Laboratory Technician Assessment of the Quality of Single-Unit Crown Preparations and Impressions as Predictors of the Clinical Acceptability of Crowns as Determined by the Treating Dentist: Findings from the National Dental Practice-Based Research Network.

PURPOSE: In-laboratory assessment by laboratory technicians may offer insight to increase clinical success of dental crowns, and research in this area is lacking. MATERIALS AND METHODS: Dentists in the National Dental Practice-Based Research Network enrolled patients in a study about single-unit crowns; laboratory technicians evaluated the quality of tooth preparations and impressions. The primary outcome for each crown was clinical acceptability (CAC), as judged by the treating dentist. A secondary outcome was "Goodness of Fit (GOF)," a composite score of several aspects of clinical fit, also judged by the study dentist. A mixed-effects logistic regression was used to analyze associations between laboratory technician ratings and the CAC and GOF. RESULTS: Dentists (n = 205) evaluated 3731 crowns. Technicians ranked the marginal detail of impressions as good or excellent in 92% of cases; other aspects of the impression were ranked good or excellent 88% of the time. Regarding tooth preparation, about 90% of preparations were considered adequate (neither excessive nor inadequate reduction). Factors associated with higher CAC were more preparation taper, and use of optical imaging. Factors associated with better GOF were higher impression quality, greater occlusal reduction, more preparation taper, and optical imaging. CONCLUSIONS: Overall quality of preparations and impressions was very high, as evaluated by laboratory technicians. Several clinical parameters were associated with higher CAC and GOF. Clinicians who struggle with crown remakes might consider less conservative tooth preparation, as well as using digital impression technology.

Clinical acceptance of single-unit crowns and its association with impression and tissue displacement techniques: Findings from the National Dental Practice-Based Research Network.

STATEMENT OF PROBLEM: The definitive impression for a single-unit crown involves many material and technique factors that may affect the success of the crown. PURPOSE: The purpose of this prospective cohort study was to determine whether impression technique (tray selection), impression material, or tissue displacement technique are associated with the clinical acceptability of the crown (CAC). MATERIAL AND METHODS: Dentists in the National Dental Practice-Based Research Network documented details of the preparation, impression, and delivery of 3730 consecutive single-unit crowns. Mixed-effects logistic regression analyses were performed to evaluate associations between impression techniques and materials and the CAC and to assess associations between the presence of a subgingival margin with the displacement technique and the outcome variables CAC and number of impressions required. RESULTS: Of the 3730 crowns, 3589 (96.2%) were deemed clinically acceptable. A significant difference in the CAC was found with different impression techniques (P<.001) and different impression materials (P<.001). The percentage of the CAC for digital scans was 99.5%, 95.8% for dual-arch trays, 95.2% for quadrant trays, and 94.0% for complete-arch impression trays. Although no statistically significant difference was found in the CAC produced with dual-arch trays without both mesial and distal contacts, crowns fabricated under these conditions were less likely to achieve excellent occlusion. The percentage of the CAC for digital scans was 99.5%, 97.0% for polyether impressions, 95.5% for polyvinyl siloxane impressions, and 90.5% for other impression materials. Accounting for the location of the margin, the use of a dual-cord displacement technique was significantly associated with lower rates of requiring more than 1 impression (P=.015, odds ratio=1.43). CONCLUSIONS: Dual-arch trays produced clinically acceptable crowns; however, if the prepared tooth was unbounded, the occlusal fit was more likely to have been compromised. Digital scans produced a slightly higher rate of CAC than conventional impression materials. The use of a dual-cord technique was associated with a decreased need to remake impressions when the margins were subgingival.

Choice of cement for single-unit crowns: Findings from The National Dental Practice-Based Research Network.

