You are confronted with a mandibular arch with only the six anterior teeth and two second molars remaining. The maxillary arch is edentulous. The anterior teeth are restorable individually and show no mobility or periodontal involvement. The molars, however, are grossly involved with caries, in fact most of the clinical crown is gone. They also show a Miller mobility classification of 1 and exhibit a 5 to 6 mm gingival crevicular depth. They can be treated periodontally and endodontically. In such a situation, if finances were not a factor, would you 1) extract both molars 2) prepare the molars for an overlay prosthesis 3) extract all the mandibular teeth and treat the patient with complete dentures?
Every consideration should be directed at preventing the need for a distal extension. In this situation, one would prepare the molars for an overlay prosthesis. If teeth can be endo treated, perio treated, and have not tipped (ie from opposing occlusion), they can serve as abutments. The tooth is prepared in a way that it ends up as a slightly elevated (just slightly above the tissue) dome shaped abutment for which the rpd will engage. This eliminates the need for a distal extension.
If the molars mentioned in the preceding section were prepared for an overlay prosthesis, state the reasons for doing so in terms of benefits to the patient.
This eliminates the need for the distal extension and problems that go along with the distal extension (ie more torque on the abutment teeth, pressure placed on the residual ridge, etc.)
Chapter 11: Surveying
1) Define a dental cast surveyor.
An instrument used to determine the relative parallelism of 2+ surfaces of teeth or other parts of the cast of a dental arch.
2) What are the basic parts of a surveyor?
-Platform on which the base is moved
-Vertical arm that supports superstructure
-Horizontal arm from which surveying tools suspend
-Table to which the cast is attached
-Base on which the table swivels
-Paralleling tool or guidance marker (contacts the convex surface of the tooth)
-Mandrel for holing special tools
3) What does the height of contour mean? How does is relate to a direct retainer assembly?
Height of contour – line encircling a tooth, designating its greatest circumference at a selected position determined by a surveyor.
The height of contour determines the location of non-retentive reciprocal and stabilizing arms and the location of retentive clasp terminals.
4) Because no component of a removable partial denture may engage an undercut except a portion of the retentive arm of a direct retainer, then both desirable and undesirable undercuts must be known in deigning a restoration. True or False?
5) When planning the design of a partial denture, 4 factors must be considered in determining the path of placement and removal. Two of these factors are retention and esthetics. Name the 2 other factors.
Guiding planes and Interference
6) With the diagnostic cast securely clamped to the adjustable table and the diagnostic stylus in the vertical spindle, what orientation of the occlusal plane to the base of the surveyor is recommended as a provisional study position?
The occlusal surfaces are approximately parallel to the platform.
7) When considering a design for a class III, modification 1 arch, which directional tilt of the cast will indicate the greatest area of parallel proximal surfaces to act as guiding planes – anteroposterior or lateral?
8) Suppose in the previous situation, that the diagnostic stylus touches only gingival areas of the proximal surfaces. What are the options to obtain guiding plane surfaces?
In making the choice btw. having contact with a proximal surface at the cervical area only or at the marginal ridge only, contact at the marginal ridge is preferred b/c a plane can be established by recontouring. When only a gingival contact exists a restoration in the only means of establishing a guiding plane.
9) When possible retentive areas are being ascertained, the cast is tilted laterally. How can one avoid changing the established anteroposterior tilt of the cast?
Rotate it about an imaginary longitudinal axis with out disturbing the anteroposterior tilt already established.
10) Uniformity of retention bilaterally is desirable. In what manner does the angle of cervical convergence contribute to obtaining uniform retention?
The amount of retention existing below the height of convexity may be determines by observing the angle of cervical convergence and tilting the cast laterally until similar areas of retention exist on the principal abutment teeth.
11) What are the most common causes of interference to the placement of a mandibular major connector?
Bony prominences and lingually inclined premolars are the most common causes of interference to a lingual bar connector.
12) Why should soft tissue contours be surveyed along with teeth?
Bony undercuts may interfere with seating of the denture base. An undercut may also leave too large of a gap for the minor connector of an I-bar which would leave objectionable spaces and trapping of food.
13) What advantages accrue in having the tip of the carbon marker touch the gingival areas intermittently when marking the heights of contour of abutment teeth?
To ensure that you are not recording a false height of contour and that the carbon marker is reaching the height of contour. (this was not in the book, I asked Dr. Madden if he knew the answer – Dr. Olin was gone that day – and he did not know the answer either, so this is just my best guess. I’m sending an email to Dr. Olin to ask, when he responds I will let you all know.)
14) After the diagnostic cast has been surveyed, how can the relationship of the cast to the vertical spindle of the surveyor in three dimensions be recorded?
There are two methods:
Tripoding: Place three widely divergent dots on the tissue surface of the cast using the tip of a carbon marker, with the vertical arm of the surveyor in a locked position. Preferably these dots should not be placed on areas of the cast involved in the framework design. The dots should be circled with a colored pencil for easy identification.
Score two sides and the dorsal aspect of the base of the cast with a sharp instrument held against the surveyor base. By tilting the cast until all three lines are again parallel to the surveyor blade, the original cast position can be reestablished. Scratch lines will be reproduced in any duplication, thereby permitting any duplicate cast to be related to the surveyor in the a similar manner.
15) What is the disadvantage of using a carbon marker that is even slightly worn?
A worn (tapered) carbon marker will indicate heights of contour more occlusally located than they actually exist.
16) What is an undercut gauge? How can it be used to measure the depth of undercut in the angle of cervical convergence?
An undercut gauge is an attachment to the surveyor which measures the amount of undercut in hundredths of an inch. To use the undercut gauge, place the vertical portion of the gauge against the height of contour on the axial surface of the tooth and the edge of the horizontal portion against the axial portion of the tooth below the height of contour so that both are touching at the same time. This will allow you to determine where you have the desired amount of undercut and it can be mark on the cast to aid in the design of clasps. (Disclaimer: This answer was not in the book so this is just my own answer that I came up with.)
