Showing papers in "Journal of Prosthetic Dentistry in 2004"

Contemporary materials and technologies for all-ceramic fixed partial dentures: a review of the literature.

Abstract: High-strength all-ceramic systems for fixed partial dentures (FPDs) are available for replacing a missing tooth. New core/framework materials have been developed and have evolved in the last decade. With the advancement of CAD/CAM technology, various fabrication techniques have been developed for fabricating improved, consistent, and predictable restorations in terms of strength, marginal fit, and esthetics and for managing core/framework materials that could not otherwise be managed. This article reviews the evolution and development of materials and technologies for all-ceramic FPDs through data published between 1966 and 2004 in the English language. Peer-reviewed articles were identified through a MEDLINE search and a hand search of relevant textbooks and annual publications. The available information suggests that clinical data on the success of these restorations are limited, and that the results of long-term clinical studies are critical to the assessment of these restorations to provide more specific guidelines for usage.

Influence of implant length and diameter on stress distribution: A finite element analysis

Abstract: Statement of problem Masticatory forces acting on dental implants can result in undesirable stress in adjacent bone, which in turn can cause bone defects and the eventual failure of implants. Purpose A mathematical simulation of stress distribution around implants was used to determine which length and diameter of implants would be best to dissipate stress. Material and methods Computations of stress arising in the implant bed were made with finite element analysis, using 3-dimensional computer models. The models simulated implants placed in vertical positions in the molar region of the mandible. A model simulating an implant with a diameter of 3.6 mm and lengths of 8 mm, 10 mm, 12 mm, 14 mm, 16 mm, 17 mm, and 18 mm was developed to investigate the influence of the length factor. The influence of different diameters was modeled using implants with a length of 12 mm and diameters of 2.9 mm, 3.6 mm, 4.2 mm, 5.0 mm, 5.5 mm, 6.0 mm, and 6.5 mm. The masticatory load was simulated using an average masticatory force in a natural direction, oblique to the occlusal plane. Values of von Mises equivalent stress at the implant-bone interface were computed using the finite element analysis for all variations. Values for the 3 most stressed elements of each variation were averaged and expressed in percent of values computed for reference (100%), which was the stress magnitude for the implant with a length of 12 mm and diameter of 3.6 mm. Results Maximum stress areas were located around the implant neck. The decrease in stress was the greatest (31.5%) for implants with a diameter ranging from of 3.6 mm to 4.2 mm. Further stress reduction for the 5.0-mm implant was only 16.4%. An increase in the implant length also led to a decrease in the maximum von Mises equivalent stress values; the influence of implant length, however, was not as pronounced as that of implant diameter. Conclusions Within the limitations of this study, an increase in the implant diameter decreased the maximum von Mises equivalent stress around the implant neck more than an increase in the implant length, as a result of a more favorable distribution of the simulated masticatory forces applied in this study.

In vitro evaluation of shear bond strengths of resin to densely-sintered high-purity zirconium-oxide ceramic after long-term storage and thermal cycling

Abstract: Statement of problem The few available studies on the resin bond to zirconium-oxide ceramic recommend airborne-particle abrasion and modified resin luting agents containing adhesive monomers for superior and long-term durable bond strengths. It is unknown whether this regimen can also be successfully applied to the intaglio surface of a commercial zirconia-based all-ceramic system. Purpose The purpose of this study was to evaluate and compare bond strengths of different bonding/silane coupling agents and resin luting agents to zirconia ceramic before and after artificial aging. Material and methods Composite cylinders (2.9 mm × 3.0 mm) were bonded to airborne-particle–abraded intaglio surfaces of Procera AllZirkon specimens (n=80) with either Panavia F (PAN) or Rely X ARC (REL) resin luting agents after pretreatment with Clearfil SE Bond/ Porcelain Bond Activator (Group SE). In another group, Rely X ARC was used with its bonding/silane coupling agent (Single Bond/Ceramic Primer, Group SB). PAN without any bonding/silane agent (Group NO) was the control. Subgroups of 10 specimens were stored in distilled water for either 3 or 180 days before shear bond strength was tested. One hundred eighty–day–old specimens were repeatedly thermal cycled for 12,000 cycles between 5 and 60°C with a 15-second dwell time. Data were analyzed with 1- and 2-way analysis of variance and the Tukey multiple comparisons test (α=.05). Failure modes were examined under original magnification ×25. Results After 3 days, SE-REL (25.15 ± 3.48 MPa) and SE-PAN (20.14 ± 2.59 MPa) groups had significantly superior mean shear bond strengths ( P =.0007) compared with either NO-PAN (17.36 ± 3.05 MPa) or SB-REL (16.90 ± 7.22 MPa). SE-PAN, NO-PAN, and SB-REL groups were not significantly different. Artificial aging significantly reduced bond strengths. After 180-day storage, SE-PAN (16.85 ± 3.72 MPa), and SE-REL (15.45 ± 3.79 MPa) groups demonstrated significantly higher shear bond strengths than NO-PAN (9.45 ± 5.06 MPa) or SB-REL (1.08 ± 1.85 MPa) groups. The modes of failure varied among 3-day groups but were 100% adhesive at the ceramic surfaces after artificial aging. Conclusion Artificial aging significantly reduced bond strength. A bonding/silane coupling agent containing an adhesive phosphate monomer can achieve superior long-term shear bond strength to airborne-particle– abraded Procera AllZirkon restorations with either one of the 2 resin luting agents tested.

