Understanding Tooth Loss: Causes, Consequences, and Prosthetic Solutions
Reasons for Loss of Teeth
- Removal due to dental disease
- Periodontal Disease
- Tooth Decay
- Other
- Developmental Defects
- Genetic Defects
- Trauma
Consequences of Tooth Loss
Loss of Aesthetics
- Changes in morphological face height due to loss of vertical dimension of occlusion.
- Lack of support for the lips and cheek from the teeth.
- Loss of anterior teeth.
Loss of Function
- Unilateral or bilateral loss of posteriors.
- Reduced chewing table.
- Uncomfortable feel of food wedging between the space.
Phonetics
- Related to loss of anterior teeth.
- Speech sounds are made by controlled air.
- Control of flow of air is done by:
- Pharynx
- Nasal Cavity
- Oral Cavity
Oral Sounds
- Labial Sounds
- Labio-dental Sounds
- Dental and Alveolar Sounds
- Palatal Sounds
- Posterior Sounds
Labio-Dental Sounds
- Sounds of ‘f’ & ‘v’ made between the upper incisor and labiolingual center to the posterior one third of the lower lip.
- If maxillary anterior too short – ‘v’ will sound as ‘f’.
- If they are too long, ‘f’ will sound as ‘v’.
Dento-Alveolar Sounds
- Sounds such as ‘th’ are made with the tip of the tongue extending slightly between upper and lower anterior teeth.
- Other alveolar sounds ‘t’, ‘d’, ‘n’, ‘s’ are made with the valve being formed by the contact of the tip of the tongue to the lingual side of the anterior teeth.
Health of Surrounding Structures & Psychological Impact
- Modifications: Mechanism of support, Masticatory load, Mechanism, Area of support, Residual ridge, Psychological.
Mechanism of Support
Natural Dentition
- Tooth is supported by the periodontium. Together with the sensory perception it provides a suspensory apparatus.
- Periodontium provides:
- Support
- Positional adjustments of the tooth
Edentulous
- Deprived of this mechanism.
- Tissue supporting the denture was not designed to serve the same purpose of the periodontium.
Masticatory Load
- Occlusal forces in natural dentition controlled by the neuromuscular mechanism.
- Natural dentition for complete dentures.
Residual Ridge
- It consists of Mucosa, Submucosa, Periosteum and Underlying residual alveolar ridge.
Function
- Can modify the internal structure of human bone.
- Pressure can cause resorption.
- Tension may bring about deposition.
- Natural tooth receives tensile load through periodontium.
In edentulous situation residual ridge receives:
- Vertical
- Diagonal and
- Horizontal
loads applied by the denture. As a direct consequence of loss of periodontium, variable progressive bone reduction may result.
Psychological Effects
- Dentures may have an adverse effect on the nervous influences.
- Increased salivation.
- Gagging.
Principal Factors Needed for Fabrication of Prosthesis
- Support: (Is the resistance to vertical component of mastication and to occlusal or other forces applied in a direction toward the basal seat. Provided by: Maxilla & Mandible)
- Stability
- Retention
Supporting Structures of Maxilla
Bony or Hard Structures
- Palatine process of the two Maxilla
- Palatine bone
- Zygomatic process
- Tuberocity
- Residual alveolar ridge
- Mid palatine raphae
Soft Tissue Structures
- Mucosa covering the bony structures
- Rugae area
- Incisive papillae
- Soft palate
Limiting Structures of Maxilla
- Labial frenum
- Buccal frenum
- Labial vestibule
- Buccal vestibule
- Pterigomaxillary notch
- Fovea palatinae
- Vibrating line
Mandible Supporting Structures
Bony or Hard Structures
- Body of the mandible
- Residual alveolar ridge
- Mylohyoid ridge
Soft Tissue Structures
- Mucosa covering the bony structures
- Retromolar pad
Limiting Structures of Mandible
- Labial frenum
- Buccal frenum
- Labial vestibule
- Buccal vestibule
- Retromolar pad
- Retromylohyoid curtain
- Alveolingual sulcus
- Lingual frenum
Stability
It’s the quality of a denture to be firm, steady and constant in position when forces are applied to it. Resistance against horizontal forces and movement.
