Observation of nonlinear optical phenomena in air and fused silica using a 100 GW, 1.54 mum source.

A 100-GW optical parametric chirped-pulse amplifier system is used to study nonlinear effects in the 1.54 mum regime. When focusing this beam in air, strong third-harmonic generation (THG) is observed, and both the spectra and efficiency are measured. Broadening is observed on only the blue side of the third-harmonic signal and an energy conversion efficiency of 0.2% is achieved. When propagated through a 10-cm block of fused silica, a collimated beam is seen to collapse and form multiple filaments. The measured spectral features span 400-2100 nm. The spectrum is dominated by previously unobserved Stokes emissions and broad emissions in the visible.

High-power optical parametric chirped-pulse amplifier system with a 1.55 microm signal and a 1.064 microm pump.

We have designed and built a chirped-pulse parametric-amplifier system that utilizes a 10 Hz, 300 ps, Nd:YAG pump laser system; a 1.575 microm fiber oscillator and amplifier as the signal source; and rubidium titanyl phosphate and potassium titanyl arsenate nonlinear crystals. We obtained 260 fs, 30 mJ pulses centered at 1.550 microm, representing a gain of > 10(9) and a peak power of 100 GW. To our knowledge, these are the highest energy and peak power pulses ever produced in the 1.5-2.0 microm region

Time-resolved measurements of self-focusing pulses in air.

The spatial, spectral, and temporal properties of self-focusing 798-nm 100-fs pulses in air are experimentally measured with high-resolution, single-shot techniques at a set propagation distance of 10.91 m. The data, obtained with an initially collimated Gaussian beam, show significant evolution of spatial narrowing as well as temporal and spectral changes at intensities lower than those required for significant ionization of air.

The effect of dental implant spacing on peri-implant bone using the rabbit (Oryctolagus cuniculus) tibia model.

PURPOSE: This study investigated the effects of implant proximity on inter-implant bone height, density, and osseointegration using digital radiography and histology. MATERIALS AND METHODS: After a feasibility study, a total of 80 endosteal implants were placed in 20 New Zealand White Rabbit tibias. With the aid of a surgical jig, four 8.5-mm implants were placed in the medial aspect of the tibial crest at inter-implant distances of approximately 1, 1.5, and 3 mm. Standardized digital radiographs using a paralleling device were made immediately after placement of implants. Implants were allowed to osseointegrate for 90 days. After this healing period, the animals were sacrificed, and the standardized radiographs were repeated. The tibias were harvested, processed, and invested in epoxy. Sagittal sections were made from each specimen for histologic evaluation. The initial and postmortem digital radiographs were evaluated for inter-implant distances, vertical bone height changes over time and between implant pairs, and bone density changes over time and between implant pairs using a computer image analysis program and computer statistics program. RESULTS: The actual inter-implant distances were consistent in a range of 0.2 mm. Bone height increased significantly from presurgical levels at all 3 locations (p < .0005). Repeated measures analysis of variance comparing change in bone height at the 3 implant pair distances showed significant differences among the 3 (p = .002). Paired t tests showed that the amount of bone growth at the 1-mm separation site was significantly greater than the 1.5-mm site (p = .026) and the 3-mm site (p = .001), whereas bone growth at the 1.5- and 3-mm sites did not show significant differences (p = .162). A repeated measures analysis of variance comparing change in bone density showed no significant differences (p > .05) among the 3 inter-implant distances for either the 8-mm position (approximately crestal bone height) or the 6-mm position (approximately 2 mm subcrestal). CONCLUSION: Within the limits of this study, it seems placing implants closely together does not adversely affect bone height or density. Conversely, it seems that placing implants closer together may increase bone growth.

Disinfection of denture base acrylic resin.