BACKGROUND: In this article, the authors present clinical factors associated with the type of cement practitioners use for restoration of single-unit crowns. METHODS: A total of 202 dentists in The National Dental Practice-Based Research Network recorded clinical details (including cement type) used for 3,468 single-unit crowns. The authors classified crowns as bonded if the dentist used a resin cement. The authors used mixed-model logistic regression to assess the associations between various clinical factors and the dentist's decision to bond. RESULTS: A total of 38.1% of crowns were bonded, and 61.9% were nonbonded; 39.1% (79 of 202) of dentists never bonded a crown, and 20.3% (41 of 202) of dentists bonded every crown in the study. Crowns with excessive occlusal reduction (as judged by laboratory technicians) were more likely to be bonded (P = .02); however, there was no association with bonding and excessive taper (P = .15) or axial reduction (P = .08). Crowns were more likely to be bonded if they were fabricated from leucite-reinforced glass ceramic (76.5%) or lithium disilicate (70.8%) than if they were fabricated from layered zirconia (38.8%), full-contour zirconia (30.1%), full metal (14.7%), or porcelain-fused-to-metal (13.8%) (P < .01) restorative material. There was no significant association between choice to bond and crown margin location (P = .35). Crowns in the anterior maxilla were more likely to be bonded (P < .01). CONCLUSIONS: Excessive occlusal tooth preparation, anterior location of a crown, and the use of glass ceramic crowns were associated significantly with the decision to bond. PRACTICAL IMPLICATIONS: In this study, the authors identified factors significantly associated with the clinical decision made by practicing dentists when selecting a cement for restoration of single-unit crowns.

Remake Rates for Single-Unit Crowns in Clinical Practice: Findings from The National Dental Practice-Based Research Network.

PURPOSE: Some crowns returned from the laboratory are clinically unacceptable, and dentists must remake them. The objectives of this study were to: (1) quantify the remake rate of single-unit crowns; and (2) identify factors significantly associated with crown remakes and intraoral fit. MATERIALS AND METHODS: Dentists participating in the National Dental Practice-Based Research Network recruited patients needing crowns and documented fabrication techniques, patient characteristics, and outcomes. Crowns were considered clinically acceptable or rejected. Also, various aspects of the clinical fit of the crown were graded and categorized as 'Goodness of Fit (GOF).' Dentist and patient characteristics were tested statistically for associations with crown acceptability and GOF. RESULTS: More than 200 dentists participated in this study (N = 205) and evaluated 3750 single-unit crowns. The mean age (years) of patients receiving a crown was 55. The remake rate for crowns was 3.8%. The range of rejection rates among individual practitioners was 0% to 42%. Most clinicians (118, or 58%) did not reject any crowns; all rejections came from 42% of the clinicians (n = 87). The most common reasons for rejections were proximal misfit, marginal errors, and esthetic failures. Fewer years in practice was significantly associated with lower crown success rates and lower fit scores. GOF was also associated with practice busyness and patient insurance status, patient gender (dentists reported better fit for female patients), and patient ethnicity. CONCLUSIONS: The crown remake rate in this study was about 4%. Remakes and crown GOF were associated with certain dentist and practice characteristics.

Preparation Techniques Used to Make Single-Unit Crowns: Findings from The National Dental Practice-Based Research Network.

PURPOSE: To: (1) determine which preparation techniques clinicians use in routine clinical practice for single-unit crown restorations; (2) test whether certain practice, dentist, and patient characteristics are significantly associated with these techniques. MATERIALS AND METHODS: Dentists in the National Dental Practice-Based Research Network participated in a questionnaire regarding preparation techniques, dental equipment used for single-unit crown preparations, scheduled chair time, occlusal clearance determination, location of finish lines, magnification during preparation, supplemental lighting, shade selection, use of intraoral photographs, and trimming dies. Survey responses were compared by dentist and practice characteristics using ANOVA. RESULTS: Of the 2132 eligible dentists, 1777 (83%) responded to the survey. The top two margin configuration choices for single-unit crown preparation for posterior crowns were chamfer/heavy chamfer (65%) and shoulder (23%). For anterior crowns, the most prevalent choices were the chamfer (54%) and the shoulder (37%) configurations. Regarding shade selection, a combination of dentist, assistant, and patient input was used to select anterior shades 59% of the time. Photographs are used to communicate shade selection with the laboratory in about half of esthetically demanding cases. The ideal finish line was located at the crest of gingival tissue for 49% of respondents; 29% preferred 1 mm below the crest; and 22% preferred the finish line above the crest of tissue. Average chair time scheduled for a crown preparation appointment was 76 ± 21 minutes. Practice and dentist characteristics were significantly associated with margin choice including practice type (p < 0.001), region (p < 0.001), and years since graduation (p < 0.001). CONCLUSIONS: Network dentists prefer chamfer/heavy chamfer margin designs, followed by shoulder preparations. These choices were related to practice and dentist characteristics.

