Fracture strength of lithium disilicate cantilever resin bonded fixed dental prosthesis

Optimal design of the retainer and connector for a lithium disilicate resin-bonded fixed partial denture: A finite element analysis study

STATEMENT OF PROBLEM

How the connector shape, retainer type, and retainer placement affect the functional stresses in lithium disilicate cantilever resin-bonded fixed partial dentures (RBFPDs) is unclear.

PURPOSE

The purpose of this finite element analysis (FEA) study was to evaluate the effects of the connector shape, retainer type, and retainer placement on the stress distribution and magnitude of stress in RBFPDs.

MATERIAL AND METHODS

Cantilever RBFPDs of the maxillary anterior lateral incisor with a retainer on the canine were modeled to conduct a 3-dimensional FEA. These designs were divided into 2 groups based on connector shape: rectangular and trapezoidal. Each group included 4 different retainer configurations-either labial or palatal veneer RBFPDs (LV-RBFPD or PV-RBFPD) or labial or palatal contact-point RBFPDs (LC-RBFPD or PC-RBFPD). FEA was performed for each RBFPD to evaluate stresses during regional and 3-point loading, including maximal intercuspal, protrusive, and lateral mandibular positions. The results were evaluated via colorimetric stress maps of the equivalent von Mises stress, maximum principal stress, and minimum principal stress in the prosthesis.

RESULTS

The connector shape, retainer type, and placement affected the RBFPD stress, and the lowest stress was observed in the rectangular group. The LC-RBFPD group presented the lowest maximum principal stress (348.2 MPa) and minimum principal stress (49.1 MPa) under regional loading and the lowest equivalent stress (273.4 MPa) and maximum principal stress (356.0 MPa) with the protrusion position. The LV-RBFPD group presented the lowest equivalent stress (52.0 MPa), the lowest maximum principal stress (47.5 MPa), and the minimum principal stress (1.04 MPa) at the maximal intercuspal position, the lowest minimum principal stress (1.04 MPa) at the protrusion position, and the lowest equivalent stress (46.7 MPa) at the lateral position. The PV-RBFPD group presented the lowest equivalent stress (268.5 MPa) under regional loading and the lowest maximum principal stress (37.7 MPa) and minimum principal stress (2.02 MPa) under lateral loading.

CONCLUSIONS

A rectangular cross-sectional connector design for all groups could help disperse occlusal force and improve the resistance of the restoration. Both the veneer and contact-point retainer in the rectangular group were clinically acceptable and could resist fracture.

A 32-month evaluation of lithium disilicate cantilever resin-bonded fixed dental prostheses to replace a missing maxillary incisor

STATEMENT OF PROBLEM

The absence of a tooth in the esthetic zone can cause emotional and social distress. The use of minimally invasive and visually pleasing lithium disilicate resin-bonded fixed dental prostheses (RBFDPs) may be a suitable option for replacing a missing maxillary incisor. However, the available literature on lithium disilicate cantilever RBFDPs is limited.

PURPOSE

This retrospective multicenter study assessed the survival and success rates of lithium disilicate anterior cantilever RBFDPs with an average follow-up period of 3 years up to 9 years.

MATERIAL AND METHODS

RBFDPs delivered by 3 operators were clinically assessed for survival using a modified United States Public Health Service criteria list. The incidence density was determined for each criterion and operator. The standard error and 95% confidence interval were calculated for each incidence density difference (α=.05 for all analyses).

RESULTS

A total of 108 RBFDPs were evaluated after a mean period of 32.45 months, ranging from 14 days to 111 months. None of the restorations exhibited failure, carious lesions, or fractures during the follow-up period. The primary reasons for reduced success rates were inflammation of the surrounding soft tissues and discoloration, with incidence densities of 0.074 and 0.057 per year, respectively. Significant differences were observed among RBFDPs from different operators for criteria that included adaptation, color match, marginal adaptation, polishability, surface staining, gingival health, and antagonist wear.

CONCLUSIONS

Cantilever lithium disilicate RBFDPs appear to be suitable for short-term restoration. RBFDPs exhibited visible changes after short-term follow-up. However, these changes did not result in failure.

