Incidence of endodontic therapy after complete or partial coverage glass-ceramic restorations with a follow-up time of over 30 years: A prospective clinical study.

STATEMENT OF PROBLEM: Long-term clinical data are lacking on the comparison of the incidence of endodontic therapy in adhesively luted complete and partial coverage glass-ceramic restorations, as well as on the effect of technique and clinical variables. PURPOSE: The purpose of this prospective clinical study was to assess the long-term incidence of teeth requiring endodontic therapy after receiving either complete or partial coverage glass-ceramic restorations. MATERIAL AND METHODS: Participants requiring single anterior complete, posterior complete, or posterior partial (inlay or onlay) coverage restoration, or a combination of these on a vital tooth were recruited from a clinical private practice. Only the participants who chose glass-ceramic partial and complete coverage restorations without the need of endodontic therapy were included in the study. The overall clinical performance of these glass-ceramic restorations was assessed by clinical factors determined at recall. The effect of various clinical parameters (type of restoration, dental arch, tooth position in the dental arch, age and sex of participant, and ceramic thickness) was evaluated by using Kaplan-Meier survival curves to account for attrition bias and other reasons for failure. The statistical significance of differences between parameters was determined by using the log rank test (α=.05). RESULTS: A total of 1800 participants requiring 4511 glass-ceramic anterior and posterior restorations were evaluated. The mean age of the participants at the time of restoration placement was 62 (range 20 to 99 years, 710 men and 1090 women). Of 4511 restorations, 1476 were anterior complete coverage, 2119 posterior complete coverage, and 916 posterior partial coverage. Endodontic therapy after restoration placement was needed for 76 restorations (10 anterior complete, 50 posterior complete, and 16 posterior partial). The total time at risk was 50 436 years providing an estimated need for endodontic therapy risk of 0.15% per year. The estimated 35-year cumulative survival was 97.36%. The majority of endodontic treatments (67%, 52/76) occurred in the first 5 years. The estimated cumulative survival of anterior complete coverage, posterior complete coverage, posterior partial inlay, and posterior partial onlay restorations was 98.89% (n=1476, 10 endodontic treatments), 96.38% (n=2119, 50 endodontic treatments), 96.78% (n=553, 11 endodontic treatments), and 98.53% (n=363, 5 endodontic treatments), respectively. Statistically significant differences occurred between anterior complete coverage, posterior complete coverage, and posterior partial coverage inlay restorations, with a higher incidence in posterior complete coverage and posterior partial inlay restorations (P<.05). First molars had the highest rate of endodontic therapy after restoration in both arches. Age and restoration thickness were significant factors, recording statistically higher number of endodontic treatments in participants >52 years and restorations with all surfaces ≥1 mm (P<.05). Other clinical variables, dental arch and sex of the participants, were not significantly related to endodontic treatments (P>.05). CONCLUSIONS: The clinical performance of 4511 units over 30 years in service was excellent, with the estimated cumulative survival of 97.36%. Posterior complete coverage and posterior partial inlay restorations had a significantly higher need for endodontic therapy than anterior complete coverage restorations. Their overall clinical performance relative to endodontic treatment was excellent with a cumulative survival of 96.38% and 96.78% over 30 years. There was no difference in the endodontic treatment rate between posterior complete and partial coverage restorations. Thickness of the restoration affected the endodontic treatment rate, with ≥1 mm resulting in higher incidence. The age of the participants influenced the endodontic treatment rate, with higher incidence in the >52-year age group. Other confounding clinical variables did not have a significant effect on the endodontic treatment rate.

10.9-year survival of pressed acid etched monolithic e.max lithium disilicate glass-ceramic partial coverage restorations: Performance and outcomes as a function of tooth position, age, sex, and the type of partial coverage restoration (inlay or onlay).