Evaluation of load transfer characteristics of five different implants in compact bone at different load levels by finite elements analysis

Abstract: Statement of problem The external contour of an implant and the magnitude of occlusal loading can have significant effects on the load transfer characteristics and may result in different bone failure rates for different implant systems. Purpose The goal of this study was to investigate the effects of external geometry and occlusal load magnitude on bone failure modes for 5 commercially available dental implant systems. Material and methods Five different implant systems; Ankylos, Astra, Bicon, ITI, and Nobel Biocare, comparable in size, but different in thread profile and crest module shapes, were compared using the finite element method. Type II bone quality was approximated and complete osseous integration was assumed. Occlusal loads of varying magnitudes (0 to 2000 N) were applied on the abutments supporting single tooth restorations at 11.3 degrees from the vertical axis with a 1-mm offset. Total overloaded bone area, where tensile and compressive normal stresses fell outside of the recommended limits of 100 and 170 MPa, respectively, was investigated for different load levels. Results For moderate levels of occlusal loads up to 300 N, the compact bone was not overloaded by any of the implant systems. At the extreme end of the occlusal load range (1000 N or more) the overloading characteristics of implants may be dependent on geometric shape. Conclusion In general, overloading occurs near the superior region of compact bone, in compression, and it is primarily caused by the normal and lateral components of the occlusal load. At the region of intersection of compact and trabecular bone, overloading occurs in tension due to the vertical component of the occlusal load. For excessive forces greater than 1000 N, the overloaded areas of the bone varied considerably among 5 different implants systems evaluated.

In vitro shear bond strength of cementing agents to fixed prosthodontic restorative materials.

Abstract: Statement of problem Durable bonding to fixed prosthodontic restorations is desirable; however, little information is available on the strength of the bond between different cements and fixed prosthodontic restorative materials. Purpose This study determined the shear-bond strength of cementing agents to high-gold-content alloy castings and different dental ceramics: high-strength aluminum oxide (Procera AllCeram), leucite-reinforced (IPS Empress), and lithium disilicate glass-ceramic (IPS Empress 2). Material and methods Prepolymerized resin composite cylinders (5.5 mm internal diameter, n=20) were bonded to the pretreated surfaces of prosthodontic materials. High-gold-content alloy and high-strength aluminum oxide surfaces were airborne-particle–abraded, and pressable ceramics were hydrofluoric acid–etched and silanized prior to cementing. The cementing agents tested were a zinc-phosphate cement (Fleck's zinc cement), glass ionomer cements (Fuji I, Ketac-Cem), resin-modified glass ionomer cements (Fuji Plus, Fuji Cem, RelyX Luting), resin cements (RelyX ARC, Panavia F, Variolink II, Compolute), and a self-adhesive universal resin cement (RelyX Unicem). Half the specimens (n=10) were tested after 30 minutes; the other half (n=10) were stored in distilled water at 37°C for 14 days and then thermal cycled 1000 times between 5°C and 55°C prior to testing. Shear-bond strength tests were performed using a universal testing machine at a constant crosshead speed of 0.5 mm/min. Statistical analysis was performed by multifactorial analysis of variance taking interactions between effects into account. For multiple paired comparisons, the Tukey method was used (α=.05). Results In a 3-way ANOVA model, the main factors substrate, cement, time, and all corresponding interactions were statistically significant (all P P Conclusion After 14 days of water storage followed by thermal cycling, only the self-adhesive universal resin cement (RelyX Unicem) and 2 of the resin cements (Panavia F and Compolute) exhibited strong bond strengths to specific prosthodontic materials. In contrast, zinc-phosphate, glass ionomer, and resin-modified glass ionomer cements showed the lowest values of all tested cementing agents after 14 days of water storage followed by thermal cycling.

The influence of occlusal loading location on stresses transferred to implant-supported prostheses and supporting bone: a three-dimensional finite element study

Abstract: Statement of problem Information about the influence of occlusal loading by location on the stress distribution in an implant-supported fixed partial denture and supporting bone tissue is limited. Purpose The purpose of this study was to investigate the effect of loading at 1 to 3 different locations on the occlusal surface of a tooth on the stress distributions in an implant-supported mandibular fixed partial denture (FPD) and surrounding bone, using 3-dimensional finite element analysis. Material and methods A 3-dimensional finite element model of a mandibular section of bone (Type 2) with missing second premolar and its superstructures were used in this study. A 1-piece 4.1 × 10-mm screw-shape ITI dental implant system (solid implant) was modeled for this study. Cobalt-Chromium (Wiron 99) was used as the crown framework material and porcelain was used for occlusal surface.The implant and its superstructure were simulated in a Pro/Engineer 2000i program. Total loads at 300 N were applied at the following locations: 1) tip of buccal cusp (300 N); 2) tip of buccal cusp (150 N) and distal fossa (150 N); or 3) tip of buccal cusp (100 N), distal fossa (100 N), and mesial fossa (100 N). Results The results demonstrated that vertical loading at 1 location resulted in high stress values within the bone and implant. Close stress levels were observed within the bone for loading at 2 locations and 3 locations; the former created the most extreme stresses and the latter the most even stresses within the bone. With loading at 2 or 3 locations, stresses were concentrated on the framework and occlusal surface of the FPD, and low stresses were distributed to the bone. Conclusion For the loading conditions investigated, the optimal combination of vertical loading was found to be loading at 2 or 3 locations which decreased the stresses within the bone. In this situation, von Mises stresses were concentrated on the framework and occlusal surface of the FPD.

Vertical marginal discrepancy of ceramic copings with different ceramic materials, finish lines, and luting agents: an in vitro evaluation.

Abstract: Statement of problem Prosthetic restorations that fit poorly may affect periodontal health and occlusion Studies that have evaluated the accuracy of fit of ceramic restorations before and after cementation assessed primarily intracoronal restorations Purpose This in vitro study evaluated the effect of different finish lines, ceramic manufacturing techniques, and luting agents on the vertical discrepancy of ceramic copings Material and methods Two stainless steel molars were prepared for complete crowns with 2 different finish lines (heavy chamfer and rounded shoulder); each molar was duplicated to fabricate 90 copings A total of 180 copings generated 18 groups (n=10 for each finish line–coping material–luting agent combination) Luting agents tested included zinc phosphate, resin-modified glass ionomer (Fuji Plus), and resin composite cements (Panavia F) A metal frame was developed on which to screw the stainless steel model and a ceramic coping; the distance (μm) between 2 predetermined points was measured before and after cementation by a profile projector under a torquing force A 4-way ANOVA with repeated measurements was performed to assess the influence of each factor in the vertical marginal discrepancy: 3 between-coping factors (finish line–coping material–luting agent) and 1 within-coping factor (before and after cementation) (α=05) Results Procera copings presented the lowest mean values ( P Conclusion Considering each factor separately, the ceramic manufacturing technique appeared to be the most important factor tested for the definitive vertical discrepancy of all-ceramic copings, with lower mean values for Procera copings

Shear strength of core-veneer interface in bi-layered ceramics.