Aesthetical and Functional Rehabilitation for an Ankylosed Maxillary Canine-A Case Report

Background: As the functional and aesthetical importance of the canine cannot be overstated, the management of a missing canine is challenging. This case report describes the treatment of an infra-occluded ankylosed maxillary canine in a patient with previously failed orthodontic treatment. Case description: A 20-year-old patient sought a second opinion for orthodontic treatment failure. The patient presented with an impacted, ankylosed, and severely infra-occluded right maxillary canine, as well as an iatrogenic clockwise cant of the maxillary occlusal plane and several root resorptions. The treatment corrected the cant of the occlusal plane while avoiding further root resorption, partially extracted the upper right canine, improved the quality and quantity of the soft tissue in the newly edentulous area, and provided a prosthetic rehabilitation using a lithium disilicate ceramic resin-bonded cantilever bridge. Conclusions: The use of a cantilevered bridge resulted in an aesthetically pleasing and minimally invasive rehabilitation. This technique is reversible, does not affect pulp vitality, and is a viable solution for rehabilitating the smiles of young patients. Clinical significance: The smile rehabilitation for an ankylosed maxillary canine, especially in the case of a previously failed orthodontic treatment, is an important clinical challenge. A minimally invasive long-term restoration with a cantilever bridge is a viable solution. Functional and aesthetically pleasant results can be achieved with a multidisciplinary approach.

Fracture strength of anterior cantilever resin-bonded fixed partial dentures fabricated from high translucency zirconia with different intaglio surface treatments

PURPOSE

To compare the fracture resistance and failure modes of anterior cantilever resin-bonded fixed partial dentures (RBFPDs) fabricated from high translucency zirconia with different intaglio surface treatments.

MATERIALS AND METHODS

Sound-extracted canines (N = 50) were randomly divided into five groups (n = 10) to be restored with high translucency zirconia RBFBDs of different intaglio surface treatments. The RBFPD was designed using exocad software and fabricated using a CAM milling machine. The RBFPDs were treated differently: abrasion with 50 µm alumina particles (Group 1); abrasion with 30 µm silica-coated alumina particles (Group 2); abrasion with silica-coated alumina particles (30 µm) and silane application (Group 3); abrasion with silica-coated alumina particles (30 µm) and 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) primer application (Group 4); abrasion with silica-coated alumina particles (30 µm) and silane, and 10-MDP primer application. All RBFPDs were cemented using dual-cured resin cement. The RBFPDs underwent 6000 thermal cycles with distilled water at 5/55°C for 2 min per cycle and then mechanical cyclic loading with 1200,000 cycles of 50 N at a 1.7 Hz frequency at an angle of 135° to the abutment's long axis. Then, RBFPDs were loaded to fracture using a universal testing machine at 1 mm/min. Maximum fracture forces and failure modes were recorded. Fractured specimens and uncemented specimens were examined using a scanning electron microscope. Data was analyzed using ANOVA and Games-Howell post hoc tests at p < 0.05.

RESULTS

Mean fracture load results showed a statistically significant difference between the research groups (p < 0.0001) and it ranged from 69.78 to 584 N. Group 4 exhibited the highest fracture load mean (p < 0.0001) which was significantly different from all other groups. Group 2 recorded a significantly higher fracture load mean than Group 3 (p = 0.029). Three modes of failure were observed: prosthesis debonding, prosthesis fracture, and abutment fracture.

CONCLUSIONS

Abrasion of zirconia surface with 30 µm silica-coated alumina particles and application of 10-MDP primer yielded the highest mean fracture loads of monolithic high translucency zirconia RBFPD. The mode of fracture of the RBFPDs was influenced by the type of surface treatments.

The cantilever contact-point resin bonded bridge; adhesion 2.0

AIM

When young patients are congenitally missing anterior teeth, different treatment modalities can be used to complement the dental arch. This article proposes a new treatment modality for the replacement of anterior teeth, the cantilever contact-point resin bonded bridge (CCP-RBB).

MATERIALS AND METHODS

In this proof of principle study, CCP-RBB's delivered by one operator were clinically assessed. Patients who were missing maxillary incisors and had suitable intra-oral conditions for a contact-point cantilever RBB were included. Three cases are presented to describe all adhesive steps. This proof of principle clinical study is presented with up to 60 months follow-up of the cantilever contact resin bonded bridges.

RESULTS

A total of 19 CCP-RBB's were evaluated after a mean period of 29.8 months. None of the restorations exhibited failure, carious lesions or fractures during the follow-up periods, demonstrating an absence of restoration debonding or the need for repair.

CONCLUSION

The new cantilever contact-point resin bonded bridge exhibited an excellent treatment modality without failure or debonding up to 5 years. More and extended duration in vivo studies are needed to evaluate this new treatment modality.

