A Note On Denture Coping Technique....

Definition

A copy denture preserves the polished surface of the existing prosthesis while allowing modifications to be carried out to the fitting and occlusal surfaces of a complete denture. As a patient's adaptive potential decreases with age the maintenance of the shape of the original polished surface results in less adjustment of the supporting musculature being required. Therefore the title 'Copy denture technique' is really a misnomer as It is only rarely that an exact copy of an existing denture will be required.

Indications

1.      An elderly patient presenting with upper and lower complete dentures which have been satisfactory for many years but are now loose or worn.

2.      A patient with a history of denture problems where it may be useful to make controlled modifications in the copy denture of the most successful previous dentures

3.      Previous immediate dentures which require replacing after bone resorption following extractions.

4.      Second 'spare' set of dentures.

Advantages

·         No alteration or mutilation of existing denture as occurs in a reline or rebase.

·         No period for patient to be without dentures as occurs in a reline or rebase.

·         Reduced number of clinical stages

·         Simple duplication procedure

Technical support for such techniques is variable,various clinical techniques are available

1.                                  Use of reversible hydrocolloid to copy dentures

                                     Murray/Woolland technique

3.                                     Replica record block technique

Standard copy technique

Definition- As previously described.

Indications- As previously described.

Advantages

• The reproduction of successful design features on which a patient's tolerance and control of the previous dentures depend.

• The accurate alteration of undesirable features.

• Simplified occlusal registration and a reduced number of clinical visits.

Disadvantages

 Increased charges may be made by commercial laboratories. The production of a template and the need for the technician to follow this exactly also often makes this technique unpopular amongst technical staff.

Procedure

 1. A mould of the original denture that is being copied is produced by whichever method the clinician wishes to use.

This is poured up, with the teeth in wax and the bases in selfcured acrylic. A stone duplicate is also poured as a guide to the original denture, both in respect of the polished surfaces and tooth position.

2. The wax and acrylic copy denture is then either used as a registration block or, if minimal occlusal alteration is required, taken to the trial stage.

3. The dentures are tried in and the occlusion and vertical dimension checked. If this is found to be satisfactory any undercuts are removed from the baseplates and a wash impression is taken within both the upper and lower bases using a closed mouth technique.

4. A master cast is then poured and the finished dentures processed in the normal manner.

Copy denture for severe tooth wear

Definition

A duplicate denture made with as few modifications to the previous existing denture as possible.

Indications

Patients who present with mutilated dentures  that they can comfortably wear and who have a history of intolerance to conventional replacement of these dentures. Clinically, there may be a place for providing the patient with a copy of their old dentures with as few modifications as possible.This will improve the chances of patient acceptance of the new prosthesis.

Advantages

 It is likely that the patient's acceptance of and adaptation to such a denture will be high as it will not be different to their 'tried and trusted' set. A further advantage is the reduction in numerous remakes.

Disadvantages

 By following such a technique, the clinician may unknowingly copy faults that may in the long term cause such problems as TMJ symptoms and denture instability.

          

A Note On Acrylic Partial Dentures...... With PDF Download

DESIGN PRINCIPLES FOR A GOOD ACRYLIC PARTIAL DENTURE

In a similar manner to an RPD design for a cobalt-chromium denture, the casts should be surveyed and, where appropriate, articulated to assist in the design. The design of acrylic dentures will follow the same principles involved with a cobalt chrome denture3 and should consider the following:

•    Saddles
•    Support
•    Retention
•    Bracing and reciprocation
•    Connector
•     Indirect retention
•     Review of completed design.

Saddles are designed to fill the edentulous space to be replaced. However, the saddle must be fully extended in the distal extension edentulous area. When designing the denture the clinician should look to increase the tooth borne support of the denture and not rely exclusively on mucosal support. This may be obtained by finishing the denture above the survey line in those places where the acrylic components contact the tooth.

The acrylic has been finished above the survey line in order to obtain support from the remaining teeth

It is possible to avoid contact with the gingiva and obtain relief by blocking out the dentogingival junction, although this is controversial. It has been found that deterioration in gingival health will occur whether relief is present or not.

Retention will generally be a wrought clasp, which will be attached to the acrylic and will require reciprocation. Connection will usually be acrylic or, where strength and reduction in bulk is indicated, then a cast cobalt chrome framework is designed. In order to obtain indirect retention, the clasp must always be placed between the saddle and the indirect retainer. Finally, the completed design is reviewed against a checklist of the design principles.

 Wherever possible, any coverage of gingival margins should be avoided or reduced to an absolute minimum and this is combined with a high level of oral hygiene.

 Any uncovering of the gingival tissues is beneficial as shown by the old denture design

(a) compared to the newer design (b).

