The quantitative and qualitative analysis of the craniofacial skeleton of mice lacking the IGF-I gene.

Insulin-like growth factors are mediators of growth hormone and are believed to also stimulate growth independently. Insulin-like growth factor I (IGF-I) null mutant mice exhibit a lower rate of skeletal growth compared with their wild-type (control) littermates. Although their general body dimensions seem proportionate, their heads appear shortened with a blunt nose compared with the controls. The aim of this project was threefold: 1) to investigate whether differences in shape/form exist between the craniofacial skeleton of the IGF-I null mutant mice and their control littermates by using three techniques; 2) to determine whether the three techniques yield similar, different, or complementary information regarding the size and shape of specimens; and 3) to investigate whether the histological sections obtained from the craniofacial skeleton exhibit any differences between the two groups. Thirty adult male mice, 12 mutant and 18 wild type, obtained from 11 litters were examined. Lateral and superio-inferior radiographs of their head were analyzed by the procrustes, the macroelement, and the traditional cephalometric techniques. Later, the animals were processed for routine histological examination. The IGF null mutant mice demonstrated a generalized decrease of craniofacial size (43-64% of the normal adult size) and a non-allometric change of shape when compared with their wild-type littermates. While the mandible did not exhibit any shape changes, the facial and cranial areas demonstrated prominent changes. Examination of histological sections did not reveal any structural difference between the two groups at the adult stage. Furthermore, procrustes and macroelement techniques offer a more complete, detailed, and comprehensive description of the specimens compared.

Effect of evaporation and mixing technique on die spacer thickness: a preliminary study.

STATEMENT OF PROBLEM: Casting relief is required for proper seating of castings to allow for luting agent thickness. The application of die spacer to the die is the most common method of obtaining casting relief. Die spacer film thicknesses that are outside the ideal range of 25 to 40 microm can cause clinical problems. Thickness can be affected by the separation of die spacer constituents, which may not be reconstituted by mixing, in the bottle and by the evaporation of volatile components while the bottle is open. PURPOSE: The purpose of this study was to determine the effects of component evaporation and die spacer mixing technique on applied die spacer thickness. MATERIAL AND METHODS: Bottles of Gold Tru-fit die spacer were left open for 0, 1, 4, 8, and 24 hours at 22 degrees C. Spacer solutions were shaken either by hand per the manufacturer's directions or on a dental vibrator for 1 minute. One even brush stroke of spacer was applied to clean glass slides. Three die spacer films were made for each combination of time and mixing technique. Eighteen thickness measurements per sample at various sites were recorded with profilometer tracings. Statistical differences were determined with a 2-way ANOVA. RESULTS: Handshaking provided greater die spacer thickness, which increased with the time that the bottle was open. Vibration provided lower thickness with no statistical increase with time. CONCLUSION: Insufficient agitation caused lower film thickness. Excessive evaporation caused higher film thickness.

Dimensional accuracy of castings produced with ringless and metal ring investment systems.

STATEMENT OF PROBLEM: The ringless casting procedure is in use in clinical dentistry, although there is no adequate scientific data to support its use. PURPOSE: This study compared the vertical margin accuracy of lost wax castings produced with the conventional casting technique using a metal ring and a technique that uses a ringless system. MATERIAL AND METHODS: From copings fabricated on a metal die, 30 castings were produced from a high palladium alloy for metal ceramic restorations (Argedent). Ten castings were cast with Bellavest T (Bego) phosphate-bonded investment with the ringless technique, 10 were cast with the same investment with a metal ring, and the final 10 were cast using Hi-temp (Whip Mix) phosphate-bonded investment with a metal ring. The internal surface of the castings were not modified before seating with finger pressure. For vertical margin discrepancy measurements, an optical microscope at a magnification of 100x was used. Data were analyzed with 1-way multivariate ANOVA (repeated measures) and the Student-Newman-Keuls test. RESULTS: When following the manufacturers' recommendations, the castings of the ringless technique provided less vertical margin discrepancy (mean value 181 +/- 71 microm) than the castings produced with the conventional metal ring technique (290 +/- 87 microm and 291 +/- 88 microm). The difference was significant (P <. 001). CONCLUSION: The ringless technique may produce accurate castings for use in fixed prosthodontics, therefore further investigation is needed to develop a protocol for its use.

