3 Clinic 1 Primary Impression-summary of the anatomical extent: Maxillary:Residual ridges, tuberosities and hamular notches, functional width and depth of the labial and buccal sulci, including frena.Hard palate and its junction with the soft palate.Mandibular:Residual ridges and retromolar pads.Functional labial and buccal sulci (including frenal and external oblique ridges)Lingual sulci, lingual frenum, mylohyoid ridges and retromylohyoid areas.
5 Mucous membraneMucosa: stratified squamus epithelium & connective tissue (lamina propria)Submucosa: connective tissues made of dens to loose areolar tissuesIf firmly attached: withstand pressureIf loose, thin, traumatized, mobile, flappy: it wont be suitable to withstand pressure-not resilient.Masticatory mucosa (keratinized): hard palate, residual ridges, residual attachment gingiva.
6 Hard palate Keratinized. Mid palatine suture: Submucosa is extremely thin- requires reliefHorizontal portion of the Hard palate: 1 support for areasRugae areas: set at an angle with the residual ridge- 2 support areas.
7 The Palatal Gingival Vestige (remnants of the lingual gingival margin) It is the remains of the palatal gingiva. After tooth extraction the position of the vestige remains relatively constant, the same as the incisive papilla. This can be a very helpful pointer for posterior tooth positioning during denture construction
8 Residual Ridges Mucous membrane: Crest of the ridge: keratinizedfirmly attached.Submucosa: devoid of glandular tissues. Dense collagenous fibers. Relatively thin, but sufficient to provide support for the denture base.Crest of the ridge:Prone to resorption.2 support area.Inclined facial surfacesLoses it’s firm attachmentOffers little supportCannot withstand pressure
9 Two orifices one each side of the midline Two orifices one each side of the midline. Coalescence of several mucous glands - always located in the soft palate. They act as collecting ducts for a group of minor palatine salivary glands
10 Usually 2mm in front of the fovea palatine Imaginary line.Usually 2mm in front of the fovea palatineNot the junction of the hard and soft palate-always on the soft palate.SubmucosaGlandular tissues-because it is not supported by bone, it could be compressed and relocated with the impression to complete the palatal seal.
12 Crest of the residual ridge Ridge is similar to that of the upper in healthy mouth.Attachment varies considerably. In some people, the submucosa is loosely attached to the bone.When securely attached to the bone, the mucous membrane is capable of providing support for the denture. However, because underlying bone is cancelous, the crest of the residual ridge may be not favorable as a primary stress bearing area for the lower denture.
13 Buccal shelf areaThe mucous membrane is more loosely attached and less keratinized than that covering the residual ridge. Although the mucous membrane may not be as suitable histological to provide support for the denture, the bone of the buccal shelf area is covered by a layer of cortical bone. This plus the fact that the shelf lies at right angle to the vertical occlusal forces, makes it the most suitable primary stress bearing area.
14 The external oblique ridge does not govern the extension of the buccal flange because the resistance or lack of it varies widely. The buccal flange may extend to the external oblique ridge, up onto it or even over it depending on the location of the muco buccal fold.The bearing of the denture on muscle fiber of the buccinator would not be possible except for the fact that the fibers run parallel to the base, and ,hence , its action is parallel to the border and not at right angle.
15 Pterygo mandibular raph. Superior constrictor The disto buccal border must converge rapidly to avoid the action of the masseter which is pushing inward the buccinator.Distal extension is limited byRamusBuccinatorPterygo mandibular raph.Superior constrictorThe sharpness of the boundaries of the retromolar fossa. (the denture should extend slightly to the lingual into the pearl shaped retro molar pad.
16 The retro molar pad is a triangular soft pad of tissue The retro molar pad is a triangular soft pad of tissue. Its mucosa is composed of thin non keratinized epithelium. It submucosa containsGlandular tissuesFibers of the buccinator and superior constrictorPterygo mandibular raphFibers of the temporalisBecause of theses structures, the denture base should only extend to one half to two third the retro molar pad.