The patient should be instructed in the correct oral hygiene measures and advised on correct denture care, both at the insertion stage and review. This should include disclosing of the denture on review appointments and indicating where the denture is not being cleaned properly. The use of a suitable denture cleanser is advocated.

If there are metallic components associated with the denture, such as clasps, then these should not be placed in the cleanser. Avoidance of candida albicans growth within the denture will prevent denture stomatitis. The subsequent inflammation and swelling of the tissues will lead to an ill-fitting denture.

(a) The oral mucosa exhibits inflammation owing to candidal infection and there is plaque retained around the teeth. (b) Disclosing of the denture shows that compliance with denture hygiene instruction is required to remove the plaque.

Processing of RPDs

A simple, but often overlooked, technique to provide well-fitting acrylic dentures is to ask the technician to block out undercuts, including any interdental spaces prior to processing. First, the cast is surveyed to the path of insertion (which is generally vertical to the occlusal plane). The undercuts on the master cast are blocked out with wax or plaster and a duplicate cast is obtained.

             The undercuts are blocked out with wax prior to obtaining a duplicate cast.

The denture is then processed on this duplicate cast. If such a simple but effective technique is not done, then the acrylic denture will only fit once the undercuts are removed. This process takes place by the chairside and may often turn out to be a lengthy procedure. As the clinician attempts to fit the denture, excessive acrylic is often removed, leading to the denture not contacting the hard and soft tissues.

     The six design features required for a successful Every denture

       

                Download A NOTE on Acrylic Partial Dentures

An Introduction to Basic Dental Students

GENERAL FEATURES OF DENTAL INSTRUMENTS

Working end(s) of instruments

•Are the functional parts of the instrument

• Can have a variety of functions including: cutting, packing, carving, placing and condensing

•Are adapted to the function of the particular instrument

•May be bevelled (i.e. the working end is cut at an angle)

• An instrument can be single-ended (one working end) or double-ended (two working ends)

Shank of an instrument

• The part between the working end and the handle

• Can be straight or angled

• The function of the instrument determines the angle and flexibility of the shank 

Handle of an instrument

• Is the part of the instrument that the operator grasps

•Provides stability and leverage

• Design is related to the function of the instrument

• Examples:

   The handle of an upper extraction forceps may be curved to facilitate a palm grasp for the operator

 The handle of a rubber dam clamp forceps is rounded to fit in the palm of the operator’s hand

 A serrated handle allows a better grip

 A large handle allows a palm grasp

THE BASIC DENTAL INSTRUMENTS

Mouth mirror and handle

Functions

•To provide indirect vision

•To reflect light

• For retraction and protection of oral tissues

• For magnification (the number of the mirror represents size of mirror head)

Varieties

• Single-sided or double-sided

• Can be disposable

• Plain or magnifying

Sickle/contra-angled probe

Functions

• Detection of:

 defective pits and fissures

 calculus

 deficient margins of restorations, crowns and bridges

 caries

• Examination (pointed tip allows good tactile sensitivity)

Varieties

• Can be single-ended or double-ended

• Many different styles available

•Working ends may vary (straight, curved)

Periodontal probe

Function and features

• Measure the depth of periodontal pockets

•Tip is calibrated in millimetres

•Blunt end reduces the possibility of tissue trauma

Varieties

• Single-ended or double-ended

• Can be straight, curved or at right angles

• Plastic types available

Briault probe

Function and feature

• Detection of caries on mesial and distal surfaces

• The angled working ends facilitate adaptation to interproximal surfaces

College tweezers and Locking college tweezers

      locking

Functions

• Placing small objects in the mouth and retrieving small objects from the mouth

• Locking type ‘lock’ to prevent dropping materials

Varieties

• Locking and non-locking types

•Working ends can be straight, curved, serrated or smooth

Metal ruler

Function

Measurement of length, e.g. endodontic K files

Varieties

• Can be calibrated in different units of measure

• Plastic type available

A Note On Mode of action of fluoride and the caries process

The use of fluorides date back to as early as 1874 when the German Erharde suggested the use of potassium fluoride tablets for expectant mothers and children in order to strengthen teeth. This recommendation was without any scientific evidence. What we now know to be dental fluorosis (mottling) was noted by dentists long ago who reported on 'Colorado Stain' without the aetiology of the tooth defect being established.

Mode of action of fluoride and the caries process

The mineral of tooth tissues exists as a carbonated apatite, which contains calcium, phosphate, and hydroxyl ions, making it a hydroxyapatite [Ca₁₀.(PO₄)₆.(OH)₂]. Carbonated portions weaken the structure and render the tissue susceptible to attack. Food remnants and debris mix with saliva and adhere to tooth surfaces as a slimy film known as dental plaque. Oral bacteria, and most importantly certain types of cariogenic bacteria (e.g. Mutans streptococci and Lactobacilli species), metabolize dental plaque and produce acid which lowers the pH of the oral environment. When the pH is below the critical pH for hydroxyapatite (< 5.5), demineralization occurs with a net outward flow of calcium and phosphorous ions from the enamel surface into plaque and saliva. 

