Concepts and techniques of denture impression

Vinay PavanKumar .K1st year PG Student

Dept of ProsthodonticsAECS Maaruti dental college

Historical review

Modified impression procedures

Steps

Theories

Anatomical landmarks

Objectives Definitions

Basic requirements

Concepts and techniques of denture

impression

“There was no strong scientific evidence that different clinical situations require different combinations of materials and techniques for impressions”

The results of the review warrant serious consideration in prosthodontic teaching and clinical practice.

Carlsson GE.etal What is the evidence base for the efficacies of differentcomplete denture impression procedures? A critical review.

journal of dentistry 41 (2013) 17–23

MEDLINE/PubMed search + Cochrane Library

Impression A negative likeness or copy in reverse of the surface of an object; an imprint of the teeth and

adjacent structures for use in dentistry

Complete Denture ImpressionThe negative registration of the entire denture

bearing stabilizing and border seal areas of either the maxillae or mandible in a plastic material that

becomes relatively hard or set while in contact with these tissues

Preliminary impression or primary impressionA negative likeness made for the purpose of diagnosis,

treatment planning or for the fabrication of a tray.

Final impressionThe negative likeness made for the purpose of

fabricating a prosthesis.

Historical reviewBefore the middle of 18th century ridges painted with dye and a block of ivory or bone was pressed on the ridge .

• 1711 Matthias Gottfried Purman recorded the use of wax

• 1736 Phillip Pfaff used plaster casts to record maxillary-mandibular relations.

• 1844 Plaster of Paris first used as impression material

• 1848 Gutta Percha introduced

1845-1899:• concepts of atmospheric pressure, max extension of denture bearing area, equal distance of pressure, and adaptation of denture bearing tissues were stressed

• secondary wash impression started, plaster within the primary impression

• retention, stability , and comfort - anatomic considerations

•impression trays developed (mostly Brittannia metal), also non metal trays used

1900-1929:

• Introduction of closed mouth impression technique.

• Border molding to capture the anatomy of the tissues (oral/perioral muscles)

• Placement of a posterior palatal seal (anatomic and mechanical), most texts recorded the termination of the posterior palatal seal as the vibrating line

• Introduced the concept of esthetics in impression

1930-1940:

•Recognized the anatomy of denture bearing areas, and muscle physiology as related to impression procedures

• Emphasis on immediate denture techniques

• New materials-reversible hydrocolloids, ZOE

• Stressed the use of plaster for final impression procedures

• Introduction of the concept of mucostatics

1950-1964:• Introduction of rubber base and silicones

• Fisher R.D laid down six Fundamental Rules for Making Full Denture Impressions

• Appreciation for rationale of border molding and posterior palatal seal

• Use of modeling compound (preliminary impressions)

• Use of ZOE or plaster (secondary impressions)

1965 – present • Two techniques were described sub atmospheric pressure (also

called as vacustatic technique) and Flange technique

• A modified impression technique for hyperplastic alveolar ridges was described where surgical preparation was contraindicated

• Applied plaster impression technique for maxillary complete denture for combination syndrome

• Dynamic impression technique

• Dr. Joseph Massad introduced a technique of controlling the path of insertion thus minimizing the incidence of overextension

Basic Requirements

• Knowledge of facial &oral anatomy

• Knowledge of basic and reliable technique

• Knowledge and understanding of materials

• Skill and Patient management

Surface anatomy of lower face• Rima oris

• Philtrum

• Vermilion zone

• Labial tubercle

• Labial commissure

• Modiolus

• Nasolabial groove

• Labiomental groove

• Labiomarginal sulcus

Structure of Oral Mucosa Epithelium

Connective tissue - Lamina Propria.

Submucosa to the underlying structure which may be bone or muscle

• Thickness and consistency of submucosa - support denture

• The submucosa is firmly attached to the periosteum of the underlying bone of the residual ridge

Organization of the Oral Mucosa

3 types according to function:

1.Masticatory Mucosa:25% of total mucosa.

2.Lining Mucosa:60% of total mucosa

3.Specialized Mucosa:15% of total mucosa.

