journal club junior resident 2

8/6/2019 JOURNAL CLUB Junior Resident 2

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Use of orthodontic

expansion screw infabricating section

custom traysJ Prosthet Dent 2000;83:474-

5.


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INTRODUCTION

In Prosthodontic treatment, the loadedimpression tray is the largest itemrequiring intraoral placement. During

impression procedures, wide mouthopening is required for proper trayinsertion and alignment.

Because this is not possible in patientswith restricted opening ability, amodification of the standard

impression procedure is often


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The use of an orthodonticexpansion screw

( 2 guide pins and a screw) without thescrew axis,serves as a guide or keyand keyway to fabricate a split

custom tray. Preparation of a butt joint along the

2 pieces of a maxillary tray can

enhance its stabilization during border correction and

impression making.


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Three-axis expansion screwafter removal of screw.


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Maxillary and Mandibular traysrequire different locations for the

key and keyway. For the maxillary tray, the holes

must be located in the overlay piece

and the guide pins are placed in theother half for better access

For the mandibular tray, guide pinsare placed in the overlay piece andholes are located in the other half(Fig. 4).


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Two pieces of maxillarysectional tray after separation.


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The expansion screw is placed verticallyin the handle of the custom tray to

accommodate the limited space (Fig.3).

The length of the guide pins in theexpansion screw can be reduced foreasier insertion and removal ifnecessary.


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Maxillary tray (underlying piece) withbutt joint alongline of separation.

First part of handle with expansionscrew is embedded in acrylic resin.

M dib l ti l t i


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Mandibular sectional trays inpatients mouth. Lengthof

guide pins reduced for easierinsertion and removal

I i d f


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Impression procedure forpatients with severely

limited mouth opening

(J Prosthet Dent 2000;84:241-4.)


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Patients with limited mouth openingare a common occurrence inprosthodontic practice. The majority

of these patients can be treated withexercise and stretching movementsbefore impressions are made.

Some will not respond to theseprocedures because of facial scarringand surgical manipulation of the

facial muscles. This article presents animpression procedure for overcomingsuch reduced mouth opening.


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The purpose of this article is todescribe an alternative to the stockimpression tray and discuss the

procedures necessary forfabricating a removable partialdenture (RPD) for a patient with

restricted oral opening.


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PRELIMINARYIMPRESSION

A stock tray is modified to make asatisfactory

preliminary impression. Trimming the flangelengths

and adding compound as necessary are oftenhelpful.

If a 1-piece tray cannot be used, then thestock tray

may be cut in half and the halvesapproximated to

form the preliminary cast. Practicality is the


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The practitioner must make apreliminary impression that isaccurate enough to fabricate the

modified custom tray to be used forthe final impression.


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CUSTOM TRAY Essential landmarks required for the

successful fabrication of aprosthesis must be identified.

In a patient with restricted opening,it is difficult to obtain the perfectimpression that captures allpossible anatomic details.


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It is more difficult to insert the tray thanto remove it from the mouth. Whenthe tray is placed in the mouth,

the operator usually stretchesone corner, making the oralopening still smaller.

During removal, the orbicularis oris can

be stretched beyond the limit of thepatients normal function. In thissituation, the muscles sphinctericshape allows the operator additional

maneuverability.


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Rounding is achieved largely by the action of theorbicularis oris muscle, (the muscle that

encircles the lips). This is a sphincter muscle, a circularband of muscle fibers that constrict an opening, like a

purse string.


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In the laboratory, the tray is usuallyplaced

and removed from the cast in avertical motion.

In a mouth with limited opening, amore horizontal motion must beused. The clinical realities of thepatients limitations must berecognized during the design of the

tray.

Because the tray is not used unloaded,flange

len th is increased when the


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PROCEDURE

1. Make a preliminary irreversiblehydrocolloid impression by sectioninga stock disposable plastic tray, and

inserting and removing it in sections. Pour cast in improved stone. Design the

custom tray so that it fits precisely,and incorporates a lockingmechanism that separates easily inthe mouth and reassemblesaccurately after the impression

procedure is completed.


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Outline landmarks essential to thedesign of the removable partialdenture on the cast for coverage bythe tray material. Use undercutblockout for all involved areas of

the cast at this time.

Incorporate relief for the impression

material and cutouts forocclusal/incisal stops only for thefirst tray section at this time, with

termination at the midline.


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Fabricate half of the custom trayusing light-cured tray material onthe duplicate cast. Align the handle

and the labial,buccal and lingualsegment edges in 1 plane at themidline to match easily with the

second half. Place a knob on the inside of the

handle that will later fit into an

opening on the handle of the


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Make the horizontal locking componentseparately,then attach it (Fig. 2).

Lubricate the hinge opening of thehorizontal latch, fill it with traymaterial, and join the added traymaterial to the superior surface of

first tray half to form a nailhead tosecure the horizontal lockingcomponent.

To ensure proper hinge movement,

manipulate thelatch back and fortharound the new material.Cure the resin for 2 minutes, and again

check thelocking component for mobility, at which


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After the first segment is completed,polish and lubricate (a precise fit isrequired). Relief wax and stops arenow placed for the final tray section.

The second handle has a hole on itsmedial surface No attempt is made tosecure the locking

mechanism at this point. The 2 halvesshould fit

together and function as 1 unit withno visible


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Complete the horizontal lockingmechanism. Lubricate the hookedarea of the locking mechanism and

fit the halves together. Add resinmaterial to the hook area and curefor 2 minutes.

The locking mechanism mustdisengage at completion. Completecuring. (The tray can now be usedas a single unit or two individual

halves [Fig. 4].


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Final impression

A medium or light viscosity elastomeric

impression material is used tominimize errors due to manipulationdistortion after setting.

Make an impression with the first half of

the tray After removing it from thepatients mouth, trim

the impression material so that it isflush with the

medial edge of the tray (Fig. 5).

For the parts of the impression tray ormaterial

that will contact the second half tray,


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Load the second tray half with impressionmaterial

and insert in the mouth. Squeezetogether the

2 tray parts at the handle. After ensuring

precise fit, engage the horizontal locking

component and allow the impression material to set.

Unlock the tray and remove the partsindividually. Reassemble the trayoutside the mouth; sticky wax or

modeling plastic may be placed across


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Advantages of the technique includesimplified tray manipulation and

decreased patient trauma; theability to use a custom fabricatedtray for optimal impression materialthickness; precise intraoral

positioning and stability; definitiveindexing of tray sections for easyreassembly both intraorally and

extraorally;and possibly eliminationof extraction of healthy teeth thatmight obstruct the placement or

removal of a conventional


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Disadvantages are the additionaltime, materials, and labor requiredfor precise fabrication of the

sectional tray and secondaryimpression;and the requirement forcorrect fitting of the components to

produce an accurate cast.


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THANK YOU!

journal club junior resident 2

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