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Statement of Problem: Although a completely digital workflow has numerous advantages, a physical definitive cast may be especially helpful for the accurate assembly of components of complex complete arch-fixed prostheses, the evaluation of esthetic and occlusion features, or prosthesis fabrication. Research on the accuracy of additive complete arch casts with implants positioned with a large anterior-posterior (A-P) spread is sparse., Purpose: The purpose of this in vitro study was to evaluate the trueness of complete arch 4-implant analog casts with a large A-P distribution fabricated with different 3-dimensional (3D) printers., Material and Methods: Ten systems were evaluated representing currently available printing technologies and materials for the additive fabrication of complete arch 4-implant analog casts and compared for deviations in the X-, Y-, and Z-axes from the master model scan (MMS), recorded in standard tessellation language (STL). The MMS was provided to the laboratory selected by the manufacturer, permitting them to create their specific cast with computer-aided design and computer-aided manufacture specific to a particular system, including analog receptacle offset settings. Laboratories fabricated N=10 casts and affixed analogs. A conventional splinted impression and stone cast (CON) was fabricated as a control. The casts were scanned with a precision laboratory scanner (D2000; 3Shape A/S), and files were imported into the Convince metrology software program (3Shape A/S) for comparison with the MMS for mean deviations in the X-, Y-, and Z- axes. A 2-way ANOVA and the Tukey HSD comparison tests were performed between system groups and the 4 implant locations (α=.05). Comparative color maps were used to determine dimensional changes of the edentulous ridges., Results: For 2-dimensional deviations from the MMS in each of the 3 axes, the printer type, implant location, and interaction between those 2 variables were found to be statistically significant (P<.05). Comparisons among printers showed the smallest deviations for Asiga Pro 4K (ASG) and Stratasys Origin One (ORI) printers in both the X- and Y-axes and for CON in the Z-axis. For 3D deviations, comparison among printers indicated that ORI, SprintRay Pro55 S (SPR), and Ackuretta SOL (ACK) had the largest deviations, whereas CON and ASG showed the smallest deviations. Comparison color mapping demonstrates a disparity between printed model dimensional changes and implant analog positioning since the color maps of the casts' ridge crests were not in concordance with the results of the implant analog deviations., Conclusions: ASG, 3D Systems ProJet MJP 2500 Plus (MJP), 3D Systems NextDent 5100 (NEX), Stratasys J5 DentaJet (PJ5), Ivoclar PrograPrint PR5 (PR5), and Prodways ProMaker LD20 (PWY) were similar in terms of 3D deviations to the conventional stone cast control. Comparative color mapping showed the direction and quantity of the dimensional changes of the ridge crest frequently did not correlate with the 3D deviations of implant analog positioning. Implant analog insertion errors were predominantly responsible for analog position 3D deviations rather than the polymerization shrinkage of additive photopolymers., (Copyright © 2023. Published by Elsevier Inc.)

