Effect of firing and fabrication technique on the marginal fit of heat-pressed lithium disilicate veneers.

STATEMENT OF PROBLEM: Studies on the fit of heat-pressed anterior lithium disilicate veneers are sparse, and whether fit is affected by glaze firing or ceramic addition is unclear. PURPOSE: The purpose of this in vitro study was to evaluate and compare the marginal fit of heat-pressed anterior lithium disilicate veneers (IPS e.max Press) fabricated with the staining or cutback technique by using 3-dimensional analysis. MATERIAL AND METHODS: Two groups of heat-pressed maxillary left central incisor lithium disilicate veneers were fabricated (n=10) differing only in core thickness and the fabrication process. The tooth preparation was standardized at 0.6 mm cervical and middle third and 0.7 mm incisal third, with 1.5 mm of incisal reduction. Group S (staining) was an anatomic contour veneer with 1 glaze firing. Group CB (cutback) had a cutback core of 0.6 mm on the cervical and middle third and 0.5 mm on the incisal areas for ceramic application with 3 firings (wash, incisal, and glaze firing). The amount of ceramic application was standardized, and all veneers had identical final dimensions. Marginal fit was evaluated at 2 stages: after pressing the copings (control) and after glaze firing or ceramic addition using the virtual replica technique and 3-dimensional analysis. The wax copings were invested, eliminated, and pressed with IPS e.max lithium disilicate high translucency ingots, and the overall marginal fit and change in marginal fit after firing were measured in the cervical, mesial, distal, and incisal areas. The Shapiro-Wilk test was used to evaluate normality. Repeated-measures ANOVAs were used to explore differences between the 2 groups (S and CB) as per time (before and after firing) for each location (cervical, mesial, distal, and incisal) (α=.05). RESULTS: A statistically significant change in marginal fit after firing was found for the mesial and distal areas of the CB group (P<.05). In all other areas of measurements, no statistically significant differences were found (P>.05). The mean ±standard deviation marginal fit of group S was 63 ±13 µm and 62 ±9 µm for group CB. CONCLUSIONS: The results suggest that firing affects the marginal fit of heat-pressed anterior lithium disilicate veneers fabricated with the cutback technique but not for the staining technique.

Flexural strength of denture base acrylic resins processed by conventional and CAD-CAM methods.

STATEMENT OF PROBLEM: High flexural strength is one of the desirable properties for denture base resins, yet only few studies have evaluated the physical properties of newer denture bases such as computer-aided design and computer aided manufacturing (CAD-CAM) milled products. PURPOSE: The purpose of this in vitro study was to compare the flexural strength of 3 different types of denture base resins: compression molded, injection molded, and CAD-CAM milled. MATERIAL AND METHODS: Three groups (n=10) of acrylic denture base resins were tested: injection molded, compression molded, and CAD-CAM milled resin. ISO-compliant, rectangular specimens were fabricated (64×10×3.3 mm) (n=30). Specimens were stored in water for 1 week, and flexural strength was measured by using a 3-point bend test until failure. The Student t test was used to evaluate differences in the flexural strength and modulus of elasticity among specimen groups. The Bonferroni formula was used to set significance at α=.017 to account for multiple comparisons among the 3 groups. RESULTS: The flexural strength of the CAD-CAM milled group was significantly higher than that of the other 2 groups (P<.001), while the strength of the compression molded group was significantly greater than that of the injection molded group (P<.001). The flexural modulus of the CAD-CAM group was significantly higher than that of the other 2 groups (P<.001). CONCLUSIONS: CAD-CAM milled denture bases may be a useful alternative to conventionally processed denture bases in situations where increased resistance to flexural strength is needed.

Accuracy of three digital workflows for implant abutment and crown fabrication using a digital measuring technique.