Abstract: Statement of problem Delamination of veneering porcelain from underlying ceramic substrates has been reported for all-ceramic restorations. Whether this phenomenon is an inherent weakness of the veneering porcelain due to a weak interface between the veneering and the core porcelains, or merely a fracture through the veneering porcelain itself, has not been explored. Purpose The purpose of this study was to investigate the strength of the substructure and veneering porcelain interface in all-ceramic systems. Methods The all-ceramic systems tested with their respective veneering porcelains were IPS-Empress2 with Eris (IE), Procera AllCeram with AllCeram (PA), Procera AllZircon with CZR (PZ), and DC-Zircon with Vita D (DC). The veneering porcelain recommended by the manufacturer for each material was fired to the ceramic core. A metal ceramic (MC) combination was tested as a control group. Sixty specimens, 12 for each system and control, were made from 1 master die. A cylinder of veneering porcelain 2.4 mm in diameter was applied using a specially designed aluminum split mold. After firing, the specimens were placed in a mounting jig and subjected to shear force in a universal testing machine. Load was applied at a crosshead speed of 0.50 mm/min until failure. Average shear strengths (MPa) were analyzed with a 1-way analysis of variance and the Tukey test (α=.05). The failed specimens were examined microscopically at original magnification ×20 to classify the mode of failure as cohesive in the core, cohesive in the veneer, or adhesive at the interface. Results The mean shear strengths (±SD) in MPa were MC control 30.16 ± 5.88; IE bonded to Eris 30.86 ± 6.47; PZ bonded to CZR 28.03 ± 5.03; DC bonded to Vita D 27.90 ± 4.79; and PA bonded to AllCeram 22.40 ± 2.40. IE, PZ, and DC were not significantly different from the MC control. Microscopic examination showed that adhesive failure, or complete delamination, did not occur between the compatible ceramic core and veneering materials. Failure primarily occurred near the interface with residual veneering porcelain remaining on the core. IE with Eris exhibited cohesive failure in both the core and the veneer. Conclusion The bond strengths of 3 of the tested all-ceramic materials (IE, PZ, and DC) were not significantly different from the control (MC) group.

Influence of occlusal forces on stress distribution in preloaded dental implant screws

Abstract: Statement of problem Abutment and prosthetic loosening of single and multiple screw-retained, implant-supported fixed partial dentures is a concern. Purpose The purpose of this study was to investigate stress distribution of preloaded dental implant screws in 3 implant-to-abutment joint systems under simulated occlusal forces. Material and methods Three abutment-to-implant joint systems were simulated by using the 3-dimensional finite element analysis method: (1) Branemark external hexagonal screw-retained abutment, (2) ITI 8-degree Morse tapered cemented abutment, and (3) ITI 8-degree Morse tapered plus internal octagonal screw-retained abutment. A thermal load and contact analysis method were used to simulate the preload resulting from the manufacturers' recommended torques in implant screw joint assemblies. The simulated preloaded implants were then loaded with 3 simulated static occlusal loads (10 N; horizontal, 35 N; vertical, 70 N; oblique) on the crown position onto the implant complex. Results Numeric and graphical results demonstrated that the stresses increased in both the abutment and prosthetic screws in the finite element models after simulated horizontal loading. However, when vertical and oblique static loads were applied, stresses decreased in the external hexagonal and internal octagonal plus 8-degree Morse tapered abutment and prosthetic screws with the exception of the prosthetic screw of ITI abutment after 70-N oblique loading. Stresses increased in the ITI 8-degree Morse tapered cemented abutment after both vertical and oblique loads. Conclusion Although an increase or decrease was demonstrated for the maximum calculated stress values in preloaded screws after occlusal loads, these maximum stress values were well below the yield stress of both abutment and prosthetic screws of 2 implant systems tested. The results imply that the 3 implant-to-abutment joint systems tested may not fail under the simulated occlusal forces.

Effect of different peroxide bleaching regimens and subsequent fluoridation on the hardness of human enamel and dentin

Abstract: Statement of problem Bleaching of teeth by "in-office" or "home" bleaching techniques are popular methods of whitening teeth. However, bleaching may reduce the surface hardness of enamel and dentin. Purpose The purpose of this study was to evaluate (1) the effect of different concentrations of 2 "in-office bleaching" and 2 "home bleaching" agents applied for different time periods on the hardness of enamel and dentin and (2) the effect of subsequent immersion in a low-concentration fluoride solution on the hardness of bleached enamel and dentin. Material and methods The enamel and dentin of 12 extracted intact human molar teeth were sectioned lengthwise, ground, polished, embedded in acrylic resin and divided into 4 groups each (n=12). An area of approximately 5 × 5 mm of enamel and dentin tested for Knoop hardness number (KHN; kg/mm 2 ) at a load of 100 g for 20 seconds (baseline). The specimens were stored in distilled water for 1 hour and the microhardness testing repeated as a control group. The groups were bleached as follows: Group OX and Group OQ were bleached "in office" with Opalescence Xtra (35% hydrogen peroxide) and Opalescence Quick (35% carbamide peroxide), respectively, for 5, 15, or 35 minutes and retested for KHN at the end of each time period. "Home bleaching" products Opalescence F (15% carbamide peroxide) and Opalescence (10% carbamide peroxide) were applied in 14-hour applications at 24-hour intervals to Groups OF and O, respectively, which were then tested for KHN. Specimens were immersed in 0.05% fluoride solution (Meridol) for 5 minutes and retested for KHN. The hardness values were analyzed by 2-way ANOVA and Scheffe post hoc test (α=.05). Comparisons of KHN between each time and the baseline measurement for each group were of interest. Results Significant decreases in KHN of enamel and dentin were found after bleaching for all test groups, dependent on the accumulated bleaching time. Group OX showed a 25% KHN reduction for enamel and 22% for dentin after 35 minutes bleaching ( P P P P P P P Conclusion The "in-office" bleaching technique reduced the hardness significantly more than the "home" bleaching technique. Low-concentration fluoride mouth rinse (Meridol) restored the softened dental tissues.

