Abstract
Aim:
The aim of the study was to investigate and compare the prosthetic parameters, clinical indices, and survival rates of two digitally fabricated extracoronal restorations, namely an onlay and a full crown, at baseline, 1 year, and 2 years.
Settings and Design:
This was a prospective clinical study conducted on endodontically treated posterior teeth.
Materials and Methods:
Endodontically treated posterior teeth (n = 15) present bilaterally in the mandibular arch were selected. Digitally fabricated lithium disilicate onlay and crown were placed on either side of the same arch after randomization. Clinical parameters and prosthetic characteristics (as per the modified United States Public Health Service criteria) were evaluated at baseline, 1-year, and 2-year follow-ups.
Statistical Analysis Used:
Data were descriptively examined. The results were evaluated using the Chi-square test and ANOVA. Statistical significance was determined at P < 0.05.
Results:
Full crowns showed a 100% survival rate, while onlays had an 83.3% survival rate, with a significant difference (P = 0.030, 95% confidence interval: 0.01–0.12). Onlays exhibited significantly better periodontal outcomes, including lower bleeding on probing (P = 0.000), plaque index (P = 0.001), and probing pocket depth (P = 0.000) at 1 and 2 years. Marginal discoloration (20%) and marginal integrity loss (13.3%) were observed in onlays, with significant differences (P = 0.001). Both groups showed no fractures, secondary caries, or significant surface texture changes, and 100% patient satisfaction throughout.
Conclusion:
In this clinical trial comparing lithium disilicate onlays and crowns for restoring posterior teeth following endodontic treatment, both options demonstrated satisfactory prosthetic parameters during subsequent follow-ups. However, marginal integrity and discoloration were more prevalent in the onlay group. Periodontal examination revealed that onlays exhibited superior periodontal outcomes compared to crowns, with full crowns showing greater periodontal damage at 1-year and 2-year follow-ups.
Keywords: Bonding, endodontically treated teeth, full crown, minimally invasive
INTRODUCTION
The restoration of endodontically treated teeth (ETT) with significant structural loss has traditionally relied on full-coverage crowns supported by posts. These methods often require extensive removal of sound tooth structure, compromising the tooth’s biomechanical properties and increasing the risk of fractures or long-term failure. In recent years, there has been a growing shift toward minimally invasive restorative approaches that aim to preserve natural tooth structure while maintaining functionality and aesthetics. This evolution in treatment philosophy reflects the increasing recognition of the benefits of conservative dentistry, both in terms of clinical outcomes and patient satisfaction.
Minimally invasive dentistry focuses on preserving as much of the healthy tooth structure as possible, reducing the risk of biomechanical complications. Proponents of this approach, including Van Meerbeek et al.,[1] Magne,[2] and Mackenzie and Banerjee,[3] have emphasized the importance of avoiding excessive removal of tooth material. Their findings suggest that preserving natural tooth integrity enhances the tooth’s strength, resilience, and longevity. Excessive reduction of tooth structure, often required for traditional crowns, can weaken the remaining tooth and lead to a higher incidence of fractures, especially in ETT, which are already structurally compromised due to endodontic procedures.[1,2,3]
The introduction of advanced dental materials, particularly ceramics and adhesive systems, has facilitated the adoption of minimally invasive techniques. Restorative options such as inlays, onlays, overlays, and endo-crowns offer viable alternatives to full crowns. Studies by Magne and Belser[4] and Belser and Ferraris[5] have demonstrated that these restorations not only conserve tooth structure but also provide excellent functional and aesthetic outcomes. Ceramic onlays, in particular, have gained popularity due to their supra-gingival margins, which reduce the risk of periodontal complications, minimize tissue trauma, and simplify maintenance compared to subgingival crown preparations. Research by Magne and Douglas[6] and Politano et al.[7] highlights these advantages, further supporting the preference for onlays over traditional crowns.
Among the available ceramic materials, lithium disilicate has emerged as a preferred choice for minimally invasive restorations. Lithium disilicate combines superior mechanical properties with excellent aesthetic outcomes, mimicking the translucency and natural color of teeth while offering high fracture resistance. Studies by Gungor et al.,[8] Fasbinder,[9] and Li et al.[10] have documented the exceptional performance of lithium disilicate restorations, with low clinical failure rates and excellent durability. For instance, Valenti and Valenti[11] evaluated 261 lithium disilicate crowns and reported a remarkable survival rate of 95.5% over 10 years, underscoring the material’s reliability and longevity.
