Mandibular single denture.

How to Overcome These Problems

The primary consideration for a continued success of a single complete denture is the preservation of that which remains.

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Proper diagnosis and full use of every factor, which favors success

for this denture,

Applying the principles of complete denture construction:

• Lip support

• Minimal vertical overlap (Overbite) • Balancing occlusion and free articulation. • Avoid broad inclined planes.

Maximum base extension within functional anatomical limits

(distributed forces over the largest possible area of supporting structures and the force per unit area kept at minimum.)

Reduction of the forces to which the denture is subjected

Diagnosis and treatment planning:

1- Complete case history is taken and oral examination is done. 2- Study upper and lower casts are obtained.

3- The upper cast is mounted on the articulator using a face bow. 4- The lower cast is mounted on the articulator using a

provisional centric interocclusal record at an acceptable vertical dimension.

5- Eccentric records are made and the condylar elements of the articulator are adjusted.

Common Occlusal disharmonies:

The remaining molars are often severely inclined mesially and then distal halves supererupted. If this situation is left unaltered there would be no occlusion in protrusive and lateral excursions except for contact on the distal half of the lower molar. This results in the maxillary denture being easily dislodged during functional movements.

a) If the molars are not severely tilted they may be reshaped by selective grinding.

b) When tooth reduction is found necessary, the ideal treatment is to restore the tilted molars with cast gold crowns, onlays, or a fixed bridge if a large edentulous space exists mesial to the molars.

c) If a large space does exist mesial to the tilted molars, another alternative treatment is to design a removable partial denture that would restore the mesial half of the molars by using an onlay mesial rest (Fig 4-1).

d) If the molars are severely tilted forward and supererupted, and modification is not possible, extraction is necessary.

Fig.4-1: Upright preparation of a premolar and tilted second molar

as abutments. (A) Teeth before preparation. (B) The mesial surface of the molar has been aligned to the existing long axis, resulting in an overtapered preparation. (C) Correct preparation of the molar and premolar. (D) The completed fixed partial denture. The mesial cusps of the molar have been raised.' the distal cusps have been lowered, and the correct occlusal plane has been restored.

Methods used for detecting occlusal modifications:

Several techniques could be used to determine occlusal modifications that are necessary prior to denture construction:

1- Use of a commercially available U shaped metal occlusal template that is slightly convex on the lower surface. This template is often an aid in detecting minor deviations in the occlusal scheme (Fig 4-2).

2- Upper and lower casts are mounted on the articulator. The upper denture is constructed. If the lower natural teeth interfere with the placement of the denture teeth, they are adjusted on the cast and the area is marked with a pencil. The natural teeth are them modified using the marked diagnostic cast as a guide. This technique is simple but time consuming. 3- Use of a clear acrylic resin template fabricated over the

modified stone cast. The inner surface of the template is coated with pressure indicating paste and placed over the patient's natural teeth.

Fig.4-2: U shaped 20°

occlusal Template

Fig.4-3:Plane of Occlusion

Evaluation

Methods used for a harmonies balanced occlusion:

In the construction of dentures to articulate with natural teeth, the prosthodonticsts must provide a harmonious occlusal scheme free of interference in any jaw relationship this will lead to a better retention and stability of the single denture which will

lead to least residual ridge damage. Many techniques have been used to achieve a balanced

occlusion of a complete maxillary denture opposing natural teeth. They basically fall into two categories:

1- Dynamic equilibration of occlusion by the use of a functionally generating path.

2- Static equilibration of occlusion with an adjustable articulator. - 54 -

Materials for artificial posterior teeth:

The materials available for occlusal posterior tooth forms are 1- Acrylic resin.

2- Porcelain. 3- Gold (Fig 4-).

4- Acrylic resin with amalgam stops.

Esthetic of single maxillary denture:

The fixed positions of mandibular teeth limit the esthetic position of maxillary anterior teeth. How to solve the esthetic problem?

1- To create enough horizontal overlap to allow freedom to balance in eccentric movements.

2- Or to steeping the posterior cusp angles so that the posterior teeth will disocclude the anterior teeth during eccentric movement.

Mandibular single denture:

The prognosis of a mandibular single denture against natural teeth is less favorable than when the full upper denture is opposed by natural lower teeth (Fig. 4-4, 4-5). It would be difficult to classify this case as clinically successful. This is due to:

1- Excessive resorption of lower ridge due to greater stresses per unit area delivered to the mandibular ridge by the natural teeth.

2- Occlusal problems: The presence of natural teeth will present difficulties in controlling the occlusal scheme.

3- Minimal denture foundation area 4- Fracture.

5- Tooth wear. 6- Tissue abuse.