17 The retro molar pad:It is split into two sections. The anterior section is usually firm and fibrous. It is important for denture support and preventing distal denture displacementThe mylohyoid ridge:Following the extraction of natural teeth and subsequent resorption, the mylohyoid ridge becomes more prominent. This can result in mucosal soreness beneath the denture bearing area over the mylohyoid ridge.
19 Mylohyoid muscleIt is a thin sheet of fibers and in a relaxed state will not resist the impression material.Carrying the border under the mylohyoid cannot be tolerated. The contraction of this muscle will displace the denture.Fortunately, the denture in the posterior area of the mylohyoid is beyond its attachment because the mucobuccal fold is not in this area.In the retro mylohyoid fossa the border of the denture move back toward the body of the mandible producing the S curve of the lingual flange.In the anterior region, a depression, the pre mylohyoid fossa can be palpated and a corresponding prominence, the pre mylohyoid eminence seen on the impression
21 Clinic 1 Making the Primary Impression Selection of the impression trayimpression trays are rigid containers used to carry the impression material into the mouth. They also support it while it sets or harden, and subsequently during removal from the mouth and when casts are poured.Wide selection is available in metal or plastic.Selection is based on:RigidityThe need to accommodate an appropriate amount of the impression material.The design or extent of the tray to the anatomical landmarks outlined previously.
22 Plastic trays are intended to be disposable Impression materials: Metal trays:RigidProvided in a wider range of sizes.Needed to be cleaned and sterilized before reuse.Plastic trays are intended to be disposableImpression materials:AlginateCompoundRubberCheck that the tray is not over extended or under extended. Then load the impression material and make the mandibular impression standing in front of the patient. For the maxillary impression, the clinician should be positioned behind the patient. As this affords more control over the upper tray and also allow the patient’s head to be leaned forward should they experienced nausea during the impression procedure.
24 Model fractures upon removal from impression. Inadequate final impression: contact clinician to discuss possible risks of proceeding with the caseModel fractures upon removal from impression.Large positive or negative defects, or flaws in critical areas.Poor surface quality of the model due to water/saliva/blood contamination or improper mixing of gypsum, showing a powdery, friable surface.Loss of or damage to critical areas during model trimming (examples: retromolar pad, hamular notch and muscle attachments).
25 Lab 1 Producing Casts & Special Trays Ensure that impressions have been decontaminated prior to dispatch to the lab.Preparing the primary cast:Principally used to provide bases on which customized special trays are constructed.Also useful for planning treatment, for example for outlining the potential supporting areas of the denture.Cast are made in Plaster of Paris ( β hemihydrate of calcium sulphate) & Stone (α- hemihydrate of calcium sulphate).Pour using 50:50 mixture of plaster of Paris/ dental stone (vacuum mixed) under vibration.Make the base at least 10mm thick to be sufficiently robust to survive subsequent handling.
26 Powder/liquid ratioThin mix: longer setting time, poor surface hardening, setting expansion is low, easier to pour.Thick mix: the opposite.Spatulation time: time taken to mix the powder & liquid into creamy consistency.(30-60 sec.)Increasing the spatulation time:Rapid set.Decreases surface hardness.Increases the setting expansion.Temperature: water temp. up to 40 cº decreases setting, above 40 cº increases setting.Chemical additives. E.g. Borax increases setting time.
27 Read the prescription before beginning all procedures. Box master model impressions- Diagnostic casts do not require boxing.Measure dental stone and water according to manufacturer's directions.Add powder to water rather than water to powder. For best results, vacuum mixing is recommended.Do not invert impressions to develop a base until the stone reaches initial set.
28 Master castsBase thickness must be 1/2-inch (13 mm) minimum for strength. This is measured from the deepest part of the palate on the upper (Figure 1c) or the "floor of the mouth" on the lower (Figure 1d).
29 After trimming, the base of the model must be parallel to the residual ridge (figures 1e and 1f). The base must be indexed for mounting and remounting. Two methods are shown here. Other techniques are acceptable as long as the index allows accurate remounting of the model.