STATEMENT OF PROBLEM: The accuracy of a full digital workflow using an Atlantis abutment and a milled zirconia crown; a full digital workflow with a 3Shape split-file workflow using a zirconia abutment and crown; and an interrupted digital workflow using an Atlantis abutment and a milled zirconia crown is unclear. PURPOSE: The purpose of this in vitro study was to compare 2 full digital workflows relative to an interrupted workflow for restoring an implant with a custom abutment and crown. The secondary purpose of this study was to validate a digital means of measuring internal fit and marginal discrepancy using engineering software programs. MATERIAL AND METHODS: Three workflows were evaluated. The first group, interrupted digital Atlantis (IDA) workflow, included a customized Atlantis abutment that was designed, received, and then rescanned for the definitive crown design. The second group, full digital Atlantis (FDA) workflow, included a customized Atlantis abutment and its corresponding standard tessellation language (STL) file, the Atlantis Core File, which was immediately imported into design software and used for crown design and milling. The third group, full digital split-file (FDSF) workflow, used 3Shape's full digital workflow for abutment and crown design called the split-file workflow, in which the crown and abutment were designed and milled simultaneously. All restorations were evaluated with standardized measurements using a scanning electron microscope (SEM) for 2D measurements, followed by standardized measurements using Geomagic Control, an engineering software program, which facilitated 3D evaluations of the specimens. RESULTS: The 2 Atlantis workflows, IDA and FDA, had statistically smaller marginal openings (P=.002) than the FDSF when measured using 2D SEM. The FDA had a statistically smaller 2D SEM marginal gap than the other 2 groups, IDA (P=.002) and FDSF (P=.002). The FDA had a statistically smaller 3D Geomagic marginal gap than the other 2 groups, IDA (P=.004) and FDSF (P=.006). The FDSF had a statistically smaller 3D Geomagic internal fit than the other 2 groups, FDA and IDA (both P=.006). CONCLUSIONS: All 3 workflows evaluated in this study showed clinically acceptable results in terms of mean marginal gap below 120 µm. The SEM evaluation of mean marginal opening revealed that IDA and FDA mean marginal openings were statistically smaller than the FDSF mean marginal opening. SEM and Geomagic measurements revealed that the FDA mean marginal gap was significantly smaller than IDA and FDSF mean marginal gaps. Geomagic evaluation of mean internal fit revealed that the FDSF was significantly smaller than IDA and FDA. The use of Geomagic to measure and evaluate mean marginal gap and mean internal fit as defined in this study proved to be an acceptable form of measurement with statistical validation.

Facebow Use in Clinical Prosthodontic Practice.

The use of a dental facebow in diagnosis and treatment by the restorative dentist has been controversial in recent years. Digital alternatives have been proposed and hold promise for the future; however, the traditional facebow still has practicality in a modern restorative practice. The purpose of this paper is to review facebow use in clinical prosthodontic practice.

An alternative digital workflow for fabricating a mandibular implant-supported complete fixed dental prosthesis with limited restorative space: A clinical report.

This clinical report describes the prosthetic rehabilitation of a patient with a mandibular implant-supported complete fixed dental prosthesis with limited interocclusal restorative space. The problem was manifested by repeated fractures of the acrylic resin teeth and distortion of the supporting framework. The definitive restoration included a custom computer-aided design and computer-aided manufacturing (CAD-CAM) titanium framework with the lingual cusps and most of the occlusal table of the mandibular posterior teeth milled in titanium as part of the framework. An esthetic CAD-CAM milled denture base along with teeth was bonded over this framework.

Complete mouth rehabilitation and gastroesophageal reflux disease: Conventional and contemporary treatment approaches.

This report describes the diagnosis and prosthodontic management of 2 patients with a history of chronic gastroesophageal reflux disease and worn dentition. Different treatment approaches were used for oral rehabilitation. Use of conventional and contemporary restorative materials resulted in functional and esthetic prosthodontic rehabilitation with a favorable prognosis.

Prosthetic rehabilitation following lateral resection of the mandible with a long cantilever implant-supported fixed prosthesis: A 3-year clinical report.

This clinical report describes the prosthetic management of the surgical reconstruction of a patient after mandibular resection. Complete oral rehabilitation was achieved with a maxillary complete denture and a mandibular implant-supported fixed prosthesis with a custom titanium framework and a long unilateral cantilever.

Custom total occlusal convergence angle sticker fabrication.

This article describes a method of fabricating a custom total occlusal convergence angle sticker with photo editing software and label stickers. The custom total occlusal convergence angle sticker can help clinicians achieve an accurate degree of taper during axial wall reduction of tooth preparation.

