Performance of two different digital evaluation systems used for assessing pre-clinical dental students' prosthodontic technical skills.

INTRODUCTION: Proper integration of newly emerging digital assessment tools is a central issue in dental education in an effort to provide more accurate and objective feedback to students. The study examined how the outcomes of students' tooth preparation were correlated when evaluated using traditional faculty assessment and two types of digital assessment approaches. Specifically, incorporation of the Romexis Compare 2.0 (Compare) and Sirona prepCheck 1.1 (prepCheck) systems was evaluated. Additionally, satisfaction of students based on the type of software was evaluated through a survey. MATERIAL AND METHODS: Students in a second-year pre-clinical prosthodontics course were allocated to either Compare (n = 42) or prepCheck (n = 37) systems. All students received conventional instruction and used their assigned digital system as an additional evaluation tool to aid in assessing their work. Examinations assessed crown preparations of the maxillary right central incisor (#8) and the mandibular left first molar (#19). All submissions were graded by faculty, Compare and prepCheck. RESULTS: Technical scores did not differ between student groups for any of the assessment approaches. Compare and prepCheck had modest, statistically significant correlations with faculty scores with a minimum correlation of 0.3944 (P = 0.0011) and strong, statistically significant correlations with each other with a minimum correlation of 0.8203 (P < 0.0001). A post-course student survey found that 55.26% of the students felt unfavourably about learning the digital evaluation protocols. A total of 62.31% felt favourably about the integration of these digital tools into the curriculum. CONCLUSIONS: Comparison of Compare and prepCheck showed no evidence of significant difference in students' prosthodontics technical performance and perception.

Micromotion and dynamic fatigue properties of the dental implant-abutment interface.

STATEMENT OF PROBLEM: Clinical loading may result in micromotion and metal fatigue in apparently stable implant screw joints. This micromotion may contribute to tissue inflammation and prosthesis failure. PURPOSE: This study investigated dental implant screw joint micromotion and dynamic fatigue as a function of varied preload torque applied to abutment screws when tested under simulated clinical loading. MATERIAL AND METHODS: Fifteen noble alloy single-tooth implant restorations, each containing a hexed UCLA-style gold cylinder, were randomly assigned to 3 preload groups (16, 32, and 48 N.cm). Each group consisted of 5 implants (each 3.75 x 15 mm) and 5 square gold alloy abutment screws. A mechanical testing machine applied a compressive cyclic sine wave load between 20 and 130 N at 6 Hz to a contact point on each implant crown. A liquid metal strain gauge recorded the micromotion of the screw joint interface after 100, 500, 1,000, 5,000, 10,000, 50,000, and 100,000 cycles. Baseline data at 0 N.cm were collected before the application of the specified preload torque. RESULTS: The 16 N.cm group exhibited greater micromotion (P<.001) than both the 32 and 48 N.cm groups at all cycle intervals (2-way ANOVA, Tukey HSD). Micromotion of the implant-abutment interface remained constant (P=.99) for each of the preload groups through 105 cycles. CONCLUSION: Under the loading parameters of this study, no measurable fatigue of the implant-abutment interface occurred. However, dental implant screw joints tightened to lower preload values exhibited significantly greater micromotion at the implant-abutment interface.

Ultimate tensile strength of five interchangeable prosthetic retaining screws.

Implant prosthetic retaining screws have been reported to serve as built-in safety factors to protect against overload in the implant's "vertical stack," although loosening and fracture of retaining screws are often considered complications. Manufacturers have responded by introducing interchangeable prosthetic retaining screws, which can give the clinician the impression that interchanging screws will not have an adverse effect on the remainder of the implant complex and/or the integration of the implant itself. The objective of this investigation was to measure the ultimate tensile strength of four retaining screws from three manufacturers and two alloy types (gold and titanium) using the Nobelpharma gold prosthetic retaining screws as a standard for the comparisons. Five screws of each type were loaded in tension in an Instron Universal Testing Machine until fracture occurred. A Tukey-Kramer Test (significance level = .05) analysis of the data showed that all of the interchangeable prosthetic retaining screws were significantly different from the control screws in respect to ultimate tensile strength. The data suggest that interchanging prosthetic retaining screws will influence their built-in safety feature.

Geometric comparison of five interchangeable implant prosthetic retaining screws.

