Choosing the Right Impressions Materials for Complete Dentures

8 years ago

Abstract

The development of impression materials has largely influenced the history of complete denture impression procedures, leading to new techniques. Dentists select materials based on their personal preferences and experience.

The success of every complete denture relies on the fulfilment of the three basic properties of retention, stability, and support.

There was no support for the frequent textbook statement that the two-step procedure is necessary and superior to the one-step method. While some special clinical situations may benefit from other combinations of materials and techniques.

Key words: Impression methods, material, complete denture prosthodontics, final impressions, Border moulding

Dental News – December Issue 2018

Dr. Oumaima Tayari – Resident in the departement of complete denture

Dr. Héla Haloui – Resident in the departement of complete denture

Prof. Jaouadi Jamila (j.jaouadi@yahoo.fr) – Director, department of prosthesis rehabilitation

Prof. Ali Ben Rahma – Head of department, department of complete denture

*Clinic of dentistry of Monastir, Department of Prosthetic Dentistry, University of Monastir, Laboratory of oro-facial rehabilitation and oral health

Introduction

From an anatomical viewpoint, tooth loss leads to the resorption of the alveolar ridge in the upper and lower jaws. This process manifests as a reduction in the attached gingival surface and an increase in the displaceable mucosal surface.

Regarding function, it affects occlusion and speech ability in patients, as well as changes of their appearance, which may result in psychosocial decompensation. ⁴

Complete dentures primarily serve as mechanical devices, but since they function in the oral cavity, you must fashion them to harmonize with normal neuromuscular function.

The development of impression materials has largely influenced the history of complete denture impression procedures, giving rise to new techniques and ideas.5

Stability of complete lower dentures has challenged dentists and patients alike. Making accurate final impression for complete dentures is a multistage process that involves a preliminary impression, a customized final impression tray and a final border impression. It is important to thoroughly examine the patient’s mouth and select the most appropriate impression technique. ⁷

The process of shaping impression material along the borders of an impression tray by manipulating the soft tissues to duplicate the contour and size of the vestibules is known as border molding. ⁵

The 2 techniques of border molding documented in published reports are the sectional and the single step techniques. The sectional technique is routinely taught in dental schools in the United States and is followed by a large number of general dental practitioners, and commonly used. ⁶ Clinicians make final impressions of complete dentures (CD) using different techniques and materials. Applying the correct impression technique and material, based on an individual’s oral condition, improves the quality of the prosthesis, which may improve quality of life.

Dental practitioners can make the impression in a single stage (abbreviated impression) or in two stages (preliminary impression made for the purposes of diagnosis, or for the construction of a tray, followed by final impression). The techniques can be grouped into mucostatic, mucocompressive, selective pressure, functional, and neutral zone impression techniques.

Using this or that technique depends on the operator, the mouth conditions and / or time we dispose. The objective of this paper was to provide procedures of final impressions in complete dentures, using standardized techniques and materials. ⁴

Impression materials

The literature reports about many different techniques of anatomical and functional impressions, as well as about different types of impression materials – from dental stones, zinc oxide eugenol pastes and thermoplastic materials to reversible hydrocolloids and elastomers.

The analysis indicates that dental professionals most often use reversible hydrocolloids and alginates for the first or anatomical impression in the fabrication of complete dentures and overdentures. They use thermoplastic materials of the latest generation in the shape of sticks to form functional margins. Aluminum wax is used for relining the vibrating line, while zinc oxide eugenol pastes and several types of elastomers, such as condensation silicones, vinyl polysiloxane, and polyethers, are used for taking functional and fixation impressions. ³

Procedures

The impression stage of fabricating complete dentures aims to customize the denture bases to the optimal denture-supporting area and to ensure that the border form of the prostheses provides a peripheral seal. ²

As the residual ridges resorb, the tissues become unsupported and displaceable; the use of conventional impression techniques will result in a distorted impression.

Therefore, you need to modify the impression technique.

You can make the secondary impression by using low fusing impression compound (green stick). Knead the green stick compound into a homogeneous mass, load it onto the special tray, and implement border movements.

You make the final impression using either zinc oxide eugenol or a medium viscosity elastomer.

You make the functional impression after checking the fit of the custom tray both statically and dynamically and making any necessary corrections. First, place 0.5-1 mm thick spacers made from thermoplastic material or light-curing acrylic resin in the middle of the alveolar ridge on both sides

anterior and posterior area. During the fabrication of spacers it is important to avoid areas of displaceable mucosa, in order to avoid rocking of the prosthesis. ³

The next step is taking impression of functional margins with a thermoplastic material, FIG II by the patient performing active, and the operator passive functional movements, to record the frenulum and plica insertion. After the impression, the custom tray should have a suction effect.

Figure 1: Complete denture final impression techniques.

Figure 2: Border molding and final impression.