Impression Techniques Used for Single-Unit Crowns: Findings from the National Dental Practice-Based Research Network.

PURPOSE: To: (1) determine which impression and gingival displacement techniques practitioners use for single-unit crowns on natural teeth; and (2) test whether certain dentist and practice characteristics are significantly associated with the use of these techniques. MATERIALS AND METHODS: Dentists participating in the National Dental Practice-Based Research Network were eligible for this survey study. The study used a questionnaire developed by clinicians, statisticians, laboratory technicians, and survey experts. The questionnaire was pretested via cognitive interviewing with a regionally diverse group of practitioners. The survey included questions regarding gingival displacement and impression techniques. Survey responses were compared by dentist and practice characteristics using ANOVA. RESULTS: The response rate was 1777 of 2132 eligible dentists (83%). Regarding gingival displacement, most clinicians reported using either a single cord (35%) or dual cord (35%) technique. About 16% of respondents preferred an injectable retraction technique. For making impressions, the most frequently used techniques and materials are: poly(vinyl siloxane), 77%; polyether, 12%; optical/digital, 9%. A dental auxiliary or assistant made the final impression 2% of the time. Regarding dual-arch impression trays, 23% of practitioners report they typically use a metal frame tray, 60% use a plastic frame, and 16% do not use a dual-arch tray. Clinicians using optical impression techniques were more likely to be private practice owners or associates. CONCLUSIONS: This study documents current techniques for gingival displacement and making impressions for crowns. Certain dentist and practice characteristics are significantly associated with these techniques.

Impression evaluation and laboratory use for single-unit crowns: Findings from The National Dental Practice-Based Research Network.

BACKGROUND: Objectives were to determine the likelihood that a clinician accepts an impression for a single-unit crown and document crown remake rates. METHODS: The authors developed a questionnaire that asked dentists about techniques used to fabricate single-unit crowns. The authors showed dentists photographs of 4 impressions and asked them to accept or reject each impression. The authors correlated answers with dentist and practice characteristics. Other questions pertained to laboratory use and crown remake rates. RESULTS: The response rate was 83% (1,777 of 2,132 eligible dentists). Of the 4 impressions evaluated, 3 received consistent responses, with 85% agreement. One impression was more equivocal; 52% accepted the impression. The likelihood of accepting an impression was associated significantly with the clinician's sex, race, ethnicity, and practice busyness. Clinicians produced 18 crowns per month on average, and 9% used in-office milling. Most dentists (59%) reported a remake rate of less than 2%, whereas 17% reported a remake rate greater than 4%. Lower remake rates were associated significantly with more experienced clinicians, optical impressions, and not using dual-arch trays. CONCLUSIONS: Although dentists were largely consistent in their evaluation of impressions (> 85%), nonclinical factors were associated with whether an impression was accepted or rejected. Lower crown remake rates were associated with more experienced clinicians, optical impressions, and not using dual-arch trays. PRACTICAL IMPLICATIONS: These results provide a snapshot of clinical care considerations among a diverse group of dentists. Clinicians can compare their own remake rates and impression evaluation techniques with those in this sample when developing best practice protocols.

Dentist material selection for single-unit crowns: Findings from the National Dental Practice-Based Research Network.

