Ceramometal Restorations Research Articles

Evaluating the Impact of Oxidation Heat Treatment and Dual Opaquing Techniques on Enhancing Metal-Ceramic Bond Strength.

This research aims to assess the impact of oxidation heat treatment (OHT) and dual opaquing techniques on enhancing the bond strength between metal and ceramic. Eighty rectangular patterns with dimensions of 0.5x3x25 mm (according to ISO 9693-2012) were fabricated in a custom-made silicon mold by using auto-polymerized pattern resin material. These rectangular patterns were cast using base metal alloys. The samples were split into two primary groups: group A, subjected to OHT, and group B, without oxidation treatment. Each primary group was then split up into subgroups according to the application of single layers (group A1, B1)or double layers (group A2, B2) of opaque porcelain.After pre-surface treatment and Ceramco 3 paste opaque application, dentin porcelain (Ceramco 3) wasapplied to the mid-region of the samples, followed by firing to achieve a standardized thickness. Flexural strength determination was conducted via a three-point bend test performed on the universal testing machine (UTM) (Instron Corp., Model 2519-107, USA), adhering to ISO standard 9693. Post-testing failure types were analyzed by morphological assessment of debonding surfaces via a scanning electron microscope (SEM). The statistical analysis was performed with SPSS version 16, incorporating ANOVA for intergroup analysis and independent t-tests for intragroup comparisons. Group A2 exhibited the highest mean flexural bond strength (P<0.05) at 41.85 MPawhen compared to group A1 at 37.60 MPa, group B2 at 35.47 MPa, and group B1 with the least mean flexural bond strength at 30.41 MPa. SEMobservations revealed cohesive bond failure for groups A1, A2, and B2and adhesive bond failure for groupsB1. It is evident that OHT and opaquing technique are important factors in determining the bond strength of ceramo-metal restorations. When combined, these techniques greatly increase the overall success and durability of metal-ceramic restorations, underscoring their significance in contemporary dental prostheses.

Use of Ultra-Translucent Monolithic Zirconia as Esthetic Dental Restorative Material: A Narrative Review

It has been observed in recent years that zirconia (Zr) is being increasingly used for a wide range of clinical applications. There are several reasons for this, but the most significant one is its excellent mechanical properties, specifically its transformation toughening properties compared to other dental ceramics and its improved natural appearance when compared to ceramometal restorations. As a result of the advancement of chairside milling and developments in rapid-sintering technology, the fabrication of dental restorations has become more computerized, time-saving, and accurate over the past few decades. However, a main disadvantage of conventional Zr restorations is that they lack the translucency of glass–ceramics, although they are extremely strong. Recently, by increasing the yttrium %, changing the grain size, and reducing the impurities, the ultra-translucent monolithic zirconia “5-mol%-yttria-stabilized tetragonal zirconia polycrystals” has been introduced, with successful attempts to make translucent Zr an aesthetically attractive option for minimally invasive veneer restorations. It is important to note that veneer restorations do not possess the mechanical retentive features of the tooth preparations and rely primarily on bonding to resin cement. This presents a great challenge for the inert Zr since it does not bond chemically with resin cement, unlike glass–ceramic materials that establish chemical adhesion with resin cement, favoring their use for indirect veneer restorations. Taking this into account, this article aims to review the progressive development of ultra-translucent monolithic Zr materials as they are available today and, in the future, represents a concerted drive toward maximum translucency and strength, which renders them a viable treatment option for esthetic veneer restorations.

Effect of Ceramic Thickness and Technician Variability on the Shade Duplication of Dental Ceramo-Metallic Restorations.

