Next Article in Journal
From Molars to Milestones: Predicting Growth Spurts via AI and Panoramic Imaging
Previous Article in Journal
A Hybrid Workflow for Auricular Epithesis: Proof of Concept Integrating Mold Design and the Virtual Patient
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Prosthesis
Volume 7
Issue 5
10.3390/prosthesis7050115
prosthesis-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Investigation of Connector Parameters for Fracture Strength of Zirconia and Lithium Disilicate Resin-Bonded Fixed Dental Prosthesis

by
Siti Mariam Ab Ghani
1,
Mas Linda Mohd Osman
1,
Hung-Chih Chang
2,
Amir Radzi Ab Ghani
3 and
Tong Wah Lim
4,*
1
Centre of Restorative Dentistry Studies, Faculty of Dentistry, Universiti Teknologi MARA, Sungai Buloh 47000, Selangor, Malaysia
2
Department of Biomedical Engineering, Hungkuang University, Taichung City 433304, Taiwan
3
College of Engineering, Universiti Teknologi MARA, Shah Alam 40450, Selangor, Malaysia
4
Division of Restorative Dental Sciences, Faculty of Dentistry, The University of Hong Kong, Hong Kong SAR, China
*
Author to whom correspondence should be addressed.
Prosthesis 2025, 7(5), 115; https://doi.org/10.3390/prosthesis7050115
Submission received: 20 June 2025 / Revised: 10 August 2025 / Accepted: 2 September 2025 / Published: 10 September 2025
(This article belongs to the Section Prosthodontics)
Browse Figures
Versions Notes

Abstract

Purpose: The study aimed to assess and compare the fracture toughness of resin-bonded fixed dental prosthesis (RBFDP) of different ceramic materials and connector parameters. Methods: Twenty extracted human incisal teeth were utilized as abutments for the RBFDP. Zirconia (Zir) and lithium disilicate (LD) were manufactured in the form of anterior cantilever RBFDPs (n = 10 per group). Each material was tested using two connector designs, with the following dimensions for height (h), base (b), and width (w): 5 (h) × 4 (b) × 1 (w) mm (n = 5), and 4 (h) × 2 (b) × 1 (w) mm (n = 5). Prostheses were computer-aided design and computer-aided manufacturing (CAD/CAM) fabricated from Zir (IPS e.max ZIRCAD prime) and LD (IPS e.max CAD). Surface pretreatment of the prosthesis was completed prior to cementation with a dual-cured resin cement (Rely-X Ultimate). The combined teeth and prostheses were subjected to thermocycling before load-to-fracture testing at 45-degrees in the center of the pontic using a universal testing machine (Shimadzu Universal Testing Machine). The types of fracture failures were observed and classified as either favorable (non-catastrophic/repairable) or unfavorable (catastrophic/non-repairable) when viewed under an electron microscope. Results: The highest fracture toughness was observed in 5 (h) × 4 (b) × 1 (w) mm for Zir, reaching 269 ± 27 N, and LD, reaching 180 ± 83 N. The lowest values were found in 4 (h) × 2 (b) × 1 (w) mm for Zir at 237 ± 52 N and LD at 116 ± 25 N. Two-way ANOVA showed the fracture strength for dimension 5 (h) × 4 (b) × 1 (w) mm was significantly higher compared to dimension 4 (h) × 2 (b) × 1 (w) mm after adjusting for the type of material (p = 0.02). One Zir sample, measuring 5 (h) × 4 (b) × 1 (w) mm, exhibited tooth fracture under applied load. Meanwhile, two LD samples of the same dimensions became decemented under load. Conclusions: RBFDPs made from Zir exhibited a pattern of higher load-to-fracture values compared to LD for all dimensions; however, this was not statistically significant. The connector parameter has a more significant influence compared to the material used to fabricate an RBFDP in the anterior region.

1. Introduction

Resin-bonded fixed dental prosthesis (RBFDP) is a highly successful and minimally invasive treatment method for replacing anterior and posterior missing teeth [1,2,3]. Traditionally, this treatment option delivered high patient satisfaction, demonstrated good longevity in the short to medium term, and had low complication rates, which mainly pertained to the metal retainer [4,5,6,7,8,9]. However, the long-term success of this treatment option was found to be limited [10,11]. Therefore, based on the existing literature connector design and material type are the two main factors affecting the clinical performance of anterior cantilever RBFDPs, and these factors require further investigation.
The connector is defined as the area that connects the pontic to the retainer wing in the prostheses. To ensure the structural integrity and rigidity of fixed partial dentures (FPDs), it is generally advantageous to maximize both the height and width of connectors. However, in clinical settings, the height and width of the connector are often restricted by the size of the abutment tooth and the embrasure space required for daily oral hygiene. Variations in tooth dimensions among patients, particularly across different genders and ethnicities can influence these values [12]. Current literature indicates that both clinical and in vitro fracture resistance of FPDs are affected by the size, shape, length, and placement of the connectors [13]. The minimum connector dimension must be sufficient to withstand the occlusal loads during function and to manage the stress concentrated by the connector design [14]. It can be postulated that as in the conventional FPDs, the prosthesis design and its geometric features determine the maximum stress the prostheses can endure and the probability of failure [14]. Several studies have recommended connector heights of 3 to 4 mm [15,16,17], and stress reduction was found with rounded edges and small interdental separation spaces [16] which supports the idea that shape influences the structural integrity. Insights from connector dimensions in FDPs should inform the design of RBFDPs. In particular, many clinicians have adopted the cantilevered RBFDP design of single retainer and connector, which has consistently demonstrated high survival rates and favorable clinical outcomes [18,19].
Additional factor influencing the structural integrity of RBFDPs is attributed to the type of material used in their fabrication. Over time, the design of RBFPDs has progressed from traditional metal–ceramic constructions to all-ceramic alternatives, aligning with the increasing demand for metal-free restorations that provide superior aesthetics, particularly in the anterior segment [2,3]. In the past, several all-ceramic materials have been investigated for RBFDPs, including glass-infiltrated high-strength ceramic core (In Ceram) [20,21,22,23], zirconia (Zir) [24,25,26,27,28,29,30,31], and lithium disilicate (LD) [29,32,33]. The longevity of all-ceramic RBFDPs, particularly in the posterior region, remains uncertain as their predominant use has been for the replacement of anterior teeth [10,34,35]. Particularly, studies about the longevity of posterior Zir RBFPDs remain limited [36,37]. With advancements in ceramic material strength and optical properties, a newer generation of Zir and LD have become increasingly popular for anterior RBFDPs due to the combination of mechanical durability and aesthetic appeal. Both materials have demonstrated adequate strength and favorable aesthetic properties [3]. Furthermore, when appropriate bonding protocols are followed for each material they exhibit high bond strengths [32]. For anterior all-ceramic RBFDPs, patient selection and adherence to strict ceramic bonding protocols have been widely explored in laboratory and clinical research to optimize treatment outcomes [38], but the connector dimension of all-ceramic RBFPDs remains varied and requires further investigation.
Although numerous studies have focused on the framework design of cantilever anterior all-ceramic RBFDPs and have investigated various materials including Zir and LD, there is still limited assessment of connector configurations. In cantilever RBFDPs with a single retainer, the pontic moves in unison with the abutment tooth, thereby reducing shear and torque forces that could lead to debonding [1,2]. A previous in vitro study has shown that maximum stress typically occurs at the connector area, potentially leading to failure, which underscores the importance of continued investigation using load-to-fracture tests [39]. Therefore, the present in vitro study aimed to examine the effects of connector dimensions and material types on the fracture resistance of anterior Zir and LD RBFDPs using a load-to-fracture test. The null hypothesis was that there would be no significant difference in fracture resistance across various connector dimensions and ceramic materials used for fabricating cantilevered RBFDPs. Additionally, this study sought to analyze the modes of failures associated with each configuration.