Statement of Problem: A typical conversion process of a complete-arch immediate loading protocol entails preparing holes in a complete denture for connection to interim copings, which reduces the strength of the prosthesis. The excellent mechanical properties of milled polymethyl methacrylate (PMMA) disks may provide interim prostheses with improved strength., Purpose: The purpose of this in vitro study was to measure the flexural strength and failure load of simulated acrylic resin immediate implant-supported interim prostheses fabricated by conventional processing and computer-aided manufacturing., Material and Methods: A master patient model was created with an acrylic resin base and 2 BioHorizons Internal 4.5-mm-diameter implants placed with a 21.5-mm span and multiunit abutments (MUA) tightened to place. Two groups with different prosthodontic designs were used: one represented the standard fixed prosthesis with support at each end (noncantilever, NC), and the other group represented the cantilever portion of the prosthesis (cantilever, C). Two connection designs of prosthesis blocks to MUA abutments were evaluated: one with typical holes in the prosthesis for capturing interim copings and one with a low-profile coping. For the heat-processed PMMA groups (HP/NC and HP/C), wax patterns were milled, and heat-polymerized denture base PMMA prostheses were processed. The milled PMMA groups (M/NC and M/C) were milled from a tooth-shaded PMMA disk for the prosthesis blocks. The milled low-profile groups (Mlp/NC and Mlp/C) had identical dimensions except that connection to the low-profile coping was designed with a cement space and a narrow diameter screw access hole and was milled from a PMMA disk. The failure load (N) of the cantilever prostheses was recorded, and for NC groups, the 3-point flexural strength formula (MPa) was calculated. The Weibull modulus, characteristic strength, and summary statistics were computed, and the groups were statistically analyzed with ANOVA and the post hoc Tukey test (α=.05)., Results: The mean flexural strengths (MPa) were HP/NC=91.35 ±18.92; M/NC=143.94 ±36.79; Mlp/NC=117.06 ±13.86. Significant differences were found among groups (P<.001). Mean failure loads (N) and Weibull modulus (WM) of cantilever prosthesis strengths were for HP/C=512.66, WM=5.597; M/C=695.06, WM=4.875; Mlp/C=254.97, WM=1.797 (P<.001)., Conclusions: Implant fixed interim structures milled from high-density PMMA blanks had a 35% higher flexural strength for both the standard prostheses and the cantilever prostheses than heat-processed denture base PMMA. The low-profile coping design was stronger than the heat-processed material, and the failure point was relocated from the lateral walls to the cervical margin area., (Copyright © 2021 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.)

Statement of Problem: Materials possessing fluorescent properties are assumed to emit sufficient visible light to change tooth color under daylight illumination. Fluorescent and nonfluorescent glaze pastes are available to finish the surface of a pressed lithium disilicate restoration. However, the effect of a fluorescent-glaze layer on the final color of the restoration remains unclear., Purpose: The purpose of this in vitro study was to measure the color dimensions of lithium disilicate glass-ceramic with different thicknesses and different surface treatments under daylight (D65) illumination conditions., Material and Methods: A total of 120 pressed lithium disilicate glass-ceramic disks were fabricated with 4 different thicknesses: 0.7, 1.2, 1.7, and 2.2 mm. In each thickness, 3 different subgroups were created based on the surface treatment performed (n=10): polished (NG), clear glaze (CG), and fluorescent glaze (FG). For the NG group, disks were polished with 180-, 320-, 600-, 800-, and 1400-grit SiC papers and a polishing machine. For the glazed groups, the CG and FG groups, the specimens were polished with 180-grit SiC papers and the same polishing machine. After the polishing sequence, the final thickness was verified in all groups by using digital calipers (0.5, 1.0, 1.5, and 2.0 mm). Additionally, 20 μL of clear glaze or fluorescent glaze was applied on the CG and FL groups by using an electronic positive displacement repeating pipette. The glaze layer was crystallized in a furnace according to the manufacturer recommendations. Color measurements in the CIELab coordinates were made with a spectrometer coupled to an integrating sphere and a standardized photography gray card as a background. Color difference (ΔE) values were calculated by using the CIE76 and CIEDE2000 formulas. The Shapiro-Wilk test revealed that the data were normally distributed. Two-way ANOVA and the Bonferroni test for multiple comparisons were used to analyze the data (α=.05)., Results: Statistically significant differences were found among the groups for the L∗, a∗, and b∗ values for the different ceramic thicknesses and surface finishing treatments evaluated (P<.001), except for the b∗ value between the FG and CG groups (P=.988). The L∗ value on the polished group was significantly higher than that on the glazed specimens, followed by the fluorescent-glazed and then by the clear-glazed specimens (P<.001). The ΔE values using the CIE76 formula varied from 0.87 to 2.76 among specimen groups and from 0.32 to 2.34 using the CIEDE2000 among the tested groups., Conclusions: Ceramic thickness and surface finishing treatment affected all color dimensions (L∗, a∗, and b∗ values) of lithium disilicate ceramic under daylight conditions. These differences resulted in a perceptible but acceptable color mismatch. The value (L∗ color dimension) of the lithium disilicate ceramic was higher on fluorescent-glazed than on not-fluorescent-glazed specimens., (Copyright © 2020 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.)

