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The main 5 objectives of impression making are: PRESS

P – Preservation of remaining tooth structures

R – Retention

E – Esthetics

S – Stability

S – Support

Retention:

It is defined as “That quality inherent in the prosthesis which resists the force of gravity, adhesiveness of foods, and the forces associated with the opening of jaws”

Anatomical factors like size of the denture bearing area, and quality of the denture bearing area. Retention increases with increase in the size of the denture bearing area. Maxillary denture bearing area is usually around 24 sq.cm. and mandibular area is 14 sq.cm. So maxillary dentures always has greater retention when compared to the mandibular dentures. Displacement of the tissues also affect the retention. Those tissues which were displaced during impression making can rebound while using dentures, leading to loss of retention.

Physiological factors like Saliva. Viscosity of saliva has been a great factor for determining the amount of retention of dentures. Thick and ropy saliva gets accumulated between the tissue surface of the denture and palate, leading to loss of retention. Thin and watery saliva also produces compromised dentures. Cases with ptyalism can lead to gagging. Dentures in patients with the Xerostomia (reduced salivary flow in mouth) condition can produce soreness and irritation.

Physical factors like Adhesion, Cohesion, Interfacial surface tension, capillarity, atmospheric pressure and peripheral seal.

• Adhesion is the physical attraction of unlike molecules to one another. Saliva plays a major role in adhesion. It wets the tissue surface of the denture, and the mucosa, and a thin film is formed between the two surfaces and it helps to hold the two surfaces to one another. In xerostomia, there is no role played by saliva for adhesion.
• Cohesion is the physical attraction of like molecules to one another. The cohesive forces act within the thin film of saliva, and the effectiveness of these forces increases with increase in denture bearing area. Watery saliva produces thinner film and more cohesion, when compared to thick mucous saliva.
• Interfacial surface tension is the tension or resistance to separation possessed by the film of liquid between two well adapted surfaces. This acts with the air-liquid interface acting between two surfaces where a thin film of liquid holds the surfaces on the either sides. Thin film of saliva resists the displacing forces, and this aids in retention. For retention to happen effectively, there needs to be a thin film of saliva, and as there is excess saliva in the borders of a mandibular denture, there is minimal interfacial surface tension seen.
• Capillarity is that quality or state, because of the surface tension causes elevation or depression of the surface of the liquid that is in contact with a solid. Closeness of adaptation of denture base to soft tissue, and greater surface area can help in a good capillarity.

Mechanical factors include undercuts, retentive springs, magnetic forces, denture adhesives, suction chambers.

• Undercuts on one side can help in retention, but bilateral undercuts would require surgical correction as they can interfere with denture insertion.
• Intramucosal magnets can be placed for retention in highly resorbed ridges.
• Denture adhesives can be used where retention is needed, and should be coated on tissue surfaces before wearing the dentures.
• Suction chambers creates areas of negative pressure, which help in retention (these are avoided now, as they are found to creating palatal hyperplasia).

Stability

It is defined as “The quality of a denture to be firm, steady or constant, to resist displacement by functional stresses and not to be subject to change of position when forces are applied.”
Its the ability of the denture to withstand horizontally acting forces, and the various factors that affect stability of the denture are -

• Vertical height of the residual alveolar ridge should be good enough. Highly resorbed ridges offers the least stability.
• Quality of the soft tissue over the ridge should be firm and resilient. Tissues that are flabby with excessive submucosa offers poor stability.
• The impression made should be as accurate as possible, and smooth, duplicating all the details of the tissues accurately.
• Occlusal plane should be oriented parallel to the ridge, and if these forces are inclined, it can lead to shifting of the sliding forces towards the denture, leading to reduced stability.
• Teeth in the denture should be placed in the neutral zone.
• Contour of the polished surface of the denture should be in harmony with the oral structures, and should not interfere with the normal action of the oral musculature and tissues.

