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Statement of problem Because crowns with open margins are a well-known problem and can lead to complications, it is important to assess the accuracy of margins resulting from the use of a new technique. Currently, data regarding the marginal fit of computer-aided design and computer-aided manufacturing (CAD-CAM) technology to fabricate a complete gold crown (CGC) from a castable acrylate resin polymer block are lacking. Purpose The purpose of this in vitro study was to compare marginal discrepancy widths of CGCs fabricated by using either conventional hand waxing or acrylate resin polymer blocks generated by using CAD-CAM technology. Material and methods A plastic model of a first mandibular molar was prepared by using a 1-mm, rounded chamfer margin on the entire circumference of the tooth. The master die was duplicated 30 times, and 15 wax patterns were fabricated by using a manual waxing technique, and 15 were fabricated by using CAD-CAM technology. All patterns were invested and cast, and resulting CGCs were cemented on their respective die by using resin-modified glass ionomer cement. The specimens were then embedded in acrylic resin and sectioned buccolingually. The buccal and lingual marginal discrepancies of each sectioned portion were measured by using microscopy at ×50 magnification. Data were subjected to repeated measures 2-way ANOVA, by using the Tukey post hoc pairwise comparison test (α=.05). Results The factor of “technique” had no significant influence on marginal discrepancy measurement (P=.431), but a significant effect of “margin location” (P=.019) was noted. The confounding combination of factors was found to be significantly lower marginal discrepancy dimensions of the lingual margin discrepancy than on the buccal side by using CAD-CAM technology. Conclusions The marginal discrepancy of CAD-CAM acrylate resin crowns was not significantly different from those made with a conventional manual method; however, lingual margin discrepancies present from CAD-CAM–prepared crowns were significantly less than those measured on the respective buccal surface.

Statement of problem Systematic reviews about the internal and marginal misfits of fixed prostheses have identified a limited number of clinical studies, suggesting the need for further research on the subject. Although the replica technique has been described as suitable for this purpose, few studies have validated it. Purpose The purpose of this in vitro study was to compare the ability of a nondestructive replica technique and a destructive cementation technique to assess internal and marginal misfits of zirconia copings, considering current materials and designs. Material and methods Twelve anatomic prefabricated abutments (Neodent) were used to manufacture zirconia copings following the Ceramill (Amann Girrbach AG) (n=6) and Lava (3M ESPE) (n=6) systems. Replications of the cementation line were obtained with polyvinyl siloxane for the replica technique, and the copings were then cemented and sectioned to obtain 5 surfaces (buccal, palatal, mesial, distal, and incisal) and the linear and angle regions (internal axiogingival and axioincisal angles). The thickness of the cement line and silicone film was measured at 45 reference points on each abutment. A total of 540 measurements were made with an optical microscope with a digital camera at magnifications of ×100 and ×200. Data were analyzed by repeated-measures ANOVA and the Bonferroni multiple comparison tests (α=.05). Results In the internal misfit evaluation, the mean values observed for the cementation technique and replica technique were as follows: angle regions, 70.6 μm and 72.2 μm; linear regions, 59.1 μm and 59.6 μm; incisal surface, 139.0 μm and 139.8 μm; buccal surface, 72.4 μm and 73.8 μm; palatal surface, 73.1 μm and 75.2 μm; mesial surface, 74.1 μm and 73.8 μm; distal surface, 75.0 μm and 76.3 μm; and overall mean, 73.6 μm and 74.8 μm, respectively. In the evaluation of the marginal misfit, the mean values found were: buccal surface, 36.7 μm and 37.8 μm; palatal surface, 37.5 μm and 36.8 μm; mesial surface, 44.0 μm and 43.7 μm; and distal surface, 44.6 μm and 45.2 μm, respectively. No significant differences were found between the 2 techniques for all locations and systems (P>.05). Conclusions Within the limitations of this in vitro study, both techniques presented the same ability to assess the internal and marginal misfits when the location and overall mean averages were evaluated (P>.05).

