Cement-retained Implant-supported Crowns Research Articles

Effect of Restoration Design on the Removal Torque Loss of Implant-supported Crowns after Cyclic Loading.

To compare the removal torque loss (RTL) percentage of screw-retained, cement-retained, and combined screw- and cement-retained implant-supported crowns after cyclic loading and measure the impact of cyclic loading on removal torque. Thirty-two dental implants (4.0 × 10 mm) in resin blocks and abutments were divided into four groups (n = 8) based on restoration design: combined screw- and cement-retained group (SC), two cement-retained groups: cemented with adhesive resin cement (AR) (Panavia V5) or provisional cement (PR) (RelyX Temp NE), and screw-retained one-piece titanium group (TI). Removal torques were measured in Newton-centimeter (Ncm) before and after 500,000-cycle cyclic loading with forces ranging from 20 to 200 N at 15 Hz. The RTL percentage in each group was calculated. The paired t-test was used to detect the difference between pre-loading (RT1) and post-loading removal torque (RT2) in each group and 1-way ANOVA was used to detect the difference of RTL percentage between groups. The post-loading removal torques in all groups were significantly lower than their pre-loading removal torques (p < 0.001). The 1-way ANOVA test found no significant difference in the RTL% between the study groups. The PR group exhibited the lower RTL% (30.74 ± 7.3%), followed by the TI (30.78 ± 5.6%), AR (32.12 ± 2.5%), and SC (35.71 ± 5.1%) groups. Combined screw- and cement-retained restorations exhibited similar RTL compared with other restoration designs, and cyclic loading significantly affected the removal torque. Combined screw- and cement-retained restorations can be utilized in single-tooth situations, offering a comparable impact on screw joint stability while providing benefit of retrievability. Cyclic loading significantly influences joint stability, periodic checkup for screw loosening is recommended. How to cite this article: Jongsiri S, Arksornnukit M, Homsiang W, et al. Effect of Restoration Design on the Removal Torque Loss of Implant-supported Crowns after Cyclic Loading. J Contemp Dent Pract 2023;24(12):951-956.

A three-dimensionally printed template for locating the screw channel in a cement-retained implant-supported crown: A digital workflow

Locating the screw channel in a cement-retained implant-supported crown is challenging. This article describes a fully digital workflow for fabricating a 3D printed template which can accurately guide the dentist to find the screw channel. A definitive implant cast from the patient and an implant planning software program are used in the workflow. This technique provides precise guidance for finding the location and angulation of the abutment screw access hole.

Effect of Indented Structures on the Retention of Cement-Retained Implant-Supported Crowns by Provisional Cement

Purpose: The objective of this study was to investigate the effect of indented structures, such as dimples and retention groove formations, on the retention of titanium abutment walls when cementing cobalt-chromium (Co-Cr) alloy crowns with zinc oxide-eugenol cement. Materials and Methods: Forty-eight titanium abutments (n = 6) were prepared, of which 24 abutments were 4.0 mm and the other 24 were 6.0 mm in height. These 4.0 mm and 6.0 mm abutments were organized into eight groups: no-dimple, 2-dimple, 4-dimple, and axial retention groove groups. The position and dimensions of the dimples and axial retention grooves were the same for all prepared abutments. Laser-sintered cobalt-chromium (Co-Cr) alloy crowns were cemented using a provisional cement. After thermocycling, a retention test was performed using a universal testing machine. Statistical analysis was performed using the nonparametric Kruskal–Wallis test and post-hoc Mann–Whitney U test (𝛼= .05) to compare the mean retentive force. Results: The lowest retentive force recorded was from the 4.0 mm no-dimple group (112.03 ± 20.30). Forming dimples and retention grooves increased the retentive force for the 4.0 mm groups, but the difference was not statistically significant (p > .05). A statistically significant difference was displayed by the 6.0 mm abutment with the 4-dimple group compared to the 6.0 mm no-dimple group (p < .05). Conclusion: Within the limitations of this in vitro study, the mean retentive force was higher with dimples and axial retention grooves for 4.0 mm titanium abutments but was statistically insignificant (p > .05). An increase in abutment height was statistically correlated with an increase in retentive force within the same number of dimple-groups (p < .05).

A device to facilitate separation of components of combined screw- and cement-retained implant-supported crowns

This article describes a technique to separate parts of cemented implant-supported restorations with a screw hole. A device was designed by using a computer-aided design (CAD) program and was milled in a milling center. The restoration was heated to 400 °C and then subjected to controlled mechanical force with the help of the device to separate the cemented parts.