Ceramic thickness and technicians' manipulative variables are critical factors affecting the resultant shade of dental ceramo-metallic restorations. This study investigated the effect of the following variables on shade duplication of ceramo-metallic specimens: (a) ceramic thickness; (b) differences between several technicians (inter-technician variability); and (c) the ability of each technician to repeat the resultant shade (intra-technician variability). Ninety ceramo-metallic specimens were prepared and divided into three main groups (n = 30/gp) according to the different technicians who built up the veneering ceramic of the specimens. Each group was further subdivided into three subgroups (n = 10/subgroup) according to the thickness of the ceramic (1, 1.5, and 2 mm built over a 0.5 mm-thick metal substructure). Three different technicians were asked to follow the same protocol as regards the same ceramic batch (Shade 3M2, Vita VM13, Zahnfabrik, Germany), firing temperature, and number of firing cycles. Meanwhile, each technician followed his own protocol with regard to other ceramic manipulative variables. The duplicated shades of the specimens were investigated using the Vita Easyshade spectrophotometer by using the verify shade mode. Color difference (∆E) values were calculated between the target shade (3M2) and the duplicated shades of the specimens automatically by the Vita Easyshade spectrophotometer (Vita, Zahnfabrik, Germany). The effect of ceramic thickness and inter- and intra-technician variability on the duplication of the target shade was investigated. The results showed that the effect of ceramic thickness on the duplicated shades depended on inter-technician variability. High inter-technician variability (∆E = 2-6.4) was noticed in contrast to low intra-technician variability (∆E = 0.2-1.5). It could be concluded that proper shade-duplication of ceramo-metallic restoration was a cumulative technique intimately related to manipulative variables and ceramic thickness.

All on four fixed prostheses versus implant overdentures for management of edentulous maxilla opposing mandibular 2- implant assisted overdentures

Purpose: This study aimed to compare two treatment modalities; All on four fixed prostheses and locator retained overdentures; to rehabilitate patients having problems associated with edentulous maxilla opposing mandibular implant assisted overdentures. Materials and methods: Ten patients complaining from looseness and instability of their maxillary dentures that oppose mandibular 2-implant-retained overdentures were randomly divided into 2 groups: Group I included 5 patients who received four implants according to the All-on- four Concept (2 parallel middle implants and 2 posterior implants with distal inclination). Implants were immediately loaded with fixed acrylic prosthesis, then after 6 months the prosthesis was replaced with fixed ceramometal restoration, Group II, included 5 patients who received four implants that were immediately loaded with Locator retained maxillary overdentures using new maxillary dentures. Clinical (plaque index (PI), gingival index (GI), probing depth (PD) and implant stability (IS)) and radiographic (marginal bone loss (MBL) outcomes were recorded at baseline (T0), 6 (T6) and 12 (T12) month after prosthesis insertion.

Caracterização metalúrgica de ligas de Ni-Cr para metalocerimica

Alternative Ni-Cr alloys applied in dentistry of two commercial brands for ceramometal restoration were evaluated. The alloys were analyzed in the commercial and after casting conditions using experimental techniques of metallography, X-ray diffraction, superficial hardness and density. The metalografics and X-ray diffraction analysis showed that, the alloys microstructure is marked with the presence of a solid solution having an ordered face- centred cubic structure, Ni-rich austenitic (y phase) matrix, and with fine precipitates particles of secondary phases. The Vicker hardness tests showed a decrease in hardness values of the studied alloys aer casting. The alloys density values, on the other hand, did not manifest changes.

Assessment of internal fit and micro leakage of conventionally fabricated ceramometallic restoration versus CAD wax and press veneering (in-vitro study)

Statement of problemAccuracy of internal fit and microleakage for CAD-CAM systems used in metal coping fabrication and veneered with layering or pressing porcelain in ceramometallic restoration is unclear.Material and methodsA master metal die was milled to resemble the right mandibular first molar preparation for coverage with ceramometallic restoration. Master die was duplicated to twenty-four resin specimen dies.They were divided into two groups according to metal coping construction technique using either conventional (C) or CAD (D) wax. Each group was subdivided into two subgroups (n = 6) according to the technique of porcelain veneering (layered or pressed) to fabricate ceramometallic restorations, where subgroup (CL, DL) were conventionally layered by porcelain and (CP, DP) were press veneered. A standardized thickness of metal and porcelain was performed in all specimens as per manufacturer’s instructions for techniques ceramometallic restoration construction.Evaluation of internal fit was done with silicone replica technique using stereomicroscope at ×24 magnification where the thickness of silicon layer was measured at 20 reference points on each specimen. Then specimens were subjected to thermocycling. Sectioned specimens were assessed for microleakage using a stereomicroscope at ×12 magnification along die-cement interface with a five scale score.ResultsMean internal gap values of veneering showed a statistically nonsignificant difference between specimens made with layering(L) and pressing(P). Different techniques of wax construction showed a non-significant difference in internal gap values between specimens made with conventional(C) and CAD(D) waxing. However, a significant difference was found in the internal gap at different sites. The highest internal gap was found at the occlusal surface, while the lowest gap was found at the finish line. The highest mean microleakage score was found with CAD wax and press veneering, while the lowest mean microleakage score was found with conventional wax and press veneering.ConclusionBoth construction techniques of ceramometallic restoration were considered reliable in restoration production within a clinically acceptable range regarding internal fit and microleakage. There is a strong positive correlation between internal fit and microleakage of ceramometallic restoration constructed.

