A technique to produce a mirror-image wax pattern of an ear using rapid prototyping technology.

This article describes the use of computer-aided techniques to produce a wax pattern of a missing ear. A 3-dimensional (3-D) computer model of a conventional cast from a patient was obtained using an optical surface capture device (scanner). The 3-D computer model was inverted, using computer-aided design software. A physical thermoplastic (wax) pattern of the inverted 3-D cast was produced using a rapid prototyping (RP) machine.

Prosthodontic application for implant carriers.

This article describes and illustrates clinical and laboratory prosthodontic procedures for the use of an implant carrier as surgical guide, positional index, impression coping, verification device, provisional abutment, implant-supported record base, and occlusal registration stop.

The influence of drill wear on cutting efficiency and heat production during osteotomy preparation for dental implants: a study of drill durability.

PURPOSE: The authors evaluated, under conditions simulating implant placement, the cutting efficiency, durability, heat production, and wear of implant drills. MATERIALS AND METHODS: Osteotomies were performed on bovine ribs using a surgical unit mounted in a testing apparatus. A software program controlled the apparatus and recorded temperatures, depths, and drilling times. Seven brands of drills were tested (Nobel Biocare, 3i/Implant Innovations, Steri-Oss, Paragon, Implamed, Lifecore, and ITI). Spade, twist, tri-flute, and TiN-coated drill designs were evaluated and compared during 100 successive osteotomies. Scanning electron microscopic and energy-dispersive x-ray spectroscopic examinations were performed, and hardness was measured. RESULTS: Two 2-mm drills (Nobel Biocare and 3i/Implant Innovations) had mean removal rates significantly greater than the others (P < .05). The 2-mm twist drill design with a low hardness (Implamed) exhibited plastic deformation at the cutting edge, loss of cutting efficiency, and drill fracture. The TiN-coated drills (Steri-Oss and Paragon) showed greater wear and significantly lower removal rates (P < .05) than noncoated drills. Temperature increases with different drills were not significantly different at depths of 5 or 15 mm or between 2-mm or 3-mm drills. With 1 exception (the 2.3-mm Paragon drill at a depth of 15 mm), the temperatures generated by the different types of drills were not significantly different. Clinically harmful temperatures were detected only at a depth of 15 mm during 5 osteotomies and coincided with a marked decrease in the rate of drill advancement with a resulting continuous drilling action. DISCUSSION: Temperatures generated at depths of 5 and 15 mm by the different drill types and diameters were not significantly different and, with only 5 exceptions, were clinically safe. Several differences between brands were noted in regard to cutting efficiency and durability, underscoring the importance of material selection and quality on drill performance. CONCLUSIONS: Drill design, material, and mechanical properties significantly affect cutting efficiency and durability. Coolant availability and temperature were the predominant factors in determining bone temperatures. Implant drills can be used several times without resulting in bone temperatures that are potentially harmful. Continuous drilling in deep osteotomies can produce local temperatures that might be harmful to the bone.

A comparison of the porcelain fracture resistance of screw-retained and cement-retained implant-supported metal-ceramic crowns.

