option from the given set of answers. A provision for writing comments was also given after each question. The data was tabulated and graphical representations were made using Microsoft Excel.

RESULTS:

It was ensured that all 50 questionnaires were filled with no question left unanswered. (All percentages in the article have been rounded to the nearest whole number).

With regards to the choice of material used for making preliminary impression, 32 respondents (64%) indicated the use of irreversible hydrocolloid (alginate) and 18 (36%) still preferred using impression compound (Figure 1).

Figure 1: Percent distribution of responses for the material used for making primary impression.

29 respondents (58%) use selective pressure technique while making the final impression, while 16 of them (32%) use the conventional method and 5 respondents (10%) use the mucocompressive or functional method (Figure 2).

A majority of the practitioners 45 (90%), used a spacer in the design of the custom tray and the rest did not use a spacer. Among the ones that use a spacer, 27 of them (54%) use a spacer covering only the secondary stress bearing and relief areas, 14 respondents (28%) use full spacer not covering the major stress areas with additional relief if required a and 9 of them (18%) use a full spacer with tissue stops and additional relief (Figure 3).

The thickness of the spacer was decided based on the amount of relief by 24 (48%) respondents. 19 of them (38%) decided it arbitrarily whereas 7 of them (14%) correlated the thickness of the spacer with the type of impression material used (Figure 4).

A majority of the respondents 35 (70%), use a spacer along with light body addition silicone while the rest of them, 15 (30%) do not use it (Figure 5).

It was overwhelming to see that all of the respondents border molded the custom tray prior to making the final impression. 41 respondents (82%) use modelling plastic impression compound or green stick compound for border molding, 5 of them (10%) use wax materials and 4 of them (8%) use polyether (Figure 6).

With regards to the material used for making secondary impression, 29 respondents (58%) use polyvinylsiloxane, 13 respondents (26%) use irreversible hydrocolloid (alginate) and 8 of them (16%) use zinc oxide eugenol paste (Figure 7). Majority of the respondents 43 (86%) give special consideration for excessive movable tissue. 23 of them (53%) make relief holes in the custom tray, 11 of them (26%) use a spacer on the cast, 6 respondents (14%) selectively reduce the custom tray and 3 of them (7%) use modified impression techniques like window technique (Figure 8).

The cost of the material seemed to influence the choice of impression material for 26 respondents (52%) (Figure 9).

Figure 2: Percent distribution of responses for impression theory used for secondary impression

Figure 3: Percent distribution of design of spacer used

Figure 4: Percent distribution of responses for determination of thickness of spacer

Figure 5: Percent distribution of responses for use of spacer along with light body addition silicone

Figure 6: Percent distribution of responses for material used for border molding of final impression

Figure 7: Percent distribution of responses for material used for Secondary Impression

Figure 8: Percent distribution of responses for methods to provide relief for flabby tissue

Figure 9: Percent distribution of responses for the influence of cost of material on choice

DISCUSSION:

The dentists participating in the survey belonged to different specialities and performed impression making as a part of their treatment plan at some point or another. With varying years of experience, the dentists were able to give their personal opinion regarding every question, thus providing better insight into the topic.

The most commonly used primary impression material in this survey was irreversible hydrocolloid (64%), impression compound being used only by 36% of the respondents. This is in contrast to the survey conducted by Rupal et al ^[3]and Kakatkar ^[4]where they reported that impression compound was used by majority of the practitioners in India. However, a study conducted by Singh G et al^[5]in four major Indian cities showed that alginate was used by 71% of the practitioners. Surveys conducted in United Kingdom^[6] and U.S Dental schools^[7] have also reported alginate to be the material of choice for making primary impressions.

Majority of the practitioners (58%) used selectively pressure technique for making the final impression followed by 32% of the respondents using the conventional method. This is in agreement with previous surveys conducted in India and foreign countries ^{[3, 8 , 9]}. Selective pressure technique makes it possible to confine the forces to the stress bearing areas and the non-stress bearing areas are relieved.