Statement of Problem: The integration of the digital workflow into routine prosthodontic practice for single-tooth implant surgery and fixed prosthesis fabrication has occurred at a remarkable pace in the last 5 years. With the greater demands of esthetics and precision, the definitive implant analog cast must ensure accurate implant positioning as well as an accurate relationship to adjacent teeth., Purpose: The purpose of this in vitro study was to evaluate the accuracy of the 3-dimensional (3D) implant position of definitive casts produced by 3D printing and analog technology., Material and Methods: A master patient model was created from a dentate typodont. The maxillary left central incisor was removed, and a Straumann RC implant was positioned for a screw-retained prosthesis. A laboratory scanner with an accuracy of 5 μm was used for all scanning. A scanbody was connected to the master model implant and scanned to create a master patient file, which served as the control master patient for all comparisons. The two 3D printing systems used for this study were the Statasys Objet500 (group OBJ), an industrial Polyjet production system, and the Formlabs Formlab 2 (group FORM), a budget SLA Vat system. In addition, a conventional gypsum cast (group GYP) with an implant analog was made with elastomeric impression material. With a sample size of 10 per group, each gypsum cast and 2 printed group casts were scanned with the D2000 laboratory scanner 5 times per cast. Convince software (3Shape) was used for 3D analysis to calculate accuracy. The following variables were measured: implant analog vertical displacement, horizontal displacement of implant platform and apex, degree of tilting in the vertical axis, and rotational position change around the vertical axis. Means and standard deviations were calculated for trueness. One-way ANOVA and the post hoc t test with Bonferroni correction were used to investigate any significant differences among the experimental groups (α=.05)., Results: For vertical displacement of the implant body, group OBJ had the lowest value of -30 ±24 μm. The values obtained for OBJ and FORM were significantly different from that obtained for GYP (P<.05). For horizontal displacement of the implant shoulder, Group OBJ had the lowest value, 85 ±12 μm, and the difference among these groups was significantly different (P<.05). The value for horizontal displacement of the implant apex was 123 ±25 μm for group OBJ and not significantly different from that obtained for group GYP (136 ±40 μm) but significantly different from that obtained for group FORM (326 ±54 µm). Also, the analysis of implant body tilting in the vertical axis showed significant differences between the values obtained for groups GYP and OBJ and between the values obtained for groups OBJ and FORM. With regard to implant rotational position change around the vertical axis, the values obtained for the gypsum cast and group FORM were not statistically different from those obtained for the master patient control model (P>.05). However, the implant orientation of group OBJ was significantly different from the orientation of groups GYP and FORM (P<.05). The actual clinical relevance of these printing system discrepancies is yet to be determined because the level of clinical acceptable discrepancy in the x, y, and z vectors is still undefined., Conclusions: This study showed statistically significant differences in accuracy among the implant analog cast fabrication systems; however; the level of clinical acceptable discrepancy is still undefined. Although further research is needed, this study supports the conclusion that the Polyjet industrial printing system was more accurate than the conventional implant analog gypsum cast., (Copyright © 2018 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.)

