Comparison of cutting rates among single-patient-use and multiple-patient-use diamond burs.

PURPOSE: The purpose of this study was to compare the volumetric cutting rates of 6 cylindrical-shaped single-patient-use and 2 cylindrical-shaped multiple-patient-use diamond burs using a machinable ceramic material. The degree of wear among burs from each type was also compared using scanning electron microscopy. MATERIALS AND METHODS: Six types of single-patient-use diamond burs and 2 types of multiple-patient-use diamond burs with similar cylindrical shape and dimensions were selected. Five burs of each type were evaluated using a high-speed handpiece mounted on a custom testing device. Using a 6-mm cutting length of each bur, 20 cuts, each 12.2-mm long, were made at exactly one half the diameter of the bur. Mean volumetric cutting rate through the ceramic substrate for Cuts 1 through 20 was calculated for each bur type in cubic millimeters prepared per second. A repeated measures analysis of variance (alpha = 0.05) and post hoc one-way analysis of variance with Scheffé's test was used to compare cutting rates among bur types for Cuts 2, 10, and 20. The topography of one bur from each group was evaluated with scanning electron microscopy after Cut 2 and again after Cut 20. RESULTS: For Cut 2, the mean cutting rates ranged from 3.3 to 5.3 mm3/s. The mean cutting rates for all bur types decreased approximately 20% by Cut 20. Bur type and length of use significantly influenced cutting rate (p < .002). However, only one type of single-patient-use diamond bur had a significantly lower mean cutting rate after Cut 2, 10, and 20, compared with other single- and multiple-patient-use diamond burs. Scanning electron microscopy showed all burs exhibited wear of diamond particles, as well as loss of diamond particles and binder. CONCLUSIONS: Five of six single-patient-use diamond burs had mean volumetric cutting rates through a ceramic that were similar to 2 multiple-patient-use diamonds for as many as 20 cuts. The gradual reduction in cutting rate during the 20 cuts for all bur types was a result of bur wear.

Bone ingrowth to implant surfaces in an inflammatory arthritis model.

Many studies have shown enhanced bone apposition to implants coated with hydroxyapatite, but the optimum implant texture, especially in abnormal trabecular bone, is unclear. The purpose of this project was to evaluate the histological and mechanical properties of cylindrical implants with three different surface textures that were placed in the cancellous bone of the distal femur of the rabbit after the production of an inflammatory knee arthritis. The three implant surfaces included a beaded surface (Group A), a beaded surface coated with hydroxyapatite (Group B), and a smooth surface coated with hydroxyapatite (Group C). The right knees of 36 rabbits were injected with carrageenan twice a week for 2 weeks. Then bilateral implantations were performed, with 12 rabbits in each group receiving identical implants in the right and left knees. The rabbits were killed 6 weeks after surgery. Mechanical (push-out test) and histomorphometric analyses were performed to determine the quality and quantity of bone ingrowth. In Group A, there was virtually no direct contact (a 20-60-microm clearance) between the bone and the beaded surfaces. Direct contact between the bone and the implant surfaces was seen in Groups B and C. The thickness and number of trabeculae were smaller on the arthritic side than on the control side for all groups but were not different between groups for either the control or the arthritic side. Mechanical testing showed that the shear strength of the interface was weaker on the arthritic side in all groups. The results suggest that inflammatory arthritis induced by carrageenan may influence the quality of local bone (osteopenic changes) and hence compromise the bone apposition and mechanical stability of the interface between the implant and bone.

Fixation elements on plate intraocular lens: large positioning holes to improve security of capsular fixation.