STATEMENT OF PROBLEM: The presence of a screw opening on the occlusal surface of implant-supported metal-ceramic crowns may decrease the porcelain fracture resistance and shorten the longevity of the crown. PURPOSE: The purpose of this study was to compare the porcelain fracture resistance between screw-retained and cement-retained implant-supported metal-ceramic crowns and to assess whether narrowing the occlusal table or offsetting the screw-access opening affects fracture resistance. MATERIAL AND METHODS: Forty standardized maxillary premolar metal copings were fabricated with a Pd-Ga alloy (Protocol) on an implant abutment. Copings were divided into 4 groups (n=10): Group 1 (Screw-retained; occlusal surface buccolingual width=5 mm), screw access opening placed in the center of the occlusal surface; Group 2 (Screw-retained; occlusal surface buccolingual width=5 mm), screw access opening positioned 1 mm offset from the center of the occlusal surface toward the buccal cusp; Group 3 (Cement-retained; occlusal surface buccolingual width=5 mm), copings were not altered; and Group 4 (Cement-retained; occlusal surface buccolingual width=4 mm), copings designed to have a reduced occlusal surface width. All castings were finished with aluminum oxide stones and airborne-particle abraded. Two layers of opaque and dentin porcelain were applied, respectively, on all specimens, which were then glazed. The crown specimens were positioned in a custom testing apparatus and vertically loaded on the middle of the occlusal surface with a universal testing machine at a crosshead speed of 0.5 mm/min until fracture. Mean values of load at fracture (Kgf) were calculated in each group and compared with a 1-way analysis of variance and Tukey's Studentized test (alpha=.05). RESULTS: Mean values of loads required to fracture the crowns were as follow: Group 1: 95.01+/-46.6 Kgf; Group 2: 108.61+/-57.9 Kgf; Group 3: 390.94+/-151.3 Kgf; Group 4: 380.04+/-211.8 Kgf. Groups 1 and 2 required a significantly lower force to fracture the crowns compared with Groups 3 and 4 (P=.0001). Comparing Group 1 with 2 (P=.9) and Groups 3 with 4 (P=.6), no significant differences were noted. CONCLUSIONS: Screw-retained implant-supported metal-ceramic crowns demonstrated a significantly lower porcelain fracture resistance than cement-retained crowns. Placing the screw access opening 1 mm offset from the center of the occlusal surface did not result in lower fracture resistance. Cement-retained crowns with 4- or 5-mm buccolingual width of the occlusal surface showed similar porcelain fracture resistance.

Maxillary and mandibular overlay removable partial dentures for the restoration of worn teeth.

This clinical report describes the fabrication of maxillary and mandibular cast overlay removable partial dentures for the restoration of severely worn teeth with accompanying loss of vertical dimension of occlusion. The frameworks supported porcelain veneers for esthetics and metal occlusal surfaces for strength and durability.

Tooth preparation: a study on the effect of different variables and a comparison between conventional and channeled diamond burs.

PURPOSE: The purpose of this study was to evaluate the different variables involved in tooth cutting to characterize intrapulpal temperature generation, cutting efficiency, and bur durability when using conventional and channeled diamond burs. MATERIALS AND METHODS: Forty premolars and 60 molars were selected for the study. Four diamond burs were paired according to grit size: 125-microm grit: Brasseler Coarse (Control 1) and TDA System (Test 1) burs; and 180-microm grit: Brasseler CRF (Control 2) and NTI Turbo Diamond (Test 2) burs. Each bur was used twice when cutting the premolar teeth, whereas it was used for 60 cuts when cutting the molar teeth. The data were analyzed to compare the correlation of bur design, grit and wear, amount of pressure, advancement rate, revolutions per minute, cutting time and rate, and proximity to the pulp chamber with intrapulpal temperature generation, cutting efficiency, and bur longevity. The mean values of test and control burs in each group were compared using an ANOVA (p < 0.05 for significant differences) for temperature generation and an ANOVA and the Tukey multiple range test (p< or = 0.05) for cutting efficiency and bur longevity. RESULTS: No significant difference was found in intrapulpal temperature generation while cutting premolar and molar teeth with conventional and channeled diamond burs. In both groups, the mean temperature recorded during and after the cutting procedure was lower than the baseline temperature. For premolar teeth, no significant difference was established for control and test burs for the load required to cut into the tooth and the cutting rate. However, both test burs showed significantly fewer revolutions per minute when compared to their control counterparts. For the molar teeth, the Brasseler CRF bur required a significantly lower cutting load when compared to the NTI bur, whereas no difference was noted between the other pair of burs. The cutting rate was significantly higher for both control burs, whereas revolutions per minute (rpm) were greater for control coarser burs only. Overall, channeled burs showed a significantly lower cutting efficiency when compared to conventionally designed burs. CONCLUSION: Within the limitations of this study, channeled burs showed no significant advantage over conventional diamond burs when evaluating temperature generation and bur durability. Moreover, the cutting efficiency of conventional burs was greater than that of channeled burs.

Comparison of the load at failure of soldered and nonsoldered porcelain-fused-to-metal crowns.