The Masticatory mucosa covers the crest of the ridge

The residual attached gingiva firmly adherent to the

supporting bone

• Hard palate

It is characterized by a well defined keratinized layer on its

outermost surface subject to changes in thickness

The specialized mucosa covers the dorsal surface of the tongue. This mucosal covering is keratinized

The Lining mucosa - nonkeratinized layer

Vestibular spaces

Alveolingual sulcus

Soft palate

Ventral surface of the tongue

Unattached gingiva found on slopes of residual

ridge.

Anatomical landmarks

Relief areas

Stress bearing areas or

supporting areas

Peripheral areas or limiting areas

Anatomical landmarks in Maxilla

Limiting structures:

• Labial frenum

• Labial vestibule

• Buccal frenum

• Buccal vestibule

• Hamular notch

• Posterior palatal seal area

Supporting structuresPrimary stress bearing areas :• Hard palate • Posterolateral slopes of the residual alveolar ridgeSecondary stress bearing areas :• Rugae• Maxillary tuberosity

Relief areas• Incisive papilla• Cuspid eminence• Mid palatine raphae• Fovea palatine

Limiting structures

Labial frenum

• A fold of mucous membrane at the

median line.

• No muscle attachment

• “v” shaped notch should be

recorded during impression making

• Excessive relief weakens denture

base

Labial vestibule

• Extends from one buccal frenum to the other on the labial side .

• The major muscle in this area is Orbicularis oris

• Impression - sufficient support to the upper lip• The labial flange of the impression -sufficient

height• No interference of the labial flange with the

action of lip in function.

Buccal Frenum• Dividing line between the labial and buccal vestibules.

• It may be a single fold, or double fold.

• Broad and fan shaped

It has the attachment of following muscles

• Levator anguli oris

• Orbicularis oris

• Buccinators

Buccal Vestibule

• Extends from the buccal frenum anteriorly to the hamular

notch posteriorly.

The size of the buccal vestibule varies:

• contraction of the buccinators

• position of mandible

• amount of bone loss in the maxilla.

• The ramus and the coronoid process of the mandible

• masseter

Hamular notch

• Depression between maxillary tuberosity and the hamulus

of the medial pterygoid plate.

• Distolateral border of the denture base rests in the hamular

notch

• Soft area of loose areolar tissue

Posterior palatal seal

• Soft tissues at or along the junction of hard and soft

palate on which pressure within the physiological limits of

the tissues can be applied by denture to aid in the

retention of the denture

• Marks the beginning of motion in the soft palate when an

individual says “ah”

• extends from one hamular notch to other

• This region contains glandular tissue

• Aids in retention by maintaining contact with soft palate

• Reduces the tendency of gag reflex

• Prevents food accumulation between the soft palate

and the denture base

• Compensate for polymerisation shrinkage

Supporting structures

Hard palate

• Foundation of hard palate

• Ultimate support

• Submucosa of antero lateral part - adipose tissue

• Postrolateral part - glandular tissue

• Horizontal portion of hard palate lateral to midline act as primary

stress bearing area

Residual ridge

• Shape and size of alveolar ridges change : natural teeth are removed

• Mucous membrane is firmly attached to the periosteum• Important area of support. • Bone undergoes resorption - secondary stress bearing area.• Removing the dentures from the mouth for 6 to 8 hrs a day,

allows keratinization

Rugae

In the area of the rugae, palate is set at an angle to the

residual ridge and is thinly covered by soft tissue.

irregularly shaped rolls of soft tissues.

should not be distorted in an impression technique: since

rebounding tissue tends to unseat the denture.

Maxillary tuberosity

• Bulbous extension of the residual ridge in the 2nd and 3rd

molar region terminating in hamular notch.

• Enlargement can be fibrous or bony

• Excess tissue : prevent proper location of the occlusal plane

and may interfere with the lower denture

Relief areas

Mid Palatine Raphe

Median palatine raphae extends from incisive papilla to

distal end of hard palate

Thin mucosal covering with less submucosa

non-resilient

Adequate relief should be given to avoid trauma from

denture base

Incisive papilla

Elevation of soft tissue over the incisive foramen or

nasopalatine canal

Burning sensation, parasthesia and pain - relief is

necessary

Fovea Palatinae

• Bilateral indentations near the midline of palate formed by

coalescence of several mucous gland ducts.

• Aids in determining vibrating line.

