৪৮তম বিশেষ বিসিএস [স্বাস্থ্য] ⎯ ডেন্টাল অংশ [Archived]

Denture teeth is the most important part of the denture as aesthetic, mastication and speech are the prime function of the denture teeth(patient's point of view)

Type of denture teeth :

Based on the material

1) Acrylic teeth[commonly used]
2)Porcelain or ceramic teeth 
3)IPN resin teeth[Inter-penetrating Polymer  Network ]
4) Gold occlusals
5) Acrylic resin with amalgam stops

Based on the morphology of the teeth

1)Anatomic teeth- Have  33° cusp angle, most commonly used of all types,resemble as natural teeth,provides good aesthetics and psychological benefit. 
2)Semi-anatomic teeth- Cusp angle range 0° to 30°,usually 20°
3) Non-anatomic /0°/Cusp less teeth-Used in bruxism patient. 
4)Cross bite teeth 
5)Metal insert  teeth 



Ref: Deepak nallaswamy 

Implants are employed as primary retentive structure because their use may vary from single tooth replacement to extra-oral implants in maxillofacial prosthetics.

Classification of maxillofacial Prosthesis : Broadly classified under 3 categories -
1. Intra oral Prosthesis 
2. Extra oral Prosthesis 
3. Treatment Prosthesis 

Ref: Deepak Nallaswamy [1st+2nd edition ]

OPG is the choice of radiographic examination for edentulous patient because of
  a) Images the entire mandible &maxilla
  b) Low radiation dose
  c) High patient acceptability 

Ref: Deepak Nallaswamy + Net

 * The submucosal layer of oral mucosa acts as main piller for supporting the denture.
* Thin submucosa gets traumatised easily leading to patient discomfort.
*Loosely attached,inflamed,edematous submucous get easily displaced leading to loss of retention of the denture.

Ref: Deepak Nallaswamy 

 

5 objectives of impression making is considered during fabrication of complete denture: 

1.Retention- Ability of the denture to withstand displacement against its path of insertion. 

2. Stability- Ability of the denture to horizontal/lateral  movement/force.
     
 [ Retention and Stability are interrelated.Main deference between stability and retention  is  the direction in which the dislodging force act. 
 In retention, denture resists dislodging force in vertical direction along its path of insertion/removal. 
Whereas, in stability, denture resists dislodging force in horizontal/lateral direction.]

3.Support-  Quality of denture that resists vertical displacement of denture or vertical forces of mastication,occlusal forces &other forces applied in denture toward the basal seat area.
   [Importance- Reduces tissueward movement and complements retention and stability. Maintain occlusal relationship. Improve. Masticatory function]

A denture must have good retention,stability and support.Because they are interlinked and complement each other.


4.Aesthetics 
5.Preservation of remaining structures.

Ref: Deepak Nallaswamy, John J Manappallil

Alternative terms of denture stomatitis-
1. Denture induced stomatitis
2.Denture sore mouth
3.Inflammatory papillary hyperplasia
4.Chronic atrophic candidiasis 

Denture stomatitis is one of the common direct sequelae of wearing complete denture.

Etiology/predisposing factor: 
Local- 
1. Presence of denture 
 Causative organism- Candida Albicans. candida induced stomatitis is often correlated with angular cheilitis or glossitis
2. Trauma
3.Poor oral hygiene 
4.High carbohydrate diet- Increases plaque accumulation 
5.Use of broad-spectrum antibiotic.
6.Smoking tobacco

Systemic-
1.Old age
2.Diabetes mellitus
3.Iron,forage,vit B-12 deficiency 
4.Immunodeficiency 
5.Malignancy

Ref: Deepak Nallaswamy 

Vertical jaw relation provides the opitimal separation between the maxilla and mandible.

Alteration in this relation results severe discomfort in both TMJ and the muscles of mastication.

Its easiest to record in complete denture fabrication but most critical,because errors in this record produce first sign of discomfort. 