Support

It is defined (accd. to GPT) as “The resistance to vertical forces of mastication, occlusal forces applied in a direction towards the denture-bearing area.”
For a proper support, the denture should be covering as much tissue as possible and this helps in distributing the forces over a wider area. This is termed as snowshoe effect. Support will improve if the forces of occlusion are localized to stress bearing areas, and other areas are relieved.

Aesthetics

It is always a matter of concern in complete denture thickness. It is to be seen that the denture and teeth color are in good harmony with the surrounding tissues of the mouth, and the thickness of denture flange is also important. Thick denture flanges usually help in long-term edentulous patients for the required mouth fullness.

Preservation of Remaining Structures

It is defined as: “The preservation of that which remains is of utmost importance and not the meticulous replacement of that which has been lost.”

While recording the impressions, the tissues should be subjected both to stress and relief, so that during the fabrication of the denture, it can be seen that the tissues are not under excess pressure while dentures are being used.
The peripheral tissues should be recorded accurately, so that the over-extension of the denture is prevented, thereby preventing the tissue irritation.

All these objectives should be kept in mind to get a perfect impression which can replicate the oral tissues in the best form.

Dry socket is a well recognized painful complication of Dental Extractions which is localized Osteitis, in which the blood clot disintegrates exposing an infected necrotic socket wall.

Synonyms:

1. Alveolitis sicca dolarsa
2. Localized alveolar Osteitis
3. Fibrinolytic Osteitis

Pathophysiology:

Alveolar Osteitis is a condition in which the blood clot disintegrates, leaving the socket bare of granulation tissue.

Causes for Clot Disintegration and Development of Dry Socket:

1. Failure of clot formation due to the use of Vasoconstrictors in the Local Anesthesia solution. However Dry socket also occurs after extraction under general Anesthesia.
2. Infection of the Clot and Underlying bone.
3. Traumatic Devitalisation of the Socket wall
4. Smocking after extraction.
5. Loss of blood clot due to rinsing the mouth or Sucking the wound.
6. Loss of blood clot due to excess intra alveolar fibrinolytic ester of P-hydroxy benzoic acid PEPH significantly reducing the incidence of dry socket.
7. Conditions with Sclerotic and relatively avascular bone also predisposes to dry socket formation.

Bacteriology Of Dry Socket:

• Anaerobes play a major role

Clinical Features:

• Patient presents within 2-5 days of extraction complaining of severe Radiating Pain to the Ear or other parts of face.
• Socket is devoid of clot or contains brown, friable clot which is easily washed out.
• Foul smell: Due to Food debris accumulated in the socket which starts disintegrating.
• On washing away of the food debris the bare pocket floor can be seen which is extremely sensitive to touch.
• Regional Lymphnodes: Tender and enlarged.
• Occasionally Pyrexia is seen.

The Critical period for the development of a drysocket is First 4 days after Extraction after which Granulation tissue starts to invade the clot.

Incidence:

• 3.2 % of all extractions.
• 22% of Third molar Extractions.
• Males : Females Ratio: 2:3
• Peak age: 20-40 yrs
• Mandibular teeth are 3 times more prone than Maxillary teeth
• Single extractions are 2 times more prone than multiple extractions

Diagnosis:

Radiograph: It is a must so as to exclude the following conditions which can be mis-diagnosed as Dry Socket:

• Retained Apices
• Bony Fragments
• Fractures of Alveolus, body of Mandible

Preventive Measures:

Careful Aseptic Extraction Technique Incidence is reduced significantly by a three day course of Metronidazole 200 mg t.d.s post operatively. Sulphonamides, Antifibrinolytic agents – tranexamic acid Corticosteroids have been tried prophylactically.

Treatment:

Aim of Treatment: Relief of Pain and speeding of resolution.

1. The socket should be irrigated with warm normal saline and the socket debridement done.
2. Sharp bony spurs should be either excised with rounger forceps or smoothened with a Bur.
3. A loose dressing composed of Zinc Oxide and Oil of Cloves on cotton wool is tucked into the socket. it must not be picked tightly in the socket or it may set hard and become very difficult to remove.
4. Analgesic tablets and hot saline mouth rinses are prescribed and patient is recalled after 24 hrs.
5. After 24 if pain stops then no need to replace dressing, but if pain persists then dressing and irrigation has to be replaced.
6. Analgesics and Antibiotics are to be used simultaneously to relieve Pain and as well as infection.

