TOPIC: PRINCIPLES OF RPD DESIGN
🎯 KEY POINTS
🔹Gillett Bridge consists of a partial denture that utilizes the Gillett clasp system. It is composed of an occlusal rest which is notched deep into the occlusal axial surface with a gingivally placed groove and a circumferential clasp for retention. The occlusal rest is custom-made with a cast restoration.
🔹Angle of gingival convergence is located apical to the height of the contour on the abutment tooth.
🔹Every denture is an all acrylic type of dentures which restores multiple edentulous spaces in the maxillary arch. There is minimal contact between the acrylic teeth and the abutment teeth to reduce the lateral stresses. The posterior most teeth are bounded by the wrought clasp which aids in retention and prevents distal tipping of the posterior teeth.
🔹Embrasure clasp is best used in Kennedy class II cases.
🔹Dr A.J. Fortunati was first to use dental surveyor.
🔹Surveyor is essentially a parallelometer which is used to determine the relative parallelism of two or more surfaces of the teeth or other parts of the cast.
🔹Microanalyser is a type of surveyor which electronically measures the amount of undercut.
🔹Cast should not be tilted more than 10° at the time of surveying.
🔹One of the most important functions of the clasp is to distribute the stresses.
🔹The main purpose of tilting the cast in surveying is to determine the most desirable path of placement.
🔹The scriber on the surveyor marks the greatest convexity of the tooth.
🔹Gold is the best material to fabricate a clasp
🔎 DEFINITION :
🔺PATH OF INSERTION: The specific direction in which the prosthesis is placed on the abutment teeth or dental implant(s). (GPT 8th Ed)
🔺STRESS BREAKER: A device or system that relieves specific dental structures of part or all of the occlusal forces and redirects those forces to other bearing structures or regions. (GPT 8th Ed)
🔺SHORTENED DENTAL ARCH CONCEPT: SDA is an arch with a reduction of teeth starting posteriorly, mostly in the permanent molars.
✳️DENTAL SURVEYOR: A paralleling instrument used in construction of a dental prosthesis to locate and delineate the contours and relative positions of abutment teeth and associated structures. (GPT 8th Ed)
✳️ SURVEYING: An analysis and comparison of the prominence of intraoral contours associated with the fabrication of the dental prosthesis.(GPT 8th Ed)
⭐ Types of surveyor :
(i) Ney’s surveyor
(ii) Wills surveyor by Jalenko
🔷 Other Commercially Available Surveyors Are:
🔸Micro-analyser
🔸Optical surveyor
🔸Stress-O-graph
🔸Bachmann’s parallelometer
🔸Retentoscope
🔸Intraoral surveyor
🔸Bego paraflex
🔸William’s surveyor
🔸Ney turbo-torque surveyor
✳️ SURVEY LINE : A line produced on a cast by a surveyor marking the greatest prominence of contour in relation to the planned path of placement of a restoration. (GPT 8th Ed)
⭐ Types of Survey Lines
(i) High survey line
(ii) Medium survey line
(iii) Low survey line
(iv) Diagonal survey line
✳️ TRIPODING : Those marks or lines drawn on a cast in a single plane perpendicular to the survey rod to assist with repositioning the cast on a dental surveyor in a previously defined orientation. (GPT 8th Ed)
⭐ Types Of Tripoding
- Tissue surface tripoding
- Art portion tripoding
📌 Concepts of RPD designing
These concepts are:
(i) Stress equalization
(ii) Physiologic basing
(iii) Broad stress distribution
📌 Methods Of Controlling Stress In RPD Are:
(i) Reduce the load on the abutment and the ridge
(ii) Distribution of load between the teeth and the residual ridge
✳️ PRECISION ATTACHMENTS: An interlocking device, one component of which is fixed to an abutment or abutments, and the other is integrated into a removable dental prosthesis in order to stabilize and/or retain it. (GPT 8th Ed)
🔎 CLASSIFICATION OF THE PRECISION ATTACHMENTS
🔶 According to Alan A. Grant and O.A. Wesley:
💠 On The Basis Of Site Of Attachment To The Abutment Tooth:
(i) Class 1: Coronal attachments –
Extracoronal Attachments and Intracoronal Attachments
(ii) Class 2: Root-face attachments – Stud Attachments and Bar Attachments
🔶 According to H.W. Prieskel (1979)
💠 On The Basis Of Shape Of Attachments:
(i) Intracoronal attachments – frictional type
- Mechanical lock
- Semi Precision attachment (custom-made)
(ii) Extracoronal attachments – projection units
- Connectors
- Combined units
(iii) Stud attachments
(iv) Bar attachments – bar joints
- Bar units
(v) Auxiliary attachments – screw units
- Friction devices
- Bolts, hinged flange