Physical dimensions, torsional performance, bending properties, and metallurgical characteristics of rotary endodontic instruments. VI. Canal Master drills.

A laboratory study was performed on machine-driven Canal Master drills to determine their physical dimensions, torsional performance, bending properties, and metallurgical characteristics in fracture. Physical dimensions were determined for each of the available sizes (#50 to #100) of Canal Master drills from the manufacturer that distributes these instruments in the United States. Samples were also tested in clockwise torsion using a Maillefer memocouple. Bending properties of cantilever specimens were measured with a Tinius Olsen stiffness tester. Bending fatigue testing was performed on a unique laboratory apparatus. Scanning electron microscope examination confirmed visual observations that the stainless steel Canal Master drills exhibited ductile torsional fracture. This study is part of a continuing investigation to establish standards for all machine-driven rotary endodontic instruments.

Color mixing in dental porcelain.

For esthetic reasons, pigments and opacifiers are added to porcelains used in restorative dentistry. The purpose of this study was to use Kubelka-Munk theory (Kubelka and Munk, 1931) to predict and analyse the colors of porcelains modified by the addition of two pigments and an opacifying agent. The base porcelain was composed of 88% potassium feldspar, 6% quartz and 6% kaolin. The porcelain was modified by the addition of a yellow (Pr-Zr-Si) or a brown (Fe-Cr-Zn) stain and an opacifier (10% SnO in base porcelain). After firing at 1200 degrees C for 30 min, reflectance spectra of the various combinations were obtained with a spectrophotometer. Reflectance spectra, except at low wavelengths, were influenced by increased scattering due to the addition of the opacifier. Calculated values from Kubelka-Munk theory for absorption coefficients and scattering coefficients with appropriate correction factors were compared with the values from the reflectance spectra of the combinations. In general, good agreement was obtained if the scattering coefficient of the opacifier is set equal to 1.0. Using the L*a*b* transform of the CIE color space, it was found that this transform provided uniform color intervals for equal changes in pigment concentration.

Physical dimensions, torsional performance, and metallurgical properties of rotary endodontic instruments. 3. Peeso drills.

A laboratory study was performed on Peeso drills to determine their physical dimensions, torsional performance, and metallurgical properties. Samples were measured from each of sizes #1 to #6 of Peeso drills (type P) and sizes #009 to #023 of Peeso drills (type B-1) from the two manufacturers that distribute these instruments in the United States. They were also tested in clockwise and counterclockwise torsion using a digital torque meter instrument. It was not possible to evaluate completely some type P drills of size #4 and larger or type B-1 drills of size #016 and larger because the torsional moments exceeded the capacity of the test instrument. Scanning electron microscopic examination confirmed visual observations that the stainless steel Peeso drills exhibited ductile torsional fracture, in contrast to the carbon steel Peeso drills which fractured in a relatively brittle manner. The carbon steel Peeso drills exhibited a much greater tendency for torsional fractures in the bur head, along with considerably smaller values of angular deflection at separation compared to the stainless steel Peeso drills. This study is part of a continuing investigation to establish standards for all rotary endodontic instruments.

Noise level evaluation of dental handpieces.

We evaluated the noise level of fourteen air-driven handpieces, six low speed (less than 20,000 rev/min) and eight high speed (greater than 160,000 rev/min), with respect to a three-directional co-ordinate system and distances of 6, 12 and 18 in. in each chosen direction. A two-way analysis of variance of the noise level between handpieces and positions indicates that large significant differences exist amongst handpieces and in different positions, and that interaction is just barely significant. The ranking and least significant differences for the mean of all handpieces v. position and for the mean of all positions v. handpiece were compared with the results for the ranking and significances from the one-way ANOVAS for each handpiece v. position and for each position v. handpiece. A trend exists with some of the handpieces of straight design (all low speed) for increased noise levels in a direction perpendicular to the handpieces and decreased levels in a direction parallel to the handpieces. For handpieces of angled design (all high speed) both directions parallel and perpendicular (the perpendicular to the longitudinal turbine axis) to the rotor axis indicate increased noise levels. The parallel direction includes the exiting air from the exhaust port. The perpendicular direction can be indicative of an aerodynamic factor associated with the established air flow patterns. The extremes in noise level were 56.8 dBA for a low-speed handpiece of straight design at the 18 in. distance in a direction parallel to the handpiece, and 87.3 dBA for a high speed handpiece at the 6 in. distance in a perpendicular direction.

A comparison of the effectiveness of dentine bonding agents.

Tensile and shear bond strengths between prepared surfaces of coronal dentine and cores of composite materials using different bonding systems were determined. Control procedures demonstrated that tensile bond strengths were approximately doubled by the use of bonding agents in systems requiring initial cleansing or etching of dentine. Similar increases were found in shear bond strengths. When bonding to different depths of dentine was compared shear and tensile bond strengths to the more occlusal dentine were greater than to more pulpally placed dentine. The factors which appear to affect bond strength under laboratory conditions are: etching of dentine (but beware of this procedure clinically); the smear layer and its removal; polymerization shrinkage of composite materials; the depth and plane of bonded dentine; the use of fresh or stored dentine; and the structure of the treated dentine.