30 The depth of the buccal sulcus is approximately 1-1 The depth of the buccal sulcus is approximately mm below the land area. Positive defects (bubbles), if any, must be in non-vital areas and small enough to be easily removed (1-mm diameter or less as a guide).Negative defects (voids), if any, should be small and in non-critical areas. These should be filled with stone to blend with the surrounding anatomy.The master cast must include all anatomical surfaces in the final impression.
31 Special TraysMaterial:Should be safe to handle, compatible with biological tissues & impression material, sufficiently rigid to preclude distortion.Examples: Self-cured or light-cured acrylic resinPeripheral extension:Cover the entire denture-bearing area within the anatomical limits previously described.2mm short of the sulcus to allow for border molding.Handles:Should be formed to avoid encroaching on the surrounding tissues.
32 Space for impression material: Should accommodate the optimum thickness of the chosen impression materialIrreversible Hydrocolloid: 3mm.Zinc oxide-eugenol : close fittingPoly vinyl siloxanes: depending on the viscosityPolyethers : 2-3mmPolysulphides: 2-3mm.Perforations??Trays for complete dentures are requested without perforations so that peripheral seal can be estimated.
33 If no specific instructions are provided, fabricate tray to the following standard: Outline the tray 1-2 mm short of the mucobuccal reflection for both upper and lower models. This will allow room for border moulding material and save time for the clinician. The tray must extend to the depth of the hamular notches on the upper and should cover the retromolar pads on the lower . The lingual extension on the lower should stop at the mylohyoid line in the posterior and at the junction with the floor of the mouth in the anterior section.
34 Place relief material such as baseplate wax to the outlined area and cut out three tissue stops. Avoid placing a tissue stop over the incisive papilla.
35 The maxillary tray is made with 1 mm wax spacer and ends short of the final tray extensions. On the maxilla, wax must not cover the posterior palatal seal area. The mandibular tray is made with no spacer(close fit)Tray is well adapted to the model with no voids.Tray must be of uniform thickness.Thickness must be sufficient in strength to prevent distortion or breakage in use. The required thickness will vary with the material used. In general, acrylic resin and similar materials (such as light cure resins) should be approximately 2 mm thick, and 1 mm short of the mucobuccal fold to allow for border moulding.The handle must be placed in the anterior so that it does not interfere with placement of tray or border moulding procedures. The handle may be placed approximately where the wax rim or anterior teeth would be positioned on a baseplate .Unless specified otherwise by the clinician, the tray borders should be between 1 to 2 mm short of the mucobuccal reflection.
36 Custom Trays - Quality Failures Border extensions significantly longer or shorter than standard.Tray not stable (flexible) due to insufficient thickness.Tray cracked or damaged.Improper handle position (interferes with border moulding or insertion).Sharp and/or rough edges, which may irritate the patient.
39 Lab 2 Base plates & Wax rims Master/secondary cast (poured in stone)Base plate:Self-cured or light-cured acrylic resin.Wax rim(review lecture: Base plates & Waxrims/3rd year course)
40 Clinic 3 Registration Stage Before complete dentures are constructed, the dentist with the aid of the technician, must build a pro-forma or template of the intended denture using-usually- wax rims.According to glossary of prosthodontic terms the registration is ‘a record made of the desired maxillomandibular relationship and is used to relate casts on the articulator’Maxillomandibular relationship is ‘ a relationship of the maxilla to the mandible; any one of the infinite relationships of the mandible to the maxilla’In simple terms: the registration stage is 3-dimensional prescription whereby the template of the intended denture is ‘prescribed and fashioned’ clinically before being dispatched to the laboratory for placement of the teeth on the trial denture.
