Flashcards in ISTR Test 1 Deck (77):
When do you clean up Glass Ionomers?
Only after they are firmly set. They are soluble until set.
When do you clean up Resin ionomers and resins?
Clean up with cotton pellets immediately upon verification of proper seating. Much less soluble.
The features of a tooth preparation that enhance the stability of a restoration and resist dislodgement ALONG THE AXIS OTHER THAN THE PATH OF PLACEMENT (insertion).
The quality inherent in the prosthesis acting to resist the forces of dislodgement ALONG THE PATH OF PLACEMENT.
Total Occlusal Convergence
An angle of convergence between 2 opposing prepared axial surfaces. Recommended between 10-20 degrees. Ideal is 6 degrees.
Occlusocervical or Incisocervical dimension
The length. Minimum for 10-20 degree TOC is 3 mm for anterior teeth an premolars and 4 mm for molars. If you have a less than adequate dimension, use auxiliary resistance features such as boxes and grooves.
Ratio of occlusocervical/incisocervical dimension to faciolingual dimension.
Recommended that the height is approximately half of the width or 0.4.
Facioproximal and linguoproximal surfaces should be preserved. AKA keep the corners. Add grooves and boxes when you need more resistance. (round teeth). Usually with mandibular molars. Most effective in proximal surfaces.
Finish line location
Supragingival when possible. Exceptions include when you need more resistance and retention, have caries below the finish line, fractures, erosion/ebrasion, ferrule, esthetics.
Finish line form and depth.
All metal restorations: Chamfer with minimal depth of 0.3 mm recommended. A feather edge is used for over contoured crowns.
Metal-ceramic: personal preference. Depth has not been determined but it must be greater than 1 mm for porcelain.
Axial and incisal/occlusal reduction depths
Affected by occlusion and tooth alignment in the arch. Over contoured restorations promote periodontal disease.
All metal is 1.5 mm axial and 1.0 mm occlusal. THIS IS MINIMUM.
Line Angle Form
Rounded. Gives you more strength for all ceramic crowns, more accurate casts and better fit of castings.
Roughness improves retention with ZnP. No correlation with roughness and adhesive cements.
Use medium grit diamond bur in slow speed.
What forces do you want to minimize and maximize in your design of your preparations.
Maximize compression (forces perpendicular to the tooth), and minimize tensile (a force directed away from the tooth), and shearing (a force parallel with the interface).
What happens to retention and resistance when you increase TOC?
You decrease both.
How does area relate to retention?
The greater the area the greater the retention. (Increasing height or diameter increases retention)
Two crowns of the same height have different diameters. Which crown has the most resistance? The greatest retention?
The crown of the smaller diameter has the greatest resistance. This is contrasted agains retention. The crown with the biggest surface area and thus the bigger diameter has the greatest retention.
What do grooves increase?
Where is the best place to place grooves?
When would you need to recontour adjacent teeth?
To establish path of insertion and improve proximal contact area. DON'T GET CARRIED AWAY ND TUNNEL VISION.
Why is flat single plane reduction a bad idea?
It is hard to get sufficient depth in the grooves and fossa with single plane reduction. In order to guarantee sufficient space for the material you are often compromising the pulp horns and reduce retention.
Explain why a functional cusp bevel is important.
A functional cusp bevel allows for enough material in a load bearing area without sacrificing tooth structure and retention. If there is not enough material between the restored tooth structure and the opposing tooth, it will be weak and prone to fracture. If tap you taper the axial wall in order to provide enough space for the material, you are reducing retention. If you don't leave adequate space for material the lab will often overbulk the crown which is really hard to fix because of the super occlusion and you can only correct it by reducing the occlusal surface of the OPPOSING tooth.
What happens in a cross bite?
The functional cusps switch!
What happens if you don't make a crown with enough axial reduction?
You get a crown that is over contoured and causes gingival disease due to the plaque producing contours.
What is the biologic width?