An in vitro study evaluating the effect of ferrule length on fracture resistance of endodontically treated teeth restored with fiber-reinforced and zirconia dowel systems

Abstract: Statement of problem There are few published studies analyzing the effects of different ferrule lengths of endodontically treated teeth in relationship to newly developed fiber-reinforced and zirconia dowel systems. Purpose This in vitro study compared the effect of 3 different ferrule lengths on the fracture resistance and fracture patterns of crowned endodontically treated teeth restored with 4 different esthetic dowel systems. Material and methods The crowns of 123 human maxillary canines were removed at the cementoenamel junction and the roots were endodontically treated. Three master tooth models were prepared to ferrule lengths of 1.0 mm, 1.5 mm, and 2.0 mm to produce 3 master analogs. Each root was embedded in autopolymerizing resin with a 0.2-mm layer of silicone impression material to simulate the periodontal ligament. Forty analogs of each master tooth, with ferrule lengths of 1.0 mm, 1.5 mm, and 2.0 mm were produced with copy-milling (Celay system). Each group was further subdivided into 4 groups of 10 specimens each and restored with 4 different esthetic dowel systems (quartz fiber, glass fiber, glass fiber plus zirconia, and zirconia). All dowels were luted with adhesive resin cement (RelyX ARC), restored with composite cores (Valux Plus), and Ni-Cr alloy (Wiron 99) complete crowns. All specimens were loaded at 130 degrees to the long axes in a universal testing machine at a crosshead speed of 1 mm/min until fracture. Fracture patterns were classified as failures above or below the incisal third of the roots. The data were analyzed with 2-way ANOVA and Tukey HSD tests (α=.05). A Fisher exact test was conducted for evaluation of the mode of failure (α=.05). Results Mean failure loads (kg) for quartz fiber, glass fiber, glass fiber plus zirconia, and zirconia groups, respectively, with the 3 ferrule lengths were: 1.0-mm ferrule specimens: 98.09 ± 2.90, 85.36 ± 2.82, 80.24 ± 1.88, 70.11 ± 2.48; 1.5-mm ferrule specimens: 101.0 ± 2.88, 87.58 ± 2.83, 89.8 ± 2.09, 82.71 ± 2.14; 2.0-mm ferrule specimens: 119.5±1.78, 99.84±1.23, 98.6 ± 1.64, 95.42 ± 1.02. Teeth prepared with 2.0-mm ferrules demonstrated significantly higher fracture thresholds ( P Conclusion Increasing the ferrule length of the endodontically treated teeth from 1 mm to 1.5 mm in specimens restored with quartz-fiber and glass-fiber dowels did not produce significant increases in the failure loads ( P =.084, P =.119, respectively). No significant difference was detected between glass-fiber and glass-fiber plus zirconia dowels with 1.5-mm and 2.0-mm ferrules ( P =.218, P =.244, respectively). However, fracture thresholds were higher for all 4 dowel systems when the specimens were prepared with a 2.0-mm ferrule length ( P

Effect of lateral cyclic loading on abutment screw loosening of an external hexagon implant system

Abstract: Statement of problem Efforts to reduce the recurrence of abutment screw loosening with single tooth implant-supported restorations have been reported. However, the current knowledge about the role of the implant external hexagon is incomplete. Purpose This in vitro study investigated the effect of lateral cyclic loading with different load positions on abutment screw loosening of an external hexagon implant system. Material and methods Fifteen Branemark implant assemblies were divided equally into 3 groups, A, B, and C. Each assembly consisted of a Mark IV implant (4 × 10 mm) mounted in a brass block, a CeraOne abutment (3 mm), and an experimental cement-retained superstructure. For group A, a cyclic load of 50 N was applied centrally and perpendicular to the long axis of the implant, whereas for group B, the same load was applied eccentrically (at a distance of 4 mm) in a loosening direction. A target of 1.0×10 6 cycles (40 months of simulated function) was defined. Group C (control) was left unloaded for the same loading time period as groups A and B. Reverse torque was recorded before and after loading and the difference was calculated. The data were analyzed with 1-way analysis of variance and compared with the Tukey test (α=.05). Results Group A exhibited a significant difference in the reverse torque difference values ([−5.6 to −3.4] ± 0.86 N·cm) compared with groups B ([−1.9 to 0.5] ± 0.99 N·cm) and C ([−0.7 to 0.0] ± 0.26 N·cm) ( P Conclusion Within the limitations of this study, reverse torque values of the screw joint were preserved under eccentric lateral loading, as compared with centric loading ( P

A review of selected dental literature on evidence-based treatment planning for dental implants: Report of the Committee on Research in Fixed Prosthodontics of the Academy of Fixed Prosthodontics

Abstract: This literature review summarizes research with the aim of providing dentists with evidence-based guidelines to apply when planning treatment with osseointegrated implants. Peer-reviewed literature published in the English language between 1969 and 2003 was reviewed using Medline and hand searches. Topics reviewed include systemic host factors such as age, gender, various medical conditions, and patient habits, local host factors involving the quantity and quality of bone and soft tissue, presence of present or past infection and occlusion, prosthetic design factors, including the number and arrangement of implants, size and coatings of implants, cantilevers and connections to natural teeth, and methods to improve outcomes of implant treatment in each category. The review demonstrated that there is no systemic factor or habit that is an absolute contraindication to the placement of osseointegrated implants in the adult patient, although cessation of smoking can improve outcome significantly. The most important local patient factor for successful treatment is the quality and quantity of bone available at the implant site. Specific design criteria are provided, including guidelines for spacing of implants, size, materials, occlusion, and fit. Limitations in the current body of knowledge are identified, and directions for future research are suggested.