2. Materials and Methods

This study was granted an exemption from ethics application review by the Ethics Committee of Universiti Teknologi MARA (UiTM), Malaysia [600-TNCP(5/1/6)]. The cross-sectional view of the connector area for the cantilevered RBFDP which connects the pontic and retainer and shows the height (h), base (b), and width (w), is illustrated in Figure 1. The connector parameters that exhibited the highest [5 (h) × 4 (b) × 1 (w) mm] and lowest [4 (h) × 2 (b) × 1 (w) mm] maximum equivalent stress (Von Mises stress) from a previous finite element analysis (FEA) [39] were selected for this in vitro load-to-fracture test (Table 1). These dimensions were then fabricated using either Zir or LD, resulting in two material groups with each having two different connector parameters.

2.1. In Vitro Experiment (Load-to-Fracture Test)

2.1.1. Sample Size Calculation

A calculation of the sample size was made based on the findings of a study [40] on the connector design of all-ceramic FDPs using Power and Sample Size Calculation (PS) version 3.1.6. Sample size was based on a statistical power of 80% to detect a difference between means with a significance level of 0.05 (two-tailed) using an independent t-test. An effect size of 2.66 was calculated, and a sample size of five per group was selected. Extracted teeth were collected from the outpatient clinic in the Faculty of Dentistry, UiTM. Teeth chosen adhered to the following inclusion and exclusion criteria with almost similar mesio-distal width (Table 2). Samples (n = 20) were randomized into two groups as in Table 1.
The coronal portions of the teeth were scanned using a 3-Shape E series Lab Scanner E1 Dental System (Copenhagen, Denmark). The size of the palatal surface for each tooth was measured to determine the bonding surface. Figure 2a shows a scanned palatal surface of the maxillary central incisor. The tooth was outlined in green color and complete 1 mm2 boxes were marked in purple, whereas the partially filled boxes were marked in red [Figure 2b]. The surface area was calculated using a mathematical formula and plotted using IBM SPSS Statistics for Windows version 29.0 (IBM Corp., Armonk, NY, USA) with the mean and standard deviation values to ensure standardize bonding surfaces for the retainer. A tooth with a bonding surface within a similar range was selected as the abutment tooth.

2.1.2. Sample Preparation

The teeth were embedded in a resin block and prepared using the same protocol as in Osman et al. [39]. Preparation of the palatal surface of the central incisor included a narrow cervical chamfer margin, a proximal box on the distal measuring 1.5 × 1.0 × 0.5 mm, and a pinhole on the cingulum with a round diamond bur (0.5 mm in depth, 1.0 mm in diameter). The slight removal of the enamel prisms on the palatal was performed using a football-shaped diamond bur. All sharp edges and surfaces were smoothened using a white stone, and all preparations were placed within enamel. To standardize the preparation, the teeth were first marked with a pencil and prepared by a prosthodontic resident (M.L.M.O). All preparations were examined by an experienced prosthodontist (S.M.A.G.).
All the preparations were scanned using a 3-Shape Dental System (Copenhagen, Denmark). The teeth were dried with a triplex syringe prior to scanning and returned to room temperature in sodium chloride 0.9% (RinsCap NS, ANS Medicare, Kota Bharu, Malaysia) after scanning was completed. All files were saved in STL and PLY format. Computer-aided design and computer-aided manufacturing (CAD/CAM) was used to design and fabricate the RBFPD. Files were imported into a digital design software (ExoCAD GmbH, Darmstadt, Germany) and prostheses were designed accordingly. Parameters such as the cement space were determined at 0.05 mm. Thickness of the retainer was designed at 0.5 mm. The connectors were designed based on the investigated parameters. Pontic dimensions were adjusted for all the specimens to match tooth design. Mesio-distal measurements of the pontic were set at 7 mm [12]. A modified ridge-lap design was used for the pontic. For LD (IPS e.max CAD), the milling process was conducted using an Amann Girrbach Ceramill Motion 2 (Amann Girrbach AG, Koblach, Austria), whereas for Zir (IPS e.max ZIRCAD prime) the milling process was conducted using an Ivoclar Digital PrograMill PM7 (Ivoclar Vivadent AG, Schaan, Liechtenstein). After milling, the prostheses were placed in the furnace for sintering. Each restoration underwent glaze firing according to the manufacturer’s instruction. The firing parameters are stated in Table 3.

