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Biomedical subjects

G N Graser

Publications and source records attributed to G N Graser.

At least 19 recordsLinked to original sources
PubMed2001

Effect of soldering on metal-porcelain bond strength in repaired porcelain-fused-to-metal castings.

STATEMENT OF PROBLEM: Chemical bonding plays a major role in the adherence between metal and porcelain. The formation of an oxide layer on solder material has not been described in the literature. It is unknown whether the application of solder negatively affects the bond strength between porcelain and metal. PURPOSE: This in vitro study assessed the effect of solder on the bond strength between metal and porcelain. MATERIAL AND METHODS: Forty 20 x 6 x 0.5 mm patterns were divided into test (20) and control (20) groups. Test samples were perforated and repaired with solder, and 2 layers of opaque and dentin porcelain subsequently were applied on all samples. The samples were subjected to a 3-point flexural test on a screw-driven mechanical testing machine at a crosshead speed of 0.5 mm/min. Failure type (adhesive vs cohesive) was quantified by digitizing photographs of test and control samples. Three samples in each group also were examined with an SEM coupled with an x-ray energy-dispersive spectroscopy apparatus (SEM/EDS). Means and standard deviations of loads at failure, sample thickness, and surface area covered with porcelain were calculated, and data were analyzed with Student t test (P < or = 0.05). RESULTS: The mean fracture load for test samples was significantly greater than for control samples (P = 0.0038). Test samples also were significantly thicker (mean thickness difference 0.14 mm) (P = 0.0001). When the data were controlled for thickness by using a multiple linear regression analysis, no significant difference was found (P = 0.68). Test samples had a greater surface area covered with opaque porcelain (P = 0.0006) as determined by visual inspection. CONCLUSION: In this study, soldered and nonsoldered samples did not show any significant difference in porcelain-to-metal bond strength. Visual analysis revealed a significant difference in the amount of porcelain remaining on the fracture surface of the test and control samples; a complete quantitative elemental analysis with SEM/EDS is in progress.

Dental Porcelain↗
PubMed2000

Effect of ring liner and casting ring temperature on the dimension of cast posts.

STATEMENT OF PROBLEM: If a post does not fit passively, binding with the radicular tooth structure occurs, possibly increasing the risk for root fracture. Therefore, it is necessary to fabricate slightly undersized cast posts to allow for passive fit and cement placement. Shrinkage of the mold cavity may be a desired effect during the casting of posts. PURPOSE: This study evaluated the influence of: (1) a cellulose ring liner, and (2) a lower casting temperature of the metal ring, on the dimensions of a cast post. MATERIAL AND METHODS: Eighty plastic posts were divided in 4 equal groups (group 1, 815 degrees C, liner; group 2, 815 degrees C, no liner; group 3, 600 degrees C, liner; and group 4, 600 degrees C, no liner), invested in phosphate-bonded investment and cast with a noble alloy. Posts were measured at 2 locations, the tip and base, before and after casting. RESULTS: Investing in a lined metal ring and using a casting ring temperature of 815 degrees C (group 1) resulted in markedly oversized posts (tip: +25.8 microm; base: +20.3 microm). The absence of the cellulose liner in the casting ring (group 2) decreased the expansion of the investment producing slightly oversized castings (tip: +9.75 microm; base: +4.52 microm). Lined rings that were heated to a final temperature of 600 degrees C (group 3) produced posts that were oversized (tip: +16.65 microm; base: +11.05 microm). Final casting ring temperature of 600 degrees C and the absence of a cellulose liner (group 4) resulted in posts slightly undersized (tip: -4.1 microm; base: -2.2 microm). CONCLUSION: The use of 2 casting ring temperatures (815 degrees C or 600 degrees C) and the influence of a ring liner were investigated. Decreasing the casting ring temperature from 815 degrees C to 600 degrees C and the absence of a ring liner significantly decreased the dimensions of a cast post.