An evaluation of impression techniques for multiple internal connection implant prostheses.

Abstract: Statement of problem Movement of impression copings inside the impression material using an open-tray impression technique during clinical and laboratory phases may cause inaccuracy in transferring the 3-dimensional spatial orientation of implants intraorally to the definitive cast. Consequently the restoration may require corrective procedures. Purpose This in vitro study evaluated the accuracy of 3 different impression techniques using polyether impression material to obtain a precise definitive cast for a multi-unit implant restoration with multiple internal connection implants. Material and methods A reference acrylic resin model with 4 internal connection implants (3i Implant Innovations) was fabricated. Forty-five medium-consistency polyether impressions (Impregum Penta) of this model were made with square impression copings using an open-tray technique. Three groups of 15 specimens each were made with different impression techniques: in the first group, nonmodified square impression copings were used (NM group); in the second group, square impression copings were used and joined together with autopolymerizing acrylic resin before the impression procedure (R [resin] group); and in the third group, square impression copings previously airborne-particle abraded and coated with the manufacturer-recommended impression adhesive were used (M [modified] group). Matching implant replicas were screwed into the square impression copings in the impressions. Impressions were poured with ADA type IV stone (New Fujirock). A single calibrated examiner blinded to the nature of the impression technique used examined all definitive casts to evaluate the positional accuracy (μm) of the implant replica heads using a profile projector (at original magnification ×10). These measurements were compared to the measurements calculated on the reference resin model which served as control. Data were analyzed with a 1-way analysis of variance at α=.05, followed by the Student Newman-Keuls test (α=.05). Results The data obtained with the profile projector revealed significant differences within the 3 impression techniques ( P P =.05). The mean distance (±SD) between the posterior implants compared to the reference acrylic resin model was 18.17 μm (± 6.4) greater for group R casts, 41.27 μm (± 8.4) greater for group M casts, and 46.21 μm (± 8.9) greater for group NM casts. Distances between the anterior implants were also greater than those recorded on the reference model. The distance was 15.23 μm (± 5.9) greater on group R casts, 38.17 μm (± 8.3) greater on group M casts, and 43.23 μm (± 8.7) greater on group NM casts. Conclusion Within the limitations of this study, improved accuracy of the definitive cast was achieved when the square impression copings joined together with autopolymerizing acrylic resin were used to make an impression of multiple internal connection implants.

The use of short, wide implants in posterior areas with reduced bone height: a retrospective investigation

Abstract: Statement of problem Reduced bone height frequently presents a challenge for implant-assisted tooth replacement in partially edentulous patients. Purpose This retrospective study evaluated the success rate of short, wide hydroxyapatite (HA)-coated implants placed in mandibular and maxillary molar areas with reduced bone height. Material and methods A total of 168 HA-coated implants (6-mm diameter × 8-mm length) were placed in 167 patients in a private-practice setting. A minimal 6-mm workable ridge height and 8-mm ridge width was available in all situations. Patients were referred back to 1 of 7 referring restorative dentists for restoration of the implants. No attempt was made to standardize the restoration of the implants except to avoid working and nonworking contacts in lateral excursions. Implant success was evaluated according to the following criteria: (1) absence of complaints, (2) absence of recurring peri-implant infection or suppuration, (3) absence of perceptible implant mobility, and (4) absence of radiolucencies at implant-bone junction. The data were analyzed with descriptive statistics. Results Fifty-four (32.1%), 35 (20.8%), 36 (21.4%), and 42 (25.0%) implants replaced maxillary first and second and mandibular first and second molars, respectively. There were 128 implant-supported single crowns. Thirty-eight implants served as abutments for fixed partial dentures connected to other implants of various sizes. Two implants were involved in cantilevered fixed partial dentures. Patients were followed for up to 68 months (mean = 34.9 months) after loading of implants. The overall cumulative success rate was found to be 100%. Conclusions For residual ridges with minimal height but adequate width, the use of short, wide HA-coated implants may offer a simple and predictable treatment alternative in posterior areas.

Alveolar distraction osteogenesis for the correction of vertically deficient edentulous ridges: A multicenter prospective study on humans

Abstract: Purpose The purposes of this prospective multicenter study were to evaluate the use of vertical distraction osteogenesis in the correction of vertically deficient alveolar ridges and to evaluate whether the vertical bone gained by distraction osteogenesis was maintained over time when dental implants were placed in the distracted areas. Materials and methods Thirty-seven patients presenting vertically deficient edentulous ridges were treated in 4 different centers by means of distraction osteogenesis with an intraoral alveolar distractor. Two to 3 months after consolidation of the distracted segments, 138 dental implants were placed in the distracted areas. Four to 6 months later, abutments were connected and prosthetic loading of the implants began. Results The mean follow-up after initial prosthetic loading was 34 months (range 15 to 55 months). The mean bone gain obtained by distraction was 9.9 mm (range 4 to 15 mm). The cumulative success rate of the implants 4 years after the onset of prosthetic loading was 94.2%, while the implants' cumulative survival rate was 100%. No statistically significant differences were found between the different centers as far as survival and success rates of implants were concerned. Discussion and conclusion The results of this study appear to demonstrate that distraction osteogenesis is a reliable technique for the correction of vertically deficient edentulous ridges. The regenerated bone appeared to withstand the functional demands of implant loading. The survival and success rates of the implants placed in the distracted areas were consistent with those reported in the literature regarding implants placed in native bone in this patient population.— Reprinted with permission of Quintessence Publishing.

Fracture resistance of three all-ceramic restorative systems for posterior applications.

