The randomized shortened dental arch study: influence of two different treatments on interdental spacing over 5 years.

OBJECTIVES: Being a secondary outcome in a multicenter randomized controlled trial, the present analysis focused on interdental spacing in the shortened dental arch (SDA). The aim was to evaluate changes in interdental spacing in dependence of two different treatments after an observation period of up to 5 years. MATERIAL AND METHODS: Patients were either treated with a partial removable dental prosthesis (PRDP) for molar replacement (PRDP group) or according to the SDA concept aiming at a premolar occlusion (SDA group) in a randomized manner. Interdental spacing in the anterior region was measured with gauges and categorized as "0" (<0.1 mm), "1" (<0.5 mm), "2" (0.5-1 mm), and "3" (>1 mm). The statistical analysis was performed with analysis of variance models followed by linear contrast. RESULTS: Ninety-one patients (SDA n = 41, PRDP n = 50) were included. Changes of interdental spacing were detected in 70.7 % of all cases. A significant difference between the mean score changes was found in the mandible comparing the PRDP group and the SDA group. The respective mean score changes from baseline to 5 years were 0.23 (SD 0.49) for the PRDP group and 0.02 (SD 0.30) for the SDA group (p = 0.023). CONCLUSIONS: Major interdental spacing could be observed in neither of the groups. The SDA concept resulted in a slightly better outcome. CLINICAL RELEVANCE: When deciding whether to replace missing molars, the present results give further support to the SDA concept.

Evaluation of a one-piece ceramic implant used for single-tooth replacement and three-unit fixed partial dentures: a prospective cohort clinical trial.

AIM: The aim of this clinical trial was to evaluate the safety and efficiency of a one-piece zirconia oral implant after 1 year of function. MATERIALS AND METHODS: Two centers included 60 subjects in need of implant-supported single-tooth restorations or three-unit bridges. A total of 71 zirconia one-piece implants were placed and immediately restored with a temporary reconstruction for at least 2 months. The final veneered zirconia restorations were then cemented and followed for 6 months and 1 year after insertion of the restorations. At each visit, a clinical evaluation was performed to analyze biological parameters of the implants and the neighboring teeth. A standardized periapical radiograph was taken at implant insertion, at the placement of the restorations and at the 1-year follow-up. RESULTS: Sixty patients with 71 implants (48 in the mandible, 23 in the maxilla) were included in this study and provided with 11 bridges and 49 crowns. Two patients with three implants (one bridge and one single crown) could not be evaluated. One patient lost his implant 5 weeks after implant insertion. Based on 58 patients, the mean survival rate was 98.3% after one year when the implants of the two patients that did not show up were not counted as lost. The mean marginal bone loss from implant insertion to the 1-year follow-up after the final prosthetic restoration was 0.78 mm with a standard deviation of 0.79 mm. The probing depth around the implants increased from 2.7 mm at insertion of the prosthetic reconstruction to 3.5 mm one year after insertion. The probing depth around the adjacent teeth remained stable at 2.5 mm. At the 1-year recall, the difference was significant. The clinical attachment levels at implants and teeth were not different at the 1-year follow-up with 3.1 mm at tooth and implant sites. CONCLUSIONS: The presently tested one-piece ceramic implant was successful in replacing single tooth and three-unit gaps after one year of function. Further long-term data are necessary to verify these initial findings.

Effect of the implant-abutment interface on peri-implant tissues: a systematic review.

OBJECTIVE: The aim of the present systematic review was to determine the peri-implant tissue response to different implant abutment materials and designs available and to assess the impact of tissue biotype. MATERIALS AND METHODS: Relevant literature published between December 2009 and August 2012 was searched to identify studies dealing with different implant abutment designs and materials, as well as the response of different tissue biotypes. The search terms used, in simple or multiple conjunctions, were 'implant abutment', 'interface', 'material', 'peri-implant', 'soft tissue' and 'esthetic'. Studies were selected according to pre-determined inclusion and exclusion criteria. RESULTS: The initial search yielded 2449 titles. After a subsequent filtering process, 23 studies were finally selected. The included studies revealed different factors responsible for the stability of peri-implant tissue and the esthetic outcome. These factors include tissue biotype and architecture, implant abutment material and implant abutment design. Several designs were suggested to prevent marginal bone loss and soft tissue recession. These included scalloped implants, platform-switched implants and gingivally converged or concave implant abutments. Due to the limited number of studies and the heterogeneity in their designs, it was not possible to perform a statistical analysis of the data. CONCLUSIONS: The current literature provides insufficient evidence about the effectiveness of different implant abutment designs and materials in the stability of peri-implant tissues.