CLINICAL SIGNIFICANCE

In this proof of principle the new cantilever contact-point resin bonded bridge obtained excellent results up to 5 years of clinical follow-up.

Terminology focused on design and retention methods used for anterior resin-bonded fixed partial dentures in English literature: A scoping review

Purpose

Novel terms describing several designs of resin-bonded fixed partial dentures (RBFPDs) continue to appear. Indeed, a variety of terms are used in the English scientific literature The use of a standard terminology is important for a fair and efficient understanding. This study aimed to investigate if the terminology used to describe designs and retention methods for anterior RBFPDs is standard.

Methods

An electronic search in the English literature was conducted in PubMed/Medline to identify all publications reporting RBFPDs in the anterior region until August 2022. This search was completed by hand searching. Terms indicating different designs of RBFPDs were listed and then classified. Percentages of their use were calculated to determine the commonly used terms. Analysis of the use of these terms was performed based on the standards determined by the latest edition of the Glossary of Prosthodontic Terms (GPT). The impacts of the MeSH Thesaurus and GPT on the nomenclature used for RBFPDs was assessed.

Results

A total of 125 articles were eligible for this review. In the retained articles, 86 terms were found. Among them, thirty-nine terms were classified into three groups. Only six terms were defined in the latest edition of GPT (GPT-9). Several classified terms that are commonly used were not identified in the GPT-9. Conversely to the GPT-9 which impact was insignificant, the MeSH Thesaurus had an important impact on the nomenclature used for RBFPDs.

Conclusion

The terminology used to describe designs and retention methods for anterior RBFPDs was non-standard. The GPT-9, constituting an important reference, defined a limited number of terms related to RBFPDs and had no significant impact on the standardization of the terminology used for RBFPDs. Efforts should therefore be continued to standardize the terminology. A specialized mini-glossary grouping and defining all the terms found in this study will helpful in clarifying the terminology used for the anterior RBFPDs.

Biomechanical behavior of posterior metal-free cantilever fixed dental prostheses: effect of material and retainer design

OBJECTIVE

To study the fracture resistance and stress distribution pattern of translucent zirconia and fiber-reinforced composite cantilever resin-bonded fixed dental prostheses (RPFDPs) with two retainer designs.

MATERIALS AND METHODS

Forty human mandibular molars were divided into two groups according to the retainer design. The restorations included a premolar pontic and 2 retainer designs: (D1) inlay ring retainer and (D2) lingual coverage retainer. Each main group was then divided according to the material used (n = 10): zirconia (Z) or fiber-reinforced composite (FRC) (F). Restorations were cemented using dual polymerizing adhesive luting resin. All specimens were thermo-cycled (5-55 °C for 10,000 cycles), then subjected to dynamic loading (50 N, 240,000, and 1.6 Hz) and fracture resistance test. The finite element analysis includes the two models of retainer designs used in the in vitro test. Modified von Mises stress values on enamel, dentin, luting resin, and restorations were examined when the restorations failed.

RESULTS

A significantly higher failure load was recorded for zirconia groups (505.00 ± 61.50 and 548.00 ± 75.63 N for D1Z and D2Z, respectively) than for FRC groups (345.00 ± 42.33 and 375.10 ± 53.62 N for D1F and D2F, respectively) (P = 0.001). With regard to failure mode, D2 showed a more favorable failure pattern than D1. Model D2 resulted in lower stresses in tooth structure than model D1, and zirconia transmitted more stresses to the tooth structure than FRC.

CONCLUSIONS

The lingual coverage retainer (D2) enhanced the biomechanical performance of the restoration/tooth complex. Considering the failure mode and tooth stress, FRC is a promising treatment option when constructing a cantilever RPFDP.

CLINICAL RELEVANCE

Dentists should be aware of the biomechanical behavior during the selection of the material and for the replacement of a single missing mandibular premolar tooth with minimally invasive RBFDP.