When the pH returns to 7.0, remineralization occurs with a net inward flow of ions into the enamel surface. If fluoride is present during remineralization, it is incorporated to form fluorapatite [Ca₁₀.(PO₄)₆.F₂], which is more stable and resistant to further acid attacks. The process of demineralization and remineralization is an ongoing one and frequently referred to as 'the ionic see-saw' or 'tug-of-war'. This is now widely believed to be the most important preventive action of fluoride, and a constant post-eruptive supply of ionic fluoride is thought to be most effective.

A number of mechanisms have been proposed to explain the action of fluoride.

The first is that fluoride has an effect during tooth formation by substitution of hydroxyl ions for fluoride ions, thereby reducing the solubility of the tooth tissues.

Second, fluoride can inhibit plaque bacterial growth and glycolysis. At pH 7.0, fluoride ions are precluded from entering bacteria. However, at pH 5.0, fluoride exists as hydrofluoric acid, which crosses the bacterial cell membrane to interfere with its metabolism, by specifically inhibiting the enzyme enolase in the glycolytic pathway. 

Third fluoride inhibits the demineralization of tooth mineral when present in solution at the tooth surface. 

Fourth, fluoride enhances remineralization by combining with calcium and phosphate to form fluorapatite. Fluoride enhances crystal growth, stabilizes and makes the tissue resistant to further acid attack.

Enamel apatite demineralizes when the pH drops to pH 5.5. However, when fluorapatite is formed during remineralization, it is even more resistant to demineralization as the critical pH for fluorapatite is pH 3.5. Therefore, it is most important to have an intraoral source of fluoride when remineralization is taking place. Lastly, fluoride affects the morphology of the crown of the tooth, making the coronal pits and fissures shallower. Such shallower pits and fissures will be less likely to collect food debris, allow stagnation and become decayed. The most important of these mechanisms is that when fluoride is present in the oral environment at the time of the acid attack it inhibits demineralization and promotes remineralization.

As early as 1890, Miller drew attention to the dissolutive process of dental caries and directed efforts to inhibit dissolution. The clinical findings of the anti-caries activity of drinking water with fluoride caused researchers to seek reasons for this. The finding that fluoride-treated enamel had a lower solubility led many to consider this as a cause and effect relationship. The anti-caries action of fluoride was thought to be one of preventing dissolution of enamel, and efforts were made to incorporate more and more amounts of fluoride into surface enamel. 

The first topical agent used, after water fluoridation, was a 2% sodium fluoride solution and there was a greater uptake of fluoride into enamel from acidified solutions. Numerous fluoride preparations with varying concentrations of fluoride were employed for topical application and used as anti-caries agents. It was noted that there was not much difference in the caries reductions reported from the topical fluoride studies despite great variations in the fluoride concentrations used. In addition, the difference in the levels of fluoride in surface enamel of residents of fluoridated and non-fluoridated areas was limited. Therefore, it is difficult to explain the 50% reduction of caries observed, on the basis of the fluoride level in the surface enamel. Furthermore, there has been no study to show any clear-cut inverse relationship between fluoride content of surface enamel and dental caries.

All the available evidence is that caries results from the presence of an acidogenic plaque on elements of the tooth mineral. The diffusion of acidic components into the tooth mineral is accompanied by the reverse diffusion of components of the mineral. During the carious process there is a preferential loss of calcium, accompanied by dissolution of magnesium and carbonate. The first clinical sign of enamel caries is the so-called 'white spot' lesion, where an apparently sound surface overlies an area of decalcification. The remineralization effect of fluoride has since come into favour. It has been reported that attacked enamel could re-harden on exposure to saliva and that softened enamel could be re-hardened by solutions of calcium phosphates in vitro. However, it is now known that it is the presence of fluoride in the oral cavity, and in particular, its presence in the liquid phase at the enamel-plaque interface, that is of most importance.

In the past it was thought that the systemic action of fluoride was important for caries prevention. This view has completely changed and it is now known that it is the topical action of fluoride that is essential for caries prevention. It is the presence of fluoride in the liquid phase at the plaque-enamel interface that is of most importance. Studies have shown that even low levels of fluoride (0.10 ppm) were effective in preventing the dissolution of enamel. It has been stated that the activity of the fluoride ion in the oral fluid that is important in reducing the solubility of the enamel rather than a high content of fluoride in the enamel. Saliva, the fluid that bathes the teeth has been extensively studied. The level of fluoride in saliva is thought to be important for caries prevention and it has been shown that caries susceptible subjects had salivary fluoride levels of <0.02 ppm, whereas caries resistant subjects had levels of >0.04 ppm.