OBJECTIVES: Dentists enrolled in the National Dental Practice-Based Research Network completed a study questionnaire about techniques and materials used for single-unit crowns and an enrollment questionnaire about dentist/practice characteristics. The objectives were to quantify dentists' material recommendations and test the hypothesis that dentist's and practice's characteristics are significantly associated with these recommendations. METHODS: Surveyed dentists responded to a contextual scenario asking what material they would use for a single-unit crown on an anterior and posterior tooth. Material choices included: full metal, porcelain-fused-to-metal (PFM), all-zirconia, layered zirconia, lithium disilicate, leucite-reinforced ceramic, or other. RESULTS: 1777 of 2132 eligible dentists responded (83%). The top 3 choices for anterior crowns were lithium disilicate (54%), layered zirconia (17%), and leucite-reinforced glass ceramic (13%). There were significant differences (p<0.05) by dentist's gender, race, years since graduation, practice type, region, practice busyness, hours worked/week, and location type. The top 3 choices for posterior crowns were all-zirconia (32%), PFM (31%), and lithium disilicate (21%). There were significant differences (p<0.05) by dentist's gender, practice type, region, practice busyness, insurance coverage, hours worked/week, and location type. CONCLUSIONS: Network dentists use a broad range of materials for single-unit crowns for anterior and posterior teeth, adopting newer materials into their practices as they become available. Material choices are significantly associated with dentist's and practice's characteristics. CLINICAL SIGNIFICANCE: Decisions for crown material may be influenced by factors unrelated to tooth and patient variables. Dentists should be cognizant of this when developing an evidence-based approach to selecting crown material.

Treatment recommendations for single-unit crowns: Findings from The National Dental Practice-Based Research Network.

BACKGROUND: The objectives of this study were to quantify practitioner variation in likelihood to recommend a crown and test whether certain dentist, practice, and clinical factors are associated significantly with this likelihood. METHODS: Dentists in The National Dental Practice-Based Research Network completed a questionnaire about indications for single-unit crowns. In 4 clinical scenarios, practitioners ranked their likelihood of recommending a single-unit crown. The authors used these responses to calculate a dentist-specific crown factor (range, 0-12). A higher score implied a higher likelihood of recommending a crown. The authors tested certain characteristics for statistically significant associations with the crown factor. RESULTS: A total of 1,777 of 2,132 eligible dentists (83%) responded. Practitioners were most likely to recommend crowns for teeth that were fractured, cracked, or endodontically treated or had a broken restoration. Practitioners overwhelmingly recommended crowns for posterior teeth treated endodontically (94%). Practice owners, practitioners in the Southwest, and practitioners with a balanced workload were more likely to recommend crowns, as were practitioners who used optical scanners for digital impressions. CONCLUSIONS: There is substantial variation in the likelihood of recommending a crown. Although consensus exists in some areas (posterior endodontic treatment), variation dominates in others (size of an existing restoration). Recommendations varied according to type of practice, network region, practice busyness, patient insurance status, and use of optical scanners. PRACTICAL IMPLICATIONS: Recommendations for crowns may be influenced by factors unrelated to tooth and patient variables. A concern for tooth fracture-whether from endodontic treatment, fractured teeth, or large restorations-prompted many clinicians to recommend crowns.

Tear Trough Incision for External Dacryocystorhinostomy.