This study aims to compare the efficacy of lithium disilicate onlays and full crowns in the restoration of mandibular posterior ETT. A controlled, prospective, randomized split-mouth design will be employed to evaluate the restorations over a 2-year period. Outcomes will be assessed based on modified United States Public Health Service (USPHS) criteria,[12] focusing on prosthodontic parameters, periodontal health, and patient satisfaction. The null hypothesis posits that both restoration types onlays and full crowns will exhibit comparable performance under standardized conditions. By analyzing critical parameters such as survival rates, functional performance, and patient-reported outcomes, this research seeks to address gaps in the existing literature and provide evidence-based guidance for clinical decision-making.
The findings of this study will have significant implications for restorative dentistry. While traditional full crowns have long been the gold standard for restoring ETT, the growing body of evidence supporting minimally invasive techniques underscores the need for re-evaluating these conventional approaches. By prioritizing the conservation of tooth structure and achieving optimal clinical outcomes, minimally invasive restorations such as lithium disilicate onlays, represent a promising alternative. This research will contribute to the ongoing evolution of restorative dentistry, helping practitioners make informed decisions that enhance patient care and satisfaction.
METHODOLOGY
Study design
A prospective split-mouth clinical experiment was used in the current study. The study was approved by the Institutional Review Board SGTDCH and RI (Ref no: FODS/EC/PROSTHO/2022/18) and has been registered under the Clinical Trial Registry-India under the registration number-CTRI/2022/09/045185.
Sample size calculation
The sample size for this study was calculated using G*Power software (version 3.1.9.7, Heinrich-Heine-University, Düsseldorf, Germany) to ensure adequate statistical power for comparing the prosthetic parameters, clinical indices, and survival rates of two types of digitally fabricated extracoronal restorations (lithium disilicate onlay and crown) in endodontically treated posterior teeth. The study employed a matched-pairs design, with each patient receiving both types of restorations, enabling intra-patient comparison.
Key parameters for sample size calculation
Effect size (Cohen’s dz): The effect size was determined to be 0.601, derived from previously published literature and clinical expectations[11]
Significance level (α): The alpha value was set at 0.05 for a two-tailed test, ensuring a 95% confidence level
Power (1− β): The power was set at 0.80, providing an 80% probability of detecting a true difference if one exists.
Formula for sample size calculation
For paired designs, the sample size was calculated using the formula for detecting differences in means for paired data:
Where:
Z1−α/2: Z-value for the desired confidence level (1.96 for 95%)
Z1−β: Z-value for the desired power (0.84 for 80%)
Δ: Expected mean difference between groups (derived from prior studies)
σ: Standard deviation of the differences.
Using these parameters and an estimated mean difference (Δ) of 0.50 with a standard deviation (σ) of 0.83 (values based on prior studies), the sample size required was calculated to be approximately 13 pairs (26 sites).
Final sample size adjustment
To account for potential dropouts or deviations during the study, the sample size was increased by 20%, resulting in a final target of 15 patients (30 sites). This ensures sufficient power to detect meaningful differences in the outcomes of interest.
The study included male and female patients over the age of 18 who were in good general health and capable of providing informed consent. Selected teeth had to be in interproximal contact with two neighboring natural teeth and functional occlusion with a natural tooth. Only molar or premolar teeth that required root canal treatment due to endodontic issues were considered. Furthermore, the chosen teeth had to be located in the mandibular arch on either side.
Pregnant women, or those who may be pregnant, were excluded due to the necessity for radiographic evaluation. Individuals under the age of 18 or those unable to provide informed consent were also excluded. Teeth with probing periodontal depths exceeding 5 mm or deemed irreparable were not included. In addition, patients with unilateral mastication were excluded from the study [Figure 1].
Figure 1.
Flow chart of the study
With the patient’s consent, the two ETT in the same arch were randomly allocated to one of the treatment groups. To ensure unbiased allocation of the two digitally fabricated extracoronal restorations (lithium disilicate onlay and crown) to the selected endodontically treated posterior teeth, a randomization process was employed using a computer-generated random number sequence. Each patient had one restoration placed on either side of the mandibular arch. A unique identification number was assigned to each tooth, and a random number table was used to determine whether the tooth on the left or right side would receive the lithium disilicate onlay or crown. This random allocation was performed by an independent researcher who was not involved in the study procedures, ensuring allocation concealment [Figure 2].
Figure 2.
Consort flow chart
All procedures were carried out by a single operator to maintain consistency and minimize variability in clinical execution. Furthermore, comparisons were standardized by evaluating molars against their contralateral molars and premolars against their contralateral premolars. This ensured that any differences between the two restoration types could be attributed to the treatment itself rather than confounding factors such as tooth type or functional variations.
Group 1 (n = 15): Tooth restored with lithium disilicate onlay
Group 2 (n = 15): Tooth restored with lithium disilicate crown.
