Crown therapy in young individuals with amelogenesis imperfecta: Long term follow-up of a randomized controlled trial.

OBJECTIVES: Amelogenesis imperfecta (AI) is a rare, genetically determined defect in enamel mineralization. Several problems are associated with AI: hypersensitivity, wear, restorations requiring replacement, gingivitis, aesthetic problems, and social avoidance. We conducted a randomized controlled trial of crown therapy in young individuals with AI showing excellent results. This study reports results from a long-term-follow-up with focus on quality, longevity and adverse events. METHODS: The RCT included 27 patients (aged 11-22 years) with severe AI in need of crown therapy and used a split-mouth technique. After placing 119 Procera® crowns and 108 IPS e.max Press crowns following randomization, we assessed longevity, quality, adverse events, and tooth sensitivity and calculated survival rates and success rates. RESULTS: We followed the original 227 crowns for 4.3-7.4 years (mean 5.5 ±â€¯0.8). In all, 79% (193) crowns were followed for at least 5 years. The survival rate was 99.6% and the success rate, 94.7%; 95% of the crowns had excellent or acceptable quality. Due to suboptimal marginal integrity, 4% of the crowns required adjustment. Sensitivity problems decreased after crown therapy (p < 0.001). All adverse events occurred in patients aged 19-23 years and involved apical periodontitis (3% of teeth); all but two events were related to dental trauma in the actual tooth. CONCLUSIONS: Ceramic crown therapy in adolescents and young adults with severe forms of AI show excellent survival and success rates and longevity with few adverse events. CLINICAL SIGNIFICANCE: Ceramic crown therapy can be recommended for adolescents and young adults with severe forms of amelogenesis imperfecta.

Comparative Evaluation of Flexural Strength of Nano-zirconia-integrated Pressable Feldspathic and Lithium Disilicate Ceramics.

AIM: The purpose of the study was to evaluate and compare the flexural strength of nano-reinforced zirconia feldspathic porcelain, lithium disilicate ceramics, and zirconia. MATERIALS AND METHODS: Ten bar-shaped specimens of computer-aided design (CAD)/computer-aided manufacturing (CAM) zirconia, reinforced feldspathic porcelain, and reinforced lithium disilicate were fabricated in accordance to International Organization for Standardization (ISO 6872; n = 10). Feldspathic porcelain and lithium disilicate ceramic specimens were reinforced with 5, 10, 15, and 20% of zirconia nanoparticles through a customized technique. The specimens were subjected to three-point flexural strength test using universal testing machine (UTM) and examined for crack propagation using a scanning electron microscope (SEM). Oneway analysis of variance (ANOVA) and Tukey test were used to analyze the data (p < 0.05). RESULTS: The flexural strength of feldsphatic porcelain increased with the increase in the concentration of zirconia particles. The mean flexural strength of 5, 10, 15, and 20% nano-zirconia-incorporated lithium disilicate was 93.8, 97.1, 100.6, and 100.8 MPa respectively, and was lower than the control group (221.7 MPa). A significant difference in the flexural strength was found with the incorporation of nano-zirconia particles. CONCLUSION: The flexural strength of zirconia-integrated feld-spathic porcelain increased and lithium disilicate ceramics decreased with the nano-zirconia reinforcement. CLINICAL SIGNIFICANCE: The simplified approach of reinforcing feldspathic porcelain with zirconia nanoparticles can be adapted in clinical situations of higher masticatory forces.

Evaluation of five CAD/CAM materials by microstructural characterization and mechanical tests: a comparative in vitro study.