Anatomical landmarks in mandibleLimiting structures

Labial frenum

Labial vestibule

Lingual frenum

Buccal frenum

Buccal vestibule

Alveolo lingual sulcus

Retromolar pad

Pterygomandibular raphe

Supporting structures

• Buccal shelf • Residual alveolar ridge

Relief areas Mylohyoid ridgeMental foramenGenial tuberclesTorus mandibularis

Limiting structure

Labial frenum

• Shorter and wider than the maxillary frenum.

• Band of fibrous connective tissue similar : to

maxilla.

• Incisive and orbicularis oris influence this

frenum.

• Unlike in maxilla, this frenum is active

Buccal Frenum

• Usually in the area of 1st pre molar.

• The oral activities in these area are horizontal as

well as vertical (ex. Grinning and puckering) thus

needing wider clearance.

Muscle acting in this region are • Buccinators • Depressor anguli oris• Orbicularis oris

Labial Vestibule

• Extends between the two buccal frenum

• Mentalis muscle is an active muscle in this region

• Length and thickness of the labial flange of denture

occupying this space is crucial in influencing lip

support and retention

• Impression will be narrowest in the anterior labial

region

Retromolar pad

• Pear shaped triangular soft pad of tissue

Bounded by:

• Buccinator

• Superior constrictor muscle

• Pterygomandibular raphe

• Terminal part of tendon of temporalis

Alveololingual sulcus

• Between lingual frenum to retromylohyoid curtain

and divided into three regionsAnterior region

• Lingual frenum to mylohyoid ridge.

• Premylohyoid fossa- premylohyoid eminence in

impression.

Middle region

• From pre-mylohyoid fossa to the distal end of the

mylohyoid ridge.

• Lingual flange extends away from the ridge- tongue

rests on the top of flange and aids in stabilizing the

lower denture.

Posterior region

• The flange deviates towards the ridge into the

retromylohyoid fossa.

• Proper recording gives typical S –form of the lingual

flange.

Buccal shelf area

The area between the mandibular buccal frenum

and the anterior edge of the masseter is known as

the buccal shelf.

It is bounded medially by the crest of the residual

ridge anteriorly by the buccal frenum , laterally by

the external oblique line and distally by retromolar

pad.

Crest of the Mandibular Ridge

• Covered by the fibrous connective tissue

• Underlying bone is of cancellous type without a

cortical bony plate covering .

• The fibrous connective tissue is favorable for

resisting the externally applied forces, such as the

denture.

Objectives of impression making

PRESS P - Preservation of the alveolar ridges. R - RetentionE - Esthetics.S - Stability. S - Support.

 

- Carl O. Boucher in 1944

Preservation of the alveolar ridges

M.M. De Van’s dictum “It is more important to preserve what already exists than to replace

what is missing”.

• Not to use heavy pressure

• Covering as much of the supporting areas as possible - minimize the possibility of soft tissue abuse and bone resorption.

Retention

Retention of a denture is that quality inherent in the dental prosthesis acting to resist the forces of dislodgment along the path of placement

• It depends upon factors that produce attachment of the denture to the mucosa.

• Resists the adhesiveness of foods, the force of gravity and the forces associated with the opening of the jaws

Factors affecting retention of dentures

Anatomical factors

Physiological factors

Physical factors

Mechanical factors

Muscular factors

Anatomical factors

Physiological factors

• Saliva and its quality

• Size of denture bearing area - Retentive force is directly proportional to the area covered.

• Quality of the denture bearing area

Physical factors

• Adhesion

• Cohesion

• Interfacial surface tension

• Capillarity and capillary attraction

• Atmospheric pressure and peripheral seal

Mechanical factors

• Retentive springs• Undercuts• Magnetic forces• Denture adhesive• Suction chambers and suction discs

Muscular factors

• The muscles apply supplementary retentive forces on the denture.

• It is most effective in the neutral zone.  

Oral and facial musculature

provides supplementary retentive forces

Denture bases must be properly extended to cover the maximum area possible

• The occlusal plane must be at the correct level

• The arch form of the teeth must be in the

neutral zone

Stability

The quality of a dental prosthesis to be firm, steady

or constant, to resist displacement by functional

horizontal or rotational stresses

• Relationship of the denture base to the underlying

bone

• Attained by more intimate contact of labial and

buccal flanges with the labial and buccal slopes

and of the lingual flanges with the lingual slopes of

the ridge.

