Single-step Border Moulding Using Putty Polyvinyl Siloxane and Auto-mix Dispensing Gun: An Alternate Technique

Karishma Jagadeesh¹ https://orcid.org/0000-0002-0024-4932, Ravishankar Krishna² https://orcid.org/0000-0002-8381-4303, Chinmaya Bhandary³, Prasanna Vadhani⁴ https://orcid.org/0000-0001-9889-9816

^1-4Department of Prosthodontics, Faculty of Dental Sciences, Ramaiah University of Applied Sciences, Bengaluru, Karnataka, India

Corresponding Author: Ravishankar Krishna, Department of Prosthodontics, Faculty of Dental Sciences, Ramaiah University of Applied Sciences, Bengaluru, Karnataka, India, Phone: +91 9886056303, e-mail: ravishankar.pr.ds@msruas.ac.in

ABSTRACT

Background: The putty viscosity of PVS material offers several advantages for single-step border moulding. However, a common problem is the thick overextended borders related to its viscosity and also due to the application of uneven thickness of putty material on the tray borders, which is commonly associated with the hand-roll application technique.

Aim and objective: To propose a reliable technique for applying even thickness of putty polyvinyl siloxane (PVS) impression material in one go and at a lower viscosity for single-step border moulding using a modified dental impression dispensing gun system.

Technique: One of the outlets of an empty PVS impression cartridge is modified to a diameter of 4 mm. A homogenous mix of putty PVS is loaded into the modified cartridge and the gun is activated. On activation, a uniform thickness of putty can be dispensed onto the custom tray borders to carry out single-step border moulding. The viscosity of such dispensed material is also low due to the shear-thinning phenomenon.

Conclusion: A simple alternate technique of single-step border moulding using putty PVS and a modified dental impression dispensing gun system has been described. The technique is reliable, based on commonly used equipment, and also cost-effective.

How to cite this article: Jagadeesh K, Krishna R, Bhandary C, et al. Single-step Border Moulding Using Putty Polyvinyl Siloxane and Auto-mix Dispensing Gun: An Alternate Technique. Int J Prosthodont Restor Dent 2021;11(4):198-201.

Source of support: Nil

Conflict of interest: None

Keywords: Clinical technique, Dental impression dispensing gun system, Poly vinylsiloxane, Putty poly vinylsiloxane, Single-step border moulding

INTRODUCTION

Border moulding is the shaping of impression material along the borders of an impression tray by manipulation of the soft tissues to duplicate the contour and size of the vestibule.¹ Ideally, the material used for border moulding when in a plastic state should contact the entire vestibular sulcus area at one insertion.² The single-step border moulding technique fulfills this requirement and is also more straightforward than the sectional border moulding technique mainly, because: (1) the number of tray insertions for maxillary and mandibular border moulding is reduced to two, and (2) development of all borders simultaneously avoids propagation of errors caused by a mistake in one section affecting the border contours in another section.

The introduction of elastomeric impression materials has led to new techniques of impression making for complete denture construction. Today’s clinicians more often follow easier impression techniques with elastomeric materials than using traditional methods.³ According to reports in the literature, single-step border moulding can also be carried out using visible light-polymerizing tray material.⁴^,⁵ This technique offers extended working time and is therefore advantageous for operators with less experience. However, the technique is not indicated in the presence of severe tissue undercuts due to the rigid nature of the material.⁵

Among the elastomers, single-step border moulding is usually performed using putty poly vinylsiloxane (PVS), heavy body PVS and polyether impression materials.⁵ Several studies have reported major benefits specific to the use of polyether and putty viscosity PVS impression materials.²^,⁶^,⁷ The important advantages of these two materials related to edentulous impression making are: (1) easy manipulation either by hand or by mechanical mixing, (2) allow preshaping of the border form, (3) possess sufficient body to remain in position on the tray borders during border moulding, (4) easy trimming and shaping of the excess material before the final impression so that excess material can be carved and the borders shaped, (5) exceptional elastic recovery, especially for PVS material, and (6) good reproduction of soft tissue details. However, both polyether and PVS impression materials present certain limitations related to the single-step border moulding procedure. A limitation of polyether impression material is its inadequate working time.⁸ Moreover, due to its stiff nature, retrieval of the impression is difficult in the presence of deep tissue undercuts and hence, causes patient discomfort. Heavy bodied PVS material does not allow preshaping with fingers and is difficult to trim after setting.⁷ Problems reported with putty PVS material include thick overextended borders and a short manipulation time during border moulding.⁸ The working time of PVS putty can be improved by incorporating the manufacturer-recommended retarder during manipulation and also by refrigerating the material before mixing.⁹ Chee et al.¹⁰ reported an increase in working time by 1½ minutes when the material was refrigerated. Single-step border moulding with putty PVS is commonly carried out by hand-rolling the material into shape before its placement on the tray borders.⁸ A drawback of this technique is the lack of control over the thickness of the preshaped putty material that could lead to overextended borders during border moulding, especially among the less experienced operators. Further, the borders have a tendency for overextension due to the viscous nature of putty. An alternate method to uniformly apply putty PVS at a lower viscosity for single-step border moulding is presented, by using a modified automatic dispensing device for elastomeric impression materials.