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The alternative line of treatment plan for such patient could be either:

1- Extraction of remaining teeth and complete upper and

lower denture are constructed.

2- Use of resilient denture liner in the mandibular denture.

3- Use of implant supported fixed or overdenture prosthesis (Fig. 4- 6,4-7).

a b

Fig.4-4 a, b: mandibular single denture against natural teeth

a _b

Fig.4-5: Conventional lower single dentures are contraindicated because they cause severe resorption as seen in this patient.

a b

Fig.4-6 a,b:Retaining roots in key positions facilitate support and prevent compression of the periosteum

Fig.4-7 a,b:Implant assisted overlay dentures opposing dentate maxilla.

Combination Syndrome and Associated Changes

( Kelly’s Syndrome)

A Combination Syndrome By Kelly (1972): destructive

problems, that may be encountered as a result of long term use of a mandibular distal extension partial denture against a complete maxillary denture

This syndrome consists of:

1- Loss of bone from the maxillary anterior edentulous ridge (Fig.4-8 a).

2- Down growth of the maxillary tuberosities (Fig.4-8b). 3- Papillary hyperplasia of the tissues of the hard palate. 4- Extrusion of the lower anterior teeth and,

5- Loss of bone beneath the removable partial denture bases.

It usually has six associated changes:

1- Loss of vertical dimension of occlusion. 2- Occlusal plane discrepancy (Fig.4-9). 3- Anterior spatial resorption of the mandible. 4- Development of epulis fissuratum (Fig.4-10). 5- Poor adaptation of the prosthesis and,

6- Periodontal changes.

The Combination Syndrome Is a Result of Three Main Factors

•the great magnitude of forces involved,

•the unsuitability of the denture foundation to resist them, and

•the particularly unfavorable occlusal relationship.

Fig.4-8 a,b:A specific pattern of resorption : The premaxilla undergoes severe resorption and is usually accompanied by the development of fibrous hyperplasia of the maxillary tuberosity.

Fig.4-9: When mandibular anterior teeth remain, patient will attempt to function in protrusive relationship to sense feeling of mastication.

Fig.4-10:The Labial Flange Of The Denture Produces A Low Grade Irritation In The Surrounding Soft Tissues, Resulting In Development Of

Epulis Fissuratum.

a Fig.4-11 a,b: Premaxilla mostly soft tissue b

OVERDENTURE

The overdenture is a complete or partial denture prosthesis constructed over existing teeth, root structure and/or dental implants. The overdenture is also called overaly denture, overlay prosthesis or super imposed prosthesis.

Objectives of overdenture prosthesis:

1. Retaining the abutments as part of the residual ridge to gain support and retention (Fig. 5-1 a).

2. Preserving the remaining residual ridge by decreasing the rate of bone resorption (Fig. 5-1 b).

3. Preserving the response of proprioceptive exist in the periodontal membrane of the abutment tooth.

Fig.5-1a, b:Retaining the abutments and Preserving the remaining

residual ridge

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Indications:

1- Cases having few remaining teeth unsuitable for fixed or removable partial dentures.

2- Remaining teeth present with unhealthy periodontal condition. The reduction of the coronal portion of the tooth i.e. decrease crown-root ratio will decrease the hypermobility of the teeth and make them favorable for supporting overdentures.

3- Patients with class II or class III Angle's classification.

4- Patients presenting abnormal jaw size large maxillary or mandibular bone defects.

5- Patients presenting congenital defects as cleft palate, microdontia, amelogenesis or dentinogenesis imperfecta or partial anodontia.

6- The construction of over-denture is an alternative line of treatment to single dentures opposing few natural teeth.

Contraindications:

1- Overdentures are contraindicated in case of poor oral hygiene. 2- Interarch space inadequate to accept the denture and the

abutments.

3- Inadequate zone of attached gingiva with grade II mobility of the abutments.

Overdentures can be classified into:

1- Tooth supported over denture. 2- Implant supported overdenture.

1- Tooth supported overdenture:

The tooth supported Overdentures improve stability retention, masticatory performance, occlusal loading and help to preserve vertical dimension and facial support.

Advantages of tooth supported overdenture prosthesis:

1- Preservation of the abutments as part of the residual ridge to gain support.

2- Preservation of the proprioception that exist in the periodontal membrane of the abutment tooth.

3- Preservation of the remaining residual ridge by decreasing the rate of bone resorption.

4- Patient acceptance and Psychological Benefits

5- Convertibility: overdentures can be converted into a conventional complete denture after loss of the abutments and relining or rebasing of the denture.

6- Conventional dental procedures.

7- Provide retention through the attachments.

Disadvantages of tooth supported overdentures:

1- Caries and periodontal break down of the abutments teeth

(Fig.5-2)