STATEMENT OF PROBLEM: During repair or adjustments of acrylic resin removable complete and partial dentures, particles of the acrylic resin from the interior of the prosthesis may expose dental personnel to microbial health hazards if the prosthesis has not been thoroughly disinfected. PURPOSE: This study investigates the efficacy of a commercially prepared microbial disinfectant (Alcide) on the external and internal surfaces of acrylic resins. MATERIAL AND METHODS: Four groups of acrylic resin were incubated in an experimental model to simulate the oral environment over time. Specimens were treated in 2 groups, disinfected and not disinfected, and then further grouped by breaking and not breaking. Analysis was performed with microbial colony counts, SEM, and statistical analyses. RESULTS: Viable microorganisms still remain on the internal and external surfaces of treated resins. CONCLUSION: Chlorine dioxide reduces, but does not eliminate, viable microorganisms on these dental prostheses.

Photoelastic comparison of stress induced by using stainless-steel versus nickel-titanium spreaders in vitro.

The vertical force applied to an endodontic spreader generates stress along the canal walls. Recognizing the potential for this stress may reduce the incidence of vertical root fractures. A photoelastic acrylic model was fabricated to exhibit the stress produced during obturation of curved canals using the lateral condensation technique. Twenty standardized models simulating curved canals (32 degrees) were formed within PL-2 photoelastic acrylic resin blocks. The canals were fitted with a gutta-percha point, and either a stainless-steel or nickel-titanium finger spreader was inserted. An Instron 4502 universal testing machine applied a vertical force of 20 Newtons to the spreader. Quarter wave and polarizing filters were used with backlighting to generate the fringe patterns in the models. Photographs of the resulting stress lines showed that the stainless-steel spreaders created three areas of concentrated stress. The nickel-titanium spreaders induced stress patterns spread out along the surface of the canals, thus reducing the concentration of stress and the potential for vertical root fracture.

Effectiveness of chlorine dioxide in disinfection on two soft denture liners.

STATEMENT OF PROBLEM: Soft tissue denture liners frequently require replacement that necessitates complete removal from the denture base. A high speed lathe located in a "clean laboratory" is often used to facilitate removal of these materials, but it is unclear whether routine disinfection procedures reduce bacterial contamination sufficiently to prevent contamination of the laboratory. PURPOSE: The first phase of this study evaluated the effectiveness of 3-minute chlorine dioxide spray and immersion disinfection procedures on 2 denture liners (Coe Soft and Coe Comfort) and stainless steel specimens used as controls. The second phase evaluated the effectiveness of spray disinfection at time intervals of 1, 3, and 10 minutes. MATERIAL AND METHODS: Specimens made of soft denture liners attached to acrylic resin bases (10 per group) were contaminated with Escherichia coli, Staphylococcus aureus, and Candida albicans. Colony-forming units were counted after different disinfection techniques were applied. Kruskal-Wallis 1-way analysis of variance on ranks and an all pairwise multiple comparison procedures (Dunn's method) were used to test for significant differences among test groups at the P <.05 level of significance. RESULTS: Chlorine dioxide was effective against nonporous stainless steel specimens but was inadequate for denture liners at the recommended 3-minute time of disinfection. The immersion technique was more effective than the spray technique, but the difference was not significant. Increasing the time of disinfection did not significantly reduce the numbers of microorganisms. CONCLUSION: Coe Soft and Coe Comfort denture liners should be removed before entering the laboratory. These materials contain sufficient viable bacteria after routine disinfection procedures to cause contamination of the "clean laboratory."

Evaluation of resistance form of dislodged crowns and retainers.