Factors Responsible
- Size and form of the basal seat.
- Quality of the final impression.
- Form of the polished surface.
- Proper location and arrangement of the artificial teeth.
- Balanced occlusion.
- Neutral zone.
Retention
It’s the ability of the denture to resist displacement in a direction opposite to that of insertion. It’s one of the most important factors which decides between success and failure of a complete denture.
Factors Responsible
- Biological: (Orofacial musculature, Neuromuscular control, Peripheral seal)
- Physical: (Interfacial surface tension, Viscosity, Adhesion, Cohesion, Atmospheric pressure, Capillarity)
- Mechanical: (Undercut, Balanced occlusion, Springs, Suction chambers, Rubber suction disc, Magnets)
- Psychological: (Patient tolerance, Patient education)
- Others: (Denture adhesive, Implants, Overdentures, Gravity)
Orofacial Musculature
It can supply supplementary retentive forces provided:
- The teeth are positioned in the neutral zone.
- Polished surfaces of the denture are properly shaped.
Adhesion
Physical attraction of unlike molecules for each other (i.e. saliva to the mucous membrane and to the denture base). Achieved through ionic forces between charged salivary glycoprotein and surface epithelium or acrylic resin.
Cohesion
It’s the physiological attraction of molecules for each other. It is within the layer of fluid (usually saliva) that is present between the denture base and the mucosa. Normal Saliva is not cohesive, can be modified with the use of denture adhesive.
Atmospheric Pressure
It is pressure applied by the atmosphere on all objects due to its weight. [14.7 lb/sq.in]
Atmospheric pressure can act to resist dislodging forces applied to dentures, if the dentures have an effective seal around their borders.
This resistance force has been called “suction” because it is a resistance to the removal of dentures from their basal seat.
Retention due to atmospheric pressure is directly proportionate to the area covered by the denture base.
Proper border moulding with physiological, selective pressure techniques is essential for taking advantage of this retentive mechanism.
Springs
Are made of coiled stainless steel or gold plated base metal. The ends of spring are attached to swivels in premolar area of both upper & lower dentures on both sides.
Rubber Suction Disks
They are buttoned on to a stud, stuck into the fitting surface of denture. Partial vacuum created by disk help in retaining the denture.
Disadvantages
- Constant irritation & damage to soft tissue.
- Perforation of palate on prolonged use.
- Even causes malignant tumor in epithelium.
Magnets
Serenium magnets are fixed in dentures in premolar, molar region with repulsive force developed in opposite denture, aids in retention.
Disadvantages
- Repulsive force results in constant pressure on basal seat causing extensive bone resorption & soreness in mucous membrane.
Psychological Factors
Patient Tolerance
A psychological factor where dentures are often retained in mouth not by accurate fit of dentures but because of Patient tolerance to dentures.
Patient Education
Patient tolerance to dentures can be improved by motivating & educating the patients properly.
Denture Adhesives
It only augments the retentive mechanism already operating when a denture is in use. Available in: powder, cream, liquid, wafer.
Synthetic Mixture
Mixture of salts, short acting carboxy methyl cellulose or CMS or long acting polyvinyl methyl ether maleate or gantrez.
Polymers
Polyvinyl pyrrolidone (povidone) less commonly used.
Mechanism of Action
When it comes in contact with saliva or water it hydrates and displays quick onset of ionic adhesive to both denture and mucous epithelium. Increase viscosity. Increase in volume eliminating voids between denture base and mucosa.
Indicated
- Neurological disease e.g. loss of neuromuscular coordination as in stroke.
- Orofacial dyskinesia.
Partial Denture
- Support: Tooth supported, Tooth and Tissue supported.
- Stability: Major connectors, Minor connectors, Indirect retainers.
- Retention: Direct retainers.
Definition
It is any unit of a removable dental prosthesis that engages the abutment tooth in such a manner as to resist displacement of the prosthesis away from basal seat tissues.
Direct Retainers
A direct retainer is any unit of a removable dental prosthesis that engages an abutment tooth in such a manner as to resist displacement of the prosthesis away from the basal seat tissues.