2.1.3. Cementation of the Prostheses

The surface pretreatment and cementation of Zir RBFDPs were performed according to the “APC” bonding concept, which stands for “air abrasion, zirconia primer, and adhesive composite resin” (Figure 3) [41]. Sandblasting was conducted at a distance of 10 mm for 10 s, with an angle between 75 and 90 degrees. For this process, 50 µm aluminum oxide powder (Cobra 50 μm, Renfert, Hilzingen, Germany) was used at a pressure of 1.5 bar. The retainer bonding surface was colored with a felt-tip pen to ensure that the entire bonding area was adequately abraded. After air abrasion, the prosthesis was placed in a plastic sachet with distilled water and cleaned in an ultrasonic cleaner to remove any residues and small particles. The prosthesis was then dried, and an adhesive primer containing phosphate monomers (Single Bond Universal, 3M ESPE, St. Paul, MN, USA) was applied. The surface pretreatment and cementation of LD RBFDPs are illustrated in Figure 4. The fitting surface of the prosthesis was treated with IPS ceramic etching gel (Ivoclar Vivadent, Schaan, Liechtenstein), containing 5% hydrofluoric acid, for 20 s using a micro-brush. The acid was then washed off and the surface dried with a three-way syringe. Silane coupling agent (Ultradent, South Jordan, UT, USA) was applied to the fitting surface and allowed to dry. Prior to cementation, the palatal surfaces of the samples in both groups were etched with 37% phosphoric acid (Eco-etch, Ivoclar, Schaan, Liechtenstein), followed by being washed and dried using a triplex syringe. Single-bond universal adhesive (Scotchbond, 3M ESPE, St. Paul, MN, USA) was applied onto the etched surface. Both groups of prostheses were then cemented using a dual-cured resin cement (Rely-X Ultimate Clicker, 3M ESPE, St. Paul, MN, USA). Excess cement was removed and super floss was used to ensure no excess is present in the connector area, with light curing for 20 s per surface.
The entire process, from sample preparation to milling the prosthesis and completing cementation, is illustrated in Figure 5. All samples were then kept at 37 °C temperature and in sodium chloride 0.9% (RinsCap NS, ANS Medicare, Kota Bahru, Malaysia) for 24 h after cementation. Samples were then grouped in a gauze pack to undergo thermocycling (Automatic Thermocyclic Dipping Machine, Zecttron, Kuala Lumpur, Malaysia). Thermocycling allowed aging so the samples would better mimic the conditions in the mouth. Temperature of the dipping tanks were set at 55 °C and 5 °C in distilled water. A cycle of 5000 with a dipping time of 15 s and a transfer time of 5 s was applied to mimic 6 months [42,43]. After the completion of thermocycling, samples were placed in room temperature saline to prepare for the next stage of testing.

2.1.4. Load-to-Fracture Test

A pilot study was conducted prior to testing on the main study samples. A simulation of loading direction and force was tested on a prepared model, as in the FEA study [39], with a cemented RBFDP milled in LD. After confirmation of the method from the pilot study, the main study using (n = 5) samples was conducted. A holder was designed to standardize the angulation of the tooth at a 45-degree angle (Figure 6). The holder was designed to be adjustable to allow movement of the resin sample to the left and right. The placement was set using adjustable screws. Since the setting of the tooth was made with its long axis perpendicular to the base, the sample angulation with the holder would ensure standardization of the loading direction. A universal testing machine (Shimadzu AGS-X, Shimadzu Corp., Kyoto, Japan) was used for the in vitro testing of all samples. The sample was placed in the holder of the universal testing machine with the load applied to the center of the palatal surface of the pontic (Figure 7). Load was applied with a 1 mm stainless steel indenter perpendicular to the occlusal surface of the pontic at a speed of 0.5 mm/min [44]. The sample setting was confirmed prior to the load testing. The angulation of the tooth was checked against a protractor to confirm the angulation of 45-degree angle.
After loading, all prostheses were examined using a stereo microscope (Olympus SZX7, Olympus Corp, Tokyo, Japan) to analyze for cracks or fracture interfaces at a magnification of 40× by a single observer (M.L.M.O). Intra-examiner reliability was confirmed through examination on different dates to ensure the precision of a single assessor. The findings were also verified by a senior researcher in materials sciences (S.M.A.G). Failure mode definitions are as stated in Table 4 [44].

2.1.5. Statistical Analysis

All data was tabulated and analyzed using a statistical software program (IBM SPSS Statistics version 29, SPSS, Chicago, IL, USA). The normality of the data was confirmed. A two-way ANOVA was conducted to compare the effect of dimension on force in Zir and LD. The level of statistical significance was determined at 0.05. Pairwise comparisons were performed using the Bonferroni post hoc test when the two-way ANOVA indicated significance (α = 0.05).

3. Results

3.1. Fracture Strength

For the materials, the mean ± SD values were 136.6 ± 77.3 N for LD and 209.6 ± 39.7 N for Zir. With regard to the connector parameters, the 4 (h) × 2 (b) × 1 (w) mm group showed a mean value of 120.4 ± 113.7 N, while the 5 (h) × 4 (b) × 1 (w) mm group had a mean value of 224.7 ± 75.1 N. The highest fracture toughness was observed in the 5 (h) × 4 (b) × 1 (w) mm group, with Zir reaching 269 ± 27 N and LD reaching 180 ± 83 N. The lowest values were found in the 4 (h) × 2 (b) × 1 (w) mm group, with Zir at 237 ± 52 N and LD at 116 ± 25 N.

3.2. Comparison of Load-to-Fracture Strengths Between Different Connector Parameters and Different Materials

The mean values for different connector parameters and different materials were compared, and it was found that the values for Zir were higher than those for LD. A two-way ANOVA was conducted to investigate the effects of material (LD vs. Zir) and connector dimensions [4 (h) × 2 (b) × 1 (w) mm vs. 5 (h) × 4 (b) × 1 (w) mm] on the measured values (Table 5). The fracture strength for the dimension 5 (h) × 4 (b) × 1 (w) mm was significantly higher compared to the dimension 4 (h) × 2 (b) × 1 (w) mm after adjusting for the type of material. The adjusted mean fracture strength was 224.71 N and 120.48 N, respectively, with an adjusted mean difference of 104.23 (95% CI: 190.23, 18.23). There was no significant difference in mean fracture strength between the type of material after adjusting for dimension. There were no significant interactions between the study factors or effects.