STATEMENT OF PROBLEM: The application of solder material to metal frameworks could affect the porcelain-to-metal failure load and possibly compromise the longevity of porcelain-fused-to-metal crowns. PURPOSE: This in vitro study assessed the influence of solder on the porcelain failure load between metal and porcelain, using crown-shaped specimens. MATERIAL AND METHODS: Forty standardized crown patterns were fabricated on a metal die and cast with noble alloy (Protocol). The specimens were divided into test (soldered, n=20) and control (nonsoldered, n=20) groups. A 2-mm-diameter perforation was produced on the buccal surface of the test specimens, 1.5 mm apical to the junction between occlusal and buccal surfaces. The perforation was repaired with high-fusing white ceramic solder material. All castings were finished with aluminum oxide stones and airborne-particle abraded with 50-microm aluminum oxide at 75 psi of pressure. Two layers each of opaque and dentin porcelain were applied on all specimens. All crowns were subjected to a vertical compressive load with a universal testing machine at a crosshead speed of 0.5 mm/min until fracture. The loading apparatus of the device contacted the buccal cusp only. In both control and test groups, 10 crowns were loaded with a stainless steel pin (phase I) whereas the remaining 10 in each group were loaded with a carbon steel pin (phase II). Means of loads at failure were recorded in each group for each pin type and compared (soldered vs nonsoldered) by use of a t test (alpha=.05). RESULTS: Mean failure load for nonsoldered crowns was 349 +/- 63 kgf in phase I and 228 +/- 49 kgf in phase II. Soldered crowns showed a significantly lower failure load (265 +/- 82 kgf [phase I; P<.02] and 154 +/- 108 kgf [phase II; P<.04]) and a greater standard deviation. CONCLUSION: Soldered metal-porcelain crown specimens demonstrated a significantly lower load at failure. Within the limits of this study, it was concluded that solder material might negatively affect porcelain-metal crowns.

Verification jig for implant-supported prostheses: A comparison of standard impressions with verification jigs made of different materials.

STATEMENT OF PROBLEM: Implant verification jigs are routinely used during the fabrication of implant-supported prostheses. The dimensional accuracy of these jigs is unknown. PURPOSE: The purposes of this study were to (1) compare the dimensional accuracy of verification jigs with that of conventional impression procedures and (2) measure the dimensional accuracy of 3 resin materials used to fabricate verification jigs. MATERIALS AND METHODS: Thirty verification jigs and 20 impressions were made of 3 externally hexed Steri-Oss implants in a master stone base according to the following groups (n = 10 per group): (Group 1) Jig: GC pattern resin; (Group 2) Jig: Duralay resin; (Group 3) Jig: Triad gel resin; (Group 4) Impression: closed-tray impression copings; and (Group 5) Impression: open-tray impression copings. A stone base was fabricated for each experimental jig and impression. Master stone base and experimental stone bases were measured with the following methods: X and Y coordinates of each implant center were obtained with a traveling microscope by averaging the X and Y coordinates of the implant external hex corners. The origins of the coordinates during measurement of each base were arbitrary. Distances between implant center points were calculated by use of the Pythagorean theorem. Vertical measurements (Z-plane) were obtained with a digital caliper at the 2 terminal-implant locations. Interimplant distances and vertical measurements were subtracted from those of the master base, and the resultant distortion values were analyzed with analysis of variance and Tukey Studentized range tests. Statistical significance was set at P<.05. RESULTS: Verification jigs were not significantly more accurate than standard impression procedures. Open-tray impressions showed a significantly greater vertical distortion (Z-R location: 262 +/- 158 microm; P=.0001; Z-L location 333 +/- 189; P=.0001) compared with the other groups. Triad gel jigs showed a significantly greater distortion in one interimplant distance (C-L) than closed-tray impressions (P=.04), whereas Duralay jigs exhibited significant greater distortion than closed-tray and open-tray impressions in the interimplant distance R-C (P=.006). Although not significantly different from other groups, the closed-tray group showed the lowest mean distortion values in all measurements. CONCLUSION: Within the limitations of this study, the accuracy provided by verification jigs was not significantly superior to standard impression procedures. The results suggest that jig fabrication does not improve the dimensional accuracy of stone casts. Open-tray impressions showed a significantly greater inaccuracy in the vertical plane.

Influence of cold working and thermal treatment on the fit of implant-supported metal-ceramic fixed partial dentures.