PURPOSE: Scar formation is a frequently cited complication of external dacryocystorhinostomy (exDCR). The purpose of this study is to evaluate scar appearance after exDCR with the skin incision placed in the tear trough. METHODS: Multicenter, prospective, noncomparative interventional study was approved by the University of Colorado Institutional Review Board. Patients undergoing exDCR from February 2013 to January 2014 were included in the study, and surgeries were performed by all authors. The incision site for all patients started just under the medial canthal tendon and extended inferolaterally into the tear trough for 10 mm to 15 mm. External dacryocystorhinostomy was performed in the usual manner, and the incision was closed according to the surgeon's preference. At 3 months postop, all patients were asked to rate their scar on the basis of the following grading scale: 0, invisible incision; 1, minimally visible incision; 2, moderately visible incision; and 3, very visible incision. Functional success of the surgery was also determined by asking the patients if their symptoms resolved, improved, or did not change. External photographs taken at 3 months after surgery were graded by 3 independent oculofacial and facial plastic surgeons using the same grading scale. RESULTS: Seventy-two surgeries were performed in 68 consecutive exDCR patients with nasolacrimal duct obstruction during the study period. Sixty-nine out of 72 patients reported improved or resolved symptoms (95.8%). The average patient scar grade was 0.21, while the average surgeon scar grade was 0.99 (p < 0.001). Sixty out of the 72 patients graded the scar as invisible (83.3%), and only 3 patients graded the scar as moderately visible (4.2%). No patients graded the scar as very visible. Of the 216 surgeon grades, 55 scars were graded as invisible (25.5%), while 8 were graded as very visible (3.7%). CONCLUSIONS: Scar appearance after exDCR with the incision placed in the tear trough is minimally visible to surgeons, and more importantly, nearly invisible to patients.

Validity and reliability of portfolio assessment of student competence in two dental school populations: a four-year study.

The purpose of this study was to empirically investigate the validity and reliability of portfolio assessment in two U.S. dental schools using a unified framework for validity. In the process of validation, it is not the test that is validated but rather the claims (interpretations and uses) about test scores that are validated. Kane's argument-based validation framework provided the structure for reporting results where validity claims are followed by evidence to support the argument. This multivariate generalizability theory study found that the greatest source of variance was attributable to faculty raters, suggesting that portfolio assessment would benefit from two raters' evaluating each portfolio independently. The results are generally supportive of holistic scoring, but analytical scoring deserves further research. Correlational analyses between student portfolios and traditional measures of student competence and readiness for licensure resulted in significant correlations between portfolios and National Board Dental Examination Part I (r=0.323, p<0.01) and Part II scores (r=0.268, p<0.05) and small and non-significant correlations with grade point average and scores on the Western Regional Examining Board (WREB) exam. It is incumbent upon the users of portfolio assessment to determine if the claims and evidence arguments set forth in this study support the proposed claims for and decisions about portfolio assessment in their respective institutions.

Orbital cellulitis and intraconal abscess formation after strabismus surgery in an adult patient.

We report a 60-year-old woman who presented with orbital cellulitis, restricted ocular motility, proptosis, and visual acuity of counting fingers in her left eye 3 days after strabismus surgery. Although she initially responded well to antibiotic and anti-inflammatory therapy, visual acuity in the left eye again decreased on postoperative day 5. Radiographic imaging revealed an intraconal orbital abscess, and she underwent left lateral orbitotomy with abscess drainage, with continued antibiotics and a tapering dose of steroids. To our knowledge, this is the first case of orbital cellulitis and intraconal abscess after strabismus surgery in an adult.

Strength comparison of four techniques to secure implant attachment housings to complete dentures.

STATEMENT OF PROBLEM: Implant overdentures become thinner and weaker after direct transfer of implant attachment housings. While much has been published on denture repair, these data do not directly apply to implant overdentures because the introduction of a metal housing changes the character of the repair. It is desirable to make a strong repair to avoid prosthesis fracture. PURPOSE: The purpose of this study was to compare the flexural strengths of 4 different methods for chairside direct transfer of implant attachment housings. MATERIAL AND METHODS: Eighty 11.5 × 9.1 × 39 mm heat-polymerized acrylic resin blocks were processed, assessed for porosities, and polished. An 8.5 mm diameter hole was drilled to a depth of 5 mm in the center of each block. Attachment housings were set into the bases with 4 different repair materials: autopolymerized acrylic resin (APAR), light-polymerized acrylic resin (LPAR), autopolymerized acrylic resin with silanated attachment housings (APSAH), and light-polymerized acrylic resin with silanated attachment housings (LPSAH). Blocks were immersed in water for 30 days in an incubator. A 3-point bend test was done in a universal testing machine, and load to fracture was recorded (MPa). Results were compared with 2-way ANOVA (α=.05). RESULTS: APSAH had the highest mean flexural strength at fracture (863.1 ±87 MPa) as compared to APAR (678.4 ±72.4 MPa), LPAR (550.9 ±119.3 MPa), and LPSAH (543.2 ±100.8 MPa). A comparison among the 4 groups showed that there were significant differences in maximum flexural strength (P<.001). The mean maximum strength of autopolymerized acrylic resin groups was significantly higher than light-polymerized acrylic resin groups. Silanation increased strength significantly compared to nonsilanated groups. CONCLUSIONS: The flexural strength of autopolymerized acrylic resin with silanated attachment housings was significantly higher than autopolymerized acrylic resin alone, light-polymerized acrylic resin alone, or light-polymerized acrylic resin with silanated attachment housings. Autopolymerized acrylic resin produced stronger constructs than light-polymerized materials.