OBJECTIVE: This study aimed to evaluate in rabbit eyes the effects of large positioning holes in one-piece silicone plate-haptic intraocular lenses (IOLs) with respect to security of capsular bag fixation. Mechanical strength of capsular fixation is correlated with the histologic findings of regenerating lens material and fibrous tissue ingrowth through the positioning holes on silicone plate IOLs, comparing capsules implanted with large-hole style plate IOLs to fellow capsules implanted with small-hole style plate IOLs. DESIGN: The study design was a prospective, randomized, experimental study. PARTICIPANTS: A total of 40 fellow capsular bags from 20 New Zealand white rabbits were examined. Capsules implanted with conventional small-hole silicone plate IOLs were used as the control in all pairs of fellow capsules. INTERVENTION: Phacoemulsification and implantation of a silicone plate IOL with small positioning holes in one eye and implantation of a silicone plate IOL with large positioning holes in the fellow eye were measured. All rabbits were killed at 2 months. The force required to extract the IOLs from the capsular bag was measured. All capsular bags underwent histopathologic analysis. MAIN OUTCOME MEASURES: Extraction force measurements and histopathologic examination, comparing capsules implanted with small-hole plate IOLs with fellow capsules implanted with large-hole plate IOLs, were measured. RESULTS: The large-hole style IOL required significantly more force to extract from the capsular bag compared to the conventional small-hole style (P = 0.003). Histologically, proliferating lens epithelial material and fibrous tissue were observed growing through all of the large positioning holes (synechia formation) but not through any of the small positioning holes. CONCLUSIONS: Silicone plate IOLs with large positioning holes become affixed more firmly within the capsular bag compared to conventional small-hole plate IOLs. These findings suggest that large holes in silicone plate IOLs allow for superior capsular bag fixation. This should reduce the rates of decentration and dislocation.

Shear bond strengths of six bonding systems using the pushout method of in vitro testing.

The newest generation of bonding systems consolidates multiple components into fewer containers in order to simplify clinical procedures and save clinicians time. Six newer adhesive systems (Scotchbond Multi-Purpose Plus, PROBOND, OptiBond FL, Prime & Bond, One Step, and Tenure Quik) were tested for in vitro shear bond strength (SBS) of a hybrid composite to both superficial and deep dentin at 24 hours and 6 months employing a pushout test method. Results showed significant differences in SBS between superficial and deep dentin for both 1-day and 6-month values for all adhesive systems except Tenure Quik. The SBS of OptiBond FL increased significantly for both superficial and deep dentin after 6 months' storage in 37 degrees C water. None of the other adhesive systems showed a significant change in SBS at 6 months. There appear to be several advantages to the testing method.

Long-term intracranial cannula stabilization in mice with light cured resin composites.

A simple and rapid method is described for the introduction and stabilization of chronic indwelling cannulae in mice. Materials and adhesive bonding techniques commonly used in restorative dentistry were used to stabilize the cannulae. The effectiveness of this method was evaluated by shear strength testing across time and histological evaluation of coronal brain sections. Shear strength increased during the first week post surgery and remained stable for up to 60 days. The force required to dislodge the cannulae from skulls ranged from 0.70 to 2.45 kg. Histological evaluation revealed no significant infection or inflammatory response due to the materials used. Cannulae stabilization by this technique appears to be suitable for most experimental conditions.

Fixation of osteotomies using bioabsorbable screws in the canine femur.

The purpose of this study was to compare the healing properties of femoral osteotomies fixed by bioabsorbable screws (20:80 polyglycolic copolylactic acid copolymer) to standard stainless steel screws of a similar design in a dog femoral model. Two osteotomies were used, the trephine osteotomy (10 mm diameter) in the metaphyseal lateral femoral condyle and in the femoral diaphysis, and a unilateral osteotomy in the lateral femoral condyle. Two months after the trephine osteotomies, the femurs that contained the polymer screws were not significantly different in mechanical strength from the femurs treated with the stainless steel screws, either in the diaphyseal or metaphyseal model. There was no histological difference in bone healing between the metallic and polymer screws for all periods (2, 9, and 17 months). There was no adverse inflammatory response to the polymeric or metallic screws. By month 17, the polymer screws were resorbed completely. All the diaphyseal screw tracks had healed with bone and areas of remodeling were evident in two specimens. For the femoral condyle osteotomy model at 2 months, the polymer screws were present and intact, and all osteotomies healed with no evidence of inflammation. By 9 months, only one specimen had polymeric material left in the screw track. At 15 months, the screw tracks still were present but no evidence of any polymer remained. The tracks were filled with fibrous and adipose connective tissue. All osteotomies stabilized with either bioabsorbable polymer screws or stainless steel screws did heal satisfactorily without any complications, inflammation, or osteolysis. The polyglycolic polylactic acid copolymer may have a clinical role as a bioabsorbable material without the concerns for the osteolysis, foreign body reaction, and sterile abscess formation that have occurred with bioabsorbable fixation methods in the past.

Composite bonding to dentin and enamel: effect of humidity.