17) Heights of contour in many instances will be more optimally located for direct retainer assemblies if axial surfaces are recontoured. How may an undercut gauge assist in determining whether they can be recontoured without exposing dentin?
The undercut gauge allows you to determine how much tooth structure would need to be removed in order to achieve the proper contour and undercut.
18) Diagnostic cast are quite often altered during design on the surveyor or in other uses. Why is it a good idea to have duplicate casts?
So that if you begin designing an RPD on one cast and it doesn’t work, you have another unaltered one to work with, without having to bring the patient back in for another impression. Also it may be nice to have a cast that has not been altered so you can see what the original arch looked like before alterations. (I did not find this answer in the book this is just my guess using logic)
19) The designed diagnostic cast can readily serve as a blueprint to accomplish contouring of abutment teeth during mouth preparation procedures. How may the contoured areas on the diagnostic cast be indicated to avoid overlooking these areas when preparing them in the mouth?
All proposed mouth changes should be indicated on the diagnostic cast in red pencil, with the exception of restoration to be done. These mouth changes include: preparation of proximal surfaces, reduction of buccal and lingual surfaces and preparation of rest seats (rest seats should always be deferred until all other mouth preparations have been completed).
20) After mouth preparation procedures are completed and a mast cast has been made, it must be surveyed to definitively locate components. What are the guides to relate the cast to the surveyor?
The prepared proximal guiding plane surfaces will indicate the correct anteroposterior tilt. The lateral tilt will be the position that provides equal retentive areas on all principal abutments in relation to the planned clasp design.
21) The terminal portion of the retentive arm of a direct retainer should engage a planned and measured undercut. Using the same degree of undercut bilaterally will not necessarily ensure relative equal retention. What factor other than the degree of undercut must be considered?
Clasp arm length, diameter form and material must be considered.
22) After the path of placement is established, undercuts areas that will be crossed by rigid parts must be eliminated. How is this accomplished? With what materials?
This is accomplished by blocking out the undesired undercuts. Hard inlay wax may be used as a blockout material. It is easy to apply and easy to trim with a surveyor blade. Parallel blockout is necessary for areas that are cervical to guiding planes and over all undercut areas that will be crossed by major or minor connectors.
23) By what means can the definitive locations of components of the framework be transferred from the master cast to the duplicate investment cast on which the pattern for the framework will be developed?
Placement of wax ledges or shelves on the master cast will be then be duplicated in the refractory cast and allow for exact placement of clasps. (figure 11-19 helped me understand what this meant)
24) Explain the differences between shaped blockout, arbitrary blockout, relief of the mast cast, and parallel blockout? (Table 11-1 is a good summary – pg. 183)
Parallel blockout – use hard baseplate wax or blockout material to eliminate undercuts gingival to the height of contour and use the surveying blade to trim the wax so that it is parallel to the path of placement. (requires use of the surveyor!)
Shaped blockout – used on the buccal and lingual surfaces to locate plastic or wax patterns for clasp arms. Use a hard baseplate was to create a ledge for the location of reciprocal clasp arms to follow height or convexity so that they may be placed as cervical as possible without becoming retentive.
Arbitrary blockout – used to blockout all gingival crevices, gross tissue undercuts beneath areas involved in design of the framework, tissue undercuts distal to the framework, and labial and buccal tooth and tissue contacts not involved in the framework. Hard baseplate wax or oil-based clay is used to do this. My understanding is that these are blocked out purely for convenience.
Relief – placed beneath lingual bar connectors or the bar portion of linguoplates, beneath framework extensions onto ridge areas for attachment of resin bases, and areas where major connectors will contact thin tissue.
25) Why should undercuts on the mast cast not involved with the framework be blocked out?
They are blocked out for convenience and to avoid difficulties in duplication.
26) How do you handle the blockout of gingival crevice that will be crossed by a component of the framework?
All gingival crevices should be arbitrarily blocked out out. In addition if there is an undercut in that area (btw. the height of contour and the gingiva) then that should be blocked out via a parallel blockout out using the surveyor, since this area will be crossed by a component of the framework.
27) What relief of a mandibular mast cast is required for the lingual aspect of the alveolar ridge that will be covered by a lingual bar or linguoplate:
When the ridge slops inferiorly and posteriorly?
Adequate relief is obtained by the initial finishing and polishing of the framework in this instance.
When the ridge is parallel to the path of placement?
When the ridge is undercut to the path of placement?
32-guage wax after parallel blockout of undercuts
28) Why should a mast cast be relieved?
To prevent tissue impingement resulting from rotation of the framework.
29) What determines the amount of palatal relief required when a major connector must traverse the median palatal raphe in a Class I arch?
In lecture we learned that there is no relief for maxillary dentures. However in the book it says that if the patient has elevated palatal raphes, a thin layer of wax flowed on with a wax spatula that is the thickness of the difference in the degree of displacement of the tissues covering the elevated raphes is what determines the amount of relief.
30) What are the requirements for relief on a master cast for minor connectors that will attach acrylic resin bases to the major connector?
31) What uses are there for a dental cast surveyor other than surveying casts for designs and preparation of master casts for duplication in a refractory investment?
To verify parallel preparations when doing a fixed partial denture or a crown.
32) How can a dental cast surveyor help develop the optimum contour for crowns?
A surveyor blade can be used as a wax carver so that the proposed path of placement can be maintained throughout the preparation of the cast restoration for abutment teeth. Also, those surfaces that will provide retention for clasp arms should be contoured so that the retentive clasps may be placed in the cervical third of the crown and the best esthetic advantage with an undercut of 0.01 to 0.02 inch depending on the clasp type to be used.