STATEMENT OF PROBLEM: Long-term clinical data on the survival of pressed lithium disilicate glass-ceramic when used with partial coverage restorations and the effect that different technical and clinical variables have on survival are sparse. PURPOSE: The purpose of this clinical study was to determine the 10.9-year survival of pressed lithium disilicate glass-ceramic partial coverage restorations and associated clinical parameters on outcomes. MATERIAL AND METHODS: Individuals requiring single unit defect-specific partial coverage restorations in any area of the mouth were recruited in a clinical private practice. Participants were offered the options of partial coverage cast gold or glass-ceramic (lithium disilicate) restorations. Only participants that chose glass-ceramic partial coverage restorations were included in the study. The overall survival of the glass-ceramic restorations was assessed by the clinical factors (participant's age, sex, dental arch, tooth position in dental arch, type of partial coverage restoration, and ceramic thickness) determined at recall. The effect of this clinical parameters was evaluated by using Kaplan-Meier survival curves accounting for attrition bias and other reasons for failure. The statistical significance of differences between parameters was determined by using the log rank test (α=.05). RESULTS: A total of 304 participants requiring 556 lithium disilicate restorations were evaluated. The mean age for the participant at the time of restoration placement was 62 with a range of 20 to 99 years, 120 were men and 184 were women. A total of 6 failures (bulk fracture or large chip) requiring replacement were recorded with the average time to failure of 2.4 (0.8-9.2) years. The total time at risk computed for these units was 1978.9 years providing an estimated failure risk of 0.3% per year. The 10-year estimated cumulative survival was 95.6%. The estimated cumulative survival of inlays (n=246) and onlays (n=305) were 93.9% and 98.3%, at 9.9 and 9.8 years, respectively (P<.05). Of the 6, there were 3 failures recorded for the partial coverage inlay restorations. The total time at risk for these inlays was 786.79 years providing an estimated risk of 0.38% per year. The other 3 failures recorded occurred for the partial coverage onlay restorations. The total time at risk for the onlays was 1032.17 years providing an estimated risk of 0.29% per year. The failures occurred in the molar region only. There were no failures recorded for the anterior partial coverage inlays (n=5). The total time at risk computed for the anterior units was 21.55 years providing an estimated risk of 0% per year. There was no statistically significant difference in the survival of partial coverage restorations among men and women, different age groups, or position in the dental arch. The thickness of the restoration had no influence on the survival of glass-ceramic partial coverage restorations. CONCLUSIONS: Pressed lithium disilicate defect-specific partial coverage restorations reported high survival rate over the 10.9-year period with an overall failure rate of 0.3% per year and limited to the molar teeth. Risk of failure at any age was minimal for both men and women.

Comparison of 16.9-year survival of pressed acid etched e.max lithium disilicate glass-ceramic complete and partial coverage restorations in posterior teeth: Performance and outcomes as a function of tooth position, age, sex, and thickness of ceramic material.

STATEMENT OF PROBLEM: Long-term clinical data are lacking on the comparison of the survival of adhesively luted pressed e.max lithium disilicate glass-ceramic complete and partial coverage restorations in posterior dentitions and the effect that different technical and clinical variables have on their survival. PURPOSE: The purpose of this clinical study was to examine and compare the 16.9-year survival of posterior pressed e.max lithium disilicate glass-ceramic complete and partial coverage restorations and associated clinical parameters on the outcome. MATERIAL AND METHODS: Patients requiring either single-unit posterior defect-specific partial coverage or complete coverage restorations were recruited in a clinical private practice. The participants were offered the options of direct restorations, partial coverage cast gold, or glass-ceramic (lithium disilicate) restorations. Those requiring complete coverage restorations were given the options of complete cast gold, metal-ceramic, or glass-ceramic restorations. Only participants who chose glass-ceramic partial and complete coverage restorations were included in the study. The overall survival of the glass-ceramic restorations was assessed by the clinical factors determined at recall. The effect of various clinical parameters (type of restoration, dental arch, tooth position in the dental arch, age and sex of participant, and ceramic thickness) was evaluated by using Kaplan-Meier survival curves to account for attrition bias and other reasons for failure. The statistical significance of differences between parameters was determined using the log rank test (α=.05). RESULTS: A total of 738 participants requiring 2392 lithium disilicate restorations in posterior teeth were evaluated. The mean age of the participants at the time of restoration placement was 62 (range: 20-99 years, 302 men and 436 women). Of 2392 units, 1782 were complete and 610 were partial coverage restorations. A total of 22 failures (bulk fracture or large chip) requiring replacement were recorded with the average time to failure 3.5 (0.02-7.9) years. The total time at risk computed for these units was 13227.9 years, providing an estimated failure risk of 0.17% per year. The 16.9-year estimated cumulative survival was 96.49%. The estimated cumulative survival of posterior complete (n=1782) and posterior partial coverage restorations (n=610) was 96.75% at 10.5 years and 95.27% at 16.9 years (P<.05). Of the 22, 16 failures were recorded for the complete coverage restorations. The total time at risk for these restorations was 10144.5 years, providing an estimated risk of 0.16 per year. The other 6 failures recorded occurred for the partial coverage restorations. The total time at risk for these restorations was 3083.5 years, providing an estimated risk of 0.19% per year. No statistically significant difference was found in the survival of posterior complete and partial coverage restorations among men and women, different age groups, or posterior tooth position in the dental arch (P>.05). The thickness of the restoration also had no influence on the survival of glass-ceramic posterior restorations (P>.05). CONCLUSIONS: Pressed e.max lithium disilicate complete and partial coverage restorations showed high survival rates in posterior teeth over a 16.9-year period, with an overall failure rate of 0.17% per year. Risk of failure at any age was low for both men and women. No statistically significant difference was found in the survival of complete and partial coverage restorations, and none of the confounding variables, including the thickness of the restoration, appeared to have a significant effect on survival.

