First Impressions Count

First Impressions Count

By Anish Mehay and Oliver Milton

The paper written by Jonathan Turner, Rebecca Moassez and Avjit Banerjee aims to cover the clinical aspects of impression taking for fixed and removable prosthodontics including the planning and preparating for the final constructed prosthesis.1DefinitionsRetention resistance of a denture to vertical movement away from the tissues

Support resistance of a denture to occlusally directed loads

Stability resistance of a denture to functional forcesIn terms of denture success, three criteria must be met in order for the denture to fit in the mouth correctly and provide its function. The british society for the study of prosthetic dentistry defines retention as the resistance of a denture to vertical movement away from the tissues, support as the resistance of a denture to occlusally directed loads and stability as the resistance of a denture of a denture to displacement by functional forces.2Important anatomical landmarks maxillary edentate arch

Incisive papilla anterior tooth position guide

Hard palate support for denture

Fovea palatinae guide for the posterior border of special tray/denture

Hamular notches guide for the posterior border of special tray/denture

PERIPHERAL SEAL AND THEREFORE RETENTION!Initially if we look at the maxillary edentate arch we can see four key anatomical areas that must be recorded when taking an impression. Each anatomical area has an effect on optimum retention, stability or support. For example, the incisive papilla is important for the guide for anterior tooth position, the hard palate is required for support of the denture, the fovae palatinae aids to guide the posterior border of the special tray/ denture and the hamular notches also aid to guide the position of the posterior border as well. It is important that the tray extends to this areas to a peripheral seal is obstained and thus denture has sufficient retention3Important anatomical landmarks mandibular edentulous arch

Retromolar pad retention

Retromylohoid fossa stability

Buccal shelf support

Residual alveolar ridge crest - stabilityIn the mandibular edentulous arch we can see the retromolar pad, retromylohyoid fossa, buccal shelf and residual alveolar ridge crest. 4Patient complains of A loose fitting dentureEstablish wether cause is from inadequate retention, support or stability, or more commonly..a combination of all threeFAULTS IN IMPRESSION TAKING

A key reason why people have inadequate retention, support and stability in their dentures is that their denture base may be under extended which is directly related to faults in impression taking. For example, if we take a maxillary complete denture which only covers half of the hard palate, it will lack adequate support, and if the denture does not extend to the fovea palatinae region ( past the vibrating area ) it will lack adequate seal and therefore retention5Primary ImpressionsWhy?Enables study model manufactureProduction of custom tray

Primary ImpressionsEdentulous patients:Outlines areas involved with denture supportOutlines correct extensions for special tray -Helps facilitate peripheral sealIf criteria not met- Impossible to record satisfactory second impressionPrimary Impressions Partial denture casesCasts can be surveyed and provisional designs can be drawn - Due to assessment of: Tooth/hard tissue undercutsDepths of sulciPosition of fraenal attachmentPresence of naturally occurring guide planesPrimary impressionsMetal or plastic stock trays can be used -Disposable plastic most common -Easy to trim if overextended -Silicon/wax used to extend underextended

Primary ImpressionsSilicon putty/impression compound used to adjust trayAlginate commonly usedSilicones/impression comp can be used-If inadequate detail- Thin wash of alginate may be used

Primary ImpressionsUpper ImpressionStand behind pt.Seat anterior first

Lower ImpressionStand in front of pt.Avoid trapping tonguePt. to protrude tongue to lower lip

Remove with snap movementInfection controlUpon taking the primary impression must disinfect for adequate time according for manufacturers instructionsPERFORM 10% for 1 minute

Upon taking impressions, the impression should be disinfected in the appropriate disinfectant according to the manufacturers instructions. Care should be taken to avoid not soaking the impression for too long as this may affect the dimensional accuracy and too short of a disinfectant time. Must ensure the impression has recorded all relevant anatomical landmarks as previously discussed. When completeing the lab prescription must be confirmed that disinfection has been carried out.12Secondary impressionsRecord of denture bearing areaRelevant abutment teeth Tissues in contact with denture base during function and the sulci, with the lips and cheeks supported, must be recordedPeripheral border seal - if its not good we can add green-stick compoundIf there is under-extension green-stick compoundThere is over-extension trim special tray with an acrylic bur

13Anterior fibrous changeIf the lower teeth occlude with an edentulous maxillary ridge we can get fibrous change to the maxillary anterior ridge can occur over time.

Use of a normal impression technique may lead to displacement of the ridge unretentive denture produce a special tray with a window over the fibrous area so excess material can flow out

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Impression is taken in 2 stages, firstly a wash impression is applied to the fit surface and tray is seateed. When set, the tray is removed and any material that has flowed into the window area is cut away using a scalpel. The tray is then re seated and zno is painted over the exposed window area. Once set the tray is removed and resulting impression should have recorded the area of fibrous change in an undisplaced state.14Replica/copy dentureReplication of current dentureTaking impression of fit surface and polished surfacehttp://www.mecourse.com/ecourse/pages/page.asp?pid=1393

Replica/copy dentureUnder-extensions corrected prior to impression of original dentureMethod:Large stock tray used with alginate or siliconEmbed denture (polished surface down)Lubricate fit surfaceFill another traySeat over fit surface + sandwichSend to lab

Replica/copy dentureOn second visitImpression of patient denture bearing tissues takenUse ZOE or Light body siliconUsing wash technique on constructed replicaTake jaw reg (after impression)

Neutral zone techniqueDefinition:A zone in which the forces of the cheeks and lips are said to be in equilibrium with those of the tongue

Neutral zone techniqueImproves stability of the lower denture if set within itImpression techniques to determine its locationAim to locate the teeth on the denture within this zoneHelpful if pt. has powerful oral muscular controlNeutral zone techniqueMethodUndertake conventional impression and jaw reg techniqueConstruct mandibular baseplate with vertical stops to upper surface (contact max. try-in denture)Wire running between retains imp. MaterialTake impression with upper in Tongue movementsLeave upper and lower together

Remove undercuts on the fit surfaceApply thin wash of flowable impression materialTwo techniquesOpen technique: using denture as a special tray, seating it in the mouth with wash materialClosed technique: patient lightly closes mouth to reach position of maximum intercuspation.Any excess material will flow out from edgesReline/Rebase:

Summary The Golden Triangle of impression takingAn appreciation of the anatomical featuresMaterial used to take the impressionClinical handling/operative technique appliedThank you for listening

Any Questions??ReferencesTurner JW, Moazzez R, Banerjee A. Restorative Dentistry: First Impressions Count. Dental Update 2012; 39: 455-471