THE TRIAL DENTURE BASE Rola M Shadid BDS

THE TRIAL DENTURE BASE Rola M. Shadid, BDS, MSc

Trial Denture Assessment on Articulator 1. § § Impression surface examination Fit Extension § Polished surface examination Position of lower teeth position of upper teeth inclination of polished surface 3. Occlusal surface 2. § §

1. § § 2. § § 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

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

Trial denture assessment in the mouth 1. 2. 3. 4. 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 n May require removal, resetting & re-processing n Procedures more costly & time consuming n

Physical retention n If the prognosis for the retention in the upper jaw is good, dislodgment may be difficult. n In lower denture retention is poor because of the relatively small denture bearing area and the difficulty in obtaining efficient border seal.

Physical retention n 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 n Movement of denture more than 2 mm suggests lack of stability of the denture. n This could be due to: Lack of fit of the denture Displaceability or unfavorable shape of the denture bearing area 1. 2.

Extension of denture bases The accuracy with which the denture borders conform to the depth and width of the sulci must be determined. n 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. n 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 n

Overextension of denture bases n 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 n The exact location of such an error can only be determined by carrying out a careful examination inside the mouth.

Overextension of denture bases n 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 n 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. n

Correction of overextension n 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. n In the case of the upper denture, however, a preliminary indication of under-extension will be given by the existence of poor physical retention. n 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 n 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. n

Neutral zone If displacement of the denture does occur, the cause must be identified and the denture modified to correct the instability. n An area where this difficulty commonly arises is the lower anterior region where the lip may exert excessive pressure n

Neutral zone n n n 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 n 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

Assessment of the occlusal vertical dimension

Verify OVD & Interocclusal Distance Same techniques used previously n Critical to measure & feel 2 -4 mm of interocclusal distance n No tooth contacts during closest speaking space n

Changing OVD n Effects: Occlusion u. Facial esthetics u

• 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 n n 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 u Undesired effect on: t Overbite relationships t Esthetics t Balancing contacts n Assess how changes will affect overall appearance n

Assessment of CR Position

n 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. n The dentist must approach the problem with negative attitude.

Methods of occlusal assessment n Visual (touch & slide method) n 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.

Touch & Slide Method

1. Guide the mandible into CR n n 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 n 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 n

Removing the posterior teeth from the lower occlusion rim n 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 n Improves record accuracy u Less resistance during closure u Reduces chance of deflection when checking record ✔ ✘ ✘ ✔

Small Amount of Registration Material Opposing cusps should not penetrate n Cuspal indentations improve accuracy compared to flat wax rim n

Accurate Mounting n Teeth interdigitate perfectly u n n n No space around the cusps Mandibular cast removed from mounting ring Mounting plaster ground thinner Cast remounted, using the new record

Evaluation of the Esthetics

Esthetics Check: u Amount of incisal display u Harmony of the maxillary teeth with the smile line* u Accuracy of the midline

Esthetics n n n 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: 1. 2. n 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 a) b) c) 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 u Proper soft tissue profile, contours u Lip support u Display of the vermilion border u Correct nasolabial angle

Esthetics Ask patients for their opinion prior to voicing your opinion n Avoids biasing the patient n May be helpful to have family or friend attend the wax try-in n

Esthetics If you or the patient have reservations about appearance u Resolve prior to final processing u Never attempt to persuade a patient out of a concern u Problems will be yours later, if the patient does not like the appearance

Evaluation of the Phonetics

Phonetics n Easier to assess u Teeth have replaced bulky rims n Crowded tongue space can adversely affect phonetics

Phonetics n If have not worn dentures for extended period or n Dramatic changes (Contour, Tooth Position, Vertical Dimension): Allow the patient to read a out loud for 5 -10 minutes to assess phonetics and comfort

Lisping Non-uniform overjet of the anterior teeth n Diastemas between teeth n Palatal contours n Diamond-shaped openings between incisors n

Bilabial sounds (p, b, m) Causes of defect in these sounds: n Insufficient support of lips by teeth or denture base n Anteroposterior position of anteriors & thickness of labial flange n Incorrect OVD

Labiodental (fricative) sounds (f, v) § § F & v are made between the upper incisors and the posterior one third of the lower lip Affected by the anteroposterior position of upper anteriors and their length If upper anteriors short, v sound will be more like an f If upper anteriors long, f sound will be more like v