STATEMENT OF PROBLEM: The concept of limiting taper has been described as a boundary between tapers that do and those that do not provide resistance form for a preparation. There is controversy as to whether this boundary that divides preparations with from those without resistance form translates clinically into a boundary for success. PURPOSE: This investigation evaluated the resistance form of abutments of crowns or retainers that have been dislodged to determine the clinical correlation between restoration dislodgment and lack of resistance form in the preparation. MATERIAL AND METHODS: Dies were fabricated from single crowns and retainers of fixed partial dentures that came loose and evaluated for resistance form. A total of 44 abutments were evaluated and included 1 incisor, 15 premolars, and 28 molars. Data from a previous study on the percentage of abutments lacking resistance form for restorations leaving a large dental laboratory was used for comparative statistical tests. RESULTS: Forty-two of the 44 abutments (95%) lacked resistance form. All molar abutments and 93% of premolar abutments lacked resistance form in one or more directions. The one incisor abutment did not lack resistance form. Chi-square test revealed a statistically significant difference in the percentage lacking resistance form between the group composed of clinical failure (uncemented crowns) and the group leaving a dental laboratory with P = .0005 for the molars, and P = .0005 for the premolars. CONCLUSION: The clinical dislodgment of cast restorations is associated with the lack of resistance form in the preparations. In this study, there was a relationship between clinical success or failure and the all-or-none nature of resistance form; dislodged crowns come almost exclusively from preparations with tapers that did not provide resistance form.

Radiographic verification of implant abutment seating.

STATEMENT OF PROBLEM: It is possible to incorrectly seat an abutment on an external hex implant. PURPOSE: This study investigated the theoretical and practical limits of radiographic verification of the complete seating of implant abutments on external hex implants. MATERIAL AND METHODS: A positioning device that could accurately place the film and/or tube head in any vertical relation desired relative to the implant and abutment was fabricated. For all records, a standard abutment was secured to the implant in both a fully seated position (closed) and with the abutment turned approximately 30 degrees and seated atop the implant external hex (open). Digital radiographs were made with the tube head fixed perpendicular to the implant and the film angled at 0, 5, 10, 15, 20, 25, 30, 35, 40, and 45 degrees. The film was then positioned parallel to the implant and the tube head was angled at 0, 5, 10, 15, 20, 25, 30, 35, 40, and 45 degrees. An image of each position was shown to 36 dentists and they were asked if the image was diagnostic for determining the status of the implant/abutment interface. RESULTS: The data were analyzed with a computer statistics program. The group with the tube head changed was analyzed with the Cochran's Q test and revealed a statistically significant (p < 0.0001) change in the diagnostic value of radiographs beginning at 20 degrees. The group with the film angle changed was analyzed with a Pearson chi-square and showed no statistical difference (p = 0.394) for the diagnostic value of any of the film angles. CONCLUSION: Maintaining the tube head to less than 20 degrees from perpendicular to the long axis of the implant resulted in a diagnostic radiograph, regardless of the angle of the film.

Comparison of occlusal contacts in maximum intercuspation for two impression techniques.

STATEMENT OF PROBLEM: At the insertion of a fixed prosthesis, occlusal interferences in maximum intercuspation are often present. PURPOSE: This study investigated and compared the accuracy of interocclusal relationships in maximum intercuspation for mounted casts obtained from a quadrant dual-arch impression technique and conventional full-arch impression techniques. MATERIAL AND METHODS: Comparisons were made between an intraoral interocclusal record and interocclusal records made on mounted casts. Irreversible hydrocolloid, reversible hydrocolloid, polysulfide, polyether, and polyvinyl siloxane were used for the full-arch impression technique. For the quadrant dual-arch impression technique, rigid polyvinyl siloxane and light-body polyvinyl siloxane injection materials were used. RESULTS: Statistical analysis revealed a statistically significant difference (p = 0.0017) in the median values among treatment groups. All pairwise multiple comparison procedures (Student-Newman-Keuls) indicated the average error of the quadrant dual-arch records was significantly different from the average error of each group of records produced with the full-arch techniques (p < 0.05). Comparison of the records of the full-arch impressions did not reveal any statistically significant differences. The average error of the full-arch records was 72 +/- 33 microns and the quadrant dual-arch average error was 5 +/- 5 microns. CONCLUSION: The quadrant dual-arch impression technique produced mounted casts with significantly more accurate maximal intercuspal relationships than mounted casts from full-arch impressions.

