A simple method for fabricating custom sectional impression trays for making definitive impressions in patients with microstomia.

OBJECTIVE: A maximum mouth opening that is smaller than the size of a complete denture can make prosthetic treatment challenging. This article describes a simple technique used to fabricate maxillary and mandibular custom sectional impression trays for making definitive impressions in patients with microstomia.

INTRODUCTION

Microstomia is defined as an abnormally small oral orifice.1 This disorder is described as a reduction in the oral aperture size associated with facial burns, diffuse scleroderma, traumatic injuries, and surgical reconstruction involving the orbicularis oris muscle. Microstomia can result in multiple debilitating sequelae such as inability to masticate, droolin g, speech problems due to poor articulation, impaired delivery of oral hygiene and dental care, and psychological problems secondary to facial disfigurement.2–8

Several methods of prosthodontic treatment for microstomia patients have been presented, and numerous devices to expand the oral commissure have been described.3,9–12 The prosthetic rehabilitation of microstomia patients presents difficulties at all stages, from preliminary impressions to prosthesis fabrication.13 Because such patients have small oral openings, using conventional methods for making definitive dental impressions and fabricating dentures may be extremely difficult. Making the accurate impressions represents the initial difficulty in the prosthetic rehabilitation of such patients.

The recommended techniques for obtaining preliminary impressions for microstomia patients include the use of modeling plastic impression compound, the use of stock impression trays with heavy and light body silicone impression materials, and flexible impression trays with silicone putty.

The casts obtained from these preliminary impressions are then used for making custom sectional impression trays. These trays typically consist of 2 locking devices or assemblies, 1 situated anteriorly and the other posteriorly, which join and provide stability to both the sections of the trays. These 2 sections of the trays are assembled and disassembled intraorally. After the definitive impressions are made, these trays are reassembled extraorally and are poured in dental stone to obtain definitive, working casts.

Several studies have described various techniques that are used for making custom sectional impression trays.14–18 Different devices used for connecting the custom sectional trays include hinges,14 plastic building blocks (Lego; Lego Systems Inc, Enfield, Conn., USA),15,16 orthodontic expansion screws,17 or locking levers.18

This article describes a simple, cost-effective, and time-saving method for fabricating custom sectional impression trays using easily available dual die-pins and sleeves as potential devices for interlocking the sectional trays. The locking mechanism design includes an anterior locking assembly for the maxillary and mandibular custom trays and a posterior locking assembly for only the maxillary custom tray.

By using the conventional method, fabricate the maxillary and mandibular custom sectional impression trays by using autopolymerizing acrylic resin (DPI-RR, Dental Products of India, Mumbai, India) on the preliminary casts.

Make the handles of the trays (minimum dimensions with 13 mm height, 10 mm length, and 10 mm width) such that they incorporate the metal sleeves of the dual die-pins (M.R.™ Dual Pin and sleeves, Select Dental).

Section both the custom impression trays at the midline by using a diamond disk (DFS, Germany).

Steps in the fabrication of the anterior lock assembly in the maxillary and mandibular custom sectional impression trays:

- The assembly basically consists of 2 dual die-pins and 2 sleeves. Closely juxtapose the 2 sleeves such that the smaller keyway of 1 sleeve faces the larger keyway of the other sleeve. Join these sleeves by inserting the 2 dual die-pins and making the assembly a rigid joint (Figure 1a–d).

Figure 1

a–d. Basic design and components of anterior locking assembly for maxillary and mandibular sectional tray. a) Dual die-pins with sleeves, b) sleeves in approximated position (Top view) and two dual die-pins, c) Dual die-pins inserted in contralateral direction making a rigid joint for anterior locking assembly (Top view), d) lateral view of anterior locking assembly.

- Make a slot on the inside portion of the handles on each half of the sectioned custom trays to incorporate the sleeve (Figure 2a & b).

Figure 2 a–b.

Slots made for attaching sleeves in each half of maxillary sectioned tray. a) Inside view, b) top view.view of anterior locking assembly.

- Attach the sleeves in the slots by using the autopolymerizing acrylic resin as mentioned previously (Figure 3).

Figure 3

Sleeves attached using autopolymerising acrylic resin.

- Verify the position of the attached sleeves by inserting die-pins such that the halves juxtapose precisely in both the sectioned trays.

- Fabricate an anterior assembly for the mandibular sectional tray in a similar manner (Figure 7).

Figure 7

Completed sectional trays with anterior lock assembled (Mandibular)

Steps in the fabrication of the posterior lock assembly in the maxillary custom sectional tray:

- Cut the 2 dual die-pins that are attached to sleeves halfway through their heights (Figure 4) by using a carborundum disk (Dentorium, New York, USA). Only the broader upper halves are used for fabricating the posterior assembly and the lower halves are discarded.

Figure 4

Components of posterior locking assembly- an acrylic block and upper halves of two dual pins and sleeves cut halfway through their height.

- Attach the half-cut sleeves on the posterior parts of the sectioned custom tray halves using acrylic resin such that the greatest dimension of each sleeve is oriented in the anteroposterior direction. Check for parallelism between the sleeves using a dental surveyor and verify the fit of the die-pins in the respective sleeves (Figure 5).

Figure 5

Half-cut sleeve positioned on each sectioned tray and corresponding pins attached to acrylic block.

- Fabricate an acrylic resin block (6 mm height, 10 mm width, and 4 mm longer than the distance between the 2 attached sleeves) using the autopolymerizing acrylic resin (Figure 4).

- Transfer the respective points of the half-cut die-pin heads on the acrylic bar by using a pressure spot indicator (Coltene® PSI, Switzerland) and drill slightly oversized holes in the acrylic bar on the marked points by using a bur (261-EF023, Brasseler, USA).

- With the closely juxtaposed sectioned trays and the die-pins of the anterior assembly placed in position, secure the heads of the half-cut die-pins into the holes by using the autopolymerizing acrylic resin (Figure 5 & Figure 6).

Figure 6

Completed sectional trays with both anterior and posterior locks assembled (Maxillary).

DISCUSSION

The 2-piece custom-made tray described above allows for a functional impression to be made despite the difficulties associated with microstomia. The anterior locking assembly described in this article does not require any special alteration in the conventional custom tray design. The die-pins with metal sleeves used in this technique provide a greater degree of stability and a precise union of the 2 sections of the tray. It also provides a rigid joint without increasing the bulk of the tray. The joint can be made more rigid by activating the 2 prongs of each dual die-pin away from each other. This technique used for fabricating custom sectional impression trays does not require any special devices or complex locking joints. The only additional materials used are the dual die-pins which are commercially available at a minimum cost.

SUMMARY

It is often difficult to use conventional methods for fabricating dentures for patients with limited mouth opening. This article described a simple, time-saving, and cost-effective method used to fabricate custom sectional impression trays for making definitive impressions in patients with microstomia.