Tooth preparation for full crown
Tooth preparation began with the placement of depth orientation grooves of 1 mm on the occlusal, buccal, and lingual surfaces using a #122 depth-cutting diamond bur (Shofu Crown Preparation Kit, Shofu Inc., San Marcos, USA). Contact between adjacent teeth was broken using a #101 bur (Shofu Crown Preparation Kit, Shofu Inc., San Marcos, USA), followed by 1 mm of axial reduction with a #201 tapered flat-end bur (Shofu Crown Preparation Kit, Shofu Inc., San Marcos, USA). The occlusal surface was reduced by 1.5 mm using a #148 double-cone regular grit bur (Shofu Crown Preparation Kit, Shofu Inc., San Marcos, USA), per the manufacturer’s requirements for IPS e.max CAD (Ivoclar, Schaan, Liechtenstein). Equigingival shoulder finish lines with rounded internal line angle and an overall 6° taper were created. All line angles and undercuts and margins were smoothened with a fine grit end-cutting bur #F414SS (Shofu Crown Preparation Kit, Shofu Inc., San Marcos, USA) [Figure 3].
Figure 3.
Tooth preparation of onlay and full crown
Tooth preparation for onlay
Uniform 1.5 mm axial reduction was achieved using a round-end tapered #102R bur (Shofu Crown Preparation Kit, Shofu Inc., San Marcos, USA). The occlusal surface was prepared with a V-shape for retention using a #148 bur (Shofu Crown Preparation Kit, Shofu Inc., San Marcos, USA), with an overall 6° taper. A 90° cavosurface angle with heavy chamfer finish lines was created on the buccal and lingual surfaces, maintaining marginal contact. A retentive depression was added to the occlusal surface, and all sharp edges and corners were smoothed [Figure 3].
Impression making and temporization
The gingival retraction was achieved using a size 00 retraction cord (GDC Marketing, India). Final impressions were taken using a two-step technique with putty and light body vinyl polysiloxane (Peakosil, Neosil, Ivoclar, Schaan, Liechtenstein) using SS white perforated rim lock trays (SS White Dental, Lakewood, NJ, USA). The putty impression was first made with a cellophane spacer, followed by the light body impression after spacer removal. Opposing arch impressions were made with only putty [Figure 4]. Temporary crowns and onlays were fabricated using an indirect technique with self-cure tooth-colored acrylic resin (GC Tempron, GC Corporation, Tokyo, Japan) [Figure 5].
Figure 4.
Impression made with addition silicone of the prepared teeth
Figure 5.
Temporisation of the prepared tooth
Laboratory procedures
Master casts were made from final impressions with Type IV dental stone (Kal Rock, Kalabhai, India) and scanned. Lithium disilicate CAD blocks (Ivoclar, Schaan, Liechtenstein) were milled using a 5-axis milling machine (MC XL, Dentsply Sirona, York, Pennsylvania, USA) and then crystallized in a sintering furnace (Programat S1, Ivoclar Vivadent, Schaan, Liechtenstein) at 840°C–850°C, enhancing strength to 160 MPa.
Bonding of the prosthesis
Bonding of the onlays and crowns was performed with Multilink N dual-cure resin cement (Ivoclar, Schaan, Liechtenstein). Hydrofluoric acid etching was applied for 20 s (Ivoclar, Schaan, Liechtenstein), followed by Monobond N primer application (Ivoclar, Schaan, Liechtenstein) on prosthesis. Primers A and B (Ivoclar, Schaan, Liechtenstein) were mixed and applied to the tooth surface. Resin cement (Multilink N, Ivoclar, Schaan, Liechtenstein) was mixed and applied to the prosthesis, which was then placed on the prepared tooth. Initial curing was performed for 5–10s, excess cement was removed, and final curing was done for 60s [Figure 6].
Figure 6.
Intraoral view post cementation
Clinical evaluation
Immediately after bonding, clinical status was assessed using modified USPHS criteria.[12] Periodontal status was evaluated by measuring bleeding on probing (BOP), plaque index (PI), probing depth (PD), and width of keratinized gingiva using a Williams probe (Hu-Friedy, Chicago, IL, USA).
Prosthetic outcome
Updated USPHS[12] standards were used to evaluate prosthetic parameters. The onlay and crown were evaluated for ceramic/restoration fracture after 2 years of use. A dental probe was used to assess the marginal integrity between the crown and abutment. Interproximal contact areas were examined with a dental floss. To evaluate occlusion, an articulating paper (Baush articulating paper) of 50 μm thickness that has been folded twice was utilized. Anatomical form, neighboring dentition, crown and onlay color, and mild marginal discoloration were visually compared. The occlusal wear of the opposing natural tooth was evaluated visually and using a dental probe to check for any exposed rough surfaces. Detachment of prosthesis from the abutment tooth was evaluated. Secondary caries was assessed using periapical radiographs and tactile examination using an explorer. Patient satisfaction, abutment fracture, and surface texture were also evaluated. No participant dropped out during the follow-up for 2 years.