It may be done in closed mouth functional impression technique. In this technique, denture bases with occlusal rim are fabricated on primary cast. Jaw relations are registered (Fig. 3) to record appropriate horizontal and vertical dimensions. ¹

Figure 3: Closed mouth functional impression technique

To sum up, you can hold final impressions under either digital or occlusal pressure. In cases of an advanced resorbed ridge or flabby ridge, the ideal procedure involves making the final impression in two steps. First, make a classic impression under correct occlusion with polyether. Then, create a spacing in front of the displaceable mucosa. Mark the border between displaceable and non-displaceable mucosa on the impression and register it a second time with low viscosity polyether, once again under correct jaw relations.(Fig. 4, Fig. 5, Fig. 6, Fig. 7).

Figures 4, 5, 6, 7: Border between displaceable and non-displaceable mucosa is marked on the impression and
registrated in a second time with a low viscosity polyether and once again under correct Jaw relations.

Discussion

The final impression techniques and materials used for complete dentures date back to 1900s . They make the impression using an open-mouth or closed-mouth approach, in one or two steps (Boucher 1951).

In the single-step procedure, border moulding and recording the final impression are performed simultaneously, using the same material, either a resinous wax, or a monophase elastomer. ¹

The two-step final-impression technique begins with border moulding, followed by a final-impression procedure (Chaffee 1999; Friedman 1957; Smith 1979).

Border moulding is defined as “the shaping of impression material along the border areas of an impression tray by functional or manual manipulation of the soft tissues adjacent to the borders to duplicate the contour and size of the vestibule”. It is also defined
as determining the extension of a prosthesis, by using tissue function or manual manipulation of the tissues to shape the border area of an impression material.
It can be accomplished by using either a sectional or a single-step technique, using different types of materials. ⁵

Many procedures used in prosthodontics, including the materials and methods used for complete denture impressions, lack support of good evidence. The aims were to systematically, and critically, review the literature on complete denture impression materials and methods
to identify an impression procedure that can be considered expedient for achieving a satisfactory clinical outcome for complete denture wearers. ²

In the literature there is a distinction between open and closed mouth techniques, techniques without pressure, techniques with selective pressure of the operator, mucostatic and mucodynamic techniques and techniques with active (patient) and passive (operator) functional movements.

This article describes techniques for taking functional impressions while simultaneously determining interjaw relationships.

Even though preferences for materials or methods vary widely among individuals, most authorities believe a two step procedure is necessary for a successful outcome.

Complete dentures primarily serve as mechanical devices, but since they function in the oral cavity, they must harmonize with normal neuromuscular function.

However, whether any one combination of material and technique yields a better long-term result for the complete denture performance than another is a question that remains open due to a lack of strong evidence. ⁷

Conclusion

Practically all dental schools and the majority of prosthodontists use a two-step procedure for complete denture impressions. All textbooks on complete dentures available to us, including the most recent ones, advocate a procedure with a preliminary impression, at present usually with an irreversible hydrocolloid (alginate) in a stock tray, and a final impression with a variety of materials in a custom tray, typically made of acrylic resin.

The objective of complete denture treatment is to enable recovery of occlusal, masticatory, esthetic, physiognomic, phonetic and psychosocial functions of the patients.

References

1. Bhupender Yadav, Manisha Jayna, Harish Yadav, Shrey Suri, Shefali Phogat, and Reshu Madan – Comparison of Different Final Impression Techniques for Management of Resorbed Mandibular Ridge: A Case Report ; Hindawi Publishing Corporation Case Reports in Dentistry Volume 2014, 1-6 .

2. Gunnar E. Carlsson , Anders O¨ rtorp , Ridwaan Omar – What is the evidence base for the efficacies of different complete denture impression procedures? A critical review ; journal of dentistry 41 ( 2013 ) 17 – 23.

3. Hrvoje Kršek, Nikša Dulčić – Functional Impressions in Complete Denture and Overdenture Treatment; Acta stomatol Croat. 2015; 49 (1) :45-53.

4. Jayaraman S, Singh BP, Ramanathan B, Pazhaniappan PillaiM, MacDonald L,Kirubakaran R.

Final-impression techniques and materials for making complete and removable partial dentures. Cochrane Database of Systematic Reviews 2018, Issue 4. Art. No.: CD012256.

5. Khajuria RR, Hajira N, Safaya R, Singh R. – Comparison of The Surface Area Coverage of The Impressions Made of Impression Compound And Alginate: An in Vitro Evaluation ; IOSR Journal of Dental and Medical Sciences Volume 16, Issue 12 (Dec. 2017), PP 06-10.

6. Ravindra S.Pawar, Rahul S. Kulkarni, and Pravin E. Raipure – A modified technique for single-step border molding ; The journal of prosthetic dentistry 2018 ;1-4.

7. Sara Nikoee Bazvand, Farshad Khamchin Moghaddam, Nazila Najari Dizaji and Shahin Shams Lahijani, The role of different impression methods for complete denture prosthodontics; Biosci. Biotech. Res. Comm. 10(3): 410-414 (2017)