BACKGROUND: Polymer infiltrated ceramics and nano-ceramic resins are the new restorative materials which have been developed in order to enhance the adverse properties of glass-matrix ceramics and resin composites. The aim of the present in vitro study was to evaluate the characteristics of various CAD/CAM materials through mechanical, microstructural, and SEM analysis. METHODS: Five test groups (n = 22) were formed by using the indicated CAD/CAM blocks: VITA Enamic (VITA Zahnfabrik), Lava Ultimate (3 M ESPE), IPS e.max CAD (Ivoclar Vivadent), IPS Empress CAD (Ivoclar Vivadent), and VITA Mark II (VITA Zahnfabrik). Two specimens from each test group were used for XRD and EDS analysis. Remaining samples were divided into two subgroups (n = 10). One subgroup specimens were thermocycled (5 °C to 55 °C, 30s, 10,000 cycles) whereas the other were not. All of the specimens were evaluated in terms of flexural strength, Vickers hardness, and fracture toughness. Results were statistically analyzed using two-way ANOVA, one-way ANOVA, Tukey's HSD, and Student's t tests (α = .05). Fractured specimens were evaluated using SEM. RESULTS: The highest Vickers microhardness value was found for VITA Mark II (p < .001), however flexural strength and fracture toughness results were lowest conversely (p < .05). IPS e.max CAD was found to have the highest flexural strength (p < .001). Fracture toughness of IPS e.max CAD was also higher than other tested block materials (p < .001). Lava Ultimate and VITA Enamic's mechanical properties were affected negatively from thermocycling (p < .05). Microhardness, flexural strength, and fracture toughness values of Lava Ultimate and VITA Enamic were found to be similar to VITA Mark II and IPS Empress CAD groups. CONCLUSIONS: It should be realised that simulated aging process seem to affect ceramic-polymer composite materials more significantly than glass ceramics.

Fracture toughness of two lithium disilicate dental glass ceramics.

STATEMENT OF PROBLEM: IPS e.max CAD and IPS e.max Press (Ivoclar Vivadent AG) are lithium disilicate glass ceramics marketed as interchangeable materials indicated for the same clinical uses. However, different crystal sizes of lithium disilicate are formed during the processing of each of these materials, a factor that could lead to significantly different mechanical properties. As mechanical failure is always associated with a crack-initiation/crack-propagation process, fracture toughness (KIC) values could be useful in comparing different ceramics and possibly predicting clinical performance. PURPOSE: The purpose of this in vitro study was to determine and compare the KIC of IPS e.max CAD and IPS e.max Press. MATERIAL AND METHODS: The notchless triangular prism (NTP) specimen KIC test was used to determine and compare the KIC of IPS e.max Press and IPS e.max CAD. Twenty 6×6×6×12-mm NTP specimens of each material were prepared. IPS e.max CAD blocks were cut, ground, and then crystallized, while IPS e.max Press specimens were prepared by pressing IPS e.max Press ingots into molds obtained from 6×6×6×12-mm wax prisms, using the lost wax technique. Each specimen was mounted into a specimen holder, and custom grips were used to attach the specimen holder assembly to a computerized universal testing machine (model 4301; Instron Canada, Inc). The assembly was loaded in tension at a crosshead speed of 0.1 mm/min, and the KIC value was calculated based on the recorded maximum load at fracture. Fractured surfaces were characterized using scanning electron microscopy (SEM). Results were statistically analyzed using Weibull statistics and the Student t test (α=.05). RESULTS: Significantly (P<.05) higher KIC value was determined for IPS e.max Press than for IPS e.max CAD and, based on the Weibull modulus (m), IPS e.max Press was also more reliable. Fractured surfaces, characterized by SEM, showed a marked difference between the 2 materials, suggesting a more complete crystallization in IPS e.max Press, which was most likely responsible for the higher KIC determined. CONCLUSION: Within the limitations of this in vitro study, the results suggest that IPS e.max Press is superior to IPS e.max CAD with regard to the KIC and characteristic Weibull parameters.

Microwave processing of a dental ceramic used in computer-aided design/computer-aided manufacturing.

Because of their favorable mechanical properties and natural esthetics, ceramics are widely used in restorative dentistry. The conventional ceramic sintering process required for their use is usually slow, however, and the equipment has an elevated energy consumption. Sintering processes that use microwaves have several advantages compared to regular sintering: shorter processing times, lower energy consumption, and the capacity for volumetric heating. The objective of this study was to test the mechanical properties of a dental ceramic used in computer-aided design/computer-aided manufacturing (CAD/CAM) after the specimens were processed with microwave hybrid sintering. Density, hardness, and bending strength were measured. When ceramic specimens were sintered with microwaves, the processing times were reduced and protocols were simplified. Hardness was improved almost 20% compared to regular sintering, and flexural strength measurements suggested that specimens were approximately 50% stronger than specimens sintered in a conventional system. Microwave hybrid sintering may preserve or improve the mechanical properties of dental ceramics designed for CAD/CAM processing systems, reducing processing and waiting times.

