Complete denture impressions: a simplified impression technique vs conventional technique for edentulous patients

Methods

This study was conducted in the Department of Prosthodontics at MS Ramaiah Dental College and Hospital. Ethical clearance was obtained. After obtaining informed consent, the study subjects included were 70 completely edentulous patients aged between 50 and 80 years of age with a completely healed denture-bearing area, moderate to well-formed ridges and adequate inter-arch space. Patients with pain in the denture-bearing area, resorbed foundations, flabby and hyperplastic tissues, poor neuromuscular control, unfavourable ridge relationships, uncontrolled diabetes, diseases related to calcium metabolism, xerostomia and temporomandibular joint disorders were excluded.

Complete denture patients were randomly divided into Group A (35 patients) and Group B (35 patients) and assigned to final year undergraduates and first year postgraduate students for treatment. The Group A patients were treated by undergraduates as well as postgraduates with a conventional impression technique (Control group) in which primary impressions were taken using impression compound in the first sitting. Custom-tray fabricated in acrylic with wax spacer and stoppers was used for border moulding with greenstick compound and wash impression was made using zinc oxide eugenol impression paste in the second sitting. The same students also treated another 35 patients with the simplified impression technique (Study group) using vinyl polysiloxane (Betasil Vario, Muller-Omicron Gmbh & Co KG) of two different consistencies:

The simplified technique makes use of perforated stock trays of proper size for the edentulous arch (Figure 1). They are modified with pliers, so that they almost enclose all the required anatomical structures without impingement.6 Tissue stoppers of 5 mm length made using modelling wax are placed in the canine and molar region (Figure 2). These stops are developed to achieve an even space of about 3–4 mm between the tray and edentulous tissues and to keep the tray steady during impression-taking. The mandibular tray borders should cover the retromolar pad, external oblique ridge, and mylohyoid ridge. The deficient tray borders are extended with soft utility wax but fall well short of the sulcular tissues by 2–3 mm (Figure 3). After applying tray adhesive, equal amounts of base and catalyst of soft putty impression material is mixed and loaded on to the tray evenly. The impression is made by ensuring complete seating of the tray as practised previously and removed after complete setting (Figure 4). All the borders should are moulded according to functional sulcus depth and width. Once set, deficient borders are corrected by adding putty and remoulding (Figure 5). Bulky and overextended borders are marked (Figures 6 and 7) for trimming with a sharp knife. The tissue surface of the impression is reduced by 1 mm with a tungsten carbide trimmer to give adequate relief and make space for light body material except in the maxillary posterior seal area. Finally, all the borders of the maxillary and mandibular impression are reduced by 1 mm with the same trimmer, and frenum areas slightly opened with an acrylic fissure bur to make space for light body material (Figure 8). This is done, as the displaceability of the sulcular tissues varies and the development of physiologic borders with putty may be difficult to achieve due to its viscosity. When the maxillary palatal area is high vaulted, vent holes may be placed through the tray to prevent air entrapment. Light body elastomeric impression material is evenly loaded on the same tray and final impressions are taken (Figure 9).

Results

The mean number of visits required to fabricate the dentures by undergraduates and postgraduates is shown in Tables 1 and 2. Mann-Whitney and Wilcoxon tests showed that the number of visits required to make dentures was significantly less (p < 0.05) with the simplified impression technique for most of the undergraduates and some of the postgraduates (Tables 3 and 4).

Discussion

A precise complete denture impression is one of the most critical factors in determining success or failure of the dentures. Most textbooks advocate a two-stage procedure where a preliminary impression is taken, often with an irreversible hydrocolloid (alginate) in a stock tray and a final impression is recorded using a custom-tray, usually made of acrylic resin. There are many materials for the final impression, such as zinc oxide and eugenol (ZOE) paste, polysulphide rubber, polyether, polyvinylsiloxane and alginate. Preferences vary among dentists. These impression appointments are generally considered as more time consuming and technically difficult in the conventional treatment sequence for complete dentures.3^, 8^,9^,10

Research has proved that, without increasing the number of post-insertion appointments or reline procedures, the abbreviated impression technique significantly reduces the number of visits for fabricating complete dentures.9^,10 A retrospective study conducted in an undergraduate dental school compared the treatment results between edentulous patients wearing complete dentures made from a traditional two-stage technique, and another edentulous group whose impressions were taken from an abbreviated technique. The abbreviated technique involved taking overextended, irreversible hydrocolloid impressions in stock trays. Heat processed acrylic resin denture bases were fabricated on the casts obtained. In the second visit, jaw relation records were made using these bases after checking their retention, stability and border extensions using pressure-indicating paste. After the aesthetic try-in, the teeth were heat processed on to the denture base. The study concluded that teaching an abbreviated impression technique in an undergraduate clinic helped to decrease the number of patient appointments, without increasing the number of adjustment or reline procedures.9

In another recent technique, called a VPS Edentulous Impression Technique,10 vinyl polysiloxane of multiple viscosities were used in stock polystyrene-based polymer trays, which could be softened through a flame or easily trimmed with an acrylic trimmer for proper adaptation to the edentulous tissues. Border moulding was achieved by placing a rope of high viscosity VPS along the maxillary tray border and medium viscosity for mandibular tray borders. Definitive or final impressions were made using low viscosity VPS. The VPS technique has the inherent disadvantage of using specific trays that may not be readily available and are possibly expensive. The use of multiple viscosities also may be confusing to the general practitioner.

Today, two of the most popular elastomers used in dental practice are the polyethers and/or vinyl polysiloxane. The popularity of the elastomer materials is acceptable, given the combination of excellent physical properties, handling characteristics, and better dimensional stability.

The use of polyether11^,12 or vinyl polysiloxane (VPS)13^,14^,15^,16^,17 impression materials for custom-tray border correction has been described extensively in the literature.

The introduction of these elastomers have made way for newer techniques of edentulous impression-taking, which has remained unchanged for decades. Vinyl polysiloxane offers a number of distinct advantages for making definitive impressions during complete denture therapy:18

Polyvinylsiloxane putty and light-body impression material are well suited for taking complete denture impressions and good results were obtained with less expenditure of time, as well as less discomfort and inconvenience for the patient. In addition, the odour, taste and colour of the polysiloxane materials improved patient acceptability and gave an easy to use result.1

Fewer visits for treatment would mean improvement in patient compliance and motivation. This reduction in appointments improves clinical revenue, whether in a general or a specialty practice. Moreover the fabrication of custom-trays with autopolymerizing resin in undergraduate dental schools has the disadvantage of possible high levels of monomer release and concerns of health and occupational safety.5 Implementation of the simplified impression technique can be a good solution.

However, the application of the simplified technique should be restricted to well-formed and moderate edentulous foundations, since modification of stock metal trays to conform to resorbed edentulous ridges will be difficult. Custom-trays are to be used when the edentulous foundations are resorbed or demonstrate excessively flabby tissues.

Conclusion

Within the limitations of this study, there was no significant difference between the groups treated with either the conventional method or the simplified impression method in terms of patient satisfaction, retention and stability. Hence, dentures made using the simplified impression technique are probably less time consuming, which benefits both patient and operator. Therefore, for moderate to well-formed ridges, the simplified edentulous one appointment impression technique can be used in place of the traditional two-appointment technique, without compromising the principles of definitive impression-taking.