K(+)-channel transgenes reduce K(+) currents in Paramecium, probably by a post-translational mechanism.

PAK11 is 1 of more than 15 members in a gene family that encodes K(+)-channel pore-forming subunits in Paramecium tetraurelia. Microinjection of PAK11 DNA into macronuclei of wild-type cells results in clonal transformants that exhibit hyperexcitable swimming behaviors reminiscent of certain loss-of-K(+)-current mutants. PAK2, a distant homolog of PAK11, does not have the same effect. But PAK1, a close homolog of PAK11, induces the same hyperexcitability. Cutting the PAK11 open reading frame (ORF) with restriction enzymes before injection removes this effect entirely. Microinjection of PAK11 ORF flanked by the calmodulin 5' and 3' UTRs also induces the same hyperexcitable phenotype. Direct examination of transformed cells under voltage clamp reveals that two different Ca(2+)-activated K(+)-specific currents are reduced in amplitude. This reduction does not correlate with a deficit of PAK11 message, since RNA is clearly produced from the injected transgenes. Insertion of a single nucleotide at the start of the PAK11 ORF does not affect the RNA level but completely abolishes the phenotypic transformation. Thus, the reduction of K(+) currents by the expression of the K(+)-channel transgenes reported here is likely to be the consequence of a post-translational event. The complexity of behavioral changes, possible mechanisms, and implications in Paramecium biology are discussed.

Bracket bond strength with transillumination of a light-activated orthodontic adhesive.

The literature describes transillumination as a means of curing orthodontic light-cured composite adhesive. The literature also recommends a 2 to 3 times increase in light exposure time when light curing using transillumination. The purpose of this study was to determine the transmittance of the curing light through human enamel and the effect of transillumination on the bond strength of orthodontic brackets. One hundred extracted human maxillary incisors were used in this study. Brackets with orthodontic composite adhesive were placed on the labial surface of the incisors and light cured from either the labial or the lingual (transillumination). The control sample was cured from the labial for a total of 40 seconds of light exposure. Experimental samples were cured from the lingual (transillumination) for 20, 30, 40, or 50 seconds. The shear-peel bond strengths were tested at 30 minutes and 24 hours after light application. The results of this study demonstrated no statistically significant difference between 40 seconds of labial curing and most of the lingually cured groups. The only experimental group that differed statistically from the control group was the 40-second lingual cure group tested at 30 minutes after light application. Actual bond strengths, however, were lower for all experimental samples. The samples tested at 24 hours that received 50 seconds of transillumination were nearly the same as the control values. This study demonstrated that transillumination of maxillary incisors is an acceptable method of curing orthodontic adhesive, particularly if the exposure time is increased from 40 to 50 seconds.

Rapid curing of bonding composite with a xenon plasma arc light.

The use of light-cured orthodontic adhesives is an increasingly popular method for the bonding of orthodontic brackets. However, one of the disadvantages of light-cured adhesives is their long curing times. The xenon plasma arc curing light is purported to dramatically reduce the required curing time. The purpose of this study was to test the efficiency of a xenon plasma arc light versus a conventional tungsten-quartz halogen light in producing effective bond strengths for orthodontic brackets. Standardized brackets were bonded to bovine enamel with 3 different orthodontic bonding materials. The bonding materials were exposed to the tungsten-quartz halogen light for 40 seconds and to the xenon light for 3, 6, and 9 seconds. Bond strength was tested 30 minutes and 24 hours after light-curing. The results showed that bond strength with the application of the xenon light was greater with longer exposures. There were no statistically significant differences between the bond strengths of the brackets exposed to the tungsten-quartz halogen light for 40 seconds and those exposed to the xenon light for 3, 6, or 9 seconds. However, xenon light exposures of 6 or 9 seconds were required to create bond strengths equal to those produced by the tungsten-quartz halogen light. The xenon light produced equivalent bond strengths at very short light exposures.

Enhancing wire-composite bond strength of bonded retainers with wire surface treatment.

Bonded orthodontic retainers with wires embedded in composite resin are commonly used for orthodontic retention. The purpose of this study was to test, in vitro, various wire surface treatments to determine the optimal method of enhancing the wire-composite bond strength. Coaxial wires and stainless steel wires with different surface treatments were bonded to bovine enamel and then pulled along their long axes with an Instron universal testing machine. Wire surface treatments included placing a right-angle bend in the wire, microetching the wire, and treating the wire with adhesion promoters; combinations of treatments were also examined. The results demonstrated a 24-fold increase in the wire-composite bond strength of wire that was microetched (sandblasted), compared with that of untreated straight wire. The difference between the amount of force required to break the bond produced by microetching alone (246.1 +/- 46.0 MPa) and that required for the bonds produced by the retentive bend (87.8 +/- 16.3 MPa), the adhesion promoters (silane, 11.0 +/- 3.1 MPa; Metal Primer, 28.5 +/- 15.8 MPa), or for any combination of surface treatments, was statistically significant. Microetching a stainless steel wire produced a higher wire-composite bond strength than that obtained from a coaxial wire (113.5 +/- 27.5 MPa). The results of this study indicate that microetching or sandblasting a stainless steel wire significantly increases the strength of the wire-composite bond.

