William W. Nagy

The effect of multiple firings on the marginal integrity of pressable ceramic single crowns

STATEMENT OF PROBLEM The marginal adaptation of metal ceramic crowns is affected by firing cycles for veneering porcelain application. The effect of multiple firings on the marginal integrity of pressable ceramic core crowns is unknown. PURPOSE The purpose of this in vitro study was to evaluate the effect of repeated firing cycles on the marginal discrepancy of veneered (layered) pressable ceramic anterior crowns with 2 different finish line configurations. MATERIAL AND METHODS Forty pressable ceramic single anterior complete crowns were fabricated from 2 systems (IPS Empress Esthetic and IPS e.max Press) with 2 finish line designs (shoulder, chamfer) on epoxy resin dies. Specimens were divided into 4 groups of 10, and measurements were made after pressing (control) and after 5 veneer firing stages: 1) wash, 2) first incisal, 3) second incisal, 4) characterization and glazing, and 5) corrective. The change in vertical marginal discrepancy was measured with a light microscope at 4 locations: facial (F), mesial (M), lingual (L), and distal (D) surfaces. One-way ANOVA (α-=.05) was used to evaluate the marginal change. A Student-Newman-Keuls test was also used for comparison among the groups. RESULTS There were no significant changes in the vertical marginal integrity related to ceramic type and marginal location and their interactions. However, there was a significant marginal integrity change during the characterization and glazing firing stage. (P<.05) CONCLUSIONS The marginal gap increased for both systems during veneer application and decreased during the characterization and glazing firing cycle. The total marginal fit change after 5 firings was 0.33 μm for IPS e.max Press, and 0.27 μm for IPS Empress Esthetic.

Fracture resistance of compromised endodontically treated teeth restored with bonded post and cores: An in vitro study

STATEMENT OF PROBLEM It is unclear which post and core system performs best when bonded to severely compromised endodontically treated teeth. PURPOSE The purpose of this study was to investigate the fracture resistance and mode of failure of severely compromised teeth restored with 3 different adhesively bonded post and core systems. MATERIAL AND METHODS Thirty extracted endodontically treated maxillary anterior teeth were randomly divided into 3 groups, CPC, gold cast post and core; TPC, titanium prefabricated post/composite resin core; and FPC, quartz fiber reinforced post/composite resin core. All posts were adhesively cemented. All cores resembled a central incisor preparation with no remaining tooth structure above the finish line. Cast gold crowns were fabricated and cemented adhesively. The specimens were aged with thermocycling and cyclic loading. Two specimens per group were randomly selected for micro-computed tomographic imaging before and after aging. Failure was induced with a universal testing machine. The mode of failure was characterized by the interface separation. Data were analyzed with 1-way ANOVA (α=.05) followed by post hoc tests (Bonferroni). RESULTS A statistically significant difference was found among the 3 groups (P=.002). CPC was significantly different than TPC (P=.008) or FPC (P=.003). The primary mode of failure for CPC and TPC was root fracture, and for FPC post debonding. CONCLUSIONS Severely compromised endodontically treated teeth restored with bonded gold cast post and cores showed significantly higher fracture resistance.

Effects of sterilization procedures on the cutting efficiency of stainless steel and carbon steel Gates Glidden drills

One-hundred fifty carbon steel Gates Glidden drills were compared with 150 stainless steel Gates Glidden drills before and after sterilization in an autoclave, salt beads, dry heat, or 2% alkaline glutaraldehyde. Cutting efficiency and separation rates of the drills were evaluated. Stainless steel #1 and 2 Gates Glidden drills resisted separation and maintained their cutting efficiency statistically better than the carbon steel #1 and 2 Gates Glidden drills after one sterilization cycle in an autoclave, salt bead sterilizer, or dry heat oven. Glutaraldehyde did not effect either type of drill.

Histologic evaluation of root response to intrusion in mandibular teeth in beagle dogs

INTRODUCTION The purpose of this article was to histologically evaluate root resorption and repair after orthodontic intrusion with different force magnitudes and fixed anchorage. METHODS A randomized split-mouth repeated-measure design was used. Intrusive forces were applied for 98 days to the mandibular second, third, and fourth premolars of 8 mature beagle dogs. Two miniscrew implants were used as anchorage to apply constant intrusive forces of 50, 100, or 200 g per tooth. Demineralized sections of each tooth were stained and histologically studied for root resorption. Multilevel statistical procedures were used to evaluate the results. RESULTS Root resorption was present in all teeth, independent of the force applied. Significant differences were found between root regions, with the apices and the interradicular regions the most affected and with dentin involvement at the furcation. There was cementum repair in 24.14% of the lacunae. Light constant intrusive forces between 50 and 200 g showed no significant differences in the amount of resorption produced. Resorption was more frequently seen at the level of the apices and the furcation. CONCLUSIONS Orthodontically induced root resorption is not clinically significant after application of continuous intrusive forces between 50 and 200 g. Moreover, there is no relationship between root resorption, the position of posterior mandibular teeth in the arch, and the amount of intrusive force applied.

A simplified matrix for making direct cores

This article describes the use of a pharmaceutical gelatin capsule as a matrix for making various posted and nonposted crown substructures. The procedure used for a cast post and core using this matrix is outlined.

Bone regeneration and docking site healing after bone transport distraction osteogenesis in the canine mandible.