In vitro evaluation of accuracy and precision of automated robotic tooth preparation system for porcelain laminate veneers.

STATEMENT OF PROBLEM: Controlling tooth reduction for porcelain laminate veneers (PLVs) in fractions of millimeters is challenging. PURPOSE: The purpose of this study was to assess an automated robotic tooth preparation system for PLVs for accuracy and precision compared with conventional freehand tooth preparation. MATERIAL AND METHODS: Twenty maxillary central incisor tooth models were divided into 2 groups. Ten were assigned to a veneer preparation with a robotic arm according to preoperative preparation design-specific guidelines (experimental group). Ten were assigned to conventional tooth preparation by a clinician (control group). Initially, all tooth models were scanned with a 3- dimensional (3D) laser scanner, and a tooth preparation for PLVs was designed on a 3D image. Each tooth model was attached to a typodont. For the experimental group, an electric high-speed handpiece with a 0.9-mm-diameter round diamond rotary cutting instrument was mounted on the robotic arm. The teeth were prepared automatically according to the designed image. For the control group, several diamond rotary cutting instruments were used to prepare the tooth models according to preoperative preparation design guidelines. All prepared tooth models were scanned. The preoperative preparation design image and scanned postoperative preparation images were superimposed. The dimensional difference between those 2 images was measured on the facial aspect, finish line, and incisal edge. Differences between the experimental and the control groups from the 3D design image were computed. Accuracy and precision were compared for all sites and separately for each tooth surface (facial, finish line, incisal). Statistical analyses were conducted with a permutation test for accuracy and with a modified robust Brown-Forsythe Levene-type test for precision (α=.05). RESULTS: For accuracy for all sites, the mean absolute deviation was 0.112 mm in the control group and 0.133 mm in the experimental group. No significant difference was found between the 2 (P=.15). For precision of all sites, the standard deviation was 0.141 mm in the control group and 0.185 mm in the experimental group. The standard deviation in the control group was significantly lower (P=.030). In terms of accuracy for the finish line, the control group was significantly less accurate (P=.038). For precision, the standard deviation in the control group was significantly higher at the finish line (P=.034). CONCLUSIONS: For the data from all sites, the experimental procedure was able to prepare the tooth model as accurately as the control, and the control procedure was able to prepare the tooth model with better precision. The experimental group showed better accuracy and precision at the finish line.

Influence of recasting on the quality of dental alloys: A systematic review.

STATEMENT OF PROBLEM: Dental alloy manufacturers advise against the reuse of previously melted alloy. However, for economic reasons, dental laboratories often reuse the casting surplus (sprue and metal remaining in the crucible former). Such reuse remains a controversial topic in dental practice. PURPOSE: The purpose of this systematic review was to assess the effects of remelting dental alloys by evaluating the following parameters: reasons for recasting and associated processes, feasible number of recastings, treatment of alloys before recasting and its effects on cytotoxicity, color of opaque porcelain, castability of alloys, marginal accuracy, mechanical properties, porcelain-metal interfaces, and corrosion. MATERIAL AND METHODS: The systematic review included all studies on dental alloy recasting. MEDLINE, Dentistry and Oral Science Source, Science Direct, and ISI Web of Science were searched (up to July 2014). Data were extracted and the quality of studies was assessed. RESULTS: Thirty-four studies published between 1983 and 2014 were included. The number of recastings ranged from 1 to 10. The percentage of new alloy ranged from 0 to 100 wt%, although the mean value was 50 wt%. CONCLUSIONS: Evidence for the feasibility of adding 50% new metal at each recasting is limited. The number of recastings should be limited to a maximum of 4. No general test protocol can be deduced from these studies, which limits the comparison and exploitation of data. Furthermore, no consensus protocol exists for the evaluation of recasting. Future studies should work toward establishing a standard protocol.

Shear bond strength of porcelain veneers rebonded to enamel.