Mechanical behavior of nano-hybrid composite in comparison to lithium disilicate as posterior cement-retained implant-supported crowns restoring different abutments

ObjectiveResin-based materials are gaining popularity in implant dentistry due to their shock absorption capacity. Therefore, the aim of this study was to evaluate the fracture strength and failure mode of resilient materials for both crowns and abutments and compare them to the most widely used materials in different combinations after subjection to long-term fatigue loading. MethodsForty-eight cement-retained implant-restorations were assembled on titanium implants. Identical custom-made CAD/CAM abutments were milled out of 3 different materials (n = 16); T: titanium, Z: zirconia and P: ceramic-reinforced PEEK. Each group was subdivided, according to the restorative crown material, into two subgroups (n = 8); C: nano-hybrid composite and L: Lithium disilicate. Specimens were subjected to dynamic load of 98 N for 1,200,000 cycles with integrated thermal cycling. The surviving specimens were subjected to quasi-static loading until failure. Shapiro–Wilk test was used to test for normality. One-way ANOVA followed by Tukey’s post-hoc test was used to detect statistically significant differences between groups. ResultsAll specimens withstood 1,200,000 load cycles. The fracture strength values varied from a minimum of 1639 ± 205 N for group PL to a maximum of 2949 ± 478 N for group ZL. SignificanceThe abutment material influenced the fracture strength and failure mode of the restoration. A combination of zirconia abutments and nano-hybrid composite showed the most favorable mode of failure within the test groups. Therefore, this combination might be recommended as an alternative for restoring single implants in the posterior area.

Additively manufactured implant abutment screw-access guide to remove a cement-retained implant crown: A technique

A complete digital workflow to remove a cement-retained implant-supported crown by using an additively manufactured implant abutment screw-access guide is described. The existing cone beam computed tomography (CBCT) scan was superimposed on the digital scans of the patient, which facilitated the visualization of the implant abutment screw access and guided the design of the device. Advantages of the technique described include the precise translation of the implant abutment screw access, safe removal of the implant crown, and conservative clinical intervention.

Healing of the periimplant mucosal tissue injury after placing retraction cord subgingivally in beagle dogs

This work aims to observe the healing of periimplant mucosal tissue injury in beagle dogs after subgingival retraction cord placement by examining the gingival index (GI), quantity of gingival crevicular fluid (GCF), and the proinflammatory cytokine in the GCF. In eight beagle dogs, the fourth mandibular premolars on the left side were extracted (n=8); after two months of healing, bone-level implants were installed. A plaque control regimen was performed throughout the duration of the experiment. After three months, retraction cords were placed subgingivally for 5 min before the cement-retained implant-supported crowns were cemented. GI, GCF quantity, and levels of tumor necrosis factor-alpha (TNF-α) in GCF were assessed before application and on days 1, 3, 7, 14, 28, and 56 after application. GI, quantity of GCF, and TNF-α were significantly increased on days 1, 3, and 7 compared with those at the baseline and on days 14, 28, and 56 (P<0.05), and no statistically significant differences were observed among those on days 14, 28, and 56 and the baseline (P>0.05). Under the circumstances of good oral hygiene, acute injury caused by placing retraction cord subgingivally in periimplant mucosal tissue of bone-level implant is reversible. GI, the quantity of GCF, and TNF-α on day 14 return to the baseline levels.

Effects of crown retrieval on implants and the surrounding bone: a finite element analysis.

PURPOSEThe aim of this study was to observe stress concentration in the implant, the surrounding bone, and other components under the pull-out force during the crown removal.MATERIALS AND METHODSTwo 3-dimensional models of implant-supported conventional metal ceramic crowns were digitally constructed. One model was designed as a vertically placed implant (3.7 mm × 10 mm) with a straight abutment, and the other model was designed as a 30-degree inclined implant (3.7 mm × 10 mm) with an angled abutment. A pull-out force of 40 N was applied to the crown. The stress values were calculated within the dental implant, the abutment, the abutment screw, and the surrounding bone.RESULTSThe highest stress concentration was observed at the coronal portion of the straight implant (9.29 MPa). The stress concentrations at the cortical bone were lower than at the implants, and maximum stress concentration in bone structure was 1.73 MPa. At the abutment screws, the stress concentration levels were similiar (3.09 MPa and 3.44 MPa), but the localizations were different. The stress at the angled abutment was higher than the stress at the straight abutment.CONCLUSIONThe pull-out force, applied during a crown removal, did not show an evident effect in bone structure. The higher stress concentrations were mostly observed at the implant and the abutment collar. In addition, the abutment screw, which is the weakest part of an implant system, also showed stress concentrations. Implant angulation affected the stress concentration levels and localizations.CLINICAL IMPLICATIONSThese results will help clinicians understand the mechanical behavior of cement-retained implant-supported crowns during crown retrieval.