Linguoalveolar sounds (t, z, s, d, v, L, ch, sh)* § § Valve formed by contact of tip of tongue with the most anterior part of palate or lingual side of anterior teeth (linguoalveolar) The upper and lower incisors should approach end to end but not touch. Affected by the length of the upper & lower anterior teeth (including their vertical overlap) Also affected by horizontal overlap of anteriors ¶

Linguoalveolar sounds n Incisors should approach end to end relationship

“S” sound The “s” sound is the most interesting one because it is influenced by the teeth and palatal part of maxillary prosthesis. Clinical experience suggests that s & t can cause most problems in a prosthodontic context.

“S” sound n n The tip of tongue is placed far forward, coming close but never touching the upper anteriors (touch rugae area) A small sagittal groove is formed in the upper front part of the tongue for air to escape between the tongue & alveolus The tongue dorsum is flat Mandible will move forward and downward, with the teeth almost in contact

“S” sound n Whistle on “S” sounds as “sh” or “th” n Causes…… n Management……. .

Denture Base Contours Affect phonetics, comfort and retention n Should not be slightly convex in shape n Convex Concave

Denture Base Contours Ensure that the denture base is not unduly thick or thin u Excess bulk will impair comfort t u Feel between index finger & thumb Base that is too thin will be weakened t Should not be able to see through

It was concluded that malformation of the palatal parts of the denture influenced speech production more than differences in OVD did.

Establishment of the posterior palatal seal

CONVENTIONAL APPROACH After assessing all the previous parameters there are certain instructions given to the patients: 1. To rinse with an astringent mouth wash that is remove to stringy saliva that might prevent clear transfer marking. There are steps to be followed

2. Location of pterygo maxillary notch is done by moving the T burnisher posterior to the maxillary tuberosity until it drops into the pterygo maxillary notch. This is necessary as there are times when small depression in the residual ridge may resemble pterygo maxillary notch. 3. Identification of posterior vibrating line by asking the patient to say “AH” in a normal unexaggerated fashion.

4. Identification of the anterior vibration line. This is done by asking the patient to say “AH” with short vigorous bursts (Valsalva Maneuver can also be used)

PROCEDURE n A line is placed with an indelible pencil through the pterygomaxillary notch & extended 3 -4 mm antero-laterally to the tuberosity approximating the mucogingival junction. The same is done on the opposite side. This complete the outlining of pterygomaxillary seal

The posterior vibrating line is marked with an indelible pencil by connecting the line through the pterygomaxillary seal with line just drown demarcating the post palatal seal n The resin or shellac denture base is inserted into the mouth & seated firmly to transfer the marks from the mouth. n Denture bases are then returned to master casts to transfer the markings to the master casts. n

n The base is trimmed until the posterior vibration line so that it decides the posterior extent of the denture border.

(A) A T burnisher is used to palpate for the hamular process. (B) Palpating for the pterygomaxillary notch

n Demarcation of anterior & posterior vibrating lines in the patient mouth n Transferring these lines to denture base

n n The shape of post palatal seal is like the cupid bow, because of the projection of the posterior nasal spine. Kingsley scraper is used to score the cast, the deepest areas are located on either side of midline, one third the distance anteriorly from the posterior vibrating line. It is usually scraped to a depth of approximately 1 -1. 5 mm.

The tissue covering the medial palatal raphe cannot withstand the same compressive force as the tissue lateral to it; so it is scraped to depth of approximately 0. 5 -1 mm within the outline of cupid bow. n The scraping tapers to a feather edge as it approaches the anterior vibrating line. n Failure to taper the posterior seal leads to tissue irritation. n

Finally………. .

Patient Input Use open ended questions “How do you like the appearance? ”, rather than “Don’t the new dentures look great? ”

Patient Input If the patient sounds unconvinced u ask more questions n Do not rush this step to save time! n

References n n Basker’s Prosthetic Treatment of the Edentulous Patient. Fourth edition. Chapter 13 Boucher's Prosthodontics Treatment for Edentulous Patients. Twelfth Edition. Chapter 19 Complete Denture Prosthodontics, 1 st Edition, 2006 by John Joy Manappallil, Chapter 17 Dalhousie coninual education