Dental Surveying

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Information about Dental Surveying

Published on May 28, 2009

Author: drmonicagupta


SURVEYING : SURVEYING Presented by Dr Monica Gupta Introduction : Introduction An essential key in the practice of Removable Partial denture is thorough, knowledgeable planning of each structural detail of the prosthesis. Surveying is the procedure of locating and delineating the contours and position of the abutment teeth and associated structures before designing a Removable Partial Denture Slide 3: In 1953, Dr. A. H. Schmidt described surveying as follows: “Reduced to its simplest terms, surveying a tooth is a mechanical method of obtaining its height of contour accurately. If a vertical plane is brought into contact with a curved surface, it will touch at the greatest bulge on the convexity and nowhere else” What is a Surveyor ? : What is a Surveyor ? A Dental Surveyor is a instrument used to determine the relative parallelism of two or more surfaces of teeth or other parts of a dental arch. Primary Purpose of surveying : Primary Purpose of surveying is to plan those modifications of oral structures necessary to fabricate a removable partial denture. Measuring a specific depth of undercut Recontouring abutment teeth on the diagnostic cast Contouring wax patterns Placing intracoronal retainers Placing internal rests Machining cast restorations Surveying and blocking out the master cast Principle of Working : Principle of Working If a vertical plane is brought into contact with a curved surface, it will touch at the greatest bulge on the convexity and nowhere else. Development of Dental Cast Surveyor : Development of Dental Cast Surveyor The Original Ney Surveyor : The Original Ney Surveyor This was the first model developed by NEY in 1923. It featured a convenient palm rest on the top of the vertical arm. Designed by Weinstein and Roth, it was the first surveyor to be commercially available to the profession. Ney’s Surveyor : Ney’s Surveyor This is the currently used surveyor, designed and developed in 1937. The Original Wills Surveyor : The Original Wills Surveyor Introduced in 1929 It was marketed by Kerr Products. It came both with and without a work light and used with several different designs of cast holders. In this example, the cast is held in place with wax. The Electronic Surveyor : The Electronic Surveyor The heated waxing instrument could be used to shape and trim the blockout wax. Paratherm Surveyor : Paratherm Surveyor The Paratherm surveying and blockout waxing instrument heats its waxing tools electrically. The surveying arms move in 3 axes Surveyor with Undercut Gauge : Surveyor with Undercut Gauge The Retentoscope - produced by the Saddle-Lock Company. Stressograph : Stressograph The Stressograph, produced by the Ticonium Company, features 2 horizontal arm assemblies. First arm - conventional surveying arm, Second arm - supports a dial gauge to measure undercuts. Broken Arm Cast Surveyor : Broken Arm Cast Surveyor Featuring the gimbal stage table, can be adjusted to any tilt in any direction. The instrument has a spring-loaded surveying arm. A straight handpiece could easily be clamped to the surveying arm. Dental Surveyor with Milling Machine : Dental Surveyor with Milling Machine The Albrecht Linear Motor Milling Machine with built-in motor & cross table. Developed for precision attachment applications, ensure the parallelism of guiding planes milled into castings. Intra Oral Surveyor : Intra Oral Surveyor For checking tooth preparations of abutment teeth for fixed or removable partial dentures. - Accurately indicates planned path of insertion - Visual guide during preparation of teeth - evaluating tooth preparations before final impression - Inexpensive, practical and readily available method. Optical Surveyor : Optical Surveyor Parallel light beams produced by light bulbs with small dense filaments and condenser lenses contained in a box. Advantages - Changes in survey lines and undercuts can be inspected easily. - Better visualization of even the slightest undercuts. Disadvantage - Requires a darkroom - Light beams reflecting from cast can pose problems in illumination Other Surveyors : Other Surveyors Microanalsyer – capable of measuring undercut electronically in mm. Krupp Model K3 Nisor Model D Anthogyr Model 1670 Advanced Parallelometer – Galloni isoparalellometer Model 1020 Bachmann Parallelometer. Parts of a Surveyor : Parts of a Surveyor Widely used – Jelenko and Ney Principal Parts - Platform on which base is moved - Vertical arm supporting superstructure - Horizontal arm - Table to which cast is attached - Base on which table