Biometric Approach In Designing Complete Dentures
4/17/2015Biometric Approach inDesigning Complete DenturesSandra AlTarawneh, DDS, MS, FACPApril, 18, 2015Objectives Pattern of bone resorption.Landmarks to positions of the predecessors.The biometric method of impression making.Biometric special trays.Land marks to determine lip support andvertical dimension of occlusion1
4/17/2015Biomechanics of the Edentulous State Maxilla resorbs primarily from the buccal andlabial surfaces Mandible:– Posterior arch width increases in sizeAnatomic Effects of ResorptionReduction in alveolar ridge leads to Reduction of the pre-extraction morphologicface height Reduction in the rest face height Causes mandible to rotate forward-upwardaffecting the vertical dimensionTallgren JPD 19722
4/17/2015Mechanism of Complete DentureSupport Forces produced on occlusal surfaces bymasticatory muscles are transmitted to ridge Maximum biting forces are 5-6 times less forcomplete dentures wearers Mean denture-bearing area in edentulousmaxilla 23cm2 and edentulous mandible12cm2{Zarb et al, 1997}It is generally accepted that impressions of edentulousmouths should place the lips and cheeks in their preextraction positions.The means of achieving this vary considerably betweendifferent operators.Denture space: is that space in the mouth which wasformerly occupied by the teeth and the supportingtissues which have since been lost.3
4/17/2015Function of impression trays ?By the ‘tray’ is meant the appliance that carriesthe impression material into the mouth, whetherthe appliance is a conventional tray or a recordblock inside which a paste-wash impression istaken.When placed in the mouth the empty tray shouldsatisfactorily restore the facial contour andprovide an airtight seal between the tray and theoral tissues. Thus, the empty tray should beretentive before the impression is taken.4
4/17/2015RESTORATION OF FACIAL CONTOURThere are several methods of ensuring that the facial contour isproperly restored:1. If the impression is to be taken within a record block, the blockshould be modified to establish the lip form and buccal contour.2. If a conventional impression tray is used, it should be built outwith impression compound until the facial form is restored.3. use measurements of the average pre-extraction buccolingualbreadth of the alveolar process to define the positions of the lipsand cheeks and to construct what we call ‘biometric’ trays. Theserestore the pre-extraction form of cheeks and lips so that thecorrect shape of the sulcus can then be recorded with a softimpression material.Construction of a maxillarybiometric tray5
4/17/2015the incisive papilla and the palatal-gingival margin(the remnant of the gingival margin on the palatalside of the dental arch, which after toothextractions often remains visible as a cordlikeelevation) work as landmarks for estimating thepreextraction dimensions of the ridge.6
4/17/2015The distance between the palatal gingivae and the labialor buccal surface of the teeth is termed the buccopalatalbreadth. The is on average about 6 mm in the incisorregion, 8mm for the canines, 10 mm for the premolarsand 12mm for the molars. Therefore, by distinguishingthe palatal gingival vestige, the position of the labialsurface of the artificial teeth can be readily identified7
4/17/2015Construction of a maxillary biometric tray1) Take the preliminary impression so that thepreliminary cast represents the full suclus width.2) On the cast from the preliminary impression, make apencil line 5 mm on the sulcus side of the mucogingivalline to indicate the depth of the buccal flange of theupper tray3) Fill the buccal sulcus with wax to form a horizontal ledge of waxround the upper cast at the level of the pencil line.4) With a pair of calipers mark on the wax the approximate averagebuccolingual horizontal measurements from the remnant of thelingual gingival margins. Sagittally in the incisor region and coronailyin the other regions, thesemeasurements areapproximately6 mm (incisor), 8 mm (canine),10 mm (premolar)and 12 mm (molar).8
4/17/20155. Draw a line on the wax joining thesemeasurements together.6. On the cast lay down a wax spacer ofappropriate thickness to provide room for theimpression material to be used.7. Make a tray so that the outer surface of theperiphery lies on the line marked on the waxledge.9
4/17/20158. Place a localizing stop in the vault of the palate to ensurecorrect placement of the tray when the Impression is taken.9. Biometric trays designed on the basis of the average preextraction measurements of buccolingual breadth displace thecheeks slightly and produce a buccal seal10. Place a post-dam of tracing stick along the posterior edge ofthe tray and mould it in the mouth. When the post-dam has beenformed, check the retention of the tray before taking theimpression. In every case the empty tray should be retentivebefore the impression is finally taken with a fluid mix ofimpression material.MANDIBULAR BIOMETRIC TRAYMeasurements of the kind made on the maxillary castare not practicable on mandibular casts10
4/17/2015Biometric lower trays are constructed to prevent the inwardcollapse of lips and cheeks and to hold them in their formerupright positions, so that the impression material is supportedas it runs round the edge of the tray and up between the trayand tissues.The front of the biometric tray slopes forward to support thelower lip and in this way the labial sulcus is correctly defined.In the molar region the buccal flange of the tray is thickenedso that the impression material is supported to delineate theform of the buccinator as its middle fibers sweep linguallytowards the pterygomandibular raphaeJaw relation registration11
4/17/2015Biometric GuidesNasolabial angleHorizontal labial angle12
4/17/2015Vermilion border showThe effect of nose form and angle of inclination ofteethThe relationship of maxillary incisors to the incisivepapilla13
Designing Complete Dentures Sandra AlTarawneh, DDS, MS, FACP April, 18, 2015 Objectives Pattern of bone resorption. Landmarks to positions of the predecessors. The biometric method of impression making. Biometric special trays. Land marks to determine lip support and vertical dimension of occlusion
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