3.3. Failure Type

Each sample was observed for failure type after the in vitro experiment testing (Figure 8). Of the 20 samples tested, only the 5 (h) × 4 (b) × 1 (w) mm in Zir demonstrated a fracture in the tooth when under load, which was classified as an unfavorable failure mode. Two LD samples measuring 5 (h) × 4 (b) × 1 (w) mm were decemented under load. The remaining samples fractured in the connector areas of the RBFDPs, with the retainers still cemented while the pontics were separated (Type I failure) (Figure 9a). Figure 9b shows an unfavorable failure of a sample, in which the abutment tooth fractured (Type II failure).

4. Discussion

This in vitro study tested the smallest connector dimensions of the strongest cantilevered RBFDPs made from all-ceramic materials in the finite element study [39] as a means of confirming their fracture strength. The fracture strength for connectors with the dimensions of 5 (h) × 4 (b) × 1 (w) mm was significantly higher than that of those with the dimensions of 4 (h) × 2 (b) × 1 (w) mm, after adjusting for material type. Therefore, the null hypothesis was rejected. In addition, the overall mean value of the fracture strength for Zir was higher than that of LD. This is supported by previous literature, which showed that when compared Zir has a higher fracture strength than LD [40,45].
When comparing the two connector dimensions 4 (h) × 2 (b) × 1 (w) mm and 5 (h) × 4 (b) × 1 (w) mm, regardless of the material used the latter showed a higher load-to-fracture value. The 5 (h) × 4 (b) × 1 (w) mm connector (volume = 10.98 mm3) had a higher volume than the 4 (h) × 2 (b) × 1 (w) mm connector (volume = 3.35 mm3), indicating that connector volume influences mean fracture strength, with greater volume being associated with higher fracture strength [46]. This finding is also supported by Murase et al. [47] and Hafezeqoran et al. [48]. The smallest connector dimension of LD tested in this study was lower than the recommended minimum connector dimension for single-retainer glass ceramic RBFDPs, which is 16 mm2 [49]. Despite this, the smallest connector volumes fabricated from LD and Zir both yielded fracture strength values exceeding or comparable to the occlusal force in the anterior region, approximately 150 N [50]. This suggests that such a connector design may be indicated for clinical cases involving short abutment teeth. Notably, if fracture strength is the main concern, Zir would be the material of choice over LD. In addition, the load-to-fracture values for connectors with identical dimensions and shapes showed that Zir demonstrated higher load-to-fracture values than LD. This superior performance can be attributed to Zir’s higher Young’s modulus compared to LD [51].
The failure modes observed in this study differed between materials. In the LD group, failures included debonding in two samples. This may be related to the highly technique-sensitive surface treatment protocols required for LD, with the use of different brands of pretreatment materials potentially contributing to the observed failures. In contrast, in the Zir group fracture of the abutment tooth was observed in one sample with larger connector dimensions. This suggests that the high rigidity of the Zir prosthesis and promising Zir-to-enamel bond strength can withstand occlusal loads [36,37,38], but may transfer excessive stress to the abutment tooth leading to catastrophic failure in a clinical setting. In contrast, both materials with smaller connector dimensions exhibited prosthesis fracture in all samples, indicating that reduced connector size compromises prosthesis rigidity [44]. Prosthesis fracture or debonding are considered favorable failure modes, as they are generally easier to manage clinically and allow for retreatment or the implementation of alternative treatments, such as implants, removable dentures, or conventional FPDs.
The differences observed in fracture strength values between this study and other in vitro experiments on RBFDPs may be attributed to variations in study design and testing methods. Several approaches are available for evaluating fracture resistance, including shear force application, dynamic loading, and load-to-fracture testing. In the load-to-fracture test, prostheses are subjected to mechanical loading to mimic occlusal forces from an opposing antagonist. Some studies also incorporated chewing simulation prior to loading to better replicate oral conditions; however, the forces generated during chewing were generally lower than those produced during biting, and their frequency varied depending on food type and individual differences [52]. The choice of loading method also depends on the specific tooth being tested. In this study, as in the FEA study by Osman et al., anterior prostheses were loaded at a 45-degree angle [39]. The direction of load application is crucial, as prostheses can withstand greater forces when subjected to a vertical (0-degree) load compared to a more horizontal direction [21]. The loading method used in this study is consistent with previous studies [20,22,23].
The limitations of this study include the use of a single loading direction and the short thermomechanical aging process. Testing only one loading path does not accurately simulate the multi-directional forces experienced during chewing in the oral environment. Furthermore, all samples underwent a 6-month artificial thermomechanical aging process, which is comparable to some studies [42,43], but shorter than others [21,44]. Therefore, future studies should consider employing a longer period of artificial aging. As stated by Kern et al., thermal cycling compromised the fracture strength of the RBFDPs [21]. Additionally, future studies should also consider utilizing dynamic masticatory forces to better simulate functional occlusal loading, incorporating scanning electron microscopy to further analyze the fractured surfaces of the prostheses, and conducting clinical studies of RBFDPs fabricated from all-ceramic materials, with attention to variations in clinical crown height and abutment tooth morphology.

5. Conclusions

The load-to-fracture values for zirconia were higher than those for lithium disilicate, with connector parameters being a key influencing factor. Therefore, when planning resin-bonded fixed partial dentures for the anterior region in clinical practice, a zirconia or lithium disilicate connector with the trapezoidal dimensions of 5 (height) × 4 (base) × 1 (width) mm should be recommended.

Author Contributions

Conceptualization, T.W.L. and S.M.A.G.; methodology, T.W.L., S.M.A.G., A.R.A.G., and M.L.M.O.; software, H.-C.C.; validation, H.-C.C.; formal analysis, S.M.A.G., T.W.L., H.-C.C., and A.R.A.G.; writing—original draft preparation, M.L.M.O.; writing—review and editing, S.M.A.G., T.W.L., A.R.A.G., and H.-C.C.; supervision, S.M.A.G., T.W.L., and A.R.A.G.; funding acquisition, M.L.M.O., T.W.L., and S.M.A.G. All authors have read and agreed to the published version of the manuscript.

Funding

This research is supported by Universiti Teknologi MARA DUCS grant, Ref 600-UiTMSEL (PI.5/4) (134/2022).