In this laboratory research, shear bond strength (SBS) and mode of failure of veneers rebonded to enamel in shear compression were determined. Three groups (A, B, and C; n=10 each) of mounted molar teeth were finished flat using wet 600-grit silicon carbide paper, and 30 leucite-reinforced porcelain veneers (5.0 × 0.75 mm) were air abraded on the internal surface with 50 µm aluminum oxide, etched with 9.5% hydrofluoric acid, and silanated. The control group (A) veneer specimens were bonded to enamel after etching with 37% phosphoric acid using bonding resin and a dual cure resin composite cement. Groups B and C were prepared similarly to group A with the exception that a release agent was placed before the veneer was positioned on the prepared enamel surface and the resin cement was subsequently light activated. The debonded veneers from groups B and C were placed in a casting burnout oven and heated to 454°C/850°F for 10 minutes to completely carbonize the resin cement and stay below the glass transition temperature (Tg) of the leucite-reinforced porcelain. The recovered veneers were then prepared for bonding. The previously bonded enamel surfaces in group B were air abraded using 50 µm aluminum oxide followed by 37% phosphoric acid etching, while group C enamel specimens were acid etched only. All specimens were thermocycled between 5°C and 55°C for 2000 cycles using a 30-second dwell time and stored in 37°C deionized water for 2 weeks. SBS was determined at a crosshead speed of 1.0 mm/min. SBS results in MPa for the groups were (A) = 20.6±5.1, (B) = 18.1±5.5, and (C) = 17.2±6.1. One-way analysis of variance indicated that there were no significant interactions (α=0.05), and Tukey-Kramer post hoc comparisons (α=0.05) detected no significant pairwise differences. An adhesive mode of failure at the enamel interface was observed to occur more often in the experimental groups (B = 40%, C = 50%). Rebonding the veneers produced SBS values that were not significantly different from the control group. Also, no significant difference in SBS values were observed whether the debonded enamel surface was air abraded and acid etched or acid etched only.

CO2 Laser Glazing Treatment of a Veneering Porcelain: Effects on Porosity, Translucency, and Mechanical Properties.

This work tested CO2 laser as a glazing agent and investigated the effects of irradiation on the porosity, translucency, and mechanical properties of veneering porcelain. Sixty discs (diameter 3.5 × 2.0 mm) of veneering porcelain for Y-TZP frameworks (VM9, VITA Zahnfabrik) were sintered and had one of their faces mirror polished. The specimens were divided into six groups (n=10/group) according to surface treatment, as follows: no treatment-control; auto-glaze in furnace following manufacturer's instructions (G); and CO2 laser (45 or 50 W/cm(2)) applied for four or five minutes (L45/4, L45/5, L50/4, L50/5). Optical microscopy (Shimadzu, 100×) was conducted and the images were analyzed with Image J software for the determination of the following porosity parameters: area fraction, average size, and Feret diameter. The translucency parameter studied was masking ability, determined by color difference (ΔE) over black and white backgrounds (CM3370d, Konica Minolta). Microhardness and fracture toughness (indentation fracture) were measured with a Vickers indenter (HMV, Shimadzu). Contact atomic force microscopy (AFM) (50 × 50 µm(2), Nanoscope IIIA, Veeco) was performed at the center of one sample from each group, except in the case of L45/5. With regard to porosity and translucency parameters, auto-glazed and laser-irradiated specimens presented statistical similarity. The area fraction of the surface pores ranged between 2.4% and 5.4% for irradiated specimens. Group L50/5 presented higher microhardness when compared to the G group. The higher (1.1) and lower (0.8) values for fracture toughness (MPa.m(1/2)) were found in laser-irradiated groups (L50/4 and L45/4, respectively). AFM performed after laser treatment revealed changes in porcelain surface profile at a submicrometric scale, with the presence of elongated peaks and deep valleys.

Effects of repeated processing on the strength and microstructure of a heat-pressed dental ceramic.