A retrospective evaluation of teeth restored with zirconia ceramic posts: 10-year results.

INTRODUCTION: Zirconia posts can be used as an esthetic alternative to metal posts. Despite their advantages, there is a lack of information about the long-term performance of zirconia posts. OBJECTIVES: This retrospective clinical study examined the survival probability, clinical performance, and reasons for failure of teeth restored with zirconia posts after an observation period of up to 10 years. MATERIALS AND METHODS: After a mean observation period of 10 years, clinical and radiographic examinations were carried out for a total of 64 posts in 45 patients. The posts received mainly either ceramic or direct composite buildups. All posts were adhesively cemented, after air abrasion with alumina particles or silica coating and silanization. The majority of the reconstructed teeth were used as abutments for metal ceramic or ceramic fixed dental prostheses. Kaplan-Meier analysis was employed to compute the survival probability of teeth restored with zirconia posts. Cox regression analysis was used to assess the risk of failure and to identify possible covariates. RESULTS: During the follow-up period, a drop-out rate of 49.4 % was recorded. The survival probability for teeth with zirconia posts was 81.3 % after 10 years. CONCLUSION: Within the limits of this study, zirconia posts can be used for abutments that will be restored with ceramic restorations. However, due to the high patient drop-out rate, careful interpretation of the current results is suggested. CLINICAL RELEVANCE: The present paper is the first 10-year clinical study on teeth restored with zirconia posts and could serve as a reference for future research. In addition, it provides long-term data about restorations already implemented by dental practitioners.

Comparison of variable-thread tapered implant designs to a standard tapered implant design after immediate loading. A 3-year multicentre randomised controlled trial.

OBJECTIVES: This randomised, controlled multicentre trial aimed at comparing two versions of a variable-thread dental implant design to a standard tapered dental implant design in cases of immediate functional loading for 36 months after loading. MATERIALS AND METHODS: 177 patients (325 implants) were included at 12 study centres and randomly allocated into one of three treatment groups: NAI (variable-thread design, NobelActive internal connection), NAE (variable-thread design, NobelActive external connection) and, as control, NR (standard tapered design, NobelReplace tapered groovy). Inclusion criteria concerned healed bony implant sites and feasibility for immediate loading. Clinical and radiographic examinations were performed at implant placement and after 3, 6, 12, 24 and 36 months. The outcome measures were marginal bone remodelling (primary outcome), implant survival and success, papilla score, plaque accumulation, and bleeding on probing. RESULTS: 127 patients (NAI: 45, NAE: 41, NR: 41) were followed-up and evaluated after 36 months. No significant differences in cumulative survival rates were seen for the groups (NAI: 95.7%; NAE: 96.3%; NR: 96.6%). In all groups, bone remodelling occurred during the first 3 months, with stable or even increasing bone levels after the initial remodelling period. The bone remodelling from insertion to 36 months for the NAI group (-0.89 ± 1.65 mm) was comparable (P = 0.98) to that of the NR group (-0.85 ± 1.32 mm). The NAE group showed comparable bone remodelling during the first year, with an increase in following years resulting in significantly less overall bone loss (-0.16 ± 1.06 mm) (P = 0.041). Overall improvement in papilla size was observed in all treatment groups. CONCLUSIONS: Over 36 months, the results show stable or improving bone levels for all treatment groups after the initial bone remodelling seen during the first 3 months after placement. The variable- thread implants showed results comparable to those of standard tapered implants in cases of immediate function, and therefore can be considered as a treatment option for immediate loading.

Is the smile line a valid parameter for esthetic evaluation? A systematic literature review.