Adult growth, aging, and the single-tooth implant.

Single-tooth implants are an increasingly popular method for replacing single teeth. While the effects of growth on implants in children have been well documented, the changes that occur in adults have not been studied with respect to single-tooth implants. It has been assumed that adults are stable and do not change; however, research in the last few years has indicated that adults do change with aging, and adult growth does occur. The changes in adults occur over decades rather than rapidly, as seen in children. Aging changes are readily apparent in the soft tissues of the face and create dramatic changes. Changes in the jaws and teeth occur as a result of continued, slow growth, in contrast to the aging effects seen in soft tissues. Growth changes occur in the arches and result in adaptive changes in the teeth over time, both vertically and horizontally, and in alignment. These dental changes may result in a lack of occlusion vertically or malposition of adjacent natural teeth relative to the implant crown. Clinicians may be well advised to observe and report these changes and warn patients that changes can occur over the service life of the implant-supported crown. These changes may require maintenance adjustments or possible remaking of the implant crown as a result of adult growth, wear, or the esthetic changes of aging.

Uprighting molars without extrusion.

BACKGROUND: Orthodontic molar uprighting often results in extrusion of the molar, which is not always beneficial. The authors present a strategy for accomplishing molar uprighting without extrusion. DESCRIPTION OF THE PROCEDURE: The authors review and compare the benefits of molar uprighting with and without extrusion. The helical uprighting spring is probably the most popular appliance used for molar uprighting. It exerts an extrusive force on the molar during uprighting. The authors explain why this appliance produces an extrusive force and present a strategy to modify the appliance so that it can be used to upright without extrusion. CLINICAL IMPLICATIONS: The information presented in this article should help the dental practitioner select a suitable appliance, understand how it works and use it appropriately so that molar uprighting can be achieved without extrusion of the molar.

Maxillary midline diastemas: a look at the causes.

BACKGROUND: Maxillary midline diastemas are a common esthetic problem that dentists must treat. Many innovative therapies have been used, varying from restorative procedures to surgery (frenectomies) and orthodontics. At times, these procedures have been performed by the dentist without full appreciation of the factors contributing to the diastemas. CASE DESCRIPTION: Before the practitioner can determine the optimal treatment, he or she must consider the contributing factors. These include normal growth and development, tooth-size discrepancies, excessive incisor vertical overlap of different causes, mesiodistal and labiolingual incisor angulation, generalized spacing and pathological conditions. A carefully developed differential diagnosis allows the practitioner to choose the most effective orthodontic and/or restorative treatment. CLINICAL IMPLICATIONS: The differential diagnosis leads to a treatment approach that most effectively addresses the patient's problem. By treating the cause of the diastema, rather than just the space, the dentist enhances both the patient's dental function and appearance.

The use of bovine enamel in bonding studies.

Bovine enamel is commonly used in enamel bonding studies, therefore, a familiarity with some aspects of bovine enamel bonding are important in order to evaluate the studies. Bovine enamel has the advantages of easy attainability and similar microstructure to human enamel. In this study the strength of the enamel bond using an orthodontic adhesive was compared between deciduous bovine, permanent bovine, and human enamel, as well as, the effect on bond strength of multiple rebonding to bovine enamel. This study found that the bond strength to bovine enamel was 21% to 44% weaker than to human enamel, and the bond strength to deciduous bovine enamel was significantly greater than to permanent bovine enamel. Either all deciduous or all permanent bovine incisors should be used, or permanent and deciduous bovine incisors evenly distributed in sample groups. Bovine enamel was rebonded five times without significantly affecting bond strength, thus, bovine enamel can be reused in bonding studies without significantly affecting the results.

Natural tooth intrusion phenomenon with implants: a survey.

A common assumption when planning for treatment for a fixed partial denture potentially involving an osseointegrated implant is to avoid connection between the implant and natural tooth abutment because of the differences in mobility and potential long-term effects. A large population was surveyed to measure the incidence of natural tooth intrusion in implant-assisted fixed partial dentures (IAFPD) and to try to identify a correlation between type of implant and/or type of connector. Natural tooth intrusion occurred in 3.5% of the patient population specifically treated with IAFPD. No correlation could be made between incidence of intrusion and the type of implant or type of connector used.

Orthodontic competency in predoctoral education in American dental schools.