STATEMENT OF PROBLEM: The excess material produced after heat pressing a lithium disilicate glass ceramic restoration can be either discarded or reused. The reuse of this material requires that any degradation of the material quality be investigated. PURPOSE: The purpose of this study was to investigate the number of times that leftover lithium disilicate material can be re-pressed and to determine the effect that repeated use has on material properties. MATERIAL AND METHODS: A large (6.1 g) lithium disilicate ingot (A3.5) was heat pressed to yield a ceramic disk (15 × 1.5 mm) for testing. The leftover material was reused to produce a further 3 disks, with the number of pressings increasing for each specimen. An additional unpressed group was included to investigate the properties before pressing so that, in total, 5 groups were established. Specimens were tested for biaxial flexural strength, Vickers hardness, and fracture toughness. X-ray diffraction was used to characterize the crystalline phase, scanning electron microscopy for the microstructure, and differential scanning calorimetry for the thermal properties. RESULTS: No significant difference was found in the biaxial flexural strength of the groups. The hardness of the material decreased, and no significant difference was seen in fracture toughness with repeated pressings. An increase in grain size was observed with increased pressings. By using x-ray diffraction analysis, lithium disilicate was identified as the main crystal phase, and no difference in crystalline composition was found with repeated processing. CONCLUSION: This material can be reused while maintaining good mechanical properties and without significantly altering the chemical or crystalline composition in an adverse manner.

Effects of different surface treatments on bond strength between resin cements and zirconia ceramics.

This study compares the bond strength of resin cement and yttrium-stabilized tetragonal zirconia polycrystalline (Y-TZP) ceramic with different surface conditioning methods. Two hundred presintered Y-TZP ceramic specimens were prepared, sintered (4 × 4 × 4 mm), and randomly assigned to four equal groups as control (C, no conditioning); airborne particle abraded (APA, air abrasion with 11 µm Al2O3); tribochemical silica coating/silane coupling system (TSC, Rocatec, air abrasion with 110 µm Al2O3, 30 µm silica-coated Al2O3 and silane); and laser (L, Er:YAG laser irradiation treated at a power setting of 200 mJ). After specimen preparation, composite resin cylinders were prepared and cemented with resin cements (Clearfil Esthetic, Panavia F 2.0, Rely X-U100, Super Bond C&B, and Multilink Automix) on the ceramic surfaces and kept in an incubator at 37°C for 60 days. All specimens were tested for shear bond strength with a universal testing machine, and fractured surfaces were evaluated by environmental scanning electron microscopy. Statistical analysis was performed using Kruskal-Wallis and Mann-Whitney U-tests (α=0.05). The bond strengths for C and L groups were not significantly different according to adhesive resin cement. APA and TSC resulted in increased bond strength for Panavia F 2.0 and Rely X-U100 resin cements. Additionally, TSC presented higher bond strength with Multilink Automix. Adhesive fracture between the ceramic and resin cement was the most common failure. Complete cohesive fracture at the ceramic or composite cylinders was not observed. Regardless of the adhesive resin cement used, laser treatment did not improve resin bond strength.

Laboratory and clinical considerations on prosthetic zirconia infrastructures for implants.

Zirconia is a ceramic material that is used for constructing prosthetic infrastructures and implant abutments using CAD/CAM techniques. Although good initial mechanical properties are obtained with zirconia that is partially stabilized by yttrium, it may age in a moist environment, compromising such properties and, consequently, the longevity of the restorative work. To optimize the longevity of this material, it is essential that the clinician and laboratory technician understand its mechanical properties and limitations and take specific precautions needed to maintain its mechanical properties and ensure long-term performance especially in implant prosthetics. This article presents a clinical case where these precautions were taken, emphasizing the key surface treatments advocated for zirconia.

Clinical performance of porcelain laminate veneers: outcomes of the aesthetic pre-evaluative temporary (APT) technique.

This article evaluates the long-term clinical performance of porcelain laminate veneers bonded to teeth prepared with the use of an additive mock-up and aesthetic pre-evaluative temporary (APT) technique over a 12-year period. Sixty-six patients were restored with 580 porcelain laminate veneers. The technique, used for diagnosis, esthetic design, tooth preparation, and provisional restoration fabrication, was based on the APT protocol. The influence of several factors on the durability of veneers was analyzed according to pre- and postoperative parameters. With utilization of the APT restoration, over 80% of tooth preparations were confined to the dental enamel. Over 12 years, 42 laminate veneers failed, but when the preparations were limited to the enamel, the failure rate resulting from debonding and microleakage decreased to 0%. Porcelain laminate veneers presented a successful clinical performance in terms of marginal adaptation, discoloration, gingival recession, secondary caries, postoperative sensitivity, and satisfaction with restoration shade at the end of 12 years. The APT technique facilitated diagnosis, communication, and preparation, providing predictability for the restorative treatment. Limiting the preparation depth to the enamel surface significantly increases the performance of porcelain laminate veneers.

