Fixed Prosthodontics and Impression Materials

Flashcards covering fixed prosthodontics, margin designs, gingival retraction, elastomeric impression materials, shade selection, investments, casting alloys, dental ceramics, provisional restorations, pontic designs, and dental cements based on the lecture transcript.

What is the primary indication for a feather edge margin design?

Cast metal restoration and the lingual margin of a metal ceramic crown.

What are the advantages and disadvantages of a chamfer margin design?

Advantages: Distinct margin, sufficient bulk, and easy to control. Disadvantage: Less conservative of tooth structure.

What is rotary curettage also known as, and on what type of tissue should it be performed?

It is known as "troughing technique" or "gingittage," and it should be performed only on healthy and inflammation-free tissues.

How long should a non-impregnated retraction cord be left in the gingival sulcus to achieve enlargement?

A minimum of $5\text{ mins}$ and not more than $10\text{ mins}$.

Who introduced the use of reversible hydrocolloid for fabricating cast restorations in 1930?

J.D. Hart of Wewoka, Oklahoma.

At what temperatures does agar transition from gel to sol and remain in sol form?

Agar changes from gel to sol at $99\,^{\circ}\text{C}$ but remains a sol as low as $50\,^{\circ}\text{C}$.

What are the components of the base and accelerator tubes in polysulfide impression material?

The base contains a liquid polysulfide polymer mixed with inert fillers. The accelerator contains lead dioxide mixed with small amounts of sulfur and oil.

What are the main components of the base paste and reactor paste in condensation silicone?

The base paste is a liquid silicone polymer with terminal hydroxyl groups mixed with inert fillers. The reactor paste consists of cross-linking agent ethyl silicate with organo-tin activator tin octoate.

Why should polyether impression material not be stored in a humidor or moist environment?

Because polyether has an affinity for water, making it hydrophilic.

What specific dental operator material can cause setting inhibition in addition silicones?

Some brands of latex gloves.

Who was the first to accurately describe the color of human teeth, and in what year?

Clark in 1931.

What is metamerism in dental shade selection?

A phenomenon occurring when the color of two objects appears to match under one lighting source but not under a different source.

What is the recommended minimal amount of room lighting for proper color matching in a dental office?

About $200\text{ foot-candles}$ measured at $30\text{ inches}$ above the floor.

According to Clark, what patient position is required for clinical shade selection and why?

The patient must be in an upright position so that the teeth are viewed under the same conditions as in social and business life.

What is the recommended viewing distance from the oral cavity for selecting a shade?

$3\text{--}6\text{ feet}$ from the oral cavity.

Which dental investment binder type is used to cast conventional noble metal alloys required for metal-ceramic restorations?

Phosphate bonded investment.

At what temperatures do the refractory silica forms cristobalite and quartz undergo thermal inversion?

Cristobalite at $232\,^{\circ}\text{C}$ ($450\,^{\circ}\text{F}$) and quartz at $566\,^{\circ}\text{C}$ ($1050\,^{\circ}\text{F}$).

What are the four traditional types of casting alloys and their physical descriptions?

Type I (simple inlays) soft, Type II (complex inlays) medium, Type III (crowns and FPD) hard, and Type IV (RPD and pin ledges) extra hard.

What are the temperature ranges and primary uses for high, medium, and low fusing dental porcelains?

High fusing ($1288\text{--}1371\,^{\circ}\text{C}$ / $2350\text{--}2500\,^{\circ}\text{F}$) for artificial denture teeth; medium fusing ($1093\text{--}1260\,^{\circ}\text{C}$ / $2000\text{--}2300\,^{\circ}\text{F}$) for all-ceramic restorations like porcelain jacket crowns; low fusing ($871\text{--}1066\,^{\circ}\text{C}$ / $1600\text{--}1950\,^{\circ}\text{F}$) for metal-ceramic crowns.

What is the composition of dental porcelains?

Feldspar ($85\%$), quartz ($12\text{--}22\%$), and kaolin ($4\%$).

What is fritting in dental ceramics?

The process of quenching medium and low fusing porcelain in water to produce internal stress or cracks (frits).

How are the three layers of porcelain used in a metal-ceramic restoration defined?

Opaque porcelain (obscures the metal coping), body porcelain (builds up the anatomic configuration), and incisal porcelain (gives a tooth-like appearance).

How does the Siebert classification categorize residual ridge deformities?

Class I: faciolingual loss of tissue width with normal ridge height; Class II: loss of ridge height with normal ridge width; Class III: combination loss of both dimension.

Why should the saddle ridge-lap pontic design be avoided?

Because its concave fitting surface overlaps the residual ridge buccolingually and is not accessible to cleaning with dental floss.

What design features define the modified ridge lap pontic?

It overlaps the residual ridge on the facial side for esthetics while remaining clear of the ridge on the lingual side with no tissue depression.

What makes the ovate pontic the most esthetically appealing pontic design?

Its convex tissue surface resides in a soft tissue depression or hollow in the residual ridge, making it appear as if the tooth is emerging directly from the gingiva.

What is the geometric shape of the modified sanitary pontic's gingival portion and what is its benefit?

It is shaped like an archway between the retainers, which increases connector size while decreasing stress concentrated in the pontic and connector.

What are the typical film thickness and working time of zinc phosphate cement?

Film thickness of about $2.5\,\mu\text{m}$ and a working time of about $5\text{ min}$.

What is the working time of zinc polycarboxylate cement?

About $2.5\text{ mins}$.

What are four advantages of glass ionomer cement?

1. Excellent adhesion to enamel and dentin. 2. Good biocompatibility. 3. Anti-carcinogenic effect. 4. Translucent color.