Theoretical cantilever lengths versus clinical variables in fifty-five clinical cases.

STATEMENT OF PROBLEM: Cantilever loading increases loads distributed to implants, potentially causing biomechanical complications. The implemented length is often less than what is considered to be optimal. PURPOSE: This study investigated the effects of clinical variables on predicted cantilever lengths. Theoretically, calculated maximum cantilever was defined as the length that would not cause gold screw loosening or fatigue failure. The variables investigated included number and distribution of implants, arches placed, and the clinician's "optimal" cantilevers. MATERIAL AND METHODS: Implant and prosthesis location coordinates of 55 clinical cases were determined from casts. The distribution of an applied 143 N vertical load to implants was calculated through the Skalak model for more than 500 loading sites. Gold screw joint overload was assumed to occur at 200 and 250 N in compression and tension. Calculated lengths were compared with clinical variables. RESULTS: For a set number of implants, the relationship between calculated cantilever length and anterior-posterior spread was linear. The sum of length on both sides versus prosthesis length between the most distal implants was linear, regardless of the number of implants. Predicted satisfaction was defined as calculated length greater than the clinicians' optimal length. Satisfaction rates were 100%, 56%, 33%, 8%, and 0% for cases supported by 8 and 7, 6, 5, 4, and 3 implants (44% overall), respectively. Ninety-eight percent of cases with anterior-posterior spreads greater than 11.1 mm were satisfied. CONCLUSION: Within the limitations of the model, predicted complications of the gold screw joint may be reduced if: (1) cantilever length is less than calculated from linear equations, and (2) anterior-posterior spread is greater than 11.1 mm.

Comparison of numeric techniques in the analysis of cleft palate dental arch form change.

OBJECTIVE: Quantitative descriptions of form (size and shape) changes are significant to the understanding of the development, treatment planning, and prognosis of patients born with cleft lip and palate. This study compared the results of traditional dental arch form change measurements, such as width, depth, perimeter, and area, with four numeric methods: finite element scaling analysis, macroelement method, Euclidean distance matrix analysis, and conventional least-squares and resistant-fit theta rho Procrustes analyses. DESIGN: Using tooth cusp landmarks on maxillary study casts, form change measurements of a male with complete bilateral cleft lip and palate at ages 2, 5, and 6 years were made comparing each age to the next older. RESULTS AND CONCLUSIONS: With the exception of the 2- to 5-year resistant-fit analysis, all numeric method: 1) provide comparable results, 2) provide more detailed descriptions than do traditional methods, and 3) provide results that correlate well with the reported effects of increased lip pressure due to lip closure surgery. The use of finite-element scaling analysis on study casts is somewhat limited since: 1) there is more than one solution at teeth shared by many finite elements, 2) gross averaging of form change occurs within triangular elements, and 3) solutions can vary with the choice of element location. The use of the macroelement method circumvented the above finite element limitations without compromising finite-element advantages. Procrustes results vary with the chosen superposition algorithm. The choice of the most appropriate Procrustes method required some a priori knowledge of form difference. The large number of results obtained by Euclidean distance matrix analysis and the nongraphic presentation of these results hamper quick interpretation but may be best suited for definitive statistical analysis. The graphic representation of both the magnitude and direction of: 1) landmark displacement in the Procrustes analyses (once size difference is eliminated), and 2) the rate of form change in the macroelement method provide an intuitive appreciation of how and where the casts differ.

Form difference computations in restorative dentistry utilizing the macroelement method.

The comparison between the size and shape (form) of two structures or the analysis of one object under differing conditions is important in restorative dentistry. Despite rapid advances in digitizing technologies, form comparison is still mainly limited to scalar measurements. The objective of this study was to test the potential use of a newly developed tensorial morphometric difference technique, the macroelement method, in a model restrative system where the processing and materials properties are known duplication of a denture anchor in stone via polysulfide, addition silicone, and polyether impression materials. Nine machined landmarks were utilized to construct a nine-sided element for macroelement analysis. Macroelement results compared well with the known impression materials properties of polymerization shrinkage and incomplete recovery in terms of: (1) larger die diameter, (2) smaller die (vertically), (3) horizontal direction of maximum expansion, and (4) vertical direction of maximum contraction. Also, macroelement results along boundary lines were equal to the traditional form difference measure of change in length/length of those lines. The macroelement method provided results which are superior to those of traditional methods in that both (1) the magnitude and direction of difference at any point on the structure could be determined, and (2) the graphical representation of the results provides an intuitive appreciation of how and where the forms differ Therefore, since macroelement results: (1) compare well with known materials properties and traditional measures, and (2) have the above-stated advantages, tensorial techniques such as the macroelement method, used in conjunction with new digitizing technologies, can be used better to describe the kinematics of form difference. With the description of the kinematics provided by the technique, the dynamic cause of the form difference can be ascertained with the investigators knowledge of materials. The investigators can then suggest changes to be made in materials and/or techniques that would enable the desired size and shape to be obtained.

