Robert G. Rashid

The Accuracy and Reliability of Measurements Made on Computer-Based Digital Models

For reasons of convenience and economy, orthodontists who routinely use and maintain pre- and posttreatment plaster casts are beginning to use computer-based digital models. The purpose of this study was to determine the accuracy (validity), reproducibility (reliability), efficacy, and effectiveness of measurements made on computer-based models. A plastic model occlusion ie, dentoform, served as a gold standard to evaluate the systematic errors associated with producing either plaster or computer-based models. Accuracy, reproducibility, efficacy, and effectiveness were tested by comparing the measurements of the computer-based models with the measurements of the plaster models--(1) accuracy: one examiner measuring 10 models made from a dentoform, twice; (2) reproducibility and efficacy: two examiners measuring 50 models made from patients, twice; and (3) effectiveness: 10 examiners measuring 10 models made from patients, twice. Reproducibility (reliability) was tested by using the intraclass correlation coefficient. Repeated measures of analysis of variance for multiple repeated measurements and Students t-test were used to test for validity. Only measurements of maxillary and mandibular space available made on computer-based models differed from the measurements made on the dentoform gold standard. There was significantly greater variance for measurements made from computer-based models. Reproducibility was high for measurements made on both computer-based and plaster models. In conclusion, measurements made from computer-based models appear to be generally as accurate and reliable as measurements made from plaster models. Efficacy and effectiveness were similar to those of plaster models. Therefore, computer-based models appear to be a clinically acceptable alternative to conventional plaster models.

Standardized portrait photography for dental patients

Photography is becoming an increasingly important tool in the dental profession. But documentation of orthodontic or orthognathic treatment with pretreatment and posttreatment photographs can be misleading if features on one or both photographs are distorted. The dental photographer must be constantly aware of the importance of standardizing photographic variables when documentation of change is important. Although total reproducibility may not be practical, the photographer can establish a reasonably standardized approach to photographing patients. In this article the authors present the major considerations for frontal and profile facial photographs. Lens selection, camera position, subject distance, and position are all variables to be understood and controlled if accurate reproduction is desired. Numerous frontal and lateral photographs were made with head position, camera position, jaw position, and lens focal length changed to allow assessment of their contribution to the final picture. Using easily recognized facial landmarks, dental photographers can standardize frontal and lateral portraits for more consistent comparison.

Effect of home bleaching systems on enamel nanohardness and elastic modulus

OBJECTIVES The purpose of this study was to evaluate the nanohardness and elastic modulus of human enamel after treatment with tray and strip bleaching systems. METHODS Fifty-five human enamel samples were exposed to five different bleaching agents. Nanoindentations were made before and after bleaching treatments following the manufacturers directions using a Nanoindenter XP (MTS Systems Corporation, Oak Ridge, TN, USA). Nanohardness and elastic modulus measurements were obtained and the results were statistically analyzed using a repeated measures analysis of variance with a post-hoc Tukey-Kramer multiple comparison test. RESULTS Nanohardness and elastic modulus measurements showed decrease of mean values for each group except the control which remained the same. There were significant differences due to time (before and after treatment) and material effects in nanohardness (P<0.0001) and elastic modulus (P=0.0241). Measurements after treatment showed significant decrease in nanohardness between all groups and the control group. There was a significant difference in hardness between CP and TO after treatment. Additionally, there were significant differences in elastic modulus between the control group when compared to OB and TO after treatment. While there were significant changes in the elastic modulus due to treatment for both CP and TO, there were no significant differences between any of the groups after treatment. CONCLUSIONS Nanohardness and elastic modulus of human enamel were significantly decreased after the application of home-bleaching systems.

Celebrity smile esthetics assessment: Smile angulation

Statement of problem. Whether deviations in the angulation discrepancy between the intercanine and interpupillary line significantly affect attractiveness is unknown. Purpose. The purpose of this prospective study was to quantify dental and facial esthetics to determine whether smile angulation discrepancies in individuals identified as having attractive smiles are smaller than those in the average population. Material and methods. An Internet search for “best smile” and “celebrity” identified 108 celebrities (Test group). Photographs showing smiles within 10 degrees of a frontal view were gathered. In mannequin testing, small head rotation (<10 degrees) was found not to affect the measurements. Photographs of dental students were used for the control group. The angulation discrepancy between the intercanine and interpupillary line was measured using computer software. Groups were compared using the Mann‐Whitney U test (&agr;=.05). Results. Usable photographs were obtained for 94 celebrities (62 women, 32 men) and were compared with photographs of 97 dental students (54 women, 43 men). Significant (P<.01) differences in angulation discrepancy were found, with celebrities having smaller mean angulation discrepancies (0.97 degrees) than dental students (1.33 degrees). The differences between men and women were not statistically significant (P>.05). Conclusions. Celebrities identified as having “best smile” had significantly smaller mean angulation discrepancies than the control group.

Split-Mouth Comparison of Splinted and Nonsplinted Prostheses on Short Implants: 3-Year Results.

