Final Impression in Complete Dentures

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

Abstract

The history of complete denture impression procedures have been influenced largely by the development of impression materials from which new techniques arose. Selection of material is left to the decision of the dentist, who makes choices based on 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

Introduction

From an anatomical viewpoint, tooth loss comes to alveolar ridge resorption of the upper and lower jaw which are manifested in a reduction of the attached gingival surface and an increase of 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 are primarily mechanical devices but since they function in the oral cavity, they must be fashioned so that they are in harmony with the normal neuromuscular function.

The history of complete denture impression procedures has been influenced largely by the development of impression materials from which new techniques and ideas arose. 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 of the type of materials that are most often used for impression taking in the fabrication of complete dentures and overdentures indicates that reversible hydrocolloids and alginates are commonly used for taking the first or anatomical impression; thermoplastic materials of the latest generation in the shape of sticks are used for the formation of functional margins; aluminum wax is used for relining of the vibrating line and zinc oxide eugenol pastes and several types of elastomers, condensation silicones vinyl polysiloxane and polyethers are used for taking functional, fixation impression. 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, the impression technique needs to be modified.

Secondary impression can be made by  using  low fusing impression compound (green stick)  ; green stick compound is kneaded to a homogenous mass and is loaded on the special tray and border movements are implemented.

Final impression is made either using zinc oxide eugenol or  with a medium viscosity elastomer.

Functional impression is made after static and dynamic checking of fit of the custom tray and its possible corrections. Firstly, 0.5-1 mm thick spacers made from a thermoplastic material or light curing acrylic resin are placed in the middle of the alveolar ridge of both the
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.

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

To sum up, final impressions can be held either under digital pressure or occlusal one; in case of advanced resorbed ridge; or flubby ridge; in fact in this last situation; the ideal way to procede is to make the final impression in two steps: first a classic  impression under correct occlusion with polyether, than a spacing will be led in front of displaceable mucosa; then the border between displaceable and non-displaceable mucosa is marked on the impression and registered in a second time with  a low viscosity polyether and once again under correct Jaw relations. (Fig. 4, Fig. 5, Fig. 6, Fig. 7).

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. Techniques of functional impression taking with simultaneous determination of interjaw relationships are also described.

Complete dentures are primarily mechanical devices but since they function in the oral cavity, they must be fashioned so that they are in harmony with the normal neuromuscular function.

Even though there are wide variations in individual preferences for a particular material or method, most authorities believe that, for a successful outcome to be achieved, a two-step procedure is required.

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)