33) By what means can some dental cast surveyors be converted into a convenient drill press or machining tool?
Because the shaft of the Ney surveyor is stable in any vertical position – yet may be moved vertically with ease – it lends itself well for use as a drill press when a handpiece holder is added.
34) Ceramo-metal restorations in many instances require machining before the final glazing procedures to make sure that the originally planned contour are accomplish. How can this be done?
By using a handpiece holder on the surveyor to create and refine parallel surfaces on a surveyed crown.
35) Internal rests on crowns may be machined with the surveyor as a drill press, or they may be made by another method involving the dental cast surveyor. What is this other method?
They may be carved in the wax pattern and further refined with the handpiece attached to the surveyor after casting.
36) Why would a dental cast surveyor be required to place some types of manufactured internal attachments?
The surveyor is used to cut recesses in wax patterns, to place internal attachment trays in wax patterns, or to cut recesses in castings and to place the keyway portion of the attachment in the casting to ensure that each keyway is parallel to the other keyways elsewhere in the arch.
37) What are some sequelae of marring a master cast during surveying or blockout procedure?
Interference to placement in the mouth
38) What are some applications for use of the dental cast surveyor in planning for a fixed partial denture?
If one tooth is tilted, you may have to remove more tooth structure in an area to make it parallel to the other abutment. Along with radiographs, the surveyor could be used to determine how far into dentin the preparation will need to go in order to achieve the parallelism and whether the decided path of draw would result in the preparation reaching the pulp. (the book didn’t really talk about this, so this is just my own answer that I came up with)
1) A prescribed prosthesis not only must replace what is missing but also, must preserve what is remaining. - Must preserve the remaining tissues and structures that will enhance the removable partial denture. (pg 231)
2) Preparations of oral structures most often involves three categories. One of these is oral surgical preparation. What are the other two? Oral surgical preparation, conditioning of abused and irritated tissue, periodontal preparation, preparation of abutment teeth (pg 231)
3) Which treatment should be accomplished first - oral surgery or preparation of abutment teeth? Why? Oral surgery- should be done far enough in advance to allow plenty of time for healing and consequently more stable denture-bearing areas (pg232)
4) Generally, all retained roots or root fragments should be removed as a mouth preparation. True or False? True - residual root adjacent to abutment teeth may contribute to the progression of periodontal pockets and compromise perio therapy (pg232)
5) All impacted teeth should be considered for removal. However, any impacted tooth that can be reached with a periodontal probe must be removed. True or False? True (pg 233)
6) Unopposed posterior teeth quite often extrude, severely limiting space for a prosthesis and the opportunity to create harmonious occlusion. Name different methods by which these discrepancies can be corrected, depending on the severity of malposition. Orthodontics - useful for many occlusal discrepancies but need teeth for anchoring
Surgical repositioning - individual or groups of teeth that can’t be move orthodiontically
Extraction - try to avoid if possible (pg 233)
7) When a suspicious radiopaque area is seen while viewing a radiograph of a patient, what procedures, listed in chronological order, must be undertaken to resolve the possible problem? Take a periapical radiograph to confirm or deny presence of lesion; Confirm diagnosis via consultation and if necessary take biopsy and submit to pathologist; Inform patient of diagnosis; Proceed as necessary (pg 233)
8) Visual examination, carefully conducted, reveals undesirable bony exostoses or tori in some patients. Unless these are removed, the restoration design will be compromised. In what areas are these various protuberances likely to be found? Palate, lingual mandible, bucal gingival
9) Why should hyperplasic tissue seen in the form of fibrous tuberosisties, flabby ridges, folds or redundant tissue in vesibular regions, and palatal paipillomatosis be surgically removed before the construction of a removable restoration? To provide a firm base for the denture (stability), reduce stress and strain on supporting discussant teeth, and provide more favorable orientation of occlusal plane for setting teeth (pg 234)
10) Discuss the influences of muscle attachments and frena that are inserted on the crest of the residual ridges in relation to denture stability. Loss of bone height may cause muscle attachment on residual crest (mylohyoid, buccinators, mentalis, and genioglossus); mentalis and genioglossus occasionally produce bony protuberances at their attachments; maxillary labial and mandibular lingual frena also provided interferences; discomfort and stability issues (pg 235)
11) Should all abnormal soft tissue lesions be excised and submitted for pathologic examination before fabrication of a removable restoration? Why or why not? Yes, new or additional stimulants to area introduced by the prosthesis may produce discomfort or even malignant changes in the tumor (pg 235)
12) Excessively resorbed residual ridges offer comparatively poor support for removable restorations. Augmentation of alveolar bone to increase ridge height and width may be a viable surgical procedure for certain patients. Name a material used for such a procedure. Autogenous and alloplastic materials (pg 237) (specific one?)