The distance from the epithelial attachment to the crest of the alveolar bone. Normally about 2 mm wide. If your restoration encroaches on the biologic width, it causes inflammation and osteoclastic activity. The likely outcome is that the BW will move apically until the alveolar crest is about 2 mm from the margin of the restoration.
Light body vs. Heavy body
Light body is about detail and flow. Heavy body is about supprt.
What do you look for in a good impression?
360 degrees of flash. (Margin). Detail. No bubbles. Accurate impression of adjacent teeth. The light body is on the margin and it is seamlessly fused with the heavy body. The entire impression is adhered to the tray.
What is a technique to improve impression removal?
Block our the lower anterior gingival embrasures.
Where do the heavy and light body go?
Light body on the teeth. Don't take the tip out. Heavy body on tray.
What is the minimum set?
When does literature show support for use of a custom tray?
Improved accuracy in FPD.
What is an important quality of a stock tray?
Must be rigid.
When is a dual arch tray used?
For single bounded teeth only. Not on the distal most teeth. And no involvement in the guidance scheme. The trays are usually too floppy and its hard to get a good impression. The patient's biting variation is very hard to manage.
What are the benefits for custom impressions trays?
Creates a uniform 2 to 3 mm space for impression material. More comfortable for the patient and effectively retracts soft tissues. Less expensive.
What is the wax spacer?
Allows for space for the impression material. Stops are created within the wax spacer to hold space during impression taking so you aren't just guessing how far to seat the tray.
What is the difference between a custom tray for for crowns vs. a custom tray for complete dentures?
Denture CT don't have the uniform wax spacer or stops. No perforations. Don't use compound. No border molding.
What are the impression materials?
Polysulfide, polyvinyl siloxane, polyether.
What impression material do we use in our clinics?
How do you manage soft tissue?
Start with healthy tissue. Use cord retraction where the cord is visible. Hemostasis. There can't be blood.
What are the reasons we use provisional restorations?
Pulpal protection. Prevent tooth movement mesio-distally and super eruption. Provide esthetics. Patient comfort. Periodontal stability. Diagnostic. Provides function.
Compare an inlay provisional and a full cast crown provisional.
Inlays use IRM because there is containment provided by the tooth. For a full cast crown, the provisional must provide all occlusal contact, all proximal contact and all axial contours.
What are the properties of a successful provisional material?
Biocompatability. Inherent strength. Tooth colored. Adjustability. Ability to remove without tooth damage.
What are the 2 provisional materials available?
Acrylic and Bis-gma which is a composite. THERE IS NO PERFECT MATERIAL.
Prefabricated crowns vs Custom formed crowns.
Prefabricated come in metallic or polycarbonate crown forms. Custom formed crowns come from a clear, putty or alginate matrix. They can also be freehanded and are an indirect process.
What does the overimpression represent?
The desired contours of the final restoration. Must be thick enough to resist deformation.
What is the type of overimpression that we use?
In a custom acrylic provisional why would it be beneficial to remove some material from the fgm on the putty matrix.
Usually the weakest area of the provisional and it creates extra bulk at the critical margin to allow for finishing.
Why is it important to trim the periphery of the putty matrix?
Allows for verification of complete seating of the putty matrix in the mouth.
What is an important pre step prior to placing the overimpression and acrylic on your prep?
LUBRICATE THE PREP, ADJACENT TEETH AND SOFT TISSUE. You want to be able to get the provisional off.
When do you remove the CAP from the mouth?
When it is still flexible and prior to the exothermic stage. You want to take it off when it is still pliable so you can get rid of undercuts. You can determine the stage by putting acrylic on top of the stint and monitor it.
How do you make sure the provisional doesn't become locked on?
Place on and off. Cotton pliers don't really work in this stage as they distort it.
What do you use to finish the CAP?
Acrylic burs or diamond and sandpaper disks. DO NOT USE HIGH SPEED BURS.
How do you repair or correct a CAP?
You can add acrylic to the margin, voids and the axial surface to improve contour. Acrylic should first be freshened.
