John A. Sorensen

Ferrule design and fracture resistance of endodontically treated teeth

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.

Effect of post adaptation on fracture resistance of endodontically treated teeth

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.

Optimum placement of osseointegrated implants

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.

A standardized method for determination of crown margin fidelity

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.

A rationale for comparison of plaque-retaining properties of crown systems

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.

Improved color matching of metal-ceramic restorations. Part I: A systematic method for shade determination

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 teams 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.

Improved color matching of metal ceramic restorations. Part II: Procedures for visual communication

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.

Marginal fidelity and microleakage of porcelain veneers made by two techniques

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.

Gingival enhancement in fixed prosthodontics. Part I: Clinical findings

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.

Marginal fidelity of four methods of swaged metal matrix crown fabrication

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.