STATEMENT OF PROBLEM: The application of porcelain may alter the fit of metal-ceramic frameworks. In fixed partial denture frameworks, this altered fit may cause marginal opening and require sectioning and soldering of the prosthesis. PURPOSE: The purpose of this study was to compare the fit of implant-supported metal-ceramic fixed partial dentures when different thermal treatments were performed. MATERIAL AND METHODS: Fifteen implant-supported metal-ceramic fixed partial denture frameworks were fabricated and divided into 3 treatment groups: Group 1 = cold working and thermal oxidation; Group 2 = unrestrained thermal treatment, cold working, and oxidation; and Group 3 = investment-restrained thermal treatment, cold working, and oxidation. After the appropriate treatment procedures, porcelain was applied. Measurements were made with a digital caliper, with the help of fiduciary marks, after each step in 3 dimensions and at 2 locations. These measurements were compared with those of the as-cast framework (baseline) to determine framework distortion. Distortion data among groups were compared with repeated-measures analysis of variance and Tukey's Studentized range test (P<.05). RESULTS: Absolute values of distortion (regardless of direction) after thermal treatment and after porcelain application were not significantly different among groups. However, total raw values of distortion, which describe the specific direction of distortion, were significantly different for 4 of the 6 recorded measurements between Groups 1 and 3 (P<.05). Although the absolute distortion values did not differ among groups, heat treatment and finishing of the alloy affected the timing and direction of distortion. CONCLUSION: Within the limitations of this study, heat treatment of implant-supported metal-ceramic fixed partial denture frameworks before cold working did not decrease the total absolute distortion. Definite patterns of distortion were, however, found in Groups 1 and 3, suggesting that specific manipulations and heat treatments of the alloy affected the direction of distortion.

Comparative evaluation of casting retention using the ITI solid abutment with six cements.

OBJECTIVE: The purpose of this study was to test the retention of metal copings fabricated to fit on the one-groove, one flat-sided solid titanium abutment using six different cements. MATERIALS AND METHODS: Ten hollow screw 3.8 mm ITI implants were mounted in acrylic resin blocks. A solid titanium abutment was placed on each implant and torqued at 35 Ncm. Prefabricated burn-out caps were placed on the titanium abutment and wax loops added to the occlusal surface to allow for subsequent retention testing. All plastic caps were embedded in phosphate-bonded investment and cast with noble alloy. Castings were inspected for surface irregularities using a stereomicroscope at 10x magnification. The six cements were: 1) eugenol-free zinc oxide (Temp Bond NE); 2) zinc-oxide eugenol (IRM); 3) zinc phosphate (Hy-Bond); 4) resin-modified glass ionomer (Protec Cem); 5) zinc polycarboxylate (Durelon) and 6) 10-methacryloyloxydecyl dihydrogen phosphate resin (Panavia 21). After cementation, implant-abutment-casting assemblies were stored for 24 h in 100% humidity. Samples were subjected to a pull-out test using an Instron universal testing machine at a crosshead speed of 0.5 mm/min. The load required to de-cement each coping was recorded and mean values for each group calculated. Means and standard deviations of loads at failure were analyzed using ANOVA and a Tukey studentized test. Statistical significance was set at P < or = 0.05. RESULTS: The mean values (+/- SD) of loads in kilograms at failure (n = 10) for the various cements were as follows: Temp Bond 3.18 (+/- 1.1) (Tukey group D), IRM 9.25 (+/- 3.83) (Tukey group CD), HY-Bond 10.9 (+/- 6.52) (Tukey group C), Protec Cem 18.98 (+/- 6.23) (Tukey group B), Durelon 23.55 (+/- 4.29) (Tukey group B) and Panavia 21, 36.53 (+/- 8.1) (Tukey group A). Means with the same letter in the Tukey grouping are not significantly different. CONCLUSIONS: The retention values of castings cemented to ITI solid abutments have not been reported in the literature. Within the limitations of this in vitro study, the results do not suggest that one cement type is better than another, but they do provide a ranking order of the cements in their ability to retain the castings. This ranking is somehow different than that obtained when the same cements are used on natural teeth. The material and surface characteristics of the implant abutment are likely responsible for this difference. Cement retention values obtained from studies that use teeth as abutments may be misleading when used in cement-retained implant-supported crowns. It is at the clinician's discretion to use a certain type of cement, based on the situation at hand.