A 24-month evaluation of amalgam and resin-based composite restorations: Findings from The National Dental Practice-Based Research Network.

BACKGROUND: Knowing which factors influence restoration longevity can help clinicians make sound treatment decisions. The authors analyzed data from The National Dental Practice-Based Research Network to identify predictors of early failures of amalgam and resin-based composite (RBC) restorations. METHODS: In this prospective cohort study, the authors gathered information from clinicians and offices participating in the network. Clinicians completed a baseline data collection form at the time of restoration placement and annually thereafter. Data collected included patient factors, practice factors and dentist factors, and the authors analyzed them by using mixed-model logistic regression. RESULTS: A total of 226 practitioners followed up 6,218 direct restorations in 3,855 patients; 386 restorations failed (6.2 percent) during the mean (standard deviation) follow-up of 23.7 (8.8) months. The number of tooth surfaces restored at baseline helped predict subsequent restoration failure; restorations with four or more restored surfaces were more than four times more likely to fail. Restorative material was not associated significantly with longevity; neither was tooth type. Older patient age was associated highly with failure (P < .001). The failure rate for children was 4 percent, compared with 10 percent for people 65 years or older. Dentist's sex and practice workload were associated significantly with restoration longevity. CONCLUSIONS: In this prospective cohort study, these factors were significantly predictive of failure for amalgam and RBC restorations: patient's age, a higher number of surfaces restored at baseline, the dentist's sex and the practice workload. Material choice was not significantly predictive in these early results. Practical Implications. If clinicians can recognize and identify the risk factors associated with early restoration failure, more effective treatment plans may be offered to the patient.

Implementation of portfolio assessment of student competence in two dental school populations.

The purpose of this article is to describe the process and procedures involved in the implementation of portfolio assessment at two dental schools. Portfolios can be defined as a purposeful collection of student work that involves reflection in which students identify gaps in their knowledge and abilities and develop strategies for correcting those gaps. Framed within the current context of dental education and the calls for change in the ways dental students are taught and assessed, these two dental schools embarked upon an assessment strategy aimed at engaging students in self-directed learning and self-assessment. Where one school chose the implementation of programmatic portfolios based on all program competencies, the other school implemented portfolio assessment around specific program competencies not typically captured easily with traditional assessment measures such as ethics and ethical decision making. In a competency-based dental curriculum in which competence has been defined as the ability to accurately self-assess, it makes sense that strategies aimed at developing the skill of self-assessment should be the goal of every dental education program.

A residual granuloma in association with a dental implant.

At times, dental implants are placed into sites with a history of periapical pathology. Sometimes the infection is active, and other times the tooth may have been extracted years before implant placement. In either case, the possibility exists for long-term residual cysts or infections that can negatively impact the prognosis of the implant. In this case report, an implant is placed into a healed mandibular ridge several months after extraction of the tooth. A radiolucency was noted on routine radiographic examination 2 years later. Surgical inspection and histology revealed a periapical granuloma with acute and chronic inflammatory cells. After surgical curettage of the site, the patient healed without complication. Implants may develop apical pathology as a result of a preexisting long-term residual infection.

A randomized clinical trial to compare diagnostic casts made using plastic and metal trays.