Institutional Review Board Statement

UiTM Research Ethics Committee acts in accordance with the ICH Good Clinical Practice Guidelines, Malaysian Good Clinical Practice Guidelines, and the Declaration of Helsinki. This study was exempted from ethics review (600-TNCP (5/1/6)) on the 30 September 2021.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available upon request from the corresponding author.

Acknowledgments

Krishanthini a/p R Jeyabalan from the Clinical Research Centre, Hospital Sultanah Aminah for statistical consultation.

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

References

  1. Gulati, J.S.; Tabiat-Pour, S.; Watkins, S.; Banerjee, A. Resin-bonded bridges–the problem or the solution? Part 1: Assessment and design. Dent. Update 2016, 43, 506–521. [Google Scholar] [CrossRef]
  2. Durey, K.A.; Nixon, P.J.; Robinson, S.; Chan, M.F.W.-Y. Resin bonded bridges: Techniques for success. Br. Dent. J. 2011, 211, 113–118. [Google Scholar] [CrossRef] [PubMed]
  3. Zlatarić, D.K.; Soldo, M. Considerations for conservative, all ceramic prosthodontic single tooth replacement in the anterior region: A systematic review. Dent. J. 2025, 13, 219. [Google Scholar] [CrossRef]
  4. Botelho, M.G.; Ma, X.; Cheung, G.J.K.; Law, R.K.S.; Tai, M.T.C.; Yu Hang Lam, W. Long-term clinical evaluation of 211 two-unit cantilevered resin-bonded fixed partial dentures. J. Dent. 2014, 42, 778–784. [Google Scholar] [CrossRef]
  5. Botelho, M.G.; Chan, A.W.; Leung, N.C.; Lam, W. Long-term evaluation of cantilevered versus fixed–fixed resin-bonded fixed partial dentures for missing maxillary incisors. J. Dent. 2016, 45, 59–66. [Google Scholar] [CrossRef][Green Version]
  6. Lim, T.W.; Idris, R.I.; Mahmud, M. Patient satisfaction following resin-bonded fixed dental prostheses cemented by using the Dahl concept. Clin. Exp. Dent. Res. 2023, 9, 1089–1095. [Google Scholar] [CrossRef]
  7. Idris, R.I.; Shoji, Y.; Lim, T.W. Occlusal force and occlusal contact reestablishment with resin-bonded fixed partial dental prostheses using the dahl concept: A clinical study. J. Prosthet. Dent. 2022, 127, 737–743. [Google Scholar] [CrossRef]
  8. Lim, T.W.; Ab Ghani, S.M.; Mahmud, M. Occlusal re-establishment and clinical complications of resin-bonded fixed partial dental prostheses cemented at an increased occlusal vertical dimension: A retrospective study. J. Prosthet. Dent. 2022, 127, 258–265. [Google Scholar] [CrossRef]
  9. Lim, T.W.; Ariff, T.F.T.M. Single tooth implant versus resin-bonded bridge: A study of patient’s satisfaction. Eur. J. Gen. Dent. 2020, 9, 90–95. [Google Scholar] [CrossRef]
  10. Kern, M. Fifteen-year survival of anterior all-ceramic cantilever resin-bonded fixed dental prostheses. J. Dent. 2017, 56, 133–135. [Google Scholar] [CrossRef] [PubMed]
  11. Botelho, M.G.; Lam, W.Y. A fixed movable resin-bonded fixed dental prosthesis—A 16 years clinical report. J. Prosthodont. Res. 2016, 60, 63–67. [Google Scholar] [CrossRef] [PubMed]
  12. Magne, P.; Gallucci, G.O.; Belser, U.C. Anatomic crown width/length ratios of unworn and worn maxillary teeth in white subjects. J. Prosthet. Dent. 2003, 89, 453–461. [Google Scholar] [CrossRef]
  13. Raigrodski, A.J.; Chiche, G.J. The safety and efficacy of anterior ceramic fixed partial dentures: A review of the literature. J. Prosthet. Dent. 2001, 86, 520–525. [Google Scholar] [CrossRef]
  14. Quinn, G.; Studart, A.; Hebert, C.; VerHoef, J.; Arola, D. Fatigue of zirconia and dental bridge geometry: Design implications. Dent. Mater. 2010, 26, 1133–1136. [Google Scholar] [CrossRef]
  15. Kamposiora, P.; Papavasiliou, G.; Bayne, S.C.; Felton, D.A. Stress concentration in all-ceramic posterior fixed partial dentures. Quintessence Int. 1996, 27, 701–706. [Google Scholar]
  16. Pospiech, P.; Rammelsberg, P.; Goldhofer, G.; Gernet, W. All-ceramic resin-bonded bridges A 3-dimensional finite-element analysis study. Eur. J. Oral Sci. 1996, 104, 390–395. [Google Scholar] [CrossRef]
  17. Sasse, M.; Kern, M. All-ceramic resin-bonded fixed dental prostheses: Treatment planning, clinical procedures, and outcome. Quintessence Int. 2014, 45, 291–297. [Google Scholar]
  18. Wei, Y.-R.; Wang, X.-D.; Zhang, Q.; Li, X.-X.; Blatz, M.B.; Jian, Y.-T.; Zhao, K. Clinical performance of anterior resin-bonded fixed dental prostheses with different framework designs: A systematic review and meta-analysis. J. Dent. 2016, 47, 1–7. [Google Scholar] [CrossRef] [PubMed]
  19. Alraheam, I.A.; Ngoc, N.C.; Wiesen, C.A.; Donovan, T.E. Five-year success rate of resin-bonded fixed partial dentures: A systematic review. J. Esthet. Restor. Dent. 2018, 31, 40–50. [Google Scholar] [CrossRef]
  20. Kern, M.; Douglas, W.H.; Fechtig, T.; Strub, J.R.; DeLong, R. Fracture strength of all-porcelain, resin bonded bridges after testing in an artificial oral environment. J. Dent. 1993, 21, 117–121. [Google Scholar] [CrossRef] [PubMed]
  21. Kern, M.; Fechtig, T.; Strub, J.R. Influence of water storage and thermal cycling on the fracture strength of all-porcelain, resin-bonded fixed partial dentures. J. Prosthet. Dent. 1994, 71, 251–256. [Google Scholar] [CrossRef]