Effect of Cathodic Arc Plasma Deposition on Shear Bond Strength between Palladium Cobalt Chromium Coated with Titanium Nitride and Titanium Aluminium Nitride with Ceramic.

Background:The success of esthetic ceramo-metal restoration is strongly influenced by its bond strength. The success of ceramo-metal restoration is subjective to its bond strength.Aim and Objectives:The aim of this study is to evaluate the shear bond strength between palladium-based cobalt chromium (Co-Cr) alloy coated with titanium nitride (TiNi) and titanium aluminum nitride with feldspathic ceramics.Materials and Methods:According to the International Organization for standardization 9693; technical report 1,140,640 samples were prepared using Palladium-based Co-Cr alloy with ×4 vertical projection resting on 5 mm diameter base. The samples were divided into Group: A (control), Group: B (Sandblasted), Group: C (TiNi coated), and Group: D (titanium aluminum nitride coated by cathodic arc plasma deposition, following which feldspathic ceramic application was performed. Shear bond test was performed using universal testing machine and surface analysis was performed using scanning electron microscope.Results:The mean shear bond strength for Group A was 172.994 ± 3.739 N, Group B 209.485 ± 5.913 N, Group C 176.536 ± 4.780 N, and Group D 260.576 ± 16.351 N. Comparison within the groups was made using one-way ANOVA, and multiple group comparisons were made using Tukey's honestly significant difference Post hoc test where the P < 0.001was considered statistically significant.Conclusion:Palladium based Co-Cr alloy coated with titanium aluminum nitride by cathodic plasma arc deposition showed maximum shear bond strength with feldspathic ceramic compared to noncoated, sandblasted, and TiNi coated alloy.

Assessment of the marginal fit, ceramo-metal shear bond strength and the fractographic analysis of sinter cast gold: An In-vitro study

Introduction: The fractographic analysis is performed by observing, measuring, and interpreting the fracture surface topography that can determine many features of the microstructure of materials and the mechanics of the fracture. The aim of this study was to assess the marginal fit and the ceramo-metal shear bond strength of sinter cast gold, and to analyze the debonded sample by fractography. Materials and Methods: A total of five sinter cast gold copings were prepared on a stainless master die resembling a maxillary 1st pre-molar to receive a ceramo-metal restoration. Each of the copings was then assessed for the marginal fit before and after ceramic firing. In addition, a total of five ceramo-metal discs were fabricated for testing shear bond strength at the metal-ceramic interface. The samples were subjected to increasing shear load on a universal testing machine with crosshead speed of 0.002 mm/s. The load at which the samples debonded completely was noted, and the fractographic analysis of the samples was performed. Results: The mean marginal fit found in this study for sinter cast gold before ceramic firing was found to be 11.5 μm with a standard deviation of ±4.64 μm, and after ceramic firing, it was found to be 9.38 μm with a standard deviation of ±3.57 μm. The average shear bond strength at the sinter cast gold ceramic interface was 18.216 MPa. The fractographic analysis showed the globular microstructure of sinter cast gold on sintering, adhesive, and mix-mode type of fracture with the presence of both gold and ceramic. Conclusion: The marginal fit observed before and after ceramic firing was within clinically acceptable range, whereas the ceramo-metal shear bond strength between sinter cast gold and ceramic was found to be inadequate.