13) What is an oral osseointegrated device? What role can be envisioned for such a device in removable prosthodontics? An implant is an example of an osseointegrated device, where there is a direct titanium-to-bone interface - for removable there is a good potential for significant control of prosthesis movement (pg 236-7)
14) What are elastopoymers used for in removable prosthodontics? As a tissue conditioning material - flows for extended period and permit distorted tissues to rebound and assume normal form (pg239)
15) Should irritated and distorted oral tissues optimally be returned to a state of health before final impressions are made? Why or why not? Yes- if not and relining a denture, the success of treatment compromised because same problem will be perpetuated (pg 238)
16) Examination of a patient having removable partial dentures discloses a palatal inflammation. What other factors must be considered in formulating a thorough differential diagnosis? The fit of the denture, nutritional deficiencies, endocrine imblances, sever health problems (diabetes or blood dyscrasias), bruxism, wearing 24 hours daily (pg 238)
17) Abused and irritated oral tissues most often respond favorably to tissue-conditioning procedures. Describe an acceptable order of procedures to be undertaken to institute a good tissue conditioning program. First things first, institute a good home care program; rinsing 3x daily with saline solution, massaging residual ridge areas, palate and tongue with soft toothbrush, removing prosthesis at night, using a multivitamin with high-protien low-carbohydrate diet
using elsopolymers as tissue conditioning materials - 1) eliminate interfering occlusal contact of old denture 2) extend denture base to proper form to enhance support, retention and stability 3) relieve tissue side of denture base (2 even mm) for conditioning material 4) apply material to provide sufficient support and cushioning 5) replace every 4 to 7 days (pg 239-40)
18) Periodontal therapy should be completed before restorative procedures are undertaken. True or False? True, the ultimate success of a partial depends of the health and integrity of the supporting structures and remaining teeth (pg 241)
19) What are the objectives of periodontal therapy for the partially edentulous patient? 1-remove and control all etiological factors contributing to periodontal disease along with elimination of bleeding on probing 2-eliminate or reduce pocket depths of all pockets, with the establishment of healthy gingival sulci whenever possible 3-establishment or functional atraumatic occlusal relationships and tooth stability 4-development of a personal plaque control program and definitive maintenance schedule (pg 241)
20) The indication for occlusal adjustment is based on the presence of a pathological condition rather than on a preconceived articular pattern. Support and explain this statement. “In the natural dentition, the attempt to create bilateral balance in the prosthetic sense has no place in the occlusal adjustment procedure. Bilateral balanced occlusion not only is difficult to obtain in a natural dentition but also is apparently unnecessary in view of its absence in most normal healthy mouths. Occlusion on natural teeth needs to be perfected to only a point at which cuspal interference with the patient’s functional range of contact is eliminated and normal physiologic function can occur (244).”
21) What procedure(s) are most often used to eliminate gross occlusal interferences initially as a phase of periodontal considerations? Selective/Spot grinding (see 244 for more descriptive details on how to do this, if you want to)
22) What is a night guard and what purpose does it serve? A removable arcylic resin splint, aids in eliminating the deleterious effects of nocturnal clenching and grinding; for RPD patients may stabilize TMJ when not wearing RPD, flat occlusal surface prevents intercuspation of teeth, eliminating lateral occlusal forces; also as a “conditioning” device for teeth that have been long unopposed to provide functional stimulation prior to RDP delivery (245-6)
23) Teeth demonstrate mobility at the time of the initial examination may be temporarily splinted. How does this help to establish a prognosis? Mobile teeth are bad for RPD’s. Temporarily splinting and trying to figure out and removing cause may help stabilize teeth. If they are still mobile after the attempt to help them out, the tooth may have to be sacrificed. (245)
24) Under what clinical circumstances should minor tooth movement by orthodontics means be considered to enhance treatment? Upright a tilted or drifted tooth for repositioning and retention of partial (246)
25) State five distinct advantages of performing periodontal therapy (when indicated) before fabricating a removable prosthesis. 1-elimination of periodontal disease removes primary cause of tooth loss 2- periodontium free of disease presents a much better environment for restorative correction 3-reponse of questionable teeth to periodontal therapy can be evaluated prior to final decision to exclude or include the questionable tooth 4-overall reaction of patient to periodontal therapy procedures provides the dentist an excellent indication of the degree of cooperation to be expected in the future (note: the book has 4 reasons but the question asks for 5) (248-249)
26) Through intelligent planning and competent execution of mouth preparations, the denture can satisfactory restore lost dental functions and contribute to the health of the remaining oral tissue. True or False? True (253)
1) What does the use of a terminal molar abutment contribute to a removable partial denture? Supports one end of a tooth-supported base, which is better than a distal free end (255)
2) Endodontic treatment of any tooth in the arch (when indicated) should be performed before making a final impression for a removable restoration. Why? If the prognosis of a tooth becomes unfavorable or it doesn’t respond to therapy you can still make changes in the removable partial denture design without having to add a tooth/claps later (much harder) (255)
3) If one is faced with a single posterior abutment (second molar) and there is some doubt that it can be retained and used as one end of a tooth-supported base, what options are available for design of the denture? It can be replaced by a distal extension base as long as the initial design included provisions for future indirect retention, flexible clasping on remaining terminal abutment, and provision for establishing tissue support by a secondary impression (255)
4) Abutment preparations on sound enamel should be accomplished in a definite order with the altered and designed diagnostic cast used as a blueprint. Give the order of preparation, including method to check this preparation. 1-Make proximal guiding planes parallel to the path of insertion 2-modify tooth contours (height of contours and undercut placement) 3-impression with irreversible hydrocolloid in fast setting stone to survey 4-Prepare occlusal rest areas (256)
5) What is the risk of preparing an occlusal rest seat before contouring the guiding planes? Occlusal rest areas should be prepared that will direct occlusal forces along long axis of tooth, need to change contours to determine long axis of tooth
6) Inlay preparations on teeth to be used as removable partial denture abutment differ from conventional inlay preparations in three requirements. What are they? 1- Bucal and lingual proximal margins must be well beyond line angles to prevent them from lying on or near minor connectors or occlusal rests; 2-Axial wall curved to conform to the external proximal contour to protect pulp; 3- Extending the gingival seat to a place where it can be easily cleaned (256-7)