  22. Koutayas, S.O.; Kern, M.; Ferraresso, F.; Strub, J.R. Influence of design and mode of loading on the fracture strength of all-ceramic resin-bonded fixed partial dentures: An in vitro study in a dual-axis chewing simulator. J. Prosthet. Dent. 2000, 83, 540–547. [Google Scholar] [CrossRef]
  23. Koutayas, S.O.; Kern, M.; Ferraresso, F.; Strub, J.R. Influence of framework design on fracture strength of mandibular anterior all-ceramic resin-bonded fixed partial dentures. Int. J. Prosthodont. 2002, 15, 223–229. [Google Scholar]
  24. Sillam, C.-E.; Cetik, S.; Ha, T.H.; Atash, R. Influence of the amount of tooth surface preparation on the shear bond strength of zirconia cantilever single-retainer resin-bonded fixed partial denture. J. Adv. Prosthodont. 2018, 10, 286–290. [Google Scholar] [CrossRef]
  25. Rosentritt, M.; Kolbeck, C.; Ries, S.; Gross, M.; Behr, M.; Handel, G. Zirconia resin-bonded fixed partial dentures in the anterior maxilla. Quintessence Int. 2008, 39, 313–319. [Google Scholar]
  26. Rosentritt, M.; Ries, S.; Kolbeck, C.; Westphal, M.; Richter, E.J.; Handel, G. Fracture characteristics of anterior resin-bonded zirconia-fixed partial dentures. Clin. Oral Investig. 2009, 13, 453–457. [Google Scholar] [CrossRef]
  27. Nemoto, R.; Nozaki, K.; Fukui, Y.; Yamashita, K.; Miura, H. Effect of framework design on the surface strain of zirconia fixed partial dentures. Dent. Mater. J. 2013, 32, 289–295. [Google Scholar] [CrossRef]
  28. Sterzenbach, G.; Tunjan, R.; Rosentritt, M.; Naumann, M. Increased tooth mobility because of loss of alveolar bone support: A hazard for zirconia two-unit cantilever resin-bonded FDPs in vitro? J. Biomed. Mater. Res. Part B Appl. Biomater. 2014, 102, 244–249. [Google Scholar] [CrossRef] [PubMed]
  29. Gresnigt, M.M.; Tirlet, G.; Bošnjak, M.; van der Made, S.; Attal, J.-P. Fracture strength of lithium disilicate cantilever resin bonded fixed dental prosthesis. J. Mech. Behav. Biomed. Mater. 2020, 103, 103615. [Google Scholar] [CrossRef] [PubMed]
  30. Kitani, J.; Komine, F.; Kusaba, K.; Nakase, D.; Ito, K.; Matsumura, H. Effect of firing procedures and layering thickness of porcelain on internal adaptation of zirconia cantilever resin-bonded fixed dental prostheses. J. Prosthodont. Res. 2022, 66, 333–338. [Google Scholar] [CrossRef] [PubMed]
  31. Noda, M.; Omori, S.; Nemoto, R.; Sukumoda, E.; Takita, M.; Foxton, R.; Nozaki, K.; Miura, H. Strain analysis of anterior resin-bonded fixed dental prostheses with different thicknesses of high translucent zirconia. J. Dent. Sci. 2021, 16, 628–635. [Google Scholar] [CrossRef]
  32. Di Fiore, A.; Stellini, E.; Savio, G.; Rosso, S.; Graiff, L.; Granata, S.; Monaco, C.; Meneghello, R. Assessment of the different types of failure on anterior cantilever resin-bonded fixed dental prostheses fabricated with three different materials: An in vitro study. Appl. Sci. 2020, 10, 4151. [Google Scholar] [CrossRef]
  33. Naguib, A.; Fahmy, N.; Hamdy, A.; Wahsh, M. Fracture resistance of different designs of a resin-bonded fixed dental prosthesis: An in vitro study. Int. J. Prosthodont. 2021, 34, 348–356. [Google Scholar] [CrossRef]
  34. Kern, M. Clinical long-term survival of two-retainer and single-retainer all-ceramic resin-bonded fixed partial dentures. Quintessence Int. 2005, 36, 141–147. [Google Scholar]
  35. Kern, M.; Sasse, M. Ten-year survival of anterior all-ceramic resin-bonded fixed dental prostheses. J. Adhes. Dent. 2011, 13, 407–410. [Google Scholar] [PubMed]
  36. Yazigi, C.; Kern, M. Clinical evaluation of zirconia cantilevered single-retainer resin-bonded fixed dental prostheses replacing missing canines and posterior teeth. J. Dent. 2022, 116, 103907. [Google Scholar] [CrossRef] [PubMed]
  37. Lam, W.Y.H.; Lim, T.W.; Yon, M.J.Y.; Chau, J.M.H.; Lai, G.C.H.; Wang, D.C.P.; Botelho, M.G. Posterior two-unit cantilevered zirconia resin-bonded fixed partial dentures: A 3-year prospective single-arm clinical trial. J. Dent. 2024, 18, 105140. [Google Scholar] [CrossRef] [PubMed]
  38. Tezulas, E.; Yildiz, C.; Evren, B.; Ozkan, Y. Clinical procedures, designs, and survival rates of all-ceramic resin-bonded fixed dental prostheses in the anterior region: A systematic review. J. Esthet. Restor. Dent. 2018, 30, 307–318. [Google Scholar] [CrossRef] [PubMed]
  39. Osman, M.L.M.; Lim, T.W.; Chang, H.-C.; Ab Ghani, A.R.; Tsoi, J.K.H.; Ab Ghani, S.M. Structural integrity of anterior ceramic resin-bonded fixed partial denture: A finite element analysis study. J. Funct. Biomater. 2023, 14, 108. [Google Scholar] [CrossRef]
  40. Plengsombut, K.; Brewer, J.D.; Monaco, E.A., Jr.; Davis, E.L. Effect of two connector designs on the fracture resistance of all-ceramic core materials for fixed dental prostheses. J. Prosthet. Dent. 2009, 101, 166–173. [Google Scholar] [CrossRef]
  41. Blatz, M.B.; Alvarez, M.; Sawyer, K.; Brindis, M. How to Bond Zirconia: The APC Concept. Compend. Contin. Educ. Dent. 2016, 37, 611–618. [Google Scholar]
  42. Jo, E.-H.; Huh, Y.-H.; Ko, K.-H.; Park, C.-J.; Cho, L.-R. Effect of liners and primers on tensile bond strength between zirconia and resin-based luting agent. J. Adv. Prosthodont. 2018, 10, 374–380. [Google Scholar] [CrossRef]
