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Biomedical subjects

F M Gardner

Publications and source records attributed to F M Gardner.

At least 19 recordsLinked to original sources
PubMed2001

2000 Judson C. Hickey Scientific Writing Award. Effect of impression materials on hybridized dentin.

STATEMENT OF PROBLEM: Tooth sensitivity after crown preparation is not an uncommon complication. For dentin bonding agents to be effective in preventing postoperative sensitivity, they must remain intact throughout the fixed prosthodontic procedures. PURPOSE: This study evaluated, by analyzing the change in dentin permeability, whether a dentin bonding agent was removed from the surface of prepared teeth in the process of making an impression. MATERIAL AND METHODS: Eighty extracted human molars were cut horizontally apical to the cemento-enamel junction and horizontally through the middle of the clinical crown. The specimens were prepared to measure dentin permeability (fluid flow rate, Lp). The specimens (n = 40) were randomly assigned to either the primer-only group (PO) or the primer + adhesive group (PA). Five different impression materials were tested: vinyl polysiloxane, polyether, polysulfide, irreversible hydrocolloid, and reversible hydrocolloid. Dentinal permeability was measured after smear layer removal (control, etched Lp = ELp), after coating the dentin with either PO or PA (coated Lp = CLp), and again after making an impression (impression Lp = ILp). A 1-way ANOVA of differences, followed by a Student-Newman-Keuls test (alpha=.05), was performed to compare the ELp, CLp, and ILp values. RESULTS: A statistically significant difference was found between the CLp and ELp for all 5 impression materials in both groups (PO and PA). No difference was found between the CLp and ILp values for any of the impression materials. No significant differences were found between any of the 5 impression materials or either of the dentin surface treatments (PO or PA) when measuring the CLp and ILp. CONCLUSION: The dentin bonding agent had a significant effect in decreasing the Lp of the treated specimens. None of the impression materials significantly affected the measured CLp. There was no significant difference between the PO or PA (CLp) values.

Acid Etching, Dental↗
PubMed2001

The effect of storage time on the accuracy and dimensional stability of reversible hydrocolloid impression material.

STATEMENT OF PROBLEM: It has been stated that reversible hydrocolloid impression material must be poured immediately to remain accurate. This may not be true with modern formulations of reversible hydrocolloid. The accuracy of the impression, if kept at 100% humidity for varying periods, may not be affected as critically as has been suspected. PURPOSE: The purpose of this study was to evaluate the effect of storage time in a 100% humidity environment on the accuracy of gypsum casts poured from a newer formulation of reversible hydrocolloid impressions. MATERIAL AND METHODS: With the use of a stainless steel master model, 5 standardized reversible hydrocolloid impressions were made for each time interval tested (n = 5). Impressions were made with the use of both Cartiloid blue syringe and Slate tray reversible hydrocolloid material (both manufactured by Van R) to simulate a common clinical protocol. Six groups, representing times at 0, 30, 60, 120, 180, and 210 minutes, were evaluated for a total of 30 specimens. Gypsum casts were measured with a traveling microscope, and dimensional changes were compared between groups with ANOVA and Tukey intervals (alpha=.05). RESULTS: Measurements made up to and including the 60-minute storage time showed clinically acceptable distortion levels. These measurements were similar to the metal model and the gypsum casts poured at time 0 minutes. The only statistically significant difference between the gypsum cast and the metal master model was the distance between abutments at storage time 180 minutes (master model = 30.04 mm [SD 0.001]; gypsum casts = 29.944 mm [SD 0.076]). This difference was -91 microm (P=.002). In general, the gypsum abutments became wider and shorter with time. There was no significant difference between any gypsum abutment in regard to width or height when compared with the metal master model for all the storage times tested. However, as time increased, measurement became harder to accomplish, leading to a larger standard deviation and less reliable results. The distance between abutments remained relatively constant for storage times up to and including 60 minutes. For times longer than 60 minutes, the distance between abutments was reduced and more difficult to read. The distance between abutments at the 3-hour storage time was significantly different than the metal standard and time 0 gypsum casts. CONCLUSION: If a discrepancy of 78 microm (twice the 39 microm single margin opening) is clinically acceptable, then the results of this study show that this type of reversible hydrocolloid can be stored in 100% humidity for at least 60 minutes.

Analysis of Variance↗
PubMed2000

Effect of dentin desensitizers and cementing agents on retention of full crowns using standardized crown preparations.