STATEMENT OF PROBLEM: Virtually every prosthodontic rehabilitation involves making diagnostic casts for analysis and prosthesis fabrication. Frequently, these casts are produced using irreversible hydrocolloid (IH) impression materials in stock metal or plastic trays. However, it is unclear whether one technique produces a more accurate cast. PURPOSE: The purpose of this randomized clinical trial was to compare the linear accuracy of diagnostic casts produced using IH with 1 of 3 different tray types: (1) perforated metal trays, (2) stock plastic trays, and (3) directed-flow stock plastic trays. All groups were compared to casts produced with custom trays and vinyl polysiloxane (VPS) impression materials, which were considered the control. MATERIAL AND METHODS: Seven subjects participated in this trial. IH impressions were made in a random order using 1 of 3 tray types: stock plastic, perforated metal, or plastic directed flow. These were compared to VPS impressions using custom trays (control group). Each impression technique was repeated 3 times per subject, for a total of 84 observations. Impressions were disinfected and poured in a type IV stone. Linear accuracy of casts was measured using computer software analysis of scanned images of the casts at x30 magnification. Three linear measurements were made on each cast: second molar to second molar, right second molar to left first premolar, and left second molar to right first premolar. Measurements were compared among techniques using mixed-model analysis of variance to account for correlation among the multiple measurements made on each subject. Dunnett's adjustment for multiple comparisons with control was used (α=.05). RESULTS: For molar-to-molar and right second molar to the left first premolar measurements, there were no significant differences in linear dimensions between casts made from different trays. However, linear measurements from the left second molar to the right first premolar demonstrated significant differences for casts made with stock metal, directed-flow, and stock plastic trays compared to custom trays. In this group, casts produced by stock metal, directed-flow, and stock plastic trays differed from controls by 102, 68, and 71 um, respectively. Generally, casts made with plastic trays (stock plastic and directed flow) had values closer to those of custom trays than did casts made with metal trays. CONCLUSIONS: Impressions made with irreversible hydrocolloid produced casts that were significantly different in linear dimension than casts produced by custom trays and VPS impressions. These differences were not uniform, but varied by location on the cast.

Variability of mechanical torque-limiting devices in clinical service at a US dental school.

PURPOSE: The purpose of this study was to measure the variability of torque produced by a population of mechanical torque-limiting devices in clinical service in a US dental school. The torque-limiting devices were divided into two categories according to their mode of action: toggle-type and beam wrenches. Proper action of these devices is essential for calibrated delivery of preload to implant prosthetic screws. MATERIALS AND METHODS: Seventeen torque-limiting devices (35 Ncm) were obtained from graduate prosthodontic, predoctoral, and faculty practice clinics. Nine of these were toggle-type devices, and eight were beam-type wrenches. Torque from each wrench was measured using an MGT electronic torque meter. Wrenches were tested in two modes, slow (over 4 seconds) and fast (over 1 second). RESULTS: Toggle-type torque wrenches produced a mean (+/- SD) torque of 38.1 +/- 16.0 Ncm; beam-type wrenches produced 32.8 +/- 1.1 Ncm. These results were not significantly different. When tested in fast mode (1 second), toggle-type wrenches produced 28.0 +/- 9.6 Ncm; in the slow mode (4 seconds) they produced significantly more force, 36.6 +/- 14.0 Ncm (p < 0.001). Beam-type wrenches produced 33.2 +/- 1.1 Ncm and 32.8 +/- 1.1 Ncm in fast and slow modes, respectively. CONCLUSIONS: Both types of wrenches tested were capable of producing accurate torque values; however, variability was higher in the toggle-type group. Some toggle-type torque wrenches in clinical service delivered unacceptably high torque values. It is recommended that clinicians calibrate toggle-type wrenches frequently. Torque wrenches should be activated slowly, over 4 seconds, when using a correctly calibrated toggle-type wrench.

Comparison of the passivity between cast alloy and laser-welded titanium overdenture bars.