UNLABELLED: The "smile line" is commonly used as a parameter to evaluate and categorize a person's smile. This systematic literature review assessed the existing evidence on the validity and universal applicability of this parameter. The latter was evaluated based on studies on smile perception by orthodontists, general clinicians, and laypeople. METHODS: A review of the literature published between October 1973 and January 2010 was conducted with the electronic database Pubmed and the search terms "smile," "smile line," "smile arc," and "smile design." RESULTS: The search yielded 309 articles, of which nine studies were included based on the selection criteria. The selected studies typically correlate the smile line with the position of the upper lip during a smile while, on average, 75 to 100% of the maxillary anterior teeth are exposed. A virtual line that connects the incisal edges of the maxillary anterior teeth commonly follows the upper border of the lower lip. Average and parallel smile lines are most common, influenced by the age and gender of a person. Orthodontists, general clinicians, and laypeople have similar preferences and rate average smile lines as most attractive. CONCLUSIONS: The smile line is a valid tool to assess the esthetic appearance of a smile. It can be applied universally as clinicians and laypersons perceive and judge it similarly.

Survival rates of teeth, implants, and double crown-retained removable dental prostheses: a systematic literature review.

PURPOSE: The aim of this systematic literature review was to investigate the survival rates of teeth, implants, and double crown-retained removable dental prostheses (RDPs). MATERIALS AND METHODS: A systematic review of the literature published from January 1973 through May 2010 was conducted using electronic databases and hand-searching to assess the clinical outcomes of teeth, implants, and double crown-retained RDPs. RESULTS: This review yielded 512 articles, which were narrowed down to 11. The included studies demonstrated tooth survival rates between 60.6% and 95.3% after an observation period of 4 to 10 years. The survival rates of RDPs supported by teeth ranged between 90.0% and 95.1% after 4 and 5.3 years, respectively. The survival rates of implants supporting prostheses in the mandible were between 97% and 100% after an observation period between 3 and 10.4 years. The survival rates of implant-retained RDPs in the mandible ranged between 95% and 100% after 9 and 10.4 years. Teeth and implants supporting prostheses in the maxilla, as well as the RDPs themselves, demonstrated a survival rate of 100% after 3.2 years. CONCLUSION: The current literature does not provide sufficient information regarding the long-term outcome of double crown-retained RDPs. Further studies based on a higher level of evidence are needed to validate the outcomes of this treatment modality.

Implant neck configurations for preservation of marginal bone level: a systematic review.

PURPOSE: The aim of this article was to evaluate the effectiveness of various implant neck configurations in the preservation of marginal bone level as well as to identify the available scientific evidence. MATERIALS AND METHODS: Online and hand searches of the literature published from 1976 through 2009 were conducted to identify studies dealing with modifications in the implant neck area and marginal bone loss for at least a 5-year observation period. The search terms that were used, alone or in combination, were "implant neck," "marginal bone loss," "neck design," "bone resorption," "bone remodeling," and "implant collar." Relevant studies were selected according to predetermined inclusion and exclusion criteria. RESULTS: The initial search yielded 3,517 relevant titles and revealed eight different implant neck configurations and/or methods suggested for the preservation of marginal bone. These methods included changes in implant neck length and design, implant surface characteristics, implant diameter, and/or insertion depth; the addition of microthreads; the use of one-piece implants; and the concept of platform switching. After subsequent filtering, 20 studies were finally selected and involved the following methods: the use of microthreads (1 study); modifications in implant surface characteristics (11 studies), implant diameter (4 studies), or insertion depth (2 studies); the use of one-piece implants (3 studies); and platform switching (1 study). Because of the heterogeneity of the studies, it was not possible to analyze the data statistically. No evidence was found regarding the effectiveness of any specific modification in the implant neck area in preserving marginal bone or preventing marginal bone loss. CONCLUSION: The current literature provides insufficient evidence about the effectiveness of different implant neck configurations in the preservation of marginal bone. Long-term randomized controlled clinical trials are needed to elucidate the effects of such modifications.

Prosthodontic complications with implant overdentures: a systematic literature review.