STATEMENT OF PROBLEM: Past research has not controlled preparation surface area when examining the influence of dentin desensitizers on the retentive strength of cemented cast crowns, leading to inconsistent results. PURPOSE: This research controlled crown preparation surface area and evaluated the effect of various dentin desensitizers and conventional cementing agents on the in vitro retentive strength of cast crowns. METHODS AND MATERIAL: Freshly extracted human molars were prepared for a standardized crown preparation (26 degrees total convergence, 4 mm axial height) with a custom-made pantograph. Dentin desensitizers included none (control), a polymerizable material (All-Bond 2), and a nonpolymerizable desensitizer (Gluma Desensitizer). Cementing agents included zinc phosphate (Fleck's), glass ionomer (Ketac-Cem), resin-modified glass ionomer (Fuji II), and resin cement (Panavia 21). Twelve teeth were prepared for each test condition (144 teeth total). Individual castings were made from a base metal alloy (Rexillium III). Crowns were removed after storage at 26 degrees C for 48 hours at 100% relative humidity using a universal testing machine at a crosshead speed of 1.27 mm/min. The proportion of cement retained on the tooth and casting after debonding was quantified according to treatment. Statistical treatment included 1- and 2-way ANOVAs, followed by the Tukey-Kramer post hoc test at a preset alpha of 0.05.Results. Resin cement exhibited the highest retentive strength and all dentin treatments resulted in significantly different retentive values (All-Bond 2 (5.68 +/- 0.70 MPa) > control (4.67 +/- 0.48 MPa) > Gluma (4.12 +/- 0.37 MPa)). Retention of resin-modified glass ionomer was between the resin cement and glass ionomer groups: All-Bond 2 (3.46 +/- 0.26 MPa) > Gluma (2.81 +/- 0.15 MPa) = control (2.96 +/- 0.18 MPa). Conventional glass ionomer values were between those of Fuji Plus and zinc phosphate groups: All Bond 2 (2.23 +/- 0. 20 MPa) = control (2.36 +/- 0.20 MPa) > Gluma (1.98 +/- 0.23 MPa). Zinc phosphate had the lowest retention values: control (1.68 +/- 0. 08 MPa) > Gluma (0.81 +/- 0.11 MPa) > All-Bond 2 (0.67 +/- 0.14 MPa). The majority of cement was retained on the debonded tooth surface versus the casting, with the exception of zinc phosphate when used with dentin pretreatments. CONCLUSION: Controlled crown surface areas reduced the variation in strength values permitting high discrimination among retention values of desensitizer/cement combinations. In all but 1 combination, Gluma desensitizer significantly decreased crown retention. With resin cement and resin-modified glass ionomer, use of All-Bond 2 desensitizer significantly increased crown retention values.

Analysis of Variance↗
PubMed1998

An in vivo study of voluntary mandibular lateral translation concerning its existence, magnitude, and timing.

STATEMENT OF PROBLEM: The existence of mandibular lateral translation and the approaches to its measurement and interpretation by using a pantograph are controversial. PURPOSE: This study evaluated the validity of using a pantograph to measure mandibular lateral translation and analyzed human pantographic tracings to determine whether they exhibited mandibular lateral translation. MATERIAL AND METHODS: A pantograph was modified by adding 2 posterior horizontal recording tables and styli at the transverse horizontal axis. Pantographic tracings of 25 human subjects were compared with the corresponding theoretically determined values for tracings that exhibited only rotation with no translation. Differences in the tracings at 2 pantographic recording table locations, relative to the transverse horizontal axis, were also compared. RESULTS: The character of the lateral component of 100 pantographic tracings all differed from the lateral component of theoretically determined values for pure rotation. In 64% of tracings, over 50% of the total mandibular lateral translation occurred by the first 1 mm of forward movement of the nonworking side condyle. In 94% of tracings, more than 50% of the translation had occurred in the first 3 mm of forward movement. For the pantographic system used, the amount of mandibular translation represented in the tracing was not changed by altering the posterior horizontal recording table position in the anterior-posterior direction, relative to the transverse horizontal axis. CONCLUSION: All subjects showed evidence of mandibular lateral translation. New definitions for timing of mandibular lateral translation are proposed. Of the tracings, 64% were classified as exhibiting early translation, 30% as intermediate, and 4% as late mandibular lateral translation.

Adult↗
PubMed1998

Effect of heating delay on conversion and strength of a post-cured resin composite.