To be stable a denture requires

• Good retention

• No interfering occlusion

• Proper tooth arrangement

• Proper form and contour of the polished surfaces

• Proper orientation of the occlusal plane

• Good control and coordination of the patient's

musculature.

Support

• The resistance to vertical forces of mastication and

to occlusal or other forces applied in a direction

toward the basal seat.

• Enhanced by selective placement of pressures

that are in harmony with the resiliency of the

tissues that make up the basal seat.

Areas of support are divided intoAreas of support Primary Maxillary: Posterior ridges and flat areas of the palate

Mandibular: Buccal shelf, posterior ridgesReason: These are the areas that are at right angles to the occlusal forces and usually do not resorb easily

Secondary Maxillary: Anterior ridge and all ridge slopes.Mandibular: Anterior ridge and all ridge slopes.Reason: These are the areas that are greater than at right angles to occlusal forces or are parallel to them; also the areas of edentulous ridge that are at right angles to occlusal forces but tend to resorb under load.

Slight All vestibular areas that provide very little support but are needed for the very important peripheral seal 

Esthetics

• Thickness of the denture flanges

• Thicker denture flanges are preferred in long-term edentulous patients - labial fullness.

• Impression should perfectly reproduce the width and height of the entire sulcus for the proper fabrication of the flanges.

Classification of impressions

A. Based on the theories of impression.

Pressure theory- Mucocompressive

Minimal pressure- Mucostatic

Selective pressure

B. Based on the position of the mouth while

making the impression.

Open mouth

Closed mouth

C. Based on the method of manipulation for

border molding.

• Hand manipulation

• Functional movements

Pressure theory :MucocompressiveDefinite pressure

• The assumption that denture retention is tested most severely during mastication, many dentists formerly considered it essential for the tissue to remain in contact with the denture during chewing

• Greene in 1896 • Records the oral tissues in a functional and displaced form

• Materials used - impression compound, waxes and soft liners.

• Dentures made by this technique tend to get displaced due to the tissue rebound at rest

Technique• Primary impression - impression compound

• Special tray - base plate.

• Second Impression - impression compound

• Bite rims with uniform occlusal surfaces are then made.

• Areas to be relieved are softened and the impression is

inserted in mouth and held under biting pressure for one or

two minutes.

• Borders are molded by asking the patient to perform functional

movements.

Advantages

• Better retention and support

Disadvantages• Excess pressure - increase alveolar bone resorption.

• Excess pressure on peripheral tissues and the palate -

transient ischaemia.

• Tissue rebound when the tissue resume their normal

resting state.

• Pressure on sharp bony ridges - pain

Minimal pressure theory : Mucostatic or non pressure or passive technique

• Page gave the concept of mucostatic based on

Pascal’s law

• “Mucostatic” Dr. Carrol W.  Jones

• Retention is mainly due to interfacial surface

tension. The mucostatic technique results in a

denture, which is closely adapted to the mucosa of

the denture-bearing area but has poor peripheral

seal.

Technique

• A compound impression is made.

• A baseplate wax space is adapted.

• A special tray is adapted over the wax spacer.

• Spacer is removed and an impression is made with

a free flowing material with little pressure.

• Escape holes are made for relief.

DisadvantagesShorter flanges prevent the wider distribution of masticatory stresses.

Reduced coverageLack of border molding : reducing retentionLack of border seal: food to slip beneath the denture.

AdvantageHigh regard for tissue health and preservation :

better prognosis

Short denture borders are readily accessible to

the tongue which might provoke some irritation.

Shorter flanges may reduce support for the face

which can affect esthetics.

The shorter flange would mean less lateral

stability.

Patients with poor residual ridges and reduced

areas of attached gingiva were difficult to treat

Selective pressure theory

Combines the principles of both pressure and minimal pressure techniques

Tissue preservation + mechanical factor of achieving retention with minimum pressure, which is within the physiologic limits of tissue tolerance

Philosophy of the selective pressure technique

Certain areas of the maxilla and mandible, are by nature better adapted for withstanding extra loads from the forces of mastication.

These tissues can be recorded under slight placement of pressure while other tissues must be recorded at rest

Boucher divided basal seat area into different zones according to capacity to withstand masticatory loads without undergoing resorption.

Primary stress bearing area

Relief areas

Secondary stress bearing area

Advantages Technique considers the physiologic functions of the tissues of the basal seat, and therefore appears more sound and appealing.