PURPOSE: Problems associated with a complete denture, such as lack of stability and retention, can be solved with the use of implant-retained or implant-supported overdentures. However, controversy exists as to the anchorage system used and indications for both the maxilla and mandible. The purpose of this review was to identify the prosthetic complications associated with the different attachment mechanisms used for implant-supported or implant-retained overdentures. MATERIALS AND METHODS: A search of the MEDLINE and PubMed databases was conducted to find articles in English and German peer-reviewed journals published between 1980 and 2008. The search focused on randomized controlled clinical trials and prospective studies with follow-up periods of at least 5 years that contained clinical data regarding success, failure, and prosthetic complications. RESULTS: The search yielded a limited number of randomized controlled clinical trials referring to implant-supported or implant-retained overdentures. Very few studies have prospectively compared prosthetic complications for a period longer than 5 years after delivery of the prosthesis. CONCLUSIONS: Implant-supported or implant-retained overdentures in the mandible provide predictable results with improved stability, retention, and patient satisfaction. Scientific evidence shows a lower rate of implant survival and a higher frequency of prosthetic complications for maxillary implant-retained or implant-supported overdentures. Although the literature presents considerable information on complications of implant prostheses, variations in study design preclude proper analysis of certain complications. Well-designed longitudinal studies are required to establish evidence-based treatment planning principles.

Interleukin-1 as a genetic marker for periodontitis: review of the literature.

Periodontitis is considered to be a multifactorial disease. Studies have indicated that part of the clinical variability in periodontitis may be explained by genetic factors. Genes can affect the immunoinflammatory host response to bacterial challenge in the periodontal tissues by means of an overproduction of proinflammatory cytokines, such as interleukin-1 (IL-1). IL-1 plays an important role in the pathogenesis of periodontitis, through its involvement in the regulation of the host's inflammatory response and bone resorption. Therefore, the genes that encode for IL-1 production have recently received most attention as potential predictors of periodontal disease progression. Hence, the relationship between IL-1 genotype and periodontal disease has been investigated by a number of studies. This review article aimed to determine whether IL-1 could be regarded as a genetic marker for periodontitis by reviewing data concerning susceptibility, clinical parameters, and treatment strategies in relation to the IL-1 genotype. The review concluded that there is currently limited evidence to implicate a specific IL-1 genotype as a risk factor for chronic periodontitis in white populations. However, there is limited evidence that genetic variation in the IL-1B polymorphism could be a risk factor for aggressive periodontitis.

Relationship between crowns and the periodontium: a literature update.

Location of the crown margin, marginal fit, crown material, and crown contour all impact periodontal tissues. This literature review evaluated available data on their relationship with the periodontium and also examines whether any changes in established knowledge and/or perspectives have been published during the past 30 years. Electronic and manual searches conducted for in vivo investigations in the English and German literature for 1953 to 2009 provided 64 studies. Findings indicate that the supragingival location remains the most advantageous from the periodontal point of view; esthetic demands, however, dictated an intracrevicular location of the margin in the anterior zone. Metal-ceramic and all-ceramic crowns show a clinically acceptable marginal fit. Ceramic materials have the lowest plaque-retaining capacity, and a normal crown contour guarantees satisfactory periodontal health and esthetics. The accompanying data confirm the results reported in the literature, revealing that nothing has substantially changed, thereby supporting current approaches.

Fixed rehabilitation of the edentulous maxilla: possibilities and clinical outcome.

PURPOSE: The aim of the present report was to describe the different treatment approaches available for fixed rehabilitation of the edentulous maxilla in the presence of varying hard and soft tissue conditions and to review the clinical outcome of each treatment approach. MATERIALS AND METHODS: A review of the published data published from 1980 through 2009 was conducted using electronic databases and manual searching to identify the treatment possibilities for the fixed rehabilitation of the edentulous maxilla and report their clinical outcomes. The search terms used, in simple or multiple conjunctions, were "fixed rehabilitation," "implants," "edentulous," "fixed dental prosthesis," "implant-supported," and "maxilla." RESULTS: Several treatment modalities were identified for the fixed rehabilitation of the edentulous maxilla, with and without bone augmentation procedures. Regular, tilted, and zygoma implants were identified for treatment modalities that do not require bone augmentation. Sinus floor elevation with the lateral window technique or Le Fort I osteotomy with interpositional bone grafts was identified as a treatment possibility that required bone augmentation procedures. The database initially yielded 230 titles. Of the 230 studies, 42 were finally selected. Although all studies reported the survival rates of the implants, only 20 provided information about the prosthetic outcome. Because of the limited number of studies, at least for the specific treatment modalities, and the heterogeneity in the design of the different studies identified, it was not possible to perform a statistical analysis of the data. Except for regular implants placed in native bone, no sufficient long-term clinical studies were found for the other procedures. CONCLUSIONS: Except for regular implants placed in nonaugmented native bone, the published data provide insufficient evidence about the outcome of other procedures. Until long-term data are available, such procedures should not be considered reliable treatment modalities.