Abstract: Statement of problem The failure loads of all-ceramic crowns are influenced not only by the fracture resistance of the component materials but also by prosthesis geometry and size and location of flaws, thus there is a need for a study that compares the fracture resistance of all-ceramic systems using a simple and reproducible specimen geometry that includes flaws occurring at material interfaces. Purpose The research aim was to compare the in vitro fracture resistance and origin of failure of simulated first molar crowns fabricated using 3 all-ceramic systems, IPS Empress 2, Procera AllCeram, and In-Ceram Zirconia. Material and methods Twenty axisymmetric crowns of each system were fabricated to fit a preparation with 1.5- to 2.0-mm occlusal reduction. The center of the occlusal surface on each of 15 specimens per ceramic system was axially loaded to fracture in a universal testing machine, and the maximum load (N) was recorded. Fractured surfaces were examined using optical and electron microscopy to determine the most prevalent origin of failure in each ceramic system. Five crowns per system were sectioned, and thickness of the luting agent, core material, and veneer porcelain layers were measured. The 95% confidence intervals of the Weibull modulus and characteristic failure load were compared between the 3 systems. Two-way multivariate analysis of variance was used to analyze the thickness of the luting agent, ceramic core, and veneer porcelain layers (α=.05). Results The 95% confidence intervals for Weibull modulus were 1.8 to 2.3 (IPS Empress 2), 2.8 to 3.6 (Procera AllCeram), and 3.9 to 4.9 (In-Ceram Zirconia). The 95% confidence intervals for characteristic failure load were 771 to 1115 N (IPS Empress 2), 859 to 1086 N (Procera AllCeram), and 998 to 1183 (In-Ceram Zirconia). The origin of failure was most commonly found at the interface between the ceramic core and veneer porcelain for IPS Empress 2 and between the ceramic core and luting agent layer for the other systems. Conclusions There was no significant difference in fracture resistance; however, there was a significant difference in failure origin between the all-ceramic systems studied.

Survival rates of resin-bonded, glass fiber–reinforced composite fixed partial dentures with a mean follow-up of 42 months: A pilot study

Abstract: Statement of problem Although short-term clinical data exist for resin-bonded, glass fiber-reinforced composite fixed partial dentures (FPDs), long-term data are needed. Purpose The survival rates of 29 resin-bonded, glass fiber-reinforced composite fixed partial dentures were evaluated in this clinical study for periods of up to 42 months. Material and methods FPDs were fabricated to replace 1 to 3 missing maxillary or mandibular teeth of 29 patients not able to be treated with conventional FPDs. Originally, there were 37 patients (the drop-out rate was 22%). The FPDs were retained with wings, inlays, complete coverage crowns, or combinations of these that were bonded to tooth structure. The FPD frameworks were made of continuous unidirectional E-glass fibers with a multiphase polymer matrix and light-polymerized particulate composite veneer. The patients were recalled for examinations, where a general dental examination was performed, 1 to 3 times per year for up to 63 months (minimum 24 months, mean 42 months). Partial or complete total debonding of the FPD or the framework fracture was considered a treatment failure. The data were analyzed with the Kaplan-Meier survival test (α=.05). Results Two resin frameworks fractured, and 3 frameworks were debonded. Kaplan-Meier survival probability at 63 months was 75%. Three of the failed FPDs were rebonded or repaired in situ, producing a functional survival rate of 93% after rebonding or repairing (mean survival time was 55 months). Conclusion The results of this clinical study of 29 prostheses suggest that glass fiber–reinforced FPDs may be a possible alternative to cast metal resin-bonded FPDs. These restorations were successfully used as multiple-unit prostheses that employed a variety of abutment tooth preparation designs.

The etiology and management of gagging: A review of the literature

Abstract: Gagging in dental patients can be disruptive to dental treatment and may be a barrier to patient care, preventing the provision of treatment and the wearing of prostheses. This article reviews the literature on the gagging problem from English-language peer-reviewed articles from the years 1940 to 2002 found by conducting an electronic search of PubMed, coupled with additional references from citations within the articles. Dentally relevant articles have been cited wherever evidence exists, and a balanced view given in situations where there is controversy. The first section considers the normal gag reflex and factors that may be associated with the etiology of gagging, including anatomical and iatrogenic factors, systemic disorders, and psychological conditions. A review of the management of patients with an exaggerated gag reflex follows and includes strategies to assist clinicians.

The effect of reinforcement with woven E-glass fibers on the impact strength of complete dentures fabricated with high-impact acrylic resin

Abstract: Statement of problem The fracture of acrylic maxillary complete dentures occurs frequently during service through heavy occlusal force or accidental damage. Purpose The purposes of this study were to measure the impact strength of maxillary complete dentures fabricated with high-impact acrylic resin and to evaluate the effect of woven E-glass fiber-reinforcement on the impact strength of the complete dentures. Material and methods Preimpregnated woven E-glass fibers (Stick Net) were used to reinforce 10 complete denture bases fabricated with a heat-polymerized high-impact acrylic resin (Lucitone 199). Ten unreinforced complete dentures served as a control group. All specimens were stored in water at 37°C for 2 months before testing. The impact strengths (J) of the dentures were measured with a falling-weight impact test. The impact strengths of both groups were compared by a repeated measures analysis of variance (α=.05). The Weibull distribution was also applied to calculate the cumulative fracture probability as a function of impact strength. Results The mean impact strength of the control dentures was 90.0±38.1 J at crack initiation, and 95.9±37.7 J at complete fracture, whereas the impact strength of reinforced dentures was 201.7±77.9 J and 277.9±102.5 J, respectively. Statistical analysis showed that impact strength of the high-impact acrylic complete denture was significantly increased by the addition of woven E-glass fiber ( P Conclusion The impact strengths of maxillary complete dentures fabricated with high-impact acrylic resin increased by a factor greater than 2 when reinforced with woven E-glass fiber.

