Robert A. Draughn

Compressive fatigue limits of composite restorative materials.

Compressive fatigue limits at 5,000 stress cycles have been measured for seven commercial composite restorative materials. The average of the ratios between fatigue limit and compressive strengths is 0.64.

Rapid quantification of staphylococci adhered to titanium surfaces using image analyzed epifluorescence microscopy

Abstract A method for rapid enumeration of S. epidermidis adhered to the surface of commercially pure titanium samples was developed using image analyzed epifluorescence microscopy. The method was used to determine the effects of different surface roughnesses of titanium samples and the influence of adsorbed human serum proteins on bacterial adherence. Bacterial suspension of S. epidermidis (VAS-11, concentration: 10 7 cfu/ml) were incubated with titanium samples (with different surface roughnesses and coated with human serum albumin or fibronectin) for 1 h at 37°C with agitation. Thereafter they were washed, stained with propidium iodide, air dried, mounted onto microslides, and counted by using image analyzed epifluorescence microscopy. The results showed that: (1) this direct counting method is quick, simple, accurate, reproducible, and suitable for counting bacteria adhered to opaque surfaces such as netal, (2) the different roughnesses of the titanium surfaces (roughness: 1.25 to 0.44 Ra) had no effect on the S. epidermidis adherence, and (3) adsorbed human serum albumin reduced the S. epidermidis adherence by more than 90%, suggesting that precoating biomaterials with albumin may reduce the possibility of prosthesis or implant colonization by staphylococci. Conversely, human serum fibronection had no effect on S. epidermidis adherence to a titanium surface.

Abrasive wear, tensile strength, and hardness of dental composite resins—Is there a relationship?

The in vitro abrasive wear resistance, tensile strength, and hardness of seven widely used composite restorative resins have been measured. Findings indicate that the values of tensile strength and hardness are not related to the measured abrasion rates. It is apparent that abrasive wear is a complex phenomenon and that materials which have high values for strength and/or hardness do not necessarily have high resistance to abrasive wear.

In vitro surface degradation of composites by water and thermal cycling

Abstract Surface degradation by water and thermal cycling was evaluated from brush abrasion curves, values of dissolution and surface roughness, and observations of the subsurface on a set of composite resins with a range of microstructures. Water and thermal cycling affected the materials differently depending on the properties of the filler particles. The effects were minimal in a composite with submicron size fillers and in a material containing quartz fillers relatively large compared to the abrasive particles. An increase in surface degradation of a glass filled composite was attributed to the formation of microcracks or failure of filler/matrix bonds. A decrease in the interfacial bond strength decreased the resistance to wear in a glass filled material after exposure to water alone, but the same effect in a quartz filled composite of similar microstructure was found only after thermal cycling.

Relationship between abrasive wear and microstructure of composite resins

The in vitro abrasion resistance of seven commercial composite resin restorative materials has been measured. Analysis of the composite microstructures shows that abrasion rates are dependent upon the size, hardness, and volume fraction of particles in the material. The most abrasion-resistant composites contain a high volume fraction of large, hard particles.

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.

When to glaze—An electron microscope study

1. A smooth porcelain surface can be obtained by glazing after grinding. There is no need for sanding or polishing with a rubber wheel. 2. A low-fusing glaze gives a slightly smoother surface than a natural glaze. The low-fusing glaze may be added at any stage of polishing, and the results will be the same.

Linear dimensional changes in addition curing silicone impression materials

Five vinyl polysiloxane addition curing impression materials were evaluated on the basis of linear dimensional change occurring as a function of time between making an impression and pouring the die. The dies were measured and compared to a master model to determine the linear change in the impression material. One material produced an overall larger die, but the greatest increase in size deviated from the master model by only 0.1%. Permagum putty-wash material consistently produced undersized dies, with the greatest change being 0.3%. Three materials randomly produced smaller or larger dies, differing from the master model by only 0.08% for the smallest die to 0.07% for the largest. No consistent pattern of increase or decrease in die size occurred with time. Dies produced at 168 hours were as accurate as those produced at 10 minutes.

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.

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.