THE TRIAL DENTURE BASE Rola M. Shadid, BDS, MSc
Trial Denture Assessment on Articulator • Impression surface examination • Fit • Extension • Polished surface examination • Position of lower teeth • position of upper teeth • inclination of polished surface • Occlusal surface
Impression surface examination • Fit • The bases of the trial dentures should be accurately adapted to the casts so there will be no movement when finger pressure is applied to occlusal surfaces. • The impression surface should be checked for any sharp projections, roughness, or excessive undercuts. • Extension • The border regions of the dentures should be shaped to conform to the depth and width of the sulci on casts. • In the upper jaw the base should be extended posteriorly to the post-dam cut in the cast, and in the lower jaw over the retromolar pad.
Polished surface examination Position of lower teeth The teeth on a lower denture should be positioned to conform to the crest of the mandibular ridges. If there are gross discrepancies between the position of the teeth and the ridge, the teeth may not be in the neutral zone, and could become the cause of instability in the mouth. Position of upper teeth The position of the anterior teeth should be checked in relation to the incisive papilla,and the posterior teeth according to guidelines in the previous lecture. Inclination of polished surface The buccal and lingual aspects of the polished surfaces must converge occlusally; so that pressure from the surrounding muscles of the cheeks, lips and tongue contributes to retention rather than displacement., the exception to this is the upper anterior area where the labial surface of the flange faces upwards and outwards.
Example of position of lower teeth Occlusal view of two lower dentures: (a) the teeth follow the crest of the ridge; (b) marked discrepancies between the position of the teeth and the crest of the ridge are present, suggesting that the teeth will not be in the neutral zone. a b
Occlusal surface examination There should normally be bilateral even contact in the intercuspal position. Opposing cusped teeth should interdigitate accurately.
Trial denture assessment in the mouth • The denture should be assessed individually for: • Physical retention • Stability • Extension of denture bases • Relationship to the neutral zone • The dentures should then be assessed together for: • OVD • CR position • Esthetics • Phonetics • Establishment of the posterior palatal seal
Don’t Overlook Problems • Difficult/impossible to change after processing • May require removal, resetting & re-processing • Procedures more costly & time consuming
Physical retention • If the prognosis for the retention in the upper jaw is good, dislodgment may be difficult. • In lower denture retention is poor because of the relatively small denture bearing area and the difficulty in obtaining efficient border seal.
Physical retention • If the physical retention of an upper trial denture is not as good as would be expected from the anatomical conditions existing in a particular patient, the cause should be identified and, if found to be a fault in the denture, must be corrected. Denture faults may include absence of a border seal resulting from: • Under-extension • Inadequate width of flange • Ineffective seal at the posterior border • Poor fit of the denture base.
Stability • Movement of denture more than 2 mm suggests lack of stability of the denture. • This could be due to: • Lack of fit of the denture • Displaceability or unfavorable shape of the denture bearing area
Extension of denture bases • The accuracy with which the denture borders conform to the depth and width of the sulci must be determined. • The all-important posterior extension of the dentures over the retromolar pad in the lower jaw and to the post dam seal area in the upper jaw must be checked. • If marked overextension of the denture flanges is present, stretching of tissues will occur when the dentures are inserted and their elastic recoil will cause denture dislodgment
Overextension of denture bases • if the denture is displaced immediately after being seated, over-extension should be suspected. A small degree of over-extension may cause dislodgement of the denture when the dentist gently manipulates the lips and cheeks or when the patient raises the tongue.
Overextension of denture bases • The exact location of such an error can only be determined by carrying out a careful examination inside the mouth.
Overextension of denture bases • When over-extension is present in areas where the visibility is good, displacement of the sulcus tissues will be seen as the denture is seated. However, in the lingual pouches, visibility is poor, so the dentist will have to make an assessment based on the behavior of the lower denture as the tongue is moved.
Overextension of denture bases • In the lingual pouches, overextension can be assessed according to denture behavior during tongue movement • When the lower denture is inserted, it should remain in place when the mouth is half open and the tongue is positioned so that its tip lies just behind the lower anterior teeth.
Correction of over-extension • Correction of over-extension is by reducing the depth of the offending flange. If this is not carried out, the finished dentures will traumatize the mucosa in that area and will be unstable because of the large displacing forces exerted by the soft tissues.
Under-extension of denture bases • The presence of under-extension is determined primarily by intra-oral examination, when the depth of the sulcus will be seen to be greater than that of the denture flange. • In the case of the upper denture, however, a preliminary indication of under-extension will be given by the existence of poor physical retention. Correction of any under-extension will usually entail taking a new impression in the trial denture
Neutral zone • The positioning of teeth in the neutral zone is of particular importance in the case of the lower denture • When the lower denture is inserted, it should remain in place when the mouth is half open and the tongue is positioned so that its tip lies just behind the lower anterior teeth.
Neutral zone • If displacement of the denture does occur, the cause must be identified and the denture modified to correct the instability. • An area where this difficulty commonly arises is the lower anterior region where the lip may exert excessive pressure
Neutral zone • Correction of this type of fault should be carried out at the chairside so that the effect of the alterations can be assessed in the patient’s mouth. • The offending teeth may be reset in the correct relationship to the soft tissues or they may be removed and replaced with a wax rim which is shaped with a wax knife until a stable denture is produced. • The dental technician is then asked to reset the teeth in the position indicated by the rim.