Bonding Performance of Surface-Treated Zirconia Cantilevered Resin-Bonded Fixed Dental Prostheses: In Vitro Evaluation and Finite Element Analysis

Debonding of zirconia cantilevered resin-bonded fixed dental prostheses (RBFDPs) remains the main treatment complication, therefore, the present in vitro study aimed to evaluate the effect of different surface pretreatments on the bonding of zirconia RBFDPs. Eighty milled zirconia maxillary central incisors, with complementary zirconia cantilevered RBFDPs, were randomly subjected to four different surface pretreatments (n = 20): as-machined (AM); airborne-particle abraded (APA); coated with nanostructured alumina coating (NAC); incisor air-abraded and RBFDP coated (NAC_APA). After bonding, half of each group (n = 10) was stored in deionized water (150 days/37 °C), thermocycled (37,500 cycles, 5-55 °C), and cyclically loaded (50 N/1.2 × 10⁶). Load-bearing capacity (LBC) was determined using a quasi-static test. Additionally, finite element analysis (FEA) and fractography were performed. t-test and one-way ANOVA were used for statistical-analysis. Before aging, the NAC group provided superior LBC to other groups (p < 0.05). After aging, the AM specimens debonded spontaneously, while other groups exhibited comparable LBC (p ˃ 0.05). The FEA results correlated with the in vitro experiment and fractography, showing highly stressed areas in the bonding interface, cement layer, and in RBFDP's retainer wing and connector. The NAC RBFDPs exhibited comparable long-term bonding performance to APA and should be regarded as a zirconia pretreatment alternative to APA.

The Effect of Surface Treatments on Zirconia Bond Strength and Durability

To evaluate the effects of airborne particle abrasion (APA) combined with MDP-containing resin cement, a glass-ceramic spray deposition (GCSD) method on the shear bond strengths (SBSs) and durability of 3 mol% yttrium oxide-stabilized zirconia ceramic (3Y-TZP) compared with lithium disilicate glass ceramics (LDGC). 3Y-TZP disks were randomly treated as follows: for Group APA+MDP, 3Y-TZP was abrased using 50 μm Al₂O₃ particles under 0.1 Mpa and bonded with MDP-containing resin cement; for Group GCSD, 3Y-TZP was treated with the GCSD method, etched by 5% HF for 90 s, silanized and bonded with resin cement without MDP. Group LDGC was bonded as the Group GCSD. X-ray diffraction (XRD), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and energy dispersive X-ray detector (EDX) were used to analyze the surface chemical and micro-morphological changes of the ceramics before bonding. The bonded ceramic specimens were randomly divided into subgroups, and the SBSs were determined before and after 10,000 thermocycling. The SBSs were analyzed with a one-way ANOVA analysis. Failure modes were determined with optical microscopy and SEM. The XRD, ATR-FTIR and XPS results identified the formation of lithium disilicate and zirconium silicate on 3Y-TZP after GCSD. The SEM micrographs revealed that 3Y-TZP surfaces were roughened by APA, while 3Y-TZP with GCSD and LDGC surfaces could be etched by HF to be porous. The APA treatment combined with MDP-containing resin cement produced the high immediate zirconia shear bond strengths (SBSs: 37.41 ± 13.51 Mpa) that was similar to the SBSs of the LDGC (34.87 ± 11.02 Mpa, p > 0.05), but, after thermocycling, the former dramatically decreased (24.00 ± 6.86 Mpa, maximum reduction by 35.85%) and the latter exhibited the highest SBSs (30.72 ± 7.97 Mpa, minimum reduction by 11.9%). The 3Y-TZP with GCSD treatment displayed the lower zirconia SBSs before thermocycling (27.03 ± 9.76 Mpa, p < 0.05), but it was similar to the 3Y-TZP treated with APA and MDP containing resin cement after thermocycling (21.84 ± 7.03 vs. 24.00 ± 6.86 Mpa, p > 0.05). The APA combined with MDP-containing resin cement could achieve the high immediate zirconia SBSs of those of the LDGC, but it decreased significantly after thermocycling. The GCSD technique could yield the immediate zirconia SBSs similar to those of LDGC before thermocycling, and long-term zirconia SBSs were similar to those of 3Y-TZP treated with APA followed by MDP-containing resin cement after thermocycling. Hence, the GCSD technique could enrich zirconia surface treatments and is an alternative to zirconia surface pretreatment for 3Y-TZP bond durability.

CAD/CAM single-retainer monolithic zirconia ceramic resin-bonded fixed partial dentures bonded with two different resin cements: Up to 40 months clinical results of a randomized-controlled pilot study

PURPOSE

This pilot study was part of a larger study planned for the future which aimed to compare the clinical success of two different resin cements used in the cementation of CAD/CAM single-retainer monolithic zirconia ceramic resin-bonded fixed dentures (RBFPDs).