DisadvantagesSome feel that it is impossible to record areas with varying pressure.

Since some areas are still recorded under functional load, the denture still faces the potential danger of rebounding and loosing retention

Open-mouth Impressions

Impressions are made with the tray that is held by the dentist

Advantage

Preferred because the operator can see whether muscle trimming is done properly

Closed-mouth Impressions

Supporting tissues are recorded in a functional relationship

Wax occlusion rims that are made on preliminary casts.

Border molding and the final impressions are completed

McMillan - tongue movements are more forceful when teeth are together.

AdvantageSaving of time

Disadvantage Appointment time may fatiguing the dentist and patient

Tendency for overextensionsProblem of limited space between the tuberosity and pear shaped pad

No control over the amount of pressure during the final impressions

Soft tissues – displaced- rebound bone resoption

Dynamic impression technique

Cagna et al, The neutral zone revisited: From historical concepts to modern application,J Prosthet Dent 2009;101:405-412

Steps in impression making

Examination and conditioning of the patient and the mouth.

Seating of the patientSelection of impression materialSelection of the impression traySelection of impression techniqueMaking the preliminary impressionConstructing the primary castFabricating the custom trayBorder molding Making the final impression

Examination and conditioning of the patient and the mouth

Inflammation of the mucosa

Distortion of denture-foundation tissues

Excessive amounts of hyperplastic tissue

Insufficient space between the upper and

lower ridges

Impression materialClassification

Elastic1. Reversible hydrocolloid2. Irreversible hydrocolloid3. Rubber impression materials a. Polyether b. Silicone

Non-elastic1. Gypsum products2. Metallic oxide pastes3. Impression compound

Based on Prosthodontic use

Preliminary impression materials :Impression compoundAlginate

Final impression materials:Plaster of paris, zinc oxide-eugenol paste, irreversible hydrocolloid, silicone, polysulfide rubber, polyether, tissue-conditioning material

SELECTION OF THE IMPRESSION TRAY

A device that is used to carry, confine, and control impression material while making an impression (GPT-8).

Classification of impression traysBases on whether they are prefabricated or individualized

Stock trays Custom trays

Depending on the presence or absence of holes or perforations

Perforated Non-perforated

Depending on whether they are meant for dentate or edentate individuals

Dentulous traysEdentulous traysCombination trays

Seating of the patient

Position of the operator for maxillary impression

Position of the operator for mandibular impression

Preliminary impression making :Maxillary

Practice positioning of the tray

Labial frenum - guide.

Anterior fingers - 1st molar region

Adhesive - silicone putty material or alginate

Impression compoundPosterior part of tray- contact with tissues

Border moulding

Labial and buccal vestibules

Coronoid process

Impression poured - stone

Primary impression : MandibularPosterior extent of tray – retromolar padTray loaded with material and catered over the ridge with tongue slightly raised

Alternating pressure on molar region with index finger

Functional movements done to get the border limit

Constructing the custom trayOutline for the wax spacer is drawn on the castPosterior palatal seal area on the cast is not covered with the wax spacer – maxilla

Buccal shelf not covered - mandibleBaseplate wax approximately 1 mm in thickness is placed on the cast

Self-curing acrylic resin tray material - uniformly adapted over the cast

Tray thickness - 2 to 3 mmResin handle is attached in the anterior region of the tray

Spacer design

Roy Mac Gregor recommends placement of a sheet of metal foil in the region of incisive papilla and mid palatine raphae

Neill recommends adaptation of 0.9 mm casing wax all over except PPS area

Boucher recommends placement of 1 mm

base plate wax on the cast except PPS area

Morrow, Rudd, Rhoads recommends to block out undercut areas with wax ,adapt full wax spacer 2 mm short of resin special tray border all over & placement of 3 tissue stops equidistant from each other

Sharry recommended Base plate wax adapted over whole area, four stops 2mm width cut from wax : cuspid and molar region- extend from palatal aspect of ridge : mucobuccal fold

Border molding

Border molding is the process by which the shape of the borders of the tray is made to conform accurately to the contours of the buccal and labial vestibules

Manipulation of the border tissues, against a moldable impression material

Borders of the tray are molded to a form that will be in harmony with the physiological action of the limiting anatomical structures

Border molding may be carried out in sections either recording one part of the border at a time or recording all parts of the borders simultaneously.