Analysis of Variance↗
PubMed2000

Influence of metal surface finishing on porcelain porosity and beam failure loads at the metal-ceramic interface.

STATEMENT OF THE PROBLEM: Investigators suggest that metals should be finished in 1 direction before porcelain application to minimize metal irregularities and trapped contaminants. These irregularities are thought to be focal points for porosity and crack propagation. PURPOSE: This study investigated the influence of metal finishing and sandblasting on (1) porosity production at the porcelain-metal interface, and (2) porcelain-metal beam failure load. MATERIAL AND METHODS: Eighty cast metal samples were divided into 4 test groups: (A) bidirectional finish/sandblasting; (B) unidirectional finish/sandblasting (C) bidirectional finish only; and (D) unidirectional finish only. The porcelain applied was 1.5 mm thick. Samples were sectioned longitudinally. Half of the samples were subjected to a 3-point flexural test. The remaining samples were sectioned into 4 slices and were examined with a light microscope (x500). Number and diameter of porosities at the metal-porcelain interface were recorded. RESULTS: Mean loads at failure (lbs) were as follows: A, 11.1 +/- 1.3 (5.03 +/- 0.58 Kg); B, 11.2 +/- 1.7 (5. 08 +/- 0.77 Kg); C, 4.0 +/- 1.8 (1.81 +/- 0.81 Kg); and D, 5.0 +/- 2. 1 (2.26 +/- 0.95 Kg). Groups A and B were significantly different from groups C and D (P<.0001). Nonsandblasted samples (C and D) exhibited a separation at the ceramometal interface, which prevented quantification of porosity size and number. Average interface porosity sizes (microm) (A, 8.99 +/- 1.92; B, 10.03 +/- 1.86) showed no significant difference. The mean interface porosity number (A, 62. 3 +/- 16.02; B, 67.4 +/- 10.01) showed no significant difference. CONCLUSION: Direction of metal finishing did not affect the porosity number and size at the ceramometal interface or the beam failure loads. Sandblasting increased the beam failure loads. Nonsandblasted samples showed detachment of the porcelain from the metal.

Aluminum Oxide↗
PubMed1999

Face-bow record without a third point of reference: theoretical considerations and an alternative technique.

Accurate mounting of dental casts is achieved by transferring the tridimensional spatial relationship of the maxillary arch to an articulator. A face-bow is used to transfer this relationship to the articulator, usually by relating the face-bow to a plane of reference. The most common reference plane is the Frankfort plane, which has been assumed to be horizontal when the patient is in the natural head position. The axis-orbitale plane has also been considered horizontal and used as reference. However, it has been shown that both planes are not horizontal, and mounting a maxillary cast according to these planes can result in an inaccurate mounting. This article describes an alternative procedure for face-bow transfer without a plane of reference, and uses the angular relationship between the occlusal plane and the condylar path to mount the maxillary cast on the articulator. The elimination of a reference plane, to which relate the functional determinants of occlusion, avoids an additional source of error during the mounting procedure.

Cephalometry↗
PubMed1998

Long-term reinforced fixed provisional restorations.

Extensive prosthodontic treatment often requires fabrication of long-term provisional restorations. Numerous materials and techniques have been described for prolonged insertion of interim restorations. This article describes a procedure for fabrication of long-term reinforced heat-processed provisional restorations based on a diagnostic wax-up. Reinforced heat-processed provisional restorations reduced flexure, which minimizes progressive loss of cement and diminished the possibility of recurrent decay. Occlusal stability and vertical dimension were maintained because of greater wear resistance. Occlusion, tooth contours, and pontic design developed in the provisional restoration were duplicated in the definitive restoration. The use of a matrix from a diagnostic wax-up facilitated fabrication of the prosthesis, and made the procedure less time-consuming and more predictable.

Acrylic Resins↗
PubMed1998

Alternative procedure for making a metal suprastructure in a milled bar implant-supported overdenture.