Assessment of marginal fit, ceramometal shear bond strength, and fractographic analysis of sinter cast gold: An In vitro study

Introduction: Fractographic analysis is performed by observing, measuring, and interpreting the fracture surface topography that can determine many features of the microstructure of materials and the mechanics of the fracture. This study was planned to put through investigation, marginal fit and ceramo-metal shear bond strength with fractographic analysis of the debonded surfaces. The aim of this study was to assess the marginal fit, ceramo-metal shear bond strength of sinter cast gold and to analyze the debonded sample by fractography. Materials and Methods: A total of 5 sinter cast gold copings were prepared on a stainless master die resembling a maxillary 1st pre-molar to receive a ceramo-metal restoration. Each of the copings were, then, assessed for marginal fit before and after ceramic firing. Also, a total of 5 ceramo-metal discs were fabricated for testing shear bond strength at the metal-ceramic interface. The samples were subjected to increasing shear load on a Universal Testing Machine with crosshead speed of 0.002mm/sec. The load at which, the samples debonded completely, was noted and the samples put-to fractographic analysis. Results: The mean marginal fit found in this study for sinter cast gold before ceramic firing was measured to be 11.5 μm with a standard deviation of ±4.64 μm and after ceramic firing was found to be 9.38 μm with a standard deviation of ±3.57 μm. The average shear bond strength at the sinter cast gold ceramic interface was 18.216 MPa. The fractographic analysis showed the globular microstructure of sinter cast gold on sintering, adhesive, and mix-mode type of fracture with the presence of both gold and ceramic. Conclusion: The marginal fit observed before and after ceramic firing was within clinically acceptable range while the ceramo-metal shear bond strength between sinter cast gold and ceramic was found to be inadequate.

Effect of two different finishing systems on surface roughness of feldspathic and fluorapatite porcelains in ceramo-metal restorations: Comparative in vitro study.

Objective:The objective of present study was to qualitatively and quantitatively evaluate and compare the effect of two ceramic finishing systems and diamond polishing paste on surface texture of two ceramic materials.Methodology:The 40 test specimens were randomly divided into two main groups (Group I and Group II). Which were subsequently veneered with feldspathic porcelain and fluorapatite leucite porcelain systems respectively. The samples in Test group I and Test group II were subjected to different abrasion and finishing systems (Soft Lex and White silicon and grey rubber respectively). The surface roughness of all the four groups was assessed qualitatively using the scanning Electron Microscope and profilometer.Results:The surface roughness of Feldspathic and fluorapetite porcelain increased after abrasion and finishing as compared to auto-glazed porcelin. The surface roughness was more in grey rubber disc group (Gp Ib) as compared to the soft lex disc groups. After polishing with the diamond paste, there was reduction in the surface roughness of both the disc groups. The Mean Ra values of the Feldspathic porcelain at three intervals were 0.52 ± 0.06, 0.54 ± 0.06, 0.32 ± 0.06 and 0.50 ± 0.04, 1.25 ± 0.10, 0.45 ± 0.6 respectively for grey rubber disc and soft lex groups. The Mean Ra values of Fluorapetite porcelain at three intervals were 0.40 ± 0.06, 0.52 ± 0.06, 0.30 ± 0.03 and 0.41 ± 0.04, 1.17 ± 0.09, 0.39 ± 0.07 respectively for grey rubber disc and soft lex groups.Discussion and Conclusion:The surface roughness was less in the polished samples as compared to the auto-glazed porcelain. The findings were more reinforcing in the soft lex group as compared to the white/grey rubber disc group. Between the two porcelain systems, the Fluorapatite leucite porcelain specimens exhibited better surface smoothness than feldspathic porcelain.