Physical property enhancement in light-cured resin composites from post-cure heating is attributed to free radicals created during initial photocuring, the number of which decreases following initial light-curing. Clinically, it is important to know when the number of remaining free radicals is too low to provide for additional conversion of monomer in post-cure-heated specimens. The hypothesis tested is that the potential for additional conversion in post-cure-heated resin composite restorations is dependent upon the time after initial light-curing at which the specimen is exposed to heat treatment. This research examined the effect of delay in post-cure heating after initial photo-activation on strength and monomer conversion of a commercial resin composite material. Discs (10 x 1 mm) of Herculite XRV (Kerr/Sybron, Orange, CA) were photocured at standardized conditions. One group was left unheated, and another was subjected to post-cure heating (Brilliant DI-500, Coltène AG, Altstätten, Switzerland) at the following times after being light-cured: 5 and 30 min, and 6, 24, 48, 72, 96, and 120 hrs. After the appropriate delay time, unheated and heated specimens (n = 10) were tested for biaxial flexural strength at a constant stressing rate. Recovered, fractured strength specimens (n = 10) were analyzed for cure by means of IR spectroscopy. Post-cure heating increased strength over that of the unheated specimens only for the shortest delay times: 5 or 30 min. Thereafter, strength values were statistically equivalent (p < 0.05). Delay in heating did not significantly enhance strength of post-cure-heated specimens, but delay in time did improve strength of the unheated groups. The greatest monomer conversion was obtained when post-cure heating was applied within 6 hrs following light-curing. The difference in cure between unheated and heated specimens remained significant up to 96 hrs of delay. Flexural strength of post-cure-heated specimens remained unchanged with time delay for heating specimens. Maximal monomer conversion of post-cured specimens is obtained only within 6 hrs of light-curing. The potential for additional conversion arising from post-cure heat treatment is dependent upon the time following initial curing at which heat is applied following initial light-curing. However, delay in heat application has no influence on flexural strength.

Analysis of Variance↗
PubMed1997

In vitro failure load of metal-collar margins compared with porcelain facial margins of metal-ceramic crowns.

PURPOSE: This in vitro study compared the load necessary to cause porcelain failure on traditionally fabricated metal-ceramic crowns cemented to metal tooth analogs with two different types of margins. MATERIAL AND METHODS: Metal-ceramic crowns were constructed with either metal facial collars or porcelain facial margins. The metal tooth analogs were embedded in polymethyl methacrylate resin blocks, so that a load applied to the lingual surface compressed the facial margins. Increasingly greater loads were applied to specimens until failure occurred and the failure load values of all specimens were statistically evaluated. RESULTS: The load required to cause porcelain fracture in the crowns with porcelain facial margins was statistically significantly greater than the load required to cause porcelain fracture for crowns with metal collars (p < 0.02).

Cementation↗
PubMed1997

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.

Artifacts↗
PubMed1995

Fabrication of a guide for radiographic evaluation and surgical placement of implants.

The use of guides for radiographic evaluation and surgical placement of dental implants can improve the final outcome of treatment for patients receiving implants. This article describes a technique in which a guide is fabricated for radiographic evaluation of implant placement and also serves as a surgical guide for placement of the implants for a patient with severely worn dentition.

Anatomy, Cross-Sectional↗
PubMed1994

A comparison of impression techniques for the CeraOne abutment.

PURPOSE: This study measured the accuracy of two impression techniques recommended by Noblepharma to be used with their CeraOne single tooth implant restoration. The first technique was to lute the impression transfer coping to the impression tray with autopolymerizing acrylic resin. The second was to leave the transfer coping free-standing in the impression material. MATERIALS AND METHODS: Thirty-five samples were made of a polyvinyl impression of the CeraOne transfer coping free-standing in the set impression material. Thirty-five samples were made of a polyvinyl impression of the CeraOne transfer coping luted to the impression tray with autopolymerizing acrylic resin. A jig was fabricated and used to record the spatial relations of the impressions and the transfer copings in reference to the jig. A light microscope was used to measure the distance between fixed markings on pressure sensitive paper, representing impression variations. RESULTS: The mean discrepancy in the horizontal plane for nonluted impressions was 0.094 mm, and for luted impressions, it was 0.275 mm. The mean discrepancy in the vertical plane for nonluted impressions was 0.154 mm, and for luted impressions, it was 0.192 mm. The differences found between the group with the luted impression tray and the group with the nonluted impression tray were found to be statistically significant. CONCLUSIONS: The more accurate of the two techniques is to transfer the impression coping without luting it to the impression tray.

Analysis of Variance↗
PubMed1993

The effect of selective die spacer placement techniques on the seatability of castings.