The predictability of implant-supported prostheses has been established. Although the original Brånemark design has been successfully used in the mandible, esthetic, speech, and hygiene-related problems have been reported in maxillary fixed prostheses. Implant-overdentures can overcome some of the problems encountered in maxillary fixed prostheses. Milled-bar implant-supported overdentures fabricated by electric discharge machining are characterized by stability similar to a fixed prostheses and are removable for hygiene procedures. However, the procedure is costly and requires highly trained technicians. An alternative procedure to produce an accurately fitting metal suprastructure is presented. This procedure does not require additional technical skills and uses instruments and materials that are readily available and relatively inexpensive. The use of simple and easy to replace attachments allows repairs to be performed in the dental office, thus reducing maintenance cost. The overall result is a prosthesis that incorporates the features of a spark erosion overdenture at a fraction of the cost and that is available to a broader patient population.

Costs and Cost Analysis↗
PubMed1994

Fracture strength of full-contoured ceramic crowns and porcelain-veneered crowns of ceramic copings.

This is vitro study compared the fracture strength of Dicor ceramic crowns with a 1 mm axial wall thickness and a 2 mm occlusal thickness with Dicor copings veneered with Vitadur-N or Dicor-Plus porcelain to create similar contours. Tooth preparations for complete crowns were made on human molars with a 10-degree total convergence and a 1 mm shoulder. The artificial crowns were internally etched, given an application of silane, and cemented with a dual-cured resinous cement. After thermocycling, each sample was loaded to failure with a vertical load on the occlusal surface. There were no significant differences in fracture strength between full-contour Dicor crowns and crowns of copings veneered with either Vitadur-N or Dicor-Plus porcelain.

Analysis of Variance↗
PubMed1992

Control of microbial contamination with commercially available cleaning solutions.

The elimination of cross-contamination from operatory to laboratory is required for effective infection control. This study determined whether microbial cross-contamination occurs during cleaning of dental prostheses with an ultrasonicator and examined ways to reduce or eliminate the contamination that might occur. The antimicrobial activities of a temporary cement remover and tartar and stain remover were compared with deionized water and a known strong antimicrobial agent. All solutions were assessed without and with ultrasonication. The microbicidal strains were cultured in brain-heart infusion broth, with and without acrylic resin slabs, and the organisms were killed either without or with sonication and without or with acrylic resin slabs. Further testing with natural plaque-contaminated denture materials is warranted.

Acrylic Resins↗
PubMed1992

Considerations for planning for and fabricating complete dentures.

During the past year, studies have been completed to advance our knowledge of the diagnosis and treatment of the edentulous patient. The need for pretreatment radiographs on every edentulous patient is not always indicated. Advances in preprosthetic surgery help to improve the predictability of these procedures. New techniques for establishing the vertical dimension of occlusion may allow this to become a more objective measurement. Evaluation of dental materials for use with complete dentures continues, with soft liners and the use of microwave energy for curing denture resin just two areas of interest. A recent study showed a very high prevalence of signs and symptoms of craniomandibular disorders among complete denture wearers. Methods for its treatment are discussed. The use of increased infection control procedures in the dental office and laboratory have created a need to evaluate the effects of disinfecting agents on the dental prosthesis. The removable complete denture remains an effective alternative for the replacement of missing teeth.

Dental Occlusion↗
PubMed1991

Dimensional accuracy of denture resin cured by microwave energy.

Microwave processing has several time-saving advantages over conventional processing of denture base resins. Little is known about the adaptation of bases processed by microwave radiation to the cast and the mouth. Comparisons were made in five regions of the palate and ridge. The microwave-processed denture bases had equal or better dimensional accuracy than conventionally processed bases.

Acrylic Resins↗
PubMed1991

Porosity of denture resin cured by microwave energy.