Neutral zone • When the tongue is relaxed, it should be able to rest on the occlusal surfaces of the teeth – a situation which favors retention of the lower denture
Verify OVD & Interocclusal Distance • Same techniques used previously • Critical to measure & feel 2-4 mm of interocclusal distance • No tooth contacts during closest speaking space
Changing OVD • Effects: • Occlusion • Facial esthetics
As mandible moves downward (opening or increasing OVD) • Incisal edge moves back • Increases overjet • Helpful Angles Class III • Problem Angles Class II
Vertical Dimension Alterations • One or both arches may require change • Made by the laboratory • May require resetting of all teeth in at least one arch • Height of both anterior & posterior teeth must be in harmony
Vertical Dimension Alterations • If only posterior teeth are changed • Undesired effect on: • Overbite relationships • Esthetics • Balancing contacts • Assess how changes will affect overall appearance
If a relatively large occlusal discrepancy is present, the dentist will be able to see this without any difficulty. However, the existence of smaller faults may be deduced from evidence such as slight tipping or lateral movement of the dentures as they occlude. • The dentist must approach the problem with negative attitude.
Methods of occlusal assessment • Visual (touch & slide method) • Patient perception The patient should be asked if the dentures are contacting evenly. Many patients are able to detect occlusal unevenness which is so slight that it could be overlooked by the dentist.
1. Guide the mandible into CR • The patient is guided into centric relation by a thumb placed on the anteroinferior portion of the chin and the index fingers bilaterally on the buccal flanges of the lower trial denture. • As tooth contact approaches, the dentist's index fingers should rise off the buccal flanges, pressure on the buccal flanges or stretching the lip with index fingers will create the risk of posteriorly displacing the lower trial denture, then the patient closes tightly.
2. The patient closes slowly so that the dentist can observe the initial occlusal contact. 3. The final occlusal relationship is not so reliable, as an uneven occlusion may have been masked by compression of the mucosa beneath the denture, tipping of the denture or posturing of the mandible.
4. The ideal occlusal contact is that at first contact, even maximum intercuspation at CR without denture shifting or instability & without pain; and all the teeth that occluded uniformly on articulator must have equally uniform contacts in the mouth
5.Errors in occlusion may prevent intercuspation of some teeth when the first contact is made. 6. Further closure will allow the teeth to slide into CO as tipping of the denture or deviation of the mandible will occur
What is your management if you found that CR not coincide with CO? You need to register new CR, mount on articulator according to new CR, and then reset teeth according to this new CR This is done either by removing the posterior teeth from the lower occlusion rim and both occlusion rims are placed in the mouth and a new centric relation record is taken; OR register new CR by applying bite registration material on occlusal surfaces of lower teeth.
Removing the posterior teeth from the lower occlusion rim • To register the new centric relation, the posterior teeth are removed from the lower occlusion rim and both occlusion rims are placed in the mouth and a new centric relation record is taken, the closure is stopped when the anterior teeth have the same vertical overlap as they had before the posterior teeth are removed thus the vertical relation of the two jaws will not be changed *
Apply Minimal Registration Material on Lower Occlusals • Improves record accuracy • Less resistance during closure • Reduces chance of deflection when checking record ✔ ✘ ✘ ✔
Small Amount of Registration Material • Opposing cusps should not penetrate • Cuspal indentations improve accuracy compared to flat wax rim
Accurate Mounting • Teeth interdigitate perfectly • No space around the cusps • Mandibular cast removed from mounting ring • Mounting plaster ground thinner • Cast remounted, using the new record
Esthetics Check: • Amount of incisal display • Harmony of the maxillary teeth with the smile line* • Accuracy of the midline
Esthetics • During a normal smile, incisal and middle thirds of maxillary anterior teeth are visible in almost all patients and the cervical third in approximately half the patients. • The incisal third of the mandibular teeth will be visible in most patients. • The lower lip is a better guide for the vertical orientation of anterior teeth than the upper lips. In most patients the incisal edges of the natural lower canines and the cusp tips of the lower first premolars are even with the lower lip at the corners of the mouth when the mouth is slightly open.
When the teeth are above the lip at the corners of the mouth, any one or a combination of the followings may exist: • the plane of occlusion may be too high • the vertical overlap of the anterior teeth may be too much • When the lower teeth are below the lip at the corners of the mouth, the opposite situations may exist
Esthetics • This figure shows reverse smile line • The fig. shows the midline is slanting to one side • The dental midline should coincide with the midline of the face
Esthetics Check • Angle of the occlusal plane The errors in location and inclination of occlusal plane can cause serious esthetic problems, in addition to functional problems and problems of stability. (The figure shows errors in occlusal plane)
Esthetics Check • Proper soft tissue profile, contours • Lip support • Display of the vermilion border • Correct nasolabial angle
Esthetics • Ask patients for their opinion prior to voicing your opinion • Avoids biasing the patient • May be helpful to have family or friend attend the wax try-in