It has been reported in the literature that impingement of the casting at the axial-occlusal line angle of the tooth preparation may be a major cause of incomplete seating following cementation. It has been suggested that an additional coat of spacer applied to these areas on the laboratory die before the fabrication of the casting may alleviate this discrepancy. This study evaluated the effect of three die spacer placement techniques on the seatability of cemented castings. Results showed no statistical difference in seating between castings made with conventional relief and those made with additional relief at the axial-occlusal line angles. Castings relieved exclusively at the axial-occlusal line angles exhibited significant post-cementation marginal openings.

Analysis of Variance↗
PubMed1993

New guidelines for preparation taper.

The purpose of this article is to provide new guidelines for minimally acceptable preparation taper by developing a theoretical mathematical foundation based on principles of resistance form. Yes and no are the possible answers to the question, "Does a preparation have resistance form?" This dual nature is useful because in graphing resistance form as a function of taper, potential tapers on the x axis are divided into two groups with an exact dividing point. Tapers less than this dividing point provide resistance form; tapers larger or equal do not provide resistance form. This dividing point makes a reasonable standard for minimally acceptable taper. Average tapers are defined as the limiting average taper and are mathematically determined to equal 1/2 arcsin (H/B), where H is the height of the preparation and B is the base. From this equation, the taper required to provide resistance form for an individual preparation can be calculated by using the preparation's height to base ratio. The equation can also be used to provide guidelines by tooth group. Dies of a prosthodontist were saved and sorted by group (incisors, canines, premolars, and molars). Measurements of 30 dies from each of these groups were used to calculate the average (H/B) ratios and standard deviations. Calculating the limiting average taper by using the average height-to-base ratio minus two standard deviations provides the dividing point taper that is acceptable for over 97% of the preparations. The values calculated are: 29 degrees for incisors, 33 degrees for canines, 10 degrees for premolars, and 8.4 degrees for molars.(ABSTRACT TRUNCATED AT 250 WORDS)

Bicuspid↗
PubMed1987

Composite dowels and cores: effect of moisture on the fit of cast restorations.

A study was undertaken to evaluate the effect of interim restorations on the dimensional stability of composite post and core buildups subjected to moisture during the fabrication of cast restorations. Dimensional change associated with composite dowel and core buildups did not significantly alter the fit of cast restorations compared with natural teeth under the same conditions. The use of composite dowels and cores for the restoration of endodontically treated teeth is not contraindicated because of potential dimensional instability of the resin when exposed to moisture. Well-fitting interim restorations for either natural teeth or composite dowel and core buildups improved the fit of cast restorations 23% to 36%.

Composite Resins↗
PubMed1986

A survey of crown and fixed partial denture failures: length of service and reasons for replacement.

The mean length of service of all restorations observed in this study was 8.3 years. Caries was the most common cause of failure, affecting 22.0% of the units failed and leading to the necessity for replacement of 24.3% of the units observed. Mechanical problems accounted for 69.5% of the failed units as opposed to 28.5% for oral disease. Resin veneer metal crowns provided the longest service of all crown types observed (13.9 years) and failed most frequently because of worn or lost veneers. The complete veneer metal crown had a life span of 6.1 years and was most likely to fail because of caries or defective margins. Ceramic-metal crowns also showed a relatively short period of service at 6.5 years, needing replacement primarily because of porcelain failure or poor esthetics. The resin-veneer metal crown also provided the longest service as a retainer, with a mean length of service of 14.7 years. This was closely followed by the partial veneer retainer (14.3 years), while the ceramic-metal retainer had the shortest life span (6.3 years). No apparent relationship was found between the span of prosthesis and its length of service. The six-unit canine-to-canine fixed partial denture exhibited the greatest longevity of the prostheses studied (10.4 years), while the two-unit cantilever fixed partial denture provided a mean of only 3.7 years of service before replacement was required.

Crowns↗
PubMed1985

A comparison of healing and pain following excision of inflammatory papillary hyperplasia with electrosurgery and blade-loop knives in human patients.

Twenty human patients participated in a study designed to compare electrosurgery with blade-loop knives for the excision of inflammatory papillary hyperplasia in a split-mouth study. Questionnaires were used to assess pain and patient preference during a 2-week postoperative period, and photographs were made to chronicle the healing process. Healing occurred at approximately the same rate following each procedure. The majority of subjects did not perceive a difference in discomfort with either technique on the day of surgery or at any time during follow-up. Of those who did have a preference, a significant majority favored electrosurgery on the day of treatment. This preference became statistically insignificant on the second postoperative day and beyond.

Adult↗