Technique

Fabricate maxillary and mandibular custom trays on primary casts using self-polymerizing resin (Clear acrylic, DPI-RR) (Fig. 1A). Ensure that the borders of both trays are 3 mm wide and short of the periphery by 2-3 mm on the cast.
Widen one of the outlets of an empty PVS impression cartridge (Elite HD+, Zhermack) to a diameter of 4 mm using a tungsten carbide bur (Carbide bur HP-702, SS White) (Fig. 1B).
Place a slender instrument like the sharp end of a wax spatula into the enlarged outlet and push the lip seal cork out through the back end of the cartridge (Fig. 2A). Use a gauge to clean the cork and inner walls of the cartridge.
Verify the custom trays intraorally and reduce any overextended borders. Make sure the borders of both the trays are 3 mm in thickness after reduction. Apply tray adhesive (Adhesive PVS, Coltene) on the borders of the tray; including 2 mm of the inner and outer flanges and the posterior palatal seal area. Allow it to dry.
Use non-latex gloved hands to mix the appropriate amount of refrigerated base and catalyst of putty PVS (Elite HD+ soft putty, Zhermack) in 1:1 proportion. Load the homogenous mix into the modified impression cartridge through its back end. Replace the lip seal cork onto the impression cartridge (Fig. 2B) and attach it to the dispensing gun.
Quickly activate the gun so that the plunger contacts the cork and the loaded material is pushed toward the dispensing end. Activate the gun to uniformly apply 4 mm thickness of putty material on the maxillary tray borders including the posterior palatal seal area (Fig. 3A).
Using index finger and thumb adapt the applied putty onto the tray borders including the inner and outer flanges of the tray. Preshape the material using the tray border thickness as a guide. This distribution pushes some material to the inside and outside of the tray border bringing down the thickness of the applied putty material from 4 mm to about 3 mm. Place the custom tray intraorally on the maxillary edentulous ridge and carry out the single-step border moulding procedure by following established clinical guidelines.
Remove the tray from the mouth after complete polymerization of the putty material and inspect the tray borders. Cut the over-extended borders with a BP blade (No. 22, Lister) and handle. Reinsert the maxillary border moulded custom tray intraorally and verify the extensions and retention.
Repeat the procedure for the mandibular arch (Fig. 3B). Reduce 0.5 mm from the borders of both the impression trays (Fig. 4A) by using a tungsten carbide bur (Carbide bur HP, WL- B1, Waldent) to make space for the low-viscosity polyvinyl siloxane material (Elite HD+ Light, Zhermack). Carefully remove the spacer without disrupting the border moulding from the trays. Make vent holes using a 702 tungsten carbide bur under low speed on both trays to allow the escape of excess final impression material.
Use low-viscosity PVS material to make maxillary and mandibular definitive impressions (Fig. 4B).

Figs 1A and B: (A) Maxillary and mandibular custom trays fabricated with self-polymerizing resin; (B) Widening one outlet of empty PVS impression cartridge to 4 mm diameter

Figs 2A and B: (A) Removal of lip seal cork using the sharp end of the wax spatula; (B) Replacement of lip seal cork after loading mixed putty PVS material

Figs 3A and B: (A) Uniform application of putty (4 mm thick) on maxillary tray borders; (B) Uniform application of putty (4 mm thick) on mandibular tray borders

Figs 4A and B: (A) Completed maxillary and mandibular border moulding; (B) Definitive impressions made with light viscosity PVS material

DISCUSSION

Though border moulding is commonly performed using a sectional technique with a low fusing impression compound, a definite tendency toward the increased use of elastomers has been noted recently.¹¹ Sectional technique is associated with many disadvantages. Major disadvantages are that it does not allow for the recording of all the borders simultaneously and also, errors developed in one section of the tray can propagate to another section. Along with the increased number of tray insertions into the patient’s mouth, low fusing impression compound can be messy and is also associated with the fear of burning the soft tissue due to the heat subjected to soften the material.⁸ These disadvantages have led to increased use of elastomers for border moulding. Recent studies also indicate higher retention of the maxillary/mandibular denture base when border moulding was performed using PVS putty as against low fusing compound.¹²^,¹³

A characteristic feature of elastomeric impression materials is shear-thinning, an apparent decrease in viscosity, and improved flow when subjected to a shear load.¹⁴ In the present technique, activating the impression dispensing gun pushes the plunger to apply a shear-thinning load on the putty material incorporated into the cartridge. A significant advantage of this is that putty can be dispensed at a lower viscosity. In the described method, the outlet of the empty impression cartridge was modified to 4 mm diameter to apply an even thickness of putty material. However, this thickness gets reduced to about 3 mm after preshaping and adapting the putty material on the tray borders. Hence, this technique prevents the application of inappropriately thick or thin material to the tray borders. This is a major advantage for clinicians as the technique is simple, easy, and therefore, can improve their confidence in single-step border moulding procedure.

The described novel technique enables the clinician to have control over the thickness and viscosity of the applied putty material for single-step border moulding so that overextensions can be minimized. This improvement in the accuracy of border moulding can minimize the chair-side adjustment of the borders of the definitive prosthesis. Additionally, this technique is more reliable to uniformly apply the impression material onto the tray borders continuously in one go than the commonly followed hand-roll application technique.

Although the use of disposable plastic syringes can yield the same results, it would directly contribute to the alarmingly increasing global plastic waste. The advantage of using an impression cartridge is not only that it is easily available to every dentist; but also that it’s providing a reusable purpose to a material that would otherwise be a plastic waste. Drawbacks of the technique include the added time required for modifying the impression cartridge and the correction of borders by the addition of new material is not recommended. A study comparing the efficacy of single-step border moulding accomplished with hand roll application as against the controlled application through a modified impression cartridge along with patient satisfaction scores can provide useful information.

CONCLUSION

This article describes an alternate technique of single-step border moulding by using putty PVS and a modified dental impression gun system. The technique is reliable, prevents additional use of plastic, utilizes commonly used equipment, and is cost-effective.

ORCID

Karishma Jagadeesh https://orcid.org/0000-0002-0024-4932

Ravishankar Krishna https://orcid.org/0000-0002-8381-4303

Prasanna Vadhani https://orcid.org/0000-0001-9889-9816

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