In this survey, 90% of the respondents recommend the use of a spacer in the design of a custom tray and a spacer covering only the secondary stress bearing and relief areas is used by the majority(54%). Previous surveys conducted to analyse the design of spacer used have also shown similar results.

Respondents were also asked the criteria used to decide the thickness of the spacer. Most of them (48%) decided the thickness based on the amount of relief, the rest made the decision arbitrarily (38%) or based on the choice of impression material (14%). In a survey of U.S dental schools, majority of them (45%) used a layer of base plate wax for relief^[8]. A. Roy Macgregor recommends the following thicknesses of the spacer based on the impression material used: 2.5mm for impression plaster, 0.5 mm for zinc-oxide eugenol paste,2mm for alginate and 1.3-3mm for elastomeric impression materials^[10].

70% of the respondents use a spacer when using light body addition silicone as the impression material of choice. This is in agreement with the fact that some amount of tissue compression occurs when using elastomeric impression materials^[11].

Border molding is a critical component of making impressions as it ensures a stable and retentive peripheral seal. This was evident from the fact that all the practitioners recommended border molding of the custom tray. Modelling plastic impression compound is the most popularly used material (82%) due to its low cost, dimensional stability, little material wastage, long shelf life, ability to be added in increments and ease of adaptation. Surveys conducted by U.S school have indicated a growind trend of the use of elastomeric materials for border molding ^[12]. The advantage of using elastomeric impression materials is that it is less time consuming and all borders can be recorded simultaneously.

A clear majority (58%) use polyvinylsiloxane as the material of choice for making the final impression. This is in contrast to previous surveys conducted in India where Zinc-Oxide Eugenol pastes were more commonly used ^[3,4]. The advantage of using elastomeric impression materials like PVS and polysulfides is their ease of handling and manipulation, dimensional stability, adequate working and setting time and improvement in overall properties. The main disadvantage of Zinc-Oxide Eugenol pastes is that it is inelastic, sticks to skin and mucosa and causes a burning sensation.

A special consideration to excessive movable flabby tissue was made by 86% of the respondent, with majority of them (53%) preferring to place relief holes. This is contrast to a previous survey by Mehra et al ^[13]where majority of them used the window technique i.e modified impression technique.

The choice of material often influences the choice of impression material. 52% of the respondents took the cost of the material into consideration before using a material. No significant correlation has been made between the cost of the material and choice of material in previous surveys.

CONCLUSION:

This survey has managed to reveal the current trends in impression making among the practitioners in Saveetha Dental College, Chennai. Knowledge about the changing trends gives us an idea about the validity of these procedures and ways to improve the treatment provided to patients.

Based on the results of the study and within its limitations, the following conclusions can be drawn.

1. Irreversible hydrocolloid was the most commonly used material for primary impressions.

2. Most practitioners adopted the selective pressure theory while making the impressions.

3. Majority of the practitioners use a spacer covering only the secondary stress bearing and relief areas.

4. The thickness of the spacer is decided based on the amount of relief by most dentists.

5. A spacer is used along with light body addition silicone by the majority.

6. Green stick compound is the material of choice for border molding the custom tray.

7. Polyvinylsiloxane has taken over eugenol pastes as the material for making final impressions.

8. Consideration for excessive movable tissue is provided by making relief holes.

9. The cost of the material does not significantly influence the choice of material.

APPENDIX:

1. What material is used for making the preliminary impression?

a) Impression Compound

b) Irreversible Hydrocolloid (Alginate)

c) Elastomeric Putty

d) Other (Please Specify)

2. What impression theory/ philosophy do you use predominantly for making the final impression?

a) Mucostatic (Non-Pressure)

b) Functional (Pressure)

c) Selective Pressure

d) Conventional

3. Do you use a spacer in the design of the custom tray?

a) Yes

b) No

4. If yes, which design of spacer is mostly used?

a) Full Spacer with Tissue Stops and Additional Relief

b) Full spacer not covering the Major Stress Areas with Additional Relief if Required

c) Spacer covering only the Secondary Stress Bearing and Relief Areas

d) Spacer in Special Circumstances only (as in cases of flabby tissue, undercut areas, high vault or prominent ridges and spicules)

