impressions for complete
TRANSCRIPT
IMPRESSIONS FOR CONVENTIONAL COMPLETE
DENTURES. Dr. Bahjat Abu Hamdan. Consultant Prosthodontist. DDS, CES, DSO . Damascus – Syria, Paris – France.
1. Introduction2. Relevant anatomy and physiology.3. Patient examination for impressions4. Impression materials.5. Classification of impressions -primary impressions -secondary impressions 1.compressive. 2. mucostatic . 3. selective.Conclusion.
1 .Introduction. The purpose of the CD is to restore
function, aesthetic, phonation and maintenance of remaining tissues.
To be able to assume these functions, dentures should enjoy the following mechanical qualities:
Retention Stability support
1 .Introduction The following anatomical factors play a
positive or negative mechanical role; 1.Bone size Height and width2. Maxillo-mandibular relationship.3. Position and orientation of the occlusal Plane.4.Muscle attachment and quality of mucous
tissue.5.Presence of opposed natural teeth to
edentulous ridge.
1.Introduction. Mechanical qualities are also related to all the
steps of complete denture construction :1. good impressions.2. correct JRR3. correct setting of the artificial teeth4. well established static and dynamic occlusion5. Good processing6. well formed and polished external surfaces of
the dentures.
Mechanical factors
Anatomical factors.
Practical procedures.
2.Relevant anatomy and physiology. Good knowledge of the anatomy,
physiology and histology of all the elements in relation with the dentures is mandatory;
Bone and mucous tissues. Kinetics of the muscles of mastication,
facial expression, tongue and floor of the mouth.
Intra oral drawing of the maxillary arch.
Neutral zone (free of muscle insertion and muscle action)
Intra oral drawing of the mandibular arch.
The disto-lingual limits to the denture flange
Glands in relation with the lower denture.
palatoglossal arch muscles.
Lateral view of pharynx
Muscles of facial expression.
3.Patient examination
Its so important to investigate all the elements that may affect the procedure and the quality of the impressions which affect the quality of the dentures.
Medical and dental past. Extra oral examination. Intra oral examination. X ray examination. Study models.
Extra oral examination.( Nilson (triad
Intra oral Exam. 1. Salivary flow. 2. Alveolar ridge resorption chronology. 3. Combination syndrome. 4. Floor mouth posture and tongue
position. 5. Neuromuscular control. 6. Oral diseases and oral lesions. 7. Existing dentures. 8. Muscle tonicity.
Alveolar ridge resorption classification.
Posterior palatal seal
Posterior palatine salivary glands
•Permits compression of tissues •Improves adaptation of
denture to compensate for shrinkage of resin
Glandular tissue
Posterior palatal seal
Different form of soft palate
Measures to slow resorption.
Preventive measures.
Floor of the mouth and retruded tongue.
shape of retro-mylohyoid area.
Combination syndrome
Combination syndrome
Severe resorbed lower ridge due to combination syndrome.
Oral diseases and oral lesions. Long term insulin dependent (diabetes) Oral lichen planus. Pemphygoid. Chronic candidiasis. Inflammatory fibrous hyperplasia. Premalgnant lesions
leukoplakia,erythroplakia. Malignant lesion.
Surgical preparatory treatment. Augmentation with bone graft. -frenectomy
-tuberosity reduction-tori removal-surgical removal of redundant tissue (epulus fissuratum)-ridge recontouring e.g. flabby ridges and -bony undercuts-removal of remaining teeth and severe undercut.
4.Impression materials
Impression Material Usage*Civilian General Dentists Complete dentures
alginate 58%vinylpolysiloxane 55%polyether 27%
Partial denturesalginate 78%vinylpolysiloxane 43%polyether 15%
DPR 2002
Handling Properties
Handling Properties
Comparison of Properties Wettability
best to worst○ hydrocolloids > polyether > hydrophilic
addition silicone > polysulfide > hydrophobic addition silicone = condensation silicone
Castabilitybest to worst
○ hydrocolloids > hydrophilic addition silicone > polyether > polysulfide > hydrophobic addition silicone = condensation silicone
5 .Classification of impressions in CD
Lower edentulous ridge.
Upper edentulous ridge.
Preliminary impression
Primary impression
Final impression.
preliminary impression; 1. Anatomic. 2. Stock tray. 3. Alginate. 4. Surgical preparatory treatment. 5. Occlusal plane adjustment of the remaining teeth.
Preliminary and primary impression
Preliminary and primary impression Primary impression 1. Anatomic. 2. Stock tray. 3. Alginate or plaster. 4. Indicate on the cast the flabby tissue, new
extraction area, sharp edge, mental foramina and thin mucous tissue area.
5. Special tray; adapted, spaced or partially spaced.
Preliminary and primaryimpression
In the practice; Choose a stock tray insuring 3-4 mm of
space away from the ridge. Tray should cover the retro-molar pad
area and extend to the palatoglosse arch, hamular notch, palatal fovea use the wax to adjust the extension of the tray.