7) Where is the most vulnerable area on an abutment tooth, with regard to cleanliness? gingival margin due to the proximal contour necessary to produce the proper guiding plane surface and the close proximity of minor connectors (257)
8) Give the sequence of contouring wax patterns for abutment restorations to obtain ideal contours for optimum location of components by use if a dental cast surveyor. Proximal surface guide planes made parallel to path of insertion; modify contours; occlusal rest seats (258)
9) A rest seat is carved on the occlusal surface of a complete coverage crown wax pattern for a posterior abutment. The occlusal morphology has been carved to satisfy occlusal requirements and axial contours have also been accomplished. The rest seat preparation, however, is inadequate because of its shallowness, created by insufficient room between the preparation and opposing occlusion in the area of the rest seat. What options exist to prevent a compromised result? Ideally, the preparation for the crown needs to incorporate additional space for the rest seat. It is inexcusable to think about it during post treatment planning. If the situation arises where you are adding a rest seat to an existing crown the same problem arises, how much thickness is there? Ideally a new restoration would need to be made. (259)
10) Crown ledges, parallel to the path of insertion, are often carved on the lingual surface of abutment crowns. How does this enhance the direct retainer assembly? Provides effective stabilization and reciprocation; allows the reciprocal arm to have greater bulk yet maintain normal crown contours (259-60)
11) Contrast the quality of a reciprocation afforded by a crown ledge on a molar abutment and that offered by the lingual surface of an unrestored molar abutment. On an unrestored molar, when a dislodging force is applied the reciprocal arm clasp and the occlusal rest break contact with the tooth and lose effectiveness. So when the retentive clasp flexes over the height of contour and exerts a horizontal force on the abutment, reciprocation is nonexistent. However, when utilizing a ledge, the inferior border of the reciprocal clasp contacts the guiding surface before the retentive clasp on the other side begins to flex. Therefore, reciprocation exits during the entire path of placement and removal. (259, lower right column-this is a bit confusing, sorry)
12) Explain the method of preparing a lingual ledge on the wax patter for an abutment crown. Include its depth, width, extent, and definitive location. Ledge placed at junction of gingival and middle thirds, curving slightly to follow the curvature of gingival tissue. Parallel to path of insertion. You want the ledge to be the desired thickness of the reciprocal arm, so that in the end you have a flush contour. (this is all the details the book gives; 260-261)
13) How may the crown ledge be refined after the crown has been cast? Return to surveyor, making sure it is parallel to path of insertion, use a fissure burs (eg 557, 558, 559) or true cylindrical carborundum stones in a handpiece held by the handpiece holder. (261)
14) Describe the contour of the component of the direct retainer assembly that occupies the crown ledge preparation. Should be continuous with the ledge inferiorly and contoured superiorly to restore the crown contour, including the tip of the cusp. (261)
15) It is rare that the ceramic surface of a ceramometal crown can be fabricated and finished freehand to exhibit the exact planned height of contour for a retentive claps arm. How may a surveyor be used to ensure the planned location of the height of contour is established? At what stage in the fabrication of the crown should the procedure be undertaken? It must precede glazing of porcelain. Use is similar to a wax pattern. (262)
16) Splinting of adjacent teeth is sometimes indicated as a means of gaining ,multiple abutment support. What examination data would indicate that splinting should be performed? Length and taper of root, crown-root ratio, number of roots (262-3)
17) Where is the most common application of multiple abutments by splinting found in an arch? Splinting two premolars or a first premolar and canine (262-3)
18) Often the design of a restoration requires lingual rests on lower anterior teeth. How can orthodontic movement of these teeth be minimized? Splinting several teeth with united cast restorations. (263)
19) Isolated abutments adjacent and anterior to edentulous residual ridges usually have a poor prognosis. What is the reason for this? Because it lacks a mesial proximal contact any lifting of the distal extension base, which is inevitable, will cause torque to the abutment and mesial tipping. (263)
20) An isolated abutment adjacent to a distal extension base, when splinted to the nearest tooth, provides two beneficial effects. What are these desirable effects? (fixing usually is accomplished via a fixed partial denture, ie bridge) 1-the anterior edentulous segment is eliminated, creating an intact dental arch anterior to edentulous space; 2-isolated abutment is splinted to the other abutments, providing multiple abutment support (263)
21) An isolated abutment adjacent to an extension base may be splinted to the nearest tooth by either a fixed partial denture or a splint bar (?) (263)
22) Missing anterior teeth should be replaced with fixed partial dentures rather than included in a removable restoration. What are the contraindications for the proceeding treatment? Esthetics and/or economics (263-4)
23) On rare occasions an abutment tooth supporting a removable partial denture will have to be restored with an inlay or crown. Describe a procedure whereby an abutment crown can be fabricated to fit an existing direct retainer. A thin acrylic resin coping made on a stone die, then placed prepared tooth where inlay wax is added to create occlusal and contact relationships in the mouth. Clasp assembly warmed and then inserted into fully seated position. RPD removed and along with it usually the wax pattern. The pattern is then placed back on the die to refine margins and occlusion. After casting, check to make sure it is in harmony with partial prior to cementation. (268)
CH. 15 Impression Materials (IMs) and procedures for RPD
Two ex.’s for each of three categories of IMs used in various phases of RPD construction:
Rigid- plaster of paris, metallic oxide paste
Thermoplastic modeling plaster, impression waxes and natural resins
Elastic-reversible hydrocolloids, irreversible hydrocolloids, mercaptan rubber-base, polyether, silicone
Which type of IM has been used longest in dentistry?
Plaster of paris
3. Why should metallic oxide paste types of IM not be used for primary impressions of partially edentulous arches?
Never used in impressions that include remaining natural teeth, cannot be removed from mouth w/o fracture and reassembly.
4.Modeling plastic compound may be used effective in modifying impression trays to make secondary impressiond of Class I or II partially edent arches. Describe how it is used and why it is not used for primary impression of rpd pt.
Color coded plastic by temp. range at which material is plastic and workable. It should be dipped in water bath and kneaded until soft and subject to no more heat than necessary before loading the tray and placing in mouth. It can then be flamed with alcohol torch for border molding. Risk of burning the pt. and have permanent distortion during withdrawal from tooth and tissue undercuts.