swivels - Paralleling tool or Guideline marker - Mandrel for holding special tools Ney’s Surveyor Surveyor Tools : Surveyor Tools Surveying Tools : Surveying Tools Analysing rod. placed against the teeth and ridges during the initial analysis of the cast to identify undercut areas and to determine the parallelism of surfaces without marking the cast. Slide 24: Graphite Marker moved around the tooth and alveolar ridge to identify and mark the position of maximum convexity (survey line) When surveying a tooth, tip of the marker should be level with gingival margin allowing the side of the marker to produce the survey line Slide 25: Undercut Gauges Used to identify the positions of desired undercuts. Supplied in 0.010, 0.020 and 0.030 inch embodiments. Slide 26: Trimming Knife Is used during the block out procedures and in the construction of a surveyed restoration. Principles of Surveying : Principles of Surveying Surveying – locating accurately the height of maximum contour in relation to a plane in which the model is positioned. Undercut – an area of tooth or soft tissue which is beyond the survey line when viewed from a particular direction. All a matter of perception! : All a matter of perception! Slide 29: Survey line – A line drawn on a tooth to indicate the greatest circumference in a given horizontal plane. The survey line divides parts of teeth or other tissues into undercut and non - undercut areas. Classification of Survey Lines : Classification of Survey Lines Ney System 3 types of survey lines Blatterfein System 4 types of survey lines Position described in 2 zones – Near and Far zones. Ney System : Ney System Class I Survey Line A- Rest B- Clasp Clasp – occlusally approaching arm with terminal third of arm entering undercut Slide 32: Class II Survey Line Clasp used is a gingivally approaching arm. Slide 33: Class III Survey Line Clasp used – wrought, occlusally approaching with terminal two thirds entering the undercut Blatterfein System : Blatterfein System Position of survey line described in 2 zones B – Near Zone C – Far Zone A – Saddle D – Contiguous tooth Slide 35: Typical or Medium Survey Line Clasps used are occlusally approaching and gingivally approaching Near Zone Far Zone Slide 36: Atypical A or Diagonal Survey Line Clasps used are gingivally approaching clasp. Near Zone Far Zone Slide 37: Atypical B or High Survey Line Clasp used is wrought, occlusally approaching arm with two thirds of retentive tip in undercut may be used Near Zone Far Zone Slide 38: Atypical C or Low Survey Line Clasp placement is contraindicated as arm would be placed too close to gingival margin. Extended arm clasp Near Zone Far Zone Slide 39: Important terms to be understood : 1. Guide planes 2. Path of insertion 3. Path of displacement Slide 40: Guide Planes or Guide Surfaces Two or more parallel axial surfaces on abutment teeth which can be used to limit the path of insertion and improve the stability of a removable prosthesis. Guide surfaces may occur naturally on teeth but more commonly need to be prepared Slide 42: The ‘path of insertion’ of a denture is the direction in which it moves from its point of initial contact with the natural teeth until it reaches its fully seated position. Single path of insertion Multiple paths of insertion Slide 43: Rotational path of insertion may be used occasionally. Factors Affecting path of insertion Retentive undercuts Interferences Esthetics Guide planes Slide 44: Path of displacement – Direction in which the denture tends to be displaced in function. Usually at right angles to the occlusal plane. Philosophy of Design : Philosophy of Design The philosophies are based on three approaches to force distribution – 1. Stress equalization 2. Physiologic basing 3. Broad stress distribution Slide 46: Stress equalization a) Stress director is in the form of a hinge b) Hinge is activated by a lifting force Slide 47: Physiologic basing Anatomic form Functional form during impression Denture base during function Denture base adaptation at rest Slide 48: Broad stress distribution What are the objectives ? : What are the objectives ? A partial denture must be designed so that it can be easily inserted and removed by the patient, will be retained against reasonable dislodging forces and will have the best possible appearance. The prime objective in surveying study casts is to determine the most advantageous path of insertion bearing these principles in mind Design of prosthesis : Design of prosthesis Slide 51: Surveying procedure is divided into 4 phases I. Preliminary visual assessment of study cast II. Initial surveying III. Analysis IV. Final survey. Preliminary visual assessment of