Eight geometric parameters of five interchangeable prosthetic retaining screws (#1-3i Implant Innovation-gold, #2-Impla-Med-gold, #3-Nobelpharma-gold, #4-3i Implant Innovation-titanium, and #5-Implant Support Systems-titanium) were recorded with an Amray 1000-B scanning electron microscope at x20 to x200 magnification. Five screws of each type were measured and eight parameters were evaluated: (A) diameter of head, (B) screw length, (C) thread pitch, (D) major diameter, (E) neck diameter (F) length of neck, (G) crest width, and (H) root width. The Nobelpharma-gold prosthetic retaining screws served as controls. The results revealed significant differences between the control and test screws in all parameters except parameters C and G (ANOVA, p < 0.05) and Duncan's multiple range test (significance level 0.05). On the basis of these differences, it was concluded that interchanging prosthetic retaining screws can introduce unknown variables in treating patients.

Comparison of "look-alike" implant prosthetic retaining screws.

PURPOSE: The maximum preload torque of implant prosthetic retaining screws from four manufacturers and of two alloy types was measured to determine one index of interchangeability of intersystem components. MATERIALS AND METHODS: Implant prosthetic retaining screws from four manufacturers (3i Implant Innovations Inc, West Palm Beach, FL; Impla-Med Inc, Sunrise, FL; Nobelpharma USA Inc, Chicago, IL; and Implant Support Systems Inc, Irvine, CA) and of two metal types (gold and titanium) were investigated using an in vitro simulation model. Five screws of each type were tightened down against a gold cylinder using a Tohnichi BTG-6 torque gauge (Tohnichi American Corporation, Northbrook, IL) until fracture occurred. RESULTS: The 3i Implant Innovations gold and the Nobelpharma gold were not significantly different. The 3i Implant Innovations titanium and the Impla-Med gold were able to withstand less preload torque than the 3i Implant Innovations gold and the Nobelpharma gold. The Implant Support Systems titanium was able to withstand significantly more preload torque than all of the other screws. CONCLUSIONS: Interchanging implant prosthetic retaining screws could introduce new and unknown variables that may affect the long-term survival of implant fixtures and/or the implant prostheses.

Effect of preload torque on the ultimate tensile strength of implant prosthetic retaining screws.

The preload concept proposes that an optimal torque exists to which implant prosthetic retaining screws should be tightened. According to this theory, the preload prevents separation of implant components, thus protecting the screw from fracture. Recent research suggests that most implant-retained prostheses in function today were placed using improper preloads. The purpose of this investigation was to determine whether or not improper preloading of prosthetic implant-retaining screws would adversely affect their ultimate tensile strength. Fifteen Nobelpharma-slotted gold screws from one lot were tightened to 6, 10, and 15 N/cm with a torque gauge and ultimate tensile strength values determined. The procedure was duplicated using 15 Nobelpharma gold screws from another lot tightened to 0, 10, and 20 N/cm. Within each of the test groups, there was no significant difference in the ultimate tensile strength among the three preload torques. However, a paired t test (P = 0.005) determined that there was a significant difference between the two lots with respect to the ultimate tensile strength of the screws preloaded to 10 N/cm. Altering the preload torque applied to Nobelpharma gold-retaining screws does not affect their ultimate tensile strength. The ultimate tensile strength of the screws from the two lots differed, suggesting an unannounced change in component specifications.

Providing optimum torque to implant prostheses: a pilot study.

Ten N/cm torque has been proposed as the optimum level for the tightening of implant retaining gold screws in order to preload the implant components to limit loosening and fracture. The purpose of this study was to determine the influence of instrumentation and operator experience on the torque generated during manual tightening of slotted gold screws. Sixteen subjects, divided into four groups based on experience, were instructed to tighten five screws into implant analogs with 20-mm and 37-mm slotted screwdrivers. The screws were then removed with a torque gauge. All of the groups of subjects were able to generate significantly greater torque with the 37-mm screwdriver. Dentists with no implant treatment experience generated significantly less torque than the other three groups. Of the 12 dentist subjects, only 3 generated the optimal amount of torque when using the 20-mm screwdriver. Operators who had little experience dealing with implant prostheses were not able to provide the recommended torque and experienced operators tended to generate more than the recommended amount. None of the subjects were able to generate consistent torque values.