Effects of altered vertical dimension are:

A. Increase vertical dimension causes -


1. Increased lower facial height 
2.Check biting 
3.Difficulty in speech
4.Stretching of facial muscles
5.Increased volume/cuboidal space of  oral cavity.
6. Increased trauma to the denture bearing area.


B. Decreased vertical dimension causes-
1. Lesser trauma 
2.Decreased lower facial height. 
3.Loss of muscle tone.
4.Loss of lip fullness
5.Corners of mouth are folded or turned down resulting in angular cheilitis
6.Decreased volume/cuboidal space of oral cavity
7.Discomfort in TMJ with headache &neuralgia.
8.Thinking of vermilion border of lip.

C. In both conditions patient faces-

1.Difficulty in swallowing 
2.Pain &Clicking in TMJ


Ref: Deepak

All materials used in dentistry broadly classified into 4 classes: 

1.Metals
2.Ceramics
3.Polymers
4.Composites

because of multiple utilities and overlapping function there is no specific classification in reality but they can be categorised into following types depend on their function -

1 Preventive materials - pit &fissure sealant and other materials to prevent onset of dental diseases.

2. Restorative Materials - repair or replace tooth structure like amalgum,composites,cements ceramic,cast metal& denture materials 


3Auxillary materials -aids in fabrication process like gypsum products,impression materials, casting investment, waxes,etching gel,custom tray materials. 


4.Prosthetic materials - replace missing teeth,oral &maxillofacial structures.these include alloy,ceramics,polymers

5Appliance materials 

6.Biometarials- can be introduced into body tissue. Traditional materials qualify as biometarials
7.Therapeutic agent- various chemical, medicament,antimicrobials &other locally applied agent. 


Ref: Manappallil

Rheology : study of flow of matter is called Rheology.
In dentistry,rheology is necessary because many dental materials are liquids at some stage of Their use.
Example: Molten alloy,
Mixed impression material &cement. 

Terms and properties in rheogy:
1.Viscosity
2 Creep.
3.Flow
4.Thixotropic
5.Relaxation 
6.Shear stress& sheaf strain rate.
7.Pseudo plastic
8.Dilatant.

Ref: Manappallil 

* study of liquidity of matter- Fluid mechanics.
*study of solubility of matter- solubility in chemistry.[Net]

Type of corrosion : 2 types 

1.Dry/chemical corrosion- Direct  combination of metallic and non metallic elements without involvement of any liquid.Type of reaction is oxidation, halogenations or sulfurization.

2.Wet/electrolytic/electrochemical corrosion- occur in presence of liquid. This type is more common in oral cavity because saliva act as a electrolytic medium.
 Alhough there is an associated  chemical corrosion  also.

Corrosion: Loss of material (metal) from the surface by chemical or electrochemical reaction on the surface particle. 

Common example rusting of iron.

Effect: It Creates-
1.Surface roughness leading to food accumulation 
2.Losing the finishing of restoration surface
3.Poor aesthetic of the restoration 

Common corrodic agent: Water,acid,alkalis  salt,oxidants. 




Ref: Dr Rowshan Akhter 

Advantages of using Implants: Implant provides 

1.Preservation of bone
2.Improved function
3 Aesthetics 
4. Good Stability and retention 
5. Moro Comfort than other Prosthesis 

Ref: Deepak

Complications and failures in implant surgery :

Complication:
A.Surgical:
Common surgical complications are-
1. Nerve injury
2.Fracture of bone
3.Penetration of nasal or sinus floor
4.Haemorrhage during osteotomy
5.Lack of primary stability 
6.Significant bleeding 
7.Failure in integration
8.Decimalization of adjacent teeth.

B. Prosthetic :
common prosthetic complication are-are-
1.Screw loosening
2.Screw fracture.
3.Abutment fracture.
4.Prosthesis dislodgement.
5.Veneer debonding.


Failure:
1.Screw loosening 
2.Fixture fracture 

Ref: Deepak.

Aids in the foundation of the denture, denture 
base-.