Zirconia in dentistry: Part 1. Discovering the nature of an upcoming bioceramic.

Advanced ceramic materials such as zirconia have great potential as substitutes for traditional materials in many biomedical applications. Since the end of the 1990s, the form of partially stabilized zirconia has been promoted as suitable for dental use due to its excellent strength and superior fracture resistance as result of an inherent transformation toughening mechanism. In addition, zirconia bioceramic presents enhanced biocompatibility, low radioactivity, and interesting optical properties. The introduction of computer-aided design/computer-aided manufacturing (CAD/CAM) techniques has increased the general acceptance of zirconia in dentistry. However, some fabrication procedures such as grinding, polishing, sandblasting, heat treatment, and veneering of the fine-grained metastable zirconia microstructures may affect the long-term stability and success of the material by influencing its aging sensitivity. The purpose of this review is to address the evolution of zirconia as a biomaterial; to explore the material's physical, chemical, biological, and optical properties; to describe strengthening procedures; and finally to examine aging, processing, and core/veneer interfacial effects.

Marginal adaptation of three different zirconium dioxide three-unit fixed dental prostheses.

STATEMENT OF PROBLEM: Marginal adaptation is important for the long-term success of dental restorations. Data on the marginal discrepancy of zirconia-based fixed dental prostheses made with different computer-aided design/computer-aided manufacturing technology is needed. PURPOSE: The purpose of this study was to evaluate the marginal adaptation of different zirconia 3-unit fixed dental prostheses at different fabrication stages and after artificial aging. MATERIAL AND METHODS: Twenty-four zirconia 3-unit fixed dental prostheses (DCS, Procera, and VITA YZ-Cerec; n=8) were fabricated using different manufacturing systems and conventionally cemented with glass ionomer cement on human teeth. Each group was aged in a masticatory simulator with thermal cycling. The marginal gaps were examined on epoxy replicas for frameworks and for restorations before and after cementation, and after masticatory simulation, at x 250 magnification. Marginal adaptation was assessed using geometric means of the marginal gap values with 95% confidence intervals. Differences between the manufacturing systems and the effect of artificial aging were tested using repeated-measures ANOVA and post hoc paired and unpaired t tests with Bonferroni-Holm correction (alpha=.05). RESULTS: The geometric mean (95% confidence limits) marginal gap values (mum) for frameworks and for restorations before cementation, after cementation, and after masticatory simulation were, respectively: DCS: 86 (80-93), 86 (83-90), 86 (78-94), and 84 (79-90); Procera: 82 (74-89), 89 (81-97), 89 (84-95), and 88 (82-94); and VITA YZ-Cerec: 64 (57-72), 67 (61-77), 76 (71-82), and 78 (76-80). The repeated-measures ANOVA showed significant group and stage effects (P<.05). Group VITA YZ-Cerec showed significantly smaller marginal gap values than groups DCS and Procera at framework (P<.05) and before-cementation (P<.05) stages. The VITA YZ-Cerec group showed significantly smaller marginal gap values than the Procera group after cementation (P<.05). The marginal gap values between different stages were not significantly different for all groups (P>.05). CONCLUSIONS: The marginal accuracy of zirconia fixed dental prostheses is influenced by manufacturing technique.

Zirconia in dentistry: part 2. Evidence-based clinical breakthrough.