Periodontal outcome
Three periodontal parameters, i.e., PI, BOP, and PD were evaluated at six pre-determined sites around each restoration, whereas the width of the keratinized mucosa (KM) was measured at the mid-buccal aspect of the two restorations. The readings were repeated at an interval of 1 and 2 years.
Statistical analysis
A master chart was prepared for all the data, which were statistically analyzed using the Chi-square test and ANOVA. Prosthetic outcomes were evaluated using Chi-square test, whereas the periodontal parameters, including BOP, PI, and probing pocket depth, were analyzed using ANOVA. The software used for the statistical analysis were Statistical Package for Social Sciences version 21.0, IBM Inc. (IBM, New york, USA) and Epi-info version 3.0 (CDC, Atlanta, Georgia, USA).
Survival and success criteria
In this study, survival was defined as the restoration of remaining functional in the oral cavity without requiring replacement, irrespective of minor clinical deficiencies. A restoration was considered successful if it exhibited no fracture, no need for intervention due to marginal discrepancies, no secondary caries, no significant occlusal wear, and maintained esthetic acceptability without severe discoloration. The assessment followed the modified USPHS criteria, with marginal integrity, discoloration, and periodontal health serving as key indicators. Failures included restorations requiring replacement due to significant deterioration in marginal integrity, esthetics, or structural compromise.
RESULTS
The present study was a split-mouth study, where on either side a lithium disilicate full crown and onlay restorations were provided. Follow-up was done at the end of 1 and 2 years.
The prosthetic outcomes were evaluated using modified USPHS criteria[12] at baseline, 1 year, and 2 years. Patient Satisfaction: At baseline, 1 year, and 2 years, 100% of patients in both the Emax onlay and crown groups were very satisfied, with no reported complaints or dissatisfaction (P value not applicable) [Tables 1-3]. Restoration Fracture: Both groups exhibited no fractures or localized chipping throughout the study period (P value not applicable) [Tables 1-3]. Abutment Fracture: There was no abutment fractures observed in either group at any time point (P value not applicable) [Tables 1-3]. Marginal Integrity: At baseline, 86.7% of the onlays showed no catch, and 13.3% had a slight catch, with statistically significant differences (P = 0.00). At 1 year and 2 years, the percentages remained the same with significant differences (P = 0.001 and P = 0.001, respectively) [Tables 1-3]. Marginal Discoloration: Both groups showed no discoloration at baseline. At 1 year, 73.3% of onlays exhibited no discoloration while 26.7% showed slight discoloration, with significant differences (P = 0.001). At 2 years, 80% of onlays had no discoloration, and 20% showed slight discoloration, with significant differences (P = 0.00) [Tables 1-3]. Surface texture: Both groups maintained polished surfaces without grit or coarseness throughout the study period (P value not applicable) [Tables 1-3]. Secondary Caries: No cases of secondary caries were reported in either group at any time point (P value not applicable) [Tables 1-3]. Occlusal wear: At baseline and 1 year, no occlusal wear on the opposing dentition was observed in both groups. At 2 years, 93.3% of onlays and crowns showed no occlusal wear, while 6.7% showed slight occlusal wear on the opposing dentition, with nonsignificant differences (P = 0.01) [Tables 1-3]. Periodontal parameters: Baseline measurements showed nonsignificant differences in BOP, PI, probing pocket depth, and width of keratinized gingiva between the groups. At 1 year and 2 years, the onlay group exhibited significantly lower mean scores for BOP, PI, and probing pocket depth compared to the crown group (P = 0.000, P = 0.001, and P = 0.000, respectively) [Table 4]. Overall survival rate: Survival rates were higher for lithium disilicate crowns (100%) [Graph 1] compared to onlays (83.3%) [Graph 2] as per the predefined survival and success criteria [Table 5]. Kaplan–Meier survival analysis showed higher survival rates for lithium disilicate crowns compared to onlays over 2 years. The median survival for onlays was 12 months (95% confidence interval [CI]: 8–16 months), while crowns maintained 100% survival at 24 months (95% CI: 24–24 months) [Graph 3]. While no fractures or secondary caries were observed, the reduced survival rate of onlays was attributed to significant marginal deterioration and discoloration over time, leading to a higher likelihood of intervention. Notably, 80% of the cases involved molars, whereas only 20% were premolars, ensuring that comparisons were predominantly made among similar tooth types to minimize variability in functional loads and anatomical differences.
Table 1.