1.Distributes and transmit all forces from denture teeth to the basal tissue.
2 Provides retention &support because of covering maximum area of the oral cavity.
3. Most commonly made in acrylic resin material as it’s  easy to fabricate &economical.

Ref: Deepak

Common pre prosthetic surgery:

1.Frenectomy
2.Alveolectomy
3.Alveoloplasty

In Complete denture -

A.primary stress bearing area:

1.Maxilla-
a)Hard palate(horizontal portion)
b) Posterolateral slopes of the residual alveolar Ridge. 
2. Mandible-
a) Buccal shelf area.
They lie perpendicular /right angle to the occlusal force.

B.Secondary stress bearing area:

1.Maxilla-
a)Rugae
b)Maxillary tuberosity
c)Alveolar tubercle

2.Mandible-
a)Residual alveolar ridge


Ref: Deepak, Manappallil

Occlusal rim are fabricated to record Maxillo-mandibular relation,lip lines, vertical & horizontal overlaps and to arrange the teeth.

Method of fabrication : 3 method

1. Rolled wax method- most common.Usually  base plate wax is used. 
2. Metal occlusal rim former.
3. Preformed occulsal rim.

Ref: Deepak

Posterior palatal seal:
1.Area that contacts the posterior surfaces of the denture bases.
2.Area between anterior and posterior vibrator lines.

Function: 
1.Primary purpose is retention.
2.Prevents food accumulation beneath the denture.
3.Reduces the tendency of gag reflexes 
4.Maintains contact with the moving soft palate.
5.Compensates for curing shrinkage. 
6.Reduces tongue irritation 
7.Post seal in impression tray, prevents impression materials from sliding down the throat.



Ref: Deepak,Manappallil

3 types of occlusion is applied in complete denture construction -
1. Balanced occlusion 
2. Monoplane occlusion
3. Lingual used occlusion 

Balanced occlusion is most important/commonly employed in complete denture because absence of occlusal balance resulting in lever action of denture during mandibular movement.
It is usually absent in natural dentition.

Treatment Prosthesis : 

A prosthetic appliance used for purpose of treating and conditioning the tissue that are called on to support and retain it is called treatment Prosthesis. 

Commonly used treatment Prosthesis are: 
1. Surgical obturators
2.Mandibular training flange
3 Radiation appliances

Ref: Deepak.

Prevention of corrosion :

1. Incorporate the alloy with noble metal; almost 50% of total alloy composition 
2.Well  finished & polished  surface of the restoration.  Notches,pits,porosities,grooves,crevicrs must be avoided in metal restoration. 

3.Avoid dissimilar metal coming in contact in the mouth.

4. Use less mercury content amalgam restoration.

5.Making oxide barrier on the metal surface by passivating effect of certain metal(chromium layer)
6.Maintain good oral hygiene.  


Ref: Dr Rowshan Akhter 

Ductility: property of metal associated with the ability to be hammered thin or stretched into wire without breaking. 
The degree of ductility occurs due to metallic bond.
It depends on tensile strength &decreases  with raised temperature. 

Malleability : Property of metal associated with the ability to be hammered into a thin sheet without breaking. 

It is not depend on strength and increases with raised temperature. 

Gold is the most ductile and most malleable metal among All materials. 


Ref: Manappallil.

Classifications of impression material :
.Based on elasticity :

1.Non elastic:
a. Rigid - Plaster of Paris
b. Plastic-
. i) Thermoplastic- Impression compound, Wax
 ii)Paste- ZnO eugenol paste 

2.Elastic:
a Hydrocolloids
  i) Reversible - Agar agar
 ii) Irreversible - Alginate 

b.Elastomer
i) Polysulphide
ii)siicones- Condensation silicone,Addition silicone
c.Gutta percha

Ref:  A H S Rahman 

Ideal requirements of dental resin: 
Both restorative &denture base,dental resin should be