Determination of cantilever length-anterior-posterior spread ratio assuming failure criteria to be the compromise of the prosthesis retaining screw-prosthesis joint.

The maximum cantilever length-anterior-posterior spread (CL-AP) ratio is often used as an indication of the ability to cantilever in completely implant-supported prostheses. The CL-AP ratios were determined assuming that failure occurs when the prosthesis retaining screw-prosthesis joint was compromised by either compressive (exceeding the pretorque value) or tensile (opening of the joint via plastic deformation) vertical forces using the Skalak model. Geometric arrangements of three, four, five, and six implants were analyzed. Force variables were 143, 200, and 400 N for the applied force, the pretorque value, and the joint tensile yield strength, respectively. The pretorque value was always exceeded before the yield strength. Allowable CL-AP ratios were (1) lower than those previously reported and (2) found to be 0.5 to 1.8, 0.7 to 1.6, 1.1 to 1.7, and 1.8 for three, four, five, and six implants, respectively. Although implant distributions with the highest AP often provide adequate occlusion, the results of this study indicate that the use of a single CL-AP ratio alone is not necessarily a good indicator of the ability to cantilever.

Effects of titanium dioxide passive film crystal structure, thickness, and crystallinity on C3 adsorption.

The effects of titanium dioxide passive film crystal structure, thickness, and crystallinity on C3 adsorption from diluted human plasma were measured. Titanium dioxide surfaces created include (1) 70-nm anatase and rutile films comprising a mixture of amorphous and microcrystalline titanium dioxide, (2) 140-nm anatase and rutile films with greater crystallinity than the 70-nm films, (3) 70-nm aged anatase films with approximately the same crystallinity as that of the 140-nm anatase films, (4) sintered anatase and sintered rutile with no underlying metal, representing completely crystalline oxide films of infinite thickness, and (5) electropolished titanium. All combinations of experimental variables of surface type, exposure time, and plasma dilution were replicated four times. Anatase and rutile C3 surface concentrations increased with increased oxide thickness and crystallinity. The 70-nm aged anatase film isotherm more closely matched that of the 140-nm than of the 70-nm film, indicating that some property associated with oxide crystallinity is more influential in C3 adsorption than properties associated with oxide thickness alone. Concentrations of C3 were equal for equivalent anatase and rutile surfaces, except at high plasma concentrations and long exposure times, in which more C3 was adsorbed to anatase, suggesting that crystal structure may not be a significant controlling factor.

Use of the boundary element method for biological morphometrics.

Tensorial morphometric assessments of form difference can aid in the understanding of the cause of the form difference by providing reference frame independent, anisotropic, non-homogenous descriptions. The majority of biological and prosthetic structures cannot be adequately analyzed by current methods due to the paucity of anatomical landmarks and methodological requirements of subdivision through the domain. Internal subdivisions can be eliminated with the boundary element method (BEM). A non-landmark (NL) method can be developed by the combination of elliptical Fourier analysis (EFA) and BEM. The appropriateness of NL and BEM was investigated. The growth of the female rat neural skull from 7 to 14 postnatal days was calculated with respect to increase in area. Linear and quadratic BEM landmark analysis were made using 10 and 5 elements, respectively. Five hundred linear BEM elements were constructed from the EFA equations for NL. The form change tensors were obtained by the solution of the Laplace equation using boundary displacements as the essential boundary conditions. For comparison, simplex triangular finite element analysis (FEA), quadrilateral FEA and macroelement analysis were made on the same structure. Results correspond well to the two major growth process in this time period; (1) high cerebellar growth, and (2) relatively higher facial versus neural growth. The results in other regions are close to the biologically observed 36% increase in area. The average difference between BEM, NL versus FEA is 1.9 and 2.8%. Trends in results with position are almost identical for BEM, NL, MEM and quadrilateral FEA. The morphometric landmark BEM technique requires an additional numerical scheme to eliminate the singularities near the boundary.(ABSTRACT TRUNCATED AT 250 WORDS)

An evaluation of growth changes and treatment effects in Class II, Division 1 malocclusion with conventional roentgenographic cephalometry and finite element method analysis.