Zirconia in fixed prosthesis. A literature review

Statement of problem: Evidence is limited on the efficacy of zirconia-based fixed dental prostheses. Objective: To carry out a literature review of the behavior of zirconium oxide dental restorations. Material and Methods: This literature review searched the Pubmed, Scopus, Medline and Cochrane Library databases using key search words “zirconium oxide,” “zirconia,” “non-metal restorations,” “ceramic oxides,” “veneering ceramic,” “zirconia-based fixed dental prostheses”. Both in vivo and in vitro studies into zirconia-based prosthodontic restoration behavior were included. Results: Clinical studies have revealed a high rate of fracture for porcelain-veneered zirconia-based restorations that varies between 6% and 15% over a 3- to 5-year period, while for ceramo-metallic restorations the fracture rate ranges between 4 and 10% over ten years. These results provoke uncertainty as to the long-term prognosis for this material in the oral medium. The cause of veneering porcelain fractures is unknown but hypothetically they could be associated with bond failure between the veneer material and the zirconia sub-structure. Key words:Veneering ceramic, zirconia-based ceramic restoration, crown, zirconia, tooth-supported fixed prosthesis.

Full-Mouth Rehabilitation for a Patient With Dentinogenesis Imperfecta: A Clinical Report

Dentinogenesis imperfecta (DI) is a genetic disorder affecting the structural integrity of the dentin that can result in weakened dentin. The affected teeth, especially posterior teeth, often need to be extracted due to severe wear or fracture. This frequently yields a loss of posterior occlusion and occlusal vertical dimension. Besides wear and fracture, anterior teeth often have an unesthetic appearance because of discoloration. Current treatments of choice, including composite bonding restorations and, more recently, all-ceramic restorations, are typically suggested to preserve the remaining teeth and tooth structure. However, there are a limited number of studies on dental implants in patients with DI. The effectiveness of dentin bonding and dental implants in patients with DI is not known. This clinical report describes a 32-year-old Asian woman with DI who underwent full-mouth rehabilitation. The posterior occlusion, mostly in the molar areas, was restored with dental implants and ceramometal restorations. The anterior teeth and premolars were restored with bonded lithium disilicate glass-ceramic pressed veneers and crowns made with computer-aided design/computer-aided manufacturing. This case demonstrates that restoring functional occlusion and esthetics for a patient with DI can be completed successfully using contemporary implant therapy and adhesive dentistry.

Shear bond strength of two forms of opaque porcelain to the metal substructure

ObjectiveThis study was designed to compared the shear bond strength of two forms of opaque porcelain (paste and conventional powder/liquid) to metal substructure. Furthermore, the Scanning Electron Microscope (SEM) was used to determine the mode of failure. Materials and methodsSixty metal specimens were casted into Talladium alloy (Talladium Inc., Los Angeles, Calif.) and prepared to receive one of three commonly used porcelain systems in market; Vita VMK 95 (VITA Zahnfabrik H. Rauter GmbH & Co. KG), Ceramco 3 (Dentsply Ceramco, Burlington, NJ) and GC Initial MC (GC America Inc., Alsip, IL). Each material was tested in two forms; conventional powder/liquid form and paste form. Six different groups were established; the conventional porcelain groups were used as reference for comparison (n=10). After 48-h storage in water at 37°C, specimens were separated using Instron machine and the maximum force needed for separation was recorded and failure stress was calculated. Scanning Electron Micrographs (SEMs) were used to determine the mode of failure at ×1500. Statistical analysis was conducted. ResultsA significant effect of shear bond strength was found across materials, forms and interaction (P<.05). Vita VMK 95 had the highest shear bond strength (14.11MPa±0.775) in the powder/liquid form, while Ceramco 3 showed the highest strength in the paste form (21.03MPa±0.5). GC Initial MC showed the lowest strength in the conventional (8.24MPa±0.097) and paste form (14.16MPa±0.28). Paste opaque porcelain produced significantly higher shear bond strength than the conventional powder/liquid form with all combinations tested. ConclusionIt was concluded from this study that paste opaque porcelain can be used with confidence during fabrication of ceramometal restorations.

The 7/8 Crown: A Lost Art

Historically, the longevity of teeth restored with gold inlays, onlays, crowns, and partial veneer restorations is excellent. However, in-office computer-aided design and computer-aided manufacturing restorations, laboratory-constructed all-ceramic bonded restorations, and conventional ceramo-metal restorations are more common. The high price of gold, the difficulty of the preparation, and the fact that most dental schools are de-emphasizing the teaching of partial veneer restorations has created a situation whereby the 7/8 crown is rarely viewed as the treatment of choice. Time and experience will determine if the new ceramic materials, along with the all-important bonding agents, can achieve the success of a well-done, all-gold restoration.

