surveyor and principles of surveying

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SURVEYOR AND PRINCIPLES OF SURVEYING

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surveying in prosthodontics

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SURVEYOR AND PRINCIPLES OF SURVEYING

DEFINITION

The surveyor (parallelometer) is aninstrument designed to locate contours and relative parallelism on teeth and associatedstructures

TYPESJELENKONEYIn all of these the casts are held in constantvertical relation to an instrument fixed in avertical surveying arm

PARTS1.Firm horizontal platform on which the base is moved2.Vertical pillar to support the horizontal arm3.Horizontal arm(fixed in Ney, have a nut at top in Jelenko to allow freedom n horizontal plane, double jointed in Williams)4.Surveying table on which the casts are fixed

5.Base on which the table swivels and can be angulated in any direction by ball and socket joint6.Surveying arm having mandrel for holding special tools7.Surveying tools(accessories) i. Analyzing rod to locate maximum curvature without marking the cast ii. Lead pencil

iii. Undercut gaugesiv. Trimming tools with blade edgesPURPOSE OF SURVEYINGI. To identify and mark the position of maximum curvature(survey line) which is to carry a claspII.To identify the depth of an undercut which can be used for the retention of the prosthesis

III .To eliminate unwanted undercutIV. It enables those parts of the denture base which fit against the crowns of the teeth to be placed above the survey lineV. It permits to design a denture with one path of insertionVI. To determine the type and material of the clasp by measuring the undercut

IDENTIFYING THE MAXIMUM CURVATUREInitially with analyzing rod and then marked with lead pencilThe area b/w the occlusal surface and the survey line is non undercut and b/w the survey line and gingival margin is undercutThe survey line is not a fixed contour and depends upon the angulations of the tooth on surveyor table

THE DEPTH OF UNDERCUTMeasured with an undercut gauge which consists of a rod with a horizontal plate of the required dimensions at its baseThree sizes are used : 0.25mm, 0.5mm, 0.75mmWith the rod held against the survey line, the required gauge is moved vertically until

the horizontal marker engages the tooth below the survey lineThis shows the precise position of the desired undercutThis can be marked with a suitable coloured pencil in contrast to the black lead

ELIMINATION OF THE UNWANTED UNDERCUTDuring laboratory stages all the unwanted undercuts are blocked out on the master castThe undercut is filled with plaster or wax which is then trimmed vertically flush with tooth surface while the cast is on the surveyor table

GUIDE PLANESA guide plane is a vertical portion of a tooth surface, 2-3mm in length, over which a partial denture component can move freelyEssential to establish a precise path of insertionThree or four are essential to give a specific path of insertion

Effective when located on opposite sides of mouth/toothGuide planes ensures that clasping is effective and mere engagement of an undercut by a clasp will not guarantee retention e.g. a clasp involving a small buccal undercut will not be retentive if the denture can be removed in a buccal direction

FACTORS IN CHOOSING PATH OF INSERTIONPerpendicular path of insertion is easy for ptAngulated path of insertion avoid displacement by sticky foodBy tilting cast on the surveyor the path of insertion may be changed at will

Following should be considered in choosing path of insertionThe angulations of posterior abutment teethThe angulations of anterior abutment teethThe position of undercutThe dexterity of the pt

THE ANGULATIONS OF POSTERIOR TEETHTwo situations must be consideredIf the proximal surfaces of a bounded saddle are both angled in the same plane, the path of insertion should be averaged along that plane. This has two advantages i. An efficient guide plane system is utilized

ii. Path of withdrawal is not perpendicular2. If the distal surface of an abutment on a free end saddle is angulated, follow that angulations. This makes the saddle more resistant to rotational displacement

THE ANGULATION OF ANTERIOR ABUTMENT TEETHFollow the angulations of anterior teeth to avoid unsightly spacesTHE POSITION OF UNDERCUTEffective undercut can be created by tilting the model on surveyor table

THE DEXTERITY OF PATIENTSElderly and physically handicapped pts can find inserting the denture difficult without guide planes

TRIPODING THE CASTDone to achieve the same degree of tilt for master castTrim the lead marker to 45 degreeAdjust the height so that it touches the lingual tissues and mark itLock the horizontal armThe surveying arm is movedMark two additional marks

After marking the primary cast is removed and master cast is placed on the surveying tableThe master cast is adjusted so that lead pencil comes in contact with the master cast in the same manner as it was in the primary cast

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