PURPOSE To compare splinted and individual restorations supported by short implants featuring an internal connection utilizing a split-mouth design. MATERIALS AND METHODS Splinted and nonsplinted implant crowns were prospectively compared in 18 patients. After verifying the need for at least two consecutive implants bilaterally, computed tomography scans were made, virtual planning was done, and qualifying patients were enrolled. Implants were placed using a two-stage surgical approach. After 3 to 5 months, patients were randomly restored with splinted prostheses on their left or right side. Nonsplinted restorations were made for contralateral sides. Radiographs were taken at prostheses seating and yearly exams. Radiographic bone levels were analyzed and compared (SAS 9.4) to determine differences between splinted and nonsplinted implants. Complications such as screw loosening, screw breakage, or porcelain fracture were assessed at recalls. RESULTS Eighteen patients (9 men and 9 women) with an age range from 49 to 76 years (mean = 56 years), received ≥ 4 implants in symmetrical posterior locations. Implants (n = 82) ranged in length from 6 to 11 mm with 70 implants ≤ 9 mm and 38 implants = 6 mm. At the time of this report, 3-year examinations and bone level comparisons were completed on 15 patients. One patient was lost to follow-up, one deviated from study protocol by smoking, and one was splinted on both sides due to repeated screw breakage. Screw loosening occurred in five patients on their nonsplinted side. These were 6-mm implants except for one patient. Porcelain chipping occurred for one patient on the splinted side. One 6-mm-length nonsplinted implant was lost after loading; this implant was successfully replaced after grafting. This patient had a total of six implants placed; ongoing bone level measurements included two pairs of implants only. For all implants combined, there was no significant difference (P > .05) at 1, 2, or 3 years for mean bone change around splinted and nonsplinted implants. However, length was identified as a significant factor (P = .0039). Further analysis revealed statistically significant differences between splinted and nonsplinted for 6-mm length implants at 24 (P = .0061) and 36 (P = .0144) months. A gain in mean bone level of 0.41 and 0.37 mm was observed for nonsplinted implants at 24 and 36 months compared with baseline. Bone levels for the splinted 6-mm implants were not statistically different from baseline measurements (P > .05). CONCLUSION Results of this prospective 3-year study of splinted ipsilateral and nonsplinted contralateral implants in 15 patients show: (1) peri-implant bone levels around splinted and nonsplinted implants were not statistically different for implants greater than 6 mm in length; (2) nonsplinted 6-mm implants revealed a gain in bone at 24 and 36 months compared with baseline; (3) all screw loosening only occurred on the nonsplinted side for 5 of 15 patients; and (4) implant loss after loading occurred for one 6-mm nonsplinted implant.

Impact energy absorption of three mouthguard materials in an aqueous environment

High impact energy absorption is an essential property for mouthguard materials. The impact test performance of three popular mouthguard materials was evaluated, using the procedure in American Society for Testing and Materials (ASTM) Standard D3763. Conventional ethylene vinyl acetate (EVA; T&S Dental and Plastics, Myerstown, PA, USA) served as the control. Pro-form (Dental Resources Inc., Delano, MN, USA), another EVA material, and PolyShok (Sportsguard Laboratories, Kent, OH, USA), an EVA product containing polyurethane were also evaluated. Specimens having dimensions of 3 inch x 3 inch x 4 mm were prepared from each material. After processing that followed manufacturer recommendations, specimens were conditioned for 1 h in 37 degrees C deionized water and loaded at 20 mph by a 0.5 inch diameter indenter containing a force transducer (Dynatup Model 9250 HV; Instron Corp., Canton, MA, USA). Both large-diameter (3 inches) and small-diameter (1.5 inch) support rings were used. For comparison, two specimens of each material were tested in the dry condition. Energy absorption was determined from the area under the force-time curve at 30 ms, and results for the water-conditioned specimens were compared using anova and the Kruskal-Wallis test. For the large-diameter support ring, energy absorption (mean +/- SD in ft x lbf inch(-1)), normalized to specimen thickness, was: EVA (n = 5), 110.2 +/- 48.4; Pro-form (n = 4), 110.0 +/- 11.3; PolyShok (n = 5), 105.7 +/- 16.5. For the small-diameter support ring, energy absorption was: EVA (n = 6), 140.5 +/- 13.9; Pro-form (n = 5), 109.0 +/- 26.0; PolyShok (n = 6), 124.4 +/- 28.4 (1 ft x lbf inch(-1) = 0.534 J cm(-1)). Because of substantial variation within some specimen groups, there was no significant difference in energy absorption for the three water-conditioned mouthguard materials and the two support ring sizes. The energy absorption for each material was much greater for other specimens tested in the dry condition.

Mirror Training in Three Dimensions for Dental Students

Dental students have significantly improved skills of indirect vision following mirror exercises in two dimensions. The objective of this study was to assess whether freshmen improved these skills after mirror training in three dimensions. A pretest was given to 60 subjects, maneuvering a handpiece-shaped probe through a brass block maze. Total time, error time, and total errors were recorded for each of three perceptually different mirror positions. Subjects were then randomly divided into two groups. Group A participated in 2 training sessions; Group B (a control) received no training. Both groups then performed a posttest. Transformed time scores examined by analysis of variance indicated a significant difference for total time between Groups A and B at posttest at each mirror position. For error time, Groups A and B were significantly different at posttest at Positions 2 and 3. For total errors, groups were significantly different at posttest at Mirror Position 3 only. Indirect vision skills improved significantly with training in three dimensions.