With floating mouth bottom use thicker consistence dental material.
Preliminary and primary impression Stock trays.
Primary impression and custom tray. L to R plaster Imp. Alg. Imp. Anterior
flabby tissue tray and Occ. Rim handle.
Final impression (compressive) . Factors controlling the pressure applied by the
impression; Type of the custom tray adapted or spaced. Consistence of the dental material light, regular or
putty. Holes opposed to a concerned area means less
pressure. Border impression is always compressive in
functional impression and partially compressive impression. If it is not, impression is mucostatic (anatomic).
Final impression (compressive) . Custom tray… adapted or spaced. Borders are 2mm far from the labial and buccal
vestibule, 3mm space in the frenum areas (lateral and median).
Tray should cover the vibration line area and hamular notch. Mandibular custom tray;
borders are 2mm far from the border in the buccal shelf and anterior sublingual area.
Checking up the custom tray is done by pulling the muscles horizontally in the concerned area.
Final impression (compressive) . Border impression includes all the
borders of the maxillae. It includes just the buccal shelf and the
anterior sublingual area. Muscle M. are done functionally by the
Pt.( open widely, suction and lateral M. Swallowing, tongue M. Grimace M.). Muscle M. are done by the dentist in case of low muscle tonicity.
Final impression (compressive) . Certain extreme muscle M. coincide with the
functional M. Muscle M. (during border impression can be
done by the dentist) but the Pt. should functionally move his muscle in the 2nd phase of final impression.
Border impression is done gradually by the thermoplastic green Kerr. Or one using the regular elastic material.
Greene Brothers
Functional movements for border impression.
Border impression. Silicone medium viscosity Impregum Thermoplastic green Kerr
Final impression (compressive) . It is important to use occlusal rim as tray
holder ( which represent the missing teeth) so that the functional M. are close to the natural.
The wash material can be ZnO eugenol paste or light elastic material.
Preferable silicone by addition.
Final impression 2nd phase. Silicone (medium) Zno eugenol paste Silicone light
Final impression (mucostatic) . Advocates of this technique believe that impression
must be recorded in an anatomic form of the tissues without distortion (resting form). Harry L page 1938, Addison 1944.
Dentures constructed by mucostatic impression technique have shorter flanges.
Short flanges are used to prevent the dentures moving in lateral direction and NOT for border seal.
Metal bases which are dimensionally stable are used.
Final impression (mucostatic). Dentures do not cover wide area. No border impression. Based on the adhesion, cohesion and surface energy
but not on the atmospheric pressure (border seal). It works only when there is good ridge and high
alveolar bone. Denture mobility during function (mucous depression
is 4/10 – 10/10 mm) (compressibility of periodontal tissue is 1/10
mm) .Bone compressibility is related to bone quality ( cancellous or cortical ).
Final impression (selective pressure).
Boucher 1950. Principles of this technique is that certain
areas of the maxilla and the mandible are by nature better adapted to withstand extra loads from the forces of mastication.
Tissues adapted for withstanding extra loads are recorded under slight placement of pressure while other tissues are recorded at rest (mucostatic)
Upper edentulous ridge
Lower edentulous ridge
Final impression (selective pressure). In this way an equilibrium is created between – the resilient and - non resilient tissues. Primary stress bearing areas are recorded under
pressure; crest of alveolar ridge, horizontal plate of palatine bone in the maxillae and buccal shelf area in the mandible.
Areas requiring minimum pressure; mid-palatine suture, incisive papilla, crest of mandibular ridge, mandibular tori, mental foramina, sharp painful edge, flabby tissue, remaining roots in case of over-denture and new extraction areas.
Final impression (selective pressure) .
Posterior palatal seal has glandular and soft tissues are readily to be displaced for maintenance of peripheral seal.
Sublingual area has similar tissue structure and behaviour as the posterior palatal seal.
Border impression includes all the borders of the maxilla, but it includes just the buccal shelf and the sublingual areas in the mandible. (after a good prime impression).
Final impression (selective pressure) .
Sublingual area is molded with the tongue in repose.
The tray is extended horizontally backward over the sublingual glands toward the tongue to affect border seal.
Pts with old dentures should remove it 24 hours before the final impression. ( mucous tissues should be at rest and normal situation).
Conclusion. In certain cases, even if all the steps are
well done mechanical qualities of the dentures are spoiled so that patient will not arrive to adapt on, these cases are confronted in case of lack of saliva and paralysis and low tonicity of the muscles in relation with the dentures.
Helping these Pts. Will be through the use of denture adhesive to improve the retention and the Pt. ability to adapt on.
Conclusion. Indication of denture adhesive; Xerostomia ( medication, systemic diseases,
irradiation and disease of salivary glands) Neurological disorders; Oro-facial dyskinesia ( muscles of lips,
cheek, tongue and face ) Medication side effects ( neuroleptic,
dopamine blocking drugs, pheothiazine and GI medications ) .