The effect of surface treatments on the microroughness of laser‐sintered and vacuum‐cast base metal alloys for dental prosthetic frameworks

This study aimed to evaluate the effect of four chemomechanical surface treatments on the surface average microroughness and profile of laser-sintered and vacuum-cast dental prosthetic structures. Square-shaped blocks (10 mm × 10 mm × 1.5 mm) were prepared as follows: (1) laser-sintered CoCr (L) (ST2724G); (2) cast Co-Cr (C) (Gemium-cn); and (3) cast Ni-Cr-Ti (T) (Tilite). Specimens of each alloy group were randomly divided into five subgroups (n = 10 each), depending on the conditioning method used: (1) no treatment (control); (2) sandblasting (125 μm Al₂O₃-particles); (3) silica coating (50 μm silica-modified Al₂O₃-particles); (4) oxidation; and (5) oxidation plus opacification. Subgroups 2 and 3 represent "inner" pretreatments proposed for ceramometal restorations to improve the metal surface area available for luting cements. Subgroups 4 and 5 are the "outer" pretreatments required for bonding the aesthetic veneering ceramics to the underlying metal frameworks. Average surface roughness (Ra/μm) was determined using a surface profilometer. Data were analyzed by two-way ANOVA and Student-Newman-Keuls tests (α = 0.05). Metal surface topography was SEM-analyzed. Despite the inner pretreatment applied, L samples resulted in the highest microroughness (P < 0.001), whereas sandblasting produced a surface-smoothing effect in cast specimens. After oxidation, a significant increase in surface roughness occurred in all groups compared with controls, L specimens being the roughest (P < 0.001). Opacification caused a flattening effect of all oxidized structures; all opacified groups resulting in similar microroughness. Laser sintering of Co-Cr enhances the roughness of metal structures, which may improve the frameworks' microretention of the cements, and of the opaquer before the copings are veneered with the aesthetic ceramics.

Effect of firing cycle and surface finishing on the sag resistance of long-span metal ceramic framework using base metal alloys—an in vitro study

BackgroundThe search for the ideal restorative material or combination of materials in dentistry is still the subject of modern dental research. In clinical practice, there are increased numbers of ceramo-metal restorations being fabricated which replace multiple missing teeth in a single framework. The literature is scanty with regard to investigations of the ‘sag’ resistance of base metal alloys commonly used for ceramo-metal restorations and specifically for long-span restorations.An in vitro study was carried out to investigate the effects of surface finishing and simulated porcelain-firing on the sag resistance of long-span ceramo-metal frameworks using base metal alloys. MethodFour types of alloys were used. A total of 80 samples were selected for the study and they were divided into four groups of 20 samples each. ‘As cast’ metal specimens in group I, group II and with surface finishing in group III and group IV. Each test sample was mounted on the sample holding accessory of the custom made thermo mechanical analyser and subjected to three firing cycles. Each sample was evaluated for the sag-related deflection recorded by the dial gauge with an accuracy of 1 µm. The data recorded was subjected to a statistical analysis using unpaired t-test to compare the relative difference in the sag-related deflection values. ResultsIt was observed that the values for sag-related deflection were significantly less for the ‘as cast’ samples of all the alloy groups. Nickelchromium (NiCr) and cobaltchromium (CoCr) exhibited value of 19.4 μm and 14.8 μm, respectively. ConclusionAmong the four groups of alloys tested, CoCr based alloy exhibited the least amount of sag-related deflection. The results show that the sag-related deflection was less in Co-Cr alloys as compared with the NiCr alloys, still Ni-Cr alloys in fixed dental prostheses frameworks are used due to their desirable physical and chemical properties.