Artifacts in recording immediate mandibular translation: a laboratory investigation.

STATEMENT OF PROBLEM: Even though immediate mandibular translation has been extensively studied and analyzed, and its clinical significance emphasized, there is controversy as to whether it actually exists or whether it is just an artifact of the pantograph. PURPOSE: The aim of this study was to determine whether what appears to be pantographic evidence of immediate mandibular translation can actually be an artifact and, if so, to find a method to avoid it. MATERIAL AND METHODS: The first part of this article explains geometrically with computer vector graphics how pure rotation can produce a pantographic tracing on the horizontal plate that is identical to what would be seen for immediate mandibular translation. The second part of the article presents a technique that uses a modified pantograph that eliminates the rotational artifact and thus permits proper interpretation of true immediate mandibular translation. RESULTS: This study shows that pure rotation about the sagittal axis mimics immediate mandibular translation on a pantographic tracing when the plates are inferior to the transverse horizontal axis, produces scribings in an opposite direction for plates in a superior position, and produces no scribing when the plates are level with it. By modifying the pantograph so the tip of the scribing pin of the horizontal plate is level with the transverse horizontal axis, true immediate mandibular translation can most easily be differentiated from rotational artifact. CONCLUSIONS AND CLINICAL SIGNIFICANCE: Rotation can cause artifacts that mimic immediate mandibular translation. A technique to avoid this problem is presented. This technique provides the foundation for a valid evaluation of patients to determine whether true immediate mandibular translation exists and whether it is clinically important.

Cement removal from restorations luted to titanium abutments with simulated subgingival margins.

STATEMENT OF PROBLEM: The process of removing excess cement from subgingival margins after cementation of restorations to implant abutments may lead to scratching of the abutments or incomplete cement removal. PURPOSE: The purpose of this study was to investigate and to compare the surfaces of abutments after the removal of three cements (glass ionomer, resin, and zinc phosphate) by use of three instruments (gold coated scaler, rigid plastic scaler, and stainless steel explorer). MATERIAL AND METHODS: Six investigators removed zinc phosphate, glass ionomer, and resin cements with explorers, gold coated scalers, and rigid plastic scalers with a model simulating clinical conditions. The surface of Brånemark abutments with cemented restorations were examined with a microscope at 20x for scratches and cement remnants. RESULTS: Statistical analysis of the results were inconclusive about which combination of instrument and cement worked most effectively. CONCLUSION: A surprising amount of cement remnants and scratching of abutments was observed. Although the six investigators were experienced in prosthodontic and implant procedures, there was variation in the results of their cement removal.

The effect of primers and surface characteristics on the adhesion-in-peel force of silicone elastomers bonded to resin materials.

Facial prostheses, when used in conjunction with craniofacial implants, require a retentive matrix to hold attachments and/or magnets. The retentive matrix is usually fabricated with autopolymerizing acrylic resin or a visible light-polymerized resin. The purpose of this study was to compare the adhesion-in-peel force of a silicone adhesive to autopolymerizing polymethyl methacrylate and light-polymerizing urethane dimethacrylate gel with two surface textures: (1) pumice polish only or (2) pumice polish and bead retention, and two surface primers: (1) Dow Corning 1205 primer or (2) Dow Corning S-2260 primer. The 1205 primer produced an adhesion-in-peel force that was statistically significantly stronger (p < 0.05) regardless of which type of resin or surface preparation was used.

Foreign body aspiration in dentistry: a review.

This article reviews the dangers of aspirating foreign bodies of dental origin. Two illustrative cases are presented, including an unusual case involving aspiration of an elastomeric impression material. The authors describe the techniques used to identify the foreign body. A radiodensimetric study of four impression materials demonstrates the difficulty of identifying most impression materials. The authors also present some strategies for reducing the risk of aspiration during dental procedures.