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| Title |
CAD-CAM Monolithic Zirconia Surveyed Crowns and Rounded Shape or Narrower Rest Seat Designs Maximize Fracture Resistance as Removable Partial Denture Abutments |
| Clinical Question |
For patients requiring removable partial denture (RPD) abutment restorations, do CAD-CAM monolithic zirconia surveyed crowns and rounded shape or narrower seat designs compared to lithium disilicate or composite resin with rest seat designs provide better fracture resistance with full contour crowns made with corresponding materials? |
| Clinical Bottom Line |
Three in vitro laboratory studies evaluating static and dynamic load limits across canine, premolar, and molar abutment configurations showed that monolithic CAD-CAM 3Y zirconia (Zir) surveyed crowns, regardless of seat design, had significantly higher fracture resistance than 4Y zirconia, lithium disilicate (LD) or composite resin (CR) crowns for removable partial denture abutments. Conservative, rounded or narrow rest seat designs maximized structural strength in all materials, and LD crowns with sharp designs only had comparable strength as CR crowns with rounded designs. All Zir group mean fracture loads substantially exceeded maximal physiological bite forces. LD and CR restorations may be susceptible to fracture under heavy posterior or bruxism loading. CR restorations with favorable rest designs could offer fracture resistance that is marginally better or comparable to LD with less favorable designs. CAD-CAM Zir surveyed crowns with rounded, narrow, or non-interproximal rest seat preparations are highly applicable for routine dental practice, offering mechanical reliability; however, with less esthetic results. On the other hand, LD surveyed crowns are highly esthetic, and could offer adequate mechanical stability for anterior restorations. |
| Best Evidence |
(you may view more info by clicking on the PubMed ID link) |
| PubMed ID |
Author / Year |
Patient Group |
Study type
(level of evidence) |
| #1) 30598310 | Manchester / 2019 | 120 CAD-CAM surveyed crowns comprised of 3 brands of zirconia, a lithium disilicate, and a composite resin | Laboratory study | | Key results | “Zirconia based surveyed crown groups fractured at twice the load as the lithium disilicate group”. Broad round shaped cingulum rests showed about 30% higher mean fracture load than sharp shaped designs. The mean ± SD of maximal loading capacity was 773.5 ± 255.0 N for CR group, 1124.9 ± 283.9 N for LD group, 2784.1 ± 400.5 N for NexxZr T block (Zir) group, 2526.9 ± 547.1 N for Lava Plus High translucency (Zir) group, and 3200.8 ± 416.8 N for ZirCAD LT (Zir) group. All Zir groups had significantly higher load capacity than all LD and CR groups, regardless of shape. However, the LD group with sharp shaped designs had comparable load capacity to that of CR with round shaped rests. | | #2) 33747393 | Chaturvedi / 2021 | 80 CAD-CAM all ceramic surveyed crowns comprised of composite, lithium disilicate, zirconia with 2 occlusal (narrow & wide) designs. | Laboratory study | | Key results | Zir surveyed crowns showed more than double the fracture strength of LD and CR crowns. Narrow occlusal (1/3) rest seats provided significantly higher fracture resistance than wide (2/3) rest seats across all materials. High translucent Zir surveyed crowns provided significantly lower fracture resistance (2375 N) compared to low translucency Zir group (3222 N). | | #3) 37471621 | Jurado et al. / 2024 | 70 CAD-CAM zirconia 4Y-PSZ surveyed crowns were 4 different occlusal rest designs and a full contour crown as a control | Laboratory study | | Key results | Surveyed crowns with occlusal rest seat design such as DO, DO extended, continuous showed similar fracture resistance. Interproximal rest seat showed lowest fracture resistance among tested groups. | |
| Evidence Search |
("Crowns" OR "CAD-CAM" OR "surveyed crown*") AND ("Denture, Partial, Removable" OR "removable partial denture*") AND ("fracture resistance" OR "rest seat*") |
Comments on
The Evidence |
Manchester et al. (2019) conducted a standardized in vitro investigation utilizing identical CAD-CAM STL files and custom composite resin dies, which was engineered to match human dentin's elastic modulus. Standardized compressive force application with custom metal rest retainers was performed. Validity is limited by static loading. SEM study helped determine the fracture origin and progression. Results showed that Zir crowns, regardless of seat design, were superior in strength to LD and CR. However, seat design affected whether LD was better than CR, with sharp designs being inferior.