Patient satisfaction with mandibular implant overdentures and conventional dentures 6 months after delivery

Abstract: Purpose This study examined patient satisfaction with conventional complete dentures and mandibular implant overdentures opposing conventional maxillary dentures 6 months after delivery. Materials and Methods Sixty edentulous subjects (aged 65 to 75 years) were randomly assigned to either a mandibular conventional denture or an overdenture supported by two implants with ball-shaped retentive anchors. Patients rated their general satisfaction and other features of their prostheses, together with their ability to eat certain food items, on 100-mm visual analogue scales before assignment, and after 2 and 6 months. Results Both treatment groups reported greater satisfaction with their new prostheses at 6 months. General satisfaction ratings were higher in the implant group than in the conventional denture group by approximately 36% (mean difference 22.3 mm). The implant group also rated comfort (mean difference 22.4 mm), stability (mean difference 28.5 mm), and ability to chew (mean difference 17.3 mm) significantly higher. Significantly higher scores were also given by the implant group for their ability to chew certain hard foods. A trend for an increase in the differences between the groups, in favor of the implant group, was observed between the 2- and 6-month recalls, although the increase was only significant for ease of cleaning. The primary influence on general satisfaction 6 months after the delivery of the prostheses was the provision of the two-implant overdenture. Conclusion Edentulous seniors who received mandibular implant overdentures opposing a conventional denture rated their general satisfaction approximately 36% higher than did a comparable group provided with new conventional dentures.

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

Abstract: 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 (α=.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.

Influence of cyclic loading and luting agents on the fracture load of two all-ceramic crown systems

Abstract: Statement of problem Inherent mechanical properties, fabrication techniques, luting agents, and intraoral conditions are primary factors attributing to longevity of all-ceramic crowns. Before doing time-consuming and costly clinical studies, preclinical in vitro studies should be conducted to evaluate the durability of these crowns. Purpose This study investigated the influence of different luting agents and cyclic loading under wet conditions on the fracture load of CAD-CAM and pressable all-ceramic crowns. Material and methods Ninety-six human premolars were prepared for all-ceramic crowns with the following preparation criteria: 6-degree axial taper, 1.5-mm shoulder finish line placed 0.5 mm occlusal to the CEJ, 2-mm occlusal reduction, and occluso-gingival height of 5 mm. Sixteen unprepared premolars served as controls. Forty-eight crowns were laboratory fabricated from a lithium disilicate glass-ceramic (IPS-Empress 2), while 48 CAD-CAM crowns were directly fabricated using a leucite-reinforced glass-ceramic (ProCAD) and the Cerec 3 CAD-CAM system. Three luting agents (Panavia F, Superbond CB dwell time 60 seconds) in a masticatory simulator. All specimens were loaded in a universal testing machine with the compressive load (N) applied along the long axis of the specimen at a crosshead speed of 1 mm/min until fracture. Fracture load was recorded for each specimen. The Kruskal-Wallis test was used first to detect overall significance, followed by Mann-Whitney U tests to identify which pairs of groups had significant differences ( P =.05). Results Cyclic loading significantly decreased the median fracture load of ProCAD crowns luted using Superbond from 987.2 to 786.0 N ( P =.014) and those luted using ProTec CEM from 914.4 to 630.7 N ( P =.007). Also, the median fracture load of Empress 2 crowns luted using ProTec CEM decreased significantly from 977.3 to 622.9 N ( P =.013). However, cyclic loading did not decrease the median fracture load of crowns luted using Panavia F, Empress 2 ( P =.431) and ProCAD ( P =.128). With the same loading conditions and luting agents, there were no significant differences in the fracture loads of ProCAD and Empress 2 crowns ( P >.05). Conclusions Cyclic loading reduced the fracture load of ProCAD crowns luted with Superbond C&B and ProTec CEM and of Empress 2 crowns luted with ProTec CEM.

Shade matching in restorative dentistry: the science and strategies

Abstract: Closely matching natural teeth with an artificial restoration can be one of the most challenging procedures in restorative dentistry. Natural teeth vary greatly in color and shape. They reveal ample information about patients' background and personality. Dentistry provides the opportunity to restore unique patient characteristics or replace them with alternatives. Whether one tooth or many are restored, the ability to assess and properly communicate information to the laboratory can be greatly improved by learning the language of color and light characteristics. It is only possible to duplicate in ceramic what has been distinguished, understood, and communicated in the shade-matching process of the natural dentition. This article will give the reader a better understanding of what happens when incident light hits the surface of a tooth and give strategies for best assessing and communicating this to the dental laboratory.— Reprinted with permission of Quintessence Publishing .

The shortened dental arch: a review of the literature.

Abstract: The functional demands of patients are highly variable and individual, requiring dental treatment to be tailored to the individual's needs and adaptive capability. The World Health Organization indicates that a functional, esthetic, natural dentition has at least 20 teeth, while the literature indicates that dental arches comprising the anterior and premolar regions meet the requirements of a functional dentition. The English-language peer-reviewed literature pertaining to the short dental arch (SDA) was identified through the Medline search engine covering the period between 1966 and the present and critically reviewed. This treatment option for the partially dentate patient may provide oral functionality, improved oral hygiene, comfort, and, possibly, reduced costs.

Residual methyl methacrylate monomer, water sorption, and water solubility of hypoallergenic denture base materials.