PURPOSE: The purpose of this study was to investigate the fit of cast alloy overdenture and laser-welded titanium-alloy bars by measuring induced strain upon tightening of the bars on a master cast as well as a function of screw tightening sequence. MATERIALS AND METHODS: Four implant analogs were secured into Type IV dental stone to simulate a mandibular edentulous patient cast, and two groups of four overdenture bars were fabricated. Group I was four cast alloy bars and Group II was four laser-welded titanium bars. The cast alloy bars included Au-Ag-Pd, Pd-Ag-Au, Au-Ag-Cu-Pd, and Ag-Pd-Cu-Au, while the laser-welded bars were all Ti-Al-V alloy. Bars were made from the same master cast, were torqued into place, and the total strain in the bars was measured through five strain gauges bonded to the bar between the implants. Each bar was placed and torqued 27 times to 30 Ncm per screw using three tightening sequences. Data were processed through a strain amplifier and analyzed by computer using StrainSmart software. Data were analyzed by ANOVA and Tukey's post hoc test. RESULTS: Significant differences were found between alloy types. Laser-welded titanium bars tended to have lower strains than corresponding cast bars, although the Au-Ag-Pd bar was not significantly different. The magnitudes of total strain were the least when first tightening the ends of the bar. CONCLUSIONS: The passivity of implant overdenture bars was evaluated using total strain of the bar when tightening. Selecting a high modulus of elasticity cast alloy or use of laser-welded bar design resulted in the lowest average strain magnitudes. While the effect of screw tightening sequence was minimal, tightening the distal ends first demonstrated the lowest strain, and hence the best passivity.

Enhancement of bonding to enamel and dentin prepared by Er,Cr:YSGG laser.

BACKGROUND AND OBJECTIVE: Erbium lasers are potential tools to remove caries and dental hard tissue but bond strengths of composites to those preparations are reported to be lower than conventional methods. The purpose of this study was to evaluate the effect of mechanical excavation and/or chemical alteration on bond strength of composites to laser irradiated enamel and dentin. MATERIALS AND METHODS: Seventy-two premolars were ground to obtain flat enamel (E, n = 36) or dentin (D, n = 36) surfaces in both buccal and lingual cusps, divided into: LaserExcavation (LEx), LaserNo-excavation (LNex), and Bur (B) groups. The laser groups were irradiated for 10 seconds by Er,Cr:YSGG laser [4.5 W, 60% air, 80% water (enamel) 3 W, 60% air, 70% water (dentin)]. Irradiated surfaces in the excavation groups (Ex) were then mechanically smoothed with a dental excavator, prepared surfaces were then etched (37% H(3)PO(4)) for 20 or 40 seconds (enamel) and 15 or 30 seconds (dentin), washed (20 seconds), adhesive was applied(Single Bond Plus), and light cured (20 seconds). A composite cylinder (Filtek Supreme Plus) formed, placed and light cured (40 seconds). The specimens were stored (37 degrees C,48 hours), shear bond tested (1 mm/minute), and statistically analyzed (P < 0.05). RESULTS: Mixed-model ANOVA showed significant differences between enamel (P = 0.0091) and between dentin groups (P = 0.0035). Tukey/Kramer showed mean shear bond strength (SBS+/-SE) of EB40 (27.01+/-2.38 MPa) was significantly higher than ELNoExc20 (14.39+/-2.5 MPa) and ELExc40 (14.90+/-2.28 MPa). Also DB30 (17.57+/- 1.67 MPa) and DLExc30 (18.6+/-1.74 MPa) were significantly higher than DLNoExc15 (9.56+/-1.86 MPa). CONCLUSION: Increasing the etching time up to 40 seconds or excavation of the laser prepared surface (but not the combination) may increase the bond strength to the level of conventional methods in enamel but excavation has a greater influence in dentin. Also the combination of both methods [excavation+longer etching time (30 seconds)] exhibit significantly better results in dentin.Mode of failure study showed mechanical excavation in both enamel and dentin can significantly reduce the cohesive failure in tooth structure.