Effect of Circumferential and Axial Grooves on the Retention of Provisionally Cement-Retained Implant-Supported Crowns (In Vitro Study)

Introduction: Retention of provisionallycemented implant-supported restorations plays an important role in success of the treatment. Uncementedrestorations may cause several problems such as restoration swallowing, increased bone loss and prosthesis failure. Therefore, suitable cementcompromising between retention and retrievability as well as extra-means of abutment retention might be preferable for durable implantrestorations.Objectives: This study introduced circumferential and axial grooves on implant abutments as retentive promoters and evaluated their effect on theretention of crown copings cemented to implant abutments with provisional luting cements.Materials and methods: Twenty straight titanium implant abutments were divided into 4 groups (n=5): without grooves, with 1 axial groove, with2 circumferential grooves, and with 3 circumferential grooves. Twenty nickel chromium crown copings were fabricated to fit all 20 abutments. Thecopings were cemented to each group of abutments with non-eugenol provisional cement. After storage for 24 hours in 100% humidity at 37°C,specimens were subjected to 500 cycles of thermal cycling, then 5000 cycles of compressive load to simulate the thermal and mechanical stresses inthe oral environment. Tensile strengths were conducted with a universal testing machine and tensile stresses were recorded in Newton. After theretention test, the copings and abutments were evaluated for cement failure mode with Stereoscopic Microscope. Collected data were analyzedusing one-way analysis of variance (ANOVA) and Tukey’s HSD tests (α=.05).Results: The mean tensile strength of the three circumferential grooves was significantly higher than the other groups (P<0.001) while there was nosignificant difference between the axial groove and control group (P=0.999). The cement failure mode was generally adhesive in nature, althoughsome mixed failures were observed.Conclusion The surface modification of an implant abutment by means of circumferential grooves was found to be an effective method ofimproving the retention of crown copings cemented with non-eugenol cement.

A simple procedure for retrieval of a cement-retained implant-supported crown: A case report

Retrieval of cement-retained implant prostheses can be more demanding than retrieval of screw-retained prostheses. This case report describes a simple and predictable procedure to locate the abutment screw access openings of cementretained implant-supported crowns in cases of fractured ceramic veneer. A conventional periapical radiography image was captured using a digital camera, transferred to a computer, and manipulated using Microsoft Word document software to estimate the location of the abutment screw access.

Misfit and microleakage of implant-supported crown copings obtained by laser sintering and casting techniques, luted with glass-ionomer, resin cements and acrylic/urethane-based agents

ObjectivesThis study evaluated the marginal misfit and microleakage of cement-retained implant-supported crown copings. MethodsSingle crown structures were constructed with: (1) laser-sintered Co–Cr (LS); (2) vacuum-cast Co–Cr (CC) and (3) vacuum-cast Ni–Cr–Ti (CN). Samples of each alloy group were randomly luted in standard fashion onto machined titanium abutments using: (1) GC Fuji PLUS (FP); (2) Clearfil Esthetic Cement (CEC); (3) RelyX Unicem 2 Automix (RXU) and (4) DentoTemp (DT) (n=15 each). After 60 days of water ageing, vertical discrepancy was SEM-measured and cement microleakage was scored using a digital microscope. Misfit data were subjected to two-way ANOVA and Student–Newman–Keuls multiple comparisons tests. Kruskal–Wallis and Dunn's tests were run for microleakage analysis (α=0.05). ResultsRegardless of the cement type, LS samples exhibited the best fit, whilst CC and CN performed equally well. Despite the framework alloy and manufacturing technique, FP and DT provide comparably better fit and greater microleakage scores than did CEC and RXU, which showed no differences. ConclusionsDMLS of Co–Cr may be a reliable alternative to the casting of base metal alloys to obtain well-fitted implant-supported crowns, although all the groups tested were within the clinically acceptable range of vertical discrepancy. No strong correlations were found between misfit and microleakage. Notwithstanding the framework alloy, definitive resin-modified glass-ionomer (FP) and temporary acrylic/urethane-based (DT) cements demonstrated comparably better marginal fit and greater microleakage scores than did 10-methacryloxydecyl-dihydrogen phosphate-based (CEC) and self-adhesive (RXU) dual-cure resin agents.

An in vitro assessment of circumferential grooves on the retention of cement-retained implant-supported crowns

Crowns cemented on short implant abutments may have insufficient retention. The purpose of this study was to evaluate the effect of circumferential grooves on the retention of cemented cast copings on implant abutments. Sixty similarly-shaped implant abutments were divided into 4 groups (n=15): without grooves, with 1 groove, with 2 grooves, and with 3 grooves. Fifteen identical NiCr cast copings were prepared to fit all 60 abutments. The castings were cemented to each group of abutments with a noneugenol provisional cement (Tempbond NE) and a zinc phosphate cement (Harvard). After thermal cycling and storage for 6 days in a water bath, retention tests were conducted with a tensile testing machine (Instron) (5 mm/min) and retentive forces were recorded. Data were subjected to 1 way-ANOVA, Tukey's (HSD) test, and repeated measures ANOVA (α=.05). For the noneugenol temporary cement, group retention values were increased according to the number of grooves (P<.001). For the zinc phosphate cement, the first groove increased the retention by approximately 60% (P<.001). The retentive values were higher for the zinc phosphate cement than the provisional cement. The influence of the grooves depended on the type of cement used (P<.001). Cement remnants were found primarily on the castings for provisional cement and for the plain abutments cemented with zinc phosphate cement. Remnants were found primarily on the abutments for the grooved abutments cemented with zinc phosphate cement. The addition of circumferential grooves to implant abutments increased the retention of cement-retained castings. For zinc phosphate cement, 1 groove was as effective as several, whereas for the provisional cement, the retention increased gradually with additional grooves.