Conventional methods of roentgenographic cephalometry will yield differences in interpretation of growth or treatment changes depending on which methods of superimposition are used. The finite element method of analysis has been reported to have significant advantages since it does not require a reference frame to describe the changes that have taken place. This article describes the growth of a patient with a Class II, Division 1 malocclusion during approximately 2 years of orthodontic treatment with the use of conventional cephalometric growth and static analyses, as well as the finite element method. Thirty cephalometric points were digitized on the pretreatment and the posttreatment lateral cephalograms of a patient undergoing orthodontic treatment between the ages of 10 and 12 years. The finite element method provided a reference frame invariant description of the size, shape, change, and rotation of each of the 12 finite elements representing different anatomic structures.

A modified direct technique versus conventional direct placement of brackets: in vitro bond strength comparison.

Bond strength and failure location were evaluated in vitro for two methods of direct bracket bonding. Sixty human premolars were divided into two groups of 30 each. In group I the brackets were bonded with a two-paste adhesive by using the conventional direct method. In group II brackets were bonded with a newly developed modified direct technique. During the modified direct technique, unfilled resin catalyst liquid was applied to a bracket, which had a coating of hardened composite cured against a dental anatomic matrix (tooth). After the acid-etched tooth was coated with unfilled resin base liquid, the bracket was placed. Mixed unfilled resin liquid (sealant) was then placed at the periphery of the bracket/tooth interface. Thus the major modification of the direct technique would entail fabrication by the manufacturer of a bracket with prehardened bis-GMA composite resin on its backing. Bond strengths were 155.2 (SD = 35.7) and 140.6 (SD = 30.1) kg/cm2 for conventional and modified techniques, respectively. With the conventional method, failure occurred mainly at the tooth/composite interface. Failure seen with the modified technique was mixed, but the major mode was composite/bracket. Therefore this modified bonding method promises similar bond strengths and some advantages over the conventional method including, elimination of composite flash from around the brackets, ample working time, consistent adhesive thickness, and reduction of porosity.

Anatomical macroelements in the study of craniofacial rat growth.

In order to avoid the arbitrary division of biological structures, rational polynomial interpolants are utilized to study growth. The major advantage of this method is the elimination of artificial internal element boundaries through anatomical structures. Since the boundary element methodology is employed in the finite element setting, other benefits, without additional computer coding, include the ability to use elements with any number of sides and reference frame invariance. Longitudinal landmark coordinates from midsagittal X-ray tracings of 22 albino female rat skulls of various ages were averaged. The skull was partitioned into three macroelements: a neural skull and two functionally distinct portions of the facial skull--olfactory and respiratory. The digital computer programming was carried out in the computer mathematics environment of Mathematica. Maximum elongation ratios were calculated for approximately 400 interior points. The elongation ratios in the neural skull compared well with previously documented growth behavior of internal brain structures. The calculated ratios from the facial skull were used to analyze the behavior of macroelement interpolation close to common anatomical boundaries.

TEM immunogold staining of C3 from plasma onto titanium oxides.

Immunogold staining in conjunction with TEM was used to observe C3 adsorption from plasma in relation to the underlying titanium structure of thermal, anodic, and electropolished oxides. Heat treatments and oxide thickness were found to have no significant effect on the adsorption behavior of C3, while surface oxide type possibly has. Surface concentration of C3 was found to be time- and plasma concentration-dependent. Evidence is given for the possible involvement of C3 in protein exchange, i.e., the Vroman effect. Diluted plasma resulted in a random distribution of gold colloids, whereas clustering occurred with undiluted plasma. Although C3 concentrations present on grain boundaries followed the same trend as that found on the surface, C3 was found to have a higher grain boundary than bulk concentration for 0.1% plasma.