5. How do you decide the thickness of spacer?

a) Arbitrary Regardless of Impression Material Used

b) Based on the Choice of Impression Material

c) Based on the Amount of Relief

d) Other (Please Specify)

6. Do you use spacer along with light body addition silicone?

a) Yes

b) No

7. Do you border mold the custom tray prior to making the final impression?

a) Yes

b) No

8. What material is used for border molding the final impression?

a) Modeling Plastic Impression Compound (Green Stick)

b) Wax

c) Polyvinylsiloxane

d) Polyether

e) Other (Please Specify)

9. What is the final impression material of choice?

a) Zinc Oxide Eugenol Paste

b) Non- Eugenol Paste

c) Polyvinylsiloxane

d) Polysulphide

e) Polyether

f) Irreversible Hydrocolloid

g) Impression Plaster

h) Other (Please Specify)

10. Is a special consideration made for excessive movable tissue?

a) Yes

b) No

If yes, how is relief provided for flabby tissue?

a) Relief Holes in Custom Tray

b) Selective Reduction of Custom Tray

c) Spacer on the cast

d) Modified Impression Technique (e.g. a window technique in conjunction with plaster, methods using light bodied impression paste e.t.c).

11. Is the cost of the material a significant factor in influencing the choice of impression material used?

a) Yes

b) No

REFERENCES:

1. Deepak Nallaswamy. Textbook of Prosthodontics. 1^st ed. (Jaypee Brothers, 2003) 45-48.

2. Smith DE et al. One-step border molding of complete denture impressions using a polyether impression material, J Prosthet Dent, 41(3), 1979, 347-351.

3. Rupal J. Shah et al. Complete Denture Impression Procedures and Techniques Practiced by Dentists across the State of Gujarat: A Survey, IOSR-JDMS, 14(6), 2015, 1-11.

4. Kakatkar VR. Complete denture impression techniques practiced by private dental practitioners: a survey, J Indian Prosthodont Soc, 13(3), 2013, 233-235.

5. Singh G et al. Application of prosthodontic techniques by private practitioners in Northern India— a survey, Internet Journal of Epidemiology, 9(2), 2010.

6. Hyde TP et al. Survey of prosthodontic impression procedures for complete dentures in general dental practice in the United Kingdom, J Prosthet Dent, 81(3), 1999, 295-299.

7. Jaggers JH et al. Complete denture curriculum survey of dental schools in the United States, J Prosthet Dent, 53(5), 1985; 736-739.

8. Petropoulos VC et al. Complete denture education in U.S.dental schools, J Prosthodont, 14(3), 2005, 191-197.

9. Al-Ahmar AO et al. Quality of master impressions and related materials for fabrication of complete dentures in the UK, J Oral Rehabil, 35(2), 2008, 111–115.

10. MacGregor A. Roy, Fenn, Liddelow and Gimson’s clinical dental prosthetics, 3rd ed. (London: Wright, 1989) 43-78.

11. Shetty S et al. The selective pressure maxillary impression: A review of the techniques and presentation of an  alternate custom tray design, J Indian Prosthodont Soc, 7(1), 2007, 8-11.

12. Petrie CS et al. A survey of U.S. prosthodontists and dental schools on the current materials and methods  for final impressions for complete denture prosthodontics, J Prosthodont, 14(4), 2005, 253-62.

13. Mehra M et al. A complete denture impression technique survey of postdoctoral prosthodontic programs in the  United States, J Prosthodont, 23(4), 2014, 320-327.

Received on 01.06.2016 Modified on 19.06.2016

Research J. Pharm. and Tech 2016; 9(8):1195-1200.

DOI: 10.5958/0974-360X.2016.00228.6