Statement of problem Wear resistance is a limitation of artificial denture teeth. Improving the wear resistance of conventional artificial denture teeth is of value to prosthodontic patients. Purpose The purpose of this in vitro study was to evaluate the wear resistance and hardness of modified polymethyl methacrylate artificial denture teeth compared to 5 commercially available artificial tooth materials. Material and methods This study evaluated 180 artificial denture teeth (6 groups) that included 3 groups of conventional artificial teeth (MajorDent, Cosmo HXL, and Gnathostar), 2 groups of composite resin artificial teeth (Endura and SR Orthosit PE), and 1 group of modified surface artificial teeth. The flattened buccal surface of each tooth (n=15) was prepared for investigation with the Vickers hardness test and the elucidate wear test (n=15) by using a brushing machine. Each group was loaded for 18 000 cycles, at 2 N, and 150 rpm. The wear value was identified with a profilometer. The data were statistically analyzed by using 1-way ANOVA and post hoc Turkey honestly significant difference tests (α=.001). The tribologies were observed under a scanning electron microscope, and the cytotoxicities were evaluated by MTT assay. Results The Vickers hardnesses ranged from 28.48 to 39.36. The wear depths and worn surface area values ranged from 1.12 to 10.79 μm and from 6.74 to 161.95 μm 2 . The data revealed that the modified artificial denture teeth were significantly harder and exhibited significantly higher wear resistance than did the conventional artificial teeth ( P 001). The scanning electron microscopic images revealed cross sections of the conventional artificial denture teeth with intensively worn surface areas after brushing. The cytotoxicity test revealed 97.85% cell viability, which indicates the nontoxicity of the modified surface of this material. Conclusions Within the limitations of this study, the polymethyl methacrylate modified surface artificial denture teeth was not significantly different from that of the composite resin artificial denture teeth, with the exceptions that the surface was harder and more wear resistant.

Statement of problem The application of solder material to metal frameworks could affect the porcelain-to-metal failure load and possibly compromise the longevity of porcelain-fused-to-metal crowns. Purpose This in vitro study assessed the influence of solder on the porcelain failure load between metal and porcelain, using crown-shaped specimens. Material and methods Forty standardized crown patterns were fabricated on a metal die and cast with noble alloy (Protocol). The specimens were divided into test (soldered, n=20) and control (nonsoldered, n=20) groups. A 2-mm–diameter perforation was produced on the buccal surface of the test specimens, 1.5 mm apical to the junction between occlusal and buccal surfaces. The perforation was repaired with high-fusing white ceramic solder material. All castings were finished with aluminum oxide stones and airborne-particle abraded with 50-μm aluminum oxide at 75 psi of pressure. Two layers each of opaque and dentin porcelain were applied on all specimens. All crowns were subjected to a vertical compressive load with a universal testing machine at a crosshead speed of 0.5 mm/min until fracture. The loading apparatus of the device contacted the buccal cusp only. In both control and test groups, 10 crowns were loaded with a stainless steel pin (phase I) whereas the remaining 10 in each group were loaded with a carbon steel pin (phase II). Means of loads at failure were recorded in each group for each pin type and compared (soldered vs nonsoldered) by use of a t test (α=.05). Results Mean failure load for nonsoldered crowns was 349 ± 63 kgf in phase I and 228 ± 49 kgf in phase II. Soldered crowns showed a significantly lower failure load (265 ± 82 kgf [phase I; P P Conclusion Soldered metal-porcelain crown specimens demonstrated a significantly lower load at failure. Within the limits of this study, it was concluded that solder material might negatively affect porcelain-metal crowns.

The purpose of this study was to examine tooth strains in Class II preparations. A Class II cavity was prepared in 16 permanent premolars, and a strain gauge was attached to the buccal surface of each tooth. Each cavity was then restored with bonded amalgam, bonded gallium, composite, or composite with a resin liner. The tooth strains created by these four restorations were determined and evaluated with a strain indicator. The results of this study indicated that composite restorations with and without resin liner created much greater strains to tooth structure than did bonded amalgam and bonded gallium restorations. The application of resin liner before placement of the composite was effective for decreased tooth strain.

aAssociate Professor, Department of Restorative Dentistry, School of Dentistry, Loma Linda University. bAssociate Professor, Department of Restorative Dentistry, School of Dentistry, Loma Linda University. cProfessor, Director, Division of Postdoctoral Prosthodontics, Department of Restorative Sciences and Biomaterials, Goldman School of Dental Medicine, Boston University. (J Prosthet Dent 2008;100:406-407) Two of the most common implant complications with the use of attachments are overdenture clip/ attachment loosening (30%) and overdenture clip/attachment fracture (17%).1 These problems are related to the nature of the nylon or plastic clips available for use with implant-retained overdentures. A metal attachment that engages the implant bar (SwissLoc NG; Attachments Intl, Inc, San Mateo, Calif ) (Fig. 1) can also be used in addition to the clips. The use of a locking, plunger-type metal attachment prolongs the useful life of plastic clips. These plunger attachments are commonly placed on the buccal surface of the overdenture flange with a mesial depression in the surrounding acrylic resin to facilitate removal by the patient’s fingernail. This buccal placement is convenient and practical, and will not interfere with esthetics when placed in a mandibular denture. However, when these attachments are placed in a maxillary denture, esthetic concerns and flange thickness commonly prevent their placement on the facial surface of the denture flange, and they are usually placed on the palatal surface of the implant-supported overdenture. Because of the depression in the acrylic resin, the plunger head may be annoying to the patient’s tongue and can cause tongue soreness (Fig. 2). When the plunger head is at the same level as the surrounding acrylic resin, access to unlock the attachment is not feasible. The purpose of the article is to describe a method of making a device to disengage a palatally placed plunger-type attachment (Fig. 3). PROCEDURE