  43. Zhang, Y.; Yang, T.; Li, B.; Li, J. Surface modifications of zirconia with plasma pretreatment and polydopamine coating to enhance the bond strength and durability between zirconia and titanium. Dent. Mater. J. 2023, 42, 449–457. [Google Scholar] [CrossRef] [PubMed]
  44. Kasem, A.T.; Abo-Madina, M.; Tribst, J.P.M.; Al-Zordk, W. Cantilever resin-bonded fixed dental prosthesis to substitute a single premolar: Impact of retainer design and ceramic material after dynamic loading. J. Prosthodont. Res. 2023, 67, 595–602. [Google Scholar] [CrossRef]
  45. Elshiyab, S.H.; Nawafleh, N.; Öchsner, A.; George, R. Fracture resistance of implant-supported monolithic crowns cemented to zirconia hybrid-abutments: Zirconia-based crowns vs. lithium disilicate crowns. J. Adv. Prosthodont. 2018, 10, 65–72. [Google Scholar] [CrossRef] [PubMed]
  46. Hamza, T.A.; Attia, M.A.; El-Hossary, M.M.K.; Mosleh, I.E.; Shokry, T.E.; Wee, A.G. Flexural strength of small connector designs of zirconia-based partial fixed dental prostheses. J. Prosthet. Dent. 2016, 115, 224–229. [Google Scholar] [CrossRef]
  47. Murase, T.; Nomoto, S.; Sato, T.; Shinya, A.; Koshihara, T.; Yasuda, H. Effect of connector design on fracture resistance in all-ceramic fixed partial dentures for mandibular incisor region. Bull. Tokyo Dent. Coll. 2014, 55, 149–155. [Google Scholar] [CrossRef] [PubMed][Green Version]
  48. Hafezeqoran, A.; Koodaryan, R.; Hemmati, Y.; Akbarzadeh, A. Effect of connector size and design on the fracture resistance of monolithic zirconia fixed dental prosthesis. J. Dent. Res. Dent. Clin. Dent. Prospect. 2020, 14, 218–222. [Google Scholar] [CrossRef]
  49. Sailer, I.; Bonani, T.; Brodbeck, U.; Hammerle, C. Retrospective clinical study of single-retainer cantilever anterior and posterior glass-ceramic resin-bonded fixed dental prostheses at a mean follow-up of 6 years. Int. J. Prosthodont. 2013, 26, 443–450. [Google Scholar] [CrossRef]
  50. Roffie, J.; Lim, T.W.; Patar, M.N.; Abdullah, S.A.; Ghani, H.A. Wireless sensor network for a bite force recorder. J. Int. Dent. Med. Res. 2020, 13, 1592–1597. [Google Scholar]
  51. Schmidt, M.B.; Rosentritt, M.; Hahnel, S.; Wertz, M.; Hoelzig, H.; Kloess, G.; Koenig, A. Fracture behavior of cantilever fixed dental prostheses fabricated from different zirconia generations. Quintessence Int. 2022, 53, 414–422. [Google Scholar] [PubMed]
  52. De Boever, J.A.; McCall, W.D., Jr.; Holden, S.; Ash, M.M., Jr. Functional occlusal forces: An investigation by telemetry. J. Prosthet. Dent. 1978, 40, 326–333. [Google Scholar] [CrossRef] [PubMed]
Prosthesis 07 00115 g001
Figure 1. Cross-sectional view of a trapezoidal-shaped connector, showing (h) height, (b) base, and (w) width. This trapezoidal shape is similar to the cross-section of an upper central incisor, with the width (w) corresponding to the incisal edge.
Figure 1. Cross-sectional view of a trapezoidal-shaped connector, showing (h) height, (b) base, and (w) width. This trapezoidal shape is similar to the cross-section of an upper central incisor, with the width (w) corresponding to the incisal edge.
Prosthesis 07 00115 g001
Prosthesis 07 00115 g002
Figure 2. (a) Scanned surface of a sample. (b) Calculation of the scanned areas [area = (complete squares) + (partial squares)]. The green line outlines the palatal surface. Purple dots indicate completely filled 1 mm2 boxes, while red dots indicate partially filled boxes.
Figure 2. (a) Scanned surface of a sample. (b) Calculation of the scanned areas [area = (complete squares) + (partial squares)]. The green line outlines the palatal surface. Purple dots indicate completely filled 1 mm2 boxes, while red dots indicate partially filled boxes.
Prosthesis 07 00115 g002
Prosthesis 07 00115 g003
Figure 3. Flowchart of cementation protocol for zirconia resin-bonded fixed dental prosthesis.
Figure 3. Flowchart of cementation protocol for zirconia resin-bonded fixed dental prosthesis.
Prosthesis 07 00115 g003
Prosthesis 07 00115 g004
Figure 4. Flowchart of cementation protocol for lithium disilicate resin-bonded fixed dental prosthesis.
Figure 4. Flowchart of cementation protocol for lithium disilicate resin-bonded fixed dental prosthesis.
Prosthesis 07 00115 g004
Prosthesis 07 00115 g005
Figure 5. (a) Tooth preparation was performed. (b) Milled cantilever resin-bonded fixed dental prosthesis. (c) The prosthesis was cemented according to the standardized protocol.
Figure 5. (a) Tooth preparation was performed. (b) Milled cantilever resin-bonded fixed dental prosthesis. (c) The prosthesis was cemented according to the standardized protocol.
Prosthesis 07 00115 g005
Prosthesis 07 00115 g006
Figure 6. Custom holder design with a 45-degree angulation. An adjustable holder on the right and left, indicated by the colors red and green, allows adjustment of the loading area onto the center of the pontic.
Figure 6. Custom holder design with a 45-degree angulation. An adjustable holder on the right and left, indicated by the colors red and green, allows adjustment of the loading area onto the center of the pontic.