PURPOSE Bone transport distraction osteogenesis provides a promising alternative to traditional grafting techniques. However, existing bone transport distraction osteogenesis devices have many limitations. The purpose of this research was to test a new device, the mandibular bone transport reconstruction plate, in an animal model with comparable mandible size to humans and to histologically and mechanically examine the regenerate bone. MATERIALS AND METHODS Eleven adult foxhounds were divided into an unreconstructed control group of 5 animals and an experimental group of 6 animals. In each animal, a 34-mm segmental defect was created in the mandible. The defect was reconstructed with a bone transport reconstruction plate. Histologic and biomechanical characteristics of the regenerate and unrepaired defect were analyzed and compared with bone on the contralateral side of the mandible after 4 weeks of consolidation. RESULTS The reconstructed defect was bridged with new bone, with little bone in the control defect. Regenerate density and microhardness were 22.3% and 42.6%, respectively, lower than the contralateral normal bone. Likewise, the anisotropy of the experimental group was statistically lower than in the contralateral bone. Half the experimental animals showed nonunion at the docking site. CONCLUSION The device was very stable and easy to install and activate. After 1 month of consolidation, the defect was bridged with new bone, with evidence of active bone formation. Regenerate bone was less mature than the control bone. Studies are underway to identify when the regenerate properties compare with normal bone and to identify methods to augment bone union at the docking site.

Removable partial denture framework try-in.

Removable partial denture frameworks must fit accurately to function properly and not cause injury to remaining teeth or soft tissue. This article presents a logical method and rationale for seating a removable partial denture framework and a review of several disclosing media used in the try-in procedure.

The effect of equilibrating mounted dental stone casts on the occlusal harmony of cast metal complete crowns

STATEMENT OF PROBLEM Fabrication of indirect complete crowns that are in occlusal harmony upon insertion remains a problem in restorative dentistry, and dental stone cast expansion may play a role. PURPOSE This 3-part investigation compared occlusal contacts in a simulated patient with a harmonious occlusion with centric occlusion equal to maximum intercuspation (CO=MI) and an inharmonious occlusion (CO not equal MI) with mounted stone casts, and compared the occlusal contacts after fabrication of a posterior complete crown fabricated on equilibrated and nonequilibrated dental stone casts. MATERIAL AND METHODS A dentoform mounted in a semi-adjustable articulator served as the simulated patient and control. In part 1, a single set of maxillary and mandibular ADA type IV and V derived dental stone casts were fabricated and mounted (CO not equal MI), and occlusal contacts/near contacts were compared. In part 2, 10 type IV and 10 type V cast mountings (CO=MI) were compared. In part 3, 10 type IV cast mountings were fabricated for adjustment (experimental) and 10 for no adjustment (control). A mandibular ADA type IV gold alloy complete crown was fabricated and adjusted on each set of casts and then returned to the dentoform. Vinyl polysiloxane interocclusal records of all mountings were scanned for optical density, and contacts were used to quantify occlusal contacts as exhibiting contact or near contact. Data were analyzed with Kruskal-Wallis ANOVA and Mann-Whitney U tests (alpha=.05). RESULTS The cast adjustment protocol (intervention) was successful in eliminating the majority of the occlusal disharmony in the casts believed to be caused by the effects of stone expansion. Actual and near contact areas for cast mountings of the equilibrated simulated patient were significantly different from those of the simulated patient (P<.001; P=.001, respectively). Actual and near contact areas for inserted crowns fabricated from adjusted casts were significantly different from those of the simulated patient (P<.001; P=.007, respectively), but actual contact areas were not different from those of the simulated patient with no crown inserted. CONCLUSIONS In this study, occlusal contacts of a simulated patient (dentoform) could not be accurately replicated with mounted dental stone casts. A cast adjustment procedure can aid in fabrication of a crown with a more accurate occlusion.

A vinyl polysiloxane die used to make interim restorations

A die made of vinyl polysiloxane is a great aid for making interim restorations and for establishing correct gingival contours for finer restorations. This article describes the rationale and procedures for such a procedure.

Fatigue lifetime prediction of a reduced-diameter dental implant system: Numerical and experimental study

OBJECTIVE To validate the fatigue lifetime of a reduced-diameter dental implant system predicted by three-dimensional finite element analysis (FEA) by testing physical implant specimens using an accelerated lifetime testing (ALT) strategy with the apparatus specified by ISO 14801. METHODS A commercially-available reduced-diameter titanium dental implant system (Straumann Standard Plus NN) was digitized using a micro-CT scanner. Axial slices were processed using an interactive medical image processing software (Mimics) to create 3D models. FEA analysis was performed in ABAQUS, and fatigue lifetime was predicted using fe-safe® software. The same implant specimens (n=15) were tested at a frequency of 2Hz on load frames using apparatus specified by ISO 14801 and ALT. Multiple step-stress load profiles with various aggressiveness were used to improve testing efficiency. Fatigue lifetime statistics of physical specimens were estimated in a reliability analysis software (ALTA PRO). Fractured specimens were examined using SEM with fractographic technique to determine the failure mode. RESULTS FEA predicted lifetime was within the 95% confidence interval of lifetime estimated by experimental results, which suggested that FEA prediction was accurate for this implant system. The highest probability of failure was located at the root of the implant body screw thread adjacent to the simulated bone level, which also agreed with the failure origin in physical specimens. SIGNIFICANCE Fatigue lifetime predictions based on finite element modeling could yield similar results in lieu of physical testing, allowing the use of virtual testing in the early stages of future research projects on implant fatigue.