1.Tasteless,odorless 
2.Nontoxic, non irritant to oral tissue
3.Ethically satisfactory 
4.Dimentionally stable
5.Strong, resilient &abrasion resistant 
6.Insoluble and impermeable to oral fluids
7.Low specific gravity(light in weight) 
8. Well tolerated with the temperature of food/liquid.
9.Easy to fabricate,repair and economical
10.Radiopaque 
11. Bonded with the tooth chemically.
12. Good thermal conductivity


Ref: Manappallil 

Function of major constituents of Amalgam alloy:

Silver:
1.Major element 
2.Whitens the alloy
3.Decrease creep
4.Increase strength,expansion on setting,tarnish resistance 

Tin:
1. Controls the reaction between silver and mercury. Without tin reaction would be too fast and setting expansion would be unacceptable. 

2.Reduces strength,hardness, resistance to tarnish and corrosion. 

 Copper: 
1. Increases hardness, strength and setting expansion. 

Zinc: 
1.acts as a scavenger 
2.Prevents oxidation of major elements 
3.Delayed expansion.

Ref: Manappallil 

Conventional GIC is nothing an acid soluble calcium fluroalumino silicate glass i.e. an ion leachable glass.


Resin modified GIC- poly acrylic acid modified with methacrylate groups and HEMA monomers

Fiber reinforced GIC- Alumina fibers are incorporated into resin modified GIC

Proline containing  GIC- An amino acid containing GIC.


Ref: Nisha Garg 

Classification of GICs:

A. According to their use:

Type I -Luting cements

Type II- Restorative cements

Type III- Liner& base materials(fast setting) 

Type IV- Pit &Fissure sealants

Type V- Orthodontic cements

Type VI- Core build up materials 

Type VII- Fluoride releasing cements

Type VIII- GIC for ART

Type X- Geriatric &Pediatric GICs. 

B.Traditional classification according to Skinner: 
 
Type I- Luting Cements 

Type II- Restorative cements

Type III- Liner or Base material 


Ref: Nisha Garg  4th edition 

Classification of Amalgam alloys:

Based on copper content 

1.Low copper alloy- contain <6% copper[Conventional alloy]
2. High copper alloy- contain 13-30% copper.

Based on Zinc content 

1. Zinc containing alloy-  >0.01% zinc
2. Zinc free alloy- <0.01% zinc

Based on shape of the Alloy particle

1.Lathe-cut alloys(irregular shape)
2.Spherical alloys
3.Spheroidal alloys

Based on size of alloy powder particle

1.Micro cut
2.Macro cut.

Based on number of alloyed metals

1 Binary alloys: silver-tin
2.Ternary alloys: silver-tin-copper
3.Quaternary alloys: silver-tin-copper-indium 


Ref: Manappallil 

Composition of ZnO eugenol cement:

Powder:

1.Zinc oxide - 69%- [principle ingredient ]
2.White rosin- reduce brittleness of set cement
3.Zinc stearate
4.Zinc acetate- improves strength.
5.Magnesium oxide.

Liquid:

1.Eugenol- 85%- reacts with zinc oxide
2.Olive oil.

Ref: Manappallil.

Because of excellent initial sealing ability and kind pulpal response Zno eugenol cement is the cement of choice for temporary restoration. 

Type :
Type I - popular for sedative treatment, temporary coverage and temporary  cementation 
Type II- Temporary restoration 


Ref: Manappallil.

Impression are the main source of spread of infection among the dental materials. Hence more complex to disinfect. 

Generally 3 process are applied to disinfect the impression :


1.Immersion in a disinfectant 
2.Spraying with a disinfectant 
3.Incorporating the disinfectant into the material. 

In dental office &Laboratory, immersion in a disinfectant is the most common method of disinfection. 


Ref: Manappallil 

In casting, flame of torch melted casting machine has 4 zone - from inward to outward 

1.Mixing Zone- dark in color

2.Combustion Zone- Green in color

3.Reducing Zone - Bule color zone just beyond the green zone. Fusion of casting alloys happens in this zone.

4.Oxidizing Zone- Outermost zone.Not used for fusion.

Ref: Manappallil 

Porosity: may be internal or external 

Internal porosity cause discoloration 

External porosity weakens the restoration 

Severe porosity at tooth restoration can cause secondary caries.