Prosthesis 07 00115 g006
Prosthesis 07 00115 g007
Figure 7. Side view showing the positioning of the sample with the indenter. The load was applied at the center of the pontic’s palatal surface.
Figure 7. Side view showing the positioning of the sample with the indenter. The load was applied at the center of the pontic’s palatal surface.
Prosthesis 07 00115 g007
Prosthesis 07 00115 g008
Figure 8. In vitro outcome for lithium disilicate and zirconia.
Figure 8. In vitro outcome for lithium disilicate and zirconia.
Prosthesis 07 00115 g008
Prosthesis 07 00115 g009
Figure 9. (a) Type I favorable failure, fracture of the prosthesis without displacement. (b) Type II unfavorable failure, fracture of the tooth.
Figure 9. (a) Type I favorable failure, fracture of the prosthesis without displacement. (b) Type II unfavorable failure, fracture of the tooth.
Prosthesis 07 00115 g009
Table 1. Distribution of connector dimensions.
Table 1. Distribution of connector dimensions.
Lithium Disilicate
Trapezoidal (h) × (b) × (w) mm		Zirconia
Trapezoidal (h) × (b) × (w) mm
5 × 4 × 1 mm5 × 4 × 1 mm
4 × 2 × 1 mm4 × 2 × 1 mm
Table 2. Inclusion and exclusion criteria.
Table 2. Inclusion and exclusion criteria.
InclusionExclusion
Maxillary central incisor teethPresence of crack/craze lines
Sound or minimally restoredFracture
Flat palatal surfaceExposed dentine on palatal surface
Intact enamel with no evidence of pathological wear
Table 3. Firing parameters of tested materials.
Table 3. Firing parameters of tested materials.
MaterialManufacturerCompositionCrystallizationGlaze Firing
IPS e.max CAD, lithium disilicateIvoclar Vivadent, Schaan, LiechtensteinSiO2: 57–80%, Li2O:
11–19%, K2O: 0–
13%, P2O5: 0–11%,
ZrO2: 0–8%, ZnO:
0–8%, coloring
oxides: 0–8%.		Standby temperature:
403 °C;
closing time: 6 min;
heating rate: 60 °C/min;
firing temperature: 770 °C;
holding time: 0:10 min;
heating rate: 30 °C/min;
firing temperature: 850 °C;
holding time: 10:00;
long-term cooling: 700 °C; vacuum on/off: 770/850 °C.		Standby temperature:
403 °C;
closing time: 6 min; temperature increasing rate: 60 °C/min;
holding temperature: 725 °C;
holding time: 1 min;
Vacuum on/off: 450/724 °C.
IPS e.max ZirCAD prime, zirconiaIvoclar Vivadent, Schaan, LiechtensteinZirconium oxide: 88–95.5%,
Yttrium oxide > 6.5–8%,
Hafnium oxide ≤ 5%, aluminum oxide ≤ 1%, other oxides ≤ 1.5%.		Standby temperature:
403 °C;
closing time: 6 min;
heating rate: 60 °C/min;
firing temperature: 710 °C;
holding time: 1:00 min;
heating rate: 15–45 °C/min;
firing temperature: 710 °C;
holding time: 1:00;
long-term cooling: 709 °C; vacuum on/off: 450 °C.		Standby temperature:
403 °C;
closing time: 6 min; temperature increasing rate: 45 °C/min;
holding temperature: 710 °C;
holding time: 1 min;
Vacuum on/off: 450 °C.
Table 4. Failure mode definitions.
Table 4. Failure mode definitions.
TypeFailure ModeDescription
IFavorable
(non-catastrophic/repairable)		Debonding of the restoration without fracture
Fracture of the restoration without displacement (no loss of adhesion)
Fracture of the restoration with displacement (loss of adhesion)
Fracture of the restoration/tooth complex above the cementoenamel junction
IIUnfavorable
(catastrophic/non-repairable)		Fracture of the restoration/tooth complex below the cementoenamel junction
Root fracture with only restoration displacement (no
restoration fracture), which requires tooth extraction
Table 5. Two-way ANOVA for material and dimension.
Table 5. Two-way ANOVA for material and dimension.
FactorsnAdjusted Mean (95% CI)Adjusted Mean Difference (95% CI)F Stats (df)p Value *
Material
Lithium disilicate10136.62
(75.81, 197.43)		−71.95
(−157.95, 14.05)		3.115 (1,17)0.096
Zirconia10208.56 (147.75, 269.38)
Dimension
4 (h) × 2 (b) × 1 (w) mm10120.48 (59.67, 181.29)−104.23 (190.23, −18.23)6.538 (1,17)0.02
5 (h) × 4 (b) × 1 (w) mm10224.71
(163.90, 285.52)
* Multifactorial ANOVA.
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Ab Ghani, S.M.; Mohd Osman, M.L.; Chang, H.-C.; Ab Ghani, A.R.; Lim, T.W. Investigation of Connector Parameters for Fracture Strength of Zirconia and Lithium Disilicate Resin-Bonded Fixed Dental Prosthesis. Prosthesis 2025, 7, 115. https://doi.org/10.3390/prosthesis7050115

AMA Style

Ab Ghani SM, Mohd Osman ML, Chang H-C, Ab Ghani AR, Lim TW. Investigation of Connector Parameters for Fracture Strength of Zirconia and Lithium Disilicate Resin-Bonded Fixed Dental Prosthesis. Prosthesis. 2025; 7(5):115. https://doi.org/10.3390/prosthesis7050115

Chicago/Turabian Style

Ab Ghani, Siti Mariam, Mas Linda Mohd Osman, Hung-Chih Chang, Amir Radzi Ab Ghani, and Tong Wah Lim. 2025. "Investigation of Connector Parameters for Fracture Strength of Zirconia and Lithium Disilicate Resin-Bonded Fixed Dental Prosthesis" Prosthesis 7, no. 5: 115. https://doi.org/10.3390/prosthesis7050115

APA Style

Ab Ghani, S. M., Mohd Osman, M. L., Chang, H.-C., Ab Ghani, A. R., & Lim, T. W. (2025). Investigation of Connector Parameters for Fracture Strength of Zirconia and Lithium Disilicate Resin-Bonded Fixed Dental Prosthesis. Prosthesis, 7(5), 115. https://doi.org/10.3390/prosthesis7050115

Article Metrics

Back to TopTop