Intergroup comparison of prosthetic outcomes for lithium dislicate onlays and crowns at baseline using Chi-square test
| Patient satisfaction | ||||||
|---|---|---|---|---|---|---|
| Group | A (very satisfied), n (%) | B (short-term complaints after treatment), n (%) | C (unsatisfied), n (%) | D (completely unsatisfied), n (%) | χ 2 | P |
| Emax onlay | 15 (100) | 0 | 0 | 0 | *** | *** |
| Emax crown | 15 (100) | 0 | 0 | 0 | ||
|
Restoration fracture | ||||||
| Group | A (no fracture), n (%) | B (localized chipping), n (%) | C (chipping down to the framework), n (%) | D (new crown is needed), n (%) | χ 2 | P |
|
| ||||||
| Emax onlay | 15 (100) | 0 | 0 | 0 | *** | *** |
| Emax crown | 15 (100) | 0 | 0 | 0 | ||
|
Abutment fracture | ||||||
| Group | A (no fracture), n (%) | B | C | D (fracture of abutment), n (%) | χ 2 | P |
|
| ||||||
| Emax onlay | 15 (100) | 0 | *** | *** | ||
| Emax crown | 15 (100) | 0 | ||||
|
Marginal integrity | ||||||
| Group | A (no catch), n (%) | B (slight catch, no gap), n (%) | C (clear gap), n (%) | D (new crown is needed), n (%) | χ 2 | P |
| Emax onlay | 13 (86.7) | 2 (13.3) | 0 | 0 | 16.333 | 0.00* |
| Emax crown | 15 (100) | 0 | 0 | 0 | ||
|
Marginal discoloration | ||||||
| Group | A (no discoloration), n (%) | B (slight discoloration at margins), n (%) | C (severe discoloration at margins), n (%) | D | χ 2 | P |
|
| ||||||
| Emax onlay | 15 (100) | 0 | 0 | *** | *** | |
| Emax crown | 15 (100) | 0 | 0 | |||
|
Surface texture | ||||||
| Group | A (polished surface), n (%) | B (gritty surface), n (%) | C (coarse surface, new crown needed), n (%) | D | χ 2 | P |
|
| ||||||
| Emax onlay | 15 (100) | 0 | 0 | *** | *** | |
| Emax crown | 15 (100) | 0 | 0 | |||
|
Secondary caries | ||||||
| Group | A (no discoloration on adjacent teeth), n (%) | B (dark discoloration on adjacent teeth), n (%) | C (new crown needed), n (%) | D | χ 2 | P |
|
| ||||||
| Emax onlay | 15 (100) | 0 | 0 | *** | *** | |
| Emax crown | 15 (100) | 0 | 0 | |||
|
Occlusal wear | ||||||
| Group | A (no occlusal wear), n (%) | B (slight occlusal wear), n (%) | C (high occlusal wear), n (%) | D | χ 2 | P |
|
| ||||||
| Emax onlay | 15 (100) | 0 | 0 | *** | *** | |
| Emax crown | 15 (100) | 0 | 0 | |||
*Statistically significant, ***Test can’t be done as cell is zero
Table 2.
Intergroup comparison of prosthetic outcomes for lithium dislicate onlays and crowns at 1 year using Chi-square test
| Patient satisfaction | ||||||
|---|---|---|---|---|---|---|
| Group | A (very satisfied), n (%) | B (short-term complaints after treatment), n (%) | C (unsatisfied), n (%) | D (completely unsatisfied), n (%) | χ 2 | P |
| Emax onlay | 15 (100) | 0 | 0 | 0 | *** | *** |
| Emax crown | 15 (100) | 0 | 0 | 0 | ||
|
Restoration fracture | ||||||
| Group | A (no fracture), n (%) | B (localized chipping), n (%) | C (chipping down to the framework), n (%) | D (new crown is needed), n (%) | χ 2 | P |
|
| ||||||
| Emax onlay | 15 (100) | 0 | 0 | 0 | *** | *** |
| Emax crown | 15 (100) | 0 | 0 | 0 | ||
|
Abutment fracture | ||||||
| Group | A (no fracture), n (%) | B | C | D (fracture of abutment), n (%) | χ 2 | P |
|
| ||||||
| Emax onlay | 15 (100) | 0 | *** | *** | ||
| Emax crown | 15 (100) | 0 | ||||
|
Marginal integrity | ||||||
| Group | A (no catch), n (%) | B (slightly catch, no gap), n (%) | C (clear gap), n (%) | D (new crown is needed), n (%) | χ 2 | P |
|
| ||||||
| Emax onlay | 13 (86.7) | 2 (13.3) | 0 | 0 | 22.533 | 0.001* |
| Emax crown | 15 (100) | 0 | 0 | 0 | ||
|
Marginal discoloration | ||||||
| Group | A (no discoloration), n (%) | B (slight discoloration at margins), n (%) | C (severe discoloration at the margins), n (%) | D, n (%) | χ 2 | P |
|
| ||||||
| Emax onlay | 11 (73.3) | 4 (26.7) | 0 | 0 | 17.131 | 0.001* |
| Emax crown | 15 (100) | 0 | 0 | 0 | ||
|
Surface texture | ||||||
| Group | A (polished surface), n (%) | B (gritty surface), n (%) | C (Coarse surface, new crown needed), n (%) | D | χ 2 | P |
|
| ||||||
| Emax onlay | 15 (100) | 0 | 0 | *** | *** | |
| Emax crown | 15 (100) | 0 | 0 | |||
|
Secondary caries | ||||||
| Group | A (no discoloration on adjacent teeth), n (%) | B (dark deep discoloration on adjacent teeth), n (%) | C (new crown needed), n (%) | D | χ 2 | P |
|
| ||||||
| Emax onlay | 15 (100) | 0 | 0 | *** | *** | |
| Emax crown | 15 (100) | 0 | 0 | |||
|
Occlusal wear | ||||||
| Group | A (no occlusal wear), n (%) | B (slight occlusal wear), n (%) | C (high occlusal wear), n (%) | D | χ 2 | P |
|
| ||||||
| Emax onlay | 15 (100) | 0 | 0 | *** | *** | |
| Emax crown | 15 (100) | 0 | 0 | |||
*Statistically significant, ***Test can’t be done as cell is zero
Table 3.