Some other dressings used in the treatment are:

• Gauze moistened with Iodoform compound. Can be left for 2-3 weeks
• Gauze moistened with Local anesthetic agent Butacaine/Benzocaine
• Antifibnolytic agents like Propyl Ester of parabenzoic acid, Dextranomer granules, Iodoform paste

Periapical:

Intra Oral Peri Apical Radiograph

• Size 0:  22×35 mm  Children
• Size 1:  24×40 mm  Anterior, Adults
• Size 2:  31×41 mm   Standard size (Ant. & Post) Adults

Bite wing films:

• Size 0:  22 x 35 mm  Ant. Children
• Size 1 : 24 x 40 mm  Posterior, Children Anterior, Adults
• Size 2 : 31 x 41 mm   Posterior, Adults (Standard size)
• Size 3:  27 x 54 mm  Posterior, Adults (All posterior teeth are seen in 1 film)

Occlusal film

Occlusal Radiograph

• Size 4  57x 76 mm  4 times layer than standard   periapical film)

EXTRA ORAL X-RAY FILMS:

• Panoramic film  -  5 x 12 inch, 6 x 12 inch

Panaromic Radiograph

• Cephatometric films  -  5 x 7 inch, 8 x 10 inch
  

  Cephalograh

]]> http://www.juniordentist.com/types-and-sizes-of-xray-films.html/feed 0 http://www.juniordentist.com/properties-of-x-ray.html http://www.juniordentist.com/properties-of-x-ray.html#comments Mon, 21 Jun 2010 06:11:22 +0000 Varun http://www.juniordentist.com/?p=844 X-Rays are defined as weightless package of pure energy (Photon) that are without electrical charge  and that travel in waves along a straight line with a specific frequency and speed.

The Properties Of X-Ray are divided into 4 headings:

1. Physical
2. Chemical
3. Biological
4. Physiochemical

A) Physical Properties:

1. X-Rays are electromagnetic radiations having a wavelength between 10A to 0.01A
2. In Free Space they travel in a straight line
3. Speed – 1,86,000 miles/sec (same as that of visible light)
4. They are Invisible to Eye.
5. Cannot be Heard
6. Cannot be Smelt
7. They cannot be Reflected, Refracted or Deflected by magnetic or Electric Field
8. They show properties of Interference, Diffraction and Refraction similar to Visible light
9. They Produce an Electric field at right angles to their path of propagation
10. They Produce an Magnetic Field at right angles to the electric field and path of propagation.
11. They donot require any medium for propagation
12. Penetration: X-Rays can penetrate liquids, solids and gases. The degree of penetration depends on Quality, intensity and wavelength of Xyray beam.
13. Absorption: X-Rays are absorbed by matter, the absorption depends on the anatomic structure of the matter and the wavelength of the xray beam.
14. Ionizing Capability: X-rays interact with materials they penetrate and cause ionization
15. Fluorescence: when X-Rays fall upon certain materials visible light will be emitted called fluorescence.
16. X-Rays have the property of Attenuation, Absorption and Scattering
17. They also show Heating effect

B) Chemical Properties:

1. X-Ray induces colour changes of several substances or their solutions Ex: Methylene Blue gets Bleached
2. X-Rays bring about chemical changes in solution because X-Rays produce highly active radical OH ions in water, which react with the solutes.
3. X-Rays cause destruction of the fermenting powers of Enzymes

C) Biological Properties:

1. The excitation property of X-Rays are used in treatment of malignant lesions.
2. X-Rays also have a germicidal or bactericidal effect
3. Somatic Effect: This ranges from simple Sun Burn to Severe dermatitis or to change in blood supply to malignancy

D) Physiochemical Property:

1. X-rays are capable of producing an image on a photographic film