The effect of oral ambient air on shear strength to etched enamel and dentin was determined for OptiBond FL (Kerr Corp., Orange, CA) and Prodigy resin composite (Kerr Corp.). Enamel and dentin specimens of extracted human teeth were treated both in a dry environment and after exposure to oral humidity according to manufacturer's instructions. Shear strengths of this system are 22.6 MPa for etched, dry enamel; 22.2 MPa for etched, wet enamel; and 18.4 MPa for etched, dry or wet dentin. Differences in shear strengths between the wet and dry enamel or the wet and dry dentin were not significant. Multiple Student's t-tests were used for statistical analysis. Fracture modes for all specimens were examined under a stereomicroscope. Within the parameters of this in vitro study, OptiBond FL was not affected by oral humidity.

Effects of multiple sterilization on surface characteristics and in vitro biologic responses to titanium.

PURPOSE: This study evaluates the surface changes and effects on in vitro cell attachment and spreading brought about on prepared commercially pure titanium by multiple exposures to common sterilization methods. MATERIALS AND METHODS: Discs of commercially pure titanium were prepared to approximate the surface roughness of commercially available bone miniplates. Samples underwent sterilization by exposure to ultraviolet light; ethylene oxide sterilization (1, 5, or 10 cycles); or by steam autoclaving (1, 5, or 10 cycles). Representative surfaces from these sterilization groups were examined using a series of surface analytical techniques including scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), auger electron spectroscopy (AES), and contact angle measurements. Cell attachment assays using murine fibroblasts were then performed on titanium surfaces from each sterilization group and on tissue culture plastic controls. Sterilized surfaces contained O, C, and N contaminants, which affected surface energetics. Mean percent cell attachment values for each group were obtained for periods of up to 1 hour. Representative samples from each group were examined using SEM to ascertain cell spreading and morphology for each sterilization group. RESULTS: Ultraviolet (UV) sterilized surfaces showed no changes from the unsterilized state macroscopically or under SEM. UV surfaces showed cell attachment levels similar to control surfaces at all intervals, and a chronologic progression of cell spreading. Ethylene oxide-sterilized surfaces showed occasional bluish discoloration and a microscopic particulate contaminant, resulting in modest decreases in cell attachment levels without strong correlation to numbers of sterilization cycles. Autoclaved surfaces generally showed the greatest discoloration and heaviest particulate contamination. Cell attachment levels were lower, and cell spreading was diminished compared with the ethylene-oxide-treated group. CONCLUSIONS: Both ethylene oxide and steam autoclave sterilization contaminated and altered the titanium surface, resulting in decreased levels of cell attachment and spreading in vitro. Although corroborative in vivo experiments should be conducted, the results of this study indicate that some multiple sterilization regimens for metallic materials may pose serious biologic concerns.

Influence of biomaterial surface texture on bone ingrowth in the rabbit femur.

The purpose of this study was to examine both the histologic and the mechanical characteristics of bone apposition to an experimental surface, arc-deposited titanium, in a rabbit model and to compare them with those of four previously studied surfaces: one layer of cobalt-chromium beads, three layers of cobalt-chromium beads, plasma-sprayed cobalt-chromium, and uncoated titanium alloy. Bilateral cylindrical implants were press-fit into the lateral femoral condyles of 70 adult New Zealand White rabbits, which were allowed unrestricted activity and then killed at 6 or 12 weeks. The distal femora were harvested, radiographed, and prepared for either mechanical or histologic evaluation. All of the implants with coated surfaces had significantly greater shear strength than the implants of grit-blasted titanium alloy after both 6 and 12 weeks. After 6 weeks, maximum bone apposition occurred in the beaded surfaces. After 12 weeks, the shear strengths and bone apposition of implants of arc-deposited titanium and of one and three layers of cobalt-chromium beads were significantly greater than those of implants of plasma-sprayed cobalt-chromium and grit-blasted titanium alloy. The histologic studies correlated with the mechanical results. After 12 weeks, the bone apposition and mechanical stability of arc-deposited titanium were similar to those of a single layer of beads. There appeared to be no advantage to multiple layers of beads, and the plasma-sprayed cobalt-chromium and grit-blasted titanium surfaces showed lower shear strength and bone apposition than the other groups.

Laser-aided degradation of composite resin.