Statement of Problem: Conventional impression techniques to obtain a definitive cast for a complete-arch implant-supported prosthesis are technique-sensitive and time-consuming. Direct optical recording with a camera could offer an alternative to conventional impression making., Purpose: The purpose of this in vitro study was to test a novel intraoral image capture protocol to obtain 3-dimensional (3D) implant spatial measurement data under simulated oral conditions of vertical opening and lip retraction., Material and Methods: A mannequin was assembled simulating the intraoral conditions of a patient having an edentulous mandible with 5 interforaminal implants. Simulated mouth openings with 2 interincisal openings (35 mm and 55 mm) and 3 lip retractions (55 mm, 75 mm, and 85 mm) were evaluated to record the implant positions. The 3D spatial orientations of implant replicas embedded in the reference model were measured using a coordinate measuring machine (CMM) (control). Five definitive casts were made with a splinted conventional impression technique of the reference model. The positions of the implant replicas for each of the 5 casts were measured with a Nobel Procera Scanner (conventional digital method). For the prototype, optical targets were secured to the implant replicas, and 3 sets of 12 images each were recorded for the photogrammetric process of 6 groups of retractions and openings using a digital camera and a standardized image capture protocol. Dimensional data were imported into photogrammetry software (photogrammetry method). The calculated and/or measured precision and accuracy of the implant positions in 3D space for the 6 groups were compared with 1-way ANOVA with an F-test (α=.05)., Results: The precision (standard error [SE] of measurement) for CMM was 3.9 μm (95% confidence interval [CI] 2.7 to 7.1 μm). For the conventional impression method, the SE of measurement was 17.2 μm (95% CI 10.3 to 49.4 μm). For photogrammetry, a grand mean was calculated for groups MinR-AvgO, MinR-MaxO, AvgR-AvgO, and MaxR-AvgO obtaining a value of 26.8 μm (95% CI 18.1 to 51.4 μm). The overall linear measurement error for accurately locating the top center points (TCP) followed a similar pattern as for precision. CMM (coordinate measurement machine) measurement represents the nonclinical gold standard, with an average error TCP distance of 4.6 μm (95% CI 3.5 to 6 μm). All photogrammetry groups presented an accuracy that ranged from 63 μm (SD 17.6) to 47 μm (SD 9.2). The grand mean of accuracy was calculated as 55.2 μm (95% CI 8.8 to 130.8 μm)., Conclusions: The CMM group (control) demonstrated the highest levels of accuracy and precision. Most of the groups with the photogrammetric method were statistically similar to the conventional group except for groups AvgR-MaxO and MaxR-MaxO, which represented maximum opening with average retraction and maximum opening with maximum retraction., (Copyright © 2017 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.)

Statement of Problem: Durable bonding to fixed prosthodontic restorations is desirable; however, little information is available on the strength of the bond between different cements and fixed prosthodontic restorative materials., Purpose: This study determined the shear-bond strength of cementing agents to high-gold-content alloy castings and different dental ceramics: high-strength aluminum oxide (Procera AllCeram), leucite-reinforced (IPS Empress), and lithium disilicate glass-ceramic (IPS Empress 2)., Material and Methods: Prepolymerized resin composite cylinders (5.5 mm internal diameter, n=20) were bonded to the pretreated surfaces of prosthodontic materials. High-gold-content alloy and high-strength aluminum oxide surfaces were airborne-particle-abraded, and pressable ceramics were hydrofluoric acid-etched and silanized prior to cementing. The cementing agents tested were a zinc-phosphate cement (Fleck's zinc cement), glass ionomer cements (Fuji I, Ketac-Cem), resin-modified glass ionomer cements (Fuji Plus, Fuji Cem, RelyX Luting), resin cements (RelyX ARC, Panavia F, Variolink II, Compolute), and a self-adhesive universal resin cement (RelyX Unicem). Half the specimens (n=10) were tested after 30 minutes; the other half (n=10) were stored in distilled water at 37 degrees C for 14 days and then thermal cycled 1000 times between 5 degrees C and 55 degrees C prior to testing. Shear-bond strength tests were performed using a universal testing machine at a constant crosshead speed of 0.5 mm/min. Statistical analysis was performed by multifactorial analysis of variance taking interactions between effects into account. For multiple paired comparisons, the Tukey method was used (alpha=.05)., Results: In a 3-way ANOVA model, the main factors substrate, cement, time, and all corresponding interactions were statistically significant (all P <.0001). In subsequent separate 1-way or 2-way ANOVA models for each substrate type, significant differences between cement types and polymerizing modes were found (all P <.001). None of the cement types provided the highest bonding values with all substrate types., Conclusion: After 14 days of water storage followed by thermal cycling, only the self-adhesive universal resin cement (RelyX Unicem) and 2 of the resin cements (Panavia F and Compolute) exhibited strong bond strengths to specific prosthodontic materials. In contrast, zinc-phosphate, glass ionomer, and resin-modified glass ionomer cements showed the lowest values of all tested cementing agents after 14 days of water storage followed by thermal cycling.