Abstract: Statement of problem Denture base materials have the potential to cause irritation and allergic reaction to the oral mucosa. Water sorption and water solubility of denture base resins affect dimensional behavior and denture stability. A correlation between residual monomer and water sorption exists. Purpose This in vitro study compared the amount of residual monomer, quantity of water sorption, and solubility of 4 denture base materials purported to be hypoallergenic with those of a polymethyl methacrylate–based (PMMA) heat-polymerizing acrylic resin. Material and methods The denture base resins Sinomer (heat-polymerized, modified methacrylate), Polyan (thermoplastic, modified methacrylate), Promysan (thermoplastic, enterephthalate-based), and Microbase (microwave polymerized, polyurethane-based), which are purported to be hypoallergenic, and Paladon 65 (heat-polymerized, methacrylate, control group) were examined. Specimens of each material were tested for residual methyl methacrylate (MMA) monomer (% wt, n=3), amount of water sorption (μg/mm 3 , n=5) and water solubility (μg/mm 3 , n=5), according to ISO 1567:2000. The residual MMA monomer concentrations were determined by gas chromatography (GC). The data were analyzed with 1-way ANOVA and the Bonferroni-Dunn multiple comparisons post hoc analysis for each test variable (α=.05). Results Significantly lower residual MMA monomer was shown for Sinomer and Polyan compared to the PMMA control group (0.90 ± 0.20% wt, P 3 ) was significantly lower than Paladon 65 (23.04 ± 3.13 μg/mm 3 , P 3 ) was not significantly lower than the PMMA material (0.40 ± 0.06 μg/mm 3 , P> .05). Except for Sinomer, the tested denture base resins passed the requirements of ISO 1567 regarding residual MMA monomer ( 3 ) and solubility ( 3 ). Conclusion The tested hypoallergenic denture base materials exhibited significantly lower residual monomer content than PMMA. Promysan and Microbase showed no detectable residual MMA.

Pharmacologic interventions in the treatment of temporomandibular disorders, atypical facial pain, and burning mouth syndrome. A qualitative systematic review

Abstract: Aims To carry out a systematic review of the literature in order to assess the pain-relieving effect and safety of pharmacologic interventions in the treatment of chronic temporomandibular disorders (TMD), including rheumatoid arthritis (RA), as well as atypical facial pain (AFP), and burning mouth syndrome (BMS). Methods Study selection was based on randomized clinical trials (RCTs). Inclusion criteria included studies on adult patients (> or = 18 years) with TMD, RA of the temporomandibular joint (TMJ), AFP, or BMS and a pain duration of >3 months. Data sources included Medline, Cochrane Library, Embase, and Psych Litt. Results Eleven studies with a total of 368 patients met the inclusion criteria. Four trials were on TMD patients, 2 on AFP, 1 on BMS, 1 on RA of the TMJ, and 3 on mixed groups of patients with TMD and AFP. Of the latter, amitriptyline was effective in 1 study and benzodiazepine in 2 studies; the effect in 1 of the benzodiazepine studies was improved when ibuprofen was also given. One study showed that intra-articular injection with glucocorticoid relieved the pain of RA of the TMJ. In 1 study, a combination of paracetamol, codeine, and doxylamine was effective in reducing TMD pain. No effective pharmacologic treatment was found for BMS. Only minor adverse effects were reported in the studies. Conclusion The common use of analgesics in TMD, AFP, and BMS is not supported by scientific evidence. More large RCTs are needed to determine which pharmacologic interventions are effective in TMD, AFP, and BMS.— Reprinted with permission of Quintessence Publishing .

CAD-CAM generated ear cast by means of a laser scanner and rapid prototyping machine

Abstract: Sculpting a wax ear cast for use when making a definitive prosthesis for a patient who has had auricle ablative surgery, is challenging. It requires a skilled anaplastologist along with complex instrumentation able to perform facial laser scans and reproduce anatomic details. The aim of this article is to present a technique to create a cast by laser scanning a stone cast of the existing ear. A 3D laser scanner develops an integrated 3D digital image of the unaffected ear, which is copied and then mirrored. A rapid prototyping machine collects the necessary data to manufacture the definitive resin ear. This procedure is time and cost effective only if the technology is free of charge.

Color stability of provisional prosthodontic materials.

Abstract: Statement of problem Discoloration of provisional prosthodontic materials may result in patient dissatisfaction and additional expense for replacement. Purpose The purpose of this study was to determine the color stability of 5 provisional prosthodontic materials before and after immersion in distilled water or coffee for 20 days or exposure to ultraviolet (UV) light for 24 hours. Material and methods A total of 105 disc-shaped specimens (20±0.1 mm by 1±0.05 mm) were fabricated with 5 provisional prosthodontic materials: polyethyl methacrylate resins (Trim II), polymethyl methacrylate resins (Duralay; Alike), and bis-acryl methacrylate resin (Luxatemp; Integrity), according to manufacturers' instructions (n=21). Seven specimens of each material were randomly selected and immersed individually in distilled water (60°C) or coffee (37°C) for 20 days or exposed to UV irradiation for 24 hours, respectively. Color was measured as CIE L ∗ a ∗ b ∗ with a colorimeter before and after the immersion or UV exposure. Color change (ΔE) was calculated and data were analyzed with 1-way ANOVA and the Tukey multiple comparisons test (α=.05). Results For specimens immersed in water, the color change of bis-acryl-methacrylate–based provisional materials (Integrity and Luxatemp) was significantly less than that of 3 methyl/ethyl methacrylate–based provisional materials (Trim II, Alike, and Duralay) ( P P P Conclusion Luxatemp and Integrity (bis-acryl-methacrylate–based resins) demonstrated acceptable color stability and were the most color-stable provisional prosthodontic materials tested compared to the methyl/ethyl methacrylate–based resins.

A technique for fabricating patterns for removable partial denture frameworks using digitized casts and electronic surveying.

Abstract: Although computer-aided design and manufacture techniques have shown some promising applications in the fabrication of crowns, inlays, and maxillofacial and oral surgery, the field of removable prosthodontics has not embraced these technologies so far. This article describes the development and investigation of computer-aided techniques that may eventually enable prosthodontic procedures such as surveying and the production of sacrificial patterns to be performed digitally. A 3-dimensional computer model of a conventional cast from a patient was obtained using an optical surface capture device (a scanner). The shape of a number of components of a removable partial denture framework was modeled on the 3-dimensional scan electronically, using computer-aided design software. A physical plastic shape of the components was produced using a Rapid Prototyping machine and used as a sacrificial pattern. Techniques to allow digital cast surveying before the production of sacrificial patterns were also developed. The results show that digital dental surveying and machine-produced sacrificial patterns can be accomplished. This article forms a basis for further developments leading to a fully integrated approach to the computer-aided design and fabrication of removable partial denture frameworks.