What happens if the provisional falls off?
You have patient discomfort if the tooth is still alive, tooth movement, periodontal inflammation, etc. Because of movement you may need a new restoration and additional tooth preparation raising your costs in terms of chairtime and patient relations.
What are the benefits of a clear matrix for provisional restorations?
Allows for good visibility and better monitoring of acrylic setting. More flexible.
What makes a clear matrix less desirable?
Requires a study model AND a secondary model. Time. Effort. Extra work.
What is important when making the clear matrix?
NO WAX. Thin and dry cast with less dense stone. You can improve the adaptation by applying pressure to the occlusal surface with a damp paper towel. Trim the matrix to extend onto the gingival tissue and at least 1 tooth on each side.
What are the benefits of a prefabricated metal crown?
No need for a study cast or previous history.
What are some setbacks with the PFMC?
Will require lining with acrylic and adjustment.
How do you select a PFMC?
M-D width. Trim to the gingival as close to the finish line as possible. Stretch as necessary. Need to allow space for the acrylic.
Prefabricated Polycarbonate Crown.
Tooth colored (good for anteriors) One shade. Requires acrylic lining.
What are important points when fitting a PFPCC?
Select by MD width. Adjust cervical to mirror finish line on the facial when the incisal edge is in the proper position and leave any significant adjustment to the lingual surface. You don't want to break the polycarbonate surface and the facial side.
When do you use the freehand or block technique?
When you are fitting an existing RPD. There is no need for a study cast. No matrix is used. Difficult to get a hang of. High risk of locking on the acrylic.
What are the indirect techniques for provisionals?
Made on a stone model. No polymerization in patients mouth. Can allow the material to completely set. You then finish the materials on the model.
What types of acrylic are available?
Polymethacrylate. Vinylethelmethacrylate. Polyvinylethylmethacrylate.
What types of bis-acryls are avalable?
protemp, integrity, etc.
Why isn't Triad or VLC urethane dimethacrylate used?
Expensive, brittle, must use flowable composite to make additions. However there is reduced shrinkage.
What are factors you need to consider before starting the preparation?
Length of clinical crown, anatomic characteristics of all surfaces, position of tooth in the arch, occlusal and proximal relationships, esthetics, supporting tissues, extent of carious lesion or previous restorations.
What is a big reason that direct restorative materials can't be used?
Limitations due to the need of support of the tooth or size of the lesion.
Internally and externally retained cast restoration involving one or more cusps. Intracoronal restoration with an occlusal veneer.
What are the advantages of indirect gold onlays?
Nearly ideal anatomy can be developed (occlusal, contours and contacts). More conservative than FGC. Gold is a strong material that rarely fractures and provides protection to the weakened tooth structure.
What are the advantages of gold?
The wear is similar to enamel with no accelerated wear to opposing teeth. It can be burnished for better marginal adaption. It has great longevity. It is inert and resistant to saliva, acidic foods and tooth whitening chemicals.
What are the disadvantages to gold?
Higher costs. Esthetics. Multiple impressions. Larger preparation.
What are the indications for Inlays?
Patient request. Abutment teeth for RPDs. Restoring a tooth to normal anatomy and contact on an odd shaped tooth.
What are the indications for onlays?
Requested by patient. Strength of cast gold needed. Conservation of tooth structure. Restoration of large previous fillings. Endodontically treated teeth. Odd shaped tooth. Longevity needed. Occlusal dental rehabilitation. Periodontal indications (margin). Periodontal splinting. RPD abutment restoration. Sensitivity to amalgam.
Contraindications for onlays.
Exceptionally thin buccal and lingual walls. Restorations or defects on the buccal and or lingual walls in addition to the MOD portion. 3/4 crowns may be indicated in both situations. Insufficient retentive characteristics. 3/4 or full crown may be indicated to gain additional surface area. High caries rate. Need to control before placing. Cost. Esthetics. A patient who is too old or young. Physical health and ability of patient to withstand the more complicated procedures. FPD abutment retainers.