An ideal all-ceramic restoration that conforms well and demonstrates enhanced biocompatibility, strength, fit, and esthetics has always been desirable in clinical dentistry. However, the inherent brittleness, low flexural strength, and fracture toughness of conventional glass and alumina ceramics have been the main obstacles for extensive use. The recent introduction of zirconia-based ceramics as a restorative dental material has generated considerable interest in the dental community, which has been expressed with extensive industrial, clinical, and research activity. Contemporary zirconia powder technology contributes to the fabrication of new biocompatible all-ceramic restorations with improved physical properties for a wide range of promising clinical applications. Especially with the development of computer-aided design (CAD)/computer-aided manufacturing (CAM) systems, high-strength zirconia frameworks can be viable for the fabrication of full and partial coverage crowns, fixed partial dentures, veneers, posts and/or cores, primary double crowns, implant abutments, and implants. Data from laboratory and clinical studies are promising regarding their performance and survival. However, clinical data are considered insufficient and the identified premature complications should guide future research. In addition, different zirconia-based dental auxiliary components (i.e., cutting burs and surgical drills, extra-coronal attachments and orthodontic brackets) can also be technologically feasible. This review aims to present and discuss zirconia manufacturing methods and their potential for successful clinical application in dentistry.

Relationship between interleukin-1 genotype and peri-implantitis: a literature review.

Endosseous implants present high survival rates within a 10-year observation time; however, implant failure and biologic complications are not completely avoidable. Although specific bacteria, dental plaque, and environmental factors are associated with peri-implant disease, there are currently no reliable predictors of peri-implantitis occurrence and severity. Disagreement about which clinical measures of peri-implant health are of diagnostic value continues because of the complexity of the disease process. Thus, identification of genes that control or modify aspects of the host response may provide a method to identify individuals at an elevated risk for peri-implant infections. Elevated levels of the inflammatory cytokine interleukin-1 (IL-1) in the crevicular fluid around diseased implants seem to play an important role in the pathogenesis and severity of peri-implantitis. The purpose of this review article was to critically address the genetic associations regarding IL-1 genotype claimed for peri-implant disease and to validate the use of IL-1 genetic susceptibility tests. It was revealed that the diagnostic value of both IL-1 genotyping and genetic tests for peri-implantitis should be reconsidered before altering treatment planning, regimens, and maintenance in implant dentistry.

Shear bond strengths between different zirconia cores and veneering ceramics and their susceptibility to thermocycling.

OBJECTIVES: The purpose of this study was to evaluate the shear bond strength between various commercial zirconia core and veneering ceramics, and to investigate the effect of thermocycling. METHODS: The Schmitz-Schulmeyer test method was used to evaluate the core-veneer shear bond strength (SBS) of three zirconia core ceramics (Cercon Base, Vita In-Ceram YZ Cubes, DC-Zirkon) and their manufacturer recommended veneering ceramics (Cercon Ceram S, Vita VM9, IPS e.max Ceram). A metal ceramic system (Degudent U94, Vita VM13) was used as a control group for the three all-ceramic test groups (n = 30 specimens/group). Half of each group (n = 15) was thermocycled (5-55 degrees C, 20,000 cycles). Subsequently, all specimens were subjected to shear force in a universal testing machine. Fractured specimens were evaluated microscopically to determine the failure mode. RESULTS: The initial mean SBS values in MPa+/-S.D. were 12.5+/-3.2 for Vita In-Ceram YZ Cubes/Vita VM9, 11.5+/-3.4 for DC-Zirkon/IPS e.max Ceram, and 9.4+/-3.2 for Cercon Base/Cercon Ceram S. After thermocycling mean SBS values of 11.5+/-1.7 MPa for DC-Zirkon/IPS e.max Ceram, 9.7+/-4.2 MPa for Vita In-Ceram YZ Cubes/Vita VM9, and 9.6+/-4.2 MPa for Cercon Base/Cercon Ceram S were observed. Neither the differences between the SBS values of the all-ceramic test groups nor the influence of thermocycling on all groups were statistically significant. Irrespective of thermocycling the metal ceramic control group (27.6+/-12.1 MPa, 26.4+/-13.4 MPa) exhibited significantly higher mean SBS than all three all-ceramic groups tested. The all-ceramic groups showed combined failure modes as cohesive in the veneering ceramic and adhesive at the interface, whereas the metal ceramic group showed predominately cohesive fractures. SIGNIFICANCE: The results indicated that the SBS between zirconia core and veneering ceramics was not affected by thermocycling. None of the zirconia core and veneering ceramics could attain the high bond strength values of the metal ceramic combination.