Types
- Intracoronal Direct Retainer
- Extracoronal Direct Retainer
Intracoronal Direct Retainer
Engages vertical walls built into the crown of the abutment tooth to create frictional resistance to removal.
Advantages
- Elimination of a visible retentive component and a visible vertical support through a rest seat.
- Provides some horizontal stabilization.
- Stimulation to the underlying tissues is greater because of intermittent vertical massage.
Disadvantages
- They require prepared abutment and castings.
- Require complicated clinical and laboratory procedures.
- Eventually wear with resulting loss of frictional resistance to denture removal.
- They are difficult to repair and replace.
- They are effective in proportion of their length and are therefore less effective on short teeth.
- Difficult to place completely within the circumference of an abutment tooth.
Extracoronal Direct Retainer
The component of clasp assembly that engages a portion of the tooth surface and either enters an undercut for retention or remains entirely above the height of contour to act as a reciprocating element.
Components of Clasp Assembly
- Rest
- Body
- Reciprocal arm
- Retentive arm
- Retentive terminal
- Minor connector
- Approach arm
- Retentive terminal of vertical projection clasp
Retentive Clasp Arm
- Shoulder: Located above the height of contour and is rigid.
- Retentive terminal: Distal 1/3rd of the clasp. Located below the height of contour & is flexible. Function: Provides retention.
Reciprocal Clasp Arm
A rigid clasp arm placed above the height of contour on the side of the tooth opposing the retentive clasp arm. Should be more rigid. Average diameter must be greater than the average diameter of the opposing retentive arm.
Functions
- To resist tipping forces generated by the retentive terminal as it passes over the height of contour when the partial denture is inserted into or withdrawn from the mouth.
- To stabilize the partial denture against lateral movement.
- As it lies on the supra bulge, it contributes to the vertical support of the prosthesis.
Basic Requirements of Clasp Design
- Retention
- Support
- Stability
- Reciprocation
- Encirclement
- Passivity
Other Requirements
- Simple to construct
- Inexpensive
- Esthetics
- Simple to adjust and repair
Factors Affecting Retention
- Depth of undercut engaged
- Flexibility of the clasp arm
- Angle of approach of the undercut
Flexibility of the Clasp Arm Depends On
- Length of the clasp arm: (Flexibility ∞ Length3. Increased flexibility = reduction of horizontal stresses on abutment & loss of retention.)
- Diameter: Flexibility is inversely proportional to diameter.
- Taper: Should be uniformly tapered from its origin to the tip. Dimensions at the tip are about half of those at the point of origin. Such clasps are about twice as flexible as ones without any taper.
- Cross-sectional form: (Round form is more flexible than half round. Half round form may flex away from the tooth but edgewise flexing is limited. Preferred in tooth borne RPD’s in which they are called on to flex only during placement and removal.)
- Kind of Alloy: (Cr-Co alloys have higher modulus of elasticity than gold, hence less flexible than gold. Smaller diameter of clasp and less depth of undercut used with Cr-Co.)
- Type of alloy: Wrought clasps are more flexible than cast clasp.
- Heat treatment: Proper heat treatment increases the flexibility. Improper heat treatment results in brittleness & no flexibility.
Basic Principles of Clasp Design
- Clasps should encircle more than 180° of the greatest circumference of the crown, passing from diverging axial surfaces to converging axial surfaces.
- The occlusal rest must be designed so that movement of the clasp arms cervically is prevented.
- Each retentive terminal should be opposed by a reciprocal arm or element capable of resisting orthodontic pressures exerted by the retentive arm.
- Unless guiding planes will positively control the path of removal, retentive clasps should be bilaterally opposed.
- Amount of retention should be minimum necessary to resist reasonable dislodging forces.
- Clasp retainers on abutment teeth adjacent to distal extension bases should be designed so that they will avoid direct transmission of tipping & rotational forces to the abutment teeth.
- Ideally reciprocal arm should be located at the junction of the gingival and middle thirds of the crown and terminal end of the retentive arm placed in the gingival third of the crown.