Recording all of the borders simultaneously has two general advantages:

The number of insertions of tray is reduced.Developing all borders simultaneously avoids propagation of errors caused by a mistake in one section affecting the borders contours in another.

Custom tray fabrication

Border moulding

Sectional Recording all borders simultaneously

Final impression

Boxing impressions and making casts

Enclosure of an impression by building up vertical walls- desired size, base of cast, preserve details of impression

Final cast

Displaceable (flabby) anterior maxillary ridge

The extent of the displaceable tissue is drawn on the impression surface. This area, and the equivalent area of the tray, are then removed, using a scalpel and acrylic bur

Use a low-viscosity material and paint or syringe these onto the displaceable tissue to record them in a minimally-displaced position.

Fibrous posterior mandibular ridge

McCord.JF ,Grant.AA ,Impression making, BDJ, 2000 ;188: 9, pp 484 – 92

Flat (atrophic) mandibular ridge covered with atrophic mucosa

• McCord and Tyson described this technique

• The impression medium here is an admix of 3 parts by weight of (red) impression compound to 7 parts by weight of greenstick; the admix is created.

McCord.JF ,Grant.AA ,Impression making, BDJ, 2000 ;188: 9, pp 484 – 92

Technique for Impressing Class IV Mandibular Edentulous Ridge

Chandrasekharan et al, A Technique for Impressing the Severely Resorbed Mandibular Edentulous Ridge, Journal of Prosthodontics, 2012; 21: 215–218

Review of literature

Study evaluated changes in impression pressure produced by different types of relief space and escape holes in the impression tray for making an impression of a simulated maxillary edentulous arch

For making impressions of an edentulous maxilla, the data suggest that a tray with an escape hole

1.0 mm or larger or a spacer thickness of base plate wax (1.40 mm) be used.

Komiyama O et al, Effects of relief space and escape holes on pressure characteristics of maxillary edentulous impressions, J Prosthet Dent 2004;91:570-6

Goodacre et al, CAD/CAM fabricated complete dentures: concepts and clinical methods of obtaining required morphological data, J Prosthet Dent 2012;107:34-46

Infante et al, Fabricating complete dentures with CAD/CAM technology,J Prosthet Dent 2014

CONCLUSION

“Ideal impression must be in the mind of the dentist before it is in his hand. He must literally make the impression rather than take it”

- M.M. De van

References Zarb G, Hobkirk JA, Eckert SE, Jacob RF, editors. Prosthodontic treatment for edentulous patients. 13th ed. St. Louis: Elsevier Mosby; 2013 pp 161-179

Sheldon Winkler, Essentials of complete Denture prosthodontics, 2nd edition,2012, AITBS Publishers, India, pp 88-105

Sharry .J.J, Complete denture Prosthodontics, 3rd edition, Mc Graw Hill company, pp 191-210.

Rudd and Morrow, Dental lab procedures, Complete dentures, 2nd edition, 1986, Mosby Publications, USA, Pp 9 - 89

Nair KC, A primer on complete denture fabrication, 1st edition, 2013, Ahuja publication, India Pp 67-77

Zimmer I.D. and Sherman, H. An analysis of the development of complete denture impression techniques. J Prosthet dent 46: 242-249, 1981.

Komiyama O et al, Effects of relief space and escape holes on pressure characteristics of maxillary edentulous impressions, J Prosthet Dent 2004;91:570-6

McCord.JF ,Grant.AA ,Impression making, BDJ, 2000 ;188: 9, pp 484 – 92

Rao.S etal, A Systematic Review of Impression Technique for Conventional Complete Denture, J Indian Prosthodont Soc (Apr-June 2010) 10(2):105–111

Chandrasekharan.NK et al, A Technique for Impressing the Severely Resorbed Mandibular Edentulous Ridge, Journal of Prosthodontics, 2012; 21: 215–218

Goodacre et al, CAD/CAM fabricated complete dentures: concepts and clinical methods of obtaining required morphological data, J Prosthet Dent 2012;107:34-46

Infante et al, Fabricating complete dentures withCAD/CAM technology,J Prosthet Dent 2014

Dwivedi A, Vyas R, Theories of impression making and their rationale in complete denture prosthodontics. J Orafac Res 2013;3(1):34-37