Types of porosity:

1.Caused by solidification shrinkage -
  a)Localized shrinkage porosity
  b) Suck back porosity(irregular in shape)
  c) Microporosities


2. Caused by gas-
a) Pin hole porosity
b)Gas inclusions(spherical in shape) 
c) subsurface porosity

3.Back pressure porosity - caused by air trapped in mould.

Casting Defects :
1.Casting size mismatch
2.Distortion 
3.Surface roughness
4.Nodules
5 Fins
6.Porosity
7.Incomplete casting 
8.Contaminated casting


.Ref: Manappallil 

Composition of Ca(OH)2 :

A.Base Paste :

1. I-methyl trimethylene disalicylate
2.Calcium sulphate
3.Titanium dioxide
4.Calcium tungstate or barium sulphate-Provides radiopacity 

B.Catalyst paste:

1.Calcium hydroxide - 50%[Principle reactive ingredient ]

2.Zinc oxide
3.Zinc stearate
4.Titanium oxide- Provides radiopacity  
5.Ethylene toluene sulfonamide 


Ref: Manappallil 

Classification of Gypsum product:

Type I - Impression plaster

Type II- Dental plaster/model plaster/Laboratory plaster/mounting plaster 
    a) class 1 for mounting 
    b) class 2 for model

Type III -Dental stone/ class 1 stone/ Hydrocal.

Type IV- Die stone( high strength low expansion)[Strongest &hardest variety ]

Type  V- Die Stone(high strength high expansion) [Most recent ] 

Ref: Manappallil 

Radiopacity: property of a material to obstruct the passage of radiant energy (X-ray)

Materials that inhibit passage of radiantion- radiopaque

Materials that allow free passage of radiation-
Radiolucent. 

Significance : 
1.help to detect problem within restorative, teeth,bone.

Commonly used elements that add in dental materials to make the radiopacity of the materials  are:
1.Strontium or barium glasses
2 Barium sulphate
3.Zirconium dioxide
4.Ytterbium oxide.

radiopacity of a material is expressed as equivalent thickness of Aluminum.  Hence, it is used as standard to measures radiopacity.


Ref: Manappallil.

Microleakage: Incomplete &localised lack of seal,microscopic in nature,leading to penetration of oral fluid and its chemical and bacterial contents through the restoration cavity interface is called microleakage.

Most frequent result of microleakage are pulpal inflammation(pulpits) and secondary  or recurrent caries

Others results are:
1.Stain or discoloration 
2.Sensitivity 
3.Foul smell in oral cavity 
4.Inflammation of adjacent tissue.


Ref: Dr Rowshan Akhter, Manappallil 

Ref: John Joy Manappallil

Characteristics  of alginate :

1. Irreversible hydrocolloid

Classification of dental waxes:

A.According to use:

1.Pattern wax
a) Inlay casting wax
b) RPD casting wax
c)Baseplate wax/Modelling wax

2 Processing wax:
a) Boxing wax
b) Utility wax
c) Sticky wax
d) Carding wax
e) Shellac

3.Impression wax:
a) Corrective wax
b) Bite registration wax

B.According to origin:
1.Mineral

2.Plant- Carnauba,Ouricury,Candelilla,Japan wax,Cocoa butter.

3.Insect- Bee wax

4.Animal


Ref: Manappallil 

Setting time of different dental materials :

Ca(OH)2 cement- 2.5 to 5.5 minutes
 
Zinc phosphate cement - 
     Base type- 2.5 to 6 minutes  
     Luting typr- 2.5 to8 minutes 

GICs-
    Restorative type- 4 to 5min 
    Luting type- 7min

ZnO eugenol cement - 4 to 10min 

Agar agar - 5min

Addition silicon - 5 to 9 min 

Silicon rubber impression material - 6 to 9 min

ZnO paste - 
     Type I -  10min
      Type II- 15min

Polysulphide - 12.5min [longest setting time at 37°C]