Key Points
Fluorides
· It is the activity of the fluoride ion in the oral fluid that is of most importance in reducing enamel solubility rather than having a high content of fluoride in surface enamel.
· A constant supply of low levels of intraoral fluoride, particularly at the saliva/ plaque/enamel interface, is of most benefit in preventing dental caries.

There are a vast number of fluoride products that are available for systemic and topical use. They can be applied professionally by the dental team or by the patient at home.

Dental Anomalies at Different Stages of Tooth Development

 1.     Dental Lamina formation stage

• Migration of ectoderm

1. If it doesn’t migrate… anodontia (no teeth)

2.     Initiation and Proliferation

• Formation of tooth bud
1. Partial anodontia, supernumerary, geminated/fused teeth

supernumerary teeth

Fusion

Germination

• Cleidocranial Dysplasia… an inherited disorder involving the cranium, face, clavicles and supernumerary teeth

                                           

                                                              Cleidocranial Dysplasia

• Ectodermal Dysplasia… lack of hair, sweat glands (hypohydrotic) and teeth (partial anodontia)

Ectodermal Dysplasia

 3.     Histodifferentiation

• Odontodysplasia… ghost teeth

                                       

1. A marked decrease in radiodensity
2. Very thin enamel and dentin, large pulp chamber
3. Cells don’t change fully

 4.     Morphodifferentiation

• Macro/micro size, dans invaginitis, dens evaginatus, Hutchinson’s Incisors, talon cusp, taurodontism, delaceration

                           taurodontism

                                                                      

                           dens evaginatus

                           macrodontia

                           microdontia

       

 5.     Apposition – matrix formation

• Amelogenesis imperfecta
• Dentinogenesis imperfecta
• Enamel Hypoplasia

                  Amelogenesis imperfecta 

Dentinogenesis imperfecta

6.     Calcification – mineralization of the matrix

• Fluorosis
• Amelogenesis Imperfecta

A Note On Tooth Development(Odontogenesis)......With Diagrams and Interactive Videos

Odontogenesis

Tooth formation is highly regulated at the molecular level

• terminal differentiation of specific cell types

• epithelial-mesenchymal interactions

• secretion of specific extracellular matrices

• controlled processing of those matrices

• regulation of ion deposition

• mineralization of the dental tissues

Tooth Formation is dependent on

Genetic Factors

   Hundreds to several thousand genes likely involved (polygenic)

Tooth development is represented by four stages: bell stage (A), initial protein-matrix secretion (B), regression of dental epithelium (D), and tooth eruption (E). Sagittal sections were stained with alcian blue, hematoxylin, and eosin. Arrowheads, dental epithelium. Asterisks, artificial gaps. (Scale bars: 10 μm.) ISH analysis revealed the expression of SCPP1 (G),SCPP2 (H), SCPP3A (I), SCPP3B (J), SCPP4 (K), SCPP5 (L), COL1 (M), and SPARC(N) in various developmental stages. The expression of SCPP genes is summarized for the initial secretory stage (C) and for the eruption stage (F). IDE, inner dental epithelium; IPE, inner pharyngeal epithelium; Ms, mesenchyme expressing COL1 and SPARC; Od, odontoblasts; ODE, outer dental epithelium; OPE, outer pharyngeal epithelium; PRM, protein matrix.

Environmental Factors

    Nutrition

    Physical phenomenon

    Infection

Molecular Determinants of Tooth Formation

• Over 10,000 genes involved in making a tooth

• Most genes involved in odontogenesis are expressed in non-dental tissues

• Some genes are relatively specific for development of the dental tissues (e.g. amelogenin gene)

Environmental Influences of Environmental Influences of Amelogenesis

• Nutrition

       Major and minor components

• Calcium, phosphorus, protein, fluoride etc…

• Hypoxia

• Hyperthermia

• Infection

         Congenital rubella, syphillus, CMV, etc…

• Physical Determinants

        Space

        Trauma

Interactions Leading to Developmental Dental Defects

Stages Required for Tooth Formation

• Initiation

• Histodifferentiation

• Morphodifferentiation

• Apposition

      Secretory Phase

      Transition Phase

      Maturation Phase

• Stages are not discrete for any given tooth. 

• Teeth develop over years beginning with the coronal portion of the crown. 

• Can be mineralizing at the cusp tips while cervically cells are differentiating.

Tooth Devolopment 3D video to understand tooth development


Tooth Development Video Explanation using Diagrams


Histology Of Tooth Development Video