Fracture load and mode of failure of ceramic veneers with different preparations.

STATEMENT OF PROBLEM: Fracture is a clinical failure modality for ceramic veneers. Whether design of tooth preparation can affect the strength of ceramic veneers remains controversial. PURPOSE: This in vitro study evaluated fracture load and mode of failure of ceramic veneers, with 4 tooth preparation designs, that were bonded on extracted human maxillary central incisors. Identical parameters were also measured on unrestored intact teeth for comparison. MATERIAL AND METHODS: Fifty maxillary central incisors were randomly divided into 5 equal groups. Each group was assigned a different tooth preparation design: (1) no incisal reduction, (2) 2 mm incisal reduction without palatal chamfer (butt joint), (3) 1 mm incisal reduction and 1 mm height palatal chamfer, (4) 4 mm incisal reduction and 1 mm height palatal chamfer, and (5) unrestored (control). Forty teeth were prepared to accommodate ceramic veneers of equal thickness and incisocervical length. Stone dies were fabricated and veneers made from IPS Empress ceramic. Ceramic veneers were bonded and all teeth mounted in phenolic rings with epoxy resin. Fracture loads were recorded with a mechanical testing machine. RESULTS: Mean fracture loads (SD) in kgf were as follows: group 1, 23.7 (6.11); group 2, 27.4 (9.63); group 3, 16.4 (3.44); group 4, 19.2 (6.18); and group 5, 31.0 (10.38). Modes of failure were also analyzed for both ceramic veneers and teeth. One-way ANOVA with multiple comparisons revealed 3 significant subsets: groups 1-2-5, groups 4-1, and groups 3-4 (P <.05). Groups 1 and 2 had no ceramic veneer fractures; group 3 had 3 ceramic veneer fractures, and group 4 had 6 ceramic veneer fractures. CONCLUSION: Groups 1 and 2 recorded the greatest fracture loads that were comparable to an unrestored control.

Temperature rise in pulpal chamber during fabrication of provisional resinous crowns.

STATEMENT OF PROBLEM: The heat generated during the exothermic polymerization reaction of autopolymerizing resinous materials and the heat generated by ultraviolet lamps during irradiation of photopolymerizing resinous materials could cause pulpal damage when a direct technique is used to fabricate provisional restorations. This could occur if temperature elevations overcome the physiological heat dissipating mechanisms of the dental-periodontal system. PURPOSE: This in vitro study compared the rise in temperatures in the pulpal chamber during fabrication of provisional complete veneer crowns by direct method with different autopolymerizing and photopolymerizing resins. The effect of curing resinous crowns in different matrices, such as a polyvinyl siloxane impression and a vaccuum-formed polypropylene sheet, was also evaluated. RESULTS: The results demonstrated that the amount of heat generated during resin polymerization and transmitted to the pulpal chamber could be damaging to pulpal tissues including odontoblasts. When curing of provisional resinous crowns was performed in the polyvinyl siloxane impression, significantly lower temperatures were recorded compared with curing in the vacuum-formed polypropylene sheet. CONCLUSIONS: To prevent pulpal damage, effective cooling procedures are strongly recommended when directly fabricating resinous provisional crowns.

Marginal fidelity of crowns fabricated from six proprietary provisional materials.

STATEMENT OF PROBLEM: The most important requirement for an interim crown is suitable marginal adaptation. PURPOSE: This in vitro study compared vertical discrepancies of margins for complete crowns made with six provisional materials (Provipont, Protemp Garant, Unifast LC, Triad VLC, Splintline, and Jet). MATERIAL AND METHODS: A direct technique was used to fabricate 60 provisional complete crowns on prepared molars with a polyvinyl siloxane impression and a vacuum-formed polypropylene sheet as matrices. A measuring microscope was used to measure vertical marginal discrepancies at x 100. Data were analyzed with Kruskal-Wallis one-way analysis of variance and Mann-Whitney U tests (alpha = 0.05). RESULTS: Significant differences were found between resinous materials tested (p = 0.0002) and multiple comparisons tests indicated no significant difference between Splintline and Protemp Garant; Provipont, Unifast LC, and Triad VLC; and Unifast LC, Triad and Jet provisional materials. CONCLUSIONS: This study indicated that provisional crowns fabricated with Splintline and Protemp Garant interim restorative materials recorded the least marginal discrepancies.

Marginal leakage of amalgam restorations pretreated with various liners.