Chaturvedi et al. (2021) evaluated CAD-CAM surveyed crowns using identical STL files on epoxy resin dies (matching dentin elastic modulus) with standardized cementation performed by a single operator. The study's internal validity is strong for comparative material analysis but is limited by static uniaxial compression testing without SEM study to determine fracture origin. Additionally, this study loaded the entire crown rather than the occlusal rest area. However, it compared 3Y and 4Y Zir and extended the applicability of the effects of material and seat design.
Jurado et al. (2023) utilized a chairside CAD-CAM workflow and incorporated 200,000 cycles of dynamic mechanical loading before compressive loading to failure. Validity is enhanced by simulating mechanical fatigue but is limited by using 3D-printed resin dies rather than natural teeth and testing a single 4Y Zir formulation. Cyclic loading of 50 N may not affect physical property of the ceramic crown.
All three articles represent moderate-to-low quality in vitro comparative trials (level 5). Standardized digital workflows, die elastic modulus matching, and controlled universal testing protocols ensure strong internal consistency. However, the absence of intraoral environmental factors (salivary degradation, complex multi-axial masticatory forces, long-term fatigue) across all studies limits direct translation to clinical adaptability without a longitudinal study.
|
| Applicability |
The selected articles' tooth selection spans anterior (canine) and posterior (premolar, molar) abutment preparations, making findings broadly generalizable across maxillary and mandibular RPD designs.
Monolithic Zir surveyed crowns across all three studies demonstrated mean fracture loads (2375 N to 4238 N) that vastly exceed normal masticatory bite forces (anterior 90–370 N, posterior 200–540 N, heavy bruxers up to 1000 N). LD and CR surveyed crowns provided sufficient strength for anterior incisal forces, but showed lower fracture resistance (687 N to 1309 N) that may increase clinical failure risk under heavy posterior teeth occlusal loads.
Rest seat design directly influences ceramic bulk and stress concentration. Preparing rounded cingulum rest seats (0.5 mm radius) on canines, narrow occlusal rest seats (1/3 B-L width) on premolars, and avoiding interproximal rest seats on molars significantly preserves structural integrity.
Digital chairside CAD-CAM workflows allow single-appointment crown fabrication, eliminate manual laboratory surveying errors, and deliver superior esthetics compared to traditional porcelain-fused-to-metal (PFM) crowns.
|
| Specialty/Discipline |
(Prosthodontics) |
| Keywords |
CAD-CAM; Monolithic Zirconia; Surveyed Crowns; Removable Partial Denture; Rest Seat Design; Fracture Resistance
|
| ID# |
3772 |
| Date of submission: |
10/18/2026 |
| E-mail |
fengw@uthscsa.edu |
| Author |
Wenbin Feng, DDS |
| Co-author(s) |
Hazem Alnamous, DDS |
| Co-author(s) e-mail |
alnamous@uthscsa.edu |
| Faculty mentor/Co-author |
Kyumin Whang, Ph.D. |
| Faculty mentor/Co-author e-mail |
whang@uthscsa.edu |
Basic Science Rationale
(Mechanisms that may account for and/or explain the clinical question, i.e. is the answer to the clinical question consistent with basic biological, physical and/or behavioral science principles, laws and research?) |
post a rationale |
| None available | |
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Comments and Evidence-Based Updates on the CAT
(FOR PRACTICING DENTISTS', FACULTY, RESIDENTS and/or STUDENTS COMMENTS ON PUBLISHED CATs) |
post a comment |
| None available | |
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