5. What is an impression wax? Do its characteristics make it appropriate for use as primary or secondary impression? Describe use.
It is a mouth-temp wax that can flow as long as it is in the mouth and is able to permit equalization of pressure and prevent displacement. Use as secondary impression. Usually used to record tissue under occlusal load. In the technique, the occlusal rim and arrangement of artificial teeth is done first. Then apply wax to tissue side of denture base and final impression is made under functional loading by using different movements to simulate functional movement.
6. Name two types of hydrocolloid IM used in dentistry.
Reversible and Irreversible
7. Are the hydrocolloid IMs elastic or thermoplastic?
8. What is the advantage in using an elastic material vs. a rigid material in making IM of partially edent arches?
Only ones that can be withdrawn from tooth and tissue undercuts w/o permanent deformation
9. Briefly compare reversible and irreversible hydrocolloid IM by composition, gelation mech. , trays, and relative accuracy.
Reversible hydrocolloid coverts from the gel form to a sol by the application of heat (which can burn the pt.). It may be reverted to gel form by a reduction in temp. This physical change is reversible. Irreversible hydrocolloid becomes a gel via a chemical reaction as a result of mixing alginate powder with water. This physical change is irreversible. Reversible demonstrate acceptable accuracy when properly used. Irreversible must be held immobile during gelation because gelation takes place first next to the tissue unlike reversible that gels from the tray towards the tissue. Air bubbles are more common with irreversible because it must be introduced into the mouth at 70F which increases surface viscosity and tension. Both can use a perforated or rim lock impression tray that is large enough to provide 4-5mm thickness of impression material between tooth/tissue and tray.
10. Mercaptan rubber-base IM may be used for primary or secondary impressions.
Though it is best suited for secondary impression.
11 Does the use of mercaptan rubber-base material and silicone IM require the use of a rigid stock tray or an individual tray. Why?
The mercaptan impression must have a uniform thickness that does not exceed 3mm requiring use of acrylic resin or another material with high rigidity and stability. The silicone does not adhere well to acrylic resin but is often used with a compatible putty material to form fit a custom tray.
12. Are the varied materials of stones and IMs necessarily compatible with each other when used to make casts. What precautions should be taken to ensure compatibility?
The only thing I really saw for this was hydrophobic silicones are difficult to pour with stone
13. What is syneresis? What effect will this phenomenon have on a cast poured in hydrocolloid impression.
It is the giving off of a mucinous exudate which has a retarding effect of gypsum products and results in a soft or chalky cast surface. The surface is then inaccurate and will cause inaccuracies in rpd framework. All modern irrreversibles have an accelerator to counteract this.
14. What is meant by the word imbibition in relation to hydrocolloid IM ? What effect does it have on hydrocolloid impression?
If immersed in water, they will take in water with accompanying swelling and dimensional changes. Satruation with wet paper towel is best for storing for a brief period.
15. How long should you wait to pour a cast into a hydrocolloid impression after it is removes from the mouth. Why?
Immediately because it is made of colloid materials and will dehydrate and shrink when exposed to air.
16. Name two types of silicone IMs and describe how they differ.
Condensation silicones have a moderate 5-7 min working time altered by amount of accelerator, pleasant odor, moderately high tear strength, excellent recovery form deformation, hydrophobic, disinfected in any of the solutions and poured within 1 hour. Addition silicones are MOST accurate of the elastic materials. They have less polymerization shrinkage, low distortion, fast recovery from deformation, moderately high tear strength, working time 3-5 min modified by retardants and temp controls, no smell or taste, both hydrophilic and hydrophobic forms, poured within 1 week, and stable in most sterilizing solutions. Sulfur can inhibit polymerization.Hydrophobic forms are difficult to pour with stone and and adhesion to acrylic resin trays is not good.
17. Thickness of IM when using rubberbased material should be about 3mm for accuracy and stability. Does this equally apply to a hydrocolloid impression material ? if not, give a rule of thumb for the desired thickness of hydrocolloid material in the impression.
No, 4-5 mm for hydrocolloid.
18. What are the advantages of perforated stock trays when making impressions of partially edent arch with irreversible hydrocolloid.
The first layer of material can flow and lock in the perforations to prevent any dislodgement after gelation.
19. In accuracies of a cast made from a hydrocolloid impression may result from Many causes. Describe six such inaccuracies.
1- distortion of impression by nonrigid tray, partial dislodgement from tray, shrinkage, expansion, attempting to pour with stone already setting.
2- water:powder ratio too high
4-trapping of air in mixing or pouring
5- soft or chalky cast surface from retarin gaction of hydrocolloid or adsorption of nec. Water for crystallization by dehydrating hydrocolloid
6-premature separation of cast from impression
7-failure to separate cast from impression for an extended period
20. Why should impressions into which stone casts have been poured not be inverted until the initial set of the stone has taken place?
21. An individual acrylic resin impression tray has two distinct advantages over any type of stock trays. What are they?
1-Sufficient clearance for impression material
2- can be trimmed just short of vestibular reflections to allow the tissue to drape naturally w/o distortion (accurate borders)
22. Descibe the procedures for making individual mx and mn impression trays, paying special attention to relief of the casts with wax spacers.
1-outline extent of tray with pencil
2-adapt one layer base plate wax for spacer, trim wax 2-3mm short of outline and in posterior seal region, expose incisal edgs of incisors for ant. stops ( additional layer of wax over teeth for irreversible hydrocolloid)
3-paint with model release agent
4-apply VLC material
5- attach handle
6-light polymerize (1min)
7-remove tray from cast and peel out wax while still warm
8-paint with air barrier and polymerize tissue side up
9- clean with brush and water
10-smooth borders and polish external surface
11-use #8 bur to plae perforations every 5mm except alveolar groove areas
12-sanitze and try in mouth
For mn wax spacer does not cover buccal shelf regions
23. Holes about 3mm in diameter should be placed at strategic locations in both mx and mn individualized trays. Give the location of the holes and describe what is accomplished by their presence.