PURPOSE: To evaluate and compare the microleakage of amalgam restorations lined with four different liners. MATERIALS AND METHODS: Cylindrical occlusal cavities were prepared in extracted human molars and the teeth were then divided into four groups and lined with one of four liners: Amalcoden, AM (glass-metal ionomer), FujiDuet, FD (glass ionomer), Amalgambond, AB (adhesive resin), or copal varnish, CV. Each cavity was then restored with a high-copper amalgam alloy and aged for 7 days in 37 degrees C distilled water. The specimens were then thermocycled for 300 cycles followed by immersion in 0.5% basic fuchsin dye solution for 24 hours. The teeth were then embedded in resin, sectioned, and dye penetration at the tooth/amalgam interface evaluated microscopically at x 100 and scored from 0 to 4 (0 = no leakage and 4 = greatest leakage). RESULTS: The median values were: AM = 1.0; FD = 0.5; AB = 1.1; and CV = 4.0. Statistical analysis using Kruskal-Wallis and Mann-Whitney U indicated no significant differences between AM and AB or FD and AB. CV was however, significantly worse at P < 0.01.

Microleakage of multi-step and simplified-step bonding systems.

PURPOSE: To measure and compare the microleakage of Class V resin composite restorations using the following three pairs of multi- and simplified-step dentin bonding systems (DBS): OptiBond vs. OptiBond FL, All-Bond 2 vs. One-Step, and Tenure vs. Tenure Quik. MATERIALS AND METHODS: V-shaped cavities were prepared in the mesial and distal surfaces of 30 extracted human mandibular molars with margins in both enamel and cementum, and randomly assigned into three equal groups of 10 each. All DBSs were applied strictly following manufacturers' specifications before three incremental layers of resin composite (Pertac-Hybrid) were applied in all cavities. Specimens were stored for 7 days in 37 degrees C water, thermocycled for 300 cycles between 5 degrees C and 55 degrees C, immersed in 0.5% basic fuchsin solution for 24 hours, and embedded in resin before being sectioned longitudinally in multiple sections. Dye solution penetration at the tooth/composite interface was scored from 0 to 4 under a microscope at x100 at both enamel (E) and cementum (C) margins. Data were analyzed by Kruskal-Wallis and Mann-Whitney U tests with alpha = 0.05. RESULTS: OptiBond FL and One-Step showed less microleakage at the cementum margins compared to their multi-step versions. At the enamel margins Tenure Quik showed less microleakage compared to Tenure, and none of the other DBSs tested showed significant dye penetration at that interface. All DBSs showed significantly less microleakage at the enamel margins compared to the cementum margins except for OptiBond FL and One-Step that did not show any significant dye penetration at the cementum margins as well.

Bond strength of multi-step and simplified-step systems.

PURPOSE: To measure and compare the in vitro shear bond strength (SBS) of the following three pairs of multi- and simplified-step dentin bonding systems: OptiBond vs. OptiBond FL, All-Bond 2 vs. One-Step, and Tenure vs. Tenure Quik. MATERIALS AND METHODS: 60 extracted human mandibular molars were sectioned perpendicular to the long axis 1 mm above the CEJ to expose the dentin bonding surface. After being wet-ground to 600 grit with SiC abrasive papers, rinsed and dried, the teeth were individually mounted in phenolic rings with epoxy resin, and randomly assigned into six equal groups of 10 each. The dentin surfaces were treated with the above mentioned dentin bonding systems, and a gelatin cylinder filled with resin composite (Pertac-Hybrid) was directly bonded to each pretreated surface. After 7-day storage in 37 degrees C water followed by thermocycling, the specimens were shear tested to failure on an Instron machine. Data were analyzed by independent t-tests, one-way ANOVA, and Duncan's Multiple Comparison tests at alpha = 0.05. RESULTS: Except for the pair Tenure/Tenure Quik, the differences between the pairs All-Bond 2/One-Step and OptiBond/OptiBond FL were statistically significant with All-Bond 2 and OptiBond FL yielding higher shear bond strength (P < 0.05). Findings of this study indicated that OptiBond FL was the only simplified-step system showing improved bond strength.

Chemical treatment of cavity walls following manual excavation of carious dentin.