Clinical performance of porcelain laminate veneers for up to 20 years.

PURPOSE: The aim of this clinical retrospective study was to evaluate the clinical quality, success rate, and estimated survival rate of anterior veneers made of silicate glass-ceramic in a long-term analysis of up to 20 years. MATERIALS AND METHODS: Anterior teeth in the maxillae and mandibles of 84 patients (38 men, 46 women) were restored with 318 porcelain veneer restorations between 1987 and 2009 at the Medical University Innsbruck, Innsbruck, Austria. Clinical examination was performed during patients' regularly scheduled maintenance appointments. Esthetic match, porcelain surface, marginal discoloration, and integrity were evaluated following modified California Dental Association/Ryge criteria. Veneer failures and reasons for failure were recorded. The study population included 42 (50.0%) patients diagnosed with bruxism and 23 (27.38%) smokers. The success rate was determined using Kaplan-Meier survival analysis. RESULTS: The mean observation time was 118 ± 63 months. Twenty-nine failures (absolute: 82.76%, relative: 17.24%) were recorded. The main reason for failure was fracture of the ceramic (44.83%). The estimated survival rate was 94.4% after 5 years, 93.5% at 10 years, and 82.93% at 20 years. Nonvital teeth showed a significantly higher failure risk (P = .0012). There was a 7.7-times greater risk of failure associated with existing parafunction (bruxism, P = .0004). Marginal discoloration was significantly greater in smokers (P ⋜ .01). CONCLUSION: Porcelain laminate veneers offer a predictable and successful restoration with an estimated survival probability of 93.5% over 10 years. Significantly increased failure rates were associated with bruxism and nonvital teeth, and marginal discoloration was worse in patients who smoked.

Clinical evaluation of fixed partial dentures made in Sweden and China.

The aim of this study was to compare the quality of fixed partial dentures (FPDs) made in a Chinese dental laboratory with corresponding FPDs made in Swedish dental laboratories. Twenty-one patients were fitted with FPDs between March 2007 and December 2008. Single crowns and prostheses of up to seven units were made. All dentures, gold and CoCr alloys covered with ceramic, were produced in duplicate: one by a dental technician in China and the other by a dental technician in Sweden. The dentures were blind-tested with regard to marginal integrity, anatomic form and color, approximal and occlusal contacts, and time taken for adjustments. The composition of dentures was analyzed, and the material used, framework weight, compliance of the laboratories, and costs (material and labour) were recorded. There was no difference in the quality of marginal integrity, anatomic form, color, approximal and occlusal contacts, or in the time taken for adjustments. The bridge frameworks made in China were thinner and lighter (p<0.01) than those made in Sweden. Three FPDs from China showed elastic deformation when tested clinically and were considered too thin for clinical use. In 11 out of 14 orders from the Chinese laboratory, the gold alloy specified was not delivered and the cobalt-chromium alloy contained small amounts (0.19%) of nickel.The prostheses with gold-alloy frameworks from China cost 47% of those from Sweden (p<0.01) and those with cobalt/chromium frameworks 44% (p<0.01). In conclusion, the quality of the FPDs made in Sweden and China was comparable, with the exception of the dimension of the Chinese bridges, which in some cases was considered too weak. The gold alloy ordered from the Chinese laboratory was often not the alloy delivered and the CoCr alloy contained small amounts of nickel. FPDs from China cost less than half the price of those from Sweden.

Testing a multistage rating scale for clinical evaluation of all-ceramic surfaces.