Ten-year survival of pressed, acid-etched e.max lithium disilicate monolithic and bilayered complete-coverage restorations: Performance and outcomes as a function of tooth position and age.

STATEMENT OF PROBLEM: Long-term clinical data on the survival of pressed lithium disilicate glass-ceramic restorations and the effect that different technical and clinical variables have on survival are lacking. PURPOSE: The purpose of this clinical study was to examine the 10-year survival of pressed lithium disilicate glass-ceramic restorations and the relationship between clinical parameters on outcomes. MATERIAL AND METHODS: Five hundred and fifty-six patients, ranging in age from 17 to 97 years, from a private clinical practice were enrolled. All participants required single-tooth replacement or repair in any area of the mouth, including single crowns, 3-unit fixed partial dentures, cantilevered anterior restorations, and foundation restorations. Together, the longevity of 1960 complete-coverage restorations was studied. Participants were offered the options of gold, conventional metal-ceramic, or lithium disilicate restoration. Participants who chose glass-ceramic restorations were included in the study. The overall survival of the glass-ceramic restorations was assessed by using clinical factors determined at recall, and the effect of various clinical parameters was evaluated by using Kaplan-Meier survival curves to account for attrition bias and other reasons for failure. The statistical significance of differences between parameters was determined using the log-rank test (α=.05). RESULTS: A total of 556 patients electing lithium disilicate restorations were evaluated. The mean age of patients at the time of restoration placement was 62 years, with a range of 17 to 97 years. Men comprised 39.5% of the patients, and women, 60.5%. Many patients required more than one restoration. Seven failures (bulk fracture or large chip requiring replacement) were recorded for the 1960 complete-coverage lithium disilicate restorations, with the average time of failure being 4.2 years. The total time at risk computed for the units was 5113 years, providing an estimated failure risk of 0.14% per year. The 10-year estimated cumulative survival was 99.6% (95% confidence : 99.4-99.8).The estimated cumulative survival rate of 1410 monolithic and 550 bilayered e.max complete-coverage restorations was 96.5% and 100%, respectively, at 10.4 and 7.9 years (P<.05). Seven failures were recorded for the monolithic complete-coverage restoration units placed. The total time at risk for these monolithic units was 3380 years, providing an estimated risk of 0.2% per year. Failures were primarily in molar teeth (5 of 7) and occurred in both arches (3/2). No failures were recorded for the bilayered complete-coverage restorations. The total time at risk computed for the bilayered units was 1733 years, providing an estimated risk of 0% per year. CONCLUSIONS: Pressed lithium disilicate restorations in this study survived successfully over the 10.4-year period studied with an overall failure rate below 0.2% per year and were primarily confined to molar teeth. The risk of failure at any age was minimal for both men and women.

Can material properties predict survival of all-ceramic posterior crowns?

Increasingly strong all-ceramic materials have been introduced often with great fanfare and promise for long-term clinical performance. However, especially on posterior teeth, performance has been less than anticipated. This article reviews failure rates and modes of all-ceramic crowns and addresses the question of whether material properties can accurately predict clinical survival. Guidelines for selecting new and existing ceramics are provided.

Survival of glass-ceramic materials and involved clinical risk: variables affecting long-term survival.

The fundamental objective of dental treatment is the continued health and longevity of the dentition. While advances in material formulations and clinical techniques promise to benefit patient care, various confounding variables (i.e., acid etching, preparation design, patient gender) affect the outcome of a dental restoration. These factors can be difficult to simulate in a laboratory setting that accurately depicts the clinical environment. As an alternative, this article presents a synopsis of the authors' prospective clinical study of all-ceramic restorations and explains the relationship of several variables to their long-term survival.

Effect of proximal wall height on all-ceramic crown core stress distribution: a finite element analysis study.