Effect of Margin Design and Processing Steps on Marginal Adaptation of Captek Restorations

This study examined the effect of four margin designs on marginal adaptation of Captek crowns during selected processing steps. Twenty-four Captek crowns were fabricated, six each of four margin designs: shoulder (Group A), chamfer (Group B), chamfer with bevel (Group C), and shoulder with bevel (Group D). Marginal discrepancies between crowns and matching dies were measured at selected points for each sample at the coping stage (Stage 1), following porcelain application (Stage 2) and cementation (Stage 3). Digital imaging methods were used to measure marginal gap. The results indicate decreasing trend of margin gap as a function of margin design in the order A>B>C>D. Between processing steps, the trend was in the order Stage 3 < Stage 1 < Stage 2. Porcelain firing had no significant effect on marginal adaptation, but cementation decreased the marginal gap. Generally, the margin gap in Captek restorations were in all cases less than the reported acceptable range of margin gaps for ceramometal restorations. These results are clinically favorable outcomes and may be associated with the ductility and burnishability of matrix phase in Captek metal coping margins.

Sinus Grafting With a Natural Flourohydroxyapatite for Immediate Load: A Study With Histologic Analysis and Histomorphometry

The goal of this retrospective study was to evaluate the survival rates of dental implants placed in sinuses grafted with a 50:50 composite ratio of autogenous bone and a natural flourohydroxyapatite (FHA) combined with platelet-rich plasma (PRP) using an immediate-load protocol. The authors hypothesized that a 50:50 composite ratio of FHA and autogenous bone combined with PRP would permit immediate loading without compromising implant survival rates. Eleven patients with bilateral partial edentulism of the posterior maxilla were enrolled in this retrospective study. Autogenous bone used in the graft procedure was harvested from the tibia of the left lower extremity. Each patient was grafted with a 50:50 composite ratio of autogenous bone and FHA. Membranes were not used to cover the lateral wall osteotomy site. Platelet-rich plasma was added to the graft material to accelerate and enhance bone regeneration. Four to 6 months after the grafting procedure, 37 hydroxyapatite-coated dental implants were surgically placed and immediately loaded between 72 hours and 5 days later with custom titanium abutments and acrylic provisional restorations placed out of functional occlusion. Six months later, definitive ceramometal restorations were cemented on to the custom abutments. Patients were observed over a 52-week period. The overall implant survival rate was 97.3%. Histologic and histomorphometric analysis of core samples revealed formation of new vital bone in different graft specimens ranging from 23% to 34%. In each core bone sample, 100% of the bone sample was determined to be vital. In the grafted maxillary sinus, the natural FHA combined with autogenous bone in a 50:50 composite ratio with PRP is a suitable graft material permitting immediate load without compromising implant survival rates while decreasing the overall healing time.

Elastic-plastic finite elements analysis of transient and residual stresses in ceramo-metal restorations

Transient and residual stresses occurring in partially fixed dental prostheses after the firing process can be calculated with elastic or elastic-plastic finite element analyses (FEA). In this study, firstly, the mechanical and thermal properties at various temperatures of the materials used in a porcelain fused metal (PFM) system were obtained by experimental and literature studies. The effects of viscoelastic and viscoplastic behaviours of the dental porcelain at the elevated temperatures were reflected onto its elastic properties. The equivalent heat transfer coefficients were determined experimentally by measuring temperatures and the results were supplied as input to the 3D finite elements analysis. It has been observed that the maximum stresses occur within a short time period after cooling begins and that stresses decrease during the cooling process and remain at a constant value at the end of cooling; these are the thermal residual stresses.

M633: Systematic Pretreatment Evaluation and Treatment of the Edentulous Maxilla With Fixed Prosthesis

Many potential candidates for implant restoration of the fully edentulous maxilla are primarily interested in receiving a fixed prosthesis as opposed to a bar/clip overdenture. In a general sense, three alternative fixed prosthetic designs have been developed. The ability to determine early in the consultation process which of the three will lead to the best functional and esthetic results is advantageous. This presentation examines two critical factors (the nature of the patient's dental defect and whether the residual ridge is visible in the non-retracted state) that can be used to direct the choice of a ceramo-metal restoration, a hybrid prosthesis, or a Marius bridge. Evaluation of a third factor (the status of the bone in three separate radiographic zones) can also help determine whether bone grafting procedures will be necessary to achieve the desired outcome.