PURPOSE: To improve the conditioning of cavity walls resulting from minimal mechanical preparation of carious lesions, such as is done in modified Class II tunnel preparations. MATERIALS AND METHODS: Proximal carious lesions in premolars and molars were excavated manually and the cavity walls studied using a stereomicroscope and by scanning electron microscopy (SEM) following treatment with either polyacrylic acid, sodium hypochlorite, the enzyme preparation Pronase, or sequential combinations of the agents. Polyacrylic acid (10%) was used according to the manufacturer's instructions, while concentrated sodium hypochlorite (5.25%) was applied with either intermittent scrubbing or with ultrasonic energy for 5-10 minutes, or the cavity wall was incubated with the agent at +/- 37 degrees C for periods up to 24 hours. Incubation with the proteolytic enzyme preparation Pronase was carried out at 37 degrees C for a period up to 48 hours. RESULTS: Manual excavation did not remove all carious dentin, neither did treatment with polyacrylic acid. Scrubbing or sonication with ample amounts of sodium hypochlorite, followed by treatment with polyacrylic acid, or prolonged incubation with sodium hypochlorite, removed most of the remaining carious dentin. However, the "cleanest" surfaces were obtained after 48 hours of incubation with Pronase. Spots of thicker, soft layers of decayed dentin that were left intentionally at some locations could be disintegrated only by the Pronase treatment. It was concluded that treatment with sodium hypochlorite and polyacrylic acid in tandem, or with Pronase may represent potential supplements to conventional cavity cleaning that deserve further investigation. In the clinic more efficient cavity cleaning may improve the bonding ability and thus reduce the risk of marginal ridge fracture in teeth with Class II tunnel restorations.

Effects of thermocycling, load-cycling, and blood contamination on cemented implant abutments.

This study compared the effects of thermocycling, load-cycling, and human blood contamination on the retentive strength of five different cements for luting posts to root-form implants. For each cement, 10 specimens (controls) were stored in an incubator, 10 specimens were thermocycled, 10 specimens were subjected to cyclic compressive loading, 10 specimens were subjected to a combination of thermocycling and cyclic compressive loading, and 10 specimens were contaminated with blood before cementation, then exposed to a combination of thermocycling and compressive loading. After 70 hours, retentive tests were performed on the Instron machine, and data were recorded in kilograms. Significant retentive differences were identified among the cements and with load-cycling, but minimal effect on the retentive strength was demonstrated from thermocycling. Blood contamination in combination with thermocycling and load-cycling adversely affected the retentive strengths of all of the cements and could be a major cause of abutment failure in dental implants.

Microleakage of posterior composite resin restorations using beta quartz glass-ceramic inserts.

The effectiveness of using beta quartz glass-ceramic inserts in Class II composite resin restorations to prevent microleakage at the gingival cementum margins was investigated. Class II cavities were prepared on both mesial and distal sides of ten extracted teeth with the gingival margins placed on cementum. Both cavities were then restored with a composite resin in exactly the same manner, except that one received a glass ceramic insert and the other did not. The specimens were then thermocycled in basic fuchsin solution, embedded in epoxy resin and sectioned. The extent of dye penetration at the gingival cementum margins was then assessed and scored. The result indicated that the use of a glass-ceramic insert substantially reduced the microleakage of gingival cementum margins of composite resin restorations.

Fracture resistance of amalgam and composite resin cores retained by various intradentinal retentive features.

The fracture strengths of amalgam and composite resin cores retained by three types of intradentinal retentive features were compared with the fracture strength of cores retained by four self-threaded retentive pins. Composite resin cores had significantly greater resistance to fracture than amalgam cores with any of the retentive features. The fracture strength of amalgam cores retained by retentive pins was comparable to that of amalgam cores retained by a post with a countersink, but significantly higher than the strength of those retained by slots or channels. The fracture strength of composite resin cores retained by retentive pins was significantly higher than that of composite resin cores retained by any of the alternative intradentinal retentive features.

Temperature rise at root surface during post-space preparation.

This study compared the changes in temperature at the root surface of extracted human central incisors during post-space preparation using the following reamers (1) Peeso, (2) Kurer, (3) Gates-Glidden, (4) Para-Post, and (5) diamond burs. A mean temperature rise ranging from 2.3 degrees C to 15.6 degrees C from the baseline of approximately 28 degrees C was recorded. Peeso reamers recorded the highest temperatures followed by Kurer system and diamond burs, whereas Gates-Glidden and Para-Post systems were the lowest.

Effect of eugenol-containing endodontic sealer on retention of prefabricated posts luted with adhesive composite resin cement.

Reported studies have implicated eugenol in the reduction in retention of restorations luted with chemically cured composite resin cement. This study investigated the effect of residual eugenol in the root canal on the retention of ParaPost dowels cemented with Panavia EX composite resin. An attempt was also made to identify and to determine the most effective cleansing procedure. Findings of this study demonstrated a substantial decrease in retention of posts luted with Panavia composite resin cement in the presence of eugenol. Irrigation with ethyl alcohol (ethanol) or etching with 37% phosphoric acid gel was found to be effective in restoring the resistance to dislodgment of the posts, but alcohol produced the most consistent and reliable results.