PURPOSE: Mechanical analyses of idealized crown-cement-tooth systems through finite element analysis (FEA) has provided valuable insight concerning design parameters and materials that favor lower stress patterns. However, little information regarding variation of basic preparation guidelines in stress distribution has been available. The primary objective of this study was to evaluate maximum principal stresses on a molar crown veneer plus core system natural tooth configuration preparation with variations in the ratio of proximal axial length (PAL) to buccal axial length (BAL) as well as loading condition and position. MATERIALS AND METHODS: Three-dimensional models comprising a crown veneer (porcelain), crown core (zirconia), cement layer, and tooth preparation (4.2 mm BAL with PAL reductions of 0.8 mm, 1.0 mm, and 1.2 mm) yielding BAL:PAL ratios of 1.23, 1.31, and 1.4 were designed by computer software (Pro/Engineering). The models were imported into an FEA software (Pro/Mechanica), with all degrees of freedom constrained at the root surface of the tooth preparation. Each tooth preparation crown configuration was evaluated under a vertical (axial) 200 N load, and under a combined vertical 200 N and horizontal (buccally) 100 N load applied at different positions from the central fossa to the cusp tip. Maximum principal stress (MPS) was determined for the crown core for each crown BAL:PAL ratio, loading condition, and position. RESULTS: Under both vertical and combined loading conditions, the highest MPSs were located at the occlusal region and in the occlusogingival region of the ceramic core. MPS values increased in the proximal region as the BAL:PAL ratio increased. Combined loading resulted in a general increase in MPS compared to vertical loading. CONCLUSION: Increasing the BAL:PAL ratio (reducing the proximal axial length of the preparation) acted as a stress concentrator at regions near the crown margins, suggesting this area may be vulnerable to damage from fit adjustment as well as during function. Such increases in stress concentration should be considered in clinical scenarios, especially when inherent flaws are present in the material, since extensive high-magnitude tensile stress fields have been noted under all loading conditions.

Engineering long term clinical success of advanced ceramic prostheses.

Biocompatability and, in some applications, esthetics make all-ceramic prostheses compelling choices but despite significant improvements in materials properties and toughening mechanisms, these still have significant failure rates. Factors that contribute to the degradation in strength and survival include material selection and prosthesis design which set the upper limit for performance. However, fabrication operations introduce damage that can be exacerbated by environmental conditions and clinical function. Using all-ceramic dental crowns as an example, experimentally derived models provide insight into the relationships between materials properties and initial critical loads to failure. Analysis of fabrication operations suggests strategies to minimize damage. Environmental conditions can create viscoplastic flow of supporting components which can contribute additional stress within the prosthesis. Fatigue is a particularly challenging problem, not only providing the energy to propagate existing damage but, when combined with the wet environment, can create new damage modes. While much is known, the influence of these new damage modes has not been completely elucidated. The role of complex prosthesis geometry and its interaction with other factors on damage initiation and propagation has yet to be well characterized.

Dental ceramics and the molar crown testing ground.

All ceramic crowns are highly esthetic restorations and their popularity has risen with the demand for life-like and cosmetic dentistry. Recent ceramic research has concentrated on developing a fundamental understanding of ceramic damage modes as influenced by microstructure. Dental investigations have elucidated three damage modes for ceramic layers in the 0.5-2 mm thickness using point contacts that duplicate tooth cuspal radii; classic Hertzian cone cracking, yield (pseudo-plastic behavior), and flexural cracking. Constitutive equations based upon materials properties have been developed that predict the damage modes operational for a given ceramic and thickness. Ceramic thickness or thickness of the stiff supporting core in layer crowns is critical in flexural cracking as well as the flaw state of the inner aspect of the crown. The elastic module of the supporting structure and of the luting cement and its thickness play a role in flexural fracture. Clinical studies of ceramics extending over 16 years are compared to the above relationships and predictions. Recommendations for clinical practice are made based upon the above.

Dental ceramics and the molar crown testing ground

All ceramic crowns are highly esthetic restorations and their popularity has risen with the demand for life-like and cosmetic dentistry. Recent ceramic research has concentrated on developing a fundamental understanding of ceramic damage modes as influenced by microstructure. Dental investigations have elucidated three damage modes for ceramic layers in the 0.5-2 mm thickness using point contacts that duplicate tooth cuspal radii; classic Hertzian cone cracking, yield (pseudo-plastic behavior), and flexural cracking. Constitutive equations based upon materials properties have been developed that predict the damage modes operational for a given ceramic and thickness. Ceramic thickness or thickness of the stiff supporting core in layer crowns is critical in flexural cracking as well as the flaw state of the inner aspect of the crown. The elastic module of the supporting structure and of the luting cement and its thickness play a role in flexural fracture. Clinical studies of ceramics extending over 16 years are compared to the above relationships and predictions. Recommendations for clinical practice are made based upon the above.