Statement of Problem: The conservation of sound tooth structure helps preserve tooth vitality and reduce postoperative sensitivity. Innovative preparation designs, like those for porcelain laminate veneers, are much less invasive than conventional complete-coverage crown preparations. However, no study has quantified the amount of tooth structure removed during these preparations., Purpose: The purpose of this study was to quantify and compare the amount of tooth structure removed when various innovative and conventional tooth preparation designs were completed on different teeth., Material and Method: . A new comprehensive tooth preparation design classification system was introduced. Typodont resin teeth representing the maxillary left central incisor, maxillary left canine, and mandibular left central incisor were prepared with the following designs: partial (V1), traditional (V2), extended (V3), and complete (V4) porcelain laminate veneer preparations; resin-bonded retainer preparation with grooves (A1) and with wing/grooves (A2); all-ceramic crown preparation with 0.8 mm axial reduction and tapering chamfer finish line (F1), all-ceramic crown preparation with 1.0 mm axial reduction and rounded shoulder finish line (F2), and metal-ceramic crown with 1.4 mm axial reduction and facial shoulder finish line (F3). After tooth preparations (10 per group), the crown was separated from the root at the CEJ. The removed coronal tooth structure was measured with gravimetric analysis. Means and standard deviations for tooth structure removal with different preparation designs were calculated and analyzed with analysis of variance at a significance level of P<.05., Results: Significant differences in the amount of tooth structure removal were noted between preparation designs. Ceramic veneers and resin-bonded prosthesis retainers were the least invasive preparation designs, removing approximately 3% to 30% of the coronal tooth structure by weight. Approximately 63% to 72% of the coronal tooth structure was removed when teeth were prepared for all-ceramic and metal-ceramic crowns. For a single crown restoration, the tooth structure removal required for an F3 preparation (metal-ceramic crown) was 4.3 times greater than for a V2 preparation (porcelain laminate veneer, facial surface only) and 2.4 times greater than for a V4 preparation (more extensive porcelain laminate veneer)., Conclusion: Within the limitations of this study, tooth preparations for porcelain laminate veneers and resin-bonded prostheses required approximately one-quarter to one-half the amount of tooth reduction of conventional complete-coverage crowns.

This study investigated the effect of combining dentin bonding agents (DBAs) with various resin cements on contraction gap formation at the cavity floor of resin-cemented ceramic inlays. Cylindrical dentin cavities were pretreated with one of five DBAs before luting of ceramic inlays with one of four dualcuring resin cements. Measurements of cross sections showed that mean gap widths were reduced from 46% to 93% compared with control specimens prepared without a DBA. The extent of the gap reduction was dependent on the type of bonding agent and resin cement. Although none of the resin cement-dentin bonding agent combinations tested were able to completely eliminate development of interfacial contraction gaps, some combinations produced considerable reductions in gap size.

The effect of dentin bonding agents (DBAs) on contraction gap formation at the cavity floor of resin-cemented ceramic inlays was investigated. Cylindrical dentin cavities were pretreated with one of 12 DBAs before luting of ceramic inlays with a dual-curing resin cement. Measurements of cross sections revealed that mean gap widths were reduced between 21% and 80% compared with control specimens prepared without a DBA. The extent of the gap reduction depended on the type of bonding agent. None of the dentin bonding agents tested were able to completely eliminate development of interfacial gaps.