Predoctoral orthodontic education is evolving in the United States to reflect the move towards competency-based education. This trend focuses on teaching to competency in an area or procedure. In orthodontics, this creates a dilemma for the educator in determining what orthodontic competency actually is and how to achieve it. A survey of United States orthodontic departments was conducted to aid in examining the change toward competency-based education in predoctoral clinical orthodontics. The results demonstrated a large amount of diversity regarding both the definition and the use of competencies. The most recent US accreditation standards and guidelines are moving away from specific treatment techniques and more towards management and recognition of malocclusions for the recently-graduated general dentist.

Implant use in growing patients. Treatment planning concerns.

The dynamic relationship of dental and craniofacial development to the use of dental implants in a growing patient must be understood before this treatment is initiated. This article describes the three dimensions of maxillary, mandibular, and skeletal growth and their relationship to the placement of dental implants. Recommendations are made for the use of dental implants in the growing individual predicated on the above parameters of growth and development.

Effective orthodontics: achieving objectives, avoiding misadventures.

The authors outline four principles that should be considered when planning orthodontic tooth movement. They suggest that dentists have clear treatment objectives, know the force requirements to achieve those objectives, choose the best equipment to provide the needed forces and prevent unwanted tooth movement during treatment. To illustrate use of these principles, the authors refer to a sample treatment scenario. They also provide a mnemonic device to help dentists recall these principles.

Ceramic bracket bonding: a comparison of shear, tensile, and torsional bond strengths of ceramic brackets.

The purpose of this study was to evaluate whether shear, tensile, or torsional forces were best suited for debonding ceramic brackets. Four commercially available ceramic brackets were evaluated. The brackets included both polycrystalline and monocrystalline types with either chemical or mechanical retention in the bracket bases. The ceramic brackets were bonded to one hundred and twenty bovine teeth, using Concise. The brackets were stressed until bond or bracket failure occurred with either shear, tensile, or torsional forces on the Instron machine. The maximum bond strength and the site of bond failure was recorded. Starfire TMB brackets fractured 30% of the time during shear debonding, whereas, Quasar 1000, Lumina, and Transcend 2000 brackets exhibited no bracket fractures. The shear bond strengths of Quasar 1000 brackets were significantly higher than Starfire TMB brackets. Starfire TMB was the only bracket type that exhibited no bracket fractures with tensile force. Tensile bond strengths were not significantly different between the four bracket types. In torsion, Lumina was the only bracket type that did not exhibit any bracket failures. Shear and tensile bond strengths of chemically retained brackets were not significantly different than mechanically retained brackets. Torsional bond strength of chemically retained brackets was significantly higher than mechanically retained brackets. The results suggest Quasar 1000, Lumina, and Transcend 2000 are best removed with shear or tensile forces. Starfire TMB is best removed with tensile forces.

Cephalometric values for adult Mexican-Americans.

Cephalometric studies of adult Mexican-Americans are incomplete. The purpose of this study was to evaluate whether significant cephalometric differences exist between adult Mexican-American, black American, and white patients. Lateral cephalometric radiographs were taken of 48 Mexican-American adults (23 men, 25 women). All subjects met the following criteria: parents, grandparents, or great-grandparents were born in Mexico; 18 to 50 years of age; Class I occlusion with minor or no crowding; good facial balance; no significant medical history or history of facial trauma; no previous orthodontic treatment or maxillofacial surgery. Twenty-five cephalometric measurements were analyzed. Significant racial and sexual differences were found in the following areas: skeletal measurement (SNA, ANB, PO-N perpendicular, Co-A, Co-Gn, ANS-Me, MP-FH, MP-SN); dental measurement (U1-A perpendicular, L1-APo, U1-L1, IMPA); soft tissue measurement (NLA, FCA, UFH (pu), ULL). Orthodontists and oral surgeons will find the cephalometric values of help in the diagnosis and treatment planning of potential orthognathic surgery patients.

Mandibular implants and the growing patient.

The dynamic relation of the anteroposterior and rotational growth of the mandible to the transverse arch width and dental height changes must be understood before placing endosseous implants in actively growing patients. Research models demonstrate that osseointegrated implants lack the compensatory growth mechanism of the natural dentition. Remodeling associated with skeletal growth in the region of the implant placement site could cause the implant to either become unsupported by bone or submerged within it. Implants placed after age 15 in girls and 18 in boys have the most predictable prognosis. When placed in the growing patient, dental implants should be closely monitored and carefully restored with implant prostheses designed to accommodate growth and development.

Maxillary implants and the growing patient.

Maxillary skeletal and dental growth results in dramatic changes in all three dimensions during active growth. Experimental evidence and the behavior of ankylosed teeth suggest that an osseointegrated object remains stationary in the bone surrounding it and does not move or adapt to bone remodeling. Growth changes may result in the burying or loss of implants depending on the placement site. Hence, implants placed in the early mixed dentition have a poor prognosis of continued usefulness through puberty. When placed early, implants may disturb growth or have to be replaced. Implants placed during late puberty or early adulthood have the best change for long-term usefulness.