Mrs D's Dental Technology space for student: May 2013

Monday, May 27, 2013

Occlusal schemes vs Occlusal concepts

Occlusal concepts relates to the maxillary and mandibular edentulous jaw relationship to each other from a buccal view.

Occlusal schemes relates to the relationship between the artificial teeth that is set for a completely edentulous jaw relationship.

Lingualized Occlussion as a concept

Lingualized Occlusion is a setup technique developed to enhance denture stability for patients with severe alveolar bone resorption resulting in little or no ridge, or resulting in a discrepancy between the size of the narrowing and receding upper ridge compared with the widening and receding lower jaw.
This setup technique is also indicated for patients with implant-supported overdentures to eliminate lateral forces that can rock abutments loose over time.
Lingualized occlusion is appropriate for free-end attachment cases to reduce stress on distal extension, or for intra-coronal attachments to avoid breakage.
In a lingualized occlusion scheme, the objective is the elimination of buccal cusp contacts in order to alleviate lateral stresses or lateral dislodging forces.
In lingualized occlusion, the lingual cusps of the upper posteriors make contact in centric relation in the central fossae of the lower posteriors.
The buccal cusps are out of contact; however the lingual cusps are in contact in centric, working and balancing movements.
For this reason, all the stresses created during working and balancing motions are of a downward nature, thus creating stability.

Ref: Jim Collis

Class III occlusal schemes and cross bites

In this type of occlusion the maxillary posterior teeth are crossed over to the mandibular posterior teeth so that the buccal cusps of the maxillary teeth are articulating in the mandibular central fossa instead of the palatal cusps.
This occlusal relationship could be either unilateral or bilateral depending on the posterior ridge relationship.
The mesio-distal tooth position is the same as in a Class I (but in all likelihood requiring mandibular incisors of slightly greater width).
This posterior tooth relationship brings about that the mandibular teeth are always set on the ridge creating a reverse overbite and overjet, thereby preventing cheek biting.
The first mandibular premolar in most Class III cross bite cases is set in a near edge to edge position to the maxillary first premolar and canine. (This crossing point varies depending on the bucco lingual vertical relationship of each particular case. It often occurs in the mandibular second premolar region.)

Post Dam and its importance in a maxillary denture

The relevance of the posterior palatal seal to the retention of the maxillary complete denture should be clearly understood. Hardy and Kapur maintain that the retention and stability that is achieved from adhesion, cohesion and interfacial surface tension are able to resist only those dislodging forces that act perpendicular to the denture base.
Horizontal forces and lateral torquing of the maxillary denture can be resisted only by adequate border seal.
Terminating the denture borders on soft resilient tissues will allow the mucosa to move with the denture base during function and thereby maintain the denture seal.
The peripheral seal of the maxillary denture is the area of contact between the mucosa and the peripheral polished surfaces of the denture base; the seal prevents passage of air between the denture and the tissues.
This seal depends upon the proper extension of the denture borders, both in width and height, so that they fill the muco-buccal space and contact the cheek tissues laterally.
At the posterior aspect of the denture, in the area of the soft palate, there are no cheek tissues to seal the denture border.
Therefore, the proper placement of the posterior palatal seal commands a definite clinical procedural protocol if one is to create an optimally retentive complete maxillary prosthesis.
The function of the posterior palatal seal in the completed maxillary prosthesis is to maintain contact with the anterior portion of the soft palate (the tissues that undergo shallow displacement) during functional movements of the stomatognathic system (that is, mastication, deglutition and phonation).
Therefore, the primary purpose of the posterior palatal seal is the retention of the maxillary denture.
The posterior palatal seal that has been correctly diagnosed and incorporated into prosthesis also will reduce patient awareness of this area with a subsequent reduction in the gag reflex, since there should be no separation of the denture base and soft palate during “normal” functional movements; reduce food accumulation beneath the posterior aspect of the denture, owing to proper utilization of tissue compressibility (palatal glandular tissue can withstand mild compressive forces); reduce patient discomfort when contact occurs between the dorsum of the tongue and the posterior end of the denture base, as the posterior denture border will closely approximate the soft palatal tissues, and compensate for the volumetric shrinkage that occurs during the polymerisation of methyl methacrylate resin.
The correctly placed posterior palatal seal will not impinge upon the non-displaceable tissues of the hard palate, nor will it limit the muscular movements of the soft palate. It will, however, create a partial vacuum beneath the maxillary denture.
This partial vacuum is activated only when horizontal or tipping forces are directed against the denture base.
The duration of time that the partial vacuum acts on the tissues is extremely small and consequently little or no irreversible alterations to the underlying mucosa will take place.

(See S. Winkler)

Thursday, May 23, 2013

Balanced Occlusion

What are the factors that affect balanced occlusion and how does it affect each other, see S. Winkler. For exams

Thursday, May 16, 2013

Please discuss all the problems a patient with a Class II jaw relationship could possibly encounter if a full maxillary and mandibular denture were set up in a Class I occlusion.

I will start off the discussion by naming one;

Exaggerated labial and buccal position of mandibular teeth would create:

Labial lip infringement of mandibular anteriors if set into normal Class I relationship.

Requirements of/for an Immediate denture

Requirements:

A denture is not living tissue but it must be accepted as part of a system composed of living tissue.

For success the following requirements:

compatibility with surrounding oral environment
restoration of masticatory (with in limits)
harmony with the function of speech, respiration (breathing), deglutition (swallowing)
aesthetic acceptability
preservation of the remaining hard and soft tissue support

(Biggest challenge – to occlude and evaluate)

For an Immediate denture the teeth can be replaced in the same position as natural teeth, there are however factors that affect the placement and function

*Remember from first year (Changes due to loss of teeth)

The two areas of concern:

a) esthetics

b) occlusion

a) Difficulty

· Over erupted teeth (no opposing teeth)

· Migration (loss of teeth)

· Natural teeth in protrusion not desirable to be reproduced (place for better appearance, more compatible to surrounding oral environment

Problem mainly arises when attempts are made to correct mal-related jaws especially Class III or heavy overbite (steep vertical overlap)

b) Occlusion

· When it comes to occlusion we find that a lot of research has been done in this part and is still done today. Often the terminology used could be defined differently depending where it was used. Or new terminology was introduced abbreviation, new definition – leading to a lot of confusion.

· What aggravated the confusion was that occlusal principles for natural teeth were applied to the occlusion of artificial teeth – and we know that the anatomical and physiological aesthetics are not the same.

i. With artificial teeth the principles of mechanics and physics are more involved.

ii. Complete dentures rest on tissue that is movable and displaceable in varying degree from one mouth to another.

iii. Natural teeth are embedded in bone and can move or be displaced only to the degree allowed by the periodontal attachments. Artificial teeth are fixed to a movable base that is capable of moving with tissue and over the tissue – a big difference between these two movements.

iv. Natural teeth can act singly or as a unit. Artificial teeth always act as a unit with the entire denture base, in its relation to the supporting tissue is affected.

v. Also the fact of the somatic nerve receptors of touch and pressure of natural teeth which are lost (to neuromuscular system) when teeth are extracted.

When doing an Immediate denture, we recommend you do the following as preparation

Preparing the cast: (Anterior teeth)

Thin pencil line around gingival.
Pencil line on long axis of each standing tooth onto labial area.
Measure 15mm from incisal edge of each tooth and mark on tissue and then at same distance onto model base