study cast : Preliminary visual assessment of study cast This stage is called as “eyeballing”. Cast is held in the hand and inspected . Obvious problems are noted Idea obtained whether to employ tilted survey or not. Initial Surveying : Initial Surveying Cast positioned - occlusal plane horizontal Surveying of teeth and ridges – identify undercut areas Position of survey lines and variations in horizontal extent of undercut noted. Undercut measured using a depth gauge. Slide 54: The amount of undercut can be judged approximately from the size of the ‘triangle of light’ between the marker and the cervical part of the tooth, or measured more precisely by using an undercut gauge Analysis : Analysis RPD is designed on the cast – surveyed with horizontal occlusal plane. Analysing rod attached to mandrel Following aspects are considered – 1. Appearance 2. Interferences 3. Retention May necessitate tilting of cast. 1.Appearance : 1.Appearance Unsightly spaces when anterior edentulous area is present. 2. Interferences : 2. Interferences 3. Retention : 3. Retention Retentive undercuts are usually found on the buccal surfaces of maxillary posterior teeth Only the terminal 1/3 of a cast Cobalt Chromium clasp engages the undercut Optimum retention should provide Resistance along the path of displacement Resistance along the path of withdrawal. Slide 59: To obtain retention, undercuts must be present on teeth relative to the horizontal survey. It is a misconception to believe that changing the tilt of the cast will produce retentive undercuts if none exist when the cast is horizontal. a) No undercuts on the tooth when the occlusal plane (OP) is horizontal. b) An apparent undercut created by tilting the cast laterally. c) Clasp arms placed in this false undercut do not provide any resistance to movement along the path of displacement. Final Survey : Final Survey If decided that the cast should be tilted, the analysing rod is exchanged for a marker different in colour from that used in the first survey Teeth to be clasped have two separate survey lines which cross each other. Slide 61: The aims for optimum retention should be to provide: • Resistance along the path of displacement. • Resistance along the path of withdrawal. Slide 62: Tripoding is carried out. Alternatively, the analysing rod is placed against one side of the base of the cast and a line drawn on the cast parallel to the rod Procedure of Surveying a Cast : Procedure of Surveying a Cast The surveyor is used with the master cast for two functions. To delineate height of convexity for location of clasp arms and magnitude of undercuts To trim blockout of any remaining interference to placement and removal of denture. Right and Left side of cast evaluated with analysing rod : Right and Left side of cast evaluated with analysing rod Locking the Surveying Table : Locking the Surveying Table Tripoding : Tripoding Transfer of Survey Lines : Transfer of Survey Lines Transfer of favorable undercuts : Transfer of favorable undercuts Clinical Objectives of Surveying : Clinical Objectives of Surveying The optimum path of insertion of the denture - Need to use guiding surfaces for pleasing appearance - Need to avoid interferences by teeth or ridges - Need to use guide surfaces for retention The design, material and position of clasps Conclusion : Conclusion Surveying is a crucial step in the treatment plan of removable prosthesis. Restorations of this type not only involve materials and leverages and physics but also the hard and soft living tissues which provide the dynamic foundation for support of partial denture. The reaction of teeth and other stabilising structures to the stresses, strains, tipping and normal functional movements of the partial denture to which they are intermittently subjected will determine the success of a restoration. Victor L Steffel Hence it is necessary to survey the model to allow a correct path of insertion and adequate retention for a successful prosthesis Slide 71: Diagnostic Cast Visual Assessment Initial Survey Tentative Design Mouth Preparations and Modifications Final Impression Master Cast Final Surveying Final Design Wax Pattern on Refractory Cast Casting of Pattern Prosthesis References : References Stewart, Rudd, Keubker – Clinical Removable Partial Prosthodontics , 3rd edition McCracken’s Removable Partial Prosthodontics , 9th edition Ernest Miller – Removable Partial Prosthodontics McCarthy M.F. – An intraoral surveyor JPD 61:462-464, 1989 Yilmaz C. Optical surveying of casts for Removable partial dentures JPD, 34:292-296, 1975 Davenport J.C., Bhasker R.M. Surveying BDJ, 189:10, 2000

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