5mm intervalsfor material escape and tissue release in those areas, locking in impression material
24. What is the advantage of drilling holes in acrylic resin trays with a bi-bevel drill rather than with fissure or round burs?
I didn’t see this mentioned but my guess is the locking feature they have asked about a zillion times in these questions
25. Under what circumstances would you use a stock tray in preference to an individual acrylic resin tray?
Final impressions for mx tooth-supported rpds often may be made in carefully selected and recontoured rigid stock impression trays
26. Does a stock or disposable impression tray have to be rigid? Why?
I would say yes always to avoid distortion
27. Rubber- base impression materials have some serious disadvantages for making final impressions for removable partial dentures. What are they?
Not be used when undercuts are present, no snap set so hold very still, needs to rebound for 7-15min, unpleasant odor and stain clothes
28. What are specific advantages of (a) polyether; (b) condensation silicone; and (c) addition silicone impression materials when used to make rpd. What are they.
Most everything in the book about the silicons are mentioned in question 16 above. The polyether is thixotropic giving good surface detail, hydrophilic for easy cast forming, don’t use with silicones to border mold custom trays, low-mod tear strength, much shorter working and setting time, flow characteristics and flexibility LOWEST of elastics, higher permanent deformation in relation to addition silicones, unpleasant taste, cannot be immersed in disinfecting solns, poured within 2 hours
29. What are specific disadvantages of a,b, and c above. See qstn 16 an 28
30. Of the impressions materials mentioned in this chapter, which ones can be immersed in a sterilizing solution w/o being damaged, and which ones must be sprayed only.
The only ones which must be sprayed as far as I can tell are both of the hydrocolloids and the polyether IMs
Chapter 18: Laboratory Procedures
Why should the dentist not only be familiar with lab procedures but also proficient in executing them?
This enables the dentist to design the RPD framework, complete a lab work authorization that communicates the desired design and authorizes its fabrication, and evaluate the quality of the framework.
Although certain lab procedures may be delegated to a dental lab tech, the dentist must be able to perform those procedures to troubleshoot, communicate, and instruct the technician. True or False? True
An intimate knowledge of dental materials employed in the fabrication of RPDs is a must for the dentist. Give 3 reasons.
See answer for question 1.
Duplicate casts are required in many instances in treating partially edentulous patients. Name one of these instances.
Fitting an RPD framework without danger of fracture or abrading the surface of the original master cast.
What armamentarium and materials are required to duplicate a cast?
Colloid materials, silicone, duplicating flask, cast material (see pg.320)
What is the difference between a reversible and irreversible hydrocolloid? Which one is most commonly used in duplicating a cast?
Reversible hydrocolloids are fluid at high temps and gel at lower temps. Irreversible hydrocolloids (alginate) cannot reverse states. (see pg. 273) Both are acceptable for cast duplication, but reversible hydrocolloid is used in this text.
Is it critical that the duplicating material chosen be compatible with the material from which the duplicate cast will be made?
Yes. Any reaction between duplicating materials could compromise the accuracy of the casting surface.
Describe a duplicating flask.
See Pg. 321
How is reversible hydrocolloid prepared for duplicating purposes? What temperature of the hydrocolloid is sufficient to duplicate a cast?
Reversible hydrocolloid is heated and mixed by automatic mixing to prevent bubble formation. The temp can’t be too high that wax used on the cast might melt.
If a blocked out master cast is being duplicated, what precautions must be exercised to prevent distortion of the blockout material?
Temp not too high that it melts the wax.
Give a step-by-step procedure for duplicating a stone cast with reversible hydrocolloid.
See pg. 321
What is the danger of soaking a stone cast in tap water? A cast must be wet before duplicating it with hydrocolloid. How is this wetting accomplished?
Wet cast with surfactant to avoid creating air bubbles at the surface.
Describe the procedure for recovering an investment cast from at duplicating mold.
See pg. ?
For what reasons should an investment cast not be trimmed on a cast trimmer?
An investment cast on which the pattern for the framework will be developed should be oven dried after it is removed from the duplicating material. True or False?
An investment cast should be lightly sprayed with a plastic model spray immediately after drying. T or F?
You should already know the specifications for all components of a RPD framework. Describe a logical order of creating the wax or plastic pattern for a mandibular RPD framework to which a wrought-wire retainer arm will be attached.
Master cast with wax relief (2x28 gage) in edentulous areas, block out undercuts (lingual anteriors). Shape blockout ledges for location of retentive and reciprocal clasp arms. Complete wax pattern using lingual bar major connector pattern, plastic clasp forms resting on investment ledges, wrought wire and open retention mesh. (pg. 323)
Describe the process of spruing a wax pattern for a RPD framework.
Use a few sprues of large diameter rather than several smaller sprues. Keep all sprues as short and direct as possible. Avoid abrupt changes in direction (T-shaped junctions). Reinforce all junctions with additional wax to prevent constrictions in the sprue channel.
There are three general rules that should be followed in spruing any wax or plastic pattern for casting. List and describe.
Sprues should be large enough that the molten metal in them will not solidify until after the metal in the casting proper has frozen.
Sprues should lead into the mold cavity as directly as possible.
Sprues should leave the crucible from a common point and be attached to the wax pattern at its bulkier sections.
After the pattern has been sprued, it must be covered with an investment (refractory) material to make a mold for wasting. The outer investment must be the same material from which the investment cast was made. What are the purposes of the outer investment?
Provides strength necessary to hold the forces exerted by the entering stream of molten metal until the metal has solidified.
It provides a smooth surface for the mold cacvity so that the final casting will require as little finishing as possible.