PURPOSE: This study tested the applicability of a multistage rating scale based on modified California Dental Association (CDA) criteria and the original criteria of the CDA for surface evaluation of all-ceramic restorations with the use of dental stone replicas, photographs, and scanning electron microscopy (SEM). MATERIALS AND METHODS: Two examiners clinically evaluated 105 all-ceramic restoration units in the posterior region after a mean observation period of 42.2 months; the examiners employed the CDA criteria and a detailed six-stage rating scale. In addition, standardized photographs and gypsum stone and epoxy replicas based on impressions were analyzed blindly using the same rating scales and examiners. SEM images of gold-coated epoxy replicas enabled indirect ceramic surface evaluation, serving as the gold standard to control indirect evaluation and clinical findings. The Cohen kappa was applied to test for concordance; intraclass correlations and Spearman rank correlations were calculated. RESULTS: Statistically significant rating correlations of the clinical situation, photographs, and stone replicas with the SEM photographs were generated from both evaluation systems. With the use of the multistage rating scale, the highest rating correlation was found for stone replica-SEM (r = 0.61, P < .001), and the lowest for clinical photography-SEM (r = 0.5, P < .001). CONCLUSIONS: A multistage rating scale based on modified CDA criteria is reliable for precise assessment of in vivo ceramic surface alterations. Stone replicas were found to be better-suited than photographs for the assessment of all-ceramic surface alterations and confirmation of clinical ratings.

Firing temperature accuracy of four dental furnaces.

In spite of using recommended firing and displayed temperatures, low-fired dental porcelain more often demonstrates unsatisfactory results after firing than porcelain fired at higher temperatures. It could therefore be anticipated that temperatures shown on the display are incorrect, implying that the furnace does not render correct firing programs for low-fired porcelain. The purpose of this study is to investigate deviations from the real temperature during the firing process and also to illustrate the service and maintenance discipline of furnaces at dental laboratories. Totally 20 units of four different types of dental furnaces were selected for testing of temperature accuracy with usage of a digital temperature measurement apparatus, Therma 1. In addition,the staffs at 68 dental laboratories in Sweden were contacted for a telephone interview on furnace brand and on service and maintenance program performed at their laboratories. None of the 20 different dental furnaces in the study could generate the firing temperatures shown on the display, indicating that the hypothesis was correct. Multimat MCII had the least deviation of temperature compared with displayfigures. 62 out of 68 invited dental laboratories chose to participate in the interviews and the result was that very few laboratories had a service and maintenance program living up to quality standards. There is room for improving the precision of dental porcelain furnaces as there are deviations between displayed and read temperatures during the different steps of the firing process.

Five-year clinical evaluation of In-Ceram crowns fabricated using GN-I (CAD/CAM) system.

This study prospectively evaluated the clinical performance of computer-assisted design and computer-assisted manufacturing (CAD/CAM)-generated In-Ceram Alumina core crowns in Japanese patients for up to 5 years. A total of 101 In-Ceram crowns with aluminium copings fabricated using the GN-I system were placed in Japanese patients. The crowns were evaluated using a California Dental Association (CDA) quality assessment system at baseline and at all follow-up examinations. Gingival condition was assessed using plaque and bleeding scores. The survival of anterior and posterior crowns was analysed according to the Kaplan-Meier method. The scores of gingival condition were compared between restored crowns and contralateral teeth using a t-test. During the observation period, six crowns were lost to follow-up. Five crowns were fractured from the copings and removed, and four crowns were removed for other reasons. Chipping within the porcelain was detected in three crowns, which were then polished. The cumulative survival rates after 60 months were 96·9% for anterior crowns and 87·7% for posterior ones, and there were no significant differences between anterior and posterior crowns. According to the CDA criteria, most of the crowns were rated as satisfactory during the observation period. There were significant differences in soft tissue conditions between In-Ceram crowns and control teeth at 2- and 5-year examinations. Despite the five fractures from copings, In-Ceram Alumina crowns with copings fabricated using the CAD/CAM (GN-I system) for replacing both anterior and posterior teeth showed predictable results during a 5-year observation period.

Porcelain veneering of titanium--clinical and technical aspects.