Statement of problem. Exposing the tooth structure to chemicals used in displacing the gingival tissue is inevitable. Purpose. This study was undertaken to microscopically examine the effect of tannic acid on the prepared dentin surface. Material and methods. Forty recently extracted intact human teeth were mounted for buccal surface preparation. Teeth were equally divided into 10 groups. One group was kept as a control and the other teeth received a topical application of 15%, 20%, and 25% aqueous tannic acid solutions each for 5, 10, and 15 minutes at room temperature. All samples were washed, air-dried, then prepared for scanning electron microscopic examination. Two different areas in the cervical region were randomly selected and examined under magnifications of ×1000 and ×2000, then photographed. The assessment of the changes was performed qualitatively. Results. The results showed an incomplete removal of the smear layer in all experimental samples. The astringent action of the tannic acid solution on both the smear layer and the surface peritubular dentin around the orifices of dentinal tubules had contributed to their constriction. The degree of constriction of the orifices of dentinal tubules increased as higher concentrations of tannic acid solutions were used and as the application time was further increased at each concentration. Conclusion. The tannic acid had an incomplete action on the removal of the smear layer. It also seemed to have an astringent action on both the smear layer and the peritubular dentin. (J Prosthet Dent 1998;79:169-74.)

A three-surface MOD preparation measuring one third of the isthmus cavity distance at the isthmus was prepared for five extracted, intact human maxillary premolar teeth. The teeth were restored with a posterior resin and a dentin bonding agent. Each tooth was tested under a cyclically varying load in a fatigue machine made at the University of Washington. The cyclic load rate was 75 cycles per minute. A strain gauge was applied to the buccal surface of each tooth. Under the load applied at an angle of 60 degrees to the long axis of the tooth, reinforcement of the tooth was established by the reduced deflection of the buccal surface of the restored tooth as compared with the unrestored tooth. The loss of this reinforcement due to the application of the cyclically varying load established the end point of the fatigue testing. Four different load values of 13, 16, 19, and 22 lb loads were applied separately to each tooth. The results of this testing were classic wherein the smallest load required the greatest number of load cycles before loss of adhesion was registered by the strain gauge. Failure always occurred within the adhesive joint.

This article describes a simplified method for making esthetic cast metal occlusal surfaces. Monoplane posterior acrylic resin block teeth, cast in a nickel-chrome alloy, are coated with silane and an esthetic composite resin veneer is applied to the buccal surface. These veneered posterior metal teeth are incorporated in the wax setup and the dentures are processed and finished. The dentist's routine technique for delivering dentures to the patient can be followed.

In the technique survey it is significant that three of the seventy-nine castings (3.8 per cent) were unacceptable. Of these, one was the direct result of the displacement of the wax pattern by secondary investment; one failure was due to accidental mechanical distortion during the final polish; the third failure was due to the casting being warped during the soldering operation. For the entire technique survey, thirty-six castings (45.5 per cent) showed some visible evidence of warpage, but not sufficient to prohibit their use. The majority of unexplained discrepancies occurred either after the soldering or the annealing operation. Eleven of the seventy-nine castings failed to fit properly after the initial polish and sprue cutting. Of these eleven, six misfits were the result of an over-polishing of the rest surfaces, and one was the result of the displacement of the wax pattern. The laboratory studies show that eight castings developed slight discrepancies immediately following the soldering operation. These discrepancies increased with the successive stages of softening and hardening operations. Both the technique and laboratory castings showed similar changes, with the only significant changes being in the seventy of distortion. In nearly all castings the lingual bar tended to spread at its distal ends in such a manner as to force the section of the bar below the major abutment teeth into closer contact with the cast, sometimes to the point of serious impingement. At the same time a relief space tended to develop under the center section of the bar, lingual to the incisor teeth. The major occlusal rests showed a tendency to raise off the tooth surface, frequently more on the buccal surface, due to a twisting action of the major connector. This action tended to force the lingual portion of the resin retention lug into closer contact with the edentulous ridge, and the buccal portion of the lug farther from the ridge. Some castings which showed less of the twisting tendency and more of a straight spreading of the distal ends resulted in the major occlusal rests contacting only on the lingual slope of the buccal cusps with a resulting space under the lingual side of the rest. When surveying all of the results for both the technique and laboratory studies, one factor seems to stand out from the others. The more heat treatment the castings receive, the greater are the chances of producing distortion. By heat treatment is meant any operation which consists of heating the casting to a high temperature and then cooling it. This included the casting process, together with the method of cooling, and the soldering, annealing, and hardening operations.