The swaged metal matrix provides a method for rapidly making a metal substructure for ceramic crowns. This study determined the vertical and horizontal marginal fidelity of swaged metal substrate crowns made with four methods. No significant difference in vertical or horizontal marginal fidelity was found for metal margin crowns formed with either a plastic spacer or a paint-on die spacer. The vertical marginal fidelity was significantly better in crowns made with a metal margin (37 microns) than in crowns made with a porcelain facial margin (62 microns), and the latter were significantly better than crowns made with a 360-degrees porcelain margin (86 microns). Crowns made with all four methods were overcontoured by 46 to 82 microns. The 360-degrees porcelain margin was technically more difficult and time-consuming to make.

This study measured the in vitro microleakage of conventional and new FPD luting agents. Standardized preparations were made on 42 freshly extracted premolars. Facial and lingual chamfer margins were placed in enamel, mesial and distal in dentin and cementum, and castings were made in Rexillium III alloy and were then cemented with a standardized technique. Six groups of seven samples were tested, (1) polycarboxylate, (2) zinc phosphate, (3) glass ionomer, (4) Den-Mat Thin Film cement, (5) Panavia Ex, and (6) Den-Mat Thin Film cement with Tenure. The ranking of groups for stain ingress was from the greatest (1) to the least (6). A one-way analysis of variance and Tukey-Student range analysis revealed significantly similar groups, p less than 0.05:(1,2,3,4) (5,6).

This study evaluated the marginal fidelity and microleakage of porcelain veneers made with the platinum foil and refractory die techniques. Maxillary incisors, matched for size and amount of enamel, were prepared with 0.5 mm uniform intraenamel reduction. The indirectly made veneers were etched, treated with silane, and luted with a composite resin, and the margins were finished and polished. The restored teeth were stored in 37 degrees C water, thermocycled 1000 times, stained with silver nitrate, embedded, sectioned buccolingually and mesiodistally, and measured at x250 magnification. The platinum foil veneers had significantly better vertical marginal fidelity but significantly more overcontouring than had the refractory die veneers. Universal microleakage at the tooth-composite resin interface and negligible microleakage at the porcelain-composite resin interface were observed. No relationship was found between the amount of vertical marginal opening and the amount of microleakage.

This study investigated the use of a silicone fit-checking medium as an indicator for internal adjustments to improve the seating of ceramic inlays. The fit-checking medium helped reduce the marginal opening by 290 microns, accounting for a 70% improvement in marginal seating.

This study obtained anamnestic data from a questionnaire given at the conclusion of a 7-week chlorhexidine gingival enhancement study regarding patients' oral hygiene practices, perception of change in gingival health, and side effects. In the patient population using the 7-week chlorhexidine treatment regimen, most patients noticed an improvement in gingival health, were willing to continue usage after the study, and would recommend the rinse to others. Of the patients who reported side effects, taste alteration was more objectionable than staining. The patients' observed gingival health benefits were more important than the patients' perception of the side effects such as staining and taste alteration.

This study assessed the changes of the subgingival/marginal microflora during fixed prosthodontic procedures and evaluated the effect of adjunctive rinsing with 0.12% chlorhexidine on the subgingival/marginal microflora during fixed prosthodontic treatment. Thirty patients scheduled for fixed prosthodontics were randomly assigned to either rinsing with 15 ml of tap water b.i.d. (control) or rinsing with 15 ml of 0.12% chlorhexidine gluconate b.i.d. (experimental). Subgingival and marginal plaque was analyzed at baseline, before crown preparation (2 weeks), before crown cementation (5 weeks), and 2 weeks after cementation (7 weeks). The fixed prosthodontic procedures alone altered the subgingival and marginal microbiota toward a more health-associated flora. Adjunctive rinsing twice daily with 0.12% chlorhexidine had a significantly greater effect in reducing putative periodontal pathogens compared with the control regimen. This medication was a useful adjunct to regular oral hygiene during fixed prosthodontic procedures by permitting the establishment and maintenance of a microflora compatible with periodontal health.