This study compared porosity of denture resin cured by microwave energy to denture resin cured by the conventional heat method. Seven groups of 10 samples each were tested. The control samples of methyl methacrylate monomer were cured in a curing tank at 165 degrees F for 9 hours. Four of the six experimental groups, consisting of samples made from Micro Liquid monomer (H.D. Justi Co., Oxnard, Calif.), were cured by microwave energy at varying wattages and times. The other two experimental groups contained samples of methyl methacrylate monomer cured by microwave energy. No significant differences were found in mean porosity between the control group and the four groups of microwave-processed samples that used Micro Liquid monomer. The two groups of microwave-processed samples of methyl methacrylate monomer showed a significantly higher mean porosity.

Acrylic Resins↗
PubMed1991

Immediate implantation of a pure titanium implant into an extraction socket: report of a pilot procedure.

The conventional osseointegration protocol calls for waiting up to 12 months for ossification of an extraction socket to heal before placing an endosseous implant. In this study the possibility of placing a pure titanium implant directly into an extraction socket immediately after extraction was investigated. A pure titanium Nobelpharma 10-mm implant was placed into a central incisor extraction socket of a stump-tailed monkey and allowed to heal for a period of 6 months, followed by functional loading of the implant. The implant was osseointegrated on a clinical and histological level. This pilot study suggests that pure titanium implants have the potential to integrate when placed immediately after extraction of the teeth and warrants further investigation.

Animals↗
PubMed1990

Predoctoral removable prosthodontics education.

As the 21st century is approached, changes are occurring that directly relate to removable prosthodontics at the undergraduate level. Edentulism will continue to decline, although the need for complete dentures will diminish slowly because of the replacement needs for the existing edentulous population. In the short- to medium-term future, partial edentulism will increase in the older population at the expense of total edentulism. Therefore, the need for removable partial dentures will increase, but subsequently will decline. In the long-term, tooth loss, regardless of etiology, will be reduced. However, the replacement of lost teeth is unlikely to disappear completely as a needed dental service. With 73% of dental schools reporting inadequate or marginal numbers of complete denture patients, Meskin and Entwistle have identified a shortage of patients needing removable prostheses. On the other hand, 50% of the schools report a surplus of removable partial denture patients. Dental school curriculum time related to prosthodontics has declined significantly over the past 20 years. However, over the past 10 years it has risen slightly. Techniques that are taught in dental schools are frequently not being used in practice. Yet the practitioner's interest in removable prosthodontics as it relates to new techniques and materials remains high according to a 1988 survey of Academy of General Dentistry members. Removable prosthodontics was rated first in regards to continuing education courses desired by its members. There are two basic objectives stated in the prologue of the Council on Dental Education Directive on Accreditation Standards. First, faculties are ultimately responsible for the quality of care rendered to the patient population by students.(ABSTRACT TRUNCATED AT 250 WORDS)

Curriculum↗
PubMed1990

Removable partial overdentures for special patients.

Removable partial overdentures are an option that should be considered by every dentist who is involved with cosmetic dentistry or dentistry for the older adult. The rationale, indications, and technique have been described for providing an aesthetic, functional prosthesis that is also conservative in nature. The reversibility of the procedure allows the patient the opportunity to pursue other forms of treatment should the result not meet his or her expectations. For appropriately selected special patients, the results can be extremely gratifying for both the patient and dentist.

Adult↗
PubMed1989

Resolving esthetic and phonetic problems associated with maxillary implant-supported prostheses. A clinical report.

A technique has been presented for placement of an implant prosthesis without a visually detectable space between the prosthesis and soft tissue or visibility of the metal abutments. The prosthesis permits better phonetics and greatly improved esthetics including better lip support. Proper presurgical planning and careful assessment of the potential level of home care are especially important when this technique is used.

Adult↗
PubMed1989

Verification of centric relation.

This article discusses the clinical uses of Centric Check Points in the edentulous and partially edentulous patient. It details the technique for centric verification, and the correction procedure if an error is discovered.

Dental Articulators↗