The removal of residual composite resin after debonding orthodontic brackets often creates surface scratches, enamel loss, and enamel tearouts. If the Nd:YAG laser could selectively degrade the resin without damaging the underlying tooth structure, these problems might be eliminated. The purpose of this study was to determine the effectiveness of the Nd:YAG laser in degrading composite resin within a time frame that will not cause pulpal damage. Minimal lasing times and optimum frequencies were determined by testing the compressive strengths of resin cylinders exposed to laser radiation for 2, 3, 5, 10, or 15 seconds at frequencies of 60, 80, or 100 Hz. The optimum condition was determined to be a 3 second lasing time at a frequency of 100 Hz. Cylinders of composite resin were divided into four groups consisting of: (1) resin, (2) resin with a laser enhancing dye, (3) resin lased for 3 seconds at 100 Hz, and (4) resin with the dye which was lased for 3 seconds at 100 Hz. The compressive strengths of the four groups were statistically compared. The resin groups that were lased for 3 seconds at 100 Hz showed a 75% reduction in compressive strength. The results of this study demonstrate that dual wavelength pulsed Nd:YAG laser energy, when used within the parameters described here, will degrade the mechanical properties of composite resin, thereby offering the potential for a quick and efficient method of removing residual composite resin.

Chairside veneering of composite resin to anterior stainless steel crowns: another look.

The chairside veneering of stainless steel crowns using the technique described in our original article (J Dent Child, 61: 321-326 September-December 1994) has proven to be a very dependable and successful technique for restoring severely damaged primary anterior teeth. In this article an advancement in the technique is described using new light-cured materials that simplify the veneering process and produce thinner veneers. The resulting veneers maintain the adaptability, strength, and gingival contour benefits of the stainless steel crown in conjunction with the cosmetics of composite facings. The chairside technique can be quickly mastered by a dental auxiliary and results in veneered crowns with very high shear and bond strengths.

Application of a fluorescent redox dye for enumeration of metabolically active bacteria on albumin-coated titanium surfaces.

A bacterial staining method using fluorescent redox dye 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) is described for quantifying actively respiring bacteria that adhere to commercially pure titanium surfaces coated with cross-linked albumin. This has not been possible to date using ordinary DNA stains such as propidium iodide (PI) or Hoechst, both of which produce a very bright background. With this technique, it was demonstrated that the cross-linked albumin inhibited the adherence of Staphylococcus aureus and Staph. epidermidis to the titanium surface.

Histological and mechanical comparison of hydroxyapatite-coated cobalt-chrome and titanium implants in the rabbit femur.

The purpose of this study was to compare hydroxyapatite (HA)-coated titanium (Ti) and HA-coated cobalt-chrome (CoCr) implants in the distal femur of the rabbit by evaluating bone apposition and interfacial shear strength. Bilateral cylindrical implants with a plasma sprayed 50-microns thick HA coating were press-fit into the metaphyseal cancellous bone of the lateral femoral condyles in a transverse fashion, and the animals were sacrificed at 2, 4, and 8 weeks postimplantation. Mechanical strength of the interface between HA and bone was measured using the pushout method. For histologic analysis, the fractional linear extent of bone apposition was quantitated. No differences were found in the interfacial shear strength between the Ti and CoCr at any time period. The amount of bone apposition increased significantly at each time interval for both substrate metals, but there were no significant differences between the two substrates at any of the time periods studied. The HA-coated CoCr implants performed in a similar manner to the HA-coated Ti implants, both mechanically and histologically, suggesting that HA-coated CoCr implants deserve further study as a viable alternative to Ti for the biological fixation of total joint components in orthopaedic surgery.

Evaluation of an adhesive system for amalgam repair: bond strength and porosity.

This study compared the shear bond strengths and the porosity at the bond sites of a spherical amalgam alloy to those of an admixed amalgam alloy, when they were bonded to like and unlike alloy specimens with or without a resin bonding material. The spherical alloy had higher bond strength and less porosity than did the admixed alloy, whether bonded to spherical or admixed alloy. The results suggest that use of a spherical alloy should be strongly considered when an amalgam restoration is to be repaired with an amalgam alloy, regardless of the type of alloy used in the original restoration. Use of a resin bonding agent did not increase bond strengths of amalgam to amalgam.

An esthetic technique for veneering anterior stainless steel crowns with composite resin.