Masticatory fatigue, fracture resistance, and marginal discrepancy of ceramic partial crowns with and without coverage of compromised cusps.

PURPOSE: To evaluate preparation designs of compromised cusps and whether or not they influence masticatory fatigue, fracture resistance, and marginal discrepancy of ceramic partial-coverage restorations (PCRs) luted on mandibular molars. MATERIALS AND METHODS: Sixty-four caries-free molars were equally divided into four groups. Control group NP received no preparation (NP). Group B-IN received a basic inlay (IN) preparation with buccal (B) cusp conservation and occlusal reduction of both lingual cusps. Group B-ON was prepared in the same way, except buccal cusps were prepared with an angle of 45 degrees to the occlusal plane (buccal onlay). Group B-OV preparation was similar to group B-ON, but buccal cusps received a further shoulder preparation on the buccal aspect (buccal overlap). Forty-eight all-ceramic IPS e.max Press PCRs were fabricated and luted adhesively. Specimens underwent mouth-motion fatigue (1.2 million cycles, 1.6 Hz, 49 N) and 5500 thermal cycles (5 degrees C/55 degrees C). Fracture patterns were observed. Surviving specimens were loaded until fracture. Marginal discrepancies were examined. RESULTS: Only one specimen of group B-ON fractured during fatigue. Median fracture loads (N) [IQR = x(.25) - x(.75)]: group NP = 1604 N [1182-1851 N], group B-IN = 1307 N [1262-1587N], group B-ON = 1396 N [817-1750N], group B-OV = 1205 N [1096-1542N]. No significant differences in fracture resistance were found between restored molars and unprepared teeth (p _ 0.18). Different preparation designs showed no significant influence on PCR fracture resistance. Mouth-motion fatigue caused a significanty decrease of marginal accuracy in groups B-IN (p = 0.009) and B-ON (p = 0.008). Marginal discrepancy values of groups B-IN and B-OV were significantly different after fatigue (p = 0.045). CONCLUSION: Ceramic coverage of compromised cusps did not demonstrate an increase of fracture resistance after fatigue when compared to less invasive partial-coverage restorations. However, enhanced exposure of restoration margins to occlusal wear could result in more extensive marginal discrepancies.

Marginal adaptation of all-ceramic crowns on implant abutments.

BACKGROUND: Studies focusing on the marginal accuracy of all-ceramic crowns on implant abutments are in short supply. PURPOSE: This study evaluated the marginal accuracy of all-ceramic crowns on different implant abutments. MATERIALS AND METHODS: Ninety-six standardized maxillary central incisor crowns (48 alumina and 48 zirconia) were fabricated for each of the six test groups (n = 16) (Ti1, titanium abutments-alumina crowns; Ti2, titanium abutments-zirconia crowns; Al1, alumina abutments-alumina crowns; Al2, alumina abutments-zirconia crowns; Zr1, zirconia abutments-alumina crowns; Zr2, zirconia abutments-zirconia crowns). The crowns were adhesively luted using a resin luting agent. The marginal gaps were examined on epoxy replicas before and after luting as well as after masticatory simulation at 200x magnification. RESULTS: The geometrical mean (95% confidence limits) marginal gap values before cementation, after cementation, and after masticatory simulation were group Ti1: 39(37-42), 57(53-62), and 49(46-53); group Ti2: 43(40-47), 71(67-76), and 64(59-69); group Al1: 57(54-61), 87(85-90), and 67(65-69); group Al2: 66(63-69), 96(90-101), and 75(72-78); group Zr1: 54(51-57), 79(76-82), and 65(63-67); and group Zr2: 64(60-68), 85(80-91), and 75(70-81). The comparison between non-cemented and cemented stages in each group demonstrated a significant increase in the marginal gap values after cementation in all groups (p < .001), while the comparison between cemented and aged stages in each group showed a significant decrease in the marginal gap values in groups Al1, Al2, and Zr1 (p < .0001). This reduction was not significant for groups Ti1, Ti2, and Zr2 (p > .05). CONCLUSION: The marginal accuracy of all tested restorations meets the requirements for clinical acceptance.