METHODS

Twenty-four RBFPDs were fabricated with monolithic zirconia (Katana™ Zirconia HT, Kuraray Noritake Dental Inc, Tokyo, Japan). Panavia F2.0 (PF2.0; n = 12) and Panavia V5 (PV5; n = 12) were used for cementation. The survival period was defined as the time when the restoration was placed in the mouth and lasted until an irreparable damage occurred. The repairable failures were identified as relative and irreparable failures were identified as absolute failure. The survival rate of the RBFPDs was determined by the Kaplan-Meier estimator. Statistical significance was set at p < 0.05.

RESULTS

The mean observation times of the PF2.0 group and the PV5 group were 40.45 ± 6.15 months and 40.18 ± 6.41 months, respectively. Four failures occurred in the PF2.0 group. No failure was observed in the PV5 group. The curves of survival rate (PF2.0 = 80%, PV5 = 100%) showed no statistically significant difference (p = 0.031), although success rate (PF2.0 = 66.7%, PV5 = 100%) showed statistically significant difference (p = 0.317).

CONCLUSION

Up to 40 months mean follow-up period, performance of RBFPDs bonded with PV5 was better than with PF2.0.

CLINICAL SIGNIFICANCE

For clinicians, it is a matter of hesitation to apply single-retainer RBFPDs. This study contains results of 40 months (minimum 32, maximum 50.47 months) clinical follow-ups of single-retainer RBFPDs. These results will enlighten clinicians about the clinical success of the resin cement type for single-retainer monolithic zirconia ceramic RBFPDs.

Preliminary Study on the Optimization of Femtosecond Laser Treatment on the Surface Morphology of Lithium Disilicate Glass-Ceramics and Highly Translucent Zirconia Ceramics

All-ceramic restorations have become increasingly popular in dentistry. Toward ensuring that these restorations adhere to the tooth structure, this study determines the optimal femtosecond laser (FL) treatment parameters for lithium disilicate glass-ceramics and highly translucent zirconia ceramics with respect to surface morphology. For both the ceramics, the following surface conditions were investigated: (1) as-sintered; (2) Al₂O₃ sandblasted; (3) FL treatment (dot pattern with line distances of 14, 20, and 40 µm); (4) FL treatment (crossed-line pattern with a line distance of 20 and 40 µm). Surface roughness parameters were estimated using a 3D confocal laser microscope; microstructures were analyzed using a scanning electron microscope. Peak fluence (F_peak) values of 4 and 8 J/cm² and irradiation numbers (N) of 20 and 10 shots were selected to create dot patterns in highly translucent zirconia and lithium disilicate glass-ceramics, respectively. Furthermore, F_peak = 8 J/cm² and N = 20 shots were chosen to obtain crossed-line patterns in both ceramics. Our results show that lithium disilicate glass-ceramics and highly translucent zirconia exhibit a similar surface morphology under each of the surface treatment conditions. Therefore, FL irradiation of dot or crossed-line patterns (at a distance of 20 and 40 µm) are potential candidates for future investigations.

Survival Rates of Anterior-Region Resin-Bonded Fixed Dental Prostheses: An Integrative Review

This study aimed to review clinical publications involving anterior-region resin-bonded fixed partial dentures to evaluate their survival rates vis-à-vis their materials and design. An electronic search was conducted using PubMed/MEDLINE to identify articles that reported on the longevity of anterior resin-bonded fixed dental prostheses published between 2000 and 2020. Only primary clinical studies that involved a follow-up after at least 3 years were included in this review. A statistical analysis was performed to evaluate resin-bonded fixed dental prostheses’ survival rates in relation to their materials and design. This review ultimately included 23 clinical publications, comprising prospective studies, retrospective studies, and randomized controlled trials. Its statistical analysis estimated the studied prostheses’ 5-year survival rate at 86.2% for metal-framed prostheses, 87.9% for zirconia prostheses, 93.3% for alumina prostheses, 100% for glass or ceramic prostheses, and 81.7% for fiber-reinforced composite restorations. Failure rates did not significantly differ between the different material groups or between the single- and double-retainer groups. Resin-bonded fixed dental prostheses present excellent 5-year clinical longevity in the anterior sector and a favorable benefit/risk/cost ratio. Currently, no consensus has been established on an ideal material for these restorations. Cantilever design tends to limit constraints on the prostheses’ retainers and, thus, increases their survival time. All-ceramic cantilever fixed partial dentures can be considered as a definitive therapy, given their high success and survival rates. They are an optimal solution for adolescents or young adults facing potentially continuous growth.