Gold and other alloys have long been used for the production of crowns and bridges as replacements for damaged or lost teeth. However, doubts have arisen on the suitability of using these materials for dental restorations, as gold has also shown a capacity to cause side-effects such as allergic reactions. This is especially valid for alloys, which during the last decades have been used as porcelain-fused-to metal restorations. This fact has led to an interest in using titanium instead of these alloys. Trials to use titanium for this purpose were initiated in Japan in the early 1980s. Titanium as an unalloyed metal differs in two aspects from the above named alloys: it has a phase transformation at 882 degrees C, which changes its outer and inner properties, and it has an expansion that lies between that of the porcelain types available on the market at the time. In Japan a technique for casting titanium was developed, where the after-treatment of the casting was elaborate, to re-establish the original properties of titanium. The porcelain developed for veneering had shortcomings as the rendering produced a rough surface and non satisfactory esthetics. In Sweden a new concept was introduced in 1989. Here the processing of titanium was performed by industrial methods such as milling, spark erosion and laser welding. The idea behind this was to avoid phase transformation. During the 1990s a number of porcelain products were launched and a vast number of both laboratory and clinical studies were performed and published, with varying results. In the first study of this thesis a prospective clinical trial was performed at a public dental health clinic in Sweden. Twenty-five patients were provided with 40 copings of pure titanium, which were veneered with porcelain. After 2 years 36 of these crowns were evaluated and the patients were also interviewed regarding problems such as shooting pains or difficulties in cleaning around the teeth that were crowned. This evaluation showed generally unchanged values for color, form, surface and fit. Regarding surfaces, one porcelain fracture was registered (3%). The patient responses were positive and no case of sensitivity was reported after 2 years, but in 3 cases food impaction was reported. The second study is a systematic review of published articles on bond strength between titanium and porcelain. The review made comparisons of bond strength using three-point bending tests between different porcelain bonds to different alloys and to titanium, between different brands of porcelain and titanium, with porcelain following various types of processing of the titanium surface, with different compositions of the porcelain and with different firing conditions. Generally it could be seen that with this type of test (three-point bending) the bond strength between porcelain and titanium was lower than with alloys. It was also seen that there are differences in bond strengths between different brands of porcelain, that processing the titanium surface and composition of the porcelain affected bond strength, and that firing conditions were also important. The third study was performed with the intention of examining the firing accuracy of different types of dental furnaces and to investigate how maintenance and quality control is performed at Swedish dental laboratories. Since titanium porcelain is fired at a temperature which is 200 degrees C below that used for most conventional alloys, there are specific demands on the furnaces used. The optimum firing temperature is judged to be 750 degrees C for porcelain veneering of titanium, according to published studies. In this study the real firing temperature at the holding period of 1 minute was recorded by a thermo-element connected to a digital temperature measurement apparatus. The accuracy of tested furnaces demonstrated a wide variation, and in almost all cases the real temperature was higher than the temperature indicated by the furnace display; in some cases this was very much higher than the temperature displayed. This means a risk for an unwanted augmentation of the oxide layer on the titanium, which could fracture on loading. Regarding maintenance and quality control, interviews performed at 62 laboratories revealed that most of these did not attain the standards expected and claimed. The fourth study was performed with the intention of studying how the bond strength between titanium and porcelain is affected by a temperature increase of 30 degrees C, performed with two firing concepts for titanium porcelain and examined by three-point bending tests. The fractured surfaces were also analyzed with SEM and EDX. These two concepts for titanium porcelain differ in that one has an oxide firing of the titanium metal as the first firing step, while the other is fired with a bonding agent as the first step in the firing procedure. Furthermore, half of the test bodies were aged by thermo-cycling. This study has shown that a moderate elevation in the firing temperature does not affect the bond strength in this case. Comparing bond strengths between the two different firing concepts, three-point bending tests showed that the test bodies that had undergone an oxidation firing had significantly higher bond strengths in all but one situation. These results were contradicted by the SEM and EDX analysis. These showed that with oxidation firing the fractures occurred in the brittle (and probably thickened) oxide layer of the titanium, while the fractures occurred in the well integrated interface with titanium oxide and porcelain components when firing without oxidation. The reasons for these contradictory results might be that oxidation firing changed the ductility of the titanium, creating a higher stiffness which could better withstand the deflection of the specimens created during the three-point bending tests. For the same reason it might also be irrelevant to test bond strength between porcelain and metals with differing properties. Considering these results and the results from other studies, the validity of the current test standard for metal-ceramic bond strengths may be questioned.