This study assessed the efficacy of a 0.12% chlorhexidine gluconate (CHX) rinse on the enhancement and maintenance of gingival health in patients receiving fixed prosthodontic treatment. Thirty patient participants in this examiner blind study were randomly assigned into two groups, one control and another group using CHX 15 ml b.i.d. in addition to normal oral hygiene. The medication was used for 2 weeks prior to crown preparation, 3 weeks during provisional crown placement, and 2 weeks after definitive crown cementation. Plaque and gingivitis indices were measured initially and at the three aforementioned points during the 7-week period. The plaque index for the control group decreased by 0.26 units; CHX decreased by 0.63 units at 7 weeks. The gingival index of the control group decreased by 0.37 units; CHX decreased by 0.87 units. Adjunctive use of chlorhexidine with fixed prosthodontic procedures significantly reduced plaque levels and significantly improved gingival health compared with the control patients. Fixed prosthodontic procedures alone decreased plaque levels and increased gingival health.

This study determined the effect of different post designs and varying amounts of post-to-canal adaptation on the fracture resistance of endodontically treated teeth. Forty freshly extracted maxillary central incisors were endodontically treated. Groups of 10 teeth were prepared according to four experimental designs. Cast post and cores and crowns were waxed, cast, and luted with zinc phosphate cement on a static loading device. The teeth were embedded in acrylic resin and the crowns were loaded on a universal testing machine at 130 degrees to the long axis of the tooth until failure. Maximum adaptation of the residual root structure with a tapered post significantly increases the fracture resistance of endodontically treated teeth, but upon failure renders the tooth nonrestorable. Tapered posts resulted in fractures that were directed more apically and lingually. Parallel-sided posts had a lower frequency of fracture upon failure, involving less tooth structure. Parallel-sided posts surrounded by large amounts of cement had no significant effect on failure loads.

Previous research on crown margin fidelity is reviewed and methods of measurement are compared and scrutinized. A standardized method for the determination of crown margin fidelity is introduced. A biologically oriented rationale is presented for analysis of the measurement parameters. This system places a strong emphasis on measuring factors that impact upon accumulation of plaque and the microbiologic environment around crowns, ultimately affecting gingival health. Crown samples were cemented on master dies and were embedded for sectioning buccolingually and mesiodistally. Photographs of margins with plastic overlays indicating emergence profiles were used to determine vertical and horizontal marginal discrepancies. Three observers measured seven crown systems for the vertical and horizontal marginal discrepancies of each crown system. The interobserver variance was 10 microns for the horizontal and 9 microns for the vertical marginal discrepancy.

Heat treatment during the burnout procedure may cause corrosion of the stainless steel post. This study was undertaken to determine whether alteration of the corrosion resistance of stainless steel posts occurs as a result of various simulated burnout procedures. Stainless steel posts were divided into five groups of five posts: group 1, control; 2, gypsum-bonded investment, bench cooled; 3, gypsum-bonded investment, quenched; 4, phosphate-bonded investment, bench cooled; and 5, phosphate-bonded investment, quenched. The posts were placed in individual containers of Ringer's solution and observed at 30, 180, and 600 days. Scanning electron microscopy, energy dispersive x-ray spectroscopy, optical emission spectroscopy, and optical microscopy were used to evaluate the posts qualitatively and quantitatively. Investment and heat treatment altered the metallic structure of stainless steel posts. Prefabricated posts submitted to simulated burnout procedures had a noticeable reduction in corrosion resistance. Direct casting to stainless steel posts is contraindicated.