Intergroup comparison of prosthetic outcomes for lithium dislicate onlays and crowns at 2 years using Chi-square test
| Patient satisfaction | ||||||
|---|---|---|---|---|---|---|
| Group | A (very satisfied), n (%) | B (short-term complaints after treatment), n (%) | C (unsatisfied), n (%) | D (completely unsatisfied), n (%) | χ 2 | P |
| Emax onlay | 15 (100) | 0 | 0 | 0 | *** | *** |
| Emax crown | 15 (100) | 0 | 0 | 0 | ||
|
Restoration fracture | ||||||
| Group | A (no fracture), n (%) | B (localized chipping), n (%) | C (chipping down to the framework), n (%) | D (new crown is needed), n (%) | χ 2 | P |
|
| ||||||
| Emax onlay | 15 (100) | 0 | 0 | 0 | *** | *** |
| Emax crown | 15 (100) | 0 | 0 | 0 | ||
|
Abutment fracture | ||||||
| Group | A (no fracture), n (%) | B, n (%) | C, n (%) | D (fracture of abutment), n (%) | χ 2 | P |
|
| ||||||
| Emax onlay | 15 (100) | 0 | 0 | 0 | *** | *** |
| Emax crown | 15 (100) | 0 | 0 | 0 | ||
|
Marginal integrity | ||||||
| Group | A (no catch), n (%) | B (slight catch, no gap), n (%) | C (clear gap), n (%) | D (new crown is needed), n (%) | χ 2 | P |
|
| ||||||
| Emax onlay | 13 (86.7) | 2 (13.3) | 0 | 0 | 22.533 | 0.001* |
| Emax crown | 15 (100) | 0 | 0 | 0 | ||
|
Marginal discoloration | ||||||
| Group | A (no discoloration), n (%) | B (slight discoloration at margins), n (%) | C (severe discoloration at margins), n (%) | D | χ 2 | P |
|
| ||||||
| Emax onlay | 12 (80) | 3 (20) | 0 | 0 | 16.131 | 0.00* |
| Emax crown | 15 (100) | 0 | 0 | 0 | ||
|
Surface texture | ||||||
| Group | A (polished surface), n (%) | B (gritty surface), n (%) | C (coarse surface, new crown needed), n (%) | D | χ 2 | P |
|
| ||||||
| Emax onlay | 15 (100) | 0 | 0 | *** | *** | |
| Emax crown | 15 (100) | 0 | 0 | |||
|
Secondary caries | ||||||
| Group | A (no discoloration on adjacent teeth), n (%) | B (dark deep discoloration on adjacent teeth), n (%) | C (new crown needed), n (%) | D | χ 2 | P |
|
| ||||||
| Emax onlay | 15 (100) | 0 | 0 | *** | *** | |
| Emax crown | 15 (100) | 0 | 0 | |||
|
Occlusal wear | ||||||
| Group | A (no occlusal wear), n (%) | B (slight occlusal wear), n (%) | C (high occlusal wear), n (%) | D | χ 2 | P |
|
| ||||||
| Emax onlay | 14 (93.3) | 1 (6.7) | 0 | 29.126 | 0.01** | |
| Emax crown | 14 (93.3) | 1 (6.7) | 0 | |||
*Statistically significant, **Statistically nonsignificant, ***Test can’t be done as cell is zero
Table 4.