It provides an avenue of escape for most of the gases entrapped by entering metal.
The casting shrinkage of gold alloys from the molten to the cold state is from 1% to 1.74%. the casting shrinkage of chromium-cobalt alloys is approximately 2.8%.
A casting ring, with a suitable liner, is used to confine the outer layer of investment around the pattern. The ring is not removed during burnout or casting procedures for gold alloys. What is the purpose of the liner in the ring?
Allows for both setting thermal expansion of the mold in all directions.
After the investment material for a chromium-cobalt alloy casting bas set, the ring is removed before burnout. Why?
Allows greater mold expansion necessary with these alloys.
Give a step-by-step procedure for investing a sprued pattern that will be cast in Chromium-cobalt alloy.
See figures on Pg. 330-331.
The casting mold is prepared to receive the molten alloy by a process known as burnout. Burnout serves three purposes. State the three purposes.
Drives off moisture in the mold
Vaporizes and eliminates the wax pattern
Expands the mold to compensate for contraction of the metal on cooling.
What different methods are used to melt gold alloys for casting? Chromium-cobalt alloys for casting?
See pg. 331
After the casting is completed, how long should the mold be allowed to bench cool before the mold and casting are plunged into water?
What is the purpose of pickling a casting? Describe a pickling procedure.
Pickling a casting??? The only thing the book says is that chromium-cobalt castings are NOT cleaned by pickling.
If the wax pattern for a casting was neatly and properly developed, and investing and casting procedures were correctly accomplished, finishing the casting should not be a time-consuming procedure. How would a chromium-cobalt alloy framework be finished?
High speed bench lathes and abrasive stones or sintered diamonds. Polish by electropolishing (controlled deplating process)
Record bases, trial denture bases, and individual impression trays are conveniently made of autopolymerizing acrylic resin. What is an autopolymerizing acrylic resin, and how does it differ from a heat-cured acrylic resin?
Autopolymerizing acrylic resin= Salt & pepper technique with monomer & polymer: when added in small increments, results in reduced overall shrinkage & greater accuracy.
Record bases or trial denture bases can be fabricated by a sprinkling technique using autopolymerizing acrylic resin, whereas individual or customized impression trays may be fabricated with adapted autopolymerizing acrylic resin. For what reason or reasons are the processes different?
The salt & pepper technique creates a close fitting base with the necessary accuracy & stability and yet can be lifted from and returned to the master cast without abrading it.
Review the procedures for making individualized acrylic resin impression trays as given in Ch. 15
If you use a secondary or altered cast impression tray for a mandibular distal extension denture, you will attach an individualized tray to the framework. Give a step-by-step procedure for making such a tray.
See pg. 335, Fig. 18.34-36
Record bases and occlusion rims are necessary to record maxiollomandibular relations for class I and II arches and in class III arches with long edentulous spans. Describe a step-by-step procedure for making record bases by the VLC method and by the sprinkle on method.
See pg. 335, Fig 18.34-36. For VLC procedure see pg. 281-283.
A record base is attached to the framework for a distal extension mandibular denture and is fabricated after the secondary impression has been made and the master cast has been recovered. How is such a record base made and attached?
What purpose does an occlusion rim serve?
Occlusal rims record functional or dynamic occlusion. Usually made of hard wax that can be carved out by opposing dentition.
If an occlusion rim represents the missing teeth and supporting structures in a partially edentulous arch, should the occlusion rims be wider than the occlusion rims be wider than the occlusal surfaces of the teeth they are replacing? NO. Should occlusion rims occupy the same position (buccolingually) of the mission teeth? YES. There are several advantages to correctly proportioned occlusion rims as opposed to badly proportioned occlusion rims. What are these advantages?
Artificial posterior teeth were arranged on mandibular and maxillary trial bases made of acrylic resin and attached to the respective frameworks. The arrangement was acceptable and approved. What procedures must now take place before the final arrangement of teeth and development of the external forms of the bases for processing?
See p. 339
Except around metal portions of the framework, should there be any difference in developing gingival contours, root indices, interdental papillae, lingual contours of individual teeth, and so on for RPD bases and complete denture bases? YES What are they?
The only difference is the waxing of and around exposed parts of the metal framework. At the framework denture base junction, undercut finishing lines should be provided whenever possible. (p. 342)
A RPD must be so invested for processing acrylic resin bases that the processed denture and its cast can be recovered intact and unmarred from the flask. This procedure will facilitate and simplify correction of occlusal discrepancies resulting from processing. T or F? True
Before investing the master cast and waxed denture in the lower half of the flask, what should be done to the base of the cast to facilitate recovery of the cast and remounting procedures?
The cast is completely covered with investing stone, exposing only artificial teeth and waxed denture bases. This eliminates undercuts in the cast. (Fig. 18.41)
After the processing flask containing the invested denture has been separated, the residual wax flushed out, and a tinfoil substitute correctly applied, there is one observation that must be made and dealt with in regard to the minor connector for attaching the acrylic resin distal extension base and its relation to the residual ridge. What is this observation, and how is it dealt with before acrylic resin is packed in the mold?
Describe the pour technique of processing finished denture bases.
Describe the VLC technique of processing finished denture bases.
Discrepancies in occlusion as a result of processing may be corrected by returning the processed denture and cast (intact) directly to the instrument on which the occlusion was developed-provided the denture are tooth supported or the occlusion was developed using an occlusal template. Describe this type of process for correction occlusal discrepancies.
See pg. 350
Correction of occlusal discrepancies for distal extension dentures should be accomplished by an entirely different procedure than the above procedure. This procedure is described in Ch. 20. Review and state how this differs.
Finishing and polishing the RPD may be accomplished in the same manner as for a complete denture. However, polishing the RPD on a lathe is made more hazardous and required more attention because of the presence of Direct Retainers.