Accuracy and bond strength of reversible with irreversible hydrocolloid impression systems: a comparative study.

Combinations of three reversible hydrocolloids with five irreversible hydrocolloids were evaluated for dimensional accuracy and bond strength. A stainless steel model representing two teeth prepared for a fixed partial denture was designed for an accuracy study. The recordings were made with a measuring microscope, and the tensile bond strength was determined with an Instron Universal Testing instrument. The accuracy of these materials was clinically acceptable, and the resulting models were suitable. The materials distributed by a common supplier exhibited better tensile strength, although one irreversible hydrocolloid, Jeltrate, performed well in the noncompanion combination groups. This reversible with irreversible hydrocolloid combination impression has an advantage compared with the traditional reversible hydrocolloid impression, because it does not require elaborate, expensive conditioning equipment and water cooled trays.

Dimensional accuracy and bond strength of addition silicones.

A cross-matching study was conducted to evaluate the effect on dimensional accuracy and tensile bond strength between the materials when intermixing brands of addition silicone impression materials in a putty-wash impression. Three brands of putty-wash systems (Reprosil, Permagum, and Express), which formed nine possible combinations, were involved in this study. The dimensional accuracy was estimated from stone casts recovered from impressions of a standardized stainless steel master model. Findings indicated no adverse effect on the bond between putty and light-bodied materials of different brands. Statistical analysis indicated significant differences. However, because the actual differences in percent deviations between the intermixed groups and their respective reference groups are very small, they are presumed to be insignificant clinically.

Effect of tray space on the accuracy of monophasic polyvinylsiloxane impressions.

The effect of tray space on the dimensional accuracy and stability of impressions made from four brands of monophasic polyvinyl siloxane material was assessed on the recovered stone casts by quantitative and qualitative methods. In general, both evaluation methods agreed that tray space and repeat pour did not affect the accuracy of the dies for individual castings. But disagreement was observed in the findings for fixed partial dentures (FPDs). Quantitative measurement of the interpreparation (IP) dimensions did suggest the possibility of a potential problem when a FPD is cast in one piece because of a significantly reduced distance between the two abutments. However, from the findings of this study it can be concluded that a rigid stock tray can be used with a monophasic polyvinyl siloxane impression material.

Fracture resistance of composite and amalgam cores retained by pins coated with new adhesive resins.

This study determined the effects of coating pins with either Panavia EX or with 4-META (Cover-Up) materials on the fracture resistance of pin-retained amalgam and composite cores. Gold-plated stainless steel (TMS) and titanium (Filpin) self-threading pins were used. Findings of this study corroborated the findings of several other studies that the use of pins reduces the fracture resistance of restorations. However, coating the pins with adhesion promoters such as Panavia EX and 4-META materials has been found to be effective in improving the fracture resistance. Cross-preference was observed between TMS and Filpin pins; that is, Panavia material coating was more effective with TMS pins, while 4-META was more effective with Filpin pins.

Seating and retention of complete crowns with a new adhesive resin cement.

The retentive property of cast gold complete crowns cemented with an adhesive resin cement (Panavia Ex) was compared with retention of crowns cemented with zinc phosphate cement (Flecks) and the conventional resin cement (Comspan). The effect of these agents on seating of crowns also was evaluated. Panavia cement exhibited the highest retentive strength, with values almost twice those obtained with zinc phosphate cement. However, the difference in mean retention values of crowns cemented with Comspan cement or with zinc phosphate cement was not statistically significant. Both resin cements used in this study provided better seating of crowns than did zinc phosphate cement.

Margin designs and fracture resistance of incisal resin composite restorations.

This study measured the resistance to fracture of Class IV resin composite restorations prepared with either butt joints, bevels, or chamfer margins. Seventy extracted intact, non-carious maxillary central incisors, of approximately the same size, were collected and randomly divided into the following seven groups: 90 degrees butt joint (control)), 1 and 2 mm 45 degrees bevels, 1 and 2 mm 60 degrees bevels, and 1 and 2 mm chamfer margins. The teeth were restored with a hybrid resin composite and tested in an Instron Universal testing machine in a compressive mode at 45 degrees to the long axis. Statistical analysis indicated that there were no significant differences between the control group and any of the 1 mm bevel or chamfer margins and that the 2 mm bevel and chamfer margins yielded the highest fracture resistance.