The effect of impression technique and implant angulation on the impression accuracy of external- and internal-connection implants.

PURPOSE: The purpose of this in vitro study was to investigate the effect of impression technique and implant angulation on the impression accuracy of external- and internal-connection implants using a novel experimental device. MATERIALS AND METHODS: An experimental device was designed and fabricated to make in vitro impressions by means of open- and closed-tray techniques. Impressions of eight implants with two different connections (four external-hex and four internal-hex) at three angulations (0, 15, and 25 degrees) were made using a medium-consistency polyether material. Evaluation of implant impression accuracy was carried out by directly measuring the difference in coordinate values between the implant body/impression coping positioned on the base and the impression coping/laboratory analog positioned in the impression using a touch-probe coordinate measuring machine. Experimental data were analyzed by two-way analysis of variance. The significance level of all hypothesis testing procedures was set at P<.05. RESULTS: The results showed that: (1) for implants with external connections, impression accuracy is not significantly affected by the impression technique, implant angulation, or their interaction; and (2) for implants with internal connections, impression accuracy is significantly affected only by implant angulation: Impression inaccuracy was greater at the 25-degree implant angulation. CONCLUSIONS: Within the limitations of this in vitro study, the open- and closed-tray techniques had no effect on the accuracy of multiple implant impressions. The interaction between impression technique and implant angulation was also not significant. However, implant angulation significantly affected the impression accuracy when implants with internal connections were used.

Three-dimensional positional changes of teeth adjacent to posterior edentulous spaces in relation to age at time of tooth loss and elapsed time.

The purpose of this study was to study the stability of teeth adjacent to posterior edentulous spaces and correlate it with patient age and time lapse since tooth loss. Dental casts, panoramic radiographs, and questionnaires of patients treated in a University setting were employed. Teeth adjacent and opposing posterior edentulous spaces were examined for the following parameters: Supraeruption, rotation, space closure, and axial inclination. One hundred twenty three patients with 229 edentulous spaces were analyzed. Statistical analysis showed that the effects of "jaw", "gender", and "age group at the time of tooth loss" were not significant for any of the variables tested. The effect of time lapse since tooth loss was significant regarding the "amount of distal tooth inclination" (P<0.001), the "amount of distal tooth rotation" (P=0.004), and "space closure" (P=0.038). Post-hoc analysis of the "amount of distal tooth inclination" revealed a marked increase in inclination 5 years after tooth loss. Within the limitations of this study, it was concluded that in the group of patients studied, minor positional changes in teeth opposing or adjacent to posterior edentulous spaces had occurred. The greatest changes in position were recorded for mandibular teeth distal to edentulous spaces.

Computer methods for automating preoperative dental implant planning: implant positioning and size assignment.

The paper presents computer-aided methods that allocate a dental implant and suggest its size, during the pre-operative planning stage, in conformance with introduced optimization criteria and established clinical requirements. Based on computed tomography data of the jaw and prosthesis anatomy, single tooth cases are planned for the best-suited implant insertion at a user-defined region. An optimum implantation axis line is produced and cylindrical implants of various candidate sizes are then automatically positioned, while their occlusal end is leveled to bone ridge, and evaluated. Radial safety margins are used for the assessment of the implant safety distance from neighboring anatomical structures and bone quantity and quality are estimated and taken into consideration. A case study demonstrates the concept and allows for its discussion.

Comparison of temperature increase in the pulp chamber during the polymerization of materials used for the direct fabrication of provisional restorations.