Intergroup comparison of various periodontal parameters among various groups at baseline, 1 year and 2 years
| Group | Mean BOP | Mean PI | Mean probing pocket depth | Mean width of keratinized gingiva | |
|---|---|---|---|---|---|
| Baseline | Emax onlay | 0.567 | 0.03 | 0.43 | 2.13 |
| Emax crown | 0.600 | 0.07 | 0.70 | 1.93 | |
| P | 0.69** | 0.37** | 0.20** | 0.176** | |
| 1 year | Emax onlay | 0.2333 | 0.0667 | 0.533 | 2.13 |
| Emax crown | 0.7333 | 0.4333 | 1.137 | 1.66 | |
| P | 0.000** | 0.000* | 0.001* | 0.000* | |
| 2 years | Emax onlay | 0.13 | 0.1167 | 0.567 | 2.20 |
| Emax crown | 0.62 | 0.5000 | 1.583 | 1.48 | |
| P | 0.000* | 0.001* | 0.000* | 0.000* |
*Statistically significant, **Statistically nonsignificant. BOP: Bleeding on probing, PI: Plaque index
Graph 1.
Representation on survival rate of lithium disilicate crown over a period of 2 years
Graph 2.
Representation on survival rate lithium disilicate onlay over a period of 2 years
Table 5.
Comparison of overall survival rate among onlay and crown
| USPHS | Onlay |
Crown |
P | ||
|---|---|---|---|---|---|
| Failure, n (%) | Success, n (%) | Failure, n (%) | Success, n (%) | ||
| Marginal discolouration (n=15) | 3 (20) | 12 (80) | 0 | 15 (100) | 0.122, NS |
| Marginal intergity (n=15) | 2 (13.3) | 13 (86.7) | 0 | 15 (100) | 0.248, NS |
| Overall (n=30) | 5 (16.7) | 25 (83.3) | 0 | 30 (100) | 0.030*, significant |
*significant. Intergroup comparison of survival rates among various groups. Chi-square test, level of significance set at P<0.05. NS: Nonsignificant, USPHS: United States Public Health Service
Graph 3.
Kaplan–Meier survival curve
DISCUSSION
The restoration of ETT requires careful consideration of functional, structural, and aesthetic factors. Minimally invasive, indirect defect-oriented procedures, such as full crowns and partial restorations, have become vital for the functional and aesthetic rehabilitation of lost hard tooth substances.
The null hypothesis that both types of restorations, i.e., lithium disilicate onlay and crown, would exhibit similar prosthodontic and periodontal parameters under standardized conditions was rejected. This prospective, cross-arch clinical study involved selecting two endodontically treated mandibular posterior teeth in random order. Mandibular posterior teeth were chosen due to their higher incidence of caries and significant occlusal load, as noted by Schmid et al.[13] and Jain.[14] The higher failure rate of ceramic restorations in posterior teeth compared to anterior teeth, as reported by Archibald et al., further justified this selection.[15]
Lithium disilicate glass is noted for its esthetic appeal and high fracture resistance after luting, as reported by Zhang et al.[16] Combined with its high esthetics and suitability for patients with metal allergies, Emax is an appropriate choice for this study.
In this study, we evaluated and compared lithium disilicate CAD onlays and crowns within the same oral environment which eliminates inter-patient variability, providing a more accurate comparison of the two restorative methods. While specific studies comparing lithium disilicate crowns and onlays in a split-mouth design are scarce, this aspect underscores the novelty of our research.
Periodontal health was assessed using a standardized periodontal probe with a tip diameter of 0.5 mm, color-coded markings at 3, 6, 9, and 12 mm, and a controlled probing force of approximately 25 g to ensure consistent and reproducible measurements. PI, BOP, pocket PD, and width of KM were recorded at baseline, 1 year, and 2 years.
Our results indicated that patient satisfaction for both onlays and full crowns was 100% at the time of restoration, at 1 year and 2 years, consistent with findings by Samer et al.[17] and Taskonak and Sertgöz[18] and Fabbri et al.[19] Both groups showed no significant differences in restoration fractures, abutment fractures, surface texture, secondary caries, or occlusal wear over 2 years. However, marginal integrity and discoloration showed statistically significant differences, favoring full crowns.
Marginal integrity values were 100% at baseline for both restorations. At 1 year, values were 86.7% for onlays and 100% for full crowns, and at 2 years, 86.7% for onlays and 100% for full crowns. These findings align with Teichmann et al.,[20] who reported better marginal integrity for full crowns, and Krämer and Frankenberger, who noted decreased marginal integrity for ceramic onlays over time.[21]
Marginal discoloration was absent at baseline for both restorations. At 1 year, 73.3% of onlays remained free of discoloration, while 26.7% exhibited slight discoloration, whereas all full crowns remained at 100%. At 2 years, 80% of onlays showed no discoloration, while 20% exhibited slight discoloration, with full crowns continuing to show no discoloration. These results are supported by Edelhoff et al.[12] and Galiatsatos and Bergou,[22] who found increased marginal discoloration in onlays over time.