41 Unless the clinician has cast the definitive impression and has scored the master cast to define the postdam, the rim will not exhibit a clinically meaningful seal.After immersing the rim in proper disinfectant material, ensure that the rim is well adapted. Alternating finger pressure on both sides of each rim should not elicit rocking.Start with the upper rim- insert it and then ensure that the infra-nasal tissues are harmonious with the soft tissues of the middle third of the face. Failure to do so may affect the form and length of the upper lip.Confirm that the upper lip is adequately supported. This should result in restoration of the vermilion border.Determine the level of the incisal point relative to the resting upper lip. Some text books recommend 2mm below the resting upper lip level. Younger patients with class II div I may require more(2-4mm) and older patient ( over 70) may require the incisal level at the level of the resting lip or 1mm above it.
42 The antero-posterior location of the incisal point can be determined by asking the patient to say a word containing a fricative consonant, e.g. ‘fish’. The incisal point should correspond to the vermilion border of the lower lip.Determining the maxillary anterior & posterior plan:The plan of the six anterior should be parallel to the inter-pupillary line. Use a fox’s occlusal plane guide.The posterior plan should be made parallel to ala- tragus lineThe tips of the maxillary canines can be determined by extending a dental floss from the inner canthus of the eye through the lateral border of alar cartilage into the rim.Using the mark on the rim corresponding to the canine tips, reduce the inferior borders of the posterior rims by 3-5 ° to create the buccal corridors.The customization of the upper rim is finished by scribingCentre line.High smile lineCanine pointsThe above technique of customizing the upper rim is the one used at the Dental Health centre-the one to be used by dental student. Another technique to customize the upper rim is Swissedent technique (review lecture on wax rims /3rd year).Face bow transfer : depending on the case, the clinician may consider it necessary to use a face-bow to transfer the relationship of the upper rim to an arbitrary hinge axis. although it may not be strictly necessary to use a face- bow in all cases, there is no valid objection to their use in the prescription of complete denture.
45 Relating the mandible to the maxilla This 3-dimensional:Vertical (vertical dimension)Sagital ( antero-posterior)Coronal (left –right)Vertical:Resting Vertical Dimension (RVD)Occlusal Vertical Dimension (OVD)Affect tolerance and appearanceFree way space (RVD-OVD)
46 RVD measurement:Select to measuring points in the midline of the face-one relate to the nose and one to the chin. These points must be on sites with minimal influence from the muscles.Ask the patient to moisten his or her lip and bring them into light contact, then ask the patient to swallow and relax his jawsThis is verified by asking the patient to say the word ‘M’ while the measurement is made.Attention should be made to unwanted skin movement. Use Willis gouge or any other device-ruler- to measure the distance between the two reference points. This the RVD.The maxillary & mandibular rims are then inserted-after the upper rim has been moulded- and the lower rim is reduced in height- usually; or added to if under sized) until it contacts the upper rim evenly at a vertical dimension of occlusion some 2-4mm less than RVD
47 methods of determining vertical dimension -1. Boos: Bimeter (an oral meter that measures pressure)-2. Silverman: closest speaking space- looked at bicuspid area-3. Pound: phonetics and esthetics-4. Lytle: neuromuscular perception-5. Pleasure: pleasure points (tip of nose and chin)
48 Sagittal (antero-posterior) Retruded Contact Position (RCP)ReporducipleSeveral techniques:Squash biteWax rimsIntra-oral tracingThis visit is finished byselecting the shade and mould.determining the post dam area.
54 Lab 3 Mounting. (indexing) Setting the teeth using the shade & mould selected by the dentist.Wax up and contouring.(hands out summarizing this laboratory procedures will be given)
55 Clinic 4 try-in visit Verify the appearance. Verify the occlusal requirements.Examine speech( Please review lecture : try-in /3rd year)
56 Lab 4 Flasking, Packing and finishing Packing & processing of the denture:Removal of waxReplacing the wax mould with PMMA(hands- out summarizing this laboratory procedures will be given)
57 Clinic 5 Fit /DeliveryMirror those of the trial stage except hopefully the patient is taking the dentures home.(review lecture on denture insertion/ 3rd year)Arrange review visits for your patient as needed.