Labial reduction guide for laminate veneer preparation.

This article describes a method of fabricating a labial reduction guide for laminate veneer preparations by using a digital tire tread depth gauge and orthodontic wire. The labial reduction guide can help clinicians to achieve accurate reduction of the labial surface.

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.

Fracture resistance of lithium disilicate restorations after endodontic access preparation: An in vitro study.

STATEMENT OF PROBLEM: Endodontic access preparation through a lithium disilicate restoration is a frequently encountered clinical situation. The common practice of repairing the accessed crown with composite resin may result in a weakened restoration. PURPOSE: The purpose of this in vitro study was to determine the effect of endodontic access preparation on the fracture resistance and microstructural integrity of monolithic pressed and monolithic milled lithium disilicate complete coverage restorations. MATERIAL AND METHODS: Twenty monolithic pressed (IPS e.max Press) and 20 monolithic milled (IPS e.max CAD) lithium disilicate restorations were fabricated. Ten of the pressed and 10 of the milled crowns were accessed for a simulated endodontic treatment and subsequently repaired by using a porcelain repair system and composite resin. All specimens were submitted to cyclic loading and then loaded to failure. Force data were recorded and analyzed with 2-way ANOVA followed by a post hoc test (Sidak correction) to indicate significant differences among the groups (α=.05). A Weibull analysis was also performed for each group. Eight (4 pressed and 4 milled) additional restorations were fabricated to complete a scanning electron microscope (SEM) analysis and evaluate the surface damage created by the endodontic access preparation. RESULTS: A statistically significant difference (P=.019) was found between the pressed intact and pressed repaired restorations and between the pressed intact and milled repaired restorations (P=.002). Specimens that were examined with an SEM showed edge chipping involving primarily the glaze layer around the access openings. CONCLUSIONS: Endodontic access preparation of lithium disilicate restorations resulted in a significantly reduced load to failure in the pressed specimens, but not in the milled specimens.

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.

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.

Three-dimensional evaluation of mandibular bone regenerated by bone transport distraction osteogenesis.

The purpose of this study was to evaluate the structure and material properties of native mandibular bone and those of early regenerate bone, produced by bone transport distraction osteogenesis. Ten adult foxhounds were divided into two groups of five animals each. In all animals, a 3- to 4-cm defect was created on one side of the mandible. A bone transport reconstruction plate, consisting of a reconstruction plate with an attached intraoral transport unit, was utilized to stabilize the mandible and regenerate bone at a rate of 1 mm/day. After the distraction period was finished, the animals were killed at 6 and 12 weeks of consolidation. Micro-computed tomography was used to assess the morphometric and structural indices of regenerate bone and matching bone from the unoperated contralateral side. Significant new bone was formed within the defect in the 6- and 12-week groups. Significant differences (P ≤ 0.05) between mandibular regenerated and native bone were found in regard to bone volume fraction, mineral density, bone surface ratio, trabecular thickness, trabecular separation, and connectivity density, which increased from 12 to 18 weeks of consolidation. We showed that regenerated bone is still mineralizing and that native bone appears denser because of a thick outer layer of cortical bone that is not yet formed in the regenerate. However, the regenerate showed a significantly higher number of thicker trabeculae.

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.

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.

The Post-endodontic Adhesive Interface: Theoretical Perspectives and Potential Flaws.

INTRODUCTION: The aim of this review was to analyze the potential of successful bonds of endodontic posts to radicular dentin as well as the limitations of the post-endodontic adhesive interface. METHODS: The MEDLINE/PubMed and Web of Science electronic databases were searched. The search was augmented by a manual search of the pertinent bibliographies. RESULTS: The post-endodontic adhesive interface finds application in the endodontic cohesive units. Many techniques and materials exist to improve the bond between endodontic posts and resin-based materials as well as between resin-based materials and radicular dentin. Different techniques used for the adhesion of metallic and fiber-reinforced posts are discussed and critically analyzed. CONCLUSIONS: Although adhesive cementation of endodontic posts is popular, a long-term predictable bond may be compromised because of procedures related to the endodontic treatment and/or the adhesive cementation procedures. Microleakage and degradation phenomena may further jeopardize the post-endodontic adhesive interface.