The restoration of primary anterior teeth presents complicated esthetic and retention problems to the clinician. A technique is described for the chairside veneering of composite resin to stainless steel crowns, which results in well contoured restorations with superior durability and esthetics. A trimmed and fitted stainless steel crown can be veneered in three to five minutes. This provides the adaptability and gingival contour benefits of the stainless steel crown in conjunction with the cosmetics of the composite facings. The technique described produced composite veneers with a mean sheer bond strength of 3520 PSI (24.4 Mpa).

Characterizations of titanium implant surfaces. III.

There are several reports in the literature concerning the similarities and the differences between the oxide on cpTi and Ti-6A1-4V alloy; however, their biological sequelae are not entirely known. In this work, a series of surface characterization techniques were used in conjunction with short term in vitro biological assays to assess the effects of materials selection (cpTi and Ti alloy) on osteoblast-like cell responses. Surface analysis indicated that with the exception of oxide thickness, there were no significant differences in surface characteristics between the two implant materials. These results were reflected in the biological studies, where the levels of cell attachment and adaptation of the attached cells to the titanium surfaces were similar. These results are in general agreement with previous in vivo studies and continue to indicate that cpTi and Ti alloy are suitable, biologically compatible materials for fabrication of dental implants.

Production of a standard closed fracture in the rat tibia.

In order to develop a technique for producing a standard closed transverse fracture in the rat tibia, the method of Bonnarens and Einhorn was modified and tested on 176 tibiae. A 0.9-mm Kirschner wire was inserted percutaneously near the tibial tuberosity into the intramedullary canal, and a tibial fracture was created at the junction of the middle and distal third of the tibia with a blunt guillotine driven by a dropped weight. Radiographs confirmed the production of a highly reproducible transverse mid-shaft tibia fracture in 90% of the fractures. Minimal comminution of the fracture or angulation of the Kirschner wires resulted. The Kirschner wires were removed without difficulty after the rats were put to death and did not disturb the fracture site. Mechanical testing and histological studies showed that a standard fracture healing process was obtained by using this method. The results indicate that this modified method creates a standard, reproducible transverse closed fracture of rat tibia.

Evaluation of polycaprolaitone custom tray material.

Custom impression trays are necessary for accurate impressions in fixed prosthodontics when using polysulfide impression materials. These custom impression trays are needed to provide for a uniform thickness of impression material to minimize distortion. Custom impression trays have historically been made from acrylic resin. New materials have been developed as alternatives to acrylic resin, and this study evaluates one product currently available that is composed of polycaprolaitone. This study evaluates the modulus of elasticity of polycaprolaitone as compared with acrylic resin, and also evaluates the amount of permanent deformation of the new material when placed under a load. The elastic modulus of polycaprolaitone was tested using three-point bending of specimens placed in a universal mechanical test system. The elastic modulus of the new material was found to be significantly lower than that of acrylic resin. The next test evaluated the amount of permanent deformation of the polycaprolatione material when specimens approximating the shape and size of custom impression trays were placed under a load. These trays were placed in a universal mechanical test system and differing loads were placed on them. Results showed that although the trays deformed at relatively low loads, all deformation was fully recovered within a clinically insignificant period of time (less than 30 seconds). From these experiments it was concluded that although the polycaprolaitone material has a lower modulus of elasticity and will deform under relatively low loads, the material recovers completely, and thus the deformation would not interfere with the clinical performance of polycaprolaitone as a custom tray material.

Short-term plasma-cleaning treatments enhance in vitro osteoblast attachment to titanium.

The purpose of this research was to characterize the in vitro cellular behavior of osteoblast-like cells on titanium surfaces prepared with argon plasma-cleaning (PC) treatments for various lengths of time. The highest levels of cell attachment were observed for surfaces which had been plasma-treated for one min. Surface analyses indicated that although PC treatments dramatically improved surface wettability, the presence of inorganic contaminants was observed with longer treatment times and may have interfered with cell attachment. Further work is suggested to investigate the longer-term phenotypic expression of osteoblasts when grown on implant surfaces.

Characterization of sterilized CP titanium implant surfaces.

Surface analysis techniques and in vitro biologic assays were used to characterize sterilized commercially pure titanium surfaces. Significant surface alterations were observed following sterilization treatments. These alterations led to decreased fibroblast cell attachment and altered cellular spreading phenomena compared to nonsterilized control surfaces.