This study evaluated the fracture resistance of pulpless teeth with various ferrule designs and amounts of coronal tooth structure. One millimeter of coronal tooth structure above the crown margin substantially increased the fracture resistance of endodontically treated teeth, whereas a contrabevel at either the tooth-core junction or the crown margin was ineffective. The thickness of axial tooth structure at the crown margin did not appreciably improve resistance to fracture.

When a method of intracoronal reinforcement is selected, many factors must be weighed. The hazards include (1) the induced stresses and the risk of fracture during placement of the dowel, (2) the probability of root perforation during post space preparation, (3) the wedging action of tapered dowels, and (4) the incidence of fracture with self-threading pins in devitalized teeth. The amount of tooth structure that remains after endodontic therapy and post space preparation is paramount. Endodontic and restorative treatment must be aimed at preserving tooth structure to provide strength and resistance to fracture of the pulpless tooth. To fabricate a large-diameter dowel with a strength that greatly exceeds that of the endodontically treated root decreases the prognosis for clinical success.

The sequence of the initiation, formation, development, and maturation of dental plaque was reviewed. The gingival response to plaque formation was identified to control plaque growth for prolonged gingival health. A strong implication has been established between rough, overcontoured metal ceramic restorations and periodontal disease. Unsightly soft tissue around crowns result from increased plaque accumulation. In comparing esthetic crowns, three critical variables are considered. The factors that mediate plaque accumulation and influence gingival health at the tissue-restoration interface are (1) surface roughness, (2) marginal fit, and (3) contour. Minimizing plaque accumulation is crucial for gingival health.

A method was described that includes a stent provided by the restorative dentist indicating optimum implant location. The stent, with imbedded metal bearings, is worn by the patient during tomographic radiographic survey. The tomogram provides a more accurate image of the quantity and quality of the osseous structures. The same template may be used as a surgical stent to aid the surgeon in initial bur placement. Through careful planning and systematic control, the predictable placement of osseointegrated implants can be achieved. With cooperative efforts of restorative dentists and surgeons, more than 400 implants have been successfully placed at University of California, Los Angeles, School of Dentistry.

Most ceramic restorations are fabricated in a location remote from the dental office. Successful fabrication of matching life-like ceramic restorations necessitates a collaborative effort between the dentist and the ceramist. To meet the demands for visual communication of shade and surface texture, the following steps are recommended. 1. A means of communicating and recording surface texture that facilitates blending the restorations with the natural dentition should be used. 2. The system should use an esthetics prescription form that functions with the Shade Indicator Chart system to relate the shade of opaque, body, and incisal porcelains and their arrangement to the ceramist. 3. An easily made identification mold to form shade tabs is needed. 4. Identification shade tabs should be made to verify and document shade formulations selected with the Shade Indicator Chart system. 5. Methods for precisely mapping and reproducing individual characterization patterns are needed. This information permits the visualization of the end result, allowing the artistic expression of the ceramist to create vital-appearing restorations intrinsically and in harmony with the natural dentition.

The inherent problems in present shade matching procedures and communication between dentist and ceramist have been discussed. These five areas of weakness include the observer, variable viewing conditions, commercially available shade guides, inadequate technology, and poor communication. A systematic procedure that breaks down shade selection to the elements of opaque, body, and incisal porcelain shades was presented. This method simplifies and adds clarity in the registration of shades, improving the communication chain between dentist and ceramist. The system is suggested as a means to overcome many of the inherent problems in shade selection and communication. This approach enhances the dentist-ceramist team's ability to esthetically match metal-ceramic restorations to the natural dentition. Future parts of this series will present procedures for improved communication and a system for porcelain application.

The ability of experienced and inexperienced dentists to follow graphic tracings of known value was compared. The mean differences from known values were low for the settings of condylar inclination, progressive side shift, and immediate side shift. Errors were high in both groups when the parameters of the top wall and rear wall were evaluated. Further work is necessary to determine the clinical significance of these errors.