STATEMENT OF PROBLEM: Polymerization of resin materials used for the fabrication of provisional restorations is associated with an exothermic reaction. This temperature rise may present a serious biological problem, since it can cause iatrogenic thermal trauma to the pulp. PURPOSE: This in vitro study compared the temperature increase in the pulp chamber of a molar placed in contact with different resins used for the direct fabrication of provisional restorations. MATERIAL AND METHODS: Polymethyl methacrylate (Jet), polyethyl methacrylate (Snap), polyvinylethyl methacrylate (Trim), Bis-acrylic composite (Protemp II), and a VLP urethane dimethacrylate (Revotec LC) were compared with respect to their exothermic reaction properties during polymerization. A mandibular molar prepared for a complete coverage restoration was placed in an acrylic resin block. A thermal probe connected to a digital thermometer was placed into the pulp chamber. Specimens were submerged in a water bath to simulate intraoral conditions. The provisional resin materials tested were measured and mixed according to manufacturer's instructions. The resin mixture was placed into a vacuum-formed acetate template and was then positioned on the prepared molar tooth. The temperature was recorded during polymerization at 30-second intervals until it was evident that the peak temperature had been reached. Temperature increase was measured ( degrees C) for both the initial crown fabrication and the reline procedures. Data were analyzed with descriptive statistics, 1-way analysis of variance, and Tukey Honestly Significant Difference tests (alpha=.05). RESULTS: One-way ANOVA revealed significant differences (F=57.010, P<.0001) in temperature rise for different provisional resin materials. Mean temperature increase for the provisional crown fabrication ranged from 37.76 degrees C for the polyvinylethyl methacrylate to 39.40 degrees C for the polymethyl methacrylate. Mean temperature rise for the reline procedures ranged from 36.80 degrees C for the polyvinylethyl methacrylate to 37.69 degrees C for the polymethyl methacrylate. All of the tested materials produced an exothermic chemical reaction. CONCLUSIONS: Polymethyl methacrylate produced the higher exothermic reaction in both initial crown fabrication and reline procedures. Polyethyl methacrylate, polyvinylethyl methacrylate, and Bis-acrylic resins tested were not significantly different from each other.

Bonding indirect resin composites to metal: part 2. Effect of alloy surface treatment on elemental composition of alloy and bond strength.

PURPOSE: This laboratory study compared the effect of different surface treatments of a medium-gold, high-noble alloy on the shear bond strength of an indirect, highly filled resin composite to the alloy and on the elemental composition of the alloy surface. MATERIALS AND METHODS: Ninety disks, cast in a medium-gold, high-noble porcelain-fused-to-metal alloy (V-Deltaloy), received three different surface treatments: sandblasting with 50-microm Al2O3 (group 1) or 250-microm Al2O3 (group 2) and chemical agents, or with 250-microm Al2O3 without chemical agents (group 3) prior to bonding of an indirect resin composite (Artglass, and chemical agents Siloc-pre and Siloc-bond). The specimens were tested in shear, half of them after 24-hour dry storage at room temperature and the rest after 10-day storage in normal saline solution at 37 degrees C and thermocycling (2,500 cycles between 5 and 55 degrees C). Morphologic and qualitative changes on the alloy surface after sandblasting with 50- or 250-microm Al2O3 were examined by SEM using EDS analysis and compared with polished specimens. Statistical analysis was performed using two-factor ANOVA. RESULTS: The mean shear bond strengths (in MPa) after dry or wet storage and thermocycling were 29 and 24 for group 1, 21 and 18 for group 2, and 17 and 12 for group 3, respectively; there was a statistically significant difference among the groups. Sandblasting of the alloy surface led to statistically significant changes in elemental composition. These changes were of greater magnitude when 50-microm Al2O3 particles were used. CONCLUSION: The particle size used for sandblasting influences the shear bond strength between a high-noble alloy and a highly filled indirect resin composite, as well as the elemental composition of the alloy surface.

Bonding indirect resin composites to metal: Part 1. Comparison of shear bond strengths between different metal-resin bonding systems and a metal-ceramic system.

PURPOSE: This laboratory study compared the shear bond strength between three indirect resin composites and a noble alloy using their respective bonding systems. MATERIALS AND METHODS: One hundred twenty disks cast in a medium-gold, high-noble metal-ceramic alloy (V-Deltaloy) were divided equally into four groups and received different treatments for veneering: Conventional feldspathic porcelain (Omega) was applied on one set of specimens to be used as a control, and three indirect resin composites (Artglass, Sculpture, Targis) with their respective bonding systems were used for the other groups. The specimens were tested in a parallel shear test, half of them after 24-hour dry storage at room temperature and the rest after 10-day storage in normal saline solution at 37 degrees C and thermocycling. The fractured specimens were evaluated to determine the nature of the failure. RESULTS: The mean shear bond strength values (in MPa), before and after wet storage and thermocycling, were 30 and 23 for the metal-ceramic group, 29 and 23 for the Artglass group, 20 and 19 for the Sculpture group, and 17 and 14 for the Targis group, respectively. The metal-ceramic and Artglass groups exhibited significantly higher bond strengths than the other two groups. All specimens, with the exception of the Sculpture group, showed a significant decrease in bond strength after wet storage and thermocycling. CONCLUSION: No group exceeded the shear bond strength of the metal-ceramic group, but the Artglass group with its respective metal-resin bonding system exhibited similar bond strengths. The Sculpture group showed a stable bond after water storage and thermocycling.