The differences in marginal integrity and discoloration between onlays and full crowns can be attributed to their design. Full crowns offer complete coverage, reducing microleakage and protecting margins from wear and staining, resulting in superior long-term performance. In contrast, onlays, with their partial coverage, are more exposed to functional stresses and oral fluids, leading to reduced marginal stability and increased discoloration over time.[23,24,25] Marginal integrity and discoloration, while significant clinical parameters, do not necessarily constitute failure in the true sense. Instead, they indicate a gradual deterioration that may require periodic monitoring or minor intervention rather than replacement of the restoration. The reduced survival rate for onlays in this study reflects the likelihood of required intervention due to marginal deterioration rather than catastrophic failure. This aligns with previous studies where onlays showed higher susceptibility to marginal changes over time while remaining functionally acceptable.[26,27,28]
Periodontal health, assessed through PI, BOP, pocket PD, and width of KM, showed significant differences at 1 year and 2 years. Onlays exhibited better periodontal outcomes, with lower PI, BOP, and pocket PD, and greater width of keratinized gingiva, compared to full crowns. The better periodontal outcomes with onlays can be attributed to their conservative design, which avoids subgingival extension, reducing plaque retention, inflammation, and pocket depths while preserving keratinized mucosa. Full crowns, with subgingival margins, are more plaque-retentive, increasing the risk of periodontal issues. These findings are consistent with Teichmann et al.’s[29] study on periodontal outcomes of lithium-disilicate restorations.
Survival rates were higher for lithium disilicate crowns (100%) compared to onlays (86.7%). These results contrast with some studies, such as those by Behr et al.[30] and Sailer et al.,[31] which reported declining survival rates for single crowns over time. However, our findings align with Edelhoff et al.’s study on occlusal onlays, which reported a 100% survival rate over 11 years.[12]
This study had a follow-up period of only 2 years, which might not fully capture the long-term performance and potential complications of lithium disilicate restorations. In addition, this split-mouth design controlled for inter-patient variability, larger sample sizes, and multi-center studies would enhance the generalizability of the results. A limitation of the study was the use of conventional impression techniques, which may introduce inaccuracies in the impression process. Intraoral scanners could have been utilized as an alternative to enhance the accuracy of the impressions and reduce potential errors, providing more reliable data for the analysis.
The precision and accuracy of intraoral scanning (IOS) versus scanning of prepared models in indirect restorations are significant considerations for clinical outcomes. IOS eliminates the need for impression materials and physical models, reducing distortion and improving efficiency. Studies[31,32,33] have shown that direct IOS can offer superior marginal accuracy and fit compared to conventional impression-based digital models. However, limitations such as scanning depth, accessibility to subgingival margins, and movement artifacts may affect its accuracy in deep or complex preparations. Conversely, scanning a prepared model ensures stability and allows multiple scanning attempts, potentially improving reliability in cases with challenging intraoral conditions.[34] In addition, model scanning enables better control over soft tissue management, particularly for restorations with subgingival margins.[35,36] However, errors in impression materials and casting processes can introduce discrepancies. Future studies should further investigate the clinical implications of these scanning techniques, particularly in terms of long-term restoration fit and adaptation.
Further research could explore the biomechanical behavior of lithium disilicate restorations under different loading conditions and in diverse patient populations. Future studies could also benefit from incorporating digital scanning technologies to more accurately assess occlusal wear. This method would provide a clearer understanding of wear progression compared to traditional visual assessments or probe measurements. The cost-effectiveness and patient-reported outcomes over extended periods could also provide valuable insights for clinical decision-making.
In conclusion, both lithium disilicate onlays and crowns demonstrated comparable prosthetic performance. However, full crowns showed superior marginal integrity and resistance to discoloration, while onlays maintained better periodontal health. These findings suggest that both restorative modalities have their unique advantages and should be selected based on individual patient needs and clinical conditions.
CONCLUSIONS
In this clinical trial, comparing onlays and full crowns for restoring posterior teeth following endodontic treatment, both prosthetic options demonstrated satisfactory prosthetic parameters during subsequent follow-ups. However, marginal integrity and discoloration were more prevalent among the onlay group. Periodontal examination indicated superior periodontal outcomes with onlays compared to full crowns, with full crowns showing greater periodontal damage at baseline, 1 year, and 2-year follow-ups.
Conflicts of interest
There are no conflicts of interest.
Acknowledgment
The authors are grateful to SGT University for providing the necessary resources and support that made this research possible. The authors also extend